Note: Descriptions are shown in the official language in which they were submitted.
1046154
The invention relates to a method and system for adjust-
ing braking force and applicable to various types of vehicle
such as for example automobiles and in particular aircraft.
A particular object of the invention is to provide a
braking-force controller of simple design and high reliability
which corrects the amount of braking force as a function of
deceleration and acceleration of the braked vehicle wheels so
that, if because of the adherence of the wheel, the braking
couple resulting from an amount of braking force is less than
10the permitted couple, deceleration of the wheel and that of the
vehicle are lower than the triggering threshold of the control- ~
ler, and the latter does not intervene. r
On the other hand, if the braking couple is greater
than the permitted couple, the wheel starts to skid with consid-
erable deceleration, and the controller then disengages the
brake and the wheel can pick up speed.
This controller must also take into account adherence
conditions during the time when the wheel is starting to turn
again so that, for example, for a considerable deceleration of
-20the wheel followed by slight acceleration, the braking couple is
reapplied only after a lengthy delay; on the other hand of
acceleration is considerable, that is to say if the wheel starts
to turn again rapidly, the braking couple is reapplied after a
very short time.
: - .
10461S4
Accordingly, the present invention provides a system of ~ -
adjusting braking force, based on the deceleration and acceleration
of the wheels of a vehicle during braking which comprises, an
elem~nt which provides a signal which is a function of the speed
of each of the wheels, a differentiating device for receiving this
signal and connected, through a firs~ diode which only lets ;
through deceleration signals, to a threshold device for sending a
control signal to a member controlling the disengagement of the
brake from the corresponding wheel and operating on an all-or-
nothing basis, in the case of excessive skidding, and a memory . . -
- storing the signal from said diode as a function of its amplitude
and duration, the signal derived from said differentiating device ~.
being transmitted, during the acceleration stage of the wheel,
through a second diode which only lets through the acceleration
signals, to a device which permits said memory to discharge beyond
a predetermined acceleration threshold.
An embodiment of the invention will now be described, by
way of a non-limiting example, with reference to the annexed
drawings in which:
Figure 1 is a block diagram of the system for adjusting
braking force in accordance with the invention;
Figure 2 is a graph showing the variation of delay period
as a function of deceleration, for various acceleration values;
and
Figure 3 is a general diagram of a system for adjusting
braking force associated, on the one hand, with an impact safety
device and, on the other hand, with a safety device for
1046154
~ preventing blocking of the braked wheels.
¦ Referring to Figure l, a braked wheel l, provided with a
¦ brake 2, drives a device 3 for electrically measuring its speed.
~ This signal is transmitted to a filter circuit 4, the purpose of
I which is to eliminate extraneous noise. The signal from the
¦ filter circuit 4 is transmitted to a differentiator device 5 which
produces the time derivative of the signal representing the speed
, of the wheel l. This derivative is amplified in an amplifier
¦ having a variable-gain as a function of frequency so as to reduce
¦ 10 the signals from the vibrations of the wheel and from the means
whereby it is secured to the vehicle. The output of this amplifier
is connected, through a diode 7 which only lets through deceler-
ation signals, to a threshold device 8 which sends a control
signal to the coil of an electric valve 13 by way of a power
amplifier 12 when the differentiated signal is greater than the
threshold of the device 8, the signal from the diode 7 is also
sent to a memory 9.
Through a diode 10 which only lets through the acceleratio
signals, the signal from the block 6 controls, during the acceler-
ation stage of the wheel, the discharge of the memory by way ofa constant-current device 11, this taking place beyond an
acceleration threshold value.
From a distributor 14 the electric valve 13 receives the
braking pressure controlled by a braking pedal 15, and transmits
it to the brake 2 when the coil is not energized.
,
... ~ .
1046154 -:
Thus, the vehicle being at a given speed, following a
braking signal controlled by the pedal 15, the pressure delivered
by the distributor 14 is transmitted to the brake 2 since the
electric valve 13 is not energized.
This pressure causes a braking couple which causes
deceleration y in the wheel 1.
If, because of the adherence of the wheel to the
ground, the braking couple is less than the permitted couple,
the deceleration of the wheel corresponds to that of the vehicle ' -
and is less than the triggering threshold of the element 8. Con- ; -
sequently the system does not come into action.
On the other hand, if the braking couple is greater
than the permitted couple, the wneel starts to skid with consid-
erable deceleration.
The signal that enters the threshold device 8 is then
greater than the threshold value, and the coil of the electric
valve 13 is energized by the power amplifier 12. The hydraulic
pressure in the brake decreases, and the wheel is allowed to
pick up speed again. :
The memory 9istores the final deceleration value (which
value is taken at the moment when the threshold value is passed).
