Motor vehicles – Steering by driving – Combined with manual steering
Patent
1994-06-20
1995-11-28
Culbreth, Eric D.
Motor vehicles
Steering by driving
Combined with manual steering
180 655, 180242, 36442405, B62D 1104
Patent
active
054699282
DESCRIPTION:
BRIEF SUMMARY
1. Field of the Invention
The invention relates to non-trackbound or non-railborne vehicles with at least two pairs of wheels, generally, and more particularly to vehicles in which the left and right wheel of at least one of the pairs can be adjusted by a steering wheel and in which each wheel of at least one of the pairs is individually driven by a corresponding drive.
2. Description of the Prior Art
Assisted steering (servo-steering) is commonly used in non-railborne vehicles, i.e. passenger cars, trucks, busses and the like, which are generally driven by means of internal combustion engines. A hydraulic pump driven by the internal combustion engine serves as an energy source providing the power required for boosting the force applied to the steered wheels by the operator of the vehicle via the steering wheel. In addition to the hydraulic pump, control valves, steering valves, steering cylinders, an oil tank and line connections are required. Accordingly, assisted steering systems were formerly very costly.
More recently, new drive concepts for vehicles have been developed which diverge sharply from the internal combustion engine drives commonly known for decades. For example, non-railborne vehicles with battery-powered electric motor drives have been suggested. There have also been suggestions for hybrid drives in which an internal combustion engine/generator unit is provided at the vehicle and the electrical power supplied by the generator is fed via power electronics to electric motors which are rigidly coupled with the driven wheels. Such drives have certain advantages, since they allow differentiated steering as pure internal combustion engine drives.
A substantial feature of vehicles with electric motors driving at least two wheels consists in that the driven wheels each have their own electric motors.
A key element in the gradual conversion of motor vehicles driven only by internal combustion engines to electric vehicles or vehicles with a hybrid drive consists in adapting the handling of these new vehicles to the handling of vehicles driven by internal combustion engines. In terms of the vehicle steering system, this would mean providing assisted steering, since substantial resistance must be overcome particularly in heavy vehicles with rubber tires. Conventional techniques for assisted steering are provided for this purpose, i.e., in the case of electrically driven hydraulic motors, conventional servo-steering could be applied. The steering could also be effected by means of electric motors, i.e. an electric motor is actuated depending on the steering wheel position in order to move the steering linkage. However, this type of assisted steering is also quite expensive.
A vehicle drive is known from JP 62-181 918 A in which a mechanical transmission controlled via hydraulic clutches is provided for the rear axle of the vehicle, by means of which the distribution of torque between the two driving wheels on the left and right sides of the rear axle can be influenced depending on the speed of the vehicle and the angle and actuating speed of the steering wheel in such a way that the driving wheel on the outside of the turn receives greater torque than the inner driving wheel. The required cost for this construction is extremely high. More detailed information regarding the applied regulating strategy in the torque adjustment is not provided in this prior art.
When making a turn, the speed of the outer wheel is naturally greater than that of the inner wheel. The so called single-track model serves as a basis for calculation, whereby with reference to the accompanying FIG. 1 with a reference turning radius R, the "Ackermann" steering angle .delta..sub.A depending on the steering wheel angle is calculated as follows: ##EQU1## with
It will be seen that the percentage wheel speed differential between the outer and inner wheels of the vehicle can be determined by this single-track model allowing for the track width of the vehicle.
Theoretically, a linear relationship is given when the percentage wheel speed
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patent: 5323866 (1994-06-01), Simard et al.
Adler Uwe
Drexl Hans-Jurgen
Lutz Dieter
Nagler Franz
Ochs Martin
Culbreth Eric D.
Hurley Kevin
Mannesmann Aktiengesellschaft
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