FR2846620A1 - Control system for automobile braking force comprises sensors detecting vehicle parameters and computer able to calculate braking instruction value - Google Patents

Abstract

The control system for the braking force applied to the automobile wheels comprises different sensors (14) for the vehicle parameters and a computer (5), receiving the sensor information, able to calculate a braking instruction value for the braking device as a function of a control action coming from the vehicle driver (8) or coming from an automatic driving assistance device (10). The computer modifies the speed of development of the braking instruction value according to the driving situation detected by the sensors. An Independent claim is included for a method of controlling the braking force applied to the wheels.

Description

System and method for controlling the braking force of a

motor vehicle.

  The subject of the present invention is a system for controlling the braking force applied to the wheels of a motor vehicle by a controllable braking device, as well as a method for controlling it.

of this braking force.

  Motor vehicles are currently being developed comprising a controllable braking device, the control of which can be decoupled, that is to say without mechanical link between the brake pedal on which the driver of the vehicle acts and the member of

actual braking.

  In vehicles of this type, a brake actuator is generally provided on each of the vehicle wheels. This braking actuator can be electromechanically controlled (EMB technology, ElectroMechanical Braking), hydraulically controlled (EJIB technology, ElectroHydrolical Braking), or digitally controlled by programming (ESP technology, Electronic Stability Program). The position of the brake pedal can be detected by a position sensor. Likewise, the force exerted by the driver on the brake pedal is detected by a

  force sensor applied to the pedal.

  The set of signals from different sensors is transmitted to a central electronic unit which is capable of analyzing these different signals and, according to the indications which are thus provided to it, of determining the braking force required or the pressure which apply to the different actuators to achieve

the desired braking force.

  In vehicles of this type, there are rapid and strong variations in the setting of the clamping or releasing force of the brake actuators, causing uncomfortable jolts for

the passengers of the vehicle.

  The object of the invention is therefore to improve the comfort of the driver and passengers of such a vehicle in order to avoid these uncomfortable jerks, in a simple manner and without requiring the addition

  additional damping elements.

  The system according to the invention enabling the braking force applied to the wheels of a motor vehicle to be controlled by a controllable braking device, comprises various sensors for vehicle parameters and a computer receiving the information from the sensors and capable of calculating a braking setpoint for the braking device, as a function of a control action from the driver of the vehicle and / or from an automatic driving assistance device. The computer is adapted to modify the speed of change of the braking setpoint according to the driving situation detected by the

above parameters.

  In this way, the clamping or loosening force exerted on each of the vehicle wheels is progressive and the comfort of the

  driver and passengers are improved.

  Preferably, the control action is detected by a

  support sensor on the vehicle brake pedal.

  In another embodiment, the control action is a signal from an external automatic driving assistance device such as a hill starting assistance system, an automatic speed control device or a device

  automatic distance control.

  The control action can also be a combination of a signal from a sensor for pressing on the vehicle's brake pedal and a signal from an external driving assistance device such as a hill start assist system, an automatic speed control device or a device

  automatic distance control.

  In an advantageous embodiment, the above-mentioned parameter sensors are capable of detecting an emergency braking situation, the computer being capable, in this case, of calculating a braking setpoint whose speed of evolution is not not changed. The braking force is therefore applied at maximum speed in such an emergency situation. The braking safety of the vehicle is thus ensured despite the system for limiting the

  rate of change of the braking force.

  Preferably, the computer is capable of memorizing 5 different maximum and minimum values for the speed of change of the braking setpoint value and of choosing from these memorized values those which are appropriate for the driving situation.

  instantaneous and / or the nature of the control action.

  The maximum speeds, possibly modified according to the driving situation, may be different for tightening and

  for releasing the braking devices.

  The method according to the invention for controlling the braking force applied to the wheels of a motor vehicle by a controllable braking device consists in calculating a braking setpoint value for the braking device, as a function of a

  control action from the driver of the vehicle or from an automatic driving assistance device, to detect the driving situation of the vehicle and to modify the speed of change of the braking setpoint according to the situation of 20 driving.

