Power train for four wheel drive vehicle.

0001This invention relates to a power transfer unit for four-wheel drive vehicles and, in particular, to a power transfer unit for four-wheel drive vehicles with easily changeable gear ratios.

0002This invention relates more precisely to the power train of four-wheel driven vehicles and, in particular, to the power train of four-wheel driven vehicles, wherein it is possible to distribute evenly the weight of the power train consisting of transmission, differential gear and power distribution devices.

0003According to the known prior art, there are four-wheel drive vehicles equipped with a power transfer system by which the driving power taken off a transmission is transmitted to drive wheels on either front or rear end of the vehicle, while the power taken off the transmission is distributed by a power distribution unit and transmitted to drive wheels on the other end of the vehicle. Examples of such four-wheel drive power train system are disclosed in patent gazettes TOKU-KO-SHO 62-43884, TOKY-KO-SO 63-5294, TOKU-KO-SHO 63-35444 and JITSU-KAI-SHO 60-84725.

0004The power transfer system disclosed by TOKU-KO-SHO 62-43884 has a differential which transmits power to either front or rear wheels, a power distribution unit which distributes the power through the diferential to wheels on the other end of the vehicles and a clutch system between the differential and the distribution unit to switch between two-and four-wheel drives.

0005The power transfer system disclosed by TOKU-KO-SHO 63-5294 has a front-rear wheel differential, which allows the power taken off the transmission to operate between front and rear wheels, a single-end differential coupled to one side of the front-rear wheel differential to drive either front or rear wheels and another single-end differential coupled to the other side of the front-rear wheel differential to drive wheels on the other end.

0006The power transfer system disclosed by TOKU-KO-SHO 63-35444 has a transmission containing a primary set of reduction gears, a secondary set of reduction gears and a common output shaft for both gear sets. The unit also has an idling shaft to carry the above-mentionned secondary set of gears installed in parallel with the output shaft. The end of these output and idling shafts on the engine side are supported outside the clutch case, whereas a clutch release arm is installed inside the clutch case wall in a spot opposite to the spot where the idling shaft is supported.

0007On the other hand, the power train disclosed in JITSU-KAI-SHO 60-84725 has a differential connected to a transmission, through a set of final reduction gears, and a power distribution unit coupled to the differential, the differential and the power distribution units being connected with each other through a set of gears other than the above-mentioned set of final reduction gears.

0008A four-wheel driven vehicle is normally equipped with a power train system consisting of a transmission box, differential gear boxes and a power distribution system (hereinafter referred to as a "transfer"), a driving shaft, 2WD-4WD (two-wheel drive/four-wheel drive) converter, wheel drive axles, etc. The transmission box, differential boxes and transfer are arranged and installed on the vehicle as the power train.

0009A problem commonly found among all such conventionnal power trains is that they are constructed with the differential and transfer installed, on one side, on a radial axis of the transmission input shaft to intersect the axis of the input shaft at right angles while the input shaft is located in line with the crankshaft of the internal combustion engine. The configuration results in the uneven distribution of the weight around the crankshaft and in the generation of harmful vibrations and noise.

0010In some prior art systems: <ul id="ul0001" list-style="dash"><li>For changing gear ratios, it is necessary to replace the drinven gear, which interlocks with the final reduction drive gear and the final reduction driven gear, by a gear with the desired number of teeth and, in addition, in order to match the revolution speed of the wheels on one end of the vehicle with that of the wheels on the other end, the input and output gears of the power distribution unit,connected with the wheels on the other end, as well as the set of final reduction gears,connected to the wheels on either end, need to be replaced by gears with the suitable number of teeth for matching. In order to change the gear ratios of the power train, it is necessary to dismantle the transmission case, the distribution unit and the final reduction case containing the final reduction gears of the final drive system and replace many of the gears contained therein by gears with the correct number of teeth. It is a labor and time consuming work to dismantle all such units and replace a large number of gears. The need for a large number of replacement gears with different numbers of teeth is also prone to increase the costs involved.</li><li>The system may include such components as a chain, sprockets, an intermediate shaft, etc., thereby rendering the construction not only difficult, but also complex, since the intermediate shaft has then to be installed so as to penetrate into the power train.</li><li>Furthermore, the need for the transfer, placed beside the transmission case, means a greater number of components required to complete the system.</li></ul>

0011The object of this invention, therefore, is to provide a four-wheel drive power train wherein the gear ratios can be easily changed, without the trouble of dismantling cases and replacing a large number of gears, and to lower the cost involved.

0012The object of this invention is reached by installing a transmission with an input shaft placed in line with the crankshaft of the internal combustion engine and a differential on one side of the input shaft on a radial axis intersecting the axis of the input shaft at right angles and, also, by installing, on the opposing side of the input shaft, a power distributor which is driven by the revolution of the input shaft, so as to attain the even distribution of the weight around the crankshaft and to eliminate unnecessary noise and vibration.

0013Furthermore, the invention aims to provide four-wheel drive vehicles with a power train of simple configuration to enable easy transmission of driving power to either front or rear wheels and, by integrating all necessary mechanisms in a single case, to reduce the required number of components.

0014Measures taken to solve these problems by this invention are as follows : The power train of this invention is constructed in such a way that the power, taken off from the transmission,drives wheels on either the front or rear end of a vehicle and, at the same time, the power, taken off from the same transmission, is also distributed by a power distribution unit to drive the wheels on the other end of the vehicle. This power train is characterized by its configuration whereby the whole system is housed in a case consisting of at least one main case and a detachable side case ;it has an intermediate shaft connected to the main shaft of the above transmission and to either front or rear wheels and, also, an input shaft of the above power distribution unit which is connected to wheels on the other end, and each of these shafts is rotatably supported by the main and side cases ; each of the main shaft, intermediate shaft and input shaft is mounted with a detachable primary and secondary sets of gears on the end toward the side case.

0015Due to the above-mentioned structure, each of the main shaft, intermediate shaft (connected to wheels on either front or rear wheels), and input shaft of the power distribution unit connected to wheels on the end other than the above-mentioned end are mounted with detachable primary and secondary sets of gears on the end towards the side case. These primary and secondary gears can be exposed by detaching the side case so that the gears can be exchanged with other sets of gears with different number of teeth.

