WO2013058752A1

WO2013058752A1 - Back driving master steering gear and steering system implementing the steering gear

Info

Publication number: WO2013058752A1
Application number: PCT/US2011/057052
Authority: WO
Inventors: Peter H. Sheppard; Scott Wilson
Original assignee: R.H. Sheppard Co., Inc.
Priority date: 2011-10-20
Filing date: 2011-10-20
Publication date: 2013-04-25

Abstract

A power steering system for multi-axle steering of a motor vehicle includes a primary steering gear controlled by the steering wheel that includes a piston attached to a steerable wheel on a first axle of the motor vehicle, a second steering gear attached to a steerable wheel on a second axle of the motor vehicle, and a transmission assembly interconnecting the first and second power steering gears. The primary steering gear includes a fluid control valve with an output member interconnected with the piston and connected to the transmission assembly.

Description

Attorney's Docket No. 6-3748-PCT

BACK DRIVING MASTER STEERING GEAR AND STEERING SYSTEM IMPLEMENTING THE STEERING GEAR

Field of the Invention

The invention relates to hydraulic power steering systems for motor vehicles.

Background of the Invention

Some wheeled motor vehicles include a multi-axle steering system in which the wheels of the front axle and the wheels of one or more other axles are steered and not fixed in a centered or straight-ahead position during a vehicle turn.

The wheels of each steerable axle may be driven by a main steering gear associated with the axle. The steering gear includes a fluid motor utilizing high-pressure fluid supplied from a pump or high-pressure accumulator to drive a piston, and a control valve controlling the operation of the fluid motor. Piston movement drives an output member extending from the steering gear and connected to a steering linkage that in turn drives the wheels towards or away from their centered positions .

Heavy-duty vehicles may include an additional slave steering gear for each axle. The slave steering gear is separate from the main steering gear and includes a fluid motor hydraulically connected to the main steering gear. The fluid motor of the slave steering gear drives a separate output member connected to the steering linkage that assists in turning the wheels of the axle.

The motor vehicle includes a steering wheel connected by a steering column to the control valve of one of the main steering gears. This primary steering gear is typically the main steering gear that drives the wheels on the front axle. Rotating the steering wheel operates the control valve and turns the front wheels of the vehicle.

The control valves of the other one or more main steering gears must operate in unison with the control valve of the primary steering gear so that the wheels of all the steerable axles turn together in response to the steering wheel . The steering system may implement a "dead band" in which rear wheels remain centered if the vehicle is moving at or above a certain speed or until the front wheels turn a set amount.

In one known multi-axle steering system, the slave steering gear associated with the primary power steering gear is used to actuate the control valves of the other one or more steering gears. The slave steering gear includes a second power output member that is driven by the piston of the slave steering gear. The movement of the second power member is transmitted to the control valves of the other main power steering gears associated with the other axles. This causes all the wheels of all steerable axles to turn in unison (subject to any system dead band) .

A problem with utilizing a slave steering gear to control the other main power steering gears is that the power demands of the multi-axle steering system may not require a slave steering gear, and installing a slave steering gear merely for control purposes may not be practical or feasible. For example, a linkage path may not be available from the slave steering gear to a second, rear steering gear. In other known multi-axle steering systems, the displacement of a wheel controlled by the primary steering gear connected by the steering wheel is digitally encoded and used as input to an automatic control system that independently controls the other one or more main steering gears associated with the other steerable axles. The automatic control system controls actuators, typically electric servomotors, that independently operate the control valves of the other main steering gears. The positions of wheels on the other axles are digitally encoded and fed back to the control system for control of the actuators.

Although automatic control systems for multi-axle steering systems have worked well, such systems are expensive and are not necessarily suitable for all operating environments .

Thus there is a need for a multi-axle hydraulic power steering system suitable for use in heavy-duty motor vehicles that does not require a slave steering gear and does not require a digitalized automatic control system.

Brief Summary of the Invention

The invention is a power steering gear for use in a multi-axle hydraulic power steering system suitable for heavy- duty motor vehicles that mechanically actuates the other control valves without the need of a slave steering system and does not require a digitalized automatic control system. The power steering gear of the present invention can be used as the primary power steering gear connected to the steering column and controlled by the steering wheel. The power steering gear includes a first output member that drives the steering linkage in a conventional manner and a second output member driven by the piston. The second output member forms part of an input member connected to the control valve of a second power steering gear to turn the wheels of a second steerable axle of the motor vehicle.