~7hen the wheel 1 starts turning again, the output signal from the
amplifier 6 changes its sign, but the electric valve 13 remains
energized by the discharge from the memory. L
To take into account adherence conditions during the
time when the wheel is picking up speed again, the acceleration r
signal obtained at the output of the diode 10 will short-circuit
the memory9, beyond a threshold value ys (see Figure 2), by ~ -
means of the discharge device 11, and this will occur propor-
tionally to the amount of acceleration of the wheel. Thus, for
considerable deceleration followed by slight acceleration, the
memory will take a long time to discharge, and the pressure will
104~154
be reapplied to the brake 2 only after a lengthy delay. On the
other hand, if acceleration is considerable, that is to say if
the wheel starts to pick up speed again rapidly, the memory will r
discharge rapidly through the discharge device 11, and the pres-
sure will be reapplied to the brake after a very short time.
Furthermore, if deceleration is slight, that is to say L
if the wheel has not skidded over a great distance, the memory is ~ -
not charged to any great extent, and its discharge will occupy
only a short time. Pressure will then be rapidly reapplied to
10the brake.
The required function is thus achieved, and the wheel
will have time to pick up speed in all cases where adherence to
the ground occurs.
Referring to Figure 2, the curve 16 represents the
change in the delay period as a function of deceleration y for
an acceleration value Yl which is less than or equal to the
threshold value ys for acceleration. It will be seen that
because the discharge of the memory is carried out using constant ,~
current, this curve 16 is a straight line which originates at '~
the time t = o, for the deceleration threshold value.
It will be clear that the times taken by the memory to
discharge ~delay value), in the case of the curve 16, are greater
for the same deceleration value than are the discharge times
respresented by the delay curve 17 for which acceleration Y2
is greater than the acceleration threshold value ys.
In a similar manner~ the times required by the memory r
to discharge, represented by the delay curve 17, are always
greater, for the same deceleration value, than those represented
by the curve 18 for which the acceleration y3 is greater than the
acceleration Y2- -
Referring to Figure 3 which illustrates the application
of the method of the invention in a vehicle having two wheels the
, - , : . ~
1~)46~54
braking of which is controlled, the adjusting system comprises an
independent adjusting circuit for each wheel, and common safety ~ -
elements. Figure 3 shows only one of the two circuits associated
with each of the two wheels, the second circuit being identical.
This circuit comprises a tachogenerator 3 associated with the
wheel, a network containing the previously mentioned components
4, 5, 6, 7, 8, 9, 10, 11 and 12, and the corresponding electric
valve 13. This circuit may optionally also comprise an impact
safety circuit 22 and an anti-blocking safety circuit 23 ensuring
complete disengagement of the brakes from the wheels whenever the
vehicle is not in contact with the ground as when a wheel is 2
blocked inopportunely. For each of the wheels, the signal from
the tachogenerator 3 is filtered in the block 4 by a series re-
sistor 41 and a capacitor 42 connected to earch. The output vol-
tage is passed to a differentiating device 5 constituted by a
resistor 51 and a capacitor 52 arranged in series. The differ-
entiated signal then enters an amplifier 6 having a gain variable
as a function of frequency and constituted by an operational ~
amplifier 61 with a feed-back resistor 62. The second input of ,
the operational amplifier 61 is connected to earth through a ,-
resistor 63. ,
A feed-back circuit, constituted by resistors 64 and ;;
65 and capacitors 66, 67 and 68 enables the gain with frequency
to be adjusted so as to attenuate the frequencies corresponding
to the vibrations of the wheel and the means whereby it is
secured to the vehicle.
The output signal from the amplifier 61 is passed
successively:
- through the diode 7 to a threshold-detection circuit 7 consti- q
tuted by an operational amplifier 81, fitted as a comparator,
the second entry receiving a positive potential defining the
threshold value through a resistance bridge 82 and 83 fitted
.
-- 6 --
11~46154
between earth and a positive voltage source;
- through the same diode 7 to a memory circuit comprising a
charging resistor 91, a memory capacitor 92 and a discharging
resistor 93;
- through the diode 10 to a circuit 11 for discharging the memory
capacitor 92 and constituted by a series resistor 111 and a
current-control transistor 112, the base of which is polarized
by the resistance bridge 113 and 114 determining a threshold
below which this circuit does not operate. The emitter of this
transistor 112 is connected to the resistor 111 whereas its
collector is connected to the memory capaciter 92 to ensure its
discharge proportional to the acceleration of the wheel.
The output signal from the threshold-detecting circuit
8 controls a power amplifier 12 which comprises, in series, a
resistor 121 and a diode 122 connected to the base of a power
transistor 123, of which the collector is connected to the coil
of the electric valve 13.
Thus, when the wheel starts to skid, the voltage
delivered by the generator decreases thus creating a positive
signal proportional to the deceleration, at the output of the
amplifier 6.