0016In the structure according to this invention, as above-mentioned, there are a transmission main shaft, an intermediate shaft, connected to either front or rear wheels, and a distriution unit input shaft connected to wheels on the other end, all of which are rotatably supported by the main case on one end and by the side case on the other end, and primary and secondary intermediate gear sets are detachably mounted on the side case end of these shafts and are interconnected with each other. The primary and secondary intermediate gear sets can be exposed by simply taking off the side case section, which is attached to the main case, and this allows to replace the set of gears with a new set having different numbers ot teeth.

0017As the gear ratio of the power train according to the invention can therefore be changed by only taking off the side case section, any extensive service, such as dismantling the power distribution unit, the final reduction case of the final reduction unit containing the final reduction gear set connected to either front or rear wheels, as was the case with conventional power tarins, is no longer necessary. Since the gear ratio according to the invention can be changed by only replacing the primary and secondary intermediate gear sets, there is no need to change so many gears as in the conventional units. Gear changes can be accomplished due to the invention without the extensive service needed for changing a great number of gears and without having to keep any excessive stock of gears. Gear changes will thus be greatly facilitated and possible at less cost.

0018In order to attain the above-mentioned objectives, this invention has for an object a transmission having an input shaft placed in line with the crankshaft of the internal combustion engine, a differential on one side of the input shaft on its radial axis and intersecting the axis of the input shaft, and a drive distributor on the other side of the input shaft to be driven by the rotation of the input shaft.

0019More particularly the invention has for an object a driving power transfer system for a four-wheel drive vehicle, wherein the wheels on either front or rear end of the vehicle are driven by the power taken off from a transmission, while the power taken off from said transmission is distributed, by a driving power distribution unit, to the wheels on the other end of the vehicle, characterized by the fact that <ul id="ul0002" list-style="dash"><li>the case of this transfer system is divided into at least one main case and at least one detachable side case mounted on said main case,</li><li>an intermediate shaft, connected to either the main shaft of the transmission or to the wheels on the front or rear end of the vehicle, and the input shaft of the intermediate power distribution system, connected to the wheels on the other end of the vehicle, are installed so as to be supported by the said main case and said side case,</li><li>on the end of the main shaft, intermediate shaft and input shaft towards the side case, detachable primary and secondery sets of intermediate gears interconnect these shafts with each other.</li></ul>

0020It has also for an object a power train system for a four-wheel driven vehicle characterized by a transmission box with an input axle disposed in line with the crankshaft of the internal combustion engine, a differential gear box disposed on a side of, and on the axis at right angle to, the axis of said input axle, which is driven by the revolution of said input axle, and a power distribution box, disposed on the other side of said input axle, which is also driven by said input axle.

0021Due to the configuration according this invention, wherein the differential is placed on one side of the input shaft on a radial axis which intersects the axis of the input shaft of the transmission at right angles, and the drive distributor on the opposite side, weight is evenly distributed around the crankshaft to prevent the generation of detrimental vibrations and noise.

0022Regardless of whether it is installed in the front or rear end of a vehicle, the system is able to drive the wheels at one end through the differential and, simultaneously, the wheels at the other end through the drive distributor, so that the distribution of driving motion to all four wheels can be attained by the simple configuration of mechanisms utilizing a number of common parts and components.

0023As herein-above explained, this invention consists in a transmission with an input shaft located in line with the crankshaft of an internal combustion engine, a differential operated by the rotation of a differential disposed on a radial side, with its axis intersecting the a is of the input shaft at right angles, and a drive distributor installed on the opposite radial side of the input shaft. This configuration provides not only for even distribution of weight around the crankshaft, so as to eliminate undesirable vibrations and noise, but also for simple means for transmitting the driving motion, regardless of whether the engine is mounted at the front or rear end of a vehicle. The all-inclusive single case construction enables minimizing the number of required parts and components.

0024The details of this invention will now be explained as follows with reference to the appended drawings in which : <ul id="ul0003" list-style="none"><li>Fig. 1 is a schematic cross-section showing a first embodiment according to invention,</li><li>Fig. 2 is a horizontal cross-sectional view of the power train,</li><li>Fig. 3 is a blow-up side view of the power train,</li><li>Fig. 4 is a horizontal cross-sectional view of the transfer and the power train with the 2WD-4WD converter dismantled,</li><li>Fig. 5 is the outline of an automatic transmission according to another embodiment,</li><li>Fig. 6 is a schematic over view thereof,</li><li>Fig. 7 a schematic frontal view of the intermediate transfer system,</li><li>Fig. 8 is a front view of the retainer,</li><li>Fig. 9 a cross-sectional view of Fig. 8 along IX-IX,</li><li>Fig. 10 is a rear view of the retainer,</li><li>Fig. 11 a schematic cross-section of the transmission of a vehicle,</li><li>Fig. 12 shows the mounting of the retainer,</li><li>Fig. 13 shows a schematic cross-section of a two-wheel drive power train,</li><li>Fig. 14 is a schematic cross-section of a four-wheel drive power train,</li><li>Fig. 15 is a front view of a partitioning seal cover or a secondary partitioning component,</li><li>Fig. 16 is a cross-section along XVI-XVI of Fig. 15,</li><li>Fig. 17 is a front view of the closing seal cover,</li><li>Fig. 18 is a cross-section along XVIII-XVIII of Fig. 17,</li></ul>

0025In Fig. 1 are shown an internal combustion engine 2, a power tarnsfer unit 4, a transmission 6 and a power distribution unit 8. The power transfer unit 4 drives the wheels on one end of the vhicle with the power taken off from the transmission 6, while, at the same time, it distributes the power taken off from the transmission 6, through the power distribution unit 8, to drive the wheels on the other end.

0026The main case 10 of the power train 4 consists of (being dividable) into a main case 10-1 and a side case 10-2. The unit of this example also has a dividable bottom case 10-3. This case 10 is provided with a space 12 allocated for a transmission 4 and a space 14 allocated for a power distribution unit.

0027The space 12 for the transmission contains components, such as a torque converter 16 and an auxiliary transmission 18 which are comprised by the transmission. The power modified by said torque converter 16 and auxiliary transmission 18, is outputed on a main shaft 20. The end of the main shaft 20, away from the internal combustion engine 2, penetrates through the main case 10-1 and protrudes out of the side case 10-2 and is rotatably supported by the main case 10-1 and the side case 10-2 carrying the main primary and secondary bearings, respectively 22-1 and 22-2.

