Title: ZTR MECHANICAL STEERING ASSEMBLY AND METHOD OF STEERING

FIELD OF THE INVENTION This invention relates to the field of motorized vehicles having ground engaging wheels and more particularly to the field of motorized ground engaging vehicles of the type that are referred to as Zero Turn Radius, or ZTR vehicles. Such motorized vehicles may be used as riding mowers, lawn tractors or the like, but have other uses as well.

BACKGROUND OF THE INVENTION

ZTR vehicles are highly maneuverable and are therefore desirable in applications where such maneuverability is required. One such application is in lawn cutting, where it may be necessary to turn tight corners to evenly cut the grass in an area that may contain obstacles of different types such as tree trunks, bushes, gardens and the like. ZTR vehicles typically have a pair of drive motors, one for each drive wheel. They are also typically provided with a continuously variable transmission, such as being powered by hydraulic pumps, so that the speed of each drive wheel can be independently and smoothly varied.

Motor speed control is often referred to as traction control in this field. In ZTR vehicles traction or speed control is also used in steering the vehicle, for example by controlling the individual speeds of the drive wheels. However, the steering of the vehicle by speed control is notoriously difficult. Early implementations of speed control steering provided the operator, who typically sits upon the vehicle to operate it, with a pair of traction control levers, or throttles, one for each hand. By manipulating the steering levers forwardly and backwardly the operator could, in theory steer the vehicle. Passive spinning or castor wheels are usually provided at the front, which simply swivel as the vehicle is steered by means of the traction control.

However, steering is very difficult to control in this manner. While it can be done, it requires much training and is difficult enough that unskilled temporary workers of the sort that might be hired by a lawn care or gardening company are unable to easily learn to use the vehicles. Furthermore, difficulties in steering result in damaged lawns, accidents and collisions and damaged equipment.

One of the problems with this type of steering is the difficulty in getting the speed of the wheels to match the turn required. When the operator wants to turn, he needs to change the relative speed between the two wheels. This can be done in a number of ways, for example, by reducing the speed of the wheel on the inside of the turn, or increasing the speed of the wheel on the outside of the turn. The natural tendency with this type of lever based traction control is to do both. But not only does the operator need to change the wheel speeds, he needs to control the wheel speeds so that the difference in wheel speeds between the inside wheel and the outside wheel is suitable to create the desired turning radius. The steering can be executed at any speed, if the speed differential is appropriate, but at higher speeds the changes in speed required to steer must be made that much more quickly and precisely. It is very difficult to get the exactly right change in speed between the wheels with the lever type steering control. An altogether common result is that the wheel speeds will be miss matched, for the turn desired. In this case the vehicle will either turn too quickly, or too slowly, or likely rapidly oscillate between the two as the driver tries to compensate. The rapid turn itself can create forces on the driver, causing further difficulties in steering. Sudden turns, especially on a slope as is often found in grass cutting operations on golf courses or the like can result in a significant overturning moment, and can cause dangerous crashes. Another issue apart from simply the direction of the vehicle, which of course is critical, is the tendency, if the speed is too great, for one or the other of the wheels

to spin, or slip. In a grass cutting environment this can create scarring in the grass and is undesirable.

The basic problem is that managing both speed control levers at once is ergonomically awkward in part because the steering by its nature is overly sensitive

As a result there have been many prior attempts to provide ZTR vehicles that are easier and safer to use. For example: United States Patent 5,850,886; United States Patent 5,042,238; United States Patent 6,257,357;

United States Patent 6,454,032; United States Patent 6,725,954; United States Patent 6,962,219; United States Patent 6,129,164; . United States Patent Publication 2004/0211615;

United States Patent Publication 2006/0096133; United States Patent 4,509,611 ; United States Patent 4,399,886; United States Patent 6,185,920; United States Patent 6,554,085;

United States Patent 6,336,513; United States Patent Publication 2006/0108155; United States Patent 6,325,396 United States Patent 3,315,759 United States Patent 4,504,074; and

United States Patent Publication 2006/0169514.

Notwithstanding these prior design attempts for an easy to steer

ZTR vehicle, there remains a need for a steering assembly and a ZTR vehicle including such a steering assembly which avoids the limitations of the prior designs and which is ergonomically intuitive to use. This wili

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lead to less training time required for operators, fewer accidents and less damage and improved results and user satisfaction.

