Methods for providing haptic information to the driver of a motor vehicle

Abstract

A method for providing haptic information to the driver of a motor vehicle equipped with a brake-by-wire braking system about the operating state of the braking system, in which the brake pedal characteristic, in the form of a functional relationship between brake pedal resistance and brake pedal travel, is generated by a simulator and modified depending on the operating state, wherein a basic brake pedal characteristic is generated by means of a passive simulator spring, which assigns a pedal travel to a given pedal force in a constant relationship, to which a pedal return travel conveying the haptic information is superimposed, wherein the superimposition of the haptic information is reversible, so that after its termination or deactivation the basic brake pedal characteristic is automatically restored without any intervention, wherein the superimposition of the haptic information consists of time-limited individual events.which are perceptible to the driver as pedal return pulses, characterized in that a disconnect valve (23b) of a hydraulic brake-by-wire braking system is temporarily opened to generate a pulse, wherein the disconnect valve (23b) is permanently energized and thus closed during normal active operation.

Description

[0001] The present invention relates to a method for providing haptic information to the driver of a motor vehicle equipped with a brake-by-wire braking system about the operating state of the braking system, in which the brake pedal characteristic in the form of a functional relation between brake pedal counterforce and brake pedal travel is generated by a simulator and modified depending on the operating state, as well as a device for carrying out the method according to the invention.

[0002] Document DE 34 09 705 A1 discloses a method for providing feedback on disturbances or errors during a braking process, in which a fault response actuator acts on the brake pedal travel simulator in such a way that a change in the brake pedal characteristic specified by the brake pedal travel simulator occurs and persists until the intended function of the by-wire system is available again. It is further proposed to preferably modify the brake pedal characteristic so that a rhythmic pulsation of the brake pedal results. For this purpose, an electromagnetic actuator controlled by the pulsating signal of an electronic oscillator circuit is to engage, via a locking lug, in a mechanism with which the simulator characteristic can be modified. The locking lug is designed to engage with a sliding element to form a locking connection, on which a spring is supported, through which a portion of the pedal force is transmitted.No technical instruction is given on how to generate a pulsation of the brake pedal by means of periodic activation of the locking mechanism. To enable periodic pedal movement, any additional pedal travel that has been released must be reversible. A corresponding pedal actuator and its power supply would therefore need to be added.

[0003] German patent application DE 10 2006 026 873 A1 describes an actuating device for a by-wire braking system. To provide the driver with haptic feedback regarding low traction or friction at the vehicle wheels or ABS activation, the brake pedal shaft is equipped with an electric, hydraulic, or pneumatic rotary actuator that generates pulsations at the brake pedal. The amplitude of these pulsations can be varied between approximately 0 mm and 5.0 mm, and their frequency between approximately 1 Hz and 10 Hz.

[0004] Finally, a method with the features specified in the preamble of claim 1 and a device for carrying out the method are known from document DE 10 2004 040 616 A1. An active pedal travel simulator generates a counterforce that opposes the actuating force exerted by the driver's foot on the brake pedal, in such a way that the driver perceives this as a limitation of comfort and / or function of the braking system. Such a limitation of comfort, as well as a perceived limitation of function, is unacceptable if the driver is to be informed about the operating status of an intact braking system.

[0005] WO 2012 / 028 568 A1 shows an actuation module for a braking system with increased operational safety. For this purpose, a simulator device has movable walls that are rigidly mechanically coupled to each other.

[0006] German patent DE 103 46 674 A1 discloses a braking system in which the driver receives haptic feedback when there is a deviation from a predefined brake pedal characteristic. However, this haptic feedback requires additional valves, which are located in various lines of the braking system.

[0007] It is therefore an object of the present invention to propose a method which, in particular using simple electronic means, provides a haptic information channel via which information can be communicated to the driver during braking in an electronically controlled manner, without giving the impression of a defect.