0028The main case 10-1 and side case 10-2 also support the intermediate shaft 24 leading to either front or rear wheels, with the intermediate primary and secondary bearings, respectively 26-1 and 26-2. The intermediate shaft 24 is installed in parallel with the main shaft 20 and mounted with a single-end final drive gear 30, which comprises a single-end final reduction drive gear set transmitting the power to either front or rear wheels. This single-end final reduction drive gear interlocks with a single-end final reduction driven gear which is secured onto the differential housing 36. The differential housing 36 is rotatably supported by the main case 10-1 and the bottom case 10-3 carrying the differential primary and secondary bearings, respectively 38-1 and 38-2. There is also a set of differential gears 39 installed inside the differential housing 36.

0029The above-mentioned space 14 for the distribution unit contains a power distribution unit 8 connected to either front or rear wheels. The power distribution unit 8 consists of a distribution gear set of an input gear 42 and output gear 44, each of which is mounted on the end of an input shaft 46 and an output shaft 48 respectively and interlocks with each other. The input shaft 46 is installed in parallel with the main shaft 20 and supported at one end by the input retainer 48, with the primary and secondary input bearings, and by the side case 10-2, with the tertiary input bearing 50-3.

0030The input retainer 48 is mounted on the input side of the mounting flange 52 of the main case 10-1 with mounting bolts 54. In this way, the input shaft 46 is rotatably supported by the input retainer with the primary and secondary input bearings, respectively 50-1 and 50-2, and the retainer is held in turn by the main case 10-1 with the primary and secondary input retainers, through the input retainer 48. There is an input side oil seal 56 surrounding the input retainer 48.

0031The output shaft 48 is supported by the output side retainer 58, with the primary and secondary output bearings, (respectively 60-1 and 60-2). The output side retainer 58 is installed inside the output gate flange 62 of the main case. This output shaft 48 is mounted with the output gear 44 on one end which interlocks with the input gear 42 at the end of the input shfat 46, whereas the other end of the output shaft is protruding out of the retainer 58.

0032The distribution unit case 64 is jointed to cover the output retainer 58. This distributor case supports a transfer shaft 66 with a transfer bearing 68. The other end of the transfer shaft 66 is coupled to the end of the ouptput shaft 46 with a shifting device 70 to connect or disconnect the joint. Moreover, the other end of this transfer shaft 66 has a coupler 72 for connection to a (not shown) propeller shaft leading to either front or rear wheels. The distribution unit case 64 is fixed with an output side oil seal 74.

0033As can be seen, the power train 4 carries the main shaft 20 of the transmission 6, the intermediate shaft 24, which is connected to either front or rear wheels, and the input shaft 46 of the power distribution unit 8, which is connected to the wheels on the other end, respectively, in the main case 10-1 and side case 10-2 sections. A set of primary and secondary intermediate gears 76 and 78 are mounted on the main shaft 20, intermediate shaft 24 and input shaft 46, at the side case (10-2) end of these three shafts for interconnection with each other and are detachable.

0034The primary intermediate gear set 76 consists of the primary intermediate drive gear 80 and driven gear 82 which transmit the power from the main shaft 20 to either front or rear wheels. The primary intermediate drive gear 80 is mounted on the splined part of the main shaft 20, between the main case 10-1 and the side case 10-2, so as to be detachable. The primary intermediate driven gear 82, which is interlocked with this primary intermediate drive gear 80, is mounted on the splined part of the intermediate shaft 24, in the side case 10-2,so as to be detachable. The primary intermediate gear set 76 is therefore installed on the end of main shaft 20 and the intermediate shaft 24 directly facing inside the side case 10-2 and is detachable.

0035The secondary intermediate gear set 78 consists of the secondary intermediate drive gear 84 and drive gear 86 which transmit the power to either front or rear wheels. The secondary intermediate drive gear 84 is attached to the primary intermediate drive gear 80 which is detachably mounted on the main shaft 20. The secondary intermediate driven gear 86, which is interlocked with the secondary intermediate drive gear 84, is detachably mounted on the splined part of the input shaft 46 of the power distribution unit 8 at the end located in the side case 10-2. Therefore, it is detachably mounted on the main shaft 20 and input shaft 46 close to the inner wall of the side case 10-2.

0036References 88 et 90 designate locking nuts screwed onto the other end of intermediate shaft 24 and input shaft 46.

0037The operation of the system of Fig. 1 is as follows:

0038The power train 4 receives power from the internal engine 2 through the torque converter 16, and auxiliary transmission 18 of the transmission 6 converts the speed automatically according to the driving condition and transmits it to drive either front or rear wheels (not shown) through the primary intermediate gear set, consisting of the primary intermediate drive gear 80 and driven gear 82, the single-ended final reduction gear set 28, consisting of the single-ended final reduction drive gear 30 and driven gear 32, and the single-ended differential 34. Furthermore, this power train 4 transmits the power received to the main shaft 20 from the transmission 6, distributes it by the input gear 42 and output gear 44 of the distribution unit 8 and transmits it, through the secondary intermediate gear set 78 consisting of the secondary intermediate drive gear 84 and driven gear 86, to the wheels on the rear or front end other than the above-mentioned end.

0039To change the gear ratios of this power train 4, one should firstly take off the side case 10-2 attached to the main case 10-1 and expose the primary and secondary intermediaire gear set 76 and 78, then dismantle locking nuts 88 and 90, secondary main bearing 22-2, secondary intermediate bearing 26-2 and tertiary input bearing 50-3, in order to take off the detachable primary and secondary intermediate gear sets 76 and 78 and afterwards mount new primary and secondary intermediate gear sets 76 and 78 with different numbers of teeth.

0040The gear ratio of the power train 4 can be changed in this way.

0041As can be seen , the mounting of the primary and secondary intermediate gear sets 76 and 78, which interconnect the main shaft 20, intermediate shaft 24 and input shaft 46 detachably to the side case end of these shafts, which are supported by the main case 10-1 and the side case 10-2, makes it easy to expose all these gears, the primary and secondary intermediate gear sets 76 and 78, by simply taking off the side case cover 10-2 attached to the main case 10-2 ; therefore they can be easily exchanged with a new set of gears with different numbers of teeth.

0042As the gear ratio can be changed by simpley taking off the side case cover 10-2, it is not necessary, as in the case of many conventional units, to dismantle the distribution unit case or disassemble the final reduction gear case of the final reduction unit housing, i.e. the final reduction gear set that relates to either front or rear wheels. Moreover, the gear ratio can be changed by simply replacing the primary and secondary intermediate gear sets 76 and 78, instead of a large number of gears required to be replaced in conventional power trains. The invention eliminates the need for the superfluous work of exchanging a great number of gears and for keeping a large stock of gears with different numbers of teeth. Thus, gear ratio change will now be a simple and inexpensive service with the power train of this invention.