SUMMARY OF THE INVENTION The present invention provides a ZTR vehicle that includes a separate traction control to control the speed of the vehicle, either in a forward or a reverse direction, which is independent from the steering control. The present invention further provides a steering interface for the driver that is easier to control and use for four wheel steering control. In a preferred embodiment the steering levers of the prior art are replaced with a steering wheel and the passive front castor wheels with steered front wheels. The present invention also provides a kit of components which can be mounted onto a vehicle platform to achieve the desired steering results as well as a ZTR vehicle incorporating the same. Therefore, according to a first aspect of the invention there is provided a mechanical steering assembly for a ground engaging vehicle having a left rear drive wheel and right rear drive wheel and a left drive motor and right drive motor operatively connected to each of the left and right rear drive wheels respectively and at least one front wheel, the steering assembly comprising: a left motor throttle cable to connect to a left throttle of said left rear drive motor and a right motor throttle cable to connect to a right throttle of said right rear drive motor; a traction control operatively connected to said throttle cables to simultaneously adjust said left throttle cable and said right throttle cable by the same amount; a steering wheel, a front wheel steering connection between said steering wheel and said at least one front wheel; and a motor steering connection between said steering wheel and said left and right throttle cables to simultaneously adjust said left throttle cable

and said right throttle cable by a different amount, wherein when said steering assembly is installed on said vehicle, turning said steering wheel simultaneously steers said at least one front wheel and differentially changes a speed said left drive motor and said right drive motor to steer said vehicle in a manner generally consistent with said steering of said at least one front wheel by said steering wheel.

According to another aspect of the present invention there is provided a method of steering a steerable vehicle having mechanical steering assembly operatively connected to a left rear drive wheel, a right rear drive wheel and at least one front steerable wheel, comprising the steps of: operating a traction control lever to cause said vehicle to move; operating a steering wheel to simultaneously steer said at least one front steerable wheel and to adjust a speed of said right rear drive wheel and said left rear drive wheel by a different amount, which is suitable to steer the vehicle by the rear wheels according to steering wheel control of the at least one front steerable wheel.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made, by way of example only, to preferred embodiments of the invention by reference to the following figures, in which:

Figure 1 is a perspective view of a vehicle having the steering mechanism of the present invention; Figure 2 is an isolation view of the steering assembly of the present invention without the vehicle frame;

Figure 3 is a bottom view of the vehicle of Figure 1; Figure 4 is a close up view of the steering control components of Figure 2; Figure 5 is a top view of the steering control components of Figure

3;

Figure 6 is a close up underside view of the steering assembly in a turning position; and

Figure 7 is an alternate form of traction control interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a vehicle 10 having ground engaging rear wheels 12 and 14 and front wheels 16, 18. The wheels 12, 14, 16 and 18 are mounted to a frame 20 with a platform 22. Mounted to the platform 22 and operatively connected to the ground engaging rear wheels 12 and 14 are drive motors 24 and 26 (see Figure 2). In this manner each of the rear wheels is provided with a separately controllable drive motor. In the preferred form of the invention, the drive motors are pumps but other forms of drive motors are also comprehended by the present invention. The use of two piston pumps mounted to a gas engine and driven by the gas engine, with each pump hydraulically connected to one of the drive wheels to drive the drive wheels has provided reasonable results. What is desired is to provide independent speed and acceleration control to each of the ground engaging rear wheels 12, 14 as described in more detail below. The vehicle 10 with platform 22 can be configured in a number of ways. Good results have been achieved with mounting a rotating grass cutting blade assembly below the platform 22 for the purpose of a grass cutting machine. Mounted above the platform 22 are the gas motor 28, a seat 30 and a steering mechanism such as steering wheel 32. Various configurations of elements can be mounted to the platform 22 without departing from the broad scope of the present invention, such as grass chutes, catchers, storage bins and the like.

Figure 2 shows a steering assembly 40 according to the present invention. The various components of the steering assembly will now be described. In a preferred embodiment, a steering wheel 32 is provided mounted to a steering post 42. The steering post 42 may include a

universal joint 44. As will be understood by those skilled in the art, the universal joint will provide for an adjustable height steering wheel that can be tilted up or down to suit the individual driver. The steering wheel may be provided with a power steering assembly 46, the details of which will be familiar to those skilled in the art and which are therefore not described in any further detail herein. Power steering, while it makes it somewhat easier to steer the vehicle, is not required and the present invention comprehends a manual steering assembly as well. Power steering is preferred however. A steering ratio gearing assembly 45 is also preferable in the steering column, with a 2:1 ratio being preferred.