  The invention will be better understood from the study of an exemplary embodiment described below, with reference to the appended drawings, in which: - Figure 1 schematically illustrates a motor vehicle 25 equipped with a controllable braking device; - Figure 2 is a diagram of the main elements of a control system of the invention; FIG. 3 shows an exemplary embodiment of a device for limiting the speed of change of the braking setpoint, according to the invention; and FIG. 4 shows different curves showing the limitation of the tightening and loosening speed, within the framework of the invention. FIG. 1 illustrates, by way of example, a vehicle referenced 1 comprising four wheels 2, each equipped with a braking actuator 3. These actuators can be of any type usually used, for example of the electromechanical, electro5 hydraulic type or with numerical control. Each brake actuator 3 receives a signal via a connection 4 from a central computing unit 5 with which the vehicle 1 is provided and which can manage not only the braking of the vehicle, but also of other functions

  necessary for running the vehicle.

  The brake pedal 6 of the vehicle is equipped with a sensor 7 capable of detecting the position of said pedal, as well as possibly the force applied by the driver of the vehicle to the pedal 6. The signal emitted by the sensor 7 is transmitted individually

control unit 5 through connection 8.

  In a vehicle of the type illustrated in FIG. 1, the braking is controlled by the central computing unit 5 without mechanical link between the brake pedal 6 and the different braking members acting on each of the wheels 2. The braking is carried out by piloting the four

  actuators 3 controlled by the central computing unit 5.

  The different set values for the clamping or releasing forces which must be applied by the different actuators 3 come either from the driver via the sensor 7 which determines the state of the brake pedal 6, or also from external events related to driving the vehicle. For example, the vehicle can be equipped with a hill start assist system or an electronic stability stability program (ESP) which can be managed by the central computing unit 5. or a calculation unit dedicated to this specific function. The setpoints can then come from such an external driving assistance system 30 and replace or combine with the setpoints coming from the wishes of the driver expressed by the action exerted.

on the brake pedal.

  As an additional example of a braking instruction coming from an external driving assistance system, there may be mentioned an automatic braking system linked to a digital driving control device, known under the name "ACC "

(Adaptive Cruise Control).

  The set of actions which thus arrive in the form of 5 signals to the central computing unit 5 results, after processing, in a set value of the tightening or loosening force which should be applied by the intermediate of the different actuators 3

on each of the four wheels 2.

  The diagram of Figure 2 illustrates the main elements of a system according to the invention.

  In FIG. 2, the signal originating from the force or pressure exerted by the driver on the brake pedal 6 is found at the input 8 of a computer block 9 forming part of the central computer unit 5. The calculation block 9 is capable of determining the set value of the tightening or loosening force as a function of the

input signals received.

  The external forces or pressures corresponding to the automatic actions mentioned above (set values from a hill start assist system, an automatic driving control system, an electronic stability maintenance system , etc.), provide different signals which are brought to the input 10 of the calculation block 9. It will be understood that this input 10 can, in reality, consist of a multitude of inputs in

  from various external electronic systems.

  The output signals 11, coming from the calculation block 9, represent the different clamping forces or pressures which should be applied to each of the actuators 3 of the four wheels 2 of the

  vehicle, taking into account the input signals 8 and 10 received.

  These signals 11 are brought to a limiting device 12 which also receives, via the connection 13, signals corresponding to the driving situation of the vehicle which is detected by various sensors shown diagrammatically by the block 14. The driving situation of the vehicle can by example being a starting state, low vehicle speed, driving with a cruise control, driving with a distance controller between vehicles, etc. The various sensors 14 of this driving situation thus provide information to the limiting device 12, in order to allow it to hold

  account of the actual driving situation of the vehicle.

  If the driving situation allows, the speed of variation of the force or the clamping pressure applied to the different actuators is then limited by the limiting device 12, so as to provide better comfort to the driver and passengers of the vehicle. The output signals 15 corresponding to forces or 10 clamping pressures whose variation over time has been limited by the limiting device 12, are then applied to the different actuators 3

  of vehicle 1 shown diagrammatically by a block in FIG. 2.

  When the various driving situation sensors 14 determine a driving situation requiring emergency braking 15, the limiter device 12 does not limit the speed of variation of the force or the clamping pressure, so that , in this case, the speed of application of the force or pressure

  tightening is maximum, so as to ensure driving safety.