[0008] This problem is solved according to the invention by a method according to claim 1. It is particularly advantageous that components of the brake-by-wire braking system, which are already present for the intended operation of the braking system, are predominantly used to apply the counterforce.

[0009] Advantageous further developments of the method according to the invention are specified in dependent claims 2 to 15 and also result from the following description with reference to figures.

[0010] The figures show: Fig. 1 a hydraulic circuit diagram of an exemplary brake system for carrying out the method according to the invention, Fig. 2 the braking system after Fig. 1 in a first state to illustrate the method according to the invention, and Fig. 3 the braking system after Fig. 1 in a second state to illustrate the method according to the invention.

[0011] The brake system shown in the drawing essentially comprises a hydraulic actuating unit 2 which can be actuated by means of an actuating or brake pedal 1, a travel simulator or simulation device 3 which interacts with the hydraulic actuating unit 2, a pressure medium reservoir 4 associated with the hydraulic actuating unit 2 which is at atmospheric pressure, an electrically controllable pressure supply device 5, an electronic control and regulation unit 12 and an electrically controllable pressure modulation device for setting individual brake pressures.

[0012] The unspecified pressure modulation device comprises, for example, an inlet valve 6a-6d and an outlet valve 7a-7d for each wheel brake 8, 9, 10, 11 of a motor vehicle not shown. These valves are hydraulically connected in pairs via center connections and are attached to the wheel brakes 8, 9, 10, 11. The inlet ports of the inlet valves 6a-6d are supplied with pressures via brake circuit supply lines 13a, 13b. In a "brake-by-wire" operating mode, these pressures are derived from a system pressure present in a system pressure line 38 connected to a pressure chamber 37 of the electrically controlled pressure supply device 5. A check valve 50a-50d, opening towards the brake circuit supply lines 13a, 13b, is connected in parallel to each inlet valve 6a-6d.In an unamplified fallback operating mode, the brake circuit supply lines 13a, 13b are pressurized via hydraulic lines 22a, 22b with the pressures of the pressure chambers 17, 18 of the actuating unit 2. The outlet ports of the discharge valves 7a-7d are connected in pairs via return lines 14a, 14b to the pressure medium reservoir 4. A pressure sensor 19, preferably redundant, is provided to detect the pressure prevailing in the system pressure line 38.

[0013] The hydraulic actuation unit 2 comprises two pistons 15, 16 arranged one behind the other in a housing 21, which define hydraulic chambers or pressure spaces 17, 18. These chambers, together with the pistons 15, 16, form a dual-circuit master brake cylinder or a tandem master cylinder. The pressure spaces 17, 18 are connected, on the one hand, to the hydraulic fluid reservoir 4 (via the return line 14a or 14b) via radial bores formed in the pistons 15, 16 and corresponding pressure equalization lines 41a, 41b. These connections can be shut off by a relative movement of the pistons 17, 18 in the housing 21. On the other hand, they are connected, via hydraulic lines 22a, 22b, to the aforementioned brake circuit supply lines 13a, 13b. The pressure equalization line 41a includes a parallel connection of a normally open (SO) diagnostic valve 28 with a check valve 27 closing towards the pressure medium reservoir 4.The pressure chambers 17, 18 accommodate unspecified return springs that position the pistons 15, 16 in a starting position when the master brake cylinder 2 is not actuated. A piston rod 24 couples the pivoting movement of the brake pedal 1 resulting from pedal actuation with the translational movement of the first (master cylinder) piston 15, the actuation travel of which is detected by a displacement sensor 25, preferably a redundant one. The corresponding piston travel signal is thus a measure of the brake pedal actuation angle. It represents a driver's braking request.

[0014] In each of the line sections 22a, 22b connected to the pressure chambers 17, 18, a shut-off valve 23a, 23b is arranged, which is designed as an electrically actuated, preferably normally open (SO), 2 / 2-way valve. The shut-off valves 23a, 23b allow the hydraulic connection between the pressure chambers 17, 18 and the brake circuit supply lines 13a, 13b to be shut off. A pressure sensor 20 connected to line section 22b detects the pressure built up in pressure chamber 18 by the movement of the second piston 16.