Also shown is a traction control lever 48 which is connected to a link element 50 to a pivoting linkage 52. Figure 3 shows the elements from below, and shows the pivoting linkage 52 connected to a rocker arm 54 with a further link element 56. A pivot 58 connects link element 56 to rocker arm 54.

Also shown is a shuttle assembly 60 which is movable along a shuttle slot 62 by the link element 56. The link element 56 is connected to the shuttle assembly 60 whereby changing the position of the traction control lever 48, through the linkage elements described above, causes the shuttle assembly 60 to move side to side within the shuttle slot 62. To provide a high wear surface it is preferred to form a metal slot liner, such as out of steel or other metal. In this way the balance of the part can be made from, for example molded plastic, provided it is strong enough. Metal stampings can warp, affecting smooth shuttle movement, thus, it is preferred to use a more dimensionally precise part, such as a precision aluminum die cast part, for the slot liner. Smooth running bearings are preferred for the components that slide relative to one another.

Throttle cables 64, 68 are connected to the shuttle assembly 60 at one end, and to throttles (not shown) of the drive motors 24, 26 at the other end. As shown in Figure 4, the throttle cables 64, 68 feed through the shuttle assembly 60 and are connected to a respective control

element 70, 72 housed within axial slots 74, 76. In Figure 4 only control element 70 in slot 74 is visible, but in Figure 5, control element 72 in slot 76 is shown. As will be understood by those skilled in the art, throttle cables 64, 68 are of the type having a sheath 78 through which passes a control wire 80. The front end 81 of the respective control wire 80 is attached to the respective control element 70, 72, and the rear end is connected to the respective throttle. The sheath 78 ends at the shuttle assembly 60, and the control wires 80 slide within the sheath in a known manner. The shuttle 60 therefore acts as a throttle cable bracket for receiving an end 81 of the sheath 78 remote from the drive motors.

It can now be appreciated that the control elements 70, 72 are slideably retained in axial slots 74, 76 respectively, which permits the position of the control elements 70, 72 to be changed. Bearings are preferred to ensure smooth running of the control elements in the axial slots. As the control elements move in the axial slots, the control wire will be pulled up and back thereby adjusting the position of the throttles on the drive motors 24, 26. Changing the throttle position changes the speed of the drive motors and hence the speed of rotation of the drive wheels. A differential throttle change causes the vehicle to turn. As shown in Figures 4 and 5, attached to the steering post 42 is a motor control plate 90 which is housed in a frame 92. In the preferred embodiment as shown, the frame 92 includes the shuttle slot 62 which includes a high wear precision surface, such as being metal lined at 63 as described above. The motor control plate 90 includes cam slots 94 and on the reverse side 96. The cam slots 94 and 96 (or motor speed control slots) are preferably mirror images of one another, as explained in more detail below. Throttle control levers 98, 100 are operatively connected to the cam slots 94 and 96 respectively by means of a cam follower located within each of the cam slots 94, 96. Respective pivot posts 102, 104 operatively connect the throttle control levers 98, 100 to the frame 92.

As shown in Figure 4, generally located towards the bottom of the steering post 42 is a rack 110, which interacts with a pinion 112 attached front steering linkage 114 or rack gear shaft. As shown in Figure 2, by means of link elements 116, 118 and 120 and 122 the front wheels, which are passive wheels, can be steered by turning the steering wheel left and right in the normal manner. Thus, in the present invention the front wheels are actively steered. It can now be understood that an aspect of the present invention is that the steering wheel 32 simultaneously causes a steering of the front wheels, and adjustment of the throttle cables 64, 68 so that the steering of the front wheels can be coordinated with the motor speed control steering of the rear wheels.

Although the present invention can be applied to a vehicle having only three wheels with one front steerable wheel, it is most preferably applied to a four wheel vehicle having two steerable front wheels. Generally the type of vehicles to which the present invention is applied will be low speed vehicles, having a top speed of less than 30 km/hr, about 25 km/hr. For such lower speed applications it is preferred to incorporate Ackerman Steering Geometry to the front wheels. As will be understood by those skilled in the art, this steering geometry solves the problem of the wheel on the inside needing to trace a turning circle of a different radius from the wheel on the outside. This is arranged by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. This arrangement provides that the centre point of all circles traced by all steered wheels will lie on a common point, at any angle of steering. Thus the most preferred form of the steering linkage of the present invention is one that provides such an Ackerman Steering Geometry. Such a geometry is particularly useful for a zero turn radius vehicle where the vehicle may be spinning about a centre of rotation - in such a case, without this steering geometry, there would be a tendency for one of the wheels (or both) not lying on a circle of a common centre point to slip and tear the grass, for example.