  The limits imposed by the limiting device 12 and 20 stored in the calculation unit 5, for the speeds of variation of the clamping or loosening pressure forces, may be different depending on the automatic driving assistance system in service at at a given time and depending on the driving situation of the

  vehicle determined by the various sensors 14.

  The invention can be applied to any vehicle, whatever the driving assistance system used, such as for example - an electronic stability maintenance system, of the ESP (Electronic Stability Program) type, - a system ACC 30 (Adaptive Cruise Control) automatic control system, - a hill start assist system, etc. FIG. 3 illustrates, in a more precise manner, an exemplary embodiment of the limiting device 12 shown schematically in FIG. 2. As shown in this example, the set value of the clamping force or pressure, referenced 11, is brought at the first input of a comparator 16 which also receives on a second input, via the connection 17, the value of the limited force or pressure 15, after the latter has undergone a delay while crossing the delay block 18. L The entire device continuously calculates the limited values 15 with a determined sampling frequency. The reference value 11, which is brought to the first input of the comparator 16, is therefore for example the value n, while the value 10 of the limited force or pressure 15 corresponds, after delay, to the

setpoint value of rank n-i.

  The output signal of the comparator 16 is brought by the connection 19 to a block 20 for determining the sign of the difference between the values of rank n and of rank n-i. It is understood that, if the difference is positive, we are in the context of applying the brakes, the tightening setpoint increasing. On the contrary, if the sign of the deviation is negative, it is a loosening operation, the set value

being decreasing.

  The output of block 20 emits a signal which is brought by connection 21 to a flip-flop block 22, which also receives two predetermined limit values stored in calculation unit 5, namely a "positive" limit 23 and a limit "negative" 24. The output signal of the flip-flop block 22 therefore corresponds to the value of one of these limits 23 or 24, according to the sign (positive or negative) of the deviation, 25 determined in block 20. The output value of block 22 is brought, on the one hand, to comparator 25 through connection 26 and, on the other hand, to adder 27 through connection 28. Comparator 25 also receives, through connection 29, the output signal of block 30 which determines the absolute value of the force or pressure setpoint 30 materialized by the output signal of comparator 16. Comparator block 25 can therefore determine whether the absolute value of the setpoint determined in block 30, is less than or greater than the variation of the pen corresponding to one of the limits 23 or 24

provided by block 22.

  The output of the timer 18, which corresponds to the limited value 15 of rank n-1 of the clamping force or pressure, is also brought by the connection 31 on the adder 27. At the output of the adder 27, the signal conveyed by connection 32 5 therefore corresponds to the new clamping force or clamping pressure setpoint, of rank n, with a limited variation speed corresponding to one of the limits 23 or 24. This signal is brought to the block of separation 33 which is able to choose between this modified value and the unmodified reference value corresponding to the input 11 which is supplied 10 directly to block 33 by connection 34. The choice is made by block 33 as a function of the signal received from the block of

comparison 25 by connection 35.

  It will be understood, of course, that other means could

  be used to effect the limitation of the rate of variation of the force or of the tightening or loosening pressure, according to the invention.

  In particular, the limitation could be progressive instead

  to be realized in the form of predetermined fixed values.

  Figure 4 illustrates a variation curve of the force of

  tightening F, expressed in Newton (N), as a function of time t, expressed in 20 seconds.

  In Figure 4, there is shown a tightening operation immediately followed by a loosening operation. The dotted curves correspond to the set value which is provided either by the driver of the vehicle or by an external device. From 25 seconds, which is the actuation waiting time, the clamping force setpoint represented by the dotted curve 36 increases. By way of example, it will be assumed that the vehicle is stationary on a hill and that it is equipped with an automatic device 30 for assisting in hill start. We know that this automatic system

  helps the driver to start by gradually releasing the brakes according to the engine torque transmitted to the wheels.

  This driving situation can be easily detected by appropriate sensors, because the vehicle is stopped (its speed is zero) and it is held on the slope by a clamping force which can be a parking brake or the service brake. When the driver's will to start has been detected, the automatic assistance system subtracts the force transmitted to the wheel from the force applied to the vehicle and due to the slope. This results in a balance of the holding forces until the vehicle is started in the form Fserrage = FFperte-Froue o - Froue is the longitudinal driving force, - Fpente is the longitudinal force exerted by the slope on the vehicle, and - Fserrage is the longitudinal force required from the

vehicle braking.