In a preferred embodiment the fluid motor includes the piston movable in a housing. The second output member is a shaft that extends out of an end cap of the housing.

In a further preferred embodiment of the invention the control valve includes an actuating shaft that extends from one side of the piston and engages the piston for operation of the control valve. The actuating shaft extends through the piston and out of the housing to form the second output member .

In such further preferred embodiments the actuating shaft is preferably formed as two elongate, coaxial shaft members, one shaft member connected to the control valve and the second shaft member extending out of the housing. The second shaft member is journaled in a bushing screwed into a piston bore and bearings carried in the end cap. The two first and second shaft members are non-rotatably connected for conjoint rotation .

The power steering gear of the present invention enables the control of a multi-axle steering system utilizing a single, compact steering gear without the need for a slave gear or electronics. This saves room, saves costs, and makes practical multi-axle steering on a wider variety of motor vehicles. Because the second output member is hydraulically powered, the driver exerts no additional steering effort to steer the additional axles beyond the effort to steer a single steering gear.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying two drawing sheets illustrating an embodiment of the invention.

Brief Summary of the Drawings

Figure 1 is a schematic representation of a motor vehicle having a hydraulic power steering system that includes a first steering gear and a second steering gear to turn respective first and second wheels of the motor vehicle, the first steering gear in accordance with the present invention; and

Figure 2 is a sectional view of the first steering gear shown in Figure 1.

Description of the Preferred Embodiment

Figure 1 schematically illustrates a motor vehicle having a primary main steering gear 10 in accordance with the present invention and a second main steering gear 12, the steering gears 10, 12 forming part of a hydraulic power steering system 14 that turns the wheels 16, 18 of the motor vehicle. The steering gear 10 turns the wheel 16 and the steering gear 12 turns the wheel 18. The wheels 16, 18 may be on different axles of the motor vehicle.

The steering gear 12 may be an M-series steering gear Model No. MHO manufactured by R.H. Sheppard Co., Inc., assignee of the present invention. The hydraulic power steering system may (but does not necessarily have to) include one or more slave steering gears 19. Each slave power steering gear 19 assists a main power steering gear 10 or 12 in turning the steerable wheels of an axle. The slave steering gears 19 are conventional and may each be an M-series steering gear Model No. M90 manufactured by the R.H. Sheppard Co. Inc., assignee of the present invention.

The power steering system 14 includes a pump 20 that flows pressurized fluid from a reservoir 22 to an inlet port 24 of the steering gear 12 and to an inlet port 26 of the second steering gear 12. Fluid returns to the reservoir 22 through a discharge port 28 in the steering gear 10 and a discharge port 30 in the steering gear 12. In other embodiments pressurized fluid can be provided from an accumulator (not shown) in addition to or instead of from a pump 20. The flow and pressure requirements of the first and second axle steering gears 10, 12 will be dependent on their unique road conditions and so must be allowed to operate independently either through a single pump or accumulator utilizing a flow divider between the two steering gears or the use of independent pumps or accumulators .

The illustrated power steering gear 10 is adapted from the Sheppard Model No. MHO steering gear. The steering gear 10 includes a fluid motor 32 and a control valve 34 that controls flow from the pump 20 to the fluid motor 32. The fluid motor 32 includes a housing 36 and a movable piston 38 in the housing. The piston 38 is connected to a first output member 40 that extends out of the housing 36 and is connected via a steerage linkage 42 to the wheel 16.

The fluid motor 32 also includes a second output member 44 operatively connected to the piston 38 that extends out of the housing 36. The second output member 44 is operatively connected to a control valve 46 of the second power steering gear 12.

The control valve 46 is similar to the control valve 34 and controls flow from the pump 20 to a fluid motor 48 of the second power steering gear 12. The fluid motor 48 is similar to the fluid motor 32 and includes a housing 50 and a movable piston 52 in the housing. The piston 52 is connected to an output member 54 that extends out of the housing 50 and is connected via a steerage linkage 56 to the wheel 18.

The control valve 34 is manually operated by a steering wheel 58. The term "steering wheel" includes both a conventional steering wheel and equivalent structures, such as hand controls and the like, that may be used by a driver for steering the vehicle. Turning the steering wheel 58 opens the control valve 34 and actuates the fluid motor 32, moving the piston 38 and the first output member 40. Motion of the first output member 40 displaces the steering linkage 42, turning the wheel 16 towards or away from a centered position of the wheel 16 (it is understood that the connection from the steering linkage 42 to the wheel 16 is illustrated schematically and other linkage members known in the steering art will be present to convert displacement of the steering linkage 42 to turning of the wheel 16) .

