Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to an anti-lock device
for vehicle brakes in whi h a w~e7 ~enerator produces signal
pulses whose frequency is proporti~nal to ~he wheel sp~ed,
more particularly, to such a device which produces a wheel speed
signal which more closely corresponds to the actual wheel speed
at the end of a measurement time interval.
~ t has been known to protect vehicle brake systems
against locking or slipping with a device which senses the
rotary speed of at least one wheel and utilizes an evaluation
circuit which controls the actuation of the vehicle brakes in
response to the sens~ wheel speedsignals. The wheel speed is
generally sensed by a generator coupled to the wheel and the
frequency of the output signals of the generator is proportional
to the wheel speed~ There are generally further provided a digital
counter connected to the generator and a control circuit
connected to the control input of the counter which alternately,
during predetermined measurement intervals, sets the counter in
readiness to count, resets the counter and/or stops the counter
at the end of a time interval. A memory is provided to which
i9 introduced the count of the counter at those times predetermined
by the control circuit.
Such a device fox a vehicle brake system is known in general
and usua]ly uses a pulse generator with rectangular output signals.
If a generator is used with sine-output signals, a pulse shaper
stage (sine/rectangular converter) is also connected with the
generator so as to produce rectangular siynals. A significant
disadvantage of such vehicle brake systems is that the value
obtained at the end of a measurement time interval is only correct
when the wheel speed of the wheel has not changed and has remained
constant during the time interval of measurement. In those
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situations where the wheel speed varies during the time
interval the measuxed value obtai~ed represents only an
avera~e ~ the wheel speed during the measurement interval.
It is pre~erred and it is most advantageous if the
vehicle brake system could be protected against locking with
respect to the actual wheel speed of the vehicle and not some
value of wheel speed which is lagging behind ~he actual wheel
speed, particularly when there are relatively rapid variations
in wheel speed such as would occur during a control cycle involving
ei~her acceleration or deceleration of the vehicle.
It is therefore the principal object of the present
invention to provide a novel and improved anti-lock device for
vehicle brakes of the type as generally disclosed herein.
It is another objec~ of the present invention to provide
such an anti lock device for vehicle brakes wherein the measured
value of the wheel speed more closely corresponds to the actual
wheel speed occurring at the end of a measurement time interval~
It is a further object of the present invention to provide
a device for preventing locking in a vehicle brake system
wherein the wheel speed value used for actuating the d~vice is
based upon the wheel speed counts for two successive time intervals,
According to one aspect of the present invention there is
provided an anti-lock device for vehicle brakes wherein means
connected to a vehicle wheel generates an output signal indicative
of the wheel speed. This output signal is transmitted to a
digital counter which is also connected to a control circuit for
setting the c~unter to count during a predetermined time interval,
locking the counter after the time interval and xesetting the
counter for a further time interval. A irst memory connected
to the counter ~ores the count ~rom the countex of the immediate
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preceding time in~erval and a second memory connected to the
contro] circuit and to either ~he ~ounter o~ first memory stores
the COUll't of the counter of the next preceding time interval.
An evaluating circuit connected to both first and second memories
then produces a wheel speed value based upon the two stored
wheel speed counts of the immedia~e preceding and next preceding
time intervals.
The anti-lock device for the vehicle brakes thus is actuated
by corrected wheel speed value obtained by extrapolation of the
measured wheel speed values of the immediate and next preceding
time intervals. This extrapolation may be linear or quadratic.
Other objects and advantages of the present invention will
be apparent upon reference to the accompanying description
when taken in conjunction with the following drawings, which are
exemplary, wherein;
Fig. 1 is a block circuit diagram of the anti-lock device
of the present invention;
Fig. 2 is a graph showing changes of wheel speed with
respect to measurement time intervals in accordance with the
anti-lock device of the present invention;
Fig. 3 is a block diagram of a modification of Fig. 1
and showing wiring connections between the several components of
the anti-lock device; and
Fig. 4 is a chart showing a single control pulse with
respect to time~
Proceeding next to the drawings wherein like reference
symbols indicate the same parts throughout the various views
a specific embodiment and modi~i~ation~ of the present invention
will be described in detail.
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As may be seen in Fig~ 1, a pulse generator 1 which
is coupled to a wheel ~f the vehicle so as to be drive~ thereby
produces a pulse-form output signal the frequency of which is
proportional to the rotary speed of the wheel. The pulse generator
could be connected together with a pulse shaper stage, if nec-
essary, in order to produce a rectangular signal.
The output of the pulse generator 1 is connected to one
input of a gate circuit 2 which i5 preferably an AN~ ga~e ~he
output of which is supplied to the counter input of a digital
counter 3. A control circuit 4 is connected to a second input
of the gate circuit 2 and also to a control input of the counter
3. The output of the counter 3 is connected to an input of a
first memory 5. The output of the memory 5 is connected to the
input of a second memory 6.
The outputs of memory 5 are also connected to an input of
a factor multiplier 7 and to the input of an adder 8. The other
input of the actor multiplier 7 is connected to a factor source
7'~ while the output of the factor multiplier 7 is connected to
the other input of the adder B.
