192 clutches and power-stop control – Vortex-flow drive and clutch – With brake
Patent
1990-02-28
1992-07-14
Bonck, Rodney H.
192 clutches and power-stop control
Vortex-flow drive and clutch
With brake
192 123, 192 133, 192 13A, B60T 712, B60K 4120
Patent
active
051294966
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a brake control system for automatically applying a braking pressure when the vehicle speed drops below a very low speed value and the brake pedal is operated, and maintaining that pressure until the vehicle is driven off again.
U.S. Pat. No. 4,684,177 discloses an automatic locking brake during the use of which a valve is activated when operating the brake and the clutch pedal. This valve permits maintaining the applied brake pressure even after the release of the brake. When the clutch pedal is released followed by an immediate pressing of gas pedal, the pressure is reduced. The use of a speed signal ensures that there is no pressure increase while the vehicle is in motion.
From German OS 35 12 716 it is known to gradually increase the brake pressure in case the vehicle speed is zero and the brake pedal is pressed down.
SUMMARY OF THE INVENTION
According to the invention, a low reference speed value v.sub.x at which the brakes are automatically applied is variable and dependent on the deceleration in such a way that the speed value v.sub.x increases as the deceleration increases. On the one hand, the transition from braking by means of the regular brake to employing the locking brake must not be noticed by the operator of the vehicle; on the other hand, the locking brake must take effect immediately after the vehicle has been brought to a complete stop. It is an essential improvement to include the vehicle deceleration when determining the start of the brake pressure build-up and when calculating the pressure build-up rate.
Considering the throttle position (TP) for prompting a sequence of pressure decrease pulses when releasing the locking brake does not always result in satisfactory transition characteristics. A substantial improvement can be achieved by calculating the instantaneous drive capacity from a characteristics field .tau..sub.d =f (TP, RPM) and additionally allowing for engine dynamics, e.g. by means of a first-order time delay.
The pulsing down is then not prompted by a prescribed position of the throttle but by a prescribed threshold .tau..sub.x of driving torques or engine loads. Moreover, high engine torques cause a more rapid pressure decrease.
A pressure decrease is triggered if r.sub.d >R.sub.x and the pauses of the decrease pulse sequence is measured, for example, according to: ##EQU1## In vehicles with a manual shift transmission, the beginning and the course of the pressure release often occur incorrectly. This can be improved in two ways:
1. evaluating the distance covered by the clutch pedal including a learning condition for a point of action; or, combined with ASR, the
2. evaluating the engine speed and the position of the throttle.
In the latter case, the engine speed is calculated from the throttle position by means of a simple engine model and prescribed parameters for the load-free engine. If the engine speed (RPM) measured is substantially lower or shows a strongly decreasing tendency, this is a sign of a clutch engaging (additional engine load). Hence a pressure decrease is prompted at
In an ASR and ABS a so-called longitudinal accelerometer or a combination of two sensors (each having an angle of inclination of 45%) is used to determine the road gradient. The pressure required for locking a vehicle is approximately proportional to the road gradient. Calculating the pressure to be supplied by making use of the road gradient is hence efficient and essential for a best-possible pressure decrease when departing. This can be carried out, for example, by determining the number of pressure build-up pulses. (Number of pressure build-up pulses=K5 gradient).
The presently used wheel speed sensors operate only after a certain minimum speed. In case the vehicle starts moving although the locking brake is applied, this can first be detected by means of the acceleration signal. If the vehicle acceleration signal changes when the operator releases the brake, for example, (BLS decrease), it is advantageous to increase the press
REFERENCES:
patent: 4131325 (1978-12-01), Bayliss
patent: 4446950 (1984-05-01), Wise et al.
patent: 4708406 (1987-11-01), Takagi et al.
patent: 4717207 (1988-01-01), Kubota et al.
patent: 4802562 (1989-02-01), Kuroyanagi et al.
Jonner Wolf-Dieter
Sigl Alfred
Bonck Rodney H.
Robert & Bosch GmbH
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