Measuring and testing – Frictional resistance – coefficient or characteristics
Patent
1992-06-11
1994-07-26
Williams, Hezron E.
Measuring and testing
Frictional resistance, coefficient or characteristics
G01N 1902
Patent
active
053318390
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
From DE-OS 37 05 983, a method is known for equipping a vehicle with an anti-locking brake system (ABS) and an automatic slip control (ASR). This reference, however, makes a method known by which only the coefficient of friction is determined and indicated in order to prompt the driver to adopt a mode of driving behavior which is adapted to the prevailing coefficient of friction. In the reference, the coefficient of friction is only determined during braking or acceleration of the vehicle.
SUMMARY OF THE INVENTION
In the present invention, determination of the current coefficient of friction between the tire and the road is desired at all times, not only during braking or acceleration, in order to be able to give early warning to the driver, for example at low friction values (snow, ice, wetness, etc.). In addition to the warning or in place of it, a visual or audible indication of the approximate coefficient of friction is possible.
If, in a front-wheel drive vehicle, for example, the right-hand front wheel VR is driven and the right-hand rear wheel HR is braked to the same degree, then there will be no change in the overall driving condition: the vehicle will continue to roll at the same speed V, but a tensioning condition will occur between front and rear wheels, and the lateral guiding forces will decrease on these wheels.
If the driving condition of the front wheel VR and the braking condition of the rear wheel HR are further increased (assuming that the output of the engine is sufficient), then the mutual tensioning condition will reach a value at which the front wheel VR will tend to spin and the rear wheel HR will tend to lock. This value A.sub.H has the following relation to the coefficient of road friction .mu.:
If N.sub.H /2 is known (by way of approximation, or to be on the safe side, an unladen vehicle is assumed), then the coefficient of friction can be calculated from the value A.sub.H. The force A.sub.H, in turn, is proportional to the braking force at the brake callipers or the pressure in the brake callipers. If this pressure is now created by being pulsed up from a constant pressure source via solenoid valves, then when taking into account the pressure-volume characteristic curve of the braking system, the sum of the accordingly corrected pulse times of the solenoid valve is a measure for the pressure in the brake callipers, and thus approximately proportional to the coefficient of road friction .mu.. A pressure increase is also possible via a ramp function, e.g. through severely throttled solenoid valves in permanently open position. The word "continuously" is used to indicate that the pressure increase should not be sudden.
The invention is to be mainly applied where ABS/ASR are used, since then only a few additional parts will be needed.
Since, with an increase in engine torque without braking, the second driven wheel would be accelerated and would create a yawing moment around the normal axis of the vehicle, it must be held at the speed prevailing when .mu. was first determined.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be explained on the basis of the drawings.
The figures show the following:
FIG. 1. A well-known ABS/ASR, which has been extended according to an embodiment of the invention.
FIG. 2 A second ABS/ASR, which has also been extended according to a further embodiment of the invention.
FIG. 3 An extended control circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an ABS and ASR for a front-wheel drive vehicle with diagonal braking circuit splitting. In the case of the ASR, for the purpose of brake control, an ABS recirculating pump 1 is set in operation which creates the required brake pressure for the left front wheel VL. This pressure is then kept constant via a then switched changeover valve 2 and a pressure limiter 3. By means of a 3/3 ABS solenoid valve 4, the pressure at the brake of the left front wheel VL is then varied. The system also has a pressure-controlled loading valve 7 and a
REFERENCES:
patent: 3893330 (1975-07-01), Shute et al.
patent: 4212063 (1980-07-01), Hardmark
patent: 4779447 (1988-10-01), Roth
Larkin Daniel S.
Robert & Bosch GmbH
Williams Hezron E.
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