Movement of the piston 38 also moves the second output member 44. Movement of the second output member 44 opens the control valve 46 and actuates the fluid motor 48, moving the piston 52 and the output member 54. Motion of the output member 54 displaces the steering linkage 56, moving the wheel 18 towards or away from a centered position of the wheel 18. Operation of the steering gear 10 is coordinated with the operation of the steering gear 12 such that the angular positions of the wheels 16, 18 are related to one another as needed for smooth turning of the motor vehicle.

Figure 2 is a sectional view of an embodiment of the steering gear 10.

The housing 36 is closed at one end by a first bearing cap 60 and is closed at its other end by a second bearing cap 62.

The first bearing cap 60 includes the input port 24 and the discharge port 28 and houses the control valve 34. The control valve 34 can be a normally-open control valve of the type disclosed in Danley et al . US Patent 7,152,627 assigned to R.H. Sheppard Company, Inc. (assignee of the present invention) or can be a normally closed control valve of the type disclosed in Tipton, PCT Published Application WO 2011106025 assigned to R.H. Sheppard Company, Inc. (assignee of the present invention). US Patent 7,5152,627 and PCT Published Application WO 2011106025 are incorporated by reference as if fully set forth herein.

The control valve 34 is a rotary-type valve that includes a fluid inlet fluidly connected to the input port 24 and a fluid discharge fluidly connected to the discharge port 28. The control valve 34 includes an outer valve member or valve sleeve 64 and in inner valve member or valve core 66. The valve core 66 is coaxially mounted in the valve sleeve 64 for rotation with respect to the valve core 66 about a common axis. The valve core 66 forms an input member of the control valve 34, with an end portion 68 of the valve core 66 configured in a conventional manner for connection to the steering column that carries the steering wheel 58. The valve sleeve 64 forms an output member of the control valve 34 wherein relative rotation of the input member 66 and the output member 64 open and close flow channels defined between the members 64, 66 in a conventional manner.

A coaxial tubular actuating shaft 70 extends from and is integral with the valve sleeve 64. The actuating shaft 70 extends into a longitudinal through-bore 72 in the piston 38 and has a threaded outer surface that forms part of a conventional recirculating ball assembly 74 carried in the piston 38. The recirculating ball assembly 74 forms a drive or transmission that interconnects the actuating shaft 70 and the piston 38 to convert motion of the piston 38 into motion of the shaft 70.

The actuating shaft 70 extends past the ball assembly 74 to a free end portion 76 in the piston bore 72. The shaft end portion 76 is received in a blind bore 78 formed in a power takeoff shaft 80 that is coaxial with the actuating shaft 70. A pin or spline connection 82 non-rotatably connects the actuating shaft 70 and the takeoff shaft 80 for conjoint rotation about the common axis.

The takeoff shaft 80 extends from the actuating shaft 70, out of the piston bore 72, and through the second end cap 62, with an end portion 84 of the takeoff shaft 80 extending outwardly away from the end cap 62. The end portion 84 forms at least a portion of the second output member 44 shown in Figure 1 and is configured to be operatively connected to the control valve 46 for conjoint rotation with the valve core of the control valve 46.

The takeoff shaft 80 is supported in an annular seal 85 carried in a piston plug or bushing 86 threaded into the piston 38 and bearings 88 carried in the end cap 62. The bushing 86 extends from the one end of the piston 38 and into the piston bore 72, with the seal 85 sealingly closing that end of the piston 38 and maintaining hydraulic separation between the two piston chambers 92, 94. A seal 90 carried in the end cap 62 seals the end cap opening for the takeoff shaft 80.

The piston 38 divides the interior of the housing 36 into first and second fluid motor chambers 92, 94 on opposite sides of the piston. A toothed rack 96 formed on one side of the piston engages a sector gear 98 attached to a sector gear shaft or output shaft 100 that extends out of the housing 36. The output shaft 100 forms the first output member 40 shown in Figure 1. A pitman arm (not shown) can be attached to the output shaft 100 to actuate the suspension linkage 42 in a conventional manner.

