GB2303829A - Vehicle skid-steer control system - Google Patents

Vehicle skid-steer control system Download PDF

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Publication number
GB2303829A
GB2303829A GB9515919A GB9515919A GB2303829A GB 2303829 A GB2303829 A GB 2303829A GB 9515919 A GB9515919 A GB 9515919A GB 9515919 A GB9515919 A GB 9515919A GB 2303829 A GB2303829 A GB 2303829A
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United Kingdom
Prior art keywords
speed
signal
speed signal
right hand
control system
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9515919A
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GB9515919D0 (en
Inventor
Michael Cosmo Barnes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Environmental Engineering Group Ltd
ENVIRONMENTAL ENGINEERING GROU
Original Assignee
Environmental Engineering Group Ltd
ENVIRONMENTAL ENGINEERING GROU
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Environmental Engineering Group Ltd, ENVIRONMENTAL ENGINEERING GROU filed Critical Environmental Engineering Group Ltd
Priority to GB9515919A priority Critical patent/GB2303829A/en
Publication of GB9515919D0 publication Critical patent/GB9515919D0/en
Publication of GB2303829A publication Critical patent/GB2303829A/en
Application status is Withdrawn legal-status Critical

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B62LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62DMOTOR VEHICLES; TRAILERS
    • B62D11/00Steering non-deflectable wheels; Steering endless tracks or the like
    • B62D11/02Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides
    • B62D11/06Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of a single main power source
    • B62D11/10Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of a single main power source using gearings with differential power outputs on opposite sides, e.g. with twin-differential or epicyclic gears
    • B62D11/14Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of a single main power source using gearings with differential power outputs on opposite sides, e.g. with twin-differential or epicyclic gears differential power outputs being effected by additional power supply to one side, e.g. power originating from secondary power source
    • B62D11/18Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of a single main power source using gearings with differential power outputs on opposite sides, e.g. with twin-differential or epicyclic gears differential power outputs being effected by additional power supply to one side, e.g. power originating from secondary power source the additional power supply being supplied hydraulically
    • B62D11/183Control systems therefor

Abstract

A control system for steering and travel of a skid-steer vehicle having right hand and left hand driving units, e.g. hydrostatic motors, has a pivoted speed input link 18 which includes two slotted cams 11, one for each of the drive units. A respective cam follower 23 engages in the slot 17 of each cam 11. The followers 23 are connected to speed control members 21 of the drive units. For steering, the follower 23 of one or both units is displaced along a slot 17 by a respective cam 25 for differential movement of control members 21. Each slot 17 is such that, with the speed signal set to zero, the movement of a follower 23 in the slot 17 causes no movement of pivot 19, and thus of either of the drive units. The operation of the steering control thus will not cause movement if the vehicle is stationary.

Description

VEHICLE STEERING AND TRAVEL CONTROL SYSTEM The invention relates to control systems for steering and travel of a vehicle having right and left hand driving units and steered by variation between the driving speeds of the driving units.

Tracked vehicles, including those having elastomeric tracks or belts, are normally driven by separate right hand and left hand drives and steered by variation between the speeds of the driving units. This mode of steering is often referred to as skid steer. Skid steer can also be employed for wheeled vehicles and is particularly useful in some multi-wheel off road vehicles. It is common practice to use variable capacity hydrostatic drives for such vehicles.

Most vehicle hydrostatic drive systems for skid steer vehicles use separate drive motors for the left hand and right hand wheel or track drive. This characteristic feature, leads to very simple and versatile steering systems by independently altering the flow entering either drive motor or by altering the displacement of either drive motor.

Many of these drive systems are controlled by one or two levers. Usually, on two lever systems, a speed lever simultaneously adjusts the flow from both pumps, and hence the speed of both motors changes simultaneously, while a steer lever biases the flow from each pump about the speed adjusted flow. Some skid steer vehicles use a single lever.

Moving the lever forward increases forward speed and moving the lever rearwards increases reverse speed. Rotation or sideways movement of the lever biases the output to each side adding to the signal on one side and subtracting from the signal on the other side. A feature of such systems is that they give undesired drive movement if the steering control is moved when the speed is set to zero.

When skid steer is controlled by a steering wheel, the driver expects a normal motor car response, i.e. that turning the steering wheel, when the vehicle is stationary, does not cause the vehicle to move. Inadvertent vehicle movement which occurs with skid steer vehicles is potentially very dangerous.

