CA1046154A - Method and system for adjusting braking force - Google Patents
Method and system for adjusting braking forceInfo
- Publication number
- CA1046154A CA1046154A CA224,399A CA224399A CA1046154A CA 1046154 A CA1046154 A CA 1046154A CA 224399 A CA224399 A CA 224399A CA 1046154 A CA1046154 A CA 1046154A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- acceleration
- wheel
- deceleration
- memory
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
- B60T8/321—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration deceleration
- B60T8/325—Systems specially adapted for aircraft
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/173—Eliminating or reducing the effect of unwanted signals, e.g. due to vibrations or electrical noise
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/176—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS
- B60T8/1761—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS responsive to wheel or brake dynamics, e.g. wheel slip, wheel acceleration or rate of change of brake fluid pressure
- B60T8/17613—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS responsive to wheel or brake dynamics, e.g. wheel slip, wheel acceleration or rate of change of brake fluid pressure based on analogue circuits or digital circuits comprised of discrete electronic elements
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- Engineering & Computer Science (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Aviation & Aerospace Engineering (AREA)
- Regulating Braking Force (AREA)
- Control Of Velocity Or Acceleration (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The braking force applied to vehicles is related to the deceleration or acceleration of each of the braked vehicle wheels, so that, for a given braking signal, the braking force is suppressed when the deceleration of the braked wheel passes a predetermined threshold (which occurs, for example, when the wheel begins to skid freely), and re-application of braking force is delayed by a time proportional to the amount of decel-eration of the wheel and of acceleration during the time it is picking up speed when the acceleration passes a predetermined threshold. Control of the braking force is effected by a system including an element for producing a signal which is a function of the speed of each of the wheels, a differentiator device for receiving the signal and connected, through a diode which passes only deceleration signals, to a threshold device 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 extreme skidding, and an element permitting transmission to a memory of the signal from the diode proportional to its amplitude and duration, the signal from the differentiator device being transmitted, during acceleration of the vehicle through a diode, which passes only acceleration signals, to a device permitting the memory to dis-charge beyond a predetermined acceleration threshold.
The braking force applied to vehicles is related to the deceleration or acceleration of each of the braked vehicle wheels, so that, for a given braking signal, the braking force is suppressed when the deceleration of the braked wheel passes a predetermined threshold (which occurs, for example, when the wheel begins to skid freely), and re-application of braking force is delayed by a time proportional to the amount of decel-eration of the wheel and of acceleration during the time it is picking up speed when the acceleration passes a predetermined threshold. Control of the braking force is effected by a system including an element for producing a signal which is a function of the speed of each of the wheels, a differentiator device for receiving the signal and connected, through a diode which passes only deceleration signals, to a threshold device 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 extreme skidding, and an element permitting transmission to a memory of the signal from the diode proportional to its amplitude and duration, the signal from the differentiator device being transmitted, during acceleration of the vehicle through a diode, which passes only acceleration signals, to a device permitting the memory to dis-charge beyond a predetermined acceleration threshold.
Description
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.
: - .
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 ~ 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.
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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 .
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 .
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 .
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 -
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.
: - .
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 ~ 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.
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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 .
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 .
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 .
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 -
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A system of adjusting braking force, based on the deceleration and acceleration of the wheels of a vehicle during braking which comprises, an element 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 first 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.
2. A system according to Claim 1, including, between the element that supplies a signal as a function of the speed of each of the wheels, and the differentiating device, an element for filtering extraneous noise from said signal.
3. A system according to Claim 1, in which the differen-tiating device is connected to an amplifier having a gain which varies as a function of frequency, and which permits the system to operate without interference from vibrations caused by displace-ment of the braked wheel.
4. A system according to Claim 1, 2 or 3 in which the deceleration signal is passed to a memory through a charging resistor so as to obtain a charge which is proportional both to the value of the signal and to its duration.
5. A system according to Claim 1, including a transistor for discharging said memory, said transistor, which operates on constant current, being controlled by the acceleration of the wheel when it is picking up speed when this acceleration is beyond a threshold value defined by the bias on the base of said transistor.
6. A system according to Claim 5 wherein the base of said transistor is biased by a resistor-bridge.
7. A system according to Claim 6 wherein the emitter of the transistor is connected to the second diode through a resistor and the collector of the transistor is directly connected to said memory.
8. A system according to Claim 1 in which said threshold device receiving the deceleration signals comprises an operational amplifier, one of the two inputs of which is biased with the aid of a reference voltage.
9. A system according to Claim 8 in which one of the two inputs is biased with the aid of a voltage-dividing bridge connected between earth and a constant voltage source.
10. A system according to Claim 1, 2 or 3 in which at the output of the threshold device for the deceleration signals, the element controlling the disengagement of the brake comprises a resistor followed by a diode connected to the base of a power transistor, the load of which is constituted by the control wind-ing of an electric valve which ensures that the brake is dis-engaged.
