Abstract:
A drive-steering control system suitable for off-road land and amphibious vehicles. The system includes first and second steering input levers, each operable to rotate in forward and rearward pivotal directions. A coupling mechanism converts and transmits rotation of the first steering input lever in the forward pivotal direction into rotation of the second steering input lever in the rearward pivotal direction, and vice-versa. A reducing mechanism operates to selectively reduce the propulsion outputs of first and second propulsion devices, and a converting mechanism operates to convert the rotations of the steering input levers into inputs to the reducing mechanism. Depending on the directions the steering input levers are rotated, the reducing mechanism reduces the propulsion output of either the first or second propulsion device, which causes either the lefthand or righthand side of the vehicle to travel at a lower speed and thereby turn the vehicle either left or right.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/019,365, filed Jan. 7, 2008, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to vehicle steering systems suitable for use with off-road, amphibious, and water vehicles that are propelled by two or more propulsion devices, such as drive wheels, drive tracks, propellers, etc. More particularly, the present invention relates to a vehicle steering control system that utilizes two synchronized steering input levers in a steer-by-driving propulsion system. 
     Ride-on self-propelled lawn care equipment, such as fertilizer and herbicide spreaders, are known and commercially available. A notable example is the Permagreen Ride-On Magnum, available from Permagreen Supreme Inc. and depicted in  FIG. 1 . As evident from  FIG. 1 , the Permagreen Ride-On Magnum utilizes an articulated steering system in which turning of the vehicle  10  occurs as a result of its front end  12  (with drive wheels  14 ) being physically turned with the handle bar  16 , causing the motorized front end  12  to articulate relative to a trailing sulky  18 . Articulated steering systems of this type usually depend entirely on an operator&#39;s muscle power to steer the vehicle. For example, U.S. Pat. No. 6,336,600 to Jessen discloses a self-propelled fertilizer spreader vehicle with an articulated steering control system, in which a front section of the vehicle is pivotally connected to a rear section and steered by changing the angle of the pivotal connection. 
     Aside from systems that control the steering angle of steering wheels (for example, conventional automobile steering systems), another type of steering system widely found in lawn care equipment is the steer-by-driving (drive-wheel steering) system. Also widely used on a variety of off-road and amphibious vehicles, steer-by-driving systems operate by controlling the relative rotation speed of at least two drive means (wheels, tracks, or other propulsion devices) to cause the vehicle to turn to the side of the slower rotating drive means. Such steer-by-driving systems are well known in the art, and include, but are not limited to, controlled differential steering, clutch-brake steering, and independent wheel-motor steering units. Controlled differential steering units generally comprise a differential that operably connects lefthand and righthand drive wheels or tracks and selectively-operable brakes that retard the rotation of one of the drive means. Examples include bulldozers and multi-wheeled vehicles such as skid steer loaders. In clutch-brake steering units, lefthand and righthand drive wheels are operably connected by selectively operable clutches with or without brakes for retarding the rotation of one of the drive wheels. A common example of this type of steering unit can be found in commercial lawn mowers and the like. Finally, in independent wheel-motor steering, each drive wheel is operably mounted directly to an electric or hydraulically driven wheel-motor or variable-displacement hydrostatic transmission that can be selectively-controlled to retard the rotation of either drive wheel. A common example of this type of steering unit is the zero-turning radius lawn mowers and the like. 
     U.S. Pat. No. 5,913,802 to Mullet et al. discloses a tiller or single-lever steering device for a drive-wheel steering system on a zero-turn-radius lawn mower. Single-lever steering devices, for example, the handlebars of tricycles and bicycles, are widely used and enable the user to become quickly proficient at operating other vehicles with single-lever steering. Both hands can remain on the lever (handlebar) for support, or one hand may be removed while the other hand still provides full steering control. Another advantage of single-lever steering devices is their compact size, which can minimize the overall size of the vehicle. Single-lever steering devices are also common on personal watercraft, personal recreational vehicles such as ATVs, amphibious vehicles, lawn and garden vehicles, and the like. In addition to drive-wheel steering systems such as Mullet et al., single-lever steering systems can be connected to a variety of other vehicle steering systems, including linkage-steering and direct-steering (for example, bicycles) systems. 
     While having the above-noted advantages, single-lever steering devices have known shortcomings. For example, the tiller motion of the lever mayforce the operator&#39;s body out of optimal alignment with the vehicle, such as when making a sharp high-speed turn, in which case the operator&#39;s body should lean to the inside of the turn for balance while the tiller must be orientated to the outside of the turn. Furthermore, vertically-orientated steering shafts common to single-lever steering devices may restrict entry to the vehicle and interfere with the placement of other vehicle components. Without some form of power-assist, the forces required to move the lever can fatigue the operator and often limit the size of the vehicle that can be controlled with a single-lever steering device. 