An object of the invention is to provide an improved steering control system for skid steer vehicles.

According to one aspect of the invention there is provided a control system for steering and travel of a vehicle having right-hand and left-hand driving units and steered by variation between the driving speeds of the driving units, the control system comprising: a speed input member for providing a speed signal between zero and maximum; a steering input member for producing a direction signal between full left, straight and full right; a right hand speed modulator responsive to the speed signal and to the direction signal to produce a right hand speed signal which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate dependent on the steer signal;; a left hand speed modulator responsive to the speed signal and to the direction signal to produce a left hand speed signal which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate dependent on the steer signal; the right hand speed signal controlling the drive to the right hand side of the vehicle and the left hand speed signal controlling the drive to the left hand side of the vehicle.

Because the right and left hand speed signals controlling operation of the right and left hand drives remain zero when the speed input member is set to zero speed, operation of the steering input member at zero vehicle speed does not result in any drive to either side of the vehicle and thus does not move the vehicle.

The invention is normally employed in vehicles capable of forward and reverse motion and thus according to a second aspect of the invention there is provided a control system for steering and travel of a vehicle having right-hand and left-hand driving units and steered by variation between the driving speeds of the driving units, the control system comprising: a speed input member for providing a speed signal ranging from full reverse, through zero to full forward; a steering input member for producing a left hand direction signal or a right hand direction signal or indicating straight ahead; a right hand speed modulator responsive to the speed signal and to the right hand direction signal to produce a right hand speed signal which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate which decreases with increasing right hand steer signal; a left hand speed modulator responsive to the speed signal and to the left hand direction signal to produce a left hand speed signal which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate which decreases with increasing left hand steer signal; the right hand speed signal controlling the drive to the right hand side of the vehicle and the left hand speed signal controlling the drive to the left hand side of the vehicle.

Embodiments of the invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 is a block diagram illustrating the principles on which the invention operates; Figure 2 is a diagrammatic side elevation of key parts of a mechanical system for controlling the right hand drive unit of a vehicle.

Figure 3 is a perspective view corresponding to Figure 2 also showing additional parts; Figure 4 is a perspective view corresponding to Figure 3 but also showing key parts of both right hand and left hand controls; and Figure 5 illustrates the profile of a cam shown in the other figures.

Figure 1 illustrates the principles of the invention mathematically by means of a block diagram. A speed signal n is derived from a speed input member such as a lever. The lever may operate in a U shaped gate with one leg controlling speed in the forward direction and the other in the reverse direction. Alternatively the lever may move forward for forward speed and backward for reverse speed, possibly with a stop or interlock to control change over between forward and reverse. As indicated in the diagram, the speed signal n can be controlled to any value between + N representing full forward speed and -N representing full reverse speed.

A steering input member may be in the form of a steering wheel and provides a direction signal t indicative of a requirement for straight line movement or for turning to left or right to varying extents. Conveniently, separate right turn and left turn signals are derived from the direction signal t. The right turn signal t, has a value defined as + 1 for straight drive, reducing through 0 to -1 for full right turn. When a left turn is indicated by the direction signal t, the right turn signal retains its value of + 1. Similarly, a left turn signal t has a value of + 1 in the straight ahead condition, reducing through 0 to -1 for full left turn and remaining at + 1 throughout any right turn.

The control system incorporates a right hand speed modulator M, and a left hand speed modulator Ml. Operation of the left hand speed modulator corresponds to the operation of the right hand speed modulator so only the right hand modulator and its function will be described in detail.

The speed signal n is modulated in the right hand modulator by the right turn signal t, by in effect multiplying n by t, to produce a right hand speed signal n,. Of course, during straight ahead drive and left turns, the value of t, is + 1 with the result that n, remains equal to n. With an increasing right turn requirement from the steering wheel, t, first reduces towards zero and then goes negative as previously explained. As a result, right hand speed signal n, reduces gradually with increasing turn signal and eventually goes negative for severe turns.

