FR2934543A3 - Motor vehicle braking method, involves applying braking action intensity setpoint in closed loop in operating mode, where braking action intensity setpoint value is sharply reduced for attaining value at input in operating mode - Google Patents

Abstract

The method involves applying a braking action on a wheel of a motor vehicle, and applying braking action intensity setpoint in a closed loop in an operating mode, where the braking action intensity setpoint value is sharply reduced for attaining a value at an input in the operating mode. The braking action intensity setpoint value variation is 600 Newton meter per second. The value at the input in the operating mode is defined from the braking action intensity setpoint value applied on a wheel. Independent claims are also included for the following: (1) a data medium comprising a set of instructions for implementing a method for braking a motor vehicle (2) a system for braking a motor vehicle.

Description

The invention relates to a braking system for the wheels of a motor vehicle comprising a braking device mechanically decoupled from the braking control. It relates in particular to a braking process implemented by such a braking system. It also relates to a data carrier comprising means for implementing such a braking method. The active safety of vehicles is currently a major issue in the automotive world, and in this context, controlled braking is an important issue.

Thus, in addition to the many devices already prevalent in the field of safety, such as anti-lock braking systems (ABS, for Antilock Braking System), trajectory control systems (or electronic stability program ESP, for Electronic Stability Program), or the emergency braking assistance (AFU), the car manufacturers offer so-called comfort services, such as hill start assistance, or control of the deceleration of the vehicle according to its state.

These services are made possible by the development on vehicles of braking devices (known as by-wire devices), in which the brake pedal actuated by a driver and the means for actuating the brakes are completely decoupled mechanically.

Such mechanical decoupling between the brake pedal and the actuator of the braking means makes it possible inter alia to improve the performance of so-called low-level braking systems, in particular the anti-locking of the wheels. It is indeed possible to finely regulate the sliding of each wheel by controlling the braking torque applied to it. MS \ REN093FR.dpt Such anti-blocking systems are already known.

For example, US Pat. No. 6,616,250 discloses a method for controlling the performance of a vehicle when forces are applied to the wheels of the vehicle, comprising a step in which control variables are used which make it possible to determine and change the pressure applied by the brakes on the wheels of the vehicle. This device uses in particular the force measured at the wheels, as well as the wheel speed and / or a reference speed of the vehicle.

Nevertheless, the proposed device has the major disadvantage of being based on logic of state machines, that is to say on quantitative reasoning that does not allow to continuously correct the application of pressure by stirrups and which do not otherwise implement modern automatic methods. One consequence is that the process of this patent is subject to the uncertainties of the system and is complex to implement. The object of the invention is to provide a braking method overcoming the disadvantages mentioned above and improving braking processes known from the prior art. In particular, the invention provides a braking method improving the braking performance and stability of the vehicle. In particular, the braking is optimized by extending the phases during which the braking level is effective.

According to the invention, the braking process of a motor vehicle comprises the application of a braking action on at least one wheel of the motor vehicle and comprises a first mode of operation in which an intensity command is applied. closed loop braking action. It is characterized in that, following the entry into the first mode of operation, the set value of the intensity of the braking action is abruptly reduced to reach a first value.

Following the entry into the first mode of operation, the rate of change of the set value of the intensity of the braking action may be at least 300 Nms ', and preferably at least 600 Nms "'. The first value can be defined from the value of the intensity of the braking action applied to the wheel just before entry into the first operating mode, the first value being, other things being equal, different depending on the transverse acceleration experienced by the motor vehicle 15. The first value may be, other things being equal, different according to the grip of the wheel on the ground.The first value may be, other things being equal, different according to whether it is a first pass in the first mode of operation since the activation of the anti-blocking function or that it is a subsequent passage in the first mode of operation.

According to the invention, the data carrier comprises software means for implementing the braking method defined above. According to the invention, the braking system of a motor vehicle comprises means for applying a braking action on at least one wheel of the motor vehicle. It is characterized in that it comprises hardware and / or software means for implementing the braking method defined above. According to the invention, the motor vehicle comprises a braking system defined above. MS \ REN093EN.dpt The appended drawing represents, by way of example, an embodiment of the braking method according to the invention and an embodiment of a braking system according to the invention. Figure 1 is a diagram of an embodiment of a braking system according to the invention.