     Two-lever steering devices are also known. Conventional two-lever steering devices use two independently operable levers, normally arranged side by side, which move fore and aft in relationship to the vehicle. Conventional two-lever steering systems are commonly used to control differential steering systems, clutch-brake steering systems, steering systems utilizing twin independent variable-displacement hydraulic pumps and fixed-displacement hydraulic wheel motors, and twin variable-displacement hydrostatic transmission steering systems. Two-lever steering devices are commonly used with drive-wheel steering control systems found on walk-behind, sit-on, stand-on, skid steer, and stand-on/walk-behind vehicles. 
     Conventional two-lever steering input device systems also have known shortcomings. When used on walk-behind, stand-on, and stand-on/walk-behind vehicles as disclosed in U.S. Pat. No. 6,490,849 to Scag and U.S. Pat. No. 6,912,831 to Velke, a fixed support bar must be provided so the operator can maintain a firm grip on the vehicle. However, the operator is often required to loosen his/her grip on the fixed support bar while operating the steering levers, which can compromise operator stability and safety. Two-lever steering has been adapted to control differential steering systems used extensively in tracked vehicles, such as bulldozers and tanks, to provide an easy way to steer a heavy vehicle by braking the track on one side of the vehicle while the power is transmitted through a differential to continue turning the track on the other side at a higher speed. Typically, independently operable right and left handles control the brakes. While controlled differential steering systems perform well when the operator is sitting, in the case of a stand-up operator position such as on ride-on self-propelled lawn care equipment, additional structure is necessary to provide the operator with stable support. For example, a fixed support bar may be necessary so that the operator can maintain a firm grip on the vehicle for both vehicle control and operator stability and safety over rough and hilly terrain. Even then, the constant use of the fingers to operate the steering levers can cause fatigue and strain on the hands and arms, and accelerations and decelerations can cause the operator&#39;s arms on the steering levers to apply a reverse input to the steering system. A one-hand steering capability to free one hand of the operator is not practical unless the two levers are closely orientated to permit one hand to operate both levers. However, close placement of both levers may restrict entry onto the vehicle or in otherwise interfere with the operator or the location of other components, necessitating the use of burdensome and complicated means to reposition the levers as disclosed in U.S. Pat. Nos. 7,299,610 to Piontek and 6,729,115 to Bartel. Lastly, conventional two-lever steering input devices are less instinctive to use, requiring a lengthy learning curve before an inexperienced operator becomes proficient in its operation. 
     Another example of a two-lever steering device is disclosed in U.S. Pat. No. 6,604,757 to Huang as installed in a conventional automobile steering wheel system. Two counter-operating steering levers are connected to a linkage steering system to adjust the steering angle of the front wheels of a beach motorized vehicle. A more complicated two-lever steering device for a conventional steering wheel system is disclosed in U.S. Pat. No. 6,827,174 to Chernoff et al. In Chernoff et al., right and left control posts (levers) mechanically communicate with each other so as to operate in opposite directions by means of gears, etc. The posts send non-mechanical steering signals to a steer-by-wire system to adjust the steering angle of the steering wheels of a vehicle. Chernoff et al. also disclose separate demand-input mechanisms on the posts to control other vehicle control systems, for example, nonmechanical accelerator and braking signals. Unfortunately, steer-by-wire systems require expensive and complicated electronic control systems, as well as expensive and complicated actuators to transform the electrical signals into mechanical motion capable of operating the steering device. As such, steer-by-wire systems tend to be impractical for use on anything less than mass production vehicles. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a synchronized two-lever drive-steering control system suitable for off-road land and amphibious vehicles. The two levers are synchronized to be counter-operating steering input levers capable of providing a vehicle operator with convenient intuitive steering as well as firm support, which is particularly advantageous when operating vehicles intended for off-road and amphibious use on rough surfaces, such as rough and hilly terrains. 
     The drive-steering control system includes first and second steering input levers, each operable to rotate in forward and rearward pivotal directions relative to the vehicle. A coupling means converts and transmits rotation of the first steering input lever in the forward pivotal direction into rotation of the second steering input lever in the rearward pivotal direction, and rotation of the second steering input lever in the forward pivotal direction into rotation of the first steering input lever in the rearward pivotal direction. The coupling means prevents the first and second steering input levers from being simultaneously rotated in the forward pivotal direction or simultaneously rotated in the rearward pivotal direction. A reducing means operates to reduce propulsion outputs of a first means for propelling a lefthand side of the vehicle and a second means for propelling a righthand side of the vehicle, and a converting means operates to convert the rotations of the first and second steering input levers into inputs to the reducing means. The reducing means reduces the propulsion output of the first propelling means when the first steering input lever is rotated in the rearward pivotal direction, so that the lefthand side of the vehicle travels at a speed lower than the righthand side of the vehicle and the vehicle turns in a lefthand direction relative to the forward and rearward directions. In addition, the reducing means reduces the propulsion output of the second propelling means when the second steering input lever is rotated in the rearward pivotal direction, so that the righthand side of the vehicle travels at a speed lower than the lefthand side of the vehicle and the vehicle turns in a righthand direction relative to the forward and rearward directions. 
