GB2332407A - Method of providing quick steering changes in a vehicle having both steerable and differentially-driven wheels - Google Patents

Abstract

A machine having a first set of steerable wheels 30 and a second set of non-steerable but differentially drivable wheels 22, 24 has the steering during a turn-around improved by providing the steerable wheels 30 with a power steering system having a pump 38 and an additional pressure source, accumulator 40. The additional pressure source of pressurized fluid is used in conjunction with the first source of pressurized fluid whenever the steering control valve 36 is moved towards its extreme position in either direction. to reduce the steering effort particularly where the machine has to be fumed through 180 degrees. The differential drive of wheels 22, 24 is through a hydrostatic transmission 48, 50 providing an additional drive to a differential 46.

Description

2332407 METHOD OF PROVIDING QUICK STEERING CIL&NGES This invention relates

generally to controlling steering in a machine and more particularly for providing a quick steering response for one of the steering arrangements in a machine having two different steering arrangements.

In various known machines one steering arrangement has steerable wheels for providing primary steering and steering assist is provided by applying independently controlled brakes on the other drive units that does not have steerable wheels. In other machines, both sets of wheels are steerable wheels and both are steered in opposite directions to provide a quick steering or small turning radius of the machine. However, in machines having only one set of steerable wheels, it is more difficult to make a sharp 180 degree turn. In these machines the turn radius is normally controlled by the maximum steer angle permitted by the steerable wheels.

When it is desirable to turn the machine 180 degrees so that it travels a return path adjacent to the initial path, it is necessary to steer the machine as far as possible in the desired direction, then stop and reverse the steer direction as far as possible, back up to properly align the machine, and reverse the steer direction again to straighten the steerable wheels. All of this maneuvering requires extra effort by the operator and adds to the fatigue of the operator. The extra maneuvering also takes extra time to turn the machine around which decreases operating efficiency.

The present invention is directed to overcoming one or more of the problems as set forth above.

In one aspect of the subject invention, an apparatus is set forth for providing quick steering response for one steering arrangement in a machine having a first steering arrangement with steerable wheels, a second steering arrangement having non-steerable drive units, and a steer input control operative to initiate a steer input command to the first and second steering arrangements. The first steering arrangement includes a fluid actuator connected to the steerable wheels and a fluid control valve operative to control the fluid flow to and from the fluid actuator. The apparatus includes a first source of pressurized fluid operatively disposed between a reservoir and the fluid control valve and a second source of pressurized fluid connected to the fluid control valve in parallel with the first source of pressurized fluid and operative to provide an extra volume of pressurized fluid to the actuator in response to the control valve being moved towards an extreme position.

one example of apparatus according to the present invention will now be described with reference to the accompanying drawings, in which:- Fig. I is a partial diagrammatic and a partial schematic representation of a machine incorporating the subject invention; and Fig. 2 is a diagram representing a typical path that a machine, such as a combine, travels when turning around.

Referring to the drawings and more particularly to Fig. 1, a machine 10 is illustrated and includes a frame 12, first and second steering arrangement 14,16, a steer input arrangement 18, an engine 19, an electronic controller 20, and a power transmission 21. The power transmission 21 is operatively connected to right and left drive units 22, 24 through respective output shafts 26,28.

The first steering arrangement 14 includes steerable wheels 30 spaced from one another by an axle 32. The axle 32 is connected to the frame 12 and a steering cylinder 34 is disposed between the steerable wheels 30 and operative to cause the respective steerable wheels 30 to angle with respect to the frame 12. This type of steering is normally referred to as Ackerman steering. Even though two wheels 30 are illustrated, it is recognized that a single steerable wheel could be connected to the frame 12 without departing from the essence of the subject invention.

A steering control valve 36 is operatively disposed between the steering cylinder 34 and a source of pressurized fluid 38, such as a hydraulic pump, that receives fluid from a reservoir 39. The steering control valve 36 of the subject invention is a three position proportional control valve that is movable between a centered, flow blocking position and first and second operative positions. The steering control valve 36 is movable from its centered position in response to receipt of an electrical signal from the electronic controller 20. When the steering control valve 36 is moved towards its first operative position, the steerable wheels 30 are angled in one direction and when the steering control valve 36 is moved towards its second operative position, the steerable wheels 30 are angled in the opposite direction.

A second source of pressurized fluid 40, such as an accumulator, is connected to the steering control valve 36 in parallel with the first source of pressurized fluid 38. A one way check valve 41 is disposed between the f irst source of pressurized fluid 38 and the steering control valve upstream of the connection of the accumulator 40.

A sensor 42 is disposed relative to the axle 32 and one of the steerable wheels 30 and operative to direct an electrical signal representative of the angle of steer or turn radius to the electronic controller 20.