FIG. 2 represents an embodiment of a module for managing the anti-lock function of a computer of the braking system.

Figure 3 is a time chart of changes in the vehicle speed and the speed of a wheel of a vehicle equipped with a braking system according to the invention. FIG. 4 is a diagram of an embodiment of the structure of the anti-lock function management module of the computer of the braking system.

FIG. 5 is a diagram of an embodiment of a pre-processing embodiment block implemented in the anti-lock function management module of the braking system computer.

FIG. 6 is a diagram of an embodiment of a storage sub-block implemented in the pre-processing embodiment block.

Figure 7 is a diagram of an embodiment of a sub-block determining whether the vehicle is cornering and implemented in the embodiment block of pre-treatments. FIG. 8 is a diagram of an embodiment of a sub-block defining a parameter determining the intensity value of the braking action upon entering a loop mode. closed, this sub-block being implemented in the embodiment block of pre-treatments. FIG. 9 is a diagram of an embodiment of a block for managing the operation of the closed loop regulation of the braking system implemented in the management module of the anti-lock function of the computer of the braking system. FIG. 10 is a diagram of an embodiment of a sub-block defining the intensity value of the braking action when entering a closed loop mode, this sub-block being set to operates in the management block of the operation of the closed-loop regulation of the braking system.

Figure 11 is a time chart of changes in the speed of the vehicle, the speed of a wheel of a vehicle equipped with the braking system according to the prior art and the braking torque applied to this wheel. FIG. 12 is a temporal graph of changes in the speed of the vehicle, the speed of a wheel of a vehicle equipped with the braking system according to the invention and the braking torque applied to this wheel.

The braking device 9 shown in FIG. 1 comprises a braking control member 1, advantageously a brake pedal equipped with a position sensor making it possible to detect and measure the depression of the pedal by a driver. This measure is likened to a braking will of the driver. At the output, the braking command 1 sends a braking command signal, this signal comprises for example the position of the braking control member. The braking device MS \ REN093FR.dpt 20 also comprises four brake calipers 5a, 5b, 5c and 5d which, in the present embodiment, are electromechanical braking calipers receiving brake force intensity instructions to be applied to the brake. each wheel. The stirrups described are electromechanical, however they can also be of another technology such as electrohydraulic technology. The braking device further comprises a computer 3, the function of which is to develop the intensity instructions of the braking action to be sent to each caliper (5a, 5b, 5c and 5d) from the brake control signal. . Each brake caliper can also be associated with a dedicated computer responsible for developing the intensity instruction of the braking action of the caliper considered. The braking system according to the invention is preferably mechanical decoupling, that is to say that no mechanical action exerted on the brake control member is transmitted to the wheels to brake them. The braking action intensity settings may comprise a braking intensity value such as a braking torque value at the level of the wheel considered. Alternatively, the braking action intensity settings may include any other value corresponding to or capable of being reduced to a braking action intensity such as a pinch force value of a brake disk or an electric supply value. an electromechanical caliper.

On the basis of the signals transmitted to the computer 3 (or the computers), the latter develops, by means of hardware and / or software contained in the computer, a braking command signal. This signal comprises a set value of intensity of the braking action to be implemented by the stirrups or stirrups. Thus, the computer comprises hardware and / or software means for implementing the braking method according to the invention and, therefore, hardware and / or software means for implementing a method of operating the braking system according to the invention. the invention. These means may comprise the blocks and sub-blocks illustrated in FIGS. 4 to 10 and described below. The calculator includes calculating means for MS \ REN093FR.dpt

7 calculating a set value of intensity of the braking action to be implemented by the stirrups and calculating the evolution over time of this setpoint value. The software means may comprise computer programs.

In the method according to the invention and therefore in the braking system according to the invention, the intensity of the braking action applied to the wheels can be controlled according to the case, in the most appropriate manner: in a loop mode open, that is to say without feedback loop 10 correcting the setpoint or in a closed loop mode, that is to say using a regulation with a feedback loop acting on the setpoint value.