     The drive-steering control system of this invention is well suited for power-driven off-road, amphibious, and water vehicles that are often operated under strenuous conditions, especially off-road vehicles operated on rough and hilly terrains, that pose a greater risk in terms of vehicle control and operator stability and safety. The first and second steering input levers are coupled, for example, mechanically or hydraulically, to each other so that the motion of one of the levers causes the other lever to move equally in the opposite direction, while equal force applied to the levers in the same direction does not move the levers or have any effect on the steering of the vehicle. As such, the steering input levers can be used by the operator for support and stability. Because the drive-steering control system is well-adapted for one-hand operation, the system can be used by certain disabled individuals, and can even be configured for hands-free operation, for example, as a foot-operated drive-steering control system. Alternatively, the drive-steering control system can be configured as a two-hand or two-foot operated system. 
     The drive-steering control system can replace a number of conventional steering input devices including, but not limited to, steering wheels and single-lever and two-lever input devices commonly used on off-road, amphibious, and water vehicles. The steering input levers are in mechanical or hydraulic communication with at least one vehicle steering system to control the direction of travel of the vehicle. The vehicle steering system can be, but is not limited to, a variety of drive-wheel steering systems commonly used on a variety of off-road and amphibious vehicles, for example, the aforementioned controlled differential steering, clutch-brake steering, and independent wheel-motor steering units. Other steering systems that can be employed with the invention include, but are not limited to, linkage steering systems in which a linkage coupled to one or both levers selectively changes the position of a steering nozzle or wheels as embodied in personal watercraft and other vehicles, articulated steering systems in which the angular relationship between front and rear portions of the vehicle is selectively controlled, and combinations of these steering systems. As a particular but nonlimiting example, the drive-steering control system of this invention can be used in combination with the articulated-steering system disclosed in U.S. Pat. No. 6,336,600 to Jessen, whose contents relating to an articulated steering system are incorporated herein by reference. When used in combination with Jessen&#39;s articulated steering system, the steering input levers of this invention can be mechanically coupled with steering brakes on the front wheels of Jessen&#39;s vehicle, a differential can connect the drive wheels, and the connecting means can comprise steering bakes that selectively slow the drive wheel associated with the operated steering input lever as the differential continues turning the wheel associated with the other steering input lever at a higher speed. 
     As evident from the above, the drive-steering control system of this invention is capable of use on a variety of vehicles including, but is not limited to, power-driven land, water and amphibious vehicles employed for a wide variety of purposes. The vehicle can be configured to enable the operator to sit on, walk behind, stand on, and/or selectively stand on or walk behind the vehicle. The vehicle may incorporate any systems commonly or necessarily employed with the particular type of vehicle. For example, one or both steering input levers can be equipped with one or more operator input devices that mechanically or hydraulically communicate with one or more additional vehicle control systems, for example, a speed control device, forward and reverse control devices, and brakes. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ride-on self-propelled lawn care vehicle of a type known in the art. 
         FIG. 2  is a schematic perspective view of a vehicle drive-steering control system in accordance with an embodiment of this invention, and capable of being used on the vehicle of  FIG. 1 . 
         FIG. 3  is a perspective view of a ride-on self-propelled lawn care vehicle similar to that of  FIG. 1  and on which a drive-steering control system of the type represented in  FIG. 2  is installed. 
         FIG. 4  is a partial perspective view detailing steering input levers of the drive-steering control system of  FIG. 3 . 
         FIG. 5  is a rear view detailing the drive-steering control system of FIGS.  3  and  4 . 
         FIG. 6  is a detailed view of a combination damper-limiter-biasing device of the drive-steering control system of  FIGS. 3 through 5 . 
         FIG. 7  is a partial perspective view detailing a brake mechanism for use with the drive-steering control system of  FIGS. 3 through 6 . 
         FIG. 8  is a schematic perspective view of a vehicle drive-steering control system in accordance with another embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of a drive-steering control system  20  of this invention is schematically represented in  FIG. 2 . The drive-steering control system  20  is capable of use with a wide variety of vehicles, a non-limiting example of which is the Permagreen Ride-On Magnum represented in  FIG. 1 . Othertypes ofvehicles within the scope of the invention include other commercial off-road land vehicles including other types of self-propelled lawn care vehicles, recreational land vehicles such as ATVs, amphibious vehicles capable of operation on both land and water, and surface and submersible watercraft intended for use on or in the water. 