11. A system according to Claim 1, 2 or 3 including an impact safety device, connected in parallel with the control circuit of the electric valve between the output of the means for measuring wheel speed and the base of the power transistor con-trolling the coil of the electric valve and operative as long as the vehicle is not in contact with the landing path and transmitt-ing a control signal to the base of said power transistor.
12. A system according to Claim l, 2 or 3 including a safety device for preventing blocking of the braked wheels, which device ensures that the wheels can pick up speed, when one or more of them is blocked inopportunely during braking, and passes a control signal to the base of said power transistor, said device being connected in parallel with the control circuit between the output of the means for measuring wheel speed and the base of the power transistor controlling the winding of the electric valve.
13. A device for adjusting the braking force applied to a vehicle, in particular an aircraft, responsive to the acceler-ation or deceleration of a braked wheel to servo-control the brake members of that wheel, the device comprising, means for providing a signal which is a function of the speed of the braked wheel, a differentiation circuit receiving this signal and connected, through a first diode only passing deceleration signals to a threshold device and a memory for storing the deceleration signals, the threshold device being connected to means for disengaging the brakes of the wheel, said threshold device passing signals exceed-ing a predetermined deceleration threshold, said differentiation circuit also being connected through a second diode only passing acceleration signals to a device for discharging the memory, whereby, in order to shorten the response time of the device and to allow a disengaged wheel to run freely for a time after dis-engagement of the brakes in a simple and reliable manner, the memory is arranged to receive the deceleration signal whatever its value and store this signal according to its amplitude and duration, and the memory is also arranged to discharge through the deceleration threshold device which, when the charge stored in the memory exceeds the predetermined threshold value, activates the means for disengaging the brakes, which means is in the form of an electric valve working on an all or nothing basis, the said discharge device being a predetermined acceleration threshold device arranged to discharge the memory according to the value of the acceleration signal so that the de-activation of the electric valve occurs after a time which is proportional to the value and duration of the deceleration and inversely proportional to the value of the acceleration of the wheel as the wheel starts to speed up again when said acceleration exceeds the predetermined acceleration threshold.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7413045A FR2267223B1 (en) | 1974-04-12 | 1974-04-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1046154A true CA1046154A (en) | 1979-01-09 |
Family
ID=9137629
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA224,399A Expired CA1046154A (en) | 1974-04-12 | 1975-04-11 | Method and system for adjusting braking force |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS50138285A (en) |
| BR (1) | BR7502070A (en) |
| CA (1) | CA1046154A (en) |
| DE (1) | DE2515504C3 (en) |
| ES (1) | ES436541A1 (en) |
| FR (1) | FR2267223B1 (en) |
| GB (1) | GB1502806A (en) |
| IL (1) | IL47032A (en) |
| IT (1) | IT1037108B (en) |
| SE (1) | SE401345B (en) |
| SU (1) | SU652877A3 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1545620A (en) * | 1967-06-22 | 1968-11-15 | Dba Sa | Anti-lock device for vehicle braking system |
| FR1561272A (en) * | 1968-01-17 | 1969-03-28 | ||
| US3615120A (en) * | 1968-09-11 | 1971-10-26 | Hayakawa Denki Kogyo Kk | Anti-skid brake control device |
| BE787426A (en) * | 1971-08-10 | 1973-02-12 | Hoechst Ag | PROCESS FOR PREPARING PENTAFLUORO-ETHYL IODIDE AND HEPTAFLUORO-ISOPROPYL IODIDE |
-
1974
- 1974-04-12 FR FR7413045A patent/FR2267223B1/fr not_active Expired
-
1975
- 1975-03-27 IT IT21753/75A patent/IT1037108B/en active
- 1975-04-07 BR BR2640/75D patent/BR7502070A/en unknown
- 1975-04-07 IL IL47032A patent/IL47032A/en unknown
- 1975-04-09 DE DE2515504A patent/DE2515504C3/en not_active Expired
- 1975-04-09 JP JP50042392A patent/JPS50138285A/ja active Pending
- 1975-04-10 SE SE7504131A patent/SE401345B/en unknown
- 1975-04-10 GB GB14819/75A patent/GB1502806A/en not_active Expired
- 1975-04-11 ES ES436541A patent/ES436541A1/en not_active Expired
- 1975-04-11 SU SU752133910A patent/SU652877A3/en active
- 1975-04-11 CA CA224,399A patent/CA1046154A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ES436541A1 (en) | 1977-01-01 |
| SE401345B (en) | 1978-05-02 |
| SE7504131L (en) | 1975-10-13 |
| JPS50138285A (en) | 1975-11-04 |
| FR2267223A1 (en) | 1975-11-07 |
| IL47032A0 (en) | 1975-07-28 |
| FR2267223B1 (en) | 1977-10-14 |
| IT1037108B (en) | 1979-11-10 |
| DE2515504A1 (en) | 1976-02-26 |
| SU652877A3 (en) | 1979-03-15 |
| BR7502070A (en) | 1976-02-10 |
| GB1502806A (en) | 1978-03-01 |
| IL47032A (en) | 1979-12-30 |
| DE2515504C3 (en) | 1983-01-20 |
| DE2515504B2 (en) | 1982-06-24 |
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