System for driving the drive wheels of an electric or hybrid vehicle

SYSTEM FOR DRIVING THE DRIVE WHEELS OF AN ELECTRIC OR HYBRID VEHICLE

TECHNICAL FIELD

The present invention relates to a system for driving the drive and optionally steer wheels of an electric or hybrid vehicle.

BACKGROUND ART

Historically, the rear axle of the urban buses has been inspired by the rear axle of heavy trucks in which one finds an imposing differential at the center of a driving axle that puts the wheels in rotation. The result of this type of arrangement is a large space requirement at the center of the vehicle, which generates a higher height of the floor and a significant unsprung mass.

Commonly today, the low-floor urban buses use an axle concept with inverted portal as described by the patent US 6,035,956, among others, in which the axle shaft and the axle structure, forming a live axle assembly, are offset vertically (downward) from the center of the wheels, and in which speed reduction gears are distributed on each side of the vehicle near the wheels. The notion of a lowered driving axle had already been introduced by the patent US 3,862,667, among others, for a front axle of commercial vehicles.

This inverted-portal axle approach is also the basis of several other patents (for example, US 6,139,464) that adapt this concept in order to introduce an electric drive means on a low-floor vehicle. In this type of approach, the shaft inside the axle is eliminated and replaced by electric motors located in the immediate vicinity of each of the wheels on each side of the axle and attached to the latter. The electric motors are independent, and the differential is typically managed electronically. This type of arrangement constitutes a simple development of the inverted-portal axle concept and, among others,

CA 2873705 2018-04-30 has the disadvantage of increasing the unsprung mass. Furthermore, although an electronic differential can be produced today, it remains complex, expensive and subject to the failure of electronic components.

As for the patent US 5,188,195 of Haustein, it introduces another arrangement. First, the differential becomes independent of the axle and is mounted directly on the chassis. Two half-shafts then transmit the power to the wheels. The Haustein system introduces the concept of longitudinally separating the structural axis which maintains the wheels in position interdependently on each side of the power train. Thus, the axis of the nondriving axle is offset with respect to the axis of the half-shafts and of the wheels. This type of arrangement makes it possible to lower the floor slightly, but not sufficiently in comparison with the inverted portal approach, and above all to reduce the unsprung mass.

With regard to the electric drive, the US patent 3,799,284 of Hender describes an epicyclic gear-type double differential. This arrangement introduces the use of two independently rotating electric motors in which the torques of the motors will be opposite of one another at similar or different speeds and directions in order to put the wheels of the vehicle in rotation. The Hender arrangement offers advantages in terms of the electric drive, but does not however make possible an arrangement for a low-floor vehicle, and it also induces in an increase of the unsprung mass.

SUMMARY

According to one aspect of the invention, a drive system is proposed in order to improve the architecture of low-floor road vehicles by taking advantage of an electric power train.

According to a general aspect, there is provided a low-floor vehicle comprising: a chassis frame and at least one left drive wheel and one right 2

CA 2873705 2018-04-30 drive wheel connected by a non-driving rigid axle, a drive system for driving the drive wheels, said drive system including a left electric motor and a right electric motor mounted on a transaxle having a H-shaped geometry and including longitudinal lateral members and an off-centered transversal member, said longitudinal lateral members including a left gear transmission assembly and a right gear transmission assembly, said off-centered transversal member including a link interconnecting the left and right gear transmission assemblies, said left and right gear transmission assemblies having an elongated shape and oriented along a front-rear axis of the vehicle, said left and right gear transmission assemblies each including an input shaft disposed at a first end of a lateral external face and an output shaft at a second end of the associated gear transmission assembly on the same lateral external face, said input and output shafts of each of the right and left gear transmission assemblies being also vertically offset one relative to the other, each of said input shafts being driven by an associated one of the left and right electric motors mounted to the chassis frame behind the corresponding one of the left and right drive wheels, each of said output shafts being mounted for joint rotation with a half-shaft disposed at an output of the left and right gear transmission assemblies, said half-shaft having ends provided with constant velocity joints and being rotatably secured to a corresponding wheel of said left and right drive wheels, each of the input shafts being rotatably drivingly connected to an input pinion of the associated one of the right and left gear transmission assemblies, each of said input pinions disposed at said first end of the right and left gear transmission assemblies driving an epicyclic gear train driven via a gear set, said epicyclic gear train having a ring gear, a planet wheel carrier and a sun gear, either one of the ring gear and of the planet wheel carrier being drivingly connected to said half-shaft arranged at the output of the second end of the gear transmission assemblies, said epicyclic gear trains of the left and right gear transmission assemblies being connected together by said link corresponding to the off-centered transversal member of the H-shaped transaxle, said link being rotatably secured to each of the sun gears of the left and right epicyclic gear trains, the sun gears of the