At the output of the diode 7, this signal is compared
with the threshold voltage within the block 8; if this signal is
greater than said threshold voltage, the block 8 sends a signal
which triggers the transistor 123 thus ensuring that current
passes into the coil of the electric switch.
The deceleration signal passing through the charging
resistor 91 will charge the memory capacitor 92 proportionally
to the value of the signal as well as to its duration, thus
ensuring that the electric valve 13 continues to be energized
after cessation of the deceleration signal.
With the brake disengaged from the wheel, the latter
. ,
1046154 :
picks up speed and sets up an acceleration signal at the output
from the block 6, which signal, by way of the diode 10, the
resistor 111 and the transistor 112, causes discharge of the
memory proportionally to the acceleration value, and when the
voltage passed into the memory drops below the threshold voltage
of the block 8, suppresses the signal for energizing the coil of
the electric valve 13, this consequently taking place after a
variable period permitting the wheel to pick up speed again.
The adjusting system illustrated in Figure 3 also
comprises an impact safety device, known per se, and used on
aircraft, which device in particular prevents braking from taking :~
place so long as the vehicle has not made contact with the
landing path. For this purpose a contact 221, associated with
the means whereby the braked wheel is secured to its vehicle,
indicates whether its shock-absorber is compressed or not. The
signal, produced when the shock-absorber is not compressed, is
sent through diodes 222 to power amplifiers 12 in each adjusting
circuit, thus ensuring that the coils 13 of the electric valves
are energized and therefore that it is not possible to apply
pressure to the brakes. Furthermore, a circuit 223, which
detects the lowest speed of the braked wheels, short-circuits,
through a Zener diode threshold detector 224 and a transistor , -
225, the signal set through the shock-absorber contact, and thus
makes it possible to apply the brakes if the wheels of the
vehicle are caused to rotate even if the shock-absorbers are
not compressed. ~ -
This is necessary since, in the case of an aircraft,
the vehicle, because of lift, may already be in contact with the i
landing path when the shock-absorbers are not compressed.
The control cabinet may also contain a safety means
23 for preventing blocking of the braked wheels and known per se.
The circuit is only active when the speed of the
-- 8 --
.
1~)4~54
vehicle is gr~ater than a given speed V, so as to permit braking
at low speed as well as when the vehicle is stop~ed.
When the circuit is active and if one of the braked
wheels is at a speed lower than the reference speed Vl, the
circuit ensures that the brake is disengaged from this wheel
and from the wheel disposed symmetrically therewith, in order
to maintain the direction of travel of the vehicle.
The speed of the vehicle is calculated in the block
231 by taking the greatest of the speeds of the braked wheels,
this signal being stored and released in the event of simul-
taneous blocking of all the wheels following deceleration in i'~
excess of the maximum that the vehicle can reach in the optimum
wheel-to-ground adherence conditions. This enables safety to be
maintained when all the wheels are blocked simultaneously which
would result in a zero vehicle-speed signal and thus in the
safety system going out of operation if there were no memory,
The vehicle-speed signal provided by the block 231
enters a threshold detector 232 which sends a signal to a pro-
hibiting system 233 which blocks the operation of the safety
means when the speed of the vehicle is less than V.
The speed signal supplied by tachodynamos 3 also pass
into a threshold detector 234 which, when one of the signals is
less than the speed Vl, sends a brake-disengagement signal to
the power amplifiers of the corresponding control circuits
through the block 233 and a diode 233'.
~hen the wheel picks up speed again and its speed again
exceeds Vl, the brake-disengagement signal is suppressed, but
after a delay (block 236) proportional to the speed of the
vehicle so as to enable the wheel to reach synchronous speed r
before further skidding is caused.
Finally, a circuit 235 for delaying the triggering of
the safety circuit, operative at low vehicle speeds, enables this
.
1046154
safety means to be used only intentionally, in view of the fact
that at speeds slightly higher than the reference speed V, it is
possibLe for a wheel speed to drop below Vl without there being
a fault in the adjusting system, the delay making it possible to
check whether the wheel picks up speed as a result of interven-
tion by the adjusting system, before causing the safety means to
operate.
It will be noted that the transmission of control
signals from the circuits 22 and 23 to the block 12 occurs
between the diode 122 and the power transistor 123.
Thus, the system for adjusting braking power in accor-
dance with the invention is clearly distinguished from the known
systems, which are generally more complex and specific to a
particular type of use and which in particular employ impedance
circuits which may comprise a plurality of capacitors, one of ~
which is automatically variable with the acceleration signal.
Furthermore, in these known systems, there is no question of an
acceleration threshold or deceleration threshold being involved.
Finally, it may be stated that this system provides a
number of advantages stemming mainly from its simplicity and from
the elements of which it is made up; examples of such advantages
are robustness, reliability, freedom from contamination, etc.
~ 10 -
