Methods for operating automobile brake systems, control devices, brake systems

Abstract

The present invention relates to a method for operating a brake system (1) of a motor vehicle (2), the brake system (1) having an operationally controllable brake force booster (4) and a brake pedal (3), the brake force booster (4) being operationally controlled to generate hydraulic pressure in the brake system (1) in response to actuation of the brake pedal (3), the method comprising monitoring the motor vehicle (2) for a stationary state of the motor vehicle (2), monitoring the actuation stroke of the brake pedal (3) for exceeding a predetermined limit value, and activating a hold function for maintaining the hydraulic pressure present in the brake system (1) upon recognition of the stationary state and exceeding the limit value, the method comprising determining at least one state variable of the motor vehicle (2), and determining the limit value in advance as a function of the at least one state variable.

Description

Technical Field

[0005]

[0001] The present invention relates to a method for operating a braking equipment of a motor vehicle, the braking equipment having an operable brake force multiplier and a brake pedal, the brake force multiplier being operably controlled to generate a hydraulic pressure of the braking equipment in response to an operation of the brake pedal, the motor vehicle being monitored for a stopped state of the motor vehicle, an operation stroke of the brake pedal being monitored for an exceedance of a predetermined limit value, and upon recognition of the stopped state and the exceedance of the limit value, activating a hold function for maintaining a hydraulic pressure existing within the braking equipment.

[0002] Furthermore, the present invention relates to a control device for implementing this type of method and a braking equipment provided with this type of control device.

Background Art

[0003] The method of the form mentioned at the beginning is known in the prior art. For example, in Patent Document 1, there is known a method for controlling a braking equipment of a vehicle having a Hillholder function for maintaining a brake force independent of an operation of a brake pedal by a vehicle driver, the method of turning on the function by applying an additional force to the brake pedal by a movement of the vehicle driver's foot (and thus an increase in an operation stroke of the brake pedal).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The method according to the present invention, having the features of claim 1, is characterized by determining at least one state variable of an automobile and predetermining a limit value according to at least one state variable. In this case, the state variable characterizes the hydraulic pressure required for holding, in particular when the hold function is activated. The state variable-dependent, i.e., variable limit value thus advantageously ensures that this hydraulic pressure is reliably achieved at all times. In other words, the minimum hydraulic pressure required to reliably hold the automobile is determined and adjusted when the hold function is activated. The automobile is reliably held at all times. Furthermore, this thus achieves protection of components, such as brake boosters, because unnecessarily high hydraulic pressures are not formed and maintained within the hydraulic circuit of the brake system. The brake booster, i.e., is no longer subjected to unnecessary load. Preferably, the hold function is deactivated when the limit value is exceeded again. This advantageously ensures that the status of the hold function can be changed or influenced by the driver at any time. Similarly, preferably additionally or alternatively, the driver's operation of the clutch pedal and / or accelerator pedal can also be used as a deactivation criterion for the hold function, thereby advantageously assisting the driver during starting. For this purpose, deactivation of the hold function is preferably carried out with a predetermined time delay or with a gradual release of hydraulic pressure.

[0006] According to a preferred evolution of the present invention, the vehicle weight of the automobile is determined as a state variable. By determining the vehicle weight as a state variable, it is advantageously guaranteed that the automobile will be reliably held by the hold function even under heavy loads, for example, when heavily loaded, i.e., when the total weight significantly exceeds the empty weight of the automobile.

[0007] Particularly preferable is the determination of the vehicle weight distribution per axle. Determining the vehicle weight distribution per axle provides a particularly advantageous possibility for distributing hydraulic pressure as needed to the wheel brakes assigned to each front or rear axle. In particular, higher pressure is applied to the wheel brakes of axles under heavier loads.

[0008] According to a preferred evolution of the present invention, at least one braking characteristic value (CP value) of the wheel brakes of the braking system is determined as a state variable. The braking characteristic value represents the ratio of the braking force to the required operating force of the wheel brakes and is generally expressed as a multiplier for the friction value of the brake lining of the wheel brakes. The friction value depends, for example, on the wear condition and / or temperature of the brake lining. Generally, each wheel of an automobile is assigned a unique wheel brake. Particularly preferably, the braking characteristic value is determined for each of these wheel brakes. By determining each braking characteristic value, it is advantageously ensured that the operating conditions, particularly the wear condition, of each wheel brake are taken into account. Thus, for example, a braking force that may be reduced is compensated by increasing the limit value so that the automobile is nevertheless reliably held when the hold function is activated.

