Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1999-02-17
2001-06-19
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C180S446000
Reexamination Certificate
active
06247550
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a control device for a power steering gear for motor vehicles with an adjusting element for changing the steering characteristics, which can be controlled as a function of the road speed of the motor vehicle.
BACKGROUND OF THE INVENTION
A control device of this type is known from European Patent Publication EP 0 141 626 B1. With this control device, a defined electrical supply current, which is controlled as a function of the road speed, is provided to a solenoid of a proportional valve for changing the steering characteristics. In order to keep the power losses in the control device as low as possible, use is made of pulse width modulation, whose cycles are controlled by a generator. By means of their vibration effects, the voltage pulses generated in the process simultaneously can minimize the magnetic and mechanical friction losses in the magnetic circuit, if the cycle frequency has been selected to be correspondingly low. This means that the frictional losses in the magnetic cycle are very low when the cycle frequency is as low as possible. Therefore the selected frequency always must be a compromise and cannot offer an optimum solution for a requirement for less friction and low noise. In addition, delays occur in the control circuit between the detection of the road speed and the reaction which the driver notices at the steering wheel, which provide an inharmonious driving sense.
OBJECTS AND SUMMARY OF THE INVENTION
It is the object of the invention to provide a control device for a power steering gear which avoids the above mentioned disadvantages. In addition, it is intended to provide the driver with assured steering of his vehicle and with a harmonious driving sense, even during acceleration and braking of the vehicle.
This object is attained by means of the control device described herein below. The attainment takes place in that, in contrast to the known control device, not only the road speed, but also the chronological change of the road speed is taken into consideration when controlling the adjusting element.
Practical and advantageous embodiments of the invention are also recited herein below. Signals being generated on the basis of the road speed and the chronological changes of the road speed, i.e. from the acceleration, or respectively braking of the vehicle, are evaluated in a device for signal processing. A common signal for controlling the adjusting element is passed on from this device for signal processing. In the course of an acceleration process, a signal corresponding to a higher road speed is being generated, while in the course of a braking process a signal corresponding to a lower road speed is being generated. For example, when turning a tight corner, adjusting of the steering is prevented by means of this invention so that the driver is not surprised by a possibly sudden change of the steering characteristics.
A differentiation element is arranged in the control device parallel with an element for detecting the road speed. Both elements pass on their signals to the device for signal processing. Different possibilities for signal processing exist. For example, the device for signal processing can contain a characteristic diagram with different characteristic lines. Several characteristic line tables and acceleration tables can be stored in the characteristic diagram. Alternatively to this, the device for signal processing can process the signals from the differentiation element mathematically or analogously.
For example, the adjusting element can operate mechanically or electromechanically. However, it is advantageous if the adjusting element is the solenoid of a proportional valve, which can be electromagnetically operated, and if the supply current providing the proportional valve is controlled by a power transistor as a function of the road speed of the vehicle and of the chronological change of the road speed.
The invention will be explained in greater detail below by means of two exemplary embodiments represented in the drawings.
REFERENCES:
patent: 4522279 (1985-06-01), Kanazawa
patent: 5299650 (1994-04-01), Wada et al.
patent: 5339243 (1994-08-01), Matsuoka et al.
patent: 5521820 (1996-05-01), Wakamatsu et al.
patent: 5913913 (1999-06-01), Okanoue et al.
patent: 5999870 (1999-12-01), Tatsumi et al.
Cerny Walter
Lang Armin
Schule Jurgen
Johnson Brian L.
Larson & Taylor PLC
Winner Tony
ZF Friedrichshafen AG
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