Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-06-12
1993-05-25
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303103, 303105, 303107, 188181A, B60T 832
Patent
active
052133982
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an anti-locking control system for preventing locking of the wheels of a vehicle during braking. WO 88/06544, to which U.S. Ser. No. 392,932 corresponds, described a system having wheel speed sensors which generate signals corresponding to the speeds of the respective wheels, an evaluation circuit which processes these signals into brake pressure control signals, and brake pressure control devices to which the control signals are fed to prevent locking. There, the vehicle deceleration is ascertained from the slope of an auxiliary reference. During a rapid drop of wheel speeds, the ascertained slope determines the progression of the reference signal needed to determine slip.
SUMMARY OF THE INVENTION
The invention aims at preventing too sensitive a control during downhill travel by using ABS control. This is achieved if the ascertained vehicle deceleration is used to vary the sensitivity of the control and to make the the control less sensitive as the vehicle deceleration increases. On high .mu., sensitive response of the controller is not required, and greater slip values and/or wheel deceleration can be permitted. In contrast, the control has to be very sensitive at low .mu.. In downhill travel, part of the frictional connection of tire/roadway is used to compensate the descending force. The vehicle deceleration during downhill drive and otherwise equal conditions is therefore smaller than with the corresponding journey on a level plane. The vehicle deceleration which is reduced due to the downhill travel would make the control very sensitive, but this is not desirable, in particular when there is snow cover; large slip values are therefore of advantage.
The sensitivity can be changed by altering the slip and/or deceleration thresholds or by altering the control variables themselves. The invention can, however, also be applied where a sum is formed of various control variables and then compared with thresholds. Here, it is possible to vary individual components, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of a first embodiment
FIG. 2 shows a block diagram of a second embodiment
FIG. 3 shows an embodiment of an identification circuit
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, a wheel speed sensor is designated 1. The wheel speed signal V is fed to a slip generator 2, which will also be fed with the control variable V.sub.Ref, which is formed, for example, in accordance with WO 88/06544. The slip value L is fed via a stage 3, on the one hand, to a multiplier 4 which forms the expression b.multidot.L, and on the other hand, to an integrator 5, which forms the expression c.intg.L dt.
The wheel speed V is differentiated in a differentiator 6; the expression a.multidot.V is then formed in a multiplier 7.
The three above mentioned expressions are then added in an adding stage 8. Block 9 which is arranged thereafter, varies the sum itself as the slope value of an auxiliary reference V.sub.H. With an increasing absolute deceleration, the above sum value must be made smaller if the sensitivity is to be reduced as the deceleration increases. In a threshold stage 10, the variable sum value S is compared with a specified threshold. When the threshold is exceeded, a 3/3 solenoid is moved into its pressure reducing position.
For example, if the identification circuit of FIG. 3 recognizes that a downhill journey takes place, it emits a signal which is fed to block 3. While block 3 usually leaves a supplied signal L uninfluenced, it now reduces the slip value L by a specified value. The two expressions formed in blocks and 5 are thus made smaller. The threshold of the threshold stage 10 is thus reached later, i.e. the controller was made insensitive.
In the embodiment of FIG. 2, the blocks 21-30 correspond to the blocks 1-10 respectively. Here again, the sum If the sum exceeds the threshold value of block 30, then inlet and outlet valve 31 and 32 are driven and pressure is reduced. In downhill travel, the express
REFERENCES:
patent: 4336592 (1982-06-01), Beck
patent: 4672547 (1987-06-01), Masaki et al.
patent: 4712839 (1987-12-01), Brearley et al.
patent: 4763262 (1988-08-01), Leiber
patent: 4852950 (1989-08-01), Murakami
Butler Douglas C.
Robert & Bosch GmbH
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