0043In Fig. 2, is shown an internal combustion engine 102 placed longitudinally in a vehicle (not shown) ; reference 104 represents the crankshaft of the engine 102 and reference 106 represents a power train which conveys the driving power generated by the engine 102 to the wheels (not shown).

0044The power train 106 consists of a transmission 108, a differential 110 and a drive distributor 112 (hereinafter referred to simply as the "transfer").

0045The transmission 108, as mentioned above, is an automatic transmission consisting of a torque converter 114, an input shaft 116 and an auxiliary transmission 118 mounted on the input shaft 116.

0046The torque converter 114, as mentioned above, is located between the crankshaft 104 and the input shaft 116 in order to provide a clutch funtion for connecting and disconnecting the revolving motion of the crankshaft 104 and also to magnify and convey the driving power of the engine 102. The torque converter 114 is housed in a converter cover 120-1 of the main case 120 which is mounted attached to the engine 102.

0047While one end of the foregoing input shaft 116 is coupled to the torque converter 114 at one end through an auxiliary transmission 118, the opposing side of it is supported by the primary bearing 122, supported by the auxiliary transmission cover 120-2 of the main case 120, and the secondary bearing, supported by the side cover 124 which is attached to an end of the auxiliary transmission cover 120-2.

0048As shown in Fig. 2, the input shaft 116 is installed on the axis "C" which is placed in line with the crankshaft 104.

0049In this embodiment, the differential 110 is installed on the side "A" of a radial axis "Y" which intersects the axis "X", at right angles, placed in line with the axis "C" of the input shaft 116, while the transfer 112 is placed on the opposing side "B".

0050The input shaft 116, placed between the foregoing auxiliary transmission cover 120-2 and the side case 124, is mounted with the gear base 130 of an intermediate drive gear 128.

0051The intermediate drive gear 128 interlocks with an intermediate driven gear 132. The intermediate driven gear 132 is mounted on one end of an intermediate shaft 134 which is placed approximately in parallel with the input shaft 116. This intermediate shaft 134 is rotatably held by a primary bearing 136, supported by the side case 124 at one end, and by a secondary bearing 138, supported by the main case 120 at the opposite end, and is placed on the radial side "Y" of the input shaft 116.

0052The final reduction drive gear 142 of the final reduction gear mechanism 140 is attached to the opposing end of the foregoing intermediate shaft 134. The final reduction drive gear 142 interlocks with a final reduction driven gear 144 of a larger diameter.

0053The final reduction driven gear 144 is secured to the differential housing 146 of the differential 110 with a gear mounting bolt 148.

0054The differential housing 146 is rotatably held at one end by a primary differential housing bearing 152 which is supported by the differential side cover 120-3 on one side and by the side of a bottom cover 150, and is rotatably held at the opposite end by a secondary differential housing bearing 154, which is supported by the other side of the differential cover 120-3 and by the other side of the bottom case 150.

0055This differential 110 is coupled with LH and RH wheel drive shafts (156-1 and 156-2 respectively).

0056In addition, the intermediate drive gear 128 and a transfer drive gear 158 are secured in parallel with the gear base 130 which is mounted on the input shaft 116.

0057A transfer driven gear 160 is interlocked with the transfer drive gear 158. The transfer driven gear 160 is mounted on an input transfer shaft 162.

0058The input transfer shaft 162 is placed approximately in parallel with the foregoing input shaft 116 on the opposite side of the above mentioned intermediate shaft 134, i.e. on the other radial side "B" of the input shaft 116.

0059The input side shaft of the transfer 162 is rotatably held on one end by an input side bearing 164, supported by the side cover 124 and by primary and secondary needle bearings, 166-1 and 166-2 respectively, on the opposing end.

0060The foregoing primary and secodary needle bearings, 166-1 and 166-2 respectively, are supported by the auxiliary transmission case 120-2 and the transfer side cover 120-4 by way of a primary cage 168 and a primary retainer 170.

0061The foregoing primary retainer 170 is held by a retainer bolt 172 on the auxiliary transmission case 120-2 and the transfer side case 120-4.

0062On the opposing end of the foregoing transfer input shaft 162, is mounted an input bevel gear 174.

0063The input bevel gear 174 interlocks with an output bevel gear 176. The output bevel gear 176 is secured to the end of a transfer output shaft 178.

0064The transfer output shaft 178 is rotatably held by the secondary needle bearings 180-1 and 180-2. The secondary needle bearings 180-1 and 180-2 are supported by the transfer side cover 120-4 by means of a secondary retainer 182 and a secondary retainer 184.

0065The opposite end of the foregoing transfer output shaft 178 is coupled to a 2WD-4WD selector 186.

0066The 2WD-4WD selector 186 has a selector sleeve 190 and a selector connecting shaft 192 inside a selector housing 188. The purpose of this selector is to select between 2WD (two-wheel drive) and 4WD (four-wheel drive) by disconnecting or connecting the drive of the internal combustion engine 102, which is transmitted to the transfer output shaft 178, by moving the selector sleeve 188 back and forth along the direction of the transfer output shaft 178.

0067A companion flange shaft 198 is coupled to the selector connecting shaft 192 inside the selector housing 188 of the 2WD-4WD selector 186. The companion flange shaft 194, in turn, is coupled to a companion flange 196 which is connected to the driving shaft (not shown).

0068The operation of this embodiment is as follows : The driving motion generated by the internal combustion engine 102 rotates the crankshaft 104 and the motion is then conveyed to the input shaft 116 through the torque converter 114.

0069The rotating motion of the input shaft 116 is then conveyed, through the intermediate drive gear 128 and the interlocking intermediate driven gear, to the intermediate shaft 134.

0070The rotating motion, thus conveyed to the final reduction drive gear 142 mounted on the shaft, rotates the final reduction drive gear 144 which, in turn, rotates the differential housing 146 fixed to the gear 144. The differential 110 is then driven by way of the rotation of the differential housing 146 and, thus, the drive generated by the internal combustion engine 102 is finally conveyed to LH and RH wheel drive shafts 156-1 and 156-2 respectively.

0071Meanwhile, the transfer drive gear 158 is rotated by the motion of the input shaft 116 and, subsequently, rotates the transfer driven gear 160, which interlocks with the transfer drive gear 158, and the transfer input shaft 162.