The result is that as right hand turn is signalled, a right hand output speed signal gradually reduces with increasing turn signal, slowing down the right hand driving unit. An increase in turn signal eventually results in a zero value for nr and a stationary drive unit while further turning leads to a negative value for nr and corresponding reverse movement of the driving unit. During the right hand turn, the left hand driving unit continues to receive speed signal n (tl = 1 so n1 = n). Thus the result of slowing down the right hand unit is to effect a right turn whilst retaining forward movement. Even when nr goes slightly negative and the drive direction reverses, the vehicle retains some forward speed because the left hand unit is driving forward at a higher speed than the reverse speed of the right hand unit.With the maximum turn signal, the right hand and left hand drive units are operated at equal and opposite speeds resulting in turning motion without forward or reverse motion.

A particular feature of this control system is that when the speed signal n is set to zero the right hand speed signal and left hand speed signal are also zero, regardless of the value of the right and left turn signals tr and t.

As a result, operation of the steering wheel while the vehicle is stationary does not cause any forward or reverse motion or steering motion of the vehicle. This is in contrast with a typical known system where a driver inadvertently pulling on a steering wheel as he climbs in or out of the vehicle would cause one side of the vehicle to move forward while the other moves back, thus swivelling the vehicle. Inadvertent surprise movement of this kind could cause injury to the driver or anyone else close to the vehicle and is to be avoided.

If a different response is required at the different vehicle speeds or if a non-linear response to steering wheel movement is required, the right and left speed signals such n, may be made a more complex function of n and t" so long as nr remains zero when n is zero. By this means, it is possible to derive a steering response which is broadly equivalent to that of a motor vehicle with steerable wheels.

During skid steering, a great deal of power is needed to move the tracks or wheels laterally to effect the change of direction. The additional power requirement can be an embarrassment if the vehicle is already operating at or near.full power or if the response of the engine speed control to increased load causes speed reduction or even stalling. It is for this reason that the speed modulators are arranged to reduce the drive speed on the inside of a turn but not to increase the drive speed on the outside of the turn. With a typical drive unit such as a hydrostatic drive, reduced speed is achieved by a reduction in drive ratio and thus makes more torque available. An alternative way of looking at the effect of a reduced ratio is that it reduces the overall vehicle velocity thus reducing drawbar power requirement and making available increased power to effect the skid steer.

The means for generating and processing the various signals referred to above in relation to Figure 1 may take any form. For example, the input signals could be represented in digital form and the data processing could be carried out electronically. However, a mechanical system is preferred and such a mechanical system will now be described.

Figures 2, 3 and 4 illustrate the mechanical system configured with the steering in the straight ahead position and the drive in its neutral position.

The condition referred to as neutral represents zero speed rather than a disconnected drive. As explained above, there are two separate subsystems, one for each side of the vehicle. The right hand sub-system alone is shown in Figures 2 and 3 for simplicity of illustration. Both subsystems are shown in Figure 4. A frame 12 is shown schematically in Figure 2 but not in Figures 3 and 4.

A speed cam 11 is pivotally mounted to the frame 12 about an axis A fixed with respect to the frame. To provide clearance for operating parts of the speed cam, it is mounted through two bosses 13 and 14 (Figure 3) to a triangular mounting plate 15 which is carried on a pivot bearing 16 mounted in the frame about axis A. The speed cam incorporates an arcuate slot 17 acting as a cam guide and this slot passes through axis A.

The speed cam 11 is rotatable by means of an integral arm 18 which pivots the speed cam about its axis A through a range of positions representing at the extremities reverse full speed and forward full speed as shown in Figure 2. Corresponding half speed positions and neutral are also illustrated in Figure 2. The speed cam is operated by a vehicle driver, through speed input linkage 20. The speed cam constitutes a speed input member and the position of arm 18 constitutes the speed signal.

A right hand speed signal lever 21 is pivotal about a fixed pivot axis B on the frame 12 and can be moved by other parts of the system to provide a right hand speed signal representative of speeds between forward full speed and reverse full speed as indicated by the positions shown in Figure 2. The right hand speed lever may for example control the displacement and effective direction of a hydrostatic pump. A link 22 extends from a cam follower 23 in the lower end (as shown) of slot 17 and a further pivot 19 on the output signal lever.

In the straight ahead steering condition, follower 23 remains in the bottom of arcuate slot 17. The circumstances in which the follower takes up other positions is described subsequently. In this straight ahead condition, arcuate movement of speed cam 11 produces corresponding arcuate movement of right hand speed signal lever 21 with the result that there is a simple and direct relationship between the speed signal represented by movement of the speed cam 11 and the right hand speed signal represented by arcuate movement of lever 21.

