Control system for a chair

<u style="single">Field of the Invention</u>

0001This invention relates generally to a hydraulic drive system and elements thereof which may be used for actuating devices having multiple operations, such as a chair having both lift and tilt features.

<u style="single">Background</u>

0002Hydraulic drive systems are used in many operations for powering multiple actions. Examples of such are power actuated chairs, such as dental chairs, which often are operated by pressurized hydraulic fluid systems in which one hydraulic cylinder, or ram, is operable to raise the chair, and a second hydraulic cylinder, or ram, is operable to tilt the chair or a portion thereof. Many prior hydraulic drive systems have been disclosed in the past, but each has had disadvantages.

0003Some prior systems use drive pumps, motor units, and control circuits which produce movement of the item to be driven in a manner which is not as smooth as may be desired. In a hydraulically actuated chair, for example, prior systems may produce movement which is too fast, too slow, or may produce jerking start and stop actuation which is uncomfortable for the user.

0004Prior systems also have been constructed in such a manner that they are more complex and expensive than may be desired to fulfill their functions. Often prior systems have been produced in such a manner that they require an undesirable number of actuating valves and are produced in a generally open architecture of hoses and connections which are subject to breakage and leakage.

0005<patcit id="pcit0001" dnum="DE3021559A"><text>DE-A-3021559</text></patcit> discloses a control system which is suitable for use with a chair.

0006The present invention seeks to provide an improved control system for a chair.

0007According to one aspect of the present invention, there is provided a control system as defined in the claims hereinafter.

0008Embodiments of the invention seek to provide a novel, efficient, and economically produced hydraulic drive system.

0009Embodiments of the invention also seek to provide a hydraulic drive system which produces smooth operation of driven components actuated by the system.

0010More specifically, embodiments of the invention seek to provide a hydraulic drive system such as is used to drive raising and tilting cylinders for a chair, such as a dental chair, in such a manner as to provide comfortable starting, stopping, and intermediate operation for a party carried in the chair.

<u style="single">Brief Description of the Drawings</u>

0011<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a side elevation view of a hydraulically actuated chair having lift and tilt mechanism operable by a hydraulic drive system according to an embodiment of the present invention;</li><li><figref idref="f0002">Fig. 2</figref> is a schematic diagram of a hydraulic drive system incorporating features according to one embodiment of the present invention;</li><li><figref idref="f0001">Fig. 3</figref> is a top perspective view of a major portion of a hydraulic drive system according to one embodiment of the present invention;</li><li><figref idref="f0003">Fig. 4</figref> is an exploded perspective view of several of the component parts of the system illustrated in <figref idref="f0001">Fig. 3</figref>;</li><li><figref idref="f0004">Fig. 5</figref> is a bottom perspective view of a manifold block in the system with gear pump and check valve assembly components ready for installation;</li><li><figref idref="f0004">Fig. 6</figref> is a top perspective view of the manifold block alone;</li><li><figref idref="f0005">Fig. 7</figref> is a top plan view of the manifold block;</li><li><figref idref="f0005">Fig. 8</figref> is an end view of the manifold block taken along line 8--8 in <figref idref="f0005">Fig. 7</figref>;</li><li><figref idref="f0005">Fig. 9</figref> is a bottom plan view of the manifold block;</li><li><figref idref="f0006">Fig. 10</figref> is a cross sectional view taken along the line 10--10 in <figref idref="f0005">Fig. 7</figref>;</li><li><figref idref="f0006">Fig. 11</figref> is a cross sectional view taken along the line 11--11 in <figref idref="f0005">Fig. 7</figref>, with a motor, gear pump, and fluid sump attached;</li><li><figref idref="f0006">Fig. 12</figref> is a cross sectional view taken along the line 12--12 in <figref idref="f0005">Fig. 7</figref> with a pair of solenoid actuated valves secured to the manifold block;</li><li><figref idref="f0007">Fig. 13</figref> is an enlarged cross sectional view taken generally along the line 13--13 in <figref idref="f0005">Fig. 8</figref> with various valve assemblies in bores in the manifold;</li><li><figref idref="f0008">Fig. 14</figref> is an enlarged cross sectional view taken generally along the line 14--14 in <figref idref="f0005">Fig. 8</figref> with cushion valve assemblies received in bores in the manifold;</li><li><figref idref="f0008">Fig. 14A</figref> is an enlarged view taken along the line 14A-14A in <figref idref="f0008">Fig. 14</figref>;</li><li><figref idref="f0008">Fig. 14B</figref> is a view taken along the line 14B-14B in <figref idref="f0008">Fig. 14A</figref>;</li><li><figref idref="f0009">Fig. 15</figref> is an enlarged cross sectional view taken generally along the line 15--15 in <figref idref="f0005">Fig. 7</figref> with check valve assemblies in bores in the manifold and a fluid sump secured thereto;</li><li><figref idref="f0010">Fig. 16</figref> is an enlarged cross sectional view taken generally along the lines 16--16 in <figref idref="f0005">Fig. 7</figref> with flow rate control valve assemblies received in bores in the manifold block;</li><li><figref idref="f0011">Fig. 17</figref> is an enlarged view of one of the solenoid valve assemblies illustrated in <figref idref="f0006">Fig. 12</figref> with an adapter through which it is connected to the manifold block;</li><li><figref idref="f0011">Fig. 18</figref> is a side elevation view of the adapter of <figref idref="f0011">Fig. 17</figref>;</li><li><figref idref="f0011">Fig. 19</figref> is a top plan view of the adapter; and</li><li><figref idref="f0011">Fig. 20</figref> is a bottom plan view of the adapter removed from the assembly.</li></ul>

<u style="single">Detailed Description of Embodiments</u>

0012Referring first to <figref idref="f0001">Fig. 1</figref>, one manner of use of a hydraulic drive system according to embodiments of the invention is illustrated for use with a dental chair 10. The chair has a base 12 adapted to rest on a floor 14 with an upper structure including a seat portion 16 and a back, or back rest, 18. The seat is mounted on a lift mechanism 20 which includes an extensible contractible ram, or cylinder, 22. Extension of the ram acts to raise the chair to the elevated position illustrated in solid outline in <figref idref="f0001">Fig. 1</figref>. Contraction of the ram lowers the chair to the position illustrated in dashed outline at 10a in <figref idref="f0001">Fig. 1</figref>.