The advantages of closed loop mode are: simplicity and robustness to system uncertainties; they make it possible to reject the disturbances of the system (adhesion variations, tire stiffness variations, for example), to directly propose nominal setting parameters which guarantee margins of stability to the system, to calculate these parameters easily from the physical characteristics of the vehicle, the use of a Proportional Integral type structure which is not very greedy in terms of calculation time and is well controlled, the management of the saturations of the control which is taken into account at the level of the control by well known devices (antiwindup).

The advantages of the open-loop mode are: - a good control of the torque up-up speed in the phases where the wheel is not locked, MS \ REN093EN.dpt the independence of this speed of torque rise vis- With respect to the dynamic adjustment of the closed-loop mode, the fact that the second slope (called the low slope in the following) constitutes the main adjustment parameter, it can be easily connected to the estimated adhesion between the wheel and the ground: indeed, it is desired to increase the braking torque faster on high adhesion than on low adhesion; this mode therefore preferably uses an estimated grip of the wheel.

The computer 3 comprises an ABS module 10 shown in Figure 2 and providing an anti-lock function of the wheels of the motor vehicle. Such a module comprises five inputs and two outputs. The inputs receive: a braking torque request signal from the driver's will (for example from the measurement of the position of a brake pedal), denoted T ABS in (for example expressed in Nm), a signal vehicle speed along the longitudinal axis (x axis) noted V VH x East (for example estimated and expressed in m / s). This speed signal can be developed by different techniques from four vehicle wheel speed sensors, a rotational speed signal of the wheel, the speed being for example measured by a sensor placed on the wheel, expressed in rad / s and noted Omega, a braking torque signal actually controlled at the wheel and noted T abs out eff: in fact, other devices are likely to change the control from the ABS module, a signal level of adhesion the wheel coming for example from another module internal to the computer and noted adherence level: the signal may comprise a two-state logic variable (by convention, it can be: 0 in case of low adhesion and 1 in case of strong adhesion ). MS \ REN093FR.dpt As main output: a signal of intensity of the braking action to be applied at the wheel wheel ABS T, this signal is for example a braking torque signal expressed in N.m. One can also output an activity indicator signal from the Flag ABS active wheel anti-lock function.

The basic principle of operation of the ABS module is: 10 - to compare the speed of the Omega wheel to the vehicle speed VVHxEst, if the wheel locks, to decrease the braking torque T ABS wheel, if the wheel is not more secure, to re-increase the braking torque, without however exceeding the torque required by the driver 15 T ABS in.

The graph in Figure 3 recalls the principle of ABS regulation based on a two-mode strategy mentioned above.

The so-called closed-loop mode makes it possible to reduce the braking torque with the aid of a PI (Integral Proportional) corrector in order to avoid the phenomenon of blockage of the wheel.

The so-called open loop mode makes it possible to re-increase the braking torque by following a ramping pace in order to brake the vehicle as much as possible (according to the request of the driver).

The first two steps start blocking noted 1 in Figure 3 and confirmed_block_ noted 2 in Figure 3 correspond to the closed loop mode. The following two steps of adhesion recovery noted 3 MS \ REN093FR.dpt5 in Figure 3 and wheel_non_bloquée noted 4 in Figure 3 correspond to the open loop mode.

Step 1: When the speed of rotation of the wheel falls below the value Threshold1, the anti-lock function becomes active. This state is named debut_lock. The regulation is in closed loop. The braking torque begins to be reduced to limit the slippage of the wheel.

Step 2: Despite the action of the closed-loop control, the speed of rotation of the wheel continues to decrease and becomes lower than the speed Only / 2. The braking torque therefore logically continues to be decreased. The regulation remains closed loop. This state is called blocking. After a certain time (depending on the level of adherence and the vehicle speed), the wheel is again driven in rotation and the speed of rotation of the wheel increases.

Step 3: When the speed of rotation of the wheel becomes greater than the value Threshold2, it means that the wheel is in the recovery phase, and thus the braking torque can, again, be increased. The braking system switches to open loop mode. Thus, the torque is increased. This state is named recovery_adherence.