0072The rotation of the transfer input shaft 162 is conveyed to the input bevel gear 174 and then on to the ouput bevel gear 176.

0073Finally, the transfer output shaft 178 is rotated by the motion of the output bevel gear 176.

0074If 4WD is selected by the 2WD-4WD selector mechanism 186, the drive of the internal combustion engine 102 is conveyed to the driving shafts (not shown) through the companion flanges 194 and 196.

0075If 2WD is selected by the 2WD-4WD selector mechanism 186, the companion flange 194 is disconnected and the drive will not be conveyed to it.

0076Due to such a configuration of this power train 102, with the differential 110 and the final reduction gear mechanism 140 located on one "Y" radial side "A" of the input shaft 116 and the transfer 112 2WD-4WD selector mechanism 186 on the opposite side "B", i.e. with the differential 110 and the transfer 112 located along the radial axis "Y" on opposite sides and the input shaft 116 in the center, the weights of the related components are evenly distributed around the input shaft and, consequently, around the crankshaft, so as to eliminate detrimental vibrations and noise.

0077In addition, it becomes possible to contain the auxiliary transmission 118 and the transfer 112 in the main case 120 so as to reduce the number of required componets and overall costs.

0078Furthermore, intermediate drive gears 128 for the differential 110 and transfer drive gears 158 for the transfer 112, mounted on the input gears 116, are properly distributed, so that it is possible to minimize the width L1, as compared with L2 of the power train 106 shown in Fig. 2.

0079In addition, while, in the conventional systems, it was necessary to avoid the rear differential for transmitting the driving motion from the rear wheel differential to the transfer, and therefore the total width of the transfer was larger than that of the clutch housing or converter housing, the width of the transfer 112, in a system according to this invention, is never larger than the converter housing, thereby facilitating the mounting on a vehicle.

0080Furthermore, as apparent from the side view of the power train 106 shown in Fig. 3, the auxiliary transmission 118, the differential 110 and the transfer 112 can be installed approximately in line ; therefore the train 106 can be flattened by minimizing its height and its bottom can be made flat to ensure the minimum height above the ground.

0081On the other hand, when the transfer 112 should be operated only for 2WD (two-wheel drive), the opening N° 1, i.e. S₁,of the main case 120 for the input end of the transfer shaft 162 should be closed with the cover N° 1, i.e. 198-1, after dismantling all the related parts of transfer 112 and the 2WD-4WD converter 186. In this cas, the cover N° 1, i.e. 198-1, should be fixed on the main case 120 with the retainer mounting bolts 172. Furthermore, the opening N° 2, i.e. S₂, or the main case 120 for the output end of the transfer shaft 182 should be closed with the cover N° 2,i.e. 198-2. This cover N° 2 shall be fixed by (not shown) securing means to the main case 120.

0082It is a practical solution since the main case 120, etc. shown in Fig. 2 can be used without the transfer 112 and 2WD-4WD converter 186 being mounted, thereby making the main case and other pertinent parts available for common use without relying on a more complicated setup.

0083In this embodiment, it is therefore not necessary to make any modification to the power train 106, regardless of whether the transversely mounted engine 102 is placed at the front or rear end of the vehicle, for easy application.

0084In another embodiment shown in Fig. 5, reference 202 represents an automatic transmission for a four-wheel drive vehicle with differential gears 204 and a transfer 206.

0085The automatic transmission 202 has an input shaft 208 to take in the power from an internal combustion engine (not shown) and also has a transmission section (not shown) converting the rotation speed to a desired level and transmitting it to an output shaft 210. Coupled to the output shaft 210 is an intermediate transfer system 212 which distributes the power to the differential gears 204 and transfer 206.

0086This intermediate transfer system 212 has primary and secondary drive gears,respectively 214 and 216, which serve as primary and secondary drives mounted on the above output shaft 210 and the object of these drive gears, respectively 214 and 216, is to interconnect the intermediate transfer 212 to the primary power train, for driving wheels on either front or rear end, and to the secondary power train, for driving wheels on the other end.

0087As shown in Figs. 5 to 7,the intermediate transfer system 212 consists of a primary drive gear 222, which in mounted on one end of the final reduction gear 220 of the final drive 218 and interlocks with the primary drive gear 214, and of a secondary driven gear 216, which is mounted on one end of the transfer input shaft 224 of the above mentioned transfer 206 and interlocks with the secodary drive gear 216.

0088In the above metioned primary power train, the other end of the final drive shaft 220 of the final drive 218 is set to be connected with differential gears 204 to transmit the power through the differential gears 204 for driving either front or rear wheels (not shown), e.g. the rear wheels.

0089Furthermore, in the above-mentioned secondary power train system, the primary bevel gear 230 is mounted on the other end of the transfer input shaft 224 of transfer 206 and the secondary bevel gear 232, which interlocks with the primary bevel gear 230, is mounted on the end of a transfer output shaft 234 for transmitting the power from the transfer output shaft 234 to the (not shown) wheels on the end other than the above-mentionned end, e.g. to the front wheels.

0090The automatic transmission 202, as shown in Fig. 5, consists of a main case 236, a side case 240, which is attached to the main case 236 for containing the intermediate transfer system 212 and forming an oil chamber 238 for the automatic transmission, a bottom case 242 containing the differential gears 204, and a transfer front case 244, so that the transfer 206 is integrated with the transmission 202 and contained in the main case 236.

0091A retainer 250 for supporting two bearings, i.e. primary and secondary bearings, respectively 246 and 248, is placed inside the main case 236, whereas the two bearings are secured on the retainer to carry the transfer input shaft 224.

0092The retainer 250 is set so that a cut-out (not shown) and a lubricant path are lined up beneath the primary bevel gear 232.

0093The operation of this system is as follows :

0094The driving power, taken off from the internal combustion engine (not shown),is transmitted to the intermediate transfer system 212, through the automatic transmission 202 (not shown) and the output shaft 210, for rotating the primary and secondary drive gears 214 and 216 respectively.

0095The driving power is then transmitted for rotating the final reduction shaft 220 of the final drive 218, through the primary driven gear, which interlocks with the primary drive gear 216, and, in turn, for rotating the differential gear 204, through the output gear 228 of the final reduction shaft 220, and driving either front or rear wheels (not shown).

0096The same driving power is transmitted for rotating the transfer input shaft 224 of the transfer 206, through the secondary driven gear 226, which interlocks with the secondary drive gear 216, and, in turn, for rotating the transfer output shaft 234, which is mounted with the secondary bevel gear 232, through the primary bevel gear 230. The transfer output shaft 234 then drives either front or rear wheels (not shown) other than the above-metioned wheels.