A direction signal from a steering input member is intended to move the follower 23 up and down in the arcuate slot 17 to modify the response of the right hand speed signal lever 21 to movement of the speed cam 11.

For example, if follower 23 is moved upward to the centre of the slot so that it is in line with the fixed pivot A, rotation of the speed cam ceases to move the link 22 and thus does not move the lever 21 from the position shown. Similarly, if the follower 23 is between the position shown and pivot A, the lever 21 responds more slowly to the speed signal than in the position shown.

Similarly, if follower 23 is moved upward beyond point A, lever 21 rotates in a direction opposite to the rotation of the speed cam. The reverse rotation of the lever 21 increases with movement of follower 23 towards the top of slot 1 7. In the extreme position at the top of slot 17, the magnitude of the reverse right hand speed signal for a given speed cam movement corresponds to the forward magnitude the position shown.

The position of follower 23 within slot 17 is adjusted by the direction signal in a manner to be described. Operation of a steering wheel (not shown) is connected through a reduction gear such as a chain and sprocket drive to a steering signal shaft 24 (Figure 3), rotatable about a fixed axis C on the frame 12. The steering input shaft 24 carries a right hand steering cam 25. Cam 25 in turn engages on a right hand steering cam follower 26 which in turn is mounted on a steer lever 27 which in turn is pivotally mounted on the frame about axis D. Follower 26 is not particularly clear in Figure 3 but the corresponding left hand follower 26L is clear in Figure 4. Steer lever 27 is biased by a compression spring assembly 28 to hold the follower 26 in contact with the cam 25.Thus, rotation of steering input shaft 24 in response to steering movement rotates cam 25 which in turn rotates steer lever 27 to an extent dependent on the cam profile.

Steer lever 27 has a forward extension 30 as shown connected by a link 29 to cam follower 23 in slot 17. By this means, rotation of steering signal input shaft 24 causes cam 25 to move lever 27 by follower 26 and thereby moves follower 23 up and down in the slot 17. The combination of cam and follower 25,26 with spring assembly 28 thus defines positively the position of follower 23 in slot 17.

A typical cam profile is shown separately in Figure 5. For convenience of explanation of the cam profile, positions of the follower are discussed although actual movement is cam rotation rather than vice versa. Position O represents the straight ahead condition as illustrated in Figures 2 to 4.

For the right hand unit, rightward input steering signals are represented by section 0 P Q R S T of the cam profile and leftward input steering signals are represented by section 0 N. A small amount of initial rightward steering movement causes a sharp rise in the cam profile in section 0 P. In section P Q there is a steady rise in the cam profile. In section Q R there is a sharp step in the profile and thereafter there is a further steady rise in section R S. The cam lift rate in sections P Q and R S may be varied within each section to give a non-linear steering response and also to give difference response rates between slowed forward drive and increasing reverse drive. In section S T the follower remains at full height in relation to the cam.For steering movement in the opposite direction, that is to the left, the cam profile is a circular arc in section 0 N and results in no rise or fall of the cam.

In general, a right hand steering signal causes the follower 26 to rise, thus pivoting steer lever 27 so that its link 29 causes follower 23 to rise up in slot 1 7. The sharp initial rise in cam profile in section 0 P provides positive feel about the straight ahead position and tends to overcome a flat central part in the response of a bi-directional hydrostatic pump.

Thereafter, the cam profile rises steadily up to position S apart from a discontinuity at Q R. This discontinuity represents a position of the follower 23 at the centre of slot 17 corresponding to zero right hand speed signal at a changeover from a positive (forward) value to a negative (reverse) value. This discontinuity also provides the driver with some feel in the steering mechanism to indicate that he has brought the right hand track to rest. It is only in the event of extreme steering movements that the driver wishes to reverse the direction of the right hand track for a right hand turn so the discontinuity Q R helps to indicate to the driver when he would be about to bring in reverse drive. The constant radius in section S T simply allows some tolerance in defining the full steering movement position.

In practice when driving a skid steer vehicle, it is usual to set a constant speed and to supply a variable direction signal. The direction signal may constitute minor adjustments to a steering wheel to keep the vehicle in a straight line or following a gently curved road or track. Another situation requiring a steering signal input is to turn a vehicle in a limited space. In these situations, continuing to consider only a right turn, movement of follower 23 due to steering movement is constrained to follow slot 17, generally resulting in a change in right hand speed signal for varying direction signal and constant (input) speed signal.