Step 4: When the speed of rotation of the wheel becomes greater than the speed Threshold1, the wheel is no longer considered blocked; the braking torque continues to be increased (always with a ramp) to reach the braking torque desired by the driver or to reduce the sliding of the wheel around the value that maximizes the braking force.

According to the braking method which is the subject of the invention, the intensity reference of the braking action is abruptly reduced at each entry into the closed loop mode MS \ REN093FR.dpt. This decrease is also called future anticipatory action.

An embodiment of the ABS module 10, making it possible to implement an embodiment of the braking method according to the invention, is described with reference to FIG. 4. It comprises five blocks 11 to 15.

Block 11 allows preprocessing and is itself composed of six sub-blocks 111 to 116 as shown in FIG.

A sub-block 111 outputs an Omega signal which corresponds to the derivative of the Omega wheel speed signal, filtered by a first-order low-pass filter to reduce measurement noise. The time constant of the filter is denoted CABS Tau Filter dWr and is for example 0.020 s.

A sub-block 112 outputs an ABS start signal which is a logic signal that is set to 1 during a sampling period when the anti-lock wheel function is activated. This signal is thus developed from the ABS wheel non-active signal developed in the block 12 described below. A sub-block 113 outputs a pass signal BF which is a logic signal which has the value 1 during a sampling period when switching from open loop mode to closed loop mode. This signal is thus developed from the stimulus signal 80 developed in the block 12 described below. A sub-block 114, shown in FIG. 6, stores, in the variable T Brk t blocking, the braking action intensity instruction actually sent to the brake caliper at the instant of the first activation of the brake. anti-blocking function and at each passage in closed-loop mode (that is to say at the beginning of blocking of the wheel). The elaborated greatness

It is very important since it is from this value that the braking action intensity setpoint which is applied when switching to the closed loop mode is defined.

A sub-block 115 comprising a filter 115a and a calculation block 115b, shown in detail in FIG. 7, determines the situation of the vehicle, namely whether or not there is a corner. It develops a Status Virage signal that takes three values: Status Turn = 1: the vehicle moves in a straight line, Status Turn = 2: the vehicle turns left, Status Turn = 3: the vehicle turns right.

The information used to develop this signal is the lateral acceleration of the vehicle noted Acc VH y_Est in Figures 5 and 7, which may come from a sensor (conventionally available in a vehicle). Alternatively, it would be possible to use steering wheel angle information that is very often available in current vehicles, this information preferably being combined with longitudinal vehicle speed information. The signal is first filtered by the first order low-pass filter 115a to reduce measurement noise. The time constant of this filter is noted Tau Filter Acc VH y and is for example 0.100s. An example of a computer embodiment of the block 115b is given in FIG. 7. The Status Virage signal is for example simply obtained by comparison with an acceleration threshold denoted threshold Acc Y turn: if the acceleration is greater than threshold Acc Y turn then Status Virage = 2, if the acceleration is lower than -Seuil Acc Y turn then Status Virage = 3, otherwise Status Virage = 1.

MS \ REN093FR.dpt A sub-block 116 determines the anticipation parameters, that is to say the parameters that are a function of the vehicle running situation and used to calculate the braking action intensity setpoint value. when switching to closed loop mode.

It is known in particular that in turns there are transverse load reports caused by transverse acceleration. As a result, the inner wheel at the turn is unloaded (it bears less vertical force) while the outer wheel is more loaded. Therefore, during cornering braking, the inner wheel will lock much faster than the outer wheel for the same braking action. To improve the behavior of the braking system, it is therefore necessary to reduce more strongly the braking action intensity setpoint for an inner wheel than for an outer wheel. Thus, a greater anticipatory action is applied for the inner wheel than for the outer wheel.

FIG. 8 shows an exemplary embodiment of this sub-block, which outputs the anticipatory action to be performed, in the form of a ratio, denoted 20 FF Ratio T BRK Action.