0013The chair back 18 is pivotally connected to the rear end of seat 16 and tilting mechanism including a tilt ram, or cylinder, 24 is operable to tilt the seat and back between a generally upright position illustrated in solid outline in <figref idref="f0001">Fig. 1</figref> and a rearwardly tilted position illustrated at 10b in dashed outline.

0014A hydraulic drive system for the lift and tilt cylinders is illustrated generally at 28 in a broken away portion of base 12. The drive system 28 includes a fluid supply tank, or reservoir, 30 for supplying hydraulic operating fluid to the primary drive unit which includes a motor and pump combination 32. The fluid in the supply tank is retained at a level above the top of a base manifold 36, described below.

0015Referring to <figref idref="f0001">Figs. 3</figref> and <figref idref="f0003">4</figref>, the motor/pump combination 32 generally includes a base manifold 36 (also referred to herein as "base" or "manifold") atop which is mounted a reversible, or bi-directional, electric motor 38. The motor used in the embodiment described is an AC motor, but others may be used also. A crescent gear pump assembly 42 is connected to the bottom of base 36 with the shaft 110 of electric motor 38 extending downwardly through the base to drive pump 42. The component parts of the gear pump and their assembly will be described in greater detail below. A fluid holding sump, or reservoir, 44 underlies the base and may be filled with hydraulic fluid from reservoir 30 to be pumped therefrom by pump 42 and distributed to operating cylinders, or rams, such as lift ram 22 and tilt ram 24 such as would be used for actuating the powered lift and/or tilt mechanism of a chair.

0016In operation more power may be required to raise the chair than may be needed to tilt the back. The motor, being bi-directional may be capable of supplying greater power, or torque, when operated in one direction than in the opposite direction. Thus the motor/pump combination preferably will be connected in the system, such that it will operate in its mode of greatest power, or torque to supply chair lifting energy. A simplified hydraulic schematic diagram for the system is shown in <figref idref="f0002">Fig. 2</figref>. Lift, or first, cylinder, or ram, 22 is shown which may be used to lift a chair upon pressurized fluid being introduced to the lower end of the ram. A tilt, or second, cylinder, or ram, 24 is provided for tilting the chair fore and aft. Introducing pressurized fluid to the lower end of the tilt cylinder causes it to tilt the chair in one direction and a spring and gravity may be utilized upon release of such fluid to return the cylinder to a retracted condition. The system, in addition to cylinders 22, 24 includes the previously described bi-directional electric motor 38, pump 42, and fluid holding sump 44. The system also includes a pair of solenoid actuated valves 48, 50, flow rate control valves 54, 56, cushion valve assemblies 60, 62, and one-way check valves 64, 66, 68, 70. The system also includes a pair of hydraulic accumulators 74, 76 and pressure relief valves indicated generally at 80, 82.

0017An operator's touch pad, or foot switch, 86 is provided which is operatively coupled to a circuit board 88 for controlling actuation of motor 38 and solenoids 48, 50 to produce desired actuation of the lift and tilt cylinders as will be described in greater detail below.

0018A plurality of filters 84 are disposed in the circuit to remove contaminants and maintain cleanliness of hydraulic fluid in the system.

0019Explaining briefly operation of the device generally as described in relation to the schematic of <figref idref="f0002">Fig. 2</figref>, should it be desired to extend ram 22 to lift the chair, motor 38 is operated in one direction to operate pump 42, such that hydraulic fluid is drawn from sump 44 through check valve 64, is pumped through pump 42 to increase its pressure, and is pumped out through check valve 70, accumulator 76, and flow-rate control valve 56, to the lower side, or end, of ram 22, thus extending the ram. Check valves 66, 68 remain closed. These components and appropriate connectors form a fluid supply circuit for the lift cylinder.

0020Should it be desired to change the tilt of the chair by extending ram 24, motor 38 is operated in the opposite direction causing pump 42 to turn in the opposite direction to draw fluid from sump 44 through check valve 68 through pump 42, and distribute it under pressure through check valve 66, accumulator 74, and flow rate control valve 54 to the tilt cylinder 24. Check valves 64, 70 remain closed. Throughout actuation of both cylinders 22, 24, solenoid valves 48, 50 are in the positions illustrated with flow prohibited through these valves, thus preventing return of fluid to the reservoir from either of the cylinders 22, 24. These components and appropriate connectors form a fluid supply circuit for the tilt cylinder.

0021To retract cylinder 22, solenoid 50 is actuated, such that flow is allowed therethrough in the direction of arrow 50a. The weight of the chair (and also of a person therein if occupied) causes fluid to flow from the ram through fluid flow rate control valve 56, accumulator 76, solenoid valve 50, and through cushion valve assembly 62 to return fluid to sump 44. These components and appropriate connectors form a fluid return circuit for the lift cylinder.

0022Similarly, should it be desired to retract tilt cylinder 24, solenoid valve 48 is actuated so that fluid may flow therethrough in the direction of arrow 48a, through a flow rate control valve 54, accumulator 74, solenoid valve 48, and through cushion valve assembly 60 to return to sump 44. These components and appropriate connectors form a fluid return circuit for the tilt cylinder. A spring, or gravity, and the weight of a person, if occupied, operating on the tilt cylinder causes fluid to flow therefrom when solenoid valve 48 is opened. Dashed lines 94, 98 illustrate fluid return lines through which fluid which may leak past seals in the operating components to which they are connected may return freely to the sump and for the transport of air from the rod end of the rams on extension of the rams. Line 96 vents the electric motor shaft seal from overpressurization. Lines 92, 100 connect the lower-pressure sides of accumulators 74, 76 to sump 44, as will be described in greater detail below. Control orifices 93, 101 are indicated in lines 92, 100, respectively, through which fluid from the lower pressure side of accumulators 74, 76 may return to sump 44. These orifices may supply additional cushioning in the hydraulic system as will become more fully apparent as the system is described in greater detail below. Referring to <figref idref="f0001 f0003 f0004 f0005 f0006">Figs. 3-12</figref>, manifold 36 is shown as a monolithic, or unitary, block having a plurality of bores and other openings machined therein. The base, or manifold, block 36 has a motor receiving cavity 104 formed in its upper side into which motor 38 fits as illustrated generally in <figref idref="f0006">Fig. 11</figref>.