A fundamental feature of this mechanical system is that with the speed signal set to zero, slot 1 7 is in the form of a circular arc centred on pivot point 1 9. In such a situation, when steering movement is effected at zero vehicle speed, movement of follower 23 in the slot 17 does not cause any movement of pivot 19 and thus does not result in any right hand (or left hand) speed signal. Due to this factor, if a driver inadvertently operates the steering control with the vehicle stationary, the vehicle does not move. For example, a driver descending from a vehicle cab could pull on the steering wheel and turn it inadvertently. With other forms of geometry, the steering wheel pull would cause one side of the vehicle to drive forward while the other drives back, resulting in dangerous uncontrolled vehicle movement.

The steering signals are capable only of reducing or of reversing and reducing the respective speed signals. In particular there is no increase in speed. This achieves the advantage of power availability referred to above in relation to the mathematical analysis of Figure 1.

Figure 4 shows not only the right hand part of the system but also the left hand part. The left hand part incorporates a second speed cam and slot corresponding to the speed cam 11. Both speed cams are joined together for operation in unison.

Similarly, the steering input shaft 24 is common to both right and left hand sections and carries a left hand cam 25L as well as the right hand cam 25. The profile for cam 25L is reversed compared with that for cam 25. As a result cam 25L responds to left hand direction signals in the same way that cam 25 responds to right hand direction signals and vice versa.

There are also two separate steer levers 27 and 27L. Although they are carried on a common shaft about axis D, they are rotatable independently and in fact rotate in different manners due to the differences between cams 25 and 25L. Similarly, separate steering output levers 21 and 21 L are provided on a common axis B. These levers 21 and 21 L operate independently of each other.

The function of the left hand part of the system corresponds with that of the right hand half except for the reversed configuration of the left hand cam 25L. Thus, for right hand direction signals, the follower 26L operates on the constant radius part of the cam, not resulting in any steering effect. For left hand direction signals, the cam 25L, follower 26L and rest of the mechanism operate in the same manner as the right hand section for right hand direction signals.

In practice, the whole mechanical installation is housed within a frame or housing 1 2 but in general the frame 12 has been removed from the drawings in the interests of clarity.

Claims (9)