CA 2873705 2018-04-30 left and right gear transmission assemblies having opposite torques, said link being horizontally and vertically offset relative to the non-driving rigid axle and relative to an axis of rotation of the left and right drive wheels and located at the level of the lowered floor of the vehicle, the transaxle further comprising a rotation reversal means in order to transmit to each of the drive wheels a rotation in a same direction.

According to another aspect, there is provided drive wheel and axle set of a vehicle having a chassis frame, the drive wheel and axle set comprising: at least one left drive wheel and one right drive wheel connected together by a non-driving rigid axle, a drive system comprising a left electric motor and a right electric motor mounted on a transaxle having a H-shaped geometry and including longitudinal lateral members and an off-centered transversal member, said longitudinal lateral members including a left and a right gear transmission assembly, said off-centered transversal member including a link interconnecting the left and right gear transmission assemblies, said left and right gear transmission assemblies having an elongated shape and each including an input shaft disposed at a first end of a lateral external face and an output shaft at a second end of the associated gear transmission assembly on the same lateral external face, said input and output shafts of each of the right and left gear transmission assemblies being also vertically offset one relative to the other, each of said input shafts being driven by an associated one of the left and right electric motors mounted to the chassis frame behind the corresponding one of the left and right drive wheels, each of said output shafts being mounted for joint rotation with a half-shaft disposed at an output of the left and right gear transmission assemblies, said half-shaft having ends provided with constant velocity joints and being rotatably secured to a corresponding wheel of said left and right drive wheels, each of the input shafts being rotatably drivingly connected to an input pinion mounted inside the associated one of the right and left gear transmission assemblies, each of said input pinions disposed at the first end of the right and left gear transmission assemblies driving an epicyclic gear train driven via a gear set,

CA 2873705 2018-04-30 said epicyclic gear train having a ring gear, a planet wheel carrier and a sun gear, either one of the ring gear and of the planet wheel carrier being drivingly connected to said half-shaft arranged at the output of the second end of the gear transmission assemblies, said epicyclic gear trains of the left and right gear transmission assemblies being connected together by said link corresponding to the off-centered transversal member of the H-shaped transaxle, said link being rotatably secured to each of the sun gears of the left and right epicyclic gear trains, the sun gears of the left and right gear transmission assemblies having opposite torques, said link being horizontally and vertically offset relative to the non-driving rigid axle and relative to an axis of rotation of the left and right drive wheels, the transaxle further comprising a rotation reversal means in order to transmit to each of the drive wheels a rotation in a same direction..

According to still another aspect, there is provided a drive system for driving the drive wheels of a vehicle having a chassis frame, and at least one left drive wheel and one right drive wheel, said drive system including a left electric motor and a right electric motor mounted on a transaxle having a Hshaped geometry, the transaxle having longitudinal lateral members and an off-centered transversal member, said longitudinal lateral members including a left gear transmission assembly and a right gear transmission assembly, said off-centered transversal member including a link interconnecting the left and right gear transmission assemblies, said transaxle being mounted to the chassis frame, said left and right gear transmission assemblies having an elongated shape and each including an input shaft disposed at a first end of a lateral external face and an output shaft at a second end of the associated gear transmission assembly on the same lateral external face, said input and output shafts of each of the right and left gear transmission assemblies being also vertically offset one relative to the other, each of said input shafts being driven by an associated one of the left and right electric motors, each of said output shafts being mounted for joint rotation with a half-shaft disposed at an output of the left and right gear transmission assemblies, said half-shaft

CA 2873705 2018-04-30 having ends provided with constant velocity joints and being rotatably secured to a corresponding wheel of said left and right drive wheels, each of the input shafts being rotatably drivingly connected to an input pinion mounted inside the associated one of the right and left gear transmission assemblies, each of said input pinions disposed at the first end of the right and left gear transmission assemblies driving an epicyclic gear train driven via a gear set, said epicyclic gear train having a ring gear, a planet wheel carrier and a sun gear, either one of the ring gear and of the planet wheel carrier being drivingly connected to said half-shaft arranged at the output of the second end of the gear transmission assemblies, said epicyclic gear trains of the left and right gear transmission assemblies being connected together by said link corresponding to the off-centered transversal member of the H-shaped transaxle, said link being rotatably secured to each of the sun gears of the left and right epicyclic gear trains, the sun gears of the left and right gear transmission assemblies having opposite torques, said link being horizontally and vertically offset relative to an axis of rotation of the left and right drive wheels, the transaxle further comprising a rotation reversal means in order to transmit to each of the drive wheels a rotation in a same direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 to 6 illustrate a drive system according to a possible embodiment of the present invention.