0023Referring to <figref idref="f0006">Fig. 11</figref>, the motor includes a stator 106, and a rotor 108 which has an elongate rotor, or drive, shaft 110 depending therefrom. A shaft seal 112 is provided to fit about shaft 110 on installation.

0024The manifold body has a bore 114 extending vertically therethrough through which shaft 110 extends. The lower end of shaft 110 opens into a shallow cylindrical bore, or cavity, 118 formed in the bottom of the manifold block 36 adapted to receive components of the pump assembly. As is best seen in <figref idref="f0005">Fig. 9</figref>, shallow bore 118 and motor shaft bore 114 which opens thereinto are non-concentric, with their center axes being offset. This is to accommodate the gear pump assembly 42 as will be described in greater detail below. As best seen in <figref idref="f0005">Fig. 9</figref>, a pair of kidney-shaped openings 120, 122 are formed, or machined, in the top of cavity 118 and extend a short distance upwardly into the manifold block 36 from cavity 118. The kidney-shaped openings are referred to as back tilt gear feed kidney and base lift gear feed kidneys, respectively, and are symmetrically disposed on opposite sides of motor shaft bore 114.

0025Referring to <figref idref="f0003">Figs. 4</figref> and <figref idref="f0004">5</figref>, pump assembly 42 includes four primary components. These include a base plate 126 to which an upstanding separator crescent 128 is secured. The crescent is substantially semi-circular in configuration having a concave inner side and a convex outer side. A pinion drive gear 130 rests on base plate 126 and within the concave inner side of crescent 128. A driven ring gear 132 is positioned to extend about the convex outer side of crescent 128 and about pinion drive gear 130 and has inwardly facing gear teeth which mesh with outwardly directed teeth of drive gear 130. When assembled the base plate is bolted to the underside of manifold block 36 as best illustrated in <figref idref="f0006">Fig. 11</figref>, to produce a substantially tight fit therebetween, with crescent 128, drive gear 130, and ring gear 132 resting within cavity 118. Drive gear 130 is keyed to the lower end of drive shaft 110 to be driven thereby.

0026The assembled gear pump is positioned in cavity 118 underlying kidney-shaped openings 120, 122. In operation the inner drive gear 130 keyed to the motor drive shaft 110 is rotated in either of opposite directions by actuation of the bi-directional motor. The teeth of the inner drive gear 130 mesh with the inwardly directed teeth of driven gear 132 and carry the driven gear with it upon rotation. Hydraulic fluid is moved through the pump by the opening of cavities between the gear teeth at what might be considered an inlet side and meshing of the teeth on moving toward the discharge side. The stationary crescent separates the suction and discharge portions of the pump. Such a pump provides smooth and almost pulseless flow of fluid being pumped. With the pump assembly received in cavity 118 and attached to motor shaft 110, operation of the motor and pump in one direction during operation will direct fluid under pressure into one of the kidney-shaped openings 120, 122 and operation in the opposite direction will direct fluid under pressure into the other kidney-shaped opening.

0027Describing manifold block 36 in greater detail, it has a plurality of substantially horizontally and longitudinally disposed bores 132, 134, 136, 138, 140, 142 extending inwardly from one end of block 36. A side bore 144 extends laterally inwardly from a side of base 36 as best illustrated in <figref idref="f0003">Figs. 4</figref> and <figref idref="f0004">5</figref>. It should be recognized that all of these horizontally extending bores 132-144 extend inwardly from their associated surfaces of the manifold block, but do not extend full therethrough to an opening at the opposite side of the block.

0028As possibly best seen in <figref idref="f0005">Figs. 9</figref> and <figref idref="f0006">11</figref>, vertically extending bores 148, 150 extend upwardly from kidney-shaped openings 120, 122, respectively, and intersect bores 136, 138, respectively. A plurality of substantially parallel, vertically extending bores open to the top side of manifold body 36, numbered 154, 156, 158, 160, 162, 164, 166, 168. Again, it should be recognized that these vertically extending bores extend inwardly from their associated surface of manifold block 36, but do not extend full through the block to the opposite side thereof. Referring more specifically to <figref idref="f0004">Figs. 5</figref> and <figref idref="f0005">9</figref>, a plurality of vertically extending bores 170, 172, 174, 176, 178, 180 are formed in the lower, or under, side of block 36. Again, these bores extend inwardly from their associated surface of manifold block 36 but do not extend fully through the manifold block to the opposite side thereof.

0029A plurality of vertically extending bores are provided in the bottom and top of the manifold block for receiving bolts or screws for holding the motor in place on the manifold block, and for bolting, or screwing, other assembly parts to the underside, or bottom, of the manifold block as will be described in greater detail below.

0030As will be seen several of the bores have threaded portions for connection of other elements in the assembly.

0031Fluid flow circuits within the manifold block are provided by intersections between selected ones of the horizontally disposed and vertically disposed bores. As best seen in <figref idref="f0006">Fig. 11</figref>, kidney-shaped opening 120 intersects vertical bore 148 which intersects horizontal bore 136. Similarly, kidney-shaped opening 122 intersects vertical bore 150 which intersects horizontal bore 138. Referring to <figref idref="f0006">Figs. 12</figref> and <figref idref="f0007">13</figref>, bore 136 intersects vertical bore 160 and bore 138 intersects vertical bore 162.

0032Referring to <figref idref="f0006">Figs. 12</figref> and <figref idref="f0008">14</figref>, vertical bore 158 intersects horizontal bore 134 adjacent one end of block 36, and at a more central portion of the block bore 134 intersects vertical bore 170 which opens to the bottom of the block. Similarly, adjacent one end of the block vertical bore 164 intersects horizontal bore 140 which, at a more central portion of the block, intersects vertical bore 172 which opens to the bottom of the block.

0033Referring to <figref idref="f0006">Figs. 12</figref> and <figref idref="f0007">13</figref>, horizontally disposed bore 132 intersects vertical bores 154, 156 adjacent one end of the block, and at a more central region of the block bore 132 intersects horizontal infeed bore 144 and vertical bore 170 which opens to the bottom of the block. Similarly, horizontally disposed bore 142 adjacent one end of the block intersects vertical bores 166, 168 and at a region more central of the block intersects vertical bore 178 which opens to the bottom of the block.