[0015] The travel simulator 3 can be hydraulically coupled to the master brake cylinder 2 and essentially consists of a simulator chamber 29, a simulator spring chamber 30, and a simulator piston 31 separating the two chambers 29 and 30. The simulator piston 31 is supported on the housing 21 by an elastic element (e.g., a spring) arranged in the simulator spring chamber 30, which is advantageously pre-tensioned. The simulator chamber 29 can be connected to the first pressure chamber 17 of the tandem master brake cylinder 2 by means of an electrically actuated simulator release valve 32. When a pedal force is applied and the simulator release valve 32 is activated, hydraulic fluid flows from the master brake cylinder pressure chamber 17 into the simulator chamber 29.A check valve 34 arranged hydraulically antiparallel to the simulator release valve 32 allows a largely unimpeded backflow of the pressure medium from the simulator chamber 29 to the master brake cylinder pressure chamber 17, regardless of the switching state of the simulator release valve 32.

[0016] The electrically controlled pressure supply device 5 is designed as a hydraulic cylinder-piston arrangement or a single-circuit electrohydraulic actuator, whose piston 36 can be actuated by a schematically indicated electric motor 35 via a schematically depicted rotary-translational transmission. A rotor position sensor, also schematically indicated, for detecting the rotor position of the electric motor 35 is designated by reference numeral 44. Additionally, a temperature sensor can be used to sensing the temperature of the motor winding. The piston 36 defines a pressure chamber 37.

[0017] The actuator pressure generated by the force exerted by the piston 36 on the pressure medium enclosed in the pressure chamber 37 is fed into the system pressure line 38 and detected by the system pressure sensor 19. In "brake-by-wire" mode, the system pressure line 38 is connected to the brake circuit supply lines 13a and 13b via the switching valves 26a and 26b. During normal braking, this results in a build-up and release of wheel brake pressure for all wheel brakes 8, 9, 10, and 11. During pressure release, the pressure medium previously displaced from the pressure chamber 37 of the actuator 5 into the wheel brakes 8, 9, 10, and 11 flows back into the pressure chamber 37 of the actuator 5 via the same path. In contrast, during braking with individually variable wheel brake pressures regulated by the modulation valves 6a-6d, 7a-7d, the hydraulic fluid released via the outlet valves 7a-7d flows into the hydraulic fluid reservoir 4.A re-suction of pressure medium into the pressure chamber 37 is possible by retracting the piston 36 with the switching valves 26a, 26b closed, whereby pressure medium from the container 4 can flow into the actuator pressure chamber 37 via a re-suction valve 52 designed as a check valve opening in the flow direction towards the actuator.

[0018] The aforementioned components 2, 3, 5, 6a-6d, 7a-7d, 12, 19, 20, 22a, 22b, 23a, 23b, 25, 26a, 26b, 27, 28, 32, 34, 38, 41a, 41b, 44, 46, 52 are preferably combined to form an electrohydraulic module (electrohydraulic actuation unit) designated by reference numeral 60. The electronic control unit 12 is used to control the electrically actuated components of module 60, in particular the valves 6a-6d, 7a-7d, 23a, 23b, 26a, 26b, 28, 32 and the electric motor 35 of the pressure supply device 5. The signals from the sensors 19, 20, 25 and 44 are also processed in the electronic control unit 12.

[0019] In normal braking mode (brake-by-wire), the master brake cylinder 2, and thus the driver, is decoupled from the wheel brakes 8, 9, 10, 11 by the closed isolating valves 23a, 23b. The brake circuit supply lines 13a, 13b are connected via the open switching valves 26a, 26b to the first pressure supply unit 5, which provides the system pressure for actuating the wheel brakes 8, 9, 10, 11. The simulation unit 3 is activated by the open simulator release valve 32, so that the volume of hydraulic fluid displaced in the master brake cylinder 2 by the driver's actuation of the brake pedal 1 is absorbed by the simulation unit 3, and the simulation unit 3 provides the driver with a familiar brake pedal feel.

