Vehicle brake controlling device for anti-skid control of vehicle wheels

A vehicle controlling device wherein an output signal proportional to vehicle velocity obtained from a vehicle velocity detector and an output signal proportional to wheel velocity obtained from a wheel velocity detector are to be compared by a comparator and the slip state of the wheel is to be detected from the result of the comparison, thereby to control a brake mechanism, characterized in that an adder circuit is provided which adds an output signal proportional to a predetermined wheel velocity at a low vehicle running speed to the output signal obtained from the wheel velocity detector and that the output signal of the adder circuit and the output signal from the vehicle velocity detector are compared by the comparator to ensure accurate brake control at all vehicle speeds.

BACKGROUND OF THE INVENTION 
This invention relates to automatic brake controlling devices for a 
vehicle, such as an automobile. 
In automobile automatic brake control systems, there has hitherto been 
provided an anti-skid controller in which the slip condition of a wheel is 
detected by comparing output signals proportional to vehicle velocity and 
wheel velocity obtained from a vehicle velocity detector and a wheel 
velocity detector, and the vehicle braking system is controlled on the 
basis of the detection, whereby the wheel is prevented from being locked 
and inducing a sideslip or a so-called skid by temporarily releasing the 
brakes. 
In such a controller, however, the wheel velocity signal of the wheel 
velocity detector can reach such an extremely low level that it cannot be 
detected or it can become ineffective as the wheel begins to stop or 
during low-speed running of the automobile. In such a case, 
notwithstanding the fact that the wheel is not actually locked and 
slipping with respect to the road surface, it is judged incorrectly to be 
slipping, and the controller operates so as to slacken the brake effect of 
the braking system. This leads to the disadvantage that the brake does not 
operate as it should even though it is applied. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a vehicle brake controlling 
device which has solved the problem occurring when the brake system 
becomes inactive during stopping or low-speed running of the vehicle. 
In order to accomplish this object, the present invention adds a fixed 
signal to the wheel velocity signal and makes a comparison between the 
signal representing the result of the addition and the vehicle velocity 
signal, thereby to more accurately control the vehicle braking system 
under all conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a prior art anti-skid controller for use in an automobile 
brake control system. Trains of pulses at frequencies f.sub.v and f.sub.w 
proportional to the vehicle velocity and the wheel velocity are produced 
by a vehicle velocity detector and a wheel velocity detector and are 
entered into counters 1 and 2 from input terminals 11 and 12, 
respectively. The counters 1 and 2 count the pulses at the frequencies 
f.sub.v and f.sub.w and provide outputs when the count values therein have 
reached predetermined values, respectively. The predetermined count value 
of the counter 1 is set to be greater than that of the counter 2 by a 
selected amount. 
The vehicle velocity detector, for example, may comprise a speed meter 
employing the Doppler system of operation and the wheel velocity detector 
may comprise a tachometer attached to a wheel axis. However, the invention 
is not restricted to such devices, and any conventional device capable of 
providing signals proportional to the vehicle velocity or wheel velocity 
may be employed. 
The respective outputs of the counters 1 and 2 are applied to a reset 
terminal R and a set terminal S of a set-reset flip-flop 3, to reset and 
set the flip-flop 3, and they are applied to clear terminals CL of the 
counters 1 and 2 through an OR circuit 5, to clear the counters 1 and 2. A 
set signal from an output terminal Q of the flip-flop 3 is impressed on an 
AND circuit 4 together with a brake signal from an input terminal 13. An 
output of the AND circuit 4 is derived from an output terminal 14 as an 
output B applied to the brake system which gives rise to a braking action. 
With such a construction, the frequencies in the case where the automobile 
is running without any slip (hereinbelow, the running is termed "normal 
transit") are set to be f.sub.v = f.sub.w. Under such condition, the 
counter 2 provides an output prior to counter 1, and an output signal "1" 
of the counter 2 is applied to the set terminal S of the flip-flop 3 to 
set the flip-flop. Simultaneously therewith, the output signal is applied 
to the clear terminals CL of both the counters 1 and 2 through the OR 
circuit 5 and clears them. 
On the other hand, the set output signal "1" from the output terminal Q of 
the flip-flop 3 is applied to the AND circuit 4. Therefore, when the brake 
signal BS is delivered from the input terminal 13 to the AND circuit 4 
under these conditions, the signal B for causing operation of the brake 
system and initiation of the braking action is provided from the output 
terminal 14. 
In contrast, in the event that the frequency f.sub.w falls below .alpha. 
f.sub.v (where .alpha. is constant dependent upon the predetermined count 
values of both counters and has a value smaller than one) due to the slip 
of a wheel, as during quick braking, the counter 1 produces an output 
before counter 2. The output signal "1" of the counter 1 is applied to the 
reset terminal R of the flip-flop 3 to reset it, and the output signal is 
also applied through the OR circuit 5 to the clear terminals CL of both 
the counters 1 and 2 to clear them. At this time, the output signal of the 
output terminal Q of the flip-flop 3 becomes "0," so that even if the 
brake signal BS is supplied from the input terminal 13 to the AND circuit 
4, the signal B cannot be obtained from the output terminal 14. That is, 
the brake signal BS is blocked at the AND circuit 4, and therefore, the 
brake does not operate. In consequence, the number of revolutions of the 
wheel begins to rise again, and the car can escape from the slip state. 