0034Referring to <figref idref="f0003">Figs. 4</figref>, <figref idref="f0004">5</figref>, and <figref idref="f0009">15</figref>, the component assembly parts for ball check valves 64, 68 are illustrated in greater detail. Each ball check valve includes a spring 184, a ball 186, and an elastomeric O-ring seal 188. One assembly including spring, ball, and O-ring is inserted into one of bores 176, 178 and the other spring, ball and O-ring assembly is inserted in the other of such bores. As is best seen in <figref idref="f0009">Fig. 15</figref> an additional relief 190 is machined in the mouth of each of the bores to receive its associated O-ring. When the ball check valve assemblies have been inserted into their respective bores a cover plate 192 having a pair of fluid flow bores 194, 196 extending therethrough is bolted to the underside of manifold block 36 using a plurality of screws, such as that indicated at 198 which extend through accommodating bores in plate 192 and are received in threaded bores on the underside of manifold block 36. The installed check valve assemblies are shown in <figref idref="f0009">Fig. 15</figref>.

0035After gear pump assembly 42 and check valve assemblies 64, 68 have been installed at the bottom side of manifold block 36, the circular, shallow pan, or sump, 44 is attached to the underside of the manifold block using a plurality of screws as indicated generally at 200 in <figref idref="f0009">Fig. 15</figref>. The sump pan has a large enough diameter that it encompasses bores 170, 172, 174, 176, 178, 180 and cavity 118. All of these bores opening to the bottom side of the manifold block therefore communicate with the sump. Previously noted fluid supply reservoir, or tank, 30 is operatively connected to the assembly via a hose connection 202 (see <figref idref="f0001">Fig. 3</figref>) which allows hydraulic fluid to flow through bore 144 in one side of the manifold block into bore 132 and then to exit into sump pan 44 through bore 170 in the bottom of the block (see <figref idref="f0007">Fig. 13</figref>). Hydraulic fluid thus will flow freely into the sump pan 44 to be available for use in the system. During use hydraulic fluid in fluid supply tank 30 is maintained at a level above the top of base manifold 36. Fluid thus may be provided to and remain in at least portions of those bores and assemblies directly connected to sump 44. These include, for example, portions of bores 132, 142, 134, 140, 136, 138 and pump assembly 42. Fluid thus will generally fill motor shaft bore 114 to the level of shaft seal 112 to assure motor shaft lubrication.

0036Referring to <figref idref="f0001">Fig. 3</figref>, a pair of hydraulic fittings 206, 208 are screwed into the threaded outer end portions of bores 154, 168, respectively. These fittings provide connections for hydraulic tubes, or hoses, 210, 212 which connect to the tilt cylinder and lift cylinder 24, 22, respectively.

0037Referring to <figref idref="f0007">Fig. 13</figref>, mounted within bore 136 is a tilt cylinder check valve 66, and a lift cylinder check valve 70 is mounted in bore 138. Both of check valves 66, 70 are similar in structure, and thus only one will be described in detail. Each check valve (66, 70) includes a cylindrical check valve seat member 216 which has a threaded exterior allowing it to be screwed into its associated bore which is internally threaded. The seat member has a central bore 218 extending longitudinally therethrough. The inner end region 218a of bore 218 is hexagonal allowing the valve seat to be turned by a hex wrench to screw it into or remove it from its threaded connection in its associated bore. The opposite end of bore 218, indicated at 218b, has a larger cylindrical cross section. A conically shaped valve seat 218c extends between regions 218a, 218b of the bore. A sealing assembly is mounted for shifting longitudinally in bore 218 relative to seat 218c. The sealing assembly includes an elongate stem 220 and an enlarged head 220a. An O-ring 222 is interposed between head 220a and seat 218c to produce sealing therebetween. A check valve spring 224 yieldably urges the check valve assembly to a closed position as illustrated for check valve 70 with head 220 pressed tightly against O-ring 222 which bears against valve seat 218c. A threaded plug 226 screwed into the threaded outer end of bore 136 with an O-ring seal 228 therebetween seals the outer end of bore 136 and provides a stop for one end of spring 224. Pressure fluid entering through end portion 218a of bore 218 acts against the check valve assembly to overcome the force of spring 224 and will open the valve to allow pressurized fluid to flow outwardly therethrough. Pressure fluid impressed against the enlarged head 220a on the spring side thereof acts to seal the check valve. Referring still to <figref idref="f0007">Fig. 13</figref>, accumulators 74, 76 are illustrated in greater detail. They are substantially similar in design, and thus only one will be described in detail. Referring to accumulator 76, it includes a piston body, or plunger, 234 having a u-cup seal 236 extending thereabout. The piston body and seal are slidably mounted in bore 142 with a spring 238 yieldably biasing the piston body toward the outer end of bore 142. A spring 239 in bore 132 associated with accumulator 74 is shorter than spring 238 and may exert a different biasing force. Mounted within piston body 234 is pressure relief valve assembly 82. A similar pressure relief valve assembly 80 is mounted in the piston body of accumulator 74 in bore 132. The pressure relief valve assembly 82 includes a check valve element 242 biased by a spring 244 toward a valve seat 246 with an O-ring 248 therebetween. The spring forces exerted by springs 238, 244 differ. Should a rapid increase in pressure beyond that which can be resisted by spring 244 be imposed upon the piston head the check valve element 242 will move away from seat 246 to allow the release of pressure fluid through piston body 234 to escape through bore 178 to the sump. These component parts are illustrated generally slidably received in bore 142 with a screw plug 250 screwed into the threaded end of bore 142 with an O-ring seal 252 therebetween to seal the end of bore 142 and hold the component elements therein. Although not illustrated in detail in <figref idref="f0007">Fig. 13</figref>, bores 170, 178 could hold control orifices 93, 100, respectively, of a selected size to provide controlled return of fluid from bores 132, 142 to sump 44. Such controlled return of fluid could enhance the operation of the accumulators.