     The control system  20  represented in  FIG. 2  comprises lefthand and righthand steering input levers  22  and  24 , respectively, and a coupling mechanism  26 . The steering input levers  22  and  24  are configured to rotate in the forward and rearward directions of a vehicle on which the system  20  is installed, and the coupling mechanism  26  is adapted to cause the input levers  22  and  24  to be counter-rotating (counter-operating). More particularly, the coupling mechanism  26  converts and transmits the forward motion of one lever  22  or  24  into a rearward motion of the other lever  24  or  22 , and the rearward motion of one lever  22  or  24  into a forward motion of the other lever  24  or  22 . In the embodiment shown, the coupling mechanism  26  is an open differential of a type known in the art, and is adapted to be attached to a frame section  28  of a vehicle. Other types of coupling mechanisms capable of achieving counter-operation of the steering input levers  22  and  24  are foreseeable, some of which will be discussed in reference with the various embodiments of the invention. 
     For purposes of illustration,  FIG. 2  represents the control system  20  as configured for installation on a vehicle having two front drive wheels. Notably, neither drive wheel is configured to be articulated by the operation of the steering input levers  22  and  24 ; in other words, the levers  22  and  24  do not cause a steering effect by changing the steering angles of the drive wheels.  FIG. 2  represents a pair of wheel hubs  30  and brake drums  32  of types known in the art. The wheel hubs  30  are attached to each axle of a transmission  34  with an internal differential of any suitable type known in the art. Other types of wheel hubs, brake drums, and transmissions are also foreseeable, and the transmission  34  can receive power from any suitable source (not shown), such as an engine or motor. Each lever  22  and  24  is operably attached by way of a connecting rod or cable system  36  to a brake band  38  wrapped around a corresponding one of the brake drums  32 . Various other means for connecting the levers  22  and  24  to the brake bands  38  and various other mechanisms for applying a braking action to the wheel hubs  30  are foreseeable. 
     Without any actuation of the levers  22  and  24 , neither brake band  38  is engaged with its brake drum  32  and the vehicle travels in a straight line, either forward or reverse depending on the input to the transmission from a separate input device (not shown). The travel speed of the vehicle is also controlled by a separate input device (not shown). If a left turn is desired, the lefthand lever  22  is pulled toward the operator, which engages the lefthand brake band  38  with the lefthand brake drum  32 , slowing the wheel (not shown) mounted to the lefthand hub  30 . The internal differential within the transmission  34  continues transmitting power to the wheel (not shown) mounted on the righthand hub  30  and increases its speed. As a result, the vehicle turns to the left. If the righthand lever  24  is pulled, the procedure is reversed and the vehicle turns to the right. 
     According to a preferred aspect of the invention, the coupling mechanism  26  enables the vehicle to be steered using either lever  22  and  24  alone. For example, by pushing the lefthand lever  22  forward, the coupling mechanism  26  causes the righthand lever  24  to travel rearward and engage the righthand brake band  38  with the righthand brake drum  32 . This capability enables the operator to steer the vehicle with one hand while the other hand is used to operate various other control levers of the vehicle. 
     If both levers  22  and  24  are simultaneously pulled rearward or pushed forward with equal force, neither lever  22  and  24  moves as a result of the synchronization effect of the coupling mechanism  26 . As a result, neither brake is applied and the vehicle continues to travel in a straight line, and the operator can use the levers  22  and  24  for support and stability and acquire a feel for the terrain. The operator can hold onto the levers  22  and  24  while leaning backwards and bending down as may be necessary to avoid low-hanging branches, or leaning forward to transfer his/her weight to the front drive axle of the vehicle for increased traction, etc. While in that position, the operator can continue to steer the vehicle, which would otherwise be difficult to do without the steering control system  20  of this invention. 
     It can be appreciated that the steering control system  20  not only provides a simple and relatively inexpensive power-assist steering system, but it also provides increased safety and control to the vehicle. Furthermore, the system  20  retains the intuitive easy-to-learn features of current articulated and single-lever steering systems for ride-on self-propelled lawn care equipment, such as the aforementioned Permagreen Ride-On Magnum. 
       FIG. 3  represents a ride-on self-propelled lawn care vehicle  50  similar to that of  FIG. 1  and on which a drive-steering control system  20  of the type represented in  FIG. 2  is installed, and  FIGS. 4 through 7  depict subsystems of the control system in greater detail. For convenience, consistent reference numbers are used in  FIGS. 3 through 7  to identify functionally similar elements to those of  FIG. 2 . The vehicle  50  is believed to be a preferred configuration for a self-propelled lawn care vehicle, in that the vehicle  50  is equipped with a sulky  18  coupled to the motorized front end  12  of the vehicle  50  with an articulating joint  58 , and the vehicle  50  is configured to enable the vehicle&#39;s operator to selectively stand on or walk behind the sulky  18  while continuing to operate the control system  20 . While the invention is particularly well suited for use on the vehicle  50  portrayed in  FIG. 3 , the control system  20  can be utilized on other types of vehicles, including but not limited to industrial vehicles, watercraft, military vehicles, powered wheel chairs, and other vehicles that can utilize a drive-wheel steering (steer-by-driving) system. 