Figure 1 is a perspective view of the drive system positioned with a wheel and axle set.

Figure 2a is a view of the right portion of the system, showing the right casing and the gear set that it contains.

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Figure 2b is a view of the left portion of the system, showing the left casing and the gear set that it contains, the latter including a rotation reversal mechanism in the form of a toothed reversal wheel in the output gears.

Figure 3a is a perspective view of another embodiment of the system in which the linking means connecting the sun gears is made up of two half-shafts and of a reversal mechanism.

Figure 3b is a view similar to Figure 3a, but in which the reversal mechanism is combined with the epicyclic gear train of one of the casings.

Figure 4 illustrates the input and output points of a casing of said drive system.

Figure 5 is a view of the gear set inside of one of the casings and showing the epicyclic gear train.

Figure 6 is a perspective view of an embodiment of the system in the presence of the wheel wells, the floor envelope and the rigid axle of a vehicle.

PREFERRED EMBODIMENTS

Figure 1 illustrates a system for driving the drive and optionally steer wheels (1) of a vehicle. The system generally includes two drive devices mechanically connected for jointly driving at least one left drive wheel and one right drive wheel which are connected by a non-driving axle. As described in more detail below, the drive devices are attached to the sprung mass of the vehicle hereafter called chassis frame in a generic sense, which includes a chassis frame separate from the body as well as an integral chassis or any other component of a chassis such as a sub-frame. Each device includes an electric motor (2) and a gear transmission assembly having a casing (3). The

CA 2873705 2018-04-30 motors (2) can be mounted on their respective casing (3) behind the wheels (1 ). As illustrated in Figures 2 to 5, each of the gear transmission assemblies includes an input pinion (8) rotatably secured to a rotor of a respective electric motor (2). Each gear train assembly - left and right - includes an epicyclic gear train (4) in which a wheel toothed on the outside and on the inside acts as ring gear (7) (or outer planet wheel) and inside of which turn the planet gears and the sun gear (5) (or inner planet wheel). The ring gear (7) is mounted in the casing (3) in order to be driven in rotation by a gear set (12) which is itself driven by the input pinion (8) of the casing. The input and the output of the gear set (12) can be horizontally and vertically offset for reasons that will be discussed below. The planet wheel carrier (6) of the epicyclic gear train (4) in each casing (3) - left and right - is rotatably secured to one of the drive wheels (1) by the intermediary of a linking means. The linking means can include a toothed wheel or a gear set (10) driven by the planet wheel carrier (6), said linking means (10) being rotatably secured to a half-shaft (11) provided at its ends with constant velocity joints (11a, 11b). According to a possible embodiment of the invention, the constant velocity joints are of Thompson type. The half-shafts (left and right) (11) contribute toward horizontally and vertically offsetting the casings (3) from the axis of the wheels (1). Finally, the sun gears (5) of each of the epicyclic gear trains (4), left and right, are connected together by a linking means (9) rotatably secured to each of the sun gears (5). The linking means could, for example, be a shaft or else an assembly of two half-shafts as described hereafter. As illustrated in the drawings, the axis of the motors, the axis of the wheels and the axis of the linking means (9) are horizontally and vertically offset relative to one another. As will be seen below, this configuration contributes numerous advantages particularly in the context of a low-floor vehicle.

It is understood that the role of the ring gears (7) and of the planet wheel carriers (6) as described above can be reversed. Indeed, the planet wheel carrier (6) of each of the epicyclic gear trains (4), left and right, could be driven by the input pinion (8) of the corresponding gear transmission

CA 2873705 2018-04-30 assembly, and the ring gear (7) of each of the epicyclic gear trains, left and right, could drive the linking means of the corresponding drive wheel (1).

Therefore, for each side, left and right, the drive system has, as illustrated in Figure 4, a casing (3) with system of gears including moreover an epicyclic gear train (4), and for each of the gear transmission assemblies, there is an input for the output shaft of an electric motor (2), a first output towards one of the wheels (1) and a second output towards a linking means (for example, a shaft) connecting the two transmission assemblies, right and left. The electric motors (2) are mounted at each of the inputs of each of the casings (3), left and right.