0038Referring to <figref idref="f0010">Fig. 16</figref>, self-actuating flow rate control valves 54, 56 are mounted in vertical bores 154, 168, respectively. Each of the flow rate control valve assemblies 54, 56 are similar, and thus only one will be described in detail. An elongate cylindrical cup-shaped body 256 having a closed bottom end and an open upper end is received in bore 168. An O-ring seal 258 seals the space between body 256 and bore 168. As is seen in the drawing, a major portion of the body 256 below O-ring seal 258 has a smaller diameter than bore 168 so that fluid may flow therepast. A cylindrical spool 260 having a fluid control orifice 262 in its upper end is slidably mounted in close contact with the inner surface of body 256. Spool 260 is yieldably urged upwardly by a spring 264 against a retaining ring 266. A side bore 268 extends through at least one side of body 256 adjacent the lower end of spool 260 when the spool is resting against retaining ring 266 as shown in its position illustrated for assembly 56.

0039The flow rate control valve assembly is inserted slidably into its associated bore 168, as would be flow rate control assembly 54 in bore 154, and then hydraulic fittings 206, 208 are screwed into the threaded outer end portions of bores 154, 156 serve to hold the flow rate control valve assemblies in their bores (see <figref idref="f0001">Fig. 3</figref>).

0040As is seen in <figref idref="f0010">Fig. 16</figref>, the lower end of bore 168 is in fluid communication with horizontal bore 142. When pressure fluid is supplied through bore 142 to bore 168 to direct operating fluid to a cylinder the assembly is in the position illustrated for assembly 56. Fluid flows from bore 142 into bore 168 through side bore 268, up through spool 260 and through orifice 262, with orifice 262 controlling the rate of fluid flow.

0041When fluid is permitted to return from a ram it may initially be at a higher pressure at the start of the return process and thus it may be necessary to provide additional restriction to the rate of fluid flow through such a valve assembly. Action of a flow rate control assembly for this purpose is illustrated in the action of flow rate control assembly 54 at the right side of <figref idref="f0010">Fig. 16</figref>. Here higher pressure fluid entering the top of bore 154 which might otherwise flow at too rapid a rate in the system produces a force against the top surface of spool 260 which will compress spring 264 sliding spool 260 downwardly to close off at least a portion of side bore 268. This provides a momentary added restriction to the flow of fluid returning from a ram. After the initial excessive pressure surge, or flow rate, has subsided somewhat spool 260 will be urged slightly upwardly again to partially open side bore 268 and provide controlled flow rate through its upper orifice 262. The specified fluid flow rating is determined mainly by the diameter of control orifice 262 and the strength of spring 264. The tolerance of fit between body 256 and spool 260, the length of spool 260 and the location and size of the side bore 268, also may have an effect on the function of this valve assembly.

0042Referring to <figref idref="f0008">Fig. 14</figref>, cushion valve assemblies 60, 62 are received in bores 134, 140, respectively. Since both of these cushion valve assemblies are substantially the same only one will be described in detail. Referring to assembly 60, it includes an elongate, generally cylindrical, plunger, or element, 274 slidably mounted in bore 134. The closed end of plunger 274 is directed toward the outer end of bore 134. A hollow internal bore 276 extends through a major portion of the plunger and opens toward the opposite end of the plunger. A spring 278 interposed between the closed inner end of bore 134 and plunger 274 yieldably biases the plunger 274 toward the outer end of bore 134. A check valve ball 280 is received within bore 276 between a conically-shaped valve seat 282 and a retainer sleeve 284 having an opening 284a at its lower end. Sleeve 284 is open at 284b along one side thereof to allow passage of fluid past the sleeve. Ball 280 is freely movable in bore 276 under the influence of fluid pressure imposed thereon between a closed position against valve seat 282 (as shown for assembly 62) and an open position spaced from valve seat 282 (as shown for assembly 60). A cross bore 288 extends through a wall of plunger 274 forwardly of valve seat 282. Plunger 274 has the elongate, generally cylindrical, configuration illustrated in <figref idref="f0008">Figs. 14, 14A, and 14B</figref>. Opposed sides of the forward end are beveled inwardly on progressing toward the forwardmost end as indicated at 274a, 274b. These beveled sides extend generally to the longitudinal midpoint of the plunger. The remainder of the forward portion of the plunger retains is generally cylindrical configuration between beveled sides 274a, 274b to provide good sliding contact and aligning engagement between the plunger 274 and its associated bore 134 throughout movement of the plunger in the bore. The beveled sides allow gradual opening of fluid flow passages from bore 34 to bore 170 as the plunger is shifted from its position as illustrated for cushion valve 62 to the position illustrated for cushion valve 60. Plunger 274 is not tightly confined, or sealed, against the walls of bore 134 and thus some fluid may seep therepast for purposes as will be described in greater detail below.

0043Plugs 290 screwed into the outer ends of bores 134, 140 with O-rings therebetween seal the outer ends of these bores.

0044Cushion valve assemblies 60, 62 are slidably mounted in their respective bores 134, 140 adjacent intersecting bores 170, 172, respectively. The cushion valve plungers are shiftable under the influence of pressure in their respective bores between a closing position as illustrated for cushion valve assembly 62 and an open flow position as illustrated for valve assembly 60. Plungers 274 each have a cross sectional configuration closely complementary to the cross sectional configuration of their associated bores 134, 140. In an at rest condition bores 134, 140, 170, 172 are below the level of the hydraulic fluid held in supply tank 30, and thus the components of the cushion valve assembly 60, 62 are submerged in hydraulic fluid. The fluid fills the space behind plungers 274 and in the region of the spring 278.

0045A close sliding fit is provided between plunger 274 and its associated bore with a slight space therebetween. In an exemplary embodiment the diameter of the bore may be approximately 0.250 inch (plus or minus 0.0005 inch) and the diameter of the plunger may be 0.248 inch (plus 0.001 and minus 0.000 inch). The hydraulic fluid, or oil, used in such exemplary system is Unocal Unax AW Grade 46. When the pressure of return fluid in a bore 134, 140 is exerted against the head of a plunger 274, fluid from the region of spring 278 will gradually seep therefrom between the walls of the plunger and the bore to exit into the outlet port (170, 172) so that the plunger may move to its retracted position as illustrated for the plunger of assembly 60.