The outputs of the second memory 6 are connected to
an input of a further factor multiplier 9 which has a second input
connected to a further factor source 9'.
The output of the adder B is connected to one input of
a subtrac~or 10. Another input of the subtractor 10 is connected
to the output of the factor multiplier 9.
The output of the subtractor 10 is a value corresponding
to the rotary speed of the wheel at the end of the last or immed-
iate preceding time measurement interval~ This wheel speed value
is a corrected value of the wheel speed of the immediate preceding
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tirne interval~ ~efer~nce to Fig. 2 will illustrate that the
value of the wheel speed ~or ~he immediate preceding time
measuremen~ interval T i5 N~Tn) which is the average of the
wheel speed during ~he time interva~, assuming a linear variation
în speed. The wheel speed value of the next immedia~e preceding
time interval Tn lis shown as N(tn 1) The value of the outp~t
of the subtractor 10 is 1~5 x N(tn~ ~-0r5. x N(tn 1) And this
value corresponds with the value of the wheel speed at the end
of the last or immediate preceding time interval T~. Again,
as illustrated in Fig. 2, this corrected value is based upon
the assumption of a linear change of wheel speed as illustrated
in Fig. 2.
This corrected wheel speed value is ~hen introduced into
an evaluation circuit which detects from the wheel speed signals
any locking or slipping of thP wheel. The correct signals are
then supplied from an evaluation circuit to the brakes to overcome
any locking of the wheel as measured by the circuit shown in
Fig. 1.
The circui~ in Fig. 3 corresponds basically to the circuit
of Fig. 1 and the components in Fig. 3 corresponding to components
Fig. 1 have the same reference symbols. However, in Fig. 3,
the factor multipliers have been replaced by fixed wire connections
between the memories 5 or 6 and the adder 8 or the sub~ractor lOo
If the outputs of the memories 5 and 6 are binary coded,
a multiplication by the factor 0.5 is simply obtained by shifting
~he individual binary position one place to the right, i~e.,
in the direction of smaller values. This thus means that the
inputs of the adder 8 are x~spectiYely connected in the correct
alloca~i~ns to ~h~ ou~pu~s Df th~ memory 50 For example~
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the bit p~sition of the mem~ry 5 w~h the value ~ is connected
to the corresponding bit positi~n 2 ~f the adder 8. However,
the other inputs of ~he adder 8 are connected to the output of
the memory 5 such that the output with the value 2n of the
memory is connected to the input with the va]ue 2n 1 of the
adder. The connections are continued in this manner until the
output with the value 21 is connected to the input with the
value 2. The input of the adder with the value 2n hence leads
to the value 0.
In a similar manner, the outputs of the memory 6 are
connected, shifted by one bit position, to the inputs of the
subtractor 10. In addition, it can also be provided that the
outputs of the subtractor 10 are connected to inputs of a further
memory 11.
The time sequence of the individual control pulses is
illustrated in Fig. 4. The control pulses A represent the gate
pulses while the gate circuit 2 passes the pulses from the pulse
generator 1. At the end of each individual pulse A there appears
a short pulse B which controls the memory 6 such that the memory
6 accepts the memory content of the memory 5. After the disappear-
ance of the respective pulses N, there also appears a short pulse
C which controls the memory 5 such that it accepts the count
value of the counter 3. After disappearance of the respective
pulse C, there then appears a reset pulse D which resets the
counter 3 to 0. Upon this resetting step, the next gate control
pulse A appears and a new measurement cycle commences.
It is therefore apparent that the circuit as described -
herein will always supply the exact value of the ~PM or wheel
speed at the end of the respective l~st or immediately preceding
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measurem~nt interv~l both wi~h incr~asing and decreasing
wheel speeds ~en the wheel speed varies linearly during a time
measurement interval.
It is to be understood that instead of a linear extra-
polation as disclosed and described above, a quadratic or
cubic extrapolation can also be use~. It is also possible to
use an exponential ~r hyperbolic extrapolation when it is raason-
ably expected ~hat the wheel speeds will vary according to such
a function and when a much higher deyree of measurement accuracy
is desired. The logic circuit of components 7 - 10 must then
be constructed such that this circuit determines the corresponding
function from the two counter values.
The accuracy of wheel speed measurement can be even further
increased by providing a third memory which is connected after ~he
memory 6 and which then contains the count value of the counter
of the second next immediate preceding time interval tTn 2).
Thus it can be seen that the present invention has provided
an improved anti-lock device for vehicle brakes wherein the
wheel speed value is based upon the actual wheel speed at the
2~ end of a time measurement interval. This value is based upon a
linear variation o~ speed during time measurement intervals, but
can also be based on the variation of the wheel speed based upon
other functions such as hyperbolic or quadratic. The signals
thus transmitted by the evaluating circult are based upon wheel
speed of the immediately preceding time measurement interval
and not upon a lagging wheel speed value, such a~ for exampl~,
the average wheel speed of a time measurement interval.
It will be understood that this invention is sueceptible
to modification in order ~o a~ap~ i to different usages and
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conditions, and acco~dingly, it i5 designç~d to comprehend such
3nodifications within this inventiorl as they fall within the
scope of the apended claims.