Thus, three adjustment parameters are available: • ABS Ratio T BRK: This is a ratio that determines the value of the anticipating action that will be applied in a straight line when switching to closed loop mode (therefore at each start of wheel lock). If the vehicle moves in a straight line, all four wheels will have the same ratio value: FF Ratio T action BRK = C ABS Ratio T BRK MS \ REN093EN.dpt • C ABS Ratio Reduct Turn T BRK: This is a decreasing value the ratio C ABS Ratio T BRK for the case where the wheel is considered as the inner wheel. This inner wheel will then have the ratio: FF Action Ratio T BRK = C ABS Ratio T BRK - CABS Ratio Reduct Turn T BRK • C ABS_Ratio Augment_Virage_T_BRK: This is a value increasing the ratio C ABS Ratio T BRK for the case where the wheel is considered the outer wheel. This outer wheel will then have the ratio: FF Ratio T BRK = C ABS Ratio T BRK - CABS Ratio Augment Vira T BRK

Block 12 already mentioned above makes it possible to elaborate the following signals: Name Type Description Relance_BO Boolean True: indicates that one is in the open-loop mode, False: indicates that one is in the closed-loop mode. ABS_roue_non_actif Boolean False: indicates that the anti-lock function is active (the braking torque is effectively reduced on the wheel), True: indicates that the anti-lock function is inactive. Flag_first cycle Boolean True: indicates that the ABS module is in the first control cycle, False: indicates that the ABS module is no longer in the first control cycle. Status_ABS_ij Integer Indicates the status of the controller. This variable is not functional here but is used to debug the system.

A block 13 develops the closed loop braking action instruction. It is described in detail below.

A block 14 develops the open loop braking action instruction. The open loop corresponds to situations where the wheel is no longer locked and MS \ REN093FR.dpt so we can allow the braking torque to grow again. In a simplified manner, the principle adopted is to achieve a rise in torque in following predefined gaits. The output signal of this block is C ABS BO.

A block 15 performs a referral instructions developed by the blocks 13 and 14 blocks depending on the situation in which the motor vehicle is. Indeed, according to this situation, it is either the command elaborated by the block 13, or that elaborated by the block 14 which is used. A logic block 151 has at the output a quantity C abs wheel ns equal to C abs BO if the stimulus magnitude BO is in the high state and equal to c abs BF in the opposite case. The value of the magnitude C abs wheel ns is then saturated by a block 152 which limits the signal between a minimum value 0 (complete suppression of the braking) and the signal T abs in (in no case can the block 152 deliver a pair of braking higher than that requested by the driver).

Block 13 may comprise two sub-blocks 131 and 132 as shown in FIG. 9.

The first sub-block 131 corresponds for example to a Proportional Integral corrector with an anti-saturation means. It comprises five inputs: Err PI ABS: it is an error signal, it corresponds to the difference between the quantity to be regulated (that is to say the threshold quantity2 illustrated in FIG. 3 corresponding to a reasonable slip of the wheel) and the wheel speed (denoted Omega), U eff Pl: it is the intensity of the braking action, in particular the braking torque, actually sent to the brake caliper at the time of previous sampling; this quantity serves the anti-saturation means; indeed the torque actually sent to the brake caliper MS \ REN093FR.dpt may be different from that defined in the ABS module because of saturation, OU PI: it is the initial value setpoint issued by the corrector (at each activation of the anti-blocking function) and which will allow anticipatory action; this value is elaborated by the block 132 which is described below, Init Pl: it is a Boolean signal which is equal to 1 when the anti-lock function is activated and therefore the corrector must perform the anticipatory action. It is calculated from the signals beginning ABS and passage_BF elaborated in the block 11. This signal is true: when the signal starts ABS is 1 or when the passage signal BF is 1. Param_ABS_ij: this signal corresponds to a vector of parameters of the corrector (the proportional gain and the integral gain).

The second sub-block 132 is described below with reference to FIG. 10. This sub-block generates the signal UO PI mentioned previously. The sub-block has four entries: T BRK t blocking: the value evoked previously and elaborated in the sub-block 114, Flag First Cycle: it is a flag (boolean) elaborated in the block 12, level adherence: it is a flag (Boolean) that comes from another module responsible for evaluating the grip level of the wheel in question (not described here). In an exemplary embodiment of such a module, the adherence level indicator takes the value: o 0, when the adhesion is evaluated as low (adhesion less than 0.5 for example) and o 1, when the adhesion is evaluated strong (adhesion greater than 0.5 for example). MS \ REN093FR.dpt FF Action Ratio T BRK: the value mentioned previously and elaborated by the sub-block 116. It defines the anticipatory action, in the form of a ratio (between 0 and 1).