[0009] Particularly preferably, the inclination angle of the vehicle relative to the horizontal is determined as a state variable. Determining the inclination angle provides the advantage that the vehicle can be reliably held regardless of surrounding conditions, especially on steep slopes. Here, horizontal is understood to be the direction perpendicular to the direction in which gravity acts. Generally, the greater the inclination of the vehicle, or the road on which the vehicle is located, the greater the hydraulic pressure required for reliable holding. Preferably, the inclination is determined by an inertial sensor. When the vehicle reaches a held state while moving uphill, a larger portion of the vehicle weight is loaded onto the rear axle than when the vehicle reaches a held state on level ground. Conversely, when the vehicle reaches a held state while moving downhill, a larger portion of the vehicle weight is loaded onto the front axle. Preferably, therefore, the direction of inclination with respect to the general direction of the vehicle's forward movement is also considered, and the hydraulic pressure is distributed to the axles as needed, as described above when determining the vehicle weight for each axle. Particularly preferably, for advantageous validation, the actual vehicle weight and its distribution for each axle are additionally determined.

[0010] According to a preferred evolution of the present invention, the tilt angle is determined in accordance with map data from the vehicle's navigation system. This allows the tilt angle to be determined particularly advantageously and easily without requiring additional sensors in the vehicle or the need to evaluate such sensor data. In particular, the vehicle's planned driving route is also taken into consideration, and consequently, the direction of the tilt with respect to the vehicle's general forward direction is also taken into consideration.

[0011] Particularly preferably, in order to adjust the hold function, the hydraulic pressure present in the brake system when the hold function is activated is increased by a predetermined value by a brake booster and maintained at that increased pressure. This provides a particularly advantageous possibility for recognizing the activation of the hold function. For example, the activation of the hold function can thus be recognized by monitoring the hydraulic pressure or its temporal changes, and / or can be notified to the driver of the vehicle, for example, visually or audibly, thereby allowing the assistance system to verify the appropriate activation signal from the control device responsible for activating the hold function. In this way, the assistance system is provided with a particularly advantageous reliability check in cases where, for example, the control device communicates that the hold function has been activated, but in reality it is not active, for example, due to a malfunction in the brake system. In this way, it is prevented that the driver will mistakenly release the brake pedal because they believe the hold function has been activated. If the brake pedal acts directly and mechanically on the piston of the main brake cylinder of the brake system, for example, together with a brake force booster, to change the hydraulic pressure, then as the hydraulic pressure increases, the brake pedal reaction force is reduced by the brake force booster, and the brake pedal sinks. The driver perceives this as tactile feedback, and as a result, the driver is confident that the hold function has been activated and can remove their foot from the brake pedal. If the brake system is configured as a "brake-by-wire" system where the brake pedal is not mechanically connected to the piston but only to a brake pedal force simulator, then as the hydraulic pressure increases, the brake pedal reaction force is preferably automatically reduced by the brake pedal force simulator. The activation of the hold function is indicated to the driver by the brake pedal, which again is indicated by the changed brake pedal force characteristics.

[0012] According to a preferred evolution of the present invention, after the hold function is activated, the hydraulic pressure within the brake system is kept constant even when the operating stroke of the brake pedal is further increased. This ensures particularly advantageous and sustained component protection for the components of the brake system. As described at the beginning, the variable limit value already determines and adjusts the minimum hydraulic pressure required to securely hold the vehicle. As long as the hold function is activated, any further increase in hydraulic pressure that would be unnecessary for the secure holding of the vehicle is not permitted, thus ensuring that, for example, the brake booster or other components of the brake system are not unnecessarily overloaded.

[0013] Particularly preferable is that the brake pedal is mechanically disconnected from the braking system, and that the hydraulic pressure is kept constant by not considering any further increase in the operating stroke of the brake pedal until the hold function is deactivated. This particularly advantageously achieves the aforementioned protection of the components. When the brake pedal is mechanically disconnected from the braking system, a so-called "brake-by-wire" type braking system exists. As already mentioned, in this case the brake pedal is only connected to a brake pedal force simulator, which determines the operating stroke of the brake pedal and transmits this to, for example, a control device to control the operation of the brake force booster. As long as the hold function is activated, this change in the operating stroke is not considered. Preferably, even if the operating stroke is increased, the pedal force simulator continues to provide brake pedal reaction force according to the operating stroke of the brake pedal, and as a result, the driver of the vehicle cannot perceive any unfamiliar change in the brake pedal characteristics. However, the brake force booster is no longer controlled to operate for any further increase in hydraulic pressure. This is because it is unnecessary for securely holding the car.