In the prior art control device, however, the output frequency f.sub.w of 
the wheel velocity detector can reach an undetectable low level or become 
ineffective as the wheel begins to stop or at low speed running. In such a 
case, notwithstanding the fact that the wheel is not actually slipping, 
the output signal "1" of the counter 1 is applied to the reset terminal R 
of the flip-flop 3 and resets it. As a result, there occurs the 
inconvenience that even when the brake is applied by the driver, it is not 
actually operated. 
FIG. 2 illustrates one of the essential portions of the vehicle controlling 
device according to this invention. Numeral 6 is a logical circuit which 
performs an addition of the numbers of pulses of pulse train signals 
applied to input terminals 7 and 8. It is constructed of a circuit which 
provides an output signal "0" (or "1") from an output terminal 9 in the 
case where the logic signals of the input terminals 7 and 8 have the same 
sign and which provides an output signal "1" (or "0") in the case where 
they have the opposite signs. By way of example, an exclusive-OR circuit 
may be employed as the logical circuit 6. 
Accordingly, in the event that the respective input terminals 7 and 8 have 
received, for example, three pulses during a fixed period T, as 
illustrated at (a) and (b) in FIG. 3, six pulses being the sum of the 
input pulses are provided from the output terminal 9, as illustrated at 
(c) in FIG. 3. Thus, an addition of the numbers of pulses is performed. 
In this case, by way of example, a train of pulses at a frequency f.sub.w 
proportional to the wheel velocity as obtained by a wheel velocity 
detector is impressed on the input terminal 8, while a train of pulses at 
a prescribed low frequency is impressed on the input terminal 7. The train 
of pulses obtained from the output terminal 9 is compared with the train 
of pulses at a frequency f.sub.v proportional to the vehicle velocity as 
obtained by the vehicle velocity detector. The braking system of the 
vehicle is controlled on the basis of the result of the comparison. 
FIG. 4 shows an embodiment of this invention in which the logical circuit 
in FIG. 2 is applied to an anti-skid controller. Elements common to the 
prior art have the same symbols as in FIG. 1. In FIG. 4 an exclusive-OR 
circuit 61 is provided which receives at its inputs a pulse train signal 
at a frequency f.sub.w proportional to a wheel velocity as obtained from 
wheel velocity detector 21 at the input terminal 12 and a pulse train 
signal at a fixed frequency f.sub.c obtained from signal generator 22 at 
the input terminal 15 and whose output pulse train is applied to the 
counter 2 as an input thereof. The remaining circuit construction is quite 
the same as the circuit illustrated in FIG. 1. Also shown in FIG. 4, in 
block diagram format, is a vehicle velocity detector 20 which generates 
the vehicle velocity signal f.sub.v applied to terminal 11, a brake signal 
generator 23 which supplies the brake signal BS at terminal 13, and a 
brake system 24 which receives the brake signal B from the output terminal 
14 of the end AND gate 4. As the fixed frequency f.sub.c, there is 
selected a frequency proportional to a wheel velocity at low speed, for 
example, at 5 km/h or so. By setting the frequency f.sub.c at the low 
frequency, there will be little influence on the frequency signal f.sub.c 
on brake control during high speed running. 
In this way, the frequency f.sub.w from the wheel velocity detector and the 
fixed frequency f.sub.c are added by the exclusive-OR circuit 61, and the 
result of the addition is entered into the counter 2. Thus, even in the 
case where the frequency f.sub.w proportional to the wheel velocity is not 
provided or is neglected as the wheel is close to stopping or during low 
speed transit, at least the fixed frequency f.sub.c is entered into the 
counter 2 and the flip-flop 3 maintains its set condition. It is therefore 
possible to establish a state under which the brake operates even at very 
low vehicle speeds. In other words, counters 1 and 2, OR gate 5, and 
flip-flop 3 cooperate to provide an output signal presents whether or not 
the ratio of the output of the exclusive-OR gate 61 to the output of the 
vehicle velocity detector 20 is less than a predetermined value, so as to 
control the brake operation even at low speeds in dependence upon this 
predetermined value. 
The circuit for adding the frequencies f.sub.c and f.sub.w is not 
restricted to the example stated above. In general, an adder circuit for 
alternate signals may be used. 
While in the above description reference has been made to an example in 
which the signals obtained from the vehicle velocity and wheel velocity 
detectors are digital signals, this invention can, of course, be similarly 
applied to a system in which signals are obtained from these detectors. In 
that case, a signal of a fixed output level is employed in place of the 
signal of the fixed frequency f.sub.c. Further, an analog adder is used as 
the adder circuit, and a comparator of a construction capable of comparing 
analog signals is used as the signal comparator.