The operation of the traction control steering of the present invention can now be more clearly understood. The shuttle 60 will have a neutral position, within the shuttle slot or race 62 such as shown in Figure 3. Good results have been obtained when the neutral position is approximately in the middle of the shuttle slot 62, but it will be understood by those skilled in the art that provided there is room for the shuttle to move in either direction from the neutral position, the exact location of the neutral position is not that important. At the neutral position, the control elements 70, 72 are also located at a neutral position in axial slots or races 74, 76. Once again, the neutral position is preferably somewhere towards the middle of the axial slots 74, 76 although the precise location of the neutral position does not matter. The traction control lever 48 may be positioned in a neutral position, which may be for example, vertical, which corresponds to the position of the shuttle assembly 62 in the neutral position and the control elements 70, 72 also in the neutral position.

To cause the vehicle 10 to go forward, the operator pushes the traction control lever forward which moves the shuttle assembly 60 in the shuttle slot 62. The control elements 70 and 72 are slideably engaged with the throttle control levers 98 and 100, which are positioned at an angle relative to the direction of movement of the shuttle 60 in the shuttle slot 62 when the steering wheel is in the neutral or straight forward position. As the shuttle assembly 60 moves in the slot 62, the control elements 70 and 72 are displaced forwardly in the axial slots 74, 76 by reason of the angle in the throttle control levers. This results in a tensioning of the control wires 80 and opens the throttles on the drive motors 24, 26. As can be seen, by positioning the control elements 70 and 72 one above another, and by positioning the throttle control levers on the same angle, also one above another, a displacement of the shuttle 60 causes an equal displacement of control element 70 as control element 72. In this way, the throttle control of drive motor 24 is identical to drive motor 26 and they will always be in synchronization for any

change of speed made through the traction control lever. Thrust or traction control lever 48 therefore permits the vehicle to be sped up or slowed down in a forwardly direction. By pulling the traction control lever backwardly, the shuttle assembly 60 is moved in the opposite direction in slot 62 and control elements 70 and 72 are also moved in the opposite directions in axial slots 74, 76 relative to their respective neutral positions. Once the shuttle assembly 60 and the control elements 70 and 72 pass through the neutral position in the opposite direction, the motors will be slowed to stop, and then will be slowly accelerated in the opposite direction. Again, each of the motors will be speed controlled by the same amount in the same direction to permit straight forward or reverse traveling. The foregoing description is relevant for changes in traction control where no change in steering direction occurs.

Turning now to the steering control, the operation of the present invention can be more clearly understood. An aspect of the present invention is to permit steering control of the vehicle 10 to be exercised by throttle control adjustment of the rear drive wheels 12 and 14 through the drive motors 24, 26, by mechanical linkage to the steering wheel. Thus motor speed control, for steering purposes is directly mechanically controlled, in a so-called fly by wire arrangement.

When the steering wheel 32 is rotated, by means of the rack 110 and pinion 112 connection, and the steering linkage 114, the front wheels 16, 18 are positively steered. However, to avoid slipping and to provide a short turning radius as is desirable in such vehicles, steering control also is exercised in respect of the speed control of the drive motors. As the steering wheel 32 is turned, steering post 42 is also turned. As shown in Figure 5, as a result, the motor control plate 90 is turned and the angle of each of the throttle control levers 98 and 100 is changed. The angle is changed as the throttle control levers 98 and 100 follow the cam slots 94, 96 at one end and pivot about respective pivot points 102, 104. Each of the top surface and the bottom surface of the motor control plate include a

