CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of the filing date of U.S. Provisional Patent Application Serial No. 61/372,217, filed August 10, 2010. the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This invention relates to a power assisted motion control system. More particularly, this invention relates to a vehicle unitary electro-hydraulic rack and pinion power steering system.

BACKGROUND OF THE INVENTION

[0003] Power assisted motion control systems of many different types are known and have been employed on many applications, including vehicle power steering systems. Such power steering systems may be hydraulic, electromechanical or electro-hydraulic. Such power steering systems may use hydraulic energy or electrical energy or both to create a controlled force on a mechanical steering linkage of the vehicle [0004] Hydraulic power steering systems may use a hydraulic pump driven by a prime mover engine of the vehicle to supply hydraulic fluid under pressure to assist in moving a steering linkage of the vehicle. Electro-mechanical power steering systems may use an electric motor to assist in moving the steering iinkage. Electro-hydraulic power steering systems may use an electric motor to drive a hydraulic pump on demand to supply hydraulic fluid under pressure to assist In moving the steering Iinkage.

[0005] Known hydraulic power steering systems and electro-mechanical power steering systems may have limitations relating to energy efficiency, cost, and/or power density, particularly for applications in small recreational vehicle or small utility vehicles such as turf maintenance applications. Known hydraulic power steering systems for such applications may include a gerotor gear set rotated by the operator controlled steering wheel. Such rotation of the gerotor gear set may meter fluid flow to a power assist hydraulic cylinder, and the fluid may be supplied under pressure by a fixed displacement hydraulic pump continuously driven by the prime mover engine of the vehicle. Due to the nature of fixed displacement pumps, a horsepower loss may be incurred at ail times during vehicle operation whether or not the power assist is being used. This is because the pump may always be driven by the prime mover engine and may therefore provide hydraulic fluid flow even when no flow is required from the power assist. In addition, packaging of these components in a typical vehicle may generally require the gerotor set and power assist hydraulic cylinder to be remote from the hydraulic pump, thereby requiring hoses and fittings to make hydraulic connections between these components. As a result, further efficiency losses may occur from flow resistance in the hoses in the system. Electro-mechanical power steering systems commonly may suffer from a lack of power density.

[0006] Electro-hydraulic power steering systems may provide advantages relating to energy efficiency, cost, and/or power density. One known electromechanical power steering system is described in United States Patent No. 5,209,317. The system described in this patent includes an electric motor driven hydraulic pump that provides fluid pressure on demand and that stores hydraulic fluid under pressure in an accumulator. Another known electromechanical power steering system is described in United States Patent No. 5,928,041 , which is incorporated herein by reference in Its entirety. The power steering system disclosed in the latter patent is described with reference to boating applications. In such boating applications, a steering input may be provided by an operator rotating a steering wheel located near one end of the boat, and power steering assist may be applied to the steering linkage at the opposite end of the boat. A mechanical push/pull cable may be employed to operably connect and transfer the rotational input of the steering wheel to the power assist mechanism. A hydraulic pump and Its associated electric drive motor may be remotely located from the power assist mechanism. SUMMARY OF THE INVENTION

[0007] The present Invention provides a motion control system that may be used in a wide variety of applications.

[0008] The motion control system includes a pinion housing, a pinion disposed in the pinion housing for rotational movement relative to the pinion housing, and a rack in meshing engagement with the pinion and disposed in the pinion housing for linear movement relative to the pinion housing and relative to the pinion.

[0009] The motion control system also includes a hydraulic cylinder housing having fluid chambers. A rod is disposed in the hydraulic cylinder housing for linear movement relative to the hydraulic cylinder housing in response to a fluid pressure differential between the fluid chambers. The rod is fixed for movement with the rack.

[0010J The fluid pressure supply system Includes a hydraulic control valve. The hydraulic control valve has an Inlet side and a fluid pressure supply side and is movable between a neutral position and an actuated position. Fluid passages hyd radically connect the fluid pressure supply side to one of the fluid chambers of the hydraulic cylinder when the hydraulic control valve is in the actuated position. The hydraulic control valve Is actuated by movement of the pinion housing relative to the rack and relative to the cylinder housing. The motion control system according to the present invention further includes a main housing, with the hydraulic control valve being carried by the main housing. The fluid passages are disposed substantially entirely within the main housing and the hydraulic cylinder housing. The fluid pressure supply system also includes a hydraulic pump, a fluid reservoir, and an accumulator, all of which are carried by the main housing. The main housing includes a cavity, and the hydraulic pump is disposed in the cavity of the main housing. Additional fluid passages hyd radically connect the hydraulic pump and the accumulator and the inlet side of the hydraulic control valve, and at least one check valve Is disposed in the additional passages between the hydraulic pump and the accumulator. The additional passages are disposed substantially entirely within the main housing.