  If the driver suddenly disengages, the clamping force increases abruptly, thus generating a sudden braking instruction.

  in the automatic hill start assist system.

  Conversely, during starting, the engine force transmitted to the wheel depends on the position of the vehicle clutch pedal and the gear ratio engaged. When the driver engages, the longitudinal driving force or Fr0ue increases suddenly and the clamping force F clamping decreases until it is canceled. Here again, the loosening setpoint can be extremely brutal, since it comes from an automatic setpoint which directly depends on the speed

  driver squeezing the clutch pedal.

  This results in very uncomfortable situations for the driver and the passengers of the vehicle, the application or release of the brakes which is done very quickly causing significant jolts. The system according to the invention makes it possible to replace the curve 36 30 of abrupt variation in the clamping force represented in dashes in FIG. 4 by a straight line 37 of predetermined constant slope which corresponds to the positive value 23 of FIG. 3, and this , up to about 15 seconds, in the example shown. From this moment, in fact, the variation of the set value of the clamping force becomes less than the predetermined limit, so that the system then adopts the input set value without modification, depending on the portion

curve 38.

  From time t = 20 seconds, a reverse loosening operation has been illustrated in FIG. Under the same conditions, the loosening instruction supplied at the input of the system varies suddenly, as illustrated by the dashed curve 39. According to the invention, the system replaces this curve with the straight line 40 of constant negative slope which corresponds to the negative value 24 of FIG. 10 3, and this until the moment when the variation of the set value is small enough that it can be adopted without modification, which corresponds to the portion of curve in lines full 41. In the example which has just been explained, corresponding to a hill start of the vehicle, it is understood that the vehicle being at almost zero speed, there is no compromise to be made in terms of limiting the values given the security requirements. In another situation, for example when driving at normal speed, whether or not the vehicle is equipped with an additional electronic assistance system, it may on the contrary be necessary to take account of an emergency situation in order to apply clamping force or pressure very quickly. In this case, this emergency situation, which is detected by one of the sensors 14, 25 illustrated in FIG. 2, gives rise to a signal which is interpreted by the limiting device 12, so as to short-circuit its operation and to adopt the setpoint coming directly from input 11, illustrated in FIG. 2, without there being any need to make a

variation limitation.

  The present invention thus makes it possible, by simple means and without the addition of additional damping elements, to considerably improve the comfort of a vehicle equipped with a

controllable braking.

he

Claims (5)

  1-System for controlling the braking force applied to the wheels of a motor vehicle by a controllable braking device, comprising different sensors (14) of vehicle parameters and a computer (5) receiving the information from the sensors and capable of calculating a braking setpoint for the braking device, as a function of a control action coming from the driver of the vehicle (8) and / or from an automatic driving assistance device (10), characterized in that the computer is adapted to modify the speed of change of the braking setpoint according to the detected driving situation   by the aforementioned parameter sensors.   2-control system according to claim 1, characterized   by the fact that the control action is detected by a sensor (7) 15 on the brake pedal of the vehicle.   3-control system according to claim 1, characterized   by the fact that the control action is a signal coming from a hill start assist system, from an automatic speed regulation device or from an automatic distance regulation device.   4-control system according to claim 1, characterized in that the control action is a combination of a signal from a support sensor on the brake pedal of the vehicle and a signal from a hill start assist system, an automatic speed control device or a device   automatic distance control.   - Control system according to any one of   previous claims, characterized in that the above-mentioned parameter sensors are capable of detecting an emergency braking situation, the computer being capable, in this case, of calculating a   braking setpoint whose speed of change is not changed. 6-Control system according to any one of   previous claims, characterized in that the computer is capable of memorizing different maximum and minimum values (23, 24) for the speed of change of the braking setpoint and of choosing from these memorized values those which are   appropriate to the instant driving situation and / or the nature of command action.   7-Method for controlling the braking force applied to the wheels of a motor vehicle by a controllable braking device 10 in which a braking setpoint value for the braking device is calculated, as a function of a command action in from the driver of the vehicle or from an automatic driving assistance device, characterized by the fact that the driving situation of the vehicle is detected and that the speed of change of the set value is modified braking depending on the driving situation.