0097Lubricant is then scooped up by the rotation of the primary bevel gear 230 and guided to the primary and secondary bearings 246 and 248, respectively, through the above-mentioned cut-out and lubricant path (not shown) of the retainer 250.

0098When the gap between the primary and secondary bearings 246 and 248, respectively, is filled up with lubricant, overflowing lubricant flows out through the drain (not shown) of the retainer 250 and also through the opening around the two bearings 246 and 248 out of the retainer 250.

0099In this way, the power is transmitted by the intermediate transfer system 212, through the primary drive gear 214, to the primary power train system, consisting of the final reduction unit 218 and differential gears 204, and, at the same time, to the secondary power train system of the transfer 206, through the secondary drive gear 216, so that the primary and secondary power systems are run independently one from the other. While such a construction facilitates any modification of reduction radios (which may be warranted by the existence or non-existence of a supercharger or possible changes in the engine performance), by changing the gear ratio of the primary and secondary drive gears 214 and 216, respectively, or the tire sizes, the intermediate transfer system 212 enables suitable distribution of the power and efficient transmission of the driving power.

0100Moreover, the driving shaft does not cross beneath the transmission (unkike what is the case in conventional prior art systems) ; therefore there is no need to provide any free space under the transmission. Such a disposition helps save space , thereby minimizing the volume of the whole unit , and lowers the production costs, thereby realizing an economical and practical system, which is light in weight and compatible with various types of units including mid-ship engine/front drive (MF), mid-ship engine/rear drive (MR) and four-wheel drive.

0101The easy-to-install construction of the transfer 206 allows more changeable design and easier operation.

0102Furthermore, the present inention is adaptable not only to the embodiments shown in the drawings but is available for a wide range of modifications thereof.

0103For instance, to the primary and secondary drive gears used for the illustrated intermediate transfer systems can be substituted other types of transmission means, such as chains, belts or the combination of both, as long as they can efficiently distribute and transmit the power to the primary and secondary power trains.

0104Primary and secondary drive sections were used in this invention in order to facilitate the selection of suitable gear ratios ; however the unit can be further simplified and reduced in volume by using a single drive section instead.

0105Fig. 8 to 12 show other embodiments of the present invention.

0106In Fig. 11 is shown an automatic transmission 302 for a vehicle, with a differential gear 304 and a transfer 306.

0107The automatic transmission 302 has an input shaft 308 for receiving power from an internal combustion egine (not shown) and a transmission (also not shown) and transmitting the power, after modifying its rotation speed to a required level, to an output shaft 310. Coupled to the output shaft 310 is an intermediate transfer system which distributes the power to a differential gear 304 and a transfer 304.

0108This intermediate transfer unit 312 consists of primary and secondary drive gears, respectively 314 and 316, a primary driven gear mounted at the end of the final reduction shaft 320 of the final reduction unit 318, which interlocks with the primary drive gear 314, and a secondary driven gear 326 mounted at one end of the transfer input shaft 324 of the transfer 306 which interlocks with the secondary drive gear 316.

0109Furthermore, the other end of the final reduction shaft 320 of the final reduction unit 318 is coupled to the differential gear 304 through an output gear 328 for driving wheels (not shown) on either front or rear end of the vehicle by way of the differential gear 304.

0110The automatic transmission 302 consists of a main case 336, a side case 340, which is attached to the main case 336 for the purpose of constituting a primary oil chamber serving as an oil chamber for the automatic transmission to contain the intermediate transfer unit 312, a bottom case 342, containing the differential gears 304, and a transfer front case 344. The transfer case 306 and the automatic transmission are built into a single integral unit.

0111Two bearings, i.e. a primary 346 and a secondary 348 bearing, for supporting the transfer input shaft 324, are mounted on a retainer 350 and the retainer, in turn, is located inside the main case 336 with an O-ring 352 to form an oil seal section 354 surrounding the transfer input shaft 324 of the transfer 306.

0112The retainer 350, while carrying the oil seal section 354 and the transfer input shaft 324, forms a secondary oil chamber 356, which is the oil chamber exclusively for the transfer, divided and partitioned from the automatic transmission 302.

0113More precisely, a spacer 360 is fitted around the transfer input shaft 324 with an O-ring 358 ; and an oil seal section 354 is fitted between the outer circumference of the spacer 360 and the inner circumference of the retainer 350 to partition and separate the primary oil chamber 338 from the secondary oil chamber 356.

0114As shown in Figs. 8 to 10, a part of the inner ring 350a of the retainer 350 is cut out at 362,, with a recess on its right end, and, at the same time, a lubricant path 364, for connecting a part of the cut-out 362 with the primary and secondary bearings, respectively 346 and 348, located inside the retainer 350, is opened in the inner circle 350i of the retainer 350 and, also, a drain 366, connecting the upper side 350a of the retainer 350 with the under side of the secondary bearing 348, is opened in the upper part of the retainer as seen in the Fig. 8.

0115The cut-out 362, as shown in Fig. 8, is formed by cuting off 1/4 to 1/6 of the circumference, so as to leave a little portion inside in the upper part of 350a of the retainer 350.

0116Furthermore, the upper edge 364a, which is a part of the lubricant path 364 formed in the inner circumference 350i of the retainer 350, cuts through a part of the cut-out 362 and reaches, at its lower end 364b, the primary and secondary bearings, respectively 346 and 348.

0117The drain 366, as shown in Fig. 8 and 9, is located about 90 degrees off the location of the path 364 along the circumference and one end of the drain 366a reaches the upper side 358a of the retainer 350, while the other end 366b reaches a spot beyond the primary and secondary bearings 346 and 348, respectively.

0118A flange 368 is formed on the other side of the retainer 350 ; six, equally spaced, mounting bolt holes 370 are bored through the flange along the circumference and there is a projection 372 formed on the edge of the flange 368,in a spot directly opposite the drain 366,as a location for mounting the retainer.

0119The protection 372 serves as a guide for mounting the retainer so that the cut-out 362 and the lubricant path 36 can be correctly located below the bevel gear 330.

0120The primary oil chamber 338, on the transmission 302 side, has to be filled with low viscosity ATF (Automatic Transmission Fluid) as lubricant, while the secondary oil chamber 356, on the transfer 306 side, has to be filled with high viscosity oil, such as gear oil.