The steer input arrangement 18 directs an input signal to the controller 20 that is representative of the desired angle of steer required by the operator. The range of input to the input arrangement 18 is limited so that the operator does not have to make continuous or multiple rotational inputs in order to provide a large or maximum steer input. The controller 20 directs respective command signals to the steering control valve 36.

A speed sensor 44 is located generally at the output of the power transmission 21 and is operative to direct a signal to the controller 20 that is representative of the speed from the power transmission 21. The controller uses the speed output from the power transmission to calculate the ground speed of the machine 10.

A differential steer mechanism 46 is disposed between the output of the power transmission 21 and the respective output shafts 26,28 and is operative to vary the relative speeds of the respective output shafts 26,28. The differential steer mechanism 46 has a fluid steer motor 48 connected thereto. The steer motor 48 is fluidily connected to a variable displacement pump 50. The displacement of the variable displacement pump 50 is is controlled in response to receipt of a signal from the controller 20. The output speed of the steer motor 48 determines the magnitude of the relative difference in speed between the respective output shafts 46,48 and therefore the difference in speed of the right and left drive units 22,24.

A sensor 52 is associated with the output of the fluid steer motor 48 and operative to deliver a signal to the controller 20 that is representative of the speed of the steer motor 48. The controller 20 uses the speed signal from the steer motor 48 to calculate the difference in speed between the output shafts 26,28 and thus determine the angle of steer or turn radius of the machine 10 that is being produced by the differential steer mechanism 46.

A first brake 54 is disposed on the first output shaft 26 and a second brake 56 is disposed on the second output shaft 28. Each of the first and second brakes 54,56 is spring applied and pressure released in response to receipt of pressurized fluid from the source of pressurized fluid 38. Respective brake control valves 58,60 are disposed between the pump 38 and the respective independently controlled brakes 54, 56. Each of the brake 1 control valves 58,60 is spring biased to a position at which the pressurized fluid from the pump 38 is blocked and the actuating chamber of the brake is open to the reservoir 39. Each is movable towards a position at which the pump 38 is in fluid communication with the associated one of the brakes 54,56 upon receipt of a signal from the electronic controller 20.

Referring to Fig. 2, a diagram illustrates a typical path of the subject machine 10 when being used in situations requiring the machine to travel in one direction and then turn around and follow a return path that is adjacent to the initial path. A straight line 70 of the diagram represents the typical path of the machine 10 in one direction. A curved line 72 represents the initial part of the turnaround. A curved line 74 represents the portion of the turnaround in which the machine is moving in a reverse direction. A straight line 76 represents the path of the machine 10 traveling in the opposite direction directly adjacent to the initial path that is represented by the line 70.

It is recognized that various arrangements of the first and second steering arrangements 14,16 could be utilized without departing from the essence of the subject invention. For example, it is recognized that the steer input command could be applied directly to the steering control valve either electrically or mechanically. Likewise, different types of second steering arrangement 16 could be used. For example, the second steering arrangement could be in the form of a clutch/brake control or a variable ratio belt system. Furthermore, the steer input could be made to the second steering arrangement 16 and then the first steering arrangement 14 is controlled to match the second steering arrangement. Additionally, the right and left drive units could be wheels, continuous tracks or continuous belts. Likewise the power transmission 21 could be in the form of a mechanism transmission or a fluid drive transmission without departing from the essence of the subject invention.

In the operation of the embodiment set forth in Fig. 1, as long as the machine 10 is not being subjected to a steer input, the machine travels in a straight line. If a steer input is made through the steer input arrangement 18, a steer input signal is directed to the controller 20. The controller 20 directs a command signal to the steering control valve 36 moving it towards the appropriate operative position to steer or angle the steerable wheels 30. As the steerable wheels 30 are being steered, the sensor 42 monitors the angle of steer and directs the information to the controller 20.

Simultaneously, the controller 20 directs a command signal to the variable displacement pump 50 to change its displacement. As a result of the change in displacement of the variable displacement pump 50, the steer motor 48 turns in proportion to the quantity of fluid being received. The speed of the motor 48 determines the relative difference between the speeds of the output shafts 26,28. The controller 20 calculates and synchronizes the angle of steer of each of the first and second steering arrangements 14,16 to control the turning of the machine 10.

By continuously sensing the steer angle of the first steering arrangement 14, the speed sensor 44 and the relative difference between the speeds of the output shafts 26,28, the controller 20 maintains a match between the angle of steer of the first and second steering arrangements 14,16. If one or the other of the first and second steering arrangements 14,16 is too great, the controller 21 directs the appropriate command signal thereto to change its angle of steer to match the other.

