DE3925828A1 - Antilock braking system with device for delaying yaw - evaluates difference between braking pressures at wheels on one axle and imposes pulsatile braking where needed - Google Patents

Abstract

The brake valve (1) operated from the brake pedal (2) supplies fluid pressure from a source (3) to left- and right-hand side braking pressure control valves (4a,4b) for respective wheels (5a,5b). Signals from wheel speed sensors and comparators (8a,8b) of actual and desired pressures (9a,9b) are forwarded to a processor (6). A yaw build-up delay device therein prevents excessive braking where the adhesion is poorer, and also provides for synchronised pulsation of the braking pressure at both wheels. ADVANTAGE - Controllability and ride comfort of vehicle enhanced even in conditions of unequal adhesion coeffts. at different wheels.

Description

State of the art

An anti-lock control system with the features of claim 1 is known from the DE-OS 32 09 369 known.

Advantages of the invention

The measure according to the invention, which is effective in the case of μ-split conditions, means that Controllability of the vehicle and the control comfort compared to the well-known Lo solution increased. The measures of the subclaims represent further improvements The brake pressures on the brakes can be measured directly, or you can in a known manner from the control times of the brake pressure control calculate orders (e.g. 3/3 valves).

Figure description

An embodiment of the invention will be explained with reference to the drawing. Show it:

Fig. 1 is a block diagram for explaining the control concept,

Fig. 2 and 3 are diagrams for explaining.

In the block diagram of FIG. 1, a service brake valve, on which the driver's foot force 2 acts and which is connected at 3 to a supply pressure source, is designated by 1 . The pressure controlled by the driver is supplied via brake pressure control valves 4 a and 4 b to the brakes of the wheels 5 a and 5 b. The brake pressure control valves 4 a and 4 b are part of an ABS; they are controlled by an evaluation circuit 6 , which in turn is supplied by the transducers contained in blocks 5 a and 5 b, the speeds of the left wheel and the right wheel corresponding signals V _L and V _R. As a rule, the ABS control the brake pressure control valves 4 a and 4 b different brake pressures P _L and P _R. In a block 7, the difference AP _is formed of these pressures.

In the simplest case, the difference value is .DELTA.P _is a comparator 8 a supplied, which also includes a fixed predetermined comparison value .DELTA.P _{is to} be supplied. If the actual value .DELTA.P _{is should be} above the predetermined reference value .DELTA.P, a signal is given to the evaluation circuit. 6

Fig. 2 shows the speed profiles and the brake pressure profiles of the two wheels when braking under µ-split conditions. It is assumed that the evaluation circuit 6 contains a known yaw moment build-up delay, which on the one hand prevents the build-up of pressure on the high wheel when the pressure is maintained and the pressure is reduced and which on the other hand causes pressure to be pulsed up synchronously at the wheels. In Fig. 2a the speed V _{H of} the high wheel is shown together with the reference speed V _Ref , in Fig. 2b the same for the low wheel V _{Lo of} the wheels. It can be seen (apart from the pressure reduction at t ₁ etc.) that the pressure of the high wheel is kept constant and then pulsed up with the low wheel (at t ₂ ). The pressure reduction at t ₁ is caused by the output signal from the comparator 8 a. If this signal occurs, the pressure difference between P _H and P _{Lo is} too large. When the low wheel comes back in its stable range (slip λ becomes small or no acceleration and deceleration signals) and the output signal of the comparator 8 a is present, a pulse is generated in the evaluation circuit 6 which causes a pressure reduction at the high Wheel generated. For this purpose, the evaluation circuit needs information as to what the high wheel is. This can be determined in block 7 : the wheel with the higher pressure is the high wheel. Whether this is on the left or on the right can be expressed by the sign ΔP _ist .

You can also make the target pressure difference variable and make it dependent on the pressure of the low wheel and thus on that on the low wheel. An electronic 9 a is this the brake pressure signal P _L of the left wheel and the .DELTA.P _is supplied, and this produces therefrom a variable .DELTA.P _intended signal which is used as comparison value for the right, ie, an output signal of the comparator 8a is for Ab-cutting at the right Wheel used. Now a second comparator 8 b and electronics 9 b are necessary, which form the comparison value ΔP _soll on the left using the pressure value P _R. The electronics 9 a and 9 b include an adaptive characteristic curve to _(is pressure of the other wheel, .DELTA.P .DELTA.P and the previous _soll) from the input signals a new value .DELTA.P _{is to} be determined. Fig. 3 shows the resulting pressure curves on the two wheels with µ ratios 0.1 / 0.8 ( Fig. 3a), 0.2 / 0.8 ( Fig. 3b) and 0.3 / 0.8 ( Fig. 3c). The electronics 9 a and 9 b are also fed the ΔP _ist signal. .DELTA.P _{is intended} on each wheel is determined by the amount of .DELTA.P _and by its sign. For small .DELTA.P .DELTA.P _{is to} be kept constant, and prevents a large yaw moment at a jump of homogeneous surface Split. If ΔP _is large, ΔP _{should be increased} on the high wheel and decreased on the low wheel and prevents a large yaw moment when the split changes. The ΔP _ist signals must be transmitted with a sign in order to identify the high or low wheel. Finally, an intervention is possible, which is indicated by an input G. The yaw factor is a vehicle-specific variable to take account of the vehicle geometry and can be varied when installing the electronics.

Claims (6)

1. Anti-lock control system for separate control of the pressure of the wheels little least one axis, containing transducers for determining the wheel speeds, an evaluation circuit for obtaining pressure control signals taking into account the transducer signals and brake pressure control arrangements for the brakes, using a yaw moment build-up delay that is used during the control in the individual control cycles on first locking tendency displayed wheel (low wheel) causes first a constant pressure on the other wheel (high wheel), and then a synchronous increase of the pressure at both wheels, characterized in that the difference (.DELTA.P _is) the pressures on the two wheel brakes are determined and that when a predetermined pressure difference (ΔP setpoint) is exceeded _, the brake pressure on the other wheel is reduced by a control pulse. 2. Anti-lock control system according to claim 1, characterized in that the predetermined target pressure difference AP _{should be} varied depending on the coefficient of friction on the low wheel such that ΔP _{should increase} with the coefficient of friction. 3. Anti-lock control system according to claim 2, characterized in that the Coefficient of friction is estimated via the brake pressure. 4. Anti-skid system according to one of claims 2 and 3, characterized in that the variation of the target pressure difference AP _should only if at least a predetermined pressure difference AP _is is made. 5. Anti-lock control system according to one of claims 1 to 4, characterized in that from the presence of a pressure difference .DELTA.P _{is a} predetermined size, the target pressure difference .DELTA.P _{is increased} on the high wheel and decreased on the low wheel. 6. Anti-lock control system according to one of claims 1 to 5, characterized records that the pressure reduction is carried out when at the end of a rule cycle the low wheel into the stable range (small λ and / or no deceleration signal) arrives.