[0014] According to a preferred evolution of the present invention, the brake pedal is mechanically connected to the braking system to regulate the hydraulic pressure, and the brake booster is controlled to maintain a constant hydraulic pressure by compensating for the hydraulic pressure changes caused by the operation of the brake pedal. This also particularly advantageously achieves the aforementioned protection of the components. Because the brake pedal is mechanically connected to the braking system, when the operating stroke of the brake pedal is increased, the hydraulic pressure first rises. Here, a closed-loop control level is provided in which this rise is compensated by an equivalent reduction in the auxiliary force from the brake booster, such as an electromechanical brake booster. Thus, the driver cannot perceive any unfamiliar change in the pedal force characteristics, and at the same time, the braking system is advantageously protected from additional unnecessary loads. Alternatively, the brake booster is controlled only when the operating stroke exceeds a predetermined limit and / or increases for a predetermined duration, resulting in a small and / or short-term increase in hydraulic pressure, thus eliminating the need for control over every still very small change in the operating stroke. This also contributes to the protection of components.

[0015] Particularly preferably, after the hold function is activated, visual, auditory, and / or tactile confirmation is output, especially on a display device facing the driver of the vehicle. This has the advantage of providing the driver with timely information about the activation. The driver can then be confident that the hold function has been activated and remove their foot from the brake pedal.

[0016] The control device according to the present invention for an automobile brake system having the features of claim 12 is characterized in that the control device is configured to carry out the method according to the present invention. This results in the advantages already mentioned.

[0017] The brake system for automobiles according to the present invention, having the features of claim 13, comprises a controllable brake booster and a brake pedal, and is characterized by a control device according to the present invention. Preferably, the brake booster is formed as an electromechanical brake booster. Alternatively, the brake booster is formed as a negative pressure type or vacuum type brake booster and has a controllable vacuum pump. From this, the advantages already mentioned arise.

[0018] Further preferred features and combinations of features can be seen from the above description and claims. The present invention will be described in detail below with reference to the drawings. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram of the braking system. [Figure 2] This diagram shows how to operate the braking system. [Modes for carrying out the invention]

[0020] Figure 1 shows a schematic diagram of the brake system 1 of automobile 2. The brake system 1 includes a brake pedal 3, which is mechanically connected to a brake booster 4, for example, via an input rod (not shown in detail). The brake booster 4 is mechanically connected to the piston 5 of the main brake cylinder 6 of the brake system 1. The piston 5 is slidably supported within the main brake cylinder 6, as schematically indicated by the bidirectional arrow 7. Hydraulic fluid 8 is present within the brake system 1, particularly within the main brake cylinder 6, and in the pipelines extending from the main brake cylinder 6.

[0021] The braking equipment further comprises four wheel braking devices 9, and each wheel braking device 9 is assigned to one wheel 10 of the motor vehicle 2 respectively. Each of the wheel braking devices 9 has a slave cylinder not shown in the figure, and the slave cylinder is fluid-technologically connected to the master brake cylinder 6. In order to operationally control the brake force multiplier device 4, the braking equipment further comprises a control device 11, and the control device 11 is communicatively connected to the brake force multiplier device 4.

[0022] The control device is formed to operationally control an operating device not shown in the figure of the brake force multiplier device 4 to move the piston 5. In this case, the brake force multiplier device 4 is particularly formed as an electromechanical brake force multiplier device. The operating device is an electric motor in this case, and the electric motor is mechanically connected to the piston 5 via, for example, a transmission mechanism so that the piston 5 slides when the electric motor is operationally controlled.

[0023] Alternatively, the brake force multiplier device 4 is formed as a vacuum brake force multiplier device and has a vacuum pump as an operating device. By suitable operation control of the vacuum pump, the negative pressure between the two diaphragms of the vacuum brake force multiplier device can be adapted so that the piston 5 mechanically connected to one of the diaphragms slides.

[0024] When the piston 5 slides or moves there, as a result, the volume in the master brake cylinder 6 is reduced, and thereby the hydraulic liquid 8 is pumped from the master brake cylinder 6 into the slave cylinder of the wheel braking device 9. That is, the hydraulic pressure in the braking equipment 1 acts on the wheel braking device 9 via the slave cylinder, and as a result, the wheel braking device 9 is operated.