If the steer angle required by the steer input arrangement 18 is greater than can be maintained by the second steering arrangement 16, the controller 20 directs a command signal to the appropriate brake 54,56 to proportionally apply the brake to assist the second steering arrangement 16. This permits the machine 10 to negotiate tighter turns under various operating conditions.

During normal steering of the machine 10, the flow from the pump 38 provides sufficient flow to make all the steering adjustments in a smooth, timely responsive manner. When needing to provide a more rapid steering of the first steering arrangement 14, such as when turning the machine around to return in an adjacent parallel path, the flow from the pump 38 is not sufficient to provide quick movement of the steerable wheels 30. When the steering control valve is being operated in or near one of its extreme positions, the flow from the pump 38 does not provide sufficient flow in order to move the steerable wheels 30 rapidly from one extreme position to the other.

When turning the machine around to travel in the opposite direction along a path that is adjacent to the initial path, the operator moves the steer input towards its extreme position in the direction of turn. This is accomplished by moving the steer input or turning a steering wheel towards its extreme position, which in previous system required several revolutions. This steer input signal is directed to both the first and second steering arrangements 14,16. Even though the second steering arrangement 16 has the ability to spot turn by rotating one of its drive units 22,24 in one direction and the other drive unit in the opposite direction, the angle of steer or turn radius is limited by the turn radius of the first steering arrangement 14. Consequently, as generally illustrated by the curved line 72 of Fig. 2, the minimum turn radius of the machine 10 does not permit the machine to turn sharp enough to return along a path adjacent to the initial path.

Once the steer input has been moved towards its extreme position, the flow of fluid through the steering control valve 36 is the combined flow that is available from both the first and second sources of pressurized fluid 38,40. Consequently, the steerable wheels 30 are moved to their extreme angle quickly and the machine turns along its shortest turn radius as generally illustrated by the curved line 72 of Fig. 2. Once the machine 10 has been turned to a desired point as noted by the curved line 72, the operator must turn the steering wheel in the opposite direction towards its extreme position in order to fully angle the steerable wheels 30 in the opposite direction. 10 The combined flow of fluid from both the first and second sources of pressurized fluid 38,40 is directed to the steering cylinder 34 to quickly move the steerable wheels 30 to their extreme angle in the opposite direction. The machine is then moved in a reverse direction as generally is illustrated by the line 74. once the machine reaches a position that it is generally parallel with the initial path, the operator reverses his steer input once again in the opposite direction to move the steering control valve 36 towards its other extreme position. Again, the 20 combined flow from both of the first and second sources of pressurized fluid 38,40 is directed to the steering cylinder 34 to quickly move the steerable wheels 30 back to their straight ahead position. once the steerable wheels 30 have reached their straight ahead position, the steer input is returned to its neutral condition and the machine is moved in a forward direction as represented by the line 76. In view of the above, it is readily apparent that the subject arrangement has the needed apparatus to provide 30 quick movement of the steerable wheels in either direction of steer in response to the steering control valve 36 being moved towards either of its extreme positions. This is accomplished without requiring a large capacity pump 38 which would be quite expensive and would also be an inefficient drain on system horsepower since the large flow is only needed during turnaround of the machine or when a sharp turn radius is needed quickly.

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Claims (6)

1. Apparatus for providing quick steering response for one steering arrangement in a machine having a first steering arrangement with steerable wheels, a second steering arrangement having non-steerable drive units, and a steer input control operative to initiate a steer input command to the first and second steering arrangements, the first steering arrangement including a fluid actuator connected to the steerable wheels and a fluid control valve operative to control the flow of pressurised fluid to and from the fluid actuator, the apparatus comprising:

a first source of pressurized fluid operatively disposed between a reservoir and the fluid control valve; is and a second source of pressurized fluid connected to the fluid control valve in parallel with the first source and operative to provide additional pressurized fluid to the actuator, when required, in response to movement of the control valve.

2. The apparatus of claim 1, wherein the second source of pressurized fluid includes an accumulator connected to the fluid control valve upstream thereof and a check valve disposed between the point of connection of the accumulator and the first source of pressurized fluid.

3. The apparatus of claim 2, wherein the second steering arrangement provides steering by changing the relative output speeds of the respective drive units.

4. The apparatus of claim 3, wherein the second steering arrangement includes a differential steer mechanism having a fluid steer motor operative to vary the relative output speeds of the respective drive units in response to rotation thereof.

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5. The apparatus of any of claims 1 to 4, including an electronic controller operative to receive the steer input command and deliver respective signals to the first and second steering arrangement to initiate steering thereof responsive to the steer input command.

6. Apparatus according to claim 1, substantially as described with reference to the accompanying drawings.