According to an embodiment, the drive system is characterized in that it is attached to the chassis frame of the vehicle. As illustrated in Figure 6, the two casings (3) can be located in the wheel wells. Moreover, the linking means (9) rotatably secured to the two sun gears (5), left and right, can be located in the envelope of the floor (14) of the vehicle. The two electric motors (2) can be located just behind the drive wheels (1). The configuration of a system combining these features is particularly well suited to the arrangement of a wheel and axle set for low-floor commercial vehicles, such as an urban bus or a delivery truck. The system has the advantage of making it possible to free up the central space of a low-floor vehicle while minimizing the unsprung mass. The particular arrangement of the gears as illustrated, just as the location of the motors (2), is just one possible configuration considered.

For a torque to be transmitted to each of the drive wheels (1), right and left, one needs a means of opposing the torque of each of the sun gears (5) in such a way as to transmit the torque to the planet wheel carrier (6). In a first configuration, the electric motors (2) are controlled for typically providing a torque in the same direction. The left and right sun gears (5) are then in opposition by the intermediary of two half-shafts each rigidly connected to a

CA 2873705 2018-04-30 sun gear (5) and connected together by a rotation reversal mechanism. According to this scenario illustrated in Figure 3a, the linking means (9) then includes two half-shafts (9a) and a reversal mechanism (9b). In this configuration, the torque in the same direction provided by each of the motors (2) will oppose the torques of the sun gears (5) in order thus to transmit a torque to each of the planet wheel carriers (6) driving the drive wheels (1). Alternatively, the rotation reversal mechanism can be combined with one of the epicyclic gear trains (4), inter alia, as illustrated in Figure 3b.

According to an alternative configuration, the left and right sun gears (5) are connected by a single shaft (the linking means (9) of Figure 1 is a single shaft without reversal mechanism) that makes them rotatably secured; the motors (2) are controlled rather for typically providing a torque each in an opposite direction such that this generates an opposite torque for each of the sun gears (5) . The torque transmitted to each of the planet wheel carriers (6) is then opposite one with respect to the another. For transmitting a rotation in the same direction to each of the drive wheels (1), one of the linking means (right or left) of a planet wheel carrier (6) to a drive wheel (1) must include a rotation reversal mechanism such as a toothed reversal wheel (10a) added inside of the casing (3) within the output gear set (10) between the planet gear carrier (6) and the toothed wheel driving the half-shaft (11), as illustrated in Figure 2b.

Therefore, a reversal mechanism can be situated at the junction of two halfshafts connecting the left and right sun gears, in the form of a reversing gear set, alternatively in one of the casings (3), right or left, combined with the epicyclic gear train (4) in order to reverse the rotation of one of the sun gears (5), or alternatively, if the motors (2) are typically controlled for transmitting an opposite torque, in the form of a toothed reversal wheel added at the output of the planet wheel carrier (left or right) whose rotation needs to be reversed.

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Furthermore, the system allows an optimal use of the torque and speed characteristics of electric motors (2) by acting as torque converter. According to the first configuration described above, in which the motors are controlled for typically providing a torque in the same direction, during starting of the vehicle, the two motors (2) put in rotation in opposite directions and sped up without any torque being transmitted to the wheels (1). The motors (2) are brought to the speed of rotation where they can develop their maximum torques. In order to move the vehicle forward, the electric motor turning in the reverse direction is temporarily used in generator mode for the purpose of applying a braking torque. When the torques of the two motors are applied (one in drive mode and the other in braking mode) and since the motors are turning in opposite directions, the resultant is such that the two torques are applied in the same direction and the power is then transmitted to the drive wheels (1). This device makes it possible to apply the maximum torque of the motors to the wheels and this from the neutral point of the vehicle. This results in obtaining a correspondence between the torque and speed characteristics that can be produced by simple and economical electric motors and the torque and speed characteristics that are required for the wheels of the vehicle.