[0020] In a fallback operating mode of the braking system, e.g., in the event of a failure of the electrical power supply to the braking system, simulation device 3 is switched off by the normally closed simulator release valve 32, and the pressure supply device 5 is disconnected from the brake circuit supply lines 13a, 13b by the normally closed switching valves 26a, 26b. Master brake cylinder 2 is connected via lines 22a, 22b to the normally open isolating valves 23a, 23b and thus to the brake circuit supply lines 13a, 13b and therefore to the wheel brakes 8, 9, 10, 11, so that the driver can directly build up pressure in the wheel brakes 8, 9, 10, 11 by actuating the brake pedal 1.

[0021] In a simulator braking system (in "brake-by-wire" mode), pedal 1 is hydraulically decoupled from wheel brakes 8-11. Therefore, the pedal feedback unavoidable in conventional braking systems during wheel brake pressure control activities is absent. To nevertheless provide the driver with haptic pedal feedback in selected operating conditions, it is proposed, for example, to electronically control this pedal feedback and temporarily superimpose it on the pedal characteristics defined by the simulator (e.g., by a spring in compartment 30).

[0022] To implement a method for generating electronically controlled pedal feedback, at least one isolating valve (23a: isolating valve of the pressure circuit, 23b: isolating valve of the float circuit) is pulsed open. This directs a pressure medium volume pulse from the system pressure side (line 13a or 13b) of the isolating valve to the driver pressure side (line 22a or 22b) of the isolating valve, which generates the desired pedal pulsation.

[0023] Preferably, the method provides that the system pressure is increased (e.g. by means of the pressure supply device 5) if the pressure difference between system and main cylinder pressure is insufficient, non-existent, or negative.

[0024] Finally, the isolating valve 23b associated with the floating circuit is preferably used to generate the pedal feedback. This has the advantage that the additional volume of pressure medium introduced as a volume pulse, after it has fulfilled its function as a pedal pulse generator, is released again via the compensating connection 100 of the floating circuit towards reservoir 4, and therefore the steady-state pedal characteristic remains unchanged.

[0025] In Fig. 2 and Fig. 3 is the braking system of the Fig. 1 shown in different states. Fig. 2 and Fig. Figure 3 shows examples of volume flows and pressure conditions relevant to the function.

[0026] During normal braking without ABS and during ABS braking ("brake-by-wire" mode), a situation often arises similar to that described in... Fig. 2 shown. The system pressure P sys The pressure in system circuit 40 is higher than the driver's pressure P. Driverin driver pressure circuit 41, since the system pressure is usually increased many times over compared to the unamplified driver pressure.

[0027] Brake pedal feedback is generated by the isolating valve 23b, which is continuously energized and thus closed during normal active operation of the braking system. In active operation, the isolating valve 23b separates the driver pressure circuit 41 from the system pressure circuit 40, preventing brake fluid volume and pressure from flowing between the two circuits. Without the exemplary procedure described below for adjusting suitable haptic brake pedal feedback for the driver in an active braking system during ABS control, the driver would be disconnected from the active system pressure and the wheel pressure circuits even during ABS control and would receive no haptic feedback via the brake pedal 1. With today's conventional ABS / ESC braking systems (e.g.,(with vacuum brake booster and return pump) the driver feels the ABS pressure fluctuations due to return pump strokes and valve switching in the brake pedal 1 during an ABS control.