[0011] The pinion housing is movable relative to the main housing, and a link fixes the rod and the input rack for movement together relative to the main housing. Additionally, another link fixes the main housing and the cylinder housing against relative movement together. A valve actuator link is fixed to the hydraulic control valve and is moveable to displace the hydraulic control valve between the neutral position and the actuated position. The hydraulic control valve includes valve gear teeth, and the valve actuator link includes actuator gear teeth in meshing engagement with the valve gear teeth. A spring connection acts between the input rack and the valve actuator link. a

[0012] Further according to the present invention, the pinion housing, the hydraulic cylinder housing, and the fluid pressure supply system are unitary. The hydraulic control valve Is a closed center valve, and the motion control system is a vehicle power steering system.

[0013] The invention also provides various ones of the additional features and structures described in the claims and description set out below, alone and in combination, and such claims are incorporated by reference in this summary of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments of this invention will now be described in further detail with reference to the accompanying drawings, in which:

[0015] Figure 1a is a front elevation view of a preferred embodiment of the present invention;

[0016] Figure 1b is a side elevation view of the embodiment shown in Figure 1a, as viewed from the left side of Figure 1a;

[0017] Figure 1c is an opposing side elevation view of the embodiment shown in Figure 1a, as viewed from the right side of Figure 1a; ?

[0018] Figure 2 is an exploded perspective view of the embodiment shown in Figure 1a;

[0019] Figure 3 is an enlarged view similar to Figure 1a, showing the embodiment of Figure 1a in partial cross section with certain components shown in cross section and other components shown in elevation;

[0020] Figure 4 is a hydraulic schematic circuit diagram of the embodiment shown In Figure 1a;

[0021] Figure 5 is a partial cross section view as in Figure 3, showing zero to initial input torque applied to the embodiment shown In Figure 1a;

[0022] Figure 6 is a view similar to Figure 5, but showing a greater input torque applied to the embodiment shown in Figure 1a;

[0023] Figure 7 is a view similar to Figure 6, but showing movement of the cylinder in response to the input torque applied; and

[0024] Figure 8 is a view similar to Figure 7, but showing input torque applied to the embodiment shown in Figure 1a further reduced to zero after the cylinder has moved to reduce the input torque to zero. DETAILED DESCRIPTION OF THE INVENTION

[0025] The principles, embodiments and operation of the present invention are shown in the accompanying drawings and described in detail herein. These drawings and this description are not to be construed as being limited to the particular illustrative forms of the invention disclosed, ft will thus become apparent to those skilled in the art that various modifications of the embodiments herein can be made without departing from the spirit or scope of the invention.

[0026] Referring now to the drawings in greater detail, Figures 1-3 illustrated a preferred embodiment of a power assisted motion control system 10 which is applied as a vehicle steering system. As illustrated in Figures 1-3, the system 10 Is a vehicle electro-hydraulic rack and pinion closed center power steering system. The system 10 is a unitary system assembly and includes a pinion housing 18 carrying an input pinion 12 and input rack 20, a hydraulic cylinder 30, and a main housing 50 carrying and connecting an electric motor 40, hydraulic pump 48, steering control valve 60, and accumulator 62. The term unitary means of a multi-piece construction assembled such that the multiple pieces function as a single device without external fluid hoses or other external fluid pressure lines. The input rack 20 and pinion 12 provide an input to the system and allow for manual steering in the event of a loss of hydraulic pressure, as further described below. [0027] The input pinion 12 is located at the end of an input shaft 14. The input shaft 14 is of a known design and, at an end opposite the input pinion 12, the input shaft 14 includes a known device connecting an operator controlled vehicle steering wheel or other input device (not shown) to the input shaft 14, The input shaft 14 illustrated in Figures 1-3 also includes two universal joints 16. The input pinion 12 is located within and rotates relative to a pinion housing 18 and, within the pinion housing 18, meshes with an input rack 20 in a known manner.