0046When fluid pressure in a bore 134, 140 subsides the plunger of a cushion valve assembly in the position illustrated for assembly 60 begins to return toward its extended position under the urging of spring 278. The space behind the plunger lacks sufficient hydraulic fluid to fill the space as the plunger is moved forwardly under the influence of spring 278. Fluid remaining in bores 134 and 170 flows through cross bore 288, opens the check valve ball 280 in the plunger, and flows into the space behind the plunger as it is extended by spring 278. Thus the space behind the plunger again becomes filled with hydraulic fluid as the plunger returns to the position illustrated for valve assembly 62. The check valve speeds up the response of the cushion valve.

0047Referring to <figref idref="f0001">Figs. 3</figref>, <figref idref="f0006">12</figref>, and <figref idref="f0011">17</figref>, a pair of electrically actuated solenoid valves 48, 50 are secured atop manifold block 36. Solenoid valve 48 overlies bores 156, 158, 160 and solenoid valve 50 overlies bores 162, 164, 166. Solenoid valve adapters indicated generally at 294, 296 are interposed between their associated solenoid valves and the underlying manifold block. Each of the solenoids and its underlying adapter is substantially the same, and thus only one set will be described in detail.

0048Solenoid control valves 48, 50 are substantially similar. As best seen in <figref idref="f0006">Fig. 12</figref>, solenoid control valve 48 is positioned to control the flow of fluid between bore 158 and bores 156, 160 adjacent thereto. Similarly, solenoid control valve 50 is positioned to control the flow of fluid between bore 164 and bores 162, 166 adjacent thereto. Each solenoid control valve is associated with a base adapter 294, 296, respectively. When the adapter is screwed into one of the threaded bores 158, 164, a second orifice in the adapter will be aligned with an adjacent bore. Although not shown in detail, a solenoid control valve includes a spring-biased plunger which is normally closed, or seated, against the top of a bore in its associated adapter to prevent flow of fluid therethrough. Upon actuation of the solenoid the plunger is lifted to permit fluid flow.

0049Referring to <figref idref="f0011">Figs. 17-20</figref>, adapter 294 comprises a unitary, or monolithic, body having a threaded lower protrusion 298 adapted to be screwed into the threaded upper end of its associated bore 158. A central bore 300 extends vertically through the adapter opening in the center of protrusion 298 and into the center of an internally threaded solenoid receiving cavity 302. A portion of bore 300, such as that shown at 300a, may be selectively sized to control fluid flow rates therethrough. Bore 300 and portion 300a should be larger in cross-section than orifice 262 in the flow rate control valve assemblies 54, 56. This allows valve assemblies 54, 56 to perform their intended function, which they may not do if orifices 300, 300a are smaller. A circumferential channel 304 extends about the underside of body 294 and is positioned to overlie the upper ends of both of bores 156, 160 in body 36. An inclined, or side, bore 306 connects channel 304 with cavity 302 in a region offset to one side of the upper end of bore 300. As is best seen in <figref idref="f0011">Fig. 17</figref>, two additional smaller annular channels 310, 312 are concentric with channel 304 and receive O-rings 314, 316, respectively, to provide a seal between adapter 294 and base 36.

0050Solenoid 48 is shown secured in the top of adapter 294 by being screwed into threaded cavity 302. A vertically shiftable plunger 320 is controlled by operation of the solenoid. Plunger 320 is shiftable between its normally-closed position as illustrated in <figref idref="f0011">Fig. 17</figref> which closes off the top of bore 300. Upon actuation of the solenoid plunger 320 is raised from the top of bore 300 to permit fluid communication between bore 300 and inclined bores 302, 306. It should be recognized that bores 156, 160 are constantly in communication with each other through annular channel 304.

0051Describing operation of the embodiment described, a chair as illustrated in <figref idref="f0001">Fig. 1</figref> initially may be in its lowered and substantially upright position illustrated in dashed outline at 10a. In this position its lift cylinder 22 is retracted and tilt cylinder 24 is extended. To cause the chair to rise the operator presses the "Up" button on the touch pad 86 which provides a signal to the circuit board 88 causing motor 38 to turn in the proper direction to actuate pump 42 to provide fluid under pressure to lift cylinder 22. Fluid is drawn from sump 44, through check valve 64, through pump 42, through check valve 70, past accumulator 76, and through flow rate control valve 56 and another filter 84 to the lower end of cylinder, or ram, 22 to cause the chair to rise. Accumulator 76 moderates the flow of pressure fluid both at starting and stopping of cylinder movement. With the flow rate valve 56 disposed in the fluid supply circuit between the accumulator and actuator 22, valve 56 and the accumulator work together to moderate any fluid pressure surges. Explaining further, should an initial fluid pressure surge be produced by pump 42 such will be somewhat blocked by the restricted orifice of valve 56 permitting time for accumulator 76 to absorb the pressure surge. The chair as raised is shown in solid outline in <figref idref="f0001">Fig. 1</figref>. To tilt the chair back to the position illustrated in dashed outline at 10b and referring to <figref idref="f0002">Fig. 2</figref>, the operator presses the "tilt back" button position on the touch pad 86 which provides a signal to the circuit board 88. This sends a signal through the circuit board to open solenoid control valve 48. Fluid then may return from ram 24 under the actuation of patient load and spring or joist the spring connected to the ram such as to return fluid under pressure from ram 24 through opened solenoid control valve 48 to sump 44. As the pressurized fluid returns flow rate control valve 54, accumulator 74, and cushion valve 60 moderate and control the flow of fluid to produce comfortable action of the chair as will be described in greater detail below. More specifically, at the start of fluid return, fluid flow moderation is provided mainly by the flow rate control valve and the cushion valve. When fluid return ceases, by closing of the solenoid control valve, fluid flow rate moderation at the end of movement is provided mainly by joint action of the accumulator and flow rate control valve.

0052Referring still to <figref idref="f0002">Fig. 2</figref>, to retract the lift cylinder the "down" button on the touch pad is actuated which sends a signal to the circuit board to open solenoid control valve 50. Fluid is returned from ram 22 under pressure produced by the weight of the party in the chair and/or the chair itself. As fluid flows from ram 22 through solenoid control valve 50 toward sump 44, the movement of the fluid, and thus the movement of the ram and the chair is moderated by action of the flow rate control valve 56, accumulator 76, and cushion valve 62 as will be described in greater detail below. More specifically, at the start of fluid return, fluid flow moderation is provided mainly by the flow rate control valve and the cushion valve. When fluid return ceases, by closing of the solenoid control valve, fluid flow rate moderation at the end of movement is provided mainly by joint action of the accumulator and flow rate control valve.

