Motor vehicles – Steering gear – No mechanical connection between steering shaft and steering...
Reexamination Certificate
1999-09-02
2001-08-28
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Steering gear
No mechanical connection between steering shaft and steering...
C180S417000, C180S421000, C701S043000
Reexamination Certificate
active
06279675
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a steering system for non-tracked motor vehicles, having a steering handle, such as a manual steering wheel, operated by the driver, and a steering adjusting drive for the steering adjustment of steerable vehicle wheels. A steering-angle desired-value generator operable by way of the steering handle. A steering-angle actual-value generator is operable via the steerable vehicle wheels. An automatic control system controls the steering adjusting drive as a function of a comparison of the desired and actual values of the steering angle and continuously monitors itself as well as a sensor system interacting with it with respect to a malfunctioning. A mechanical or hydraulic forced coupling is arranged between the steering handle and the steerable vehicle wheels and is opened up or remains open (inoperative normal condition) when the automatic control system operates correctly and is automatically closed when the automatic control system is defective (operative special condition).
Steering systems of this type, which operate according to the “steer-by-wire” concept, are basically known and are developed for future motor vehicles. These systems offer the basic advantage that they are suitable at least with respect to the automatic control system as well as the pertaining sensor system without any constructive changes for many different vehicles. As the result of a corresponding programming, on one hand, virtually any transmission ratio can be implemented between the adjusting stroke of the steering handle and the steering angle change of the steered vehicle wheels. Furthermore, the automatic control system can be connected with additional sensors in order to be able to automatically take into account parameters to be defined, such as cross wind influences, or control deviations with respect thereto.
In order to be able to ensure the required amount of safety in the event of the occurrence of a defect in the automatic control system or in the event of a failure of signals which are to be analyzed by the automatic control system, an operating mode is automatically switched on for an abnormal operation or an emergency operation. In this operating mode, a forced coupling is provided between the steering handle and the steered vehicle wheels so that the steering system operates in principle in the manner of a conventional steering system. The mechanical steering column, which is customary in conventional steering systems, can be replaced, however, by other mechanical systems or by hydraulic systems, particularly hydrostatic systems.
SUMMARY OF THE INVENTION
An object of the present invention is to permit, in a steering system of a steered-by-wire type, extreme steering adjusting forces for the steerable vehicle wheels.
According to the invention, this object has been achieved by providing that the automatic control system analyzes or detects a parameter which is correlated with forces or torques transmitted between the steering adjusting drive and the steerable vehicle wheels. In the event of a high loading of the adjusting drive, the forced coupling operative in an assisting manner is switched for the steering adjusting drive.
The present invention is based on the recognition of the advantages of a steering adjusting drive, which, in the normal operation of the steering system, is solely effective for the steering adjustment of the steerable vehicle wheel, with a limited output which, although is must always be sufficient for implementing typical steering maneuvers, is not sufficient for steering maneuvers with an extreme power requirement. Such a case with an extreme power requirement may occur, for example, when the vehicle reaches or takes up a position in which a steerable vehicle wheel by way of a wheel flank or tire flank is directly adjacent to a step or curbstone or slides along the step or curbstone via the wheel flank or tire flank. If a steering maneuver now becomes necessary in which this wheel is steered against the step or curbstone and is to drive over the step or curbstone in the upward direction, extremely high steering forces are required. Such situations may occur when only little maneuvering space is available for a vehicle parked on the road side directly next to a higher curbstone, because other vehicles are parking closely in front or closely behind the above-mentioned vehicle.
In such extreme situations, the present invention provides that the forced coupling between the steering handle and the steered vehicle wheels becomes operative in parallel to the adjusting drive. The driver can thus assist the adjusting drive by manual force, with the result that total steering forces can be generated which clearly exceed the efficiency of the adjusting drive.
As the result of the corresponding dimensioning of the steering adjusting drive, similar manual forces occur on the steering handle during the above-mentioned extreme steering maneuvers as those occurring in comparable driving situations in conventional power steering systems, which have a continuously effective mechanical drive-through between the manual steering wheel and the steered vehicle wheels and whose servo motor only generates a limited auxiliary force which assists the respective steering maneuver, in addition to the manual force to be applied by the driver.
In operation of the forced coupling which assists the steering adjusting drive, a parameter is analyzed or detected by the automatic control system. This parameter is correlated with forces or torques transmitted between the steering handle and steerable vehicle wheels, whereby the automatic control system controls the steering adjusting drive only in parallel to the steering adjusting forces generated by the steering handle.
Because the automatic control system in addition, as in the normal operation, detects the parameter correlated with the transmitted forces or torques between the steering adjusting drive and the steered vehicle wheels or the parameter correlated with the forces on the steering adjusting drive, the automatic control system therefore always “knows” which total steering forces are effective on the steered vehicle wheels.
Correspondingly, the forced coupling can be opened up again as soon as the sum of the forces and torques transmitted between the steering handle and the steerable vehicle wheels as well as the forces and torques transmitted between the adjusting drive and the steered vehicle wheels falls below a definable or defined threshold value which is (at least slightly) below the maximal value of the forces or torques which can be generated by the adjusting drive.
With a view to the operational reliability, it has been recognized now as expedient for the automatic control system to record the relative positions of the steering-angle actual-value generator and of the steering-angle desired-value generator during the closing of the forced coupling. As a result, the automatic control system “knows”, taking into account the steering kinematics, while the forced coupling is switched on of mutually corresponding signals of the desired-value generator and the actual-value generator. In this manner, it then becomes possible to automatically control the steering adjusting drive as a function of the amount and the direction of the deviation of the actual-value generator signal with respect to the signal of the actual-value generator which corresponds to the respective desired-value generator signal. Because of the unavoidable or constructively intended elasticities in the forced coupling, a deviation will occur between the signals of the actual-value generator, on one hand, and the above-mentioned corresponding values, on the other hand, which is analogous to the forces transmitted between the steering handle and the steered vehicle wheels.
REFERENCES:
patent: 5097917 (1992-03-01), Serizawa et al.
patent: 5862878 (1999-01-01), Bohner et al.
patent: 5893427 (1999-04-01), Bohner et al.
patent: 6047788 (1999-01-01), Bohner et al.
patent: 6059068 (2000-05-01), Kato et al.
paten
Bohner Hubert
Moser Martin
Schneckenburger Reinhold
Crowell & Moring LLP
Daimler-Chrysler AG
DePumpo Daniel G.
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