Motor vehicles – Steering by driving – Independently operable drive motors
Reexamination Certificate
2003-03-28
2004-04-27
Hurley, Kevin (Department: 3611)
Motor vehicles
Steering by driving
Independently operable drive motors
Reexamination Certificate
active
06725954
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a steering control apparatus and method for a vehicle having a continuously variable transmission. More particularly, present invention relates to a steering control device or system in which a steering wheel and a transmission operating device can combine to control a pair of left and right continuously variable transmissions such that the vehicle has zero turning radius (ZTR) capability.
BACKGROUND ART
Many types of vehicles, and particularly utility vehicles such as lawnmowers, tractors and the like, are steered to the left and right through the operation of independently controlled drive wheels. For instance, to turn such a vehicle to the left, the left drive wheel can be slowed relative to the right drive wheel such that the greater percentage of torque produced by the vehicle's motor is transmitted to the right drive wheel. One popular technique for independently controlling the drive wheels is to employ a transmission system in which separate continuously variable transmission (CVT) devices respectively control each drive wheel. The CVT devices are typically controlled by a pair of hand-operated levers, foot-operated pedals, or the like. In addition to transmission-controlled steering systems, these types of vehicles can also rely on their steering wheels to turn non-driven wheels in a conventional manner. Recently, some of these vehicles are capable of executing zero radius turns to provide greater maneuverability.
In commonly assigned U.S. Pat. No. 5,850,886 to Kuono et al., the content of which is incorporated herein in its entirety, a vehicle equipped with a useful CVT-controlled steering system is disclosed. The vehicle includes a steering wheel linked to a pair of non-driven front wheels, and a pair of rear drive wheels controlled by a corresponding pair of CVT devices. The steering wheel not only controls the non-driven front wheels, but also controls the CVT devices and thus the rear drive wheels through a pair of cables such as Bowden wires that actuate a transmission control system. The ability to control the CVT devices by means of the steering wheel is highly advantageous in the mass consumer market, because the steering wheel constitutes a steering control interface with which consumers are generally familiar and comfortable.
While the steering wheel-controlled transmission system disclosed in U.S. Pat. No. 5,850,886 is advantageous, it is not designed to provide its vehicle with zero turn radius capability. It would therefore be advantageous to provide an apparatus and method for steering a vehicle using a steering wheel controlled transmission system, and also provide the apparatus with the ability to steer the vehicle at a zero turn radius.
SUMMARY
The present invention in general terms provides an apparatus and method for steering a vehicle with zero turning radius capability. The invention is particularly advantageous as applied to a riding-type vehicle, such as a lawnmower, tractor, or other utility vehicle having at least a pair of left and right drive wheels and one or more non-driven wheels. The apparatus generally comprises a steering handle such as a steering wheel, a transmission control device, and a pair of continuously variable transmission devices. The steering handle and transmission control device are intercoupled through a suitable steering linkage assembly, which preferably includes a pair of cables such as Bowden wires. The steering handle preferably is not linked to any wheels of the vehicle, such that the vehicle is turned solely by means of the interactive operation of the steering handle, the transmission control device, and the continuously variable transmission devices. Preferably, in addition to the drive wheels, the vehicle comprises one or more non-driven wheels that are provided as caster wheels. The caster wheels swivel freely in response to turning of the vehicle, and independently of the operation of the steering handle. The caster wheels advantageously facilitate the steering of the vehicle at a zero turn radius. The zero turn radius capability of the vehicle is described in detail hereinbelow.
By moving the steering handle in a desired direction, such as by turning a steering wheel, one of the cables of the steering linkage assembly actuates certain components of the transmission control device in a manner that adjusts the respective states of the continuously variable transmission devices. Each continuously variable transmission device controls an individual drive wheel of the vehicle and, more specifically, controls the angular velocity of each drive wheel in terms of both rotational speed and direction (forward or reverse) of rotation. Thus, for instance, if the steering handle is turned to the left while the vehicle is being driven forwardly, the transmission control device is actuated so as to cause one of the continuously variable transmission devices to drive the right drive wheel at a relatively fast speed in the forward direction, while the other continuously variable transmission device drives the left drive wheel either at a slower forward speed, at a zero speed (i.e., a neutral state of the left drive wheel), or even at a reverse speed. The vehicle is turned or steered as a result of the differential angular velocities of the drive wheels. In the case of driving the left drive wheel at a reverse speed while driving the right drive wheel at a forward speed, the left and right drive wheels are accordingly driven in different directions, thereby enabling the vehicle to be turned to the left (or to the right by analogy) at a zero turn radius while moving at a certain speed range in the forward (or, if desired, reverse) direction.
In some embodiments, the transmission control device comprises a moving, and preferably pivoting, guide member or members, and a mixing lever. The mixing lever is coupled to the continuously variable transmission devices through a suitable transmission linkage assembly, a preferred example of which is described hereinbelow. Preferably, the mixing lever is coupled to a hand-operated speed change lever similar to a stick shift lever. The speed change lever is employed to pivot or rotate the mixing lever about a first axis (e.g., a lateral or transverse axis) to select a speed or speed range and a direction (forward or reverse) at which the vehicle is to be driven. The speed change lever is also employed to select a neutral state. In a preferred embodiment in which the continuously variable transmission devices are based on a hydrostatic system, the neutral state corresponds to a stop state of the vehicle. The mixing lever also pivots or rotates about a second axis (e.g., a longitudinal axis) that is substantially perpendicular to the first axis. Movement of the steering handle actuates the guide member of the transmission control device to contact and move the mixing lever such that the mixing lever pivots about this second axis. Accordingly, both the steering handle and the speed change lever determine the position of the mixing lever, and in turn the state of the continuously variable transmission devices and, consequently, the respective angular velocities of the drive wheels.
In some embodiments, the transmission control device comprises a guide plate and a pair of spring-loaded guide members that cooperatively move the mixing lever in response to movement of the steering handle. For this purpose, the mixing lever extends through a distinctively shaped aperture of the guide plate and between the spring-loaded guide members. The position of the mixing lever within the aperture determines whether the vehicle moves in the forward or reverse direction, whether the vehicle is in a neutral state, the range of speed at which the vehicle moves, and whether the vehicle can be steered at a zero turn radius. The spring-loaded guide members are positioned so as to contact the mixing lever during initial movement of the steering handle, prior to contact by an edge of the guide plate aperture. Further movement of the steering handle in
Doklovic Brian C.
Keane James C.
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