[0028] As already mentioned in connection with Fig. As mentioned in section 1, to generate haptic brake pedal feedback during ABS braking in an active braking system, a pressure or volume pulse ΔV 42 is preferably fed from the system pressure circuit 40 into the driver pressure circuit 41 by briefly opening the isolating valve 23b. This generates a force pulse on the floating piston 16, which transmits the force pulse via the first return spring located in the first pressure chamber of the master brake cylinder and the brake fluid in the first pressure chamber 17 to the first piston 15 via the pushrod 24 to the brake pedal 1 and thus to the driver's foot resting on it during braking. Thus, by briefly opening the isolating valve 23b, a pressure or volume pulse ΔV and consequently a force pulse is generated on the brake pedal 1 and the driver's foot. The driver therefore feels a force pulse in the foot, and the driver's foot is dynamically moved by a few millimeters.The pedal is moved by fractions of a millimeter because the counterforce to the driver's foot force exceeds the force impulse. This allows for haptic feedback via brake pedal 1 without altering the pedal's fundamental characteristics.

[0029] Preferably, the intensity of the force impulse is varied via the opening time of the separating valve 23b, since this determines the size of the volume pulse ΔV 42.

[0030] Furthermore, the frequency of the force impulses in the pedal is preferably varied by varying the pause time between the valve openings.

[0031] To make the haptic feedback suitable and subjectively plausible for the driver, the frequency and intensity of the feedback are preferably adjusted or varied appropriately.

[0032] According to a further development of the inventive method, the frequency and intensity of the brake pedal feedback are adapted to the frequencies and amplitudes of the wheel brake pressure modulations in the wheel pressure circuits.

[0033] For this purpose, the ABS pressure modulations on all wheel brakes are given priority.

[0034] Preferably, the frequency of the brake pedal feedback is chosen depending on the duration of one or more ABS pressure build-up cycles until the ABS pressure is released.

[0035] At a higher ABS control frequency of the pressures in the wheel pressure circuits of the active system, a higher frequency of volume pulses ΔV for brake pedal feedback is preferentially set. This results in a plausible correlation for the driver between the behavior of the vehicle / ABS control and the haptic pedal feedback.

[0036] From a driving dynamics perspective, it can be particularly valuable for the driver to know when the tires have reached their limit of grip on the road while braking, i.e., when the ABS engages. For example, on wet or wintry roads, the driver can determine the road surface friction coefficient (µ) by braking until the ABS engages, as this assessment is difficult to make visually and can vary considerably. Furthermore, this is useful for conveying the limit of grip to the driver when braking in a curve by indicating the ABS activation. Therefore, the haptic feedback from the brake pedal when the ABS engages can be especially important for the driver.For example, when ABS activation begins, the brake pedal feedback is activated at a relatively high frequency and with a suitable intensity to optimally communicate the ABS engagement to the driver. Similarly, when ABS activates during braking while cornering, the brake pedal feedback is also activated at a relatively high frequency and with a suitably high intensity.

[0037] This enables the driver to learn to associate the pulsation with the driving condition and thus be able to draw conclusions about the operating condition of his vehicle from the pedal behavior.

[0038] During ABS braking on surfaces with a low coefficient of friction µ or when the driver applies very high force to the brake pedal, a phenomenon similar to that described in [reference to a specific description of ABS function] can occur. Fig. The resulting state (pressure ratio) is shown in section 3. Here, the system pressure is P. Sys In system pressure circuit 40, the pressure is lower than the driver pressure P. Driverin driver pressure circuit 41. Thus, when the isolating valve 23b opens, a volume pulse ΔV 43 flows from driver pressure circuit 41 into system pressure circuit 40. Since the brake fluid volume flows pulse by pulse from driver pressure circuit 41 into system pressure circuit 40, the driver's foot force on the brake pedal would cause the floating piston 16, the primary piston 15, and therefore the brake pedal 1 to move further and sink in the direction of actuation. This could give the driver the unwarranted impression of a brake system defect. Furthermore, a sinking brake pedal in the event of a failure of the active system, i.e., a switch to the hydraulic fallback system (in which all solenoid valves are de-energized), could lead to a safety-critical condition of the vehicle, since with the brake pedal already depressed, little or no brake fluid volume would be available in the master cylinder as a reserve for the now active fallback system.