Turning the steering wheel 58 operates the control valve 34 and rotates the valve core 66, placing the control valve 34 in an off-centered condition. The control valve 34 fluidly connects the input port 24 to one of the motor chambers 92, 94 and fluidly connects the discharge port 28 to the other of the motor chambers 92, 94. The piston 38 moves left or right, rotating the sector gear 98 and the output shaft 100 to turn the wheel 16 to the left or right. Axial movement of the piston 38 causes the recirculating ball assembly 74 to rotate the actuating shaft 70. Because of the nonrotatable connection between the actuating shaft 70 and the takeoff shaft 80, the takeoff shaft 80 rotates with rotation of the actuating shaft 70. The angular displacement of the takeoff shaft 70 corresponds to the linear displacement of the piston 38 that in turn corresponds to the turning of the wheel 16.

Rotation of the takeoff shaft 80 operates the control valve 46, placing the control valve 46 into an off-center condition and causing the piston 52 to move left or right in the housing 50. The angular displacement of the valve core of the control valve 46 is a function of the angular displacement of the takeoff shaft 80, which in turn is related to the turning of the wheel 16 as previously described.

Movement of the piston 52 rotates the output member 54 in the same manner as movement of the piston 38 rotates the output member 40, thereby turning the wheel 18 to the left or right at the same time the wheel 16 is turning. Because the off-center condition of the control valve 46 corresponds to the turning of the wheel 16, the amount by which the wheel 18 turns is related to the amount the wheel 16 turns.

Continued axial motion of the pistons 38, 52 returns the control valves 34, 46 to their centered conditions when the wheels 16, 18 have turned to the extent set by the driver in turning of the steering wheel 58.

Movement of the piston 38 from its off-center position and back to its centered position returns the wheel 16 to its straight-ahead position. The same movement of the piston 38 rotates the takeoff shaft 80 in the opposite direction and places the control valve 46 into an off-center condition that causes the piston 52 to move back to its centered position and returns the wheel 18 to its straight ahead position.

The output member 44 represents a transmission assembly 44 that transmits force/displacement from the takeoff shaft 80 to the movable input member of the control valve 46. If desired, the transmission assembly 44 may be include other mechanisms placed between the takeoff shaft 80 and the control valve 46 that act in transmitting force and displacement from the takeoff shaft 80 to the control valve 46. Braun et al . US Patent 7,073,620 discloses examples of such mechanisms. Such mechanisms may include gear trains, torque multipliers, universal joints, reversers that reverse the direction or ratio of rotation or translation, rotary-to-linear or linear- to-rotary motion converters, dead band generators, and other transmission members. For example, the main steering gear 10 may be located near a front axle of the motor vehicle and the main steering gear 12 located near a rear axle of the motor vehicle. The output member 44 may include universal joints, miter gears, spur gears, or the like that enable a non- straight or non-linear transmission path from the first power steering gear 10 to the second power steering gear 10, 12.

The illustrated embodiment utilizes rotary movement of the takeoff shaft 80 and transfers such rotary movement to operate the control valve 46. In alternative embodiments the takeoff shaft 80 may move axially with the piston 38. For example, the inner end of the takeoff shaft 80 may be fixed to the piston 38 for axial movement with the piston 38 and not connected to the actuating shaft 70. Linear motion of the takeoff shaft 80 may be preferred when the "downstream" steering gear 12 utilizes a control valve that is controlled by linear translation of an input member.

The steering system 14 can be designed for use with multi-axle steering systems to turn wheels on both the front and rear axles of a motor vehicle. The steering system 14 may simultaneously turn both wheels 16, 18 in the same direction (when, for example, the steering gear 14 is utilized in turning the wheels 16 on a front axle and the wheels 18 on a rear axle in the same direction for so-called "crab steering") or may be designed to simultaneously turn the wheels 16, 18 in opposite directions (when, for example, the steering gear 14 is utilized in turning the wheels 16 on a front axle and the wheels 18 on a rear axle in the opposite direction for so- called "coordinated steering").

The functional relationship between the angular displacement of the wheel 16 and the corresponding angular displacement of the wheel 18 (including the relative magnitudes and directions of displacement) when moving to or from the centered positions of the wheels 16, 18 can be established by the design of the steering linkage geometry, the sector gear size, the designs of the control valves, the transmission path and mechanisms in the transmission path between the power steering gear 10 and power steering gear 12, and other design factors as is known in the vehicle steering art .

The illustrated steering wheel 58 is mechanically connected to the control valve 34. In alternative embodiments the steering wheel 58 may be indirectly connected to the control valve 34 by, for example, a "steer-by-wire" control system that utilizes the steering wheel 58 as a data input member to the control system.