0053To return the chair from its tilted back position indicated at 10b in <figref idref="f0001">Fig. 1</figref> to its solid outline position illustrated in <figref idref="f0001">Fig. 1</figref>, the operator presses the tilt return button on the touch pad 86. This causes motor 38 to turn in the proper direction to actuate pump 42 to provide fluid under pressure to tilt cylinder 24. Fluid is drawn from sump 44 through check valve 68, through pump 42, through check valve 66, past accumulator 74, and thence through flow rate control valve 54 to the lower end of tilt cylinder, or ram, 24. Accumulator 74 moderates the initial flow of pressure fluid to smooth its operation and flow rate control valve assists in this as previously described in the operation of accumulator 76 and flow rate control valve 56. Referring to the physical structure of the embodiment described, as opposed to the schematic drawing described in <figref idref="f0002">Fig. 2</figref> above, in <figref idref="f0007 f0008 f0009 f0010 f0011">Figs. 13-17</figref> operative elements for control of fluid supply and return to the lift cylinder 22 are shown in their at rest position, neither extending nor retracting cylinder 22. In the illustrations such assemblies relate to check valve 64 (<figref idref="f0009">Fig. 15</figref>) which is closed, check valve 70 (closed in <figref idref="f0007">Fig. 13</figref>), accumulator 76 and its pressure relief valve 80 (<figref idref="f0007">Fig. 13</figref>), flow rate control valve 56 (<figref idref="f0010">Fig. 16</figref>), and cushion valve 62 (<figref idref="f0008">Fig. 14</figref>). The actual position of the piston body 234 may be retracted somewhat dependent upon the position of the chair and thus the pressure of fluid imposed upon the piston body.

0054The operative positions of such valve assemblies will be described initially in regard to operation of the tilt cylinder 24, recognizing that operation of the valve assemblies in the side of the control circuit for the lift cylinder would be substantially the same.

0055Referring to <figref idref="f0006">Figs. 11</figref>, <figref idref="f0007">13</figref>, and <figref idref="f0009">15</figref>, upon actuation of motor 38 and pump 42 in a rotational direction to supply fluid to extend tilt ram 24, fluid is drawn upwardly from sump 44 through check valve 68 in which ball 186 lifts off of O-ring seal 190 against the urging of spring 184, as illustrated in <figref idref="f0009">Fig. 15</figref>, upwardly through bore 178, and into bore 138. Fluid then flows downwardly through bore 150 into kidney-shaped opening 122 to be acted upon by crescent gear pump assembly 42 which pumps the fluid under higher pressure through kidney-shaped opening 120 up through bore 148 and into horizontal bore 136. Pressure fluid thus supplied into horizontal bore 136 acts to hold ball check valve 64 closed as illustrated in <figref idref="f0009">Fig. 15</figref> and to open check valve assembly 66 as illustrated in <figref idref="f0007">Fig. 13</figref>. With check valve assembly 66 opened, and head 220aand seal ring 222 moving away from seat 218c, fluid may flow upwardly through vertical bore 160, under the annular channel 304 in adapter 294 (as illustrated in <figref idref="f0011">Fig. 17</figref>) and downwardly through bore 156 into bore 132. The actual initial position of the piston body of accumulator 74 may be retracted somewhat with spring 239 slightly compressed depending on weight of patient and position of back (spring load). Additional piston movement is a result of initial rush of fluid. As pressurized fluid enters bore 132 on the pressure side of piston 234 of accumulator 74, it causes the piston to move rearwardly into what may be considered to be a lower pressure side of the piston against the yieldable biasing force of spring 239. This moderates the initial rush of pressurized fluid moving toward tilt ram 24. Since bore 132 on the lower pressure side of piston 234 (the side of spring 239) normally is filled with fluid, a portion of such fluid wall be forced from bore 132, through bore 170 to return to the sump. Pressure relief valve 82 also is capable of release to allow pressurized fluid to move therethrough to flow from the pressure side of the accumulator piston body to the lower pressure side of the piston and to drain therefrom through bore 170 back into the sump, if the pressure of the fluid supplied is greater than that to be controlled by the pressure relief valve 82.

0056Fluid moving past the accumulator enters bore 154 (as seen in <figref idref="f0007">Figs. 13</figref> and <figref idref="f0010">16</figref>) to flow rate control valve 54. The fluid flows through side port, or bore, 268 through orifice 262 in spool 260 and continues therefrom toward the tilt ram 24. When fluid is flowing toward the tilt ram, fluid rate control valve 54 would be in the position as illustrated for valve 56 in <figref idref="f0010">Fig. 16</figref>. Port, or bore, 268 would be substantially clear for fluid to flow therethrough and the rate of fluid flow would be controlled solely by the size of orifice 262 in the end of spool 260. The moderating action of the accumulator and flow rate control valve produces a comfortable rate of tilt for a user of the chair.

0057Throughout this action the solenoid control valves 48, 50 remain closed. Also check valves 64, 70 remain closed.

0058To operate the system to extend ram 22 and raise the chair, motor 38 and pump 42 are operated in such a direction that fluid is drawn upwardly from sump 44 through ball check valve 64, into horizontally disposed bore 136, and down through bore 148 into kidney-shaped opening 120. Fluid thus delivered to the gear pump is pumped under pressure through kidney-shaped opening 122 to bore 150 and into horizontally disposed bore 138. This causes ball check valve 68 to close and check valve 70 in bore 13 8 to open. Fluid flows upwardly through bore 162 through annular channel 304 in a solenoid adapter, downwardly through vertical bore 166 into accumulator bore 142 to impact accumulator piston 234. Again, this accumulator piston, as was described previously for accumulator piston 74, may shift longitudinally of bore 142 under the influence of fluid pressure against one side of its head and spring 238 and fluid in bore 142 on its opposite side to moderate fluid pressure surges. Fluid then travels from bore 142 into vertical bore 168, through flow rate control valve 56, and to the lift cylinder. The valves and valve assemblies in the circuit supplying fluid to the lift ram operate similarly to those described for the circuit supplying the tilt cylinder.