[0028] A link 24 fixes the input rack 20 for movement with a rod 28 of a hydraulic cylinder housing 30. The hydraulic cylinder housing 30 is fixed to and carried by a main housing 50 by suitable threaded fastener links illustrated in Figure 2. The rod 28 is movable for causing and controlling motion of a controlled device. In the preferred embodiment shown in Figures 1-3, the controlled device is a steering linkage of a vehicle in which the system 10 is arranged. For example, in a wheeled vehicle, the cylinder 30 is a steering cylinder and opposite ends of the rod 28 of the steering cylinder 30 may be connected either directly or indirectly through a linkage to steerable control arms of the vehicle in a known manner. The rod 28 of the steering cylinder 30 connects to a piston 32 (Figure 2) for dividing an interior chamber of the cylinder housing 34 into two chambers, in a known manner. The piston 32 and thus, the rod 28, are movable relative to the cylinder housing 34 in response to a differential pressure in the two chambers. [0029] The unitary steering system 10 further includes a hydraulic system for providing hydraulic fluid to the steering cylinder 30. The hydraulic system includes an electric motor driven pump 48 and an electric motor 40. In one embodiment, the eiectric motor 40 is a one-direction direct current electric motor. An electrical connector 42 connects the motor 40 to an outside electrical power source. The electric motor 40 is operatively coupled to the hydraulic pump 48 (Figure 2). In the embodiment shown in Figures 1-3, the hydraulic pump 48 is a known gear type pump that provides hydraulic fluid flow under pressure when the pump 48 is rotated by the electric motor 40. The hydraulic pump 48 is received In a cavity of a main housing 50, and an open end of the cavity receives and is closed by the electric motor 40. The cavity forms a portion of a reservoir 56 within the housing 50. The reservoir 56 Is located immediately above the cavity and is closed with a fill cap 58.

[0030] The electric motor 40 Is operably connected to the pump 48 for driving the hydraulic pump 48 for drawing fluid from the reservoir 56 and providing the fluid to a closed center control valve 60. The closed center valve 60 includes a fluid inlet side 60a and a work cylinder side 60b. In the illustrated embodiment, the hydraulic system also includes an accumulator 62 for storing hydraulic fluid under pressure and, when necessary, providing hydraulic fluid to the control valve 60. The control valve 60 is a known rotary type control valve having a closed center neutral position, a first open or actuated position when rotated clockwise away from the center position, and a second open or actuated position when rotated counter-clockwise away from the center position. As shown with reference to Figure 3, the control valve 60 has a generally circular profile and includes gear teeth on a portion of its outer circumference. The control valve 60 is preferably of a construction shown in above referenced U.S. patent number 5,928,041. The hydraulic pump 48, accumulator 62, control valve 60, reservoir 56, and hydraulic cylinder housing 30 are all fixed to and carried by the main housing 50 and are all hydrauf really connected by passages 68 that are disposed substantially entirely within the main housing 50.

[0031] Still referring to Figures 1-3, the unitary steering system 10 further includes a control valve actuator link 70, which is a control valve spool rack for Interacting with and controlling the rotation of the control valve 60. The spool rack 70 is tubular and includes opposite first and second ends. Gear teeth are formed in a central portion of the exterior of the spool rack 70 for meshing with the gear teeth of the control valve 60 for forming a rack and pinion type interaction. The input rack 20 extends through the center of the spool rack 70 and is supported relative to the spool rack 70 by bushings that enable the input rack 20 to move axially relative to the spool rack 70. A first end of the spool rack 70 is fixed relative to the pinion housing 18. Figure 3 illustrates a linking member 72 that is received in a groove in the spool rack 70 and is fixed to the pinion housing 18 for fixing the spool rack 70 relative to the pinion housing 18. Those skilled in the art will recognize other ways of fixing the spool rack 70 to the pinion housing 18. Alternatively, the spool rack 70 and the pinion housing 18 may be formed as a one-piece, monolithic structure.

[0032] Referring to Figures 2 and 3, the spool rack 70 extends through a passage in the main housing 50 for interacting with the rotary control valve 60. A centering link mechanism acts between the main housing 50, at opposite ends of the passage in which the spool rack 70 is disposed, and the spool rack 70. The centering link mechanism includes two springs 80, two annular cap members 82 and two flat washers 84. The flat washers 84 are affixed to the spool rack 70, one on each side of the gear teeth of the spool rack 70. The cap members 82 close opposite ends of the passage and support seal members for sealing against the rack spool 70 for preventing fluid leakage out of the passage. One spring 80 is located between each cap member 82 and its nearest lock washer 84. The springs 80 have equal spring forces and thus, operate to bias the spool rack 70 toward a neutral position.

[0033] During operation of the steering system 10, an input torque is applied to the input pinion 12, for example by a human operator applying torque to begin to rotate the steering wheel described above. If a resistance to movement of the input rack 20 is below a threshold value, manual steering without power assist occurs. In this mode, the input torque on the input pinion 12 causes rotation of the pinion 12 and associated linear movement of the input rack 20. The input rack 20 is connected to the rod 28 of the steering cylinder 30 by the link 24, and this linear movement of the input rack 20, in turn, causes the rod 28 of the steering cylinder 30 to move so that steering movement of the associated vehicle occurs.