     In the embodiment of  FIGS. 3 through 7 , which is believed to represent a preferred embodiment of the invention, the steering input levers  22  and  24  and a coupling mechanism  26  (not shown in  FIG. 4 ) are mounted to a frame section  28  (or other part) of the vehicle  50 . As better seen in  FIG. 5 , each lever  22  and  24  has a roughly horizontal upper handle portion  22 A and  24 A, a roughly horizontal shaft  22 B and  24 B rotatably assembled with the coupling mechanism  26 , and a connecting portion  22 C and  24 C therebetween. The handle portions  22 A and  24 A of the levers  22  and  24  are equipped with hand grips  22 D and  24 D by which an operator grips and rotates (pivots) the levers  22  and  24  about the axis of the lever shafts  22 B and  24 B. The lever shafts  22 B and  24 B are offset and parallel within the coupling mechanism  26 , and are equipped with synchronizing gears  22 E and  24 E that are in mesh. Also attached to each steering input lever  22  and  24  is a bellcrank  23  for a steering cable system  36 , and a bracket  25  for mounting a limiter unit  40  discussed below. The levers  22  and  24 , bellcranks  23 , and brackets  25  can be assembled by welding or any other suitable assembly technique. 
     It should be apparent that the steering input levers  22  and  24  can be constructed of a variety of materials, assembled in any manner, and configured in size and shape as may be required to fulfil the intended purpose of the control system  20 . Furthermore, the handle portions  22 A and  24 A can be fixed or adjustable to be extended, retracted, and orientated to provide the operator optimal comfort and convenience. 
     In the embodiment of  FIG. 5 , the coupling mechanism  26  comprises a housing  26 A having lefthand and righthand pairs of plates  26 B, with each pair of plates  26 B having coaxially aligned holes that are offset from the aligned holes of the other pair of plates  26 B. The holes accommodate bearings  26 C, for example, bronze flange bearings, that journally support the lever shafts  22 B and  24 B in the aforementioned offset parallel arrangement. The shafts  22 B and  24 B can be retained in the housing  26 A by E-clips (not shown) or any other suitable fastening device. The gears  22 E and  24 E of the levers  22  and  24  mesh so that rotation of one lever  22 / 24  causes an opposite rotation of the other lever  24 / 22 . The housing  26 A can be constructed of any suitable material and in any suitable manner to provide a desired orientation for the levers  22  and  24 . Furthermore, the housing  26 A could be built into the frame of the vehicle  50 , rather than as a separate component attached to the section frame  28 . In addition, counter-operating mechanisms other than the gears  22 E and  24 E could be employed, for example, any gear or bevel in an open differential with a center differential cover, and bevel gears operably connected by a movable third bevel gear (similar to a differential) that enables the levers  22  and  24  to be selectively synchronized or independently operated. Other synchronizing means are also foreseeable, such as an external linkage system, a cable and pulley system, a push/pull cable system, a belt and pulley system, a roller chain and sprockets system, a hydraulic system, or a combination of these possibilities. 
     The housing  26 A also has left and a right housing brackets  26 D welded thereto and coupled to the limiter units  40  associated with the lefthand and righthand levers  22  and  24 . In the preferred embodiment, each limiter unit  40  is a multipurpose device that also provides a biasing effect and a damping effect, in addition to limiting the rotation of its lever  22 / 24 . An example of a commercial-available product that can be used for each limiter unit  40  is a Universal Mount part number 60166, with a static load rating of about 20 psi (about 2900 N/mm 2 ), manufactured by Tech Products Corporation of Dayton Ohio. The Universal Mount comprises an elastomeric ring  40 A, elastomeric bushing  40 B bonded to a center metal spacer  40 C, and a snubbing washer  40 D. The ring  40 A is inserted between the bracket  25  and the housing bracket  26 D, a reduced-diameter portion of the bushing  40 B is inserted through a hole in the housing bracket  26 D, a bolt  40 E is inserted through the snubbing washer  40 D, the spacer tube  40 C of the bushing  40 B, and a hole in the bracket  25 , and a lock nut  40 F secures the limiter unit  40  to the housing bracket  26 D and the bracket  25  of the lever  22 / 24 . The spacer tube  40 C limits the rotation of the lever  22 / 24  (indicated by a double-headed arrow in  FIG. 6 ) and, in conjunction with the ring  40 A and bushing  40 B, damps the motion of the lever  22 / 24  and biases the lever  22 / 24  to a non-steering position. 
     Other types of systems capable of providing the desired limiting, biasing, and/or damping effect are also foreseeable. For example, each of these effects can be achieved mechanically or hydraulically with cylinders, springs, etc. Furthermore, the limiting, biasing, and/or damping effect can be fixed or adjustable, and coupled to the steering cable system  36  or the mechanism that applies the braking effect to the drive wheels (e.g., the brake drums  32  and bands  38  of  FIG. 2 ), instead of being directly coupled to the steering levers  22  and  24 . Lastly, it should be understood that a limiting, biasing, and/or damping effect is preferred but an optional aspect of the invention. 