cam slot 94 or 96. The cam slots 94 and 96 are mirror images of one another to provide precise and symmetrical motor steering control. For example, turning the steering wheel to the right will cause one motor control element to move within the axial slot by an equal and opposite amount to the movement of the other control element within the other axial slot. In this way, one drive wheel is sped up while another drive wheel is slowed down by an amount that is appropriate to make a turn of a specific radius. This results in efficient steering of the vehicle through a turn, without under steering or over steering by reason of either under speed or over speed on the inside or the outside wheels. As can now be appreciated this precise motor steering control is exercised with the simple expedient of the driver turning the steering wheel. This is very easy and intuitive to learn to drive and to use. Each degree of turn is throttle controlled by means of positioning a cam follower within the cam slot. The vehicle can be operated at any speed through any turn, as the position of the shuttle 60 in slot 62 is independent of the position of the motor control plate. Also, the appropriate speed difference will be applied to the respective drive motors, for a defined turn radius, at any given degree of turning or displacement of the steering wheel. In a preferred embodiment, the closer the steering wheel gets to a zero turn radius, the slower the speed of the motors. In other words, the cam slot can be formed as a part spiral as shown in Figures 4 and 5 to slow the speed of the vehicle through a close turn by a predetermined amount. The actual speed of the vehicle will be determined by the position of the shuttle assembly in the shuttle slot but the relative change in speed will be determined by the degree of arc in the spiral i.e. how quickly it slows will be controlled by how the spiral portion of the motor control slot changes the angle of the motor control levers across the turn.

As previously discussed, the configuration of the cam slots on the upper side and the lower side are matching mirror images so that identical, but opposite, speed control is provided to each of the drive

motors. In other words, one motor is sped up by an equal and opposite amount to how much the other motor is slowed down. This is due to the different displacement of the motor control levers 100, 102 through the turn. As will now be understood by those skilled in the art the present invention translates the angular displacement of the steering wheel into an appropriate amount of axial displacement of a throttle control wire for opposite but matched speed control of individual and respective drive motors for the rear wheels.

An aspect of the present invention is the actual configuration of the cam slots which have been determined to effect smooth control for a specific vehicle. The factors that control the shape and position of the motor control grooves or cam slots include the wheel base length (distance between the front and rear wheels) and the track width (width of vehicle between the rear wheels). Different vehicles will require different shaped grooves, but small changes in wheel base or track width can be accommodated by a single groove design. A preferred maximum vehicle speed for this application is less than about 25 km/hour, and so at such low speeds the grooves may not need to be redesigned for small changes in wheel base design or the like. For higher speeds and for larger wheel base differences, a new groove design is likely required. The actual shape of the cam slots in the motor control plates can vary to achieve different speed control for different shaped vehicles, and the precise shape shown is only one example. However, reasonable results have been obtained from the cam slot described and shown. As can now be understood the geometric profile for each cam or motor control slot is determined by a number of factors. They include the rear drive wheel rolling diameters, and the rear wheel drive motors rotational speed. Most preferably the throttle control will provide a linearly changing speed change for a specific displacement. Thus, for a certain change in position a known change in speed can be expected. Assisting in determining the change in position is the steering gear ratio, which in

the preferred embodiment is 2:1 as previously noted. This means that for a 360" turn of the steering wheel, a 180" turn of the front wheels is accomplished. The change in throttle position, to create a change in speed for each drive wheel, is co-ordinated through the degree of rotation of the steering wheel to match the motor drive turning radius to the steered turning radius. As will be understood by those skilled in the art the term match in this sense means substantially the same as. While there is no precise mathematical description of what substantially the same means, it will be understood that the turning radius of the front steered wheels and of the rear driven wheels will be sufficiently close so as to prevent wheel slip at either the front or the rear wheels.

Figure 7 shows an alternate embodiment of a traction control interface 200 according to the present invention. Instead of the hand operated lever, in this embodiment a foot operated pedal assembly is shown with a forward foot plate 210 and a rearward foot plate 220 on opposite sides of a pivot 212. The pedal assembly is connected to a link rod 230, which is in turn connected to the traction control link elements, such as 56, as previously described in respect of the lever embodiment. By rocking the foot pedal back and forth (by stepping on plate 210 or 220 respectively) the shuttle 60 can be moved in shuttle slot 62 in either direction relative to the neutral position of the shuttle 60, to effect speed control of the vehicle. The traction control interface 200 is thus analogous to a gas pedal in a conventional vehicle, except that of course it also controls reverse/forward direction. While various modifications and alterations are possible to the present invention, the true scope of the invention is defined by the attached claims. Some variations have been discussed above and others will be apparent to those skilled in the art. For example, while a top and bottom configuration for the motor control levers has been described, through mechanical linkages the orientation of the motor control plate can be at any angle provided that the cam slots are appropriately configured.

Also, the present invention can be in the form of an OEM assembly, or as a kit of components which can be added to an existing vehicle platform, to effect the controlled steering of a ZTR vehicle. The elements of the kit include, the steering wheel, the front wheel steering linkage, the throttle cables, and the motor control steering linkage.