A feature of the system relates to the double differential function fulfilled by the two epicyclic gear trains (4). The combination of the two epicyclic gear trains (4) makes possible an equal distribution of the torque to the two wheels (1), even during turning and mainly when the two motors are not turning at exactly the same speed. It is simpler, less expensive and more energy efficient to control only the torque of the motors without regard to their relative positions. Additionally, this device makes possible a redundancy of motor means in which the vehicle can be kept in service (with reduced but sufficient characteristics) while only functioning on a single motor. Indeed, even with a single motor in service (with the other kept stationary by a blocking mechanism), an equal torque is transmitted to each of the drive wheels, enabling the vehicle to be used with a deterioration of the starting torque and 11

CA 2873705 2018-04-30 a maximum speed reduced by half. This feature allows a tolerance of the failure of a large portion of the propulsion system without total loss of service. It is an important feature for vehicles with a high level of service such as public transport vehicles.

The system is also characterized by the fact that when a surplus of torque is available, at least one electric motor can be controlled in generator mode for recharging an electrical energy storage system.

The particular arrangement of the components in the wheel wells (13) and in the envelope of the floor (14) allows the drive system to be used on various types of wheel and axle sets. The drive system can be applied to any type of vehicle with drive wheels, for a front or rear wheel and axle set. The drive system also allows tandem arrangements, namely in the front and/or in the rear of the vehicle, with various combinations of drive and/or steer wheels. The fact that the drive wheels in the rear of the vehicle can also be steer wheels allows tandem arrangements in which the spacing between the axles is increased in comparison with the usual spacing. This allows a better distribution of the load on the road while minimizing wear on the tires and losses due to friction of the tires on the road. The proposed system for driving the drive wheels is an empowering element making it possible to design commercial vehicles of very different architecture. The possibility of drive and steer wheel and axle sets in the rear opens the way to single-track articulated or multi-articulated vehicles. Drive and steer rear wheels also open the way to driving articulated and multi-articulated vehicles in reverse.

The proposed drive system makes it possible to minimize the height of the floor of the vehicle while maximizing the ground clearance (two sought-after but generally conflicting features for low-floor vehicles). The system can enable one to minimize the space requirement as well as to minimize the unsprung mass by separating the power transfer function from the structural

CA 2873705 2018-04-30 function of the rigid axle. By separating these functions, the power transfer components are then combined in the equivalent of a transaxle mounted on the chassis frame with the electric motors. A non-driving rigid axle (15) and half-shafts can be positioned longitudinally in the axis of the wheels. The assembly functioning as transaxle is offset longitudinally in order to make room for the rigid axle (15) and vertically in order to position it in the envelope of the floor (14) and wheel wells (13), thus freeing a maximum amount of space. As clearly shown in Fig. 1, the transaxle is characterized by a Hshaped geometry including longitudinal lateral members formed by the left casing and the right casing and an off-centered transversal member formed by the link (9) interconnecting the left and right casings. The elongated lateral members are oriented along a front-rear axis of the vehicle and extend behind the drive wheels (1). The motors (2) are mounted to the transaxle behind the wheels.

The epicyclic gear trains and the shaft connecting the sun gears of these epicyclic gear trains enable the left and right motors to have a combined effect which is also transmitted to the left and right wheels by the epicyclic gear trains. According to the techniques of the prior art, in this type of case in which two motors are combined, the arrangement is such that the transmission of the power occurs either in the axis of the electric motors or in the axis of the wheels. According to one of the features of the present invention, a 3^rd axis is introduced, namely that of the sun gears of the epicyclic gear trains which do not correspond to the axis of the motors or to the axis of the wheels. This feature is illustrated clearly in the drawings. Therefore, there is a horizontal and vertical positioning inside of the drive system in which the axis of the motors, the axis of the sun gears and the axis of the wheels are all offset horizontally and vertically. Just as an illustration, the output pinion could be at a height of 17 (center of the wheel), the shaft of the sun gear could be at a height of 12 (center of the floor) and the pinion of the motors could be at a height of 15.

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Various elements work together to allow the positioning of this 3^rd axis at the level of the floor. Thus, from the axis of the input pinions (8) of the casings connected to the electric motors (2), a first horizontal and vertical displacement is introduced by the input gear set (12) between the input pinion (8) and the epicyclic gear train (4). The configuration of this gear set (12) is chosen according to the specific configuration of the vehicle and therefore plays a role that goes beyond the simple speed reduction, all in order to shift the axis of the linking means (9) towards the floor of the vehicle. Next, the half-shafts (11) and the constant velocity joints (11a, 11b) allow greater freedom as to the relative positioning between the output point of the casing (3) and the input point of the wheel (1). Moreover, these joints make it possible to have different angles at the two ends of the half-shaft (11), thereby allowing steer wheels. This arrangement is of interest particularly for a lowfloor vehicle and with a view to using two motors for purposes of redundancy and reliability.

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