       FIGS. 4 and 5  depict multiple additional demand input levers as being mounted in the vicinity of the steering input levers  22  and  24 . For example, a speed input lever  42  is shown adjustably mounted on the righthand steering input lever  24  in a conveniently operable position that enables an operator to operate the speed input lever  42  with his/her right hand without requiring the operator to remove his/her hand from the righthand steering input lever  24 . The input lever  42  and its control cable  42 A can be of any suitable type, including those commercially available for operating control cables in vehicles of the type shown in  FIG. 3 . The speed input lever  42  can be coupled by the cable  42 A to a throttle input of a motor or engine  54  mounted on the vehicle  50  ( FIG. 3 ). A suitable example is a GX200URH2 internal combustion engine distributed by Honda Power Equipment Group, Alpharetta, Ga. USA, which has a built-in centrifugal clutch. As engine speed is increased, the centrifugal clutch engages and transmits power by means of a v-belt to an input pulley  34 A ( FIG. 7 ) on the transmission  34 . A suitable example for the transmission is a gear-driven differential transaxle identified as Peerless 855 manufactured by Tecumseh Power, Charlotte, N.C., USA, preferably equipped with a neutral safety switch for operating a neutral safety starting module, an example of which is commercially available from Delta Systems Inc. of Cleveland Ohio USA, as well as others. Alternatively, if the transmission  34  is a hydrostatic transaxle, such as the LT-0510 manufactured by Hydro-Gear of Sullivan, Ill., USA, a swash plate input of the hydrostatic transaxle can be operated by the speed input lever  42  via a push-pull cable to control both forward and reverse speeds. A vertical-shaft internal combustion engine, such as the Honda GXV160 distributed by Honda Power Equipment Group, can power the hydrostatic transaxle by means of a belt and pulleys. The swash plate input may include damping, limiting and biasing means, such as a hydraulic damping cylinder and a biasing device available from Hydro-Gear. 
       FIG. 4  also shows a brake lever  44  adjustably mounted on the lefthand steering input lever  22 , again in a conveniently operable position that enables the operator to operate the brake lever  44  with his/her left hand while the hand remains on the lefthand steering input lever  22 . The brake lever  44  can be coupled by a control cable  44 A to a braking system, for example, band service brakes (not shown), associated with the non-drive wheels  56  on the rear sulky  18  of the vehicle  50 . Other suitable braking systems are also within the scope of the invention. 
     Other demand input levers that may be mounted in the vicinity of the steering input levers  22  and  24  will depend on the particular type of vehicle. In the embodiment shown in which the vehicle  50  is a ride-on self-propelled lawn care vehicle  50 , other controls would include levers for controlling the flow of dry and liquid fertilizers, herbicides, insecticides, etc. For example, a third lever  46  shown in  FIGS. 4 and 5  as adjustably mounted on the lefthand steering input lever  22  may be used to control a liquid sprayer, for example, by operating a ball valve (not shown) through another cable  46 A. As with the other levers  42  and  44 , the lever  46  is positioned so that the operator can operate the lever  46  with his/her left hand while it remains on the lefthand steering input lever  22 . 
     A pair of levers  48  are shown pivotally mounted to the coupling mechanism  26  and positioned near both levers  22  and  24  for operating a push-pull cable  48 A that controls the opening and closing of a door to a hopper ( 52  in  FIG. 3 ) containing a dry granular material. Finally, an additional lever  49  shown in  FIG. 4  selectively controls the operating position of the steering control system  20  by releasing a latch (not shown) that allows the frame section  28  to be rotated forward and rearward. For example, the frame section  28  may be positioned in a forward position while the operator is riding the sulky  18 , and rotated rearwardly to allow the operator to continue operating the control system  20  after stepping off the back of sulky  18  and while walking behind the vehicle  50 . 
     Still other demand input levers can be mounted in the vicinity of the steering input levers  22  and  24  that allow their operation by the operator without removing his/her hands from the levers  22  and  24 . While represented as operating cables, additional levers contemplated by the invention can use various other actuation components, including commercially-available lever-operated hydraulic master cylinders, rotatable demand input handgrips (for example, motorcycle throttles), and various other levers and devices capable of operating a cable, rod, hydraulic slave cylinder, or other type of mechanical or hydraulic system. Additionally, such demand input devices may be capable of being selectively locked in a particular setting, selectively locked to prevent motion in one direction, and comprise paired levers on either side of the levers  22  and  24  and operatively connected, for example, to permit the operator to push the rear lever of the pair forward to cause forward motion of the vehicle  50  or pull back on the front lever of the pair to cause backward motion of the vehicle  50 . 