0059To retract a ram, such as the tilt ram 24, solenoid control valve 48 is opened, by raising plunger 320 (see <figref idref="f0011">Fig. 17</figref>). This permits fluid to flow from the tilt cylinder 24 to cause the ram 24 to retract. Fluid under pressure flows initially into flow rate control valve 54. The initial rush of higher pressure fluid is such as to impact upon the head of spool 260 and urge it to move downwardly as illustrated in <figref idref="f0010">Fig. 16</figref> against the yieldable urging force of spring 264. The lower end of the spool partially covers side bore 268 to add additional control for the rate of fluid flow through this valve.

0060After the initial rush of fluid, spool 260 will reach a stabilized condition within sleeve 256 such that fluid will flow at a controlled rate outwardly therefrom to accumulator bore 132 where additional moderating will occur of the fluid pressure and flow.

0061Fluid flows from accumulator bore 132 upwardly through bore 156 and around channel 304 and up bore 306. Since check valve 66 will be closed at this time the only escape for such fluid is through the upper end of bore 300 of the adapter (which has been opened by raising plunger 320) and downwardly through bores 300 and 158. Bore 158 intersects horizontally disposed bore 134 as best seen in <figref idref="f0006">Figs. 12</figref> and <figref idref="f0008">14</figref>. Fluid flowing therein impacts the head end of plunger 274 which initially is in the position shown at the left side of <figref idref="f0008">Fig. 14</figref> for cushion valve 62. As the pressurized fluid in bore 134 presses the plunger rearwardly against the biasing force of spring 278, fluid captured in the region of spring 278 behind the plunger seeps outwardly around the periphery of the plunger to exit through fluid return bore 170 which leads to the sump. Due to the length of plunger stroke as well as the close fit between the plunger and bore wall only a limited rate of fluid seepage occurs past the plunger so that the start of retraction of the ram is cushioned. Eventually sufficient fluid will seep from the region behind plunger 274 that it reaches the position illustrated for the plunger at the right side of <figref idref="f0008">Fig. 14</figref> which exposes a larger portion of bore 170 for the flow of fluid from bore 134.

0062When solenoid valve 48 is closed again fluid pressure in bore 134 will be reduced and plunger 274 will be urged forwardly under the influence of spring 278 against a body of fluid trapped between bore 134 and the solenoid control valve. As this occurs, since fluid previously has been expressed from the rear side of the plunger, as the plunger moves forwardly under the action of spring 278 a lower pressure occurs in the area of spring 278 causing fluid in bores 134 and 170 to enter through cross bore 288, unseat ball 280, and allowing fluid to again fill the space behind the plunger, such that it is in position again for providing cushioning for the next return cycle. This occurs quickly so the tilt down movement is quick and responsive to quickly energizing the touchpad.

0063Retraction of lift cylinder 22 is effectuated in much the same manner, but here solenoid control valve 50 is opened with the cushioning and flow rate control therein provided by flow rate control valve 56, accumulator 76, and cushion valve 62.

0064The apparatus disclosed herein and its method of operation provide many advantages over prior systems. First, the system is simplified both in the hydraulic control circuit and the electrical control circuit to provide both lifting and tilting for the chair. By use of the crescent gear drive pump higher pressure capabilities are obtained with a smoother and quieter flow and operation. In the present device the gears are formed in involute profiles which do not require tight tolerances. In one embodiment 14 pinion teeth and 19 driven teeth may be provided for smooth and quiet operation.

0065The monolithic manifold with a number of intersecting bores machined therein extending inwardly from external surfaces of the block, but not extending fully therethrough, with a plurality of valve and control assemblies received in the bores and closing plugs with seals, provides a compact efficient system which minimizes possibilities of leakage. Further, it provides a system which has a small external configuration making it more compact for use in selected systems.

0066The accumulators disclosed are inexpensive and simple to manufacture and operate. Since the rear side of each accumulator piston is connected to the sump the spring and piston may be bathed in oil for lubrication purposes and any small leakage across the piston seal will not greatly affect assembly performance. Further, since the entire accumulator assembly is incorporated into the base, or manifold, no external hoses or connectors are needed for the accumulators.

0067Pressure compensated flow rate controls, which are self-actuating, provide restrictions so that the accumulator valves function properly and can compensate for a load so that the cylinders may retract at the same general speed regardless of the load on the chair. They provide a pressure drop so the accumulators may work for a wide variety of patient loads.

0068By including pressure relief valves in the accumulator pistons an inexpensive method is achieved for providing a relief path for hydraulic fluid in the event of overpressurization. Addition of such pressure limiting devices allows the omission of limit switches which normally would shut off a pump at full cylinder extension.

0069Timers are provided on the circuit board to limit the time that the pump operates. Further, similar time restraints are placed on the solenoids to limit the amount of time in which they are open or producing return action of the rams. The inlet check valve assemblies are simple and inexpensive ways to accomplish the need for sealing in one direction and minimal pressure drop free flow in the other direction. Particularly of interest are the O-rings in the check valves at the base of the unit which are improvements over hard seat-type valves which may be inclined to leak. The O-rings provided supply a soft seal which produces generally trouble-free sealing.

0070The solenoid adapter base providing a circular path for oil between spaced apart bores not only provides a convenient method for providing desired fluid paths, but also may be supplied with different sized orifices and solenoid mounts so that different applications may be achieved.

0071The cushion valves provide smooth start of the lowering or return tilt action. They provide a smooth, slow chair movement at first and then allow more rapid movement through intermediate actuation.

0072The design of the monolithic base, or manifold, is such that there are a minimal number of plugged bores and the stacking of parts on a machining center for producing such may be optimized. Also, combining these parts into the pump assembly minimizes costs, reduces potential leak points, and minimizes the volume of the assembly for convenient installation and use. Further, minimization of the height of the assembly allows the chair to move lower than would be permitted with earlier units.

0073With the kidney-shaped openings machined into the manifold, or base, they may be precisely located with respect to the gears in the gear pump. This assists in providing quiet and smooth operation.