[0039] In the Fig. In the situation shown in Figure 3, the system pressure is therefore preferably increased (by means of the pressure supply device) above the driver's pressure. The system pressure is thus not maintained at the level of the highest ABS wheel pressure requirement, but rather increased above the driver's pressure to achieve a volume flow, as shown in Figure 3. Fig. 2 shown, to achieve from the system pressure circuit 40 to the driver pressure circuit 41 and thus prevent the brake pedal 1 from sinking.

[0040] One advantage of the invention is that no additional actuators, such as an additional actuator in the pedal simulator unit or on the brake pedal, are required for the haptic brake pedal feedback function. The function is demonstrated in the exemplary system shown. Fig. 1. Can be implemented purely via software.

Claims

[1] Method for providing haptic information to the driver of a motor vehicle equipped with a brake-by-wire braking system about the operating state of the braking system, wherein the brake pedal characteristic in the form of a functional relation between brake pedal resistance and brake pedal travel is generated by a simulator and modified depending on the operating state, wherein a basic brake pedal characteristic is generated by means of a passive simulator spring which assigns a pedal travel to a given pedal force in a constant relation, to which a pedal return travel conveying the haptic information is superimposed, wherein the superimposition of the haptic information is reversible, so that after its termination or deactivation the basic brake pedal characteristic is automatically restored without any actuator intervention, wherein the superimposition of the haptic information consists of time-limited individual events,which are perceptible to the driver as pedal return pulses, characterized by , that to generate a pulse a separating valve (23b) of a hydraulic brake-by-wire brake system is temporarily opened, wherein the separating valve (23b) is permanently energized and thus closed during normal active operation. [2] Method according to claim 1, characterized by , that several pedal return pulses are sequentially arranged in time, resulting in a periodic pedal pulsation superimposed on the basic brake pedal characteristic. [3] Method according to claim 2, characterized by , that the frequency, intensity and pause duration of the periodic pedal pulsation are selected depending on the operating state of the braking system and the vehicle. [4] Method according to claim 3, characterized by , that the frequency and intensity of the brake pedal feedback are chosen depending on parameters of a wheel brake pressure modulation such as control frequency, intensity and duration. [5] Method according to claim 4, characterized by , that at the beginning of a wheel brake pressure modulation a higher frequency of pedal pulsation is chosen than in its further course and that when cornering the intensity of the pulsation is additionally increased. [6] Method according to claim 5, characterized by that the assignment of frequency and intensity of the periodic pedal pulsation to the operating state of the vehicle and braking system is chosen reproducibly. [7] Method according to claim 1, characterized by , that to generate a pulse before opening the isolating valve (23b) the by-wire brake system pressure is increased. [8] Device for carrying out the method according to any one of claims 1 to 7, characterized by, that the brake-by-wire braking system is hydraulically equipped for operation in a brake-by-wire mode as well as for operation in another, non-electronic mode with direct hydraulic transmission from the brake pedal (1) to the wheel brakes (8 - 11). [9] Device according to claim 8, characterized by , that pedal force and simulator spring force as well as pedal travel and simulator spring travel are coupled together via a first hydraulic circuit in brake-by-wire operating mode. [10] Device according to claim 8 or 9, characterized by , that the pedal return path superimposed on the basic brake pedal characteristic is generated by means of a second hydraulic circuit. [11] Device according to any one of claims 8 to 10, characterized by , that the first and second hydraulic circuits are assigned to the two pressure chambers (17, 18) of a tandem master brake cylinder (2). [12] Device according to any one of claims 8 to 11, characterized bya first and a second isolating valve (23a, 23b) with which the two pressure chambers (17, 18) of the tandem master brake cylinder (2) are separated from the wheel brakes (8 - 11) in brake-by-wire mode, as well as a device (5) for providing the by-wire brake system pressure and pressure medium volume and wheel brake pressure control devices (6a - 6d; 7a - 7d) for generating wheel-individual wheel brake pressures from the brake system pressure.

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