0121Reference 374 represents a locking bolt for securing the spacer 360 on the transfer input shaft 324.

0122The operation is as follows:

0123The driving power, generated by an internal combustion engine (not shown), is transmitted, through the automatic transmission 302, a transmission (not shown) and the output shaft 310, to the intermediate transfer unit 312 for driving the primary and secondary drive gears 314 and 316, respectively.

0124The driving power then drives the final reduction shaft 320 through the primary driven gear 322, which interlocks with the primary drive gear 316, for rotating the differential gear 304, through the output gear 328 of the final redution shaft 320, for driving either front or rear wheels.

0125Meanwhile, the driving power is also conveyed, through the secondary driven gear 326, which interlocks with the secondary drive gear 316, to the transfer input shaft 326 of the transfer 306 and, then, through the primary bevel gear 330 of the transfer input shaft 324, rotates the transfer output shaft 334 which carries the secondary bevel gear 332. The transfer output shaft 334 then drives the wheels on the other end of the vehicle.

0126The above mentioned primary and secondary oil chambers 338 and 356, respectively, are securely divided and partitioned from each other by the retainer 350 with the oil seal section 356 and the spacer 360. Low viscosity ATF (Automatic Transmission Fluid) filled in the primary oil chamber 338 effectively and adequately lubricates the automatic transmission 302, while gear oil filled in the secondary oil chamber 356 serves as an efficient and suitable lubricant for the transfer 306.

0127Lubricant is scooped up by the rotation of the primary bevel gear 330, collected at the upper side 364a of the lubricant path 364 and led to the primary and secondary bearings 346 and 348, respectively, through the lubricant path 364.

0128Lubricant is thus drawn in, to fill up the gap between primary and secondary bearings 346 and 348 and then to be drawn out of the retainer 350 through the drain 366, and, at the same time, flows out of the retainer 350 from the gap between 346 and 348.

0129Thus, the primary and secondary oil chambers are effectively divided and partitioned from each other with the retainer 350, spacer 360 and oil seal section 354, for preventing excess change in the oil level and for efficiently lubricating bearings and gears in each chamber, including the transfer input shaft 324 of the transfer 306 and, at the same time, for helping to reduce the required quantity of ATF and keeping ATF clean much better than in conventional units of the prior art wherein ATF is used to serve both as transmission fluid and lubricant for gears and bearings.

0130In addition, the oil seal section 354 is securely supported by the retainer 350 for improving the sealing capacity of the spacer 360, which is in contact with the oil seal 354.

0131When correcting mounting distance of the transfer input shaft 324, it is not necessary to dismount the transfer input shaft 324, as is the case with conventioal units, since it is possible to adjust the distance with one of the shafts tightly fixed with a nut 374 ; therefore there is no risk of damaging the sealed section and its good sealing capacity can be safely maintained.

0132Furthermore, the configuration, according to which sealing is achieved by installing the oil seal section 359 within the retainer 350 closely in contact with the spacer 360 fitted around the transfer input shaft 324, enables minimizing the seal diameter. Thereby the circumferential speed of the sealed part or the spacer can be held low to maintain the high level of sealing capacity to a practical advantage.

0133The multiple purposes of the retainer 350, i.e supporting the transfer input shaft 324, supporting the oil seal section 354 and, at the same time, dividing and partitioning the secondary oil chamber, allows to minimize the weight and size of the entire system, as well as the number of required parts, and consequently the total costs.

0134Figs. 13 to 18 show another example of an actual embodiment of a power train according to this invention.

0135In Figs. 13 and 14, reference 402 represents an internal combustion engine with a power train 404, a transmission 406 and a power distribution 408. In the case of this power train, 404, the transmission 406 and the power distribution unit 408 are integrated into one unit. The power train case 410 consists of a main case 410-1, a side case 410-2 and a bottom case 410-3. In the case 410, are secured a space 412 for installing the transmission 404 and a space 414 for installing the power distribution unit 408.

0136In the space 412 for installing the transmission, components for the transmission 406,such as a torque converter 416 and an auxiliary speed reduction unit 418, are installed. The power, taken off and modified by said torque converter 416 and auxiliary speed reduction unit 418 is outputed by way of a main shaft 420. One end of the main shaft 420, away from the engine, penetrates through the main case 410-1 and protrudes in the direction of the side case 410-2, supported by a primary 422-1 and secondary 422-2 main bearing, which are held by the main case 410-1 or one side and by the side case 410-2 on the other side.

0137An intermediate drive gear 424 for one side of the wheels is mounted on the main shaft 420, held between the main case 410-1 and the side case 410-2, and interlocks with an intermediate driven gear 426 for wheels on that end. In addition, an intermediate drive gear 428 for wheels on the other end is mounted on the main shaft 420, held between the main case 410-1 and the side case 410-2 and interlocks with an intermediate driven gear 430 for that end of wheels.

0138The intermediate driven gear 426, which interlocks with the intermediate drive gear 426, is mounted on an intermediate shaft 432. This intermediate shaft 432 is installed in parallel with the foregoing main shaft 420 and held between the main case 410-1 on one side and the side case 410-2 on the other side, by way of intermediate primary and secondary bearings, respectively 434-1 and 434-2. The intermediate driven gear 426 is mounted one the other side of the intermediate shaft 432. On the other end of the intermediate shaft 432, is mounted a final reduction drive gear 436 for wheels on one end. This final reduction drive gear 436 interlocks with a final reduction driven gear 438 installed for the wheels on that end. The final reduction driven gear 438 is fixed to a differential housing 442 of the differential 440 for the wheels at that end. The differential housing 442 is rotatably held between the main case 410-1 and the bottom case 410-3 by means of primary and secondary differential bearings, 444-1 and 444-2 respectively.

0139Thus, the power train 404 takes off the driving power from the internal combustion engine 402 and automatically modifies the rotation speed according to actual driving conditions, by means of the torque converter 416 and the auxiliary speed reduction unit 418 of the transmission 416, and transmits it to either front or rear wheels (not shown), whichever applicable, through the intermediate drive gear 424, intermediate driven gear 426, final reduction drive gear 436, final reduction driven gear 438 and the differential 440 for the wheels at that end.