1. A control system for steering and travel of a vehicle having righthand and left-hand driving units and steered by variation between the driving speeds of the driving units, the control system comprising: a speed input member for providing a speed signal between zero and maximum; a steering input member for producing a direction signal between full left, straight and full right; a right hand speed modulator responsive to the speed signal and to the direction signal to produce a right hand speed signal derived from the input signals which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate dependent on the steer signal;; a left hand speed modulator responsive to the speed signal and the direction signal to produce a left hand speed signal derived from the input signals which remains zero when the input speed signal is zero and increases with increasing input speed signal at a rate dependent on the steer signal; the right hand speed signal controlling the drive to the right hand side of the vehicle and the left hand speed signal controlling the drive to the left hand side of the vehicle.
2. A control system for steering and travel of a vehicle having righthand and left-hand driving units and steered by variation between the driving speeds of the driving units, the control system comprising: a speed input member for providing a speed signal ranging from full reverse, through zero to maximum; a steering input member for producing a left hand direction signal or a right hand direction signal or indicating straight ahead; a right hand speed modulator responsive to the speed signal and to the right hand direction signal to produce a right hand speed signal which remains zero when input speed is zero and increases with increasing input speed signal at a rate which decreases with increasing right hand steer signal;; a left hand speed modulator responsive to the speed signal and to the left hand direction signal to produce a left hand speed signal which remains zero when input speed is zero and increases with increasing input speed signal at a rate which decreases with increasing left hand steer signal; the right hand speed signal controlling the drive to the right hand side of the vehicle and the left hand speed signal controlling the drive to the left hand side of the vehicle.
3. A control system as claimed in Claim 1 or Claim 2 wherein each speed modulator comprises a speed cam which has a cam slot and is rotatable about an axis passing through the slot, a follower movable in the slot in response to direction signals and a connection from the follower to a right hand or left hand (as the case may be) speed signal lever.
4. A control system as claimed in Claim 3 further comprising a steer lever responsive to the direction signal and operative to move the follower in the slot 5. A control system as claimed in Claim 4 wherein the steer signal lever is operated by a cam driven by the direction signal.
6. A control system as claimed in Claim 3 wherein the speed cam slot is in the form of a circular arc centred on the connection to the right hand or left hand (as the case may be) speed signal lever.
Amendments to the claims have been filed as follows 1. A control system for steering and travel of a vehicle having right hand and left hand driving units and steered by variation between the driving speeds of the driving units, the control system comprising: a speed input member for providing a speed signal ranging from full reverse, through zero to maximum; a steering input member for producing a left hand direction signal or a right hand direction signal or indicating straight ahead; a right hand speed modulator responsive to the speed signal and to the right hand direction signal to produce a right hand speed signal which remains zero when input speed is zero and increases with increasing input speed signal at a rate which decreases with increasing right hand steer signal;; a left hand speed modulator responsive to the speed signal and to the left hand direction signal to produce a left hand speed signal which remains zero when input speed is zero and increases with increasing input speed signal at a rate which decreases with increasing left hand steer signal; the right hand speed signal controlling the drive to the right hand side of the vehicle and the left hand speed signal controlling the drive to the left hand side of the vehicle.
2. A control system as claimed in Claim 1 or Claim 2 wherein each speed modulator comprises a speed cam which has a cam slot and is rotatable about an axis passing through the slot, a follower movable in the slot in response to direction signals and a connection from the follower to a right hand or left hand (as the case may be) speed signal lever.
3. A control system as claimed in Claim 2 further comprising a steer lever responsive to the direction signal and operative to move the follower in the slot.
4. A control system as claimed in Claim 3 wherein the steer signal lever is operated by a cam driven by the direction signal.
5. A control system as claimed in Claim 4 wherein the cam driven by the direction signal is a variable ratio cam such that the rate of movement of the follower in the slot for a given change of direction signal varies over the range of movement of the steering input member.
6. A control system as claimed in Claim 5 wherein the cam driven by the direction signal has a sharp rise coincident with the change of the respective right or left speed signal from positive to negative while the other left or right speed signal remains positive.
7. A control system as claimed in Claim 5 or Claim 6 wherein the cam driven by the direction signal has one rate of rise over a range representing steering with both right and left speed signals positive and a higher rate of rise over a range representing steering with one right or left speed signal positive and the other negative.
8. A control system as claimed in Claim 5 or Claim 6 or Claim 7 wherein the cam driven by the direction signal has a sharp rise coincident with the straight steering condition.
9. A control system as claimed in Claim 3 wherein the speed cam slot is in the form of a circular arc centred on the connection to the right hand or left hand (as the case may be) speed signal lever.
GB9515919A 1995-08-03 1995-08-03 Vehicle skid-steer control system Withdrawn GB2303829A (en)

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GB9515919A GB2303829A (en) 1995-08-03 1995-08-03 Vehicle skid-steer control system
JP26510595A JPH0939599A (en) 1995-08-03 1995-10-13 Control device for maneuvering and progressing vehicle

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GB2303829A true GB2303829A (en) 1997-03-05

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EP1038757A2 (en) * 1999-03-26 2000-09-27 Deere & Company Steering for a vehicle and vehicle
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US6312354B1 (en) 1999-01-22 2001-11-06 Kanzaki Kokyukoki Mfg. Co., Ltd. Integral hydrostatic transaxle apparatus for driving and steering
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US6540633B1 (en) 1998-09-25 2003-04-01 Tuff Torq Corporation Transmission for speed changing and steering of a vehicle
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US6591936B2 (en) 2000-11-13 2003-07-15 Tuff Torq Corporation Driving apparatus for speed changing and steering of a vehicle
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US7857079B2 (en) 1998-12-03 2010-12-28 Kanzaki Kokyukoki Mfg. Co., Ltd.: Multi-wheel vehicle
US7914022B2 (en) 2006-10-17 2011-03-29 Mtd Products Inc Vehicle control systems and methods
US7992659B2 (en) 2005-07-22 2011-08-09 Infinitrak, Llc Steering systems, steering and speed coordination systems, and associated vehicles
US8011458B2 (en) 2001-09-17 2011-09-06 Mtd Products Inc Steering and driving systems and related vehicles
US8136613B2 (en) 2008-03-26 2012-03-20 Mtd Products Inc Vehicle control systems and methods
US8157030B2 (en) 2005-08-22 2012-04-17 Mtd Products Inc Driving and steering of motor vehicles
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JPH0939599A (en) 1997-02-10

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