[0034] If, during operation of the steering system 10, a resistance to movement of the input rack 20 is above a threshold value, power assisted steering occurs. In this mode of operation, the input torque on the input pinion 12 alone is insufficient to axially move the input rack 20 and the rod 28 of the steering cylinder 30. As a result, the pinion 12 moves a short distance along the input rack 20 in an attempt to relieve the input torque. This short distance axial movement of the pinion 12 relative to the input rack 20 results in the pinion housing 18 also moving a short distance relative to the main housing 50. Note that the universal joints 16 of the steering shaft 14 allow for this movement without a change of mounting location of the steering wheel. n one embodiment, the pinion housing 18 may move approximately one-quarter of one inch in either direction. As the pinion housing 18 moves relative to the main housing 50, the spool rack 70, which is fixed to the pinion housing 18 as described above, also moves relative to the main housing 50. This linear movement of the spool rack 70 relative to the main housing 50 results in a rotation of the control valve 60 away from its closed center neutral position and toward one of the open actuated positions due to the interaction of the gear teeth. As illustrated in Figure 4, rotation of the control valve 60 in a first direction results in hydraulic fluid from the cylinder side 60b being directed to a first chamber of the steering cylinder 30 described above and connection of the second chamber to the reservoir. Rotation of the control valve 60 in a second direction results in hydraulic fluid from the cylinder side 60b being directed to the second chamber of the steering cylinder 30 described above and connection of the first chamber to the reservoir. The hydraulic fluid directed by the control valve 60 causes a differential pressure in the steering cylinder 30, which tends to move the piston 32 and rod 28 relative to the cylinder housing 34 for steering the vehicle. The input rack 20 is fixed to the rod 28 by the link 24 and moves with movement of the rod 28. Thus, as the rod 28 of the steering cylinder 30 moves, the input rack 20 moves and the pinion 12 rotates relative to the input rack 20. As the input torque is removed from the input pinion 12, the forces imparted by the springs 80 of the centering mechanism cause the spool rack 70 and thus, the pinion housing 18, to move back to its neutral position to stop further hydraulic power steering assist.

[0035] Figures 5-8 illustrate this operation of the steering system 10. In Figure 5, an input torque on the input shaft and input pinion 12 between zero and the threshold torque is imparted on the input shaft 14 and input housing 18 relative to the input rack 20. In Figure 6, this input torque exceeds the threshold value. In this mode of operation, the pinion housing 18 along with the spool rack 70 moves rightward along the input rack 20 causing the spool rack 70 to open the control valve 60. In Figure 7, the applied input torque above the threshold value that provides the mode of operation illustrated in Figure 6 is reduced below the threshold value. When this occurs, movement of the rod 28 and input rack 20 relative to the pinion housing 18 cause the control valve 60 by operation of the spool rack 70 to begin movement back toward the closed center position. Figure 8 illustrates the control valve 60 back in the closed center position, which is the same as the closed position illustrated in Figure 5.

[0036] The threshold value at which the pinion housing 18 and spool rack 70 move for moving the spool valve 60 and initiating power assist is determined in large part by the spring forces of the springs 80. During the power assist mode of operation, the input pinion 12, input rack 20, spool rack 70 and spool valve 60 are arranged so that about one (1) degree of rotation of the input pinion 12 results in about two thirds (2/3) degree of rotation of the barrel valve 60.

[0037] The accumulator 62 of the hydraulic system 10 enables the use of a pump 48 having a displacement that is smaller than a maximum fluid flow requirement to steer at the steering system's peak steering velocity. During operator inputs that require higher velocities, fluid stored in the accumulator 62 is used to supplement the flow from the pump 48. The hydraulic system 10 also includes a pressure switch 94 for monitoring a pressure in the accumulator 62. As the accumulator 62 reaches a low accumulator pressure threshold selected by the system designer, the electric motor 40 and pump 48 continue to operate for a short period of time after steering assist is no longer needed for increasing the fluid pressure In the accumulator 62. [0038] The unitary steering system 10 also includes check valves 90, as illustrated in Figure 4, which are disposed within the passages 68 within the main housing 50. The left check valve 90 illustrated in Figure 4 is spring biased and provides a flow loss check valve to prevent reverse fluid flow from the accumulator 62 to the tank 56 after the electric motor 40 is turned off. To enable movement of the rod 28 (and thus, the piston 32) of the steering cylinder 30 without the use of hydraulic power, the right check valve illustrated in Figure 4 opens for allowing a flow of fluid to the chambers of the steering cylinder 30 during manual movement of the rod 28.

[0039] The motion control system 10 of the present invention provides a unitary system that permits manual and power assisted operation, eliminates external hoses and fittings, minimizes hydraulic energy use when the system is in the manual mode of operation, provides ease of installation, and permits optimum design efficiency. When used as a vehicle steering system, the system 10 enables both manual steering and hydraulic assisted steering, with the hydraulic fluid supplied by one or both of an electric driven pump and an accumulator.

[0040] Presently preferred embodiments of the invention are shown in the drawings and described in detail above. The invention is not, however, limited to these specific embodiments. Various changes and modifications can be made to this invention without departing from its teachings, and the scope of this invention is defined by the claims set out below.