Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1998-10-05
2001-11-20
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C192S048900, C310S105000, C074S3880PS, C074S664000
Reexamination Certificate
active
06318496
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a steering booster system for a motor vehicle, and more particularly, to a system in which an electronic control unit senses, via force or torque sensors, the amount and direction of forces and torques applied by a driver to a manual steering wheel and correspondingly controls, via a transmission arrangement, the steering-force-assisting connection of an electric motor into a steering gear line coupling the manual steering wheel and the steered vehicle wheels. The transmission arrangement has an electrically switchable clutch for each steering direction (left or right) are arranged such that, in the event of the same rotation direction at the input of the transmission arrangement assigned to the electric motor, they cause a different rotation direction at the output of the transmission arrangement assigned to the steering gear line. The electronic control system controls the amount of the steering force assistance by way of the slip of the respective clutch and/or by way of the torque of the electric motor.
In a known steering booster system, which normally is also called a power steering system, the manual steering force exercised by the driver on the manual steering wheel is detected by corresponding sensors and is analyzed in an electronic control unit. As a function of the manual force applied by the driver, the control unit will then determine the required steering force assistance and correspondingly control the electric motor of this power steering system.
SUMMARY OF THE INVENTION
The present invention addresses and solves the problem of providing a particularly advantageous embodiment for such a steering booster system at lower manufacturing expenditures while maintaining good control characteristics.
According to the present invention, this problem has been solved by a steering booster system in which a transmission system contains a worm drive associated with two electrically switchable or controllable clutches.
The present invention is based on the general recognition of the desirability causing the force transmission between the electric motor used as the power drive and the steering gear line to be boosted by the power drive, by the two electrically switchable or controllable clutches. The clutches are arranged with respect to a transmission arrangement between the electric motor and the steering gear line such that, while the rotation direction of the electric motor remains the same, by way of one clutch, a steering force boosting can be caused to the left and, by way of the other clutch, a steering force boosting can be caused to the right. In order to obtain a defined amount of steering force boosting, the control unit controls the slip existing between the clutch input and the clutch output and/or the torque applied by the electric motor. This approach permits the apportioning of the steering force boosting to be correlated particularly precisely with the manual steering force applied by the driver and can be adjusted particularly precisely.
Furthermore, the steering booster system according to the present invention permits the adjustment of different dependencies between the manual steering force applied by the driver and the steering booster force applied by the electric motor by way of the respective clutch and the transmission arrangement. As a result, the characteristic curve of the steering booster system can be individually adapted to the respective vehicle and/or to the requirements of the respective driver. For example, the power steering for a heavy sedan can be preadjusted to be particularly smooth and the power steering for a vehicle with sporty ambitions can be preadjusted to be comparatively stiff. In addition, the steering force boosting can be made dependent on the respective driving situation, particularly on the driving speed, so that, for example, for parking maneuvers, a particularly high steering force boosting is available and, when driving on a turnpike, a comparatively smaller steering force boosting is available. In addition, the steering booster system according to the present invention can be constructed such that it is simultaneously used as a steering damper system, in which case the extent of the damping can be preset because of the electronic control.
A particularly advantageous embodiment of the steering booster system according to the present invention is characterized in that a rotor of the electric motor is non-rotatably connected with a first gear wheel which is in an operative engagement with a second gear wheel. The first and the second gear wheel each interact by way of one of the clutches with one shaft respectively, which each carry a worm pinion, which are in operative engagement with the worm gear of the worm drive coupled with a steering gear line. The inventive measures have the result that, during the clutch operations, only very low moments of inertia must be overcome so that the used clutches may have relatively small dimensions. In addition, the steering booster system can respond rapidly and operate with low wear.
In another relatively advantageous embodiment of the steering booster system according to the invention, eddy current clutches can be used as clutches. Such a clutch has no physical connection between the clutch input and the clutch output because the force transmission takes place by way of electromagnetic forces. As a result, such a clutch causes no mechanical friction and therefore no wear. In addition, such a clutch operates very smoothly because, on a regular basis, no vibrations can be transmitted. Other electrically shifted clutches which are suitable for use in the steering booster system according to the invention may, for example, be induction couplings or synchronous couplings, magnetic coil couplings and multiple disk clutches.
Corresponding to an expedient further aspect of the steering booster system according to the present invention, the force sensors or torque sensors can be constructed as eddy current measured value generators. Such an eddy current measured value generator is distinguished by a compact construction and has a low sensitivity to lateral forces. In addition, there is no mechanical wear at the measured value generator. Furthermore, such an eddy current measured value generator is easy to mount and is fully operable in a large temperature range. Other sensors which can be used as force or torque sensors are: inductive path sensors, photodiode sensors, ultrasonic sensors, light wave sensors, inductive angle generators, incremental path measuring systems, digital-absolute path measuring systems, laser interferometers, piezo sensors and wire strain gauges.
Other special embodiments of the steering booster system according to the present invention such that basic differences exist between embodiments with a worm drive and those without a worm drive. While the embodiments with the worm drive have a certain self-locking, which may essentially act as a steering damping, the embodiments without a worm drive have a significantly lower self-locking, whereby, for example, the steering action can be improved in the event of a failure of the power assistance. In addition, the special embodiments differ mainly because of different assembly dimensions so that the variants are selected mainly on the basis of the spatial conditions existing at the respective vehicle.
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Koehler Karl-Hans
Peetz Michael
Pluschke Albrecht
Speidel Gerd
Crowell & Moring LLP
Johnson Brian L.
Lerner Avraham H.
Mercedes-Benz Lenkungen GmbH
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