The function performed is as follows: If we are in a situation of low adhesion and we are in the first cycle of regulation ABS, then we know that the anticipatory action must be very strong; Indeed, in case of emergency braking (very fast pedal support) and low grip, the wheel locks very quickly because it requires a braking torque very above what is acceptable given the grip . This is true only when activating the anti-lock function (when Flag first cycle is TRUE), because then, in regulation, the braking torque is slaved to a value close to that which is admissible. In this situation (low adhesion and first activation cycle of the anti-blocking function), the anticipatory action is: UO Pl = Action FF Ratio T BRK_premier cycle. T BRK t lock Action FF Ratio T BRK first cycle is the value of the anticipating action (in the form of ratio) and is a setting parameter of the braking process. In other situations, (strong adherence or steady state of the anti-blocking function), the anticipatory action is: UO Pl = Action FF Ratio T BRK. Preferably, the braking action intensity setpoint sent to the brake caliper undergoes a discontinuity when switching from the open loop mode to the closed loop mode and when the control function is activated. anti-blocking where we pass for the first time in closed loop mode, this discontinuity to reach the UO_PI value. Alternatively, the value changes continuously but suddenly to reach the value UO_PI MS \ REN093FR.dpt with a rate of variation greater than 300 N.m.sup.-2 and preferably greater than 600 N.m.sup.-2.

Figure 11 shows an example of a result obtained from a low traction track test. The test corresponds to an emergency braking at 70 km / h to a standstill. The curves of braking torque, wheel speed and longitudinal speed of the vehicle are shown. This test is carried out with a vehicle equipped with a braking system known from the prior art.

FIG. 12 shows an example of a result obtained under the same conditions with a vehicle equipped with a braking system according to the invention. FIG. 12 clearly shows the improvement in the operation of the braking system since the starts in wheel lock are smaller in FIG. 12 than in FIG. 11. The anticipatory action is clearly visible in FIG. 12 at the moments of passage. in a closed loop, the braking torque decreases abruptly, which avoids too much blockage of the wheel.

The braking method according to the invention reveals variables allowing the developer to fine-tune the adjustment of the braking system.

The term cycle is used in the description. By cycle 25 is meant an alternation of the closed loop operating mode and the open loop operating mode. MS \ REN093FR.dpt

Claims (9)

Claims: 1 A method of braking a motor vehicle comprising the application of a braking action on at least one wheel of the motor vehicle, comprising a first operating mode in which an intensity instruction of the action of closed-loop braking, characterized in that, after entering the first operating mode, the set value of the intensity of the braking action is abruptly reduced to reach a first value. Braking method according to claim 1, characterized in that, after entering the first operating mode, the rate of change of the set value of the intensity of the braking action is at least 300 Nms- 'and preferably at least 600 Nms'. 3. Braking method according to claim 1 or 2, characterized in that the first value is defined from the value of the intensity of the braking action applied to the wheel just before entering the first mode. operation. 20 4. Braking method according to one of the preceding claims, characterized in that the first value is, all things being equal, different according to the transverse acceleration experienced by the motor vehicle. 5. A method of braking according to one of the preceding claims, characterized in that the first value is, all things being equal, different according to the adhesion of the wheel on the ground. 30 6. A method of braking according to one of the preceding claims, characterized in that the first value is, all things being equal, different depending on whether it is a first pass in the first MS 21 REN093FR.dpt 19 25 operating mode since the activation of the anti-lock function or that it is a subsequent changeover in the first operating mode. 7. Support (3) data comprising software means for implementing the braking method according to one of the preceding claims. 8. System (9) for braking a motor vehicle comprising means (5a, 5b, 5c, 5d) for applying a braking action on at least one wheel of the motor vehicle, characterized in that it comprises material means (1, 3, 10, 11, 12, 13, 14, 15) and / or software for implementing the braking method according to one of claims 1 to 6. 9. Motor vehicle comprising a braking system according to claim 8. MS \ REN093FR.dpt