In other possible embodiments of the present invention the second output member 44 may be an input member whose angular position is encoded for use by an automatic control system that independently controls the other one or more main steering gears associated with the other steerable axles. The automatic control system uses the angular position of the output member 44 to establish the desired wheel positions of a second and/or nth axle.

While we have illustrated and described a preferred embodiment of our invention, it is understood that this is capable of modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

Claims

1. A steering gear for a motor vehicle hydraulic power steering system that utilizes a source of pressurized fluid for turning steerable wheels of the motor vehicle, the steering gear comprising:

a housing extending between two open ends;

a piston movable axially in the housing and dividing the housing into chambers on opposite sides of the piston;

a first end cap closing one end of the housing and a second end cap closing the other end of the housing;

a control valve mounted in the first end cap, the control valve comprising a shaft extending through the second end cap, the shaft movable with respect to an axis; and

a shaft drive interconnecting the piston and the shaft, the shaft drive moving the shaft with linear translation of the piston.

2. The steering gear of claim 1 wherein the shaft is rotatable about the axis.

3. The steering gear of claim 1 wherein the shaft forms part of an output member of the control valve and the control valve comprises an input member relatively movable with respect to the output member to open and close flow channels defined between the input and output members.

4. The steering gear of claim 1 wherein the piston includes a through-bore and the shaft extends through said piston bore.

5. The steering gear of claim 4 comprising a seal in a sealing relationship with the shaft, the seal fluidly separating the chambers.

6. The steering gear of claim 5 wherein the seal is carried in a bushing attached to the piston, the shaft extending through the bushing.

7. The steering gear of claim 1 wherein the shaft is supported in a bearing carried in the second end cap.

8. The steering gear of claim 1 wherein the shaft includes a first shaft portion and a separate second shaft portion, the shaft portions non-rotatably connected to one another .

9. The steering gear of claim 8 wherein the first and second shaft portions are non-rotatably connected together by a pinned connection or splined connection.

10. The steering gear of claim 1 wherein the shaft extends through an opening in the second end cap and including a fluid seal extending between the shaft and the second end cap fluidly sealing said end cap opening around the shaft.

11. The steering gear of claim 1 comprising a sector gear and a sector gear shaft connected to the sector gear and extending out of the housing, the piston comprising a rack meshed with a sector gear.

12. A hydraulic power steering system of a motor vehicle having a first steerable wheel on a first axle and a second steerable wheel on a second axle separate from the first axle, the power steering system comprising:

a fluid source, a first steering gear, second steering gear, and a transmission assembly interconnecting the first and second steering gears; WO 2013/058752 ^" -¹ '^" PCT/US2011/057052 the first steering gear comprising a first control valve fluidly connected to the fluid source, a fluid motor comprising a piston fluidly connected to the first control valve, and a transmission engaging the piston and the first control valve, the first hydraulic motor fluidly connected to the first control valve, the piston axially movable in a housing closed by first and second end caps, the piston connected to the first wheel for turning the first wheel;

the second steering gear comprising a movable input member connected to the transmission assembly and operatively connected to the second wheel for turning the second wheel; the first control valve mounted in the first end cap and comprising an input member and an output member, the input and output members relatively movable with respect to one another to open and close flow channels defined between the input and output members, the input member operatively connected to a steering wheel, the output member engaging said transmission and extending out of the housing and connected to the force transmission assembly outside of the housing; and

the transmission assembly transferring motion from the output member of the first control valve to the input member of the second control valve in response to movement of said output member thereby operating the input member of the second control valve in response to operation of the first control valve .

13. The power steering system of claim 12 wherein the second control valve is a hydraulic valve.

14. The power steering system of claim 12 wherein the output member of the first control valve extends through the second end cap.

15. The power steering system of claim 12 including a slave steering gear fluidly connected to at least one of the first and second steering gears.

16. The power steering system of claim 12 wherein the output member of the first control valve is supported by a bearing installed in the second end cap.

17. The power steering system of claim 12 wherein the piston comprises a through-bore, the output member extending through the through-bore.

18. The power steering system of claim 17 wherein the piston separates a pair of chambers on opposite sides of the piston, the output member extending from one chamber to the other chamber, and including a fluid seal around the output member that fluidly separates the pair of chambers.

19. The power steering system of claim 12 wherein the input and output members of the first control valve are relatively rotatable about a common axis of rotation.