     The steering input levers  22  and  24 , coupling mechanism  26 , and cable system  36  can be provided in the form of a kit for installation on and retrofitting an existing vehicle with a conventional steering system, or installed as original equipment on a vehicle specifically designed to make use of the steering control system  20  of this invention. 
     As evident from  FIG. 2 , the steering control system  20  further includes or is otherwise intended to work in combination with a mechanism capable of selectively reducing the propulsion provided by a pair of drive wheels  14  or other propulsion devices, such as multiple drive wheels, tracks, propellers, etc. Similar to  FIG. 2 , a particular example of a propulsion-reducing device for the vehicle  50  of  FIG. 3  is represented in  FIG. 7  as a brake drum assembly comprising a drum  32  and band  38 .  FIG. 7  depicts the brake drum assembly located on the lefthand side of the vehicle  50 , though it should be understood that the brake drum assembly on the righthand side of the vehicle  50  will generally be a mirror image of  FIG. 7 . 
     The lefthand steering input lever  22  is in operable communication with the lefthand brake band  38  via the steering cable system  36 . One end of the cable  36 A can be adjustably coupled to the lefthand bellcrank  23  with, for example, a threaded stud and adjusting nut ( FIG. 4 ), while the other end of the cable  36 A is connected by an eyelet  36 B to the brake band  38 . As commonly constructed, the brake band  38  is wrapped around the brake drum  32 , resulting in the band  38  being C-shaped with adjacent formed connecting ends  38 A and  38 B. A clevis pin  36 C passes through the connecting end  38 A of the brake band  38  and the eyelet  36 B. A cotter pin  36 D secures the clevis pin  36 C to the brake band  38 . The sheath  36 E of the cable system  36  has a sheath stop  36 F in communication with a slot in the connecting end  38 B of the brake band  38  and a brake band plate  38 C. The brake band plate  38 C has a pin  38 D formed therein inserted through the connecting end  38 B, and a cotter pin  38 E secures the brake band  38  to the brake band plate  38 C. The brake drum  32  is attached to the wheel hub  30 , which is mechanically and rotatably attached to the left propelling output shaft of the transmission (not shown, corresponding to  34  in  FIG. 2 ) of the vehicle  50 . A suitable example for the transmission is the aforementioned Peerless 855 manufactured by Tecumseh Power. As conventional, the rim and tire  14  ( FIG. 3 ) are attached to the wheel hub  30 , providing the ground-engaging propulsion for the vehicle  50 . 
     While  FIG. 7  represents an exemplary braking and propulsion system for the drive-steering control system  20  of this invention, other suitable braking systems and transmission/transaxle systems are also foreseeable. For example, the invention could utilize gear or hydrostatic transmissions, disk or drum brakes (externally mounted or internally mounted within a transaxle), power transmissions with clutches and with or without brakes (externally mounted or internally mounted within a transaxle), tracks or multiple lefthand and righthand drive wheels, etc. 
       FIG. 8  schematically represents an alternative embodiment for the drive-steering control system  20  of this invention. In the embodiment of  FIG. 8 , a vertical-shaft internal combustion engine (not shown), such as the aforementioned Honda GXV160, is operably connected by belts and pulleys to a twin variable-displacement hydraulic pump and motor system  60 , which effectively replaces the transmission  34  represented in  FIG. 2  and the braking system represented in  FIG. 7 . In particular,  FIG. 8  depicts a pair of variable-displacement hydraulic pumps  62 , each with a swash plate input  64  in operable fluid communication with a fixed-displacement hydraulic wheel motor  65 . Examples of suitable variable-displacement hydraulic pumps and fixed-displacement hydraulic motors include, respectively, the PG series and HGM series manufactured by Hydro-Gear. The travel of each swash plate input  64  is preferably limited by the limiter unit  40  and damped and biased in a neutral non-steering position, for example, using hydraulic damping (not shown) and return-to-neutral biasing (not shown), which are commercially available from manufacturers such as Hydro-Gear. The output of each pump  62  is coupled to one of the drive wheels  14  of the vehicle  50  via its associated fixed-displacement hydraulic wheel motor  65  and hub  30  (corresponding to the wheel hubs  30  of  FIG. 2 ). As known in the art, the lefthand and righthand pumps  62  and their motors could be replaced by variable-displacement hydrostatic transmissions, such as the EZT series manufactured by Hydro-Gear. 
     The system  60  further includes a steering control column  66  attached to a steering bracket  68 , which together form an assembly that rotates about a vertical axis of the column  66 . The column  66  and steering bracket  68  are supported by an E-clip  70  on a bearing block  74  containing, for example, a bronze flange bearing (not shown). The bearing block  74  is secured to the frame  76  of the vehicle  50 , and the lower end of the steering control column  66  extends through the bearing block  74  and a hole (not shown) in the frame  76 , and is retained with another E-clip (not shown). 
