Data processing: measuring – calibrating – or testing – Measurement system – Speed
Reexamination Certificate
1998-11-25
2001-04-24
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Speed
C702S145000
Reexamination Certificate
active
06223135
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method and an apparatus for determining a variable describing vehicle speed.
BACKGROUND INFORMATION
Many methods and apparatuses for determining a variable describing vehicle speed are known from the existing references in many modifications.
German Patent Publication No. 38 33 212 (which corresponds to U.S. Pat. No. 5,272,634).
German Offenlegungsschrift 38 33 212 (U.S. Pat. No. 5,272,634) describes, for a vehicle driven at a single axle and equipped with an antilock braking control system, the creation of a reference variable for the vehicle speed outside the braking pressure control system. This is done essentially by determining an averaged wheel speed on the basis of the speeds of the two driven wheels. If the derivative over time of this averaged wheel speed is greater than zero, the reference variable is defined by the speed of the slower of the two driven wheels. If the derivative over time of this averaged wheel speed is less than zero, the reference variable is then defined by the speed of the faster of the two driven wheels. The slope of the reference variable for the vehicle speed is thus limited to a maximum value.
German Patent Publication No. 40 09 195 (which corresponds to U.S. Pat. No. 5,364,174). German Offenlegungsschrift 40 09 195 (U.S. Pat. No. 5,364,174) describes, for an antilock braking control system used in an all-wheel-drive vehicle, the creation of a reference speed required for traction control. In this context, the reference speed is essentially defined by the speed of the slowest wheel in the case of a speed increase, and by the speed of the third-fastest wheel in the case of a speed decrease. In the transition region between increase and decrease, the value attained by the slowest wheel speed is held constant. For the case where the speed of the third-fastest wheel deviates too greatly from an auxiliary reference speed, the reference speed is maintained concurrently with that auxiliary reference speed. The auxiliary reference speed is created by raising it by the speed of the third-fastest wheel, and decreasing it by the speed of the fastest wheel. It also is held constant in a transition region. If an instability exists due to incipient locking, the slope of the reference speed is defined by the slope of the auxiliary reference speed. If the wheels are slipping, the reference speed is held constant and the rise in the auxiliary reference speed is limited to a physically possible vehicle acceleration. If the rear wheels of the all-wheel-drive vehicle are decoupled from the drive system during braking, a slightly modified approach to creating the reference speed is used. Outside the control system, the reference speed is raised if the speeds of all the wheels are greater than it. If two or three wheels are faster than the reference speed, it is held constant. If none or only one of the wheels is faster than the reference speed, the reference speed is set downward.
Systems for controlling brake slip or traction are known in general form, for example from the book “Bremsanlagen für Kraftfahrzeuge” Braking systems for motor vehicles. Produced by Robert Bosch GmbH Stuttgart (VDI-Verlag, Dusseldorf, 1st edition 1994).
Systems for controlling a variable describing the dynamics of a vehicle are known, for example, from the publication “FDR—die Fahrdynamikregelung von Bosch” FDR—the Bosch vehcile dynamnics control system, which appeared in Automobiltechnische Zeitschrift (ATZ) 96, 1994, Vol. 11, pp. 674-689.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the manner in which a variable describing the speed of a vehicle is determined.
SUMMARY OF THE INVENTION
One advantage of the method and the apparatus according to the present invention as compared to the references described above is that according to the present invention, the variable describing the speed of the vehicle can be determined for a vehicle driven in any fashion, i.e., for a vehicle with front-, all-, or rear-wheel drive, for any operating condition of the vehicle. The manner in which the variable describing vehicle speed is determined is, in this context, independent of whether a brake slip control system or a traction control system, or a system for controlling a variable describing the dynamics of the vehicle, which for example is at a higher level than the brake slip or traction control system, is implemented in the vehicle.
The variable describing the speed of the vehicle will hereinafter be referred to as the reference speed of the vehicle.
The method and apparatus according to the present invention are particularly advantageous for use in all-wheel-drive vehicles. In all-wheel-drive vehicles, it may happen under certain conditions, when drive is being applied, that the value of the reference speed of the vehicle that is determined is too high by comparison with the value of the actual speed of the vehicle. The method and the apparatus according to the present invention ensure that in these situations, the reference speed of the vehicle approaches the actual speed of the vehicle.
In the case of the method according to the present invention implemented in the apparatus according to the present invention, the reference speed of the vehicle is determined as a function of the speed of one selected wheel which is best suited for determination of the reference speed of the vehicle at that time and with the vehicle in that operating state. For selection of the wheel, on the one hand the operating state of the vehicle is determined; on the other hand, plausibility queries are performed as a function of the operating state of the vehicle.
Two plausibility queries have proven particularly advantageous in this connection, both of which are performed on the basis of the speeds of the wheels. On the basis of a first plausibility query, it is ascertained whether the reference speed of the vehicle can be determined as a function of a wheel whose speed is greater than the reference speed of the vehicle. On the basis of this first plausibility query, it is thus ascertained whether the reference speed of the vehicle must be supported upward, i.e., toward higher values. On the basis of a second plausibility query, it is ascertained whether the reference speed of the vehicle can be determined as a function of a wheel whose speed is less than the reference speed of the vehicle. On the basis of this second plausibility query, it is thus ascertained whether the reference speed of the vehicle must be supported downward, i.e., toward lower values.
Advantageously, on the basis of a third plausibility query it is ascertained whether the result of the first or the result of the second plausibility query is analyzed. For this purpose, the third plausibility query has at least two queries.
The first plausibility query has at least two queries. In each of these queries, a variable representing the speed difference of the two wheels is determined on the basis of the speed of two wheels. Advantageously, in a first query a first speed difference, which is constituted on the basis of the lowest and the highest wheel speed, and in a second query a second speed difference, which is determined from the lowest and the second-lowest wheel speed, are respectively compared to a threshold value. By way of these two queries, the synchronization of the speeds of the vehicle's wheels is determined.
Advantageously, the first plausibility query contains a third query. In this third query, a first variable describing the acceleration of the vehicle, which corresponds in particular to the drive shaft acceleration of the vehicle, is compared at least to a second variable describing the acceleration of the vehicle, which corresponds in particular to the longitudinal acceleration of the vehicle. In this context, the second variable can advantageously be corrected with the aid of an offset value which is determined as a function of a variable describing the state of the vehicle.
The second plausibility query, on the basis of which it is ascertained w
Hoff Marc S.
Kenyon & Kenyon
Raymond Edward
Robert & Bosch GmbH
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