0140Furthermore, as shown in Fig. 14,there are components for the power distribution unit 408, such as an input shaft 446, an output shaft 448 and a set of distribution gears, consisting of inpart gear 450 and output gear 452, installed in the space 414 allocated for the distribution unit. The input shaft 446 is set in parallel with the main shaft 420 and rotatably held by an input retainer 454 by means of primary and secondary bearings 456-1 and 456-2 respectively, on one end, and by a tertiary input bearing 456-3 in the side case 410-2. The input retainer 454 is installed at the location 458 on the input side of the main case 410-1. A hole 460 is bored through the input retainer 454. Mounting bolt holes 462 are bored into the flange 454 in the input side of the case. The input side retainer 454 is fixed to the input side of the case with a mounting bolt 464 screwed into a threaded hole 462 through a penetrating hole 460. Furthermore, the input shaft 446 is mounted with the input gear 452 on one end and the foregoing intermediate driven gear 430 for wheels on the other end.

0141In addition, the foregoing output shaft 448 is installed as supported by the output side retainer 466 by means of primary and secondary bearings, respectively 468-1 and 468-2. This output side retainer 466 is fixed to the output side of the case at the spot 470 on the main case 410-1. The output shaft 448 carries an output gear 452, which interlocks with the foregoing input gear 450, at one end, and protrudes out of the output retainer 466, at the other end. The end of the output retainer 466 is covered by a distribution unit case 472 on the outside. This distribution unit case 472 supports a transfer shaft 476 by means of a transfer bearing 476. One end of the transfer shaft 476 is detachably mounted at the other end of the output shaft 448 by means of a transfer device. Furthermore, the other end of the transfer shaft 474 has a coupler which couples with a driving shaft (not shown) leading to either front or rear wheels. A distribution unit oil seal 482 is installed on the distribution unit 472.

0142Thus, the power train 404 drives either front or rear wheels (not shown) by distributing driving power taken off from the transmission 406 through to the input gear 450 and output gear 452, by means of the intermediate drive gear 428 and intermediate driven gear 430, for the wheels on the other end.

0143The power train 404 includes a space 412 allocated for a transmission, i.e. for installing the transmission, and a space 414 allocated for a distribution unit, i.e. for installing the power distribution unit within its case. The input retainer 454, which is a component of the power distribution unit 408 to be installed in the space 414 allocated for the distribution unit, has an oil seal 408, the primary partition component for partitioning the specific volume of space 412 for the transmission, with reference to the space for a distribution system. This oil seal 484 partitions the specific volume of space 412 for a transmission off from the space 414 for a distribution unit.

0144Furthermore, as shown in Fig. 14, the partition seal cover 486, a secondary partitioning component, is detachably mounted with the mounting bolt 464 to the spot 458 on the input side of the main case 410-1 of the case 410 after the power distribution unit 408 is removed from the space 414 allocated for the distribution unit. This partitioning seal cover 486 has a flat part 488 for mounting and a protruding part shaped like a closed cylinder 490 toward the side case 410-2. Bolt holes 492 are bored through the flat part 488 for receiving mounting bolts 464. The protruding part 490 is facing the side case 410-2 and has the same volume as the total volume of the intermediate driven gear 430 for the wheel on the other end and the input shaft 446.

0145The item 494 is a sealing cover to cover the opening 474 at the output side of the main case 410-1 after the distribution unit 408 is removed. This sealing cover 494 consists of a mounting part and sealing part and has bolt holes 499 for receiving mounting bolts (not shown).

0146The operation or this embodiment is as follows:

0147As shown in Fig. 14, when using the unit as a four-wheel drive unit, the power distribution system 408 is installed in the space 414 allocated for the distribution unit. Four-wheel drive is then achieved by the power train 404 wherein the driving power generated by the internal combustion engine 402 is taken off and modified, according to actual driving conditions, by the torque converter 416 of the transmission 406 and the auxiliary transmission 418, and is transmitted to either front or rear wheels (not shown) through the intermediate drive gear 424, intermediate driven gear 426, final reduction drive gear 436, final reduction driven gear 438 and differential 440, all for the wheels at the involved end of the vehicle. Meanwhile, the power taken off from the transmission 406 is distributed, by the input gear 450 and the output gear 452 of the power distribution unit 408, to the intermediate drive gear 428 and intermediate driven gear 430 and transmitted to the wheels at the other end.

0148In this situation, the specific volume of space 412 for a transmission, with reference to the space 414 allocated for a distribution unit, is partitioned by the partitioning oil seal 484 attached to the input retainer 454, a component of the power distribution system 408 installed in the space 414 for the distribution unit.

0149When converting the unit for use as a two-wheel drive, as shown in Fig. 13, the power distribution unit 408 is removed from the space 414 allocated for a distribution unit and the partitioning seal cover 486 is attached to the mounting flange 458, at the input side of the case, with the mounting bolt 464, and, at the same time, the seal cover 494 is attached to the flange 472, at the output side of the main case 410-1. Thus, wheels on either front or rear end of the vehicle are not driven in the case of two-wheel drive and the driving power is taken off from internal combustion engine 402 and modified in revolution speed, according to the actual driving conditions, by the torque converter 416 of the transmission 406 and the auxiliary transmission 418, and is transmitted to either front or rear wheels, whichever applicable, by drive gear 424, intermediate driven gear 421, final reduction drive gear 436 and final reduction driven gear 438 through the differential 440, all for the wheels at the involved end.

0150In this situation, the specific volume of the space 412 for the transmission is partitioned, with reference to the space 414 for the distribution unit, by the partitioning seal cover 486 attached to the input side 458 of the main case 410-1 after the power distribution unit 408 is removed from the space 414 allocated for the distribution unit.

0151Thus, the case 410 of the power train 404 is made for common use between two-wheel and four-wheel drives. When the power distribution unit 408 is installed in the space 414, allocated for the distribution unit within the case 410 of the power train 404, for converting it for a four-wheel drive, the specific volume of the space 412 for the transmission is partitioned off from the space 414 allocated for the distribution unit by means of the oil sal 484 attached to the input retainer 454. When the power distribution unit 408 is removed from the space 414, allocated for the distribution unit within the case 410 of the power train 404, for the purpose of converting it into a two-wheel drive, the specific volume of the space 412 for the transmission, with reference to the space 414 allocated for the distribution unit, is partitioned by the seal cover 486 attached to the case 410. In this way, the specific volume of the space 412 allocated for the transmission always remains constant, regardless of whether the power train 407 is converted into two-wheel drive or four-wheel drive.

0152By maintaining the space 412 for the transmission in the specific volume, despite the conversion of the power train for two-wheel or four-wheel drive, it becomes possible to prevent any change in the required oil level or in the lubricant flow and to shorten the time required for the development, as well as to facilitate oil level control in the production line.