     A U-shaped control bracket  72  is horizontally rotatably mounted on a bolt  84  that passes through a horizontal hole in the steering control column  66 . Spacers  82  on the bolt  84  align the control bracket  72  to the steering control column  66 . Bearings (not shown), such as bronze flange bearings, are preferably provided at the pivot points of the holes in the steering control column  66  and control bracket  72 . Connecting rods  88  operably connect the swash plate inputs  64  to respective lefthand and righthand legs  72 A and  72 B of the control bracket  72 . 
     Vertical rotational steering motion of the steering control column  66 , steering bracket  68 , and control bracket  72  is controlled with the lefthand and righthand steering input levers  22  and  24 , which can be essentially identical or otherwise functionally equivalent to the levers  22  and  24  of  FIGS. 2 through 6  and counter-operating as a result of a coupling mechanism  26  that can be essentially identical or otherwise functionally equivalent to the mechanism  26  of  FIGS. 2 through 6 . A steering push-pull cable system  36  operably connects the steering bracket  68  to a bellcrank associated with the righthand steering input lever  24 , so that push and pull actions transmitted from the levers  22  and  24  through the cable system  36  cause vertical rotational steering motion of the control bracket  72  via the control column  66 . A separate directional/speed control cable system  42 A operably connects the control bracket  72  to a bellcrank associated with a directional/speed input lever  42  (corresponding to the input lever  42  of  FIGS. 2 through 6 ). To eliminate binding and provide an adjustment capability, each end of the steering push-pull cable system  36 , connecting rods  88 , and directional/speed control cable system  42 A can comprise a ball-joint linkage, as illustrated for the ends of the cable systems  36  and  42 A coupled to the steering and control brackets  68  and  72 , respectively. A suitable example of a ball-joint linkage is Part No. 6058K41 available from McMaster-Carr, Chicago, Ill. USA. While only the ends of the cable systems  36  and  42 A coupled to the steering and control brackets  68  and  72  are illustrated in  FIG. 8  as being equipped with ball-joint linkages, it should be understood that the ends of the cable systems  36  and  42  coupled to the bellcranks of their respective levers  24  and  42  would be similarly equipped. 
     Pushing the directional/speed input lever  42  forward causes the control bracket  72  to rotate about the horizontal axis of the bolt  84  in the direction corresponding to the (+) side of the arrow, thereby equally pushing the lefthand and righthand connecting rods  88  (in the (+) direction of their respective arrows) and rotating the lefthand and righthand swash plate inputs  64  to provide equal forward propulsion to the lefthand and righthand drive wheels  14  via the pumps  62 . As a result, the vehicle  50  travels in a straight line at a speed proportional to the amount of driver input provided to the directional/speed input lever  42 . In comparison, as the directional/speed input lever  42  is pulled rearward, the control bracket  72  rotates about the horizontal axis of the bolt  84  in the (−) direction of its arrow to equally pull the lefthand and righthand connecting rods  88  in the (−) direction of their respective arrows, thereby rotating the lefthand and righthand swash plate inputs  64  to provide equal rearward propulsion to the lefthand and righthand drive wheels  14  via the pumps  62 . The result is that the vehicle  50  travels in a straight line rearward at a speed proportional to the amount of driver input provided to the directional/speed input lever  42 . 
     When the vehicle  50  is either in forward or rearward motion as described above and the righthand steering input lever  24  is pulled to the rear or the lefthand steering input lever  22  is pushed forward, the steering control column  66  and control bracket  72  are rotated counter-clockwise (in the R-direction of the arrow), causing the lefthand connecting rod  88  to push and rotate the lefthand swash plate input  64  in the (+) direction of its corresponding arrow to increase the rotational speed output of the lefthand pump  62  to the lefthand drive wheel  14 . Simultaneously, rotation of the control bracket  72  causes the righthand connecting rod  88  to pull the righthand swash plate input  64  in the (−) direction of its corresponding arrow and decrease the rotational speed output of the righthand pump  62  to the righthand drive wheel  14 . As a result, the vehicle  50  turns to the right at a rate proportional to the rotation of the levers  22  and  24 . If the righthand steering input lever  24  is pushed and/or the lefthand steering input lever  22  is pulled, the procedure is reversed and the vehicle  50  turns to the left. 
     Finally, if the vehicle  50  is at a stop and the righthand steering input lever  24  is pulled rearward or the lefthand steering input lever  22  is pushed forward, the vehicle  50  executes a zero radius turn to the right. Conversely, if the righthand steering input lever  24  is pushed and/or the lefthand steering input lever  22  is pulled, the vehicle  50  executes a zero radius turn to the left. 
     While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, while certain components and embodiments thereof are shown for performing specific functions, including the creation and transmission of certain motions, it is foreseeable that other structures and systems could be used to achieve the same or comparable functions. Therefore, the scope of the invention is to be limited only by the following claims.