[0025] Normally, the piston 5 is moved by an operating device in response to the operation of the brake pedal 3 by the driver of the motor vehicle 2. The driver has to apply a brake pedal force to the brake pedal 3 in order to overcome the brake pedal reaction force, which is particularly dependent on the hydraulic pressure in the braking equipment 1, for the operation of the brake pedal 3. The brake pedal force should be understood as meaning, in particular, the force required to pump the hydraulic liquid 8 from the master brake cylinder 6 into the slave cylinder.

[0026] The piston 5 can, however, also be moved independently of the operation of the brake pedal by an operating device. Based on the mechanical connection of the brake force multiplier device 4 to the piston 5 and the brake pedal 3, the brake pedal reaction force is reduced when the operation of the brake pedal 3 is constant. The corresponding brake pedal force is also reduced accordingly.

[0027] In order to ensure that the brake pedal 3 returns to its initial non-operated position again after the driver no longer applies the brake pedal force to the brake pedal 3, a return device, not shown in particular, is assigned to the brake pedal 3, which pushes the brake pedal 3 back to its initial position by means of a spring force. The spring force is, in this case, part of the brake pedal reaction force that the driver has to overcome when operating the brake pedal 3.

[0028] According to another exemplary embodiment not shown, the brake pedal 3 is alternatively only mechanically connected to a brake pedal force simulator, by means of which the brake pedal reaction force can also be adjusted independently of the hydraulic pressure in the braking equipment 1 in particular.

[0029] Regarding FIG. 2 below, an advantageous method for operating the braking equipment 1 of the motor vehicle 2 will be described. For this purpose, FIG. 2 shows this method in the form of a flowchart. In particular, by means of this method, it is ensured that the motor vehicle 2 is reliably held at all times when the hold function is activated.

[0030] In step S1, the method begins with the brake booster 4 being controlled to generate hydraulic pressure within the brake system 1 in response to the operation of the brake pedal 3. This method starts immediately, in particular, as soon as the operation of the brake pedal 3 is recognized. To implement this method, a control device 11 specifically assigned to the brake booster 4 is used.

[0031] In step S2, at least one state variable of the vehicle 2 is determined, and a limit value for the operating stroke of the brake pedal 3 is predetermined according to the state variable. Preferably, the state variable is the vehicle weight of the vehicle 2 (especially the distribution of the vehicle weight per axle), the braking characteristic value of one or more of the wheel brake devices 9, and / or the inclination angle of the vehicle 2 relative to the horizontal. Particularly preferably, in this case, the inclination angle is determined according to the map data of the navigation system of the vehicle 2.

[0032] In step S3, the vehicle 2 is monitored for its stopped state, and the operating stroke of the brake pedal 3 is monitored for exceeding the limit value predetermined in step S2. Monitoring is performed based on signals from sensors in the vehicle 2, such as a wheel rotation speed sensor or a stroke sensor assigned to the brake pedal.

[0033] These signals are captured and evaluated simultaneously. Alternatively, the system first monitors for a stopped state, and if a stopped state is detected, it also monitors for exceeding the limit value. Monitoring continues indefinitely as long as the brake pedal 3 is operated. Otherwise, the system is first stopped and only resumed when the brake pedal 3 is operated again.

[0034] When both a stopped state and an exceedance of the limit are recognized, the hold function is activated in step S4. In the hold function, the hydraulic pressure present in the brake equipment 1 is maintained independently of the operation of the brake pedal 3. For this method, it is not important which of the two prerequisites occurs first, but both must be satisfied for the hold function to be meaningfully activated.

[0035] As long as the hold function is activated, the hydraulic pressure in the brake system 1 is preferably kept constant even when the operating stroke of the brake pedal 3 is further increased. When the brake pedal 3 is mechanically disconnected from the brake system 1, the hydraulic pressure is kept constant, for example, by not considering further increases in the operating stroke of the brake pedal 3 until the hold function is deactivated. In contrast, when the brake pedal 3 is mechanically connected to the brake system 1 to adjust the hydraulic pressure, the hydraulic pressure is kept constant, in particular by controlling the operation of the brake booster 4 to compensate for the hydraulic pressure changed by the operation of the brake pedal 3.

[0036] In an optional step S5, to adjust the hold function, the hydraulic pressure present in the brake system 1 when the hold function is activated is increased by a predetermined value by the brake booster 4, and the increased hydraulic pressure is then maintained. Along with the activation of the hold function, that is, the hydraulic pressure that has already been predetermined or adjusted in response to the operation of the brake pedal 3 is preferably increased disproportionately by the movement of the piston 5 of the main brake cylinder 6 by the brake booster 4, preferably abruptly or at a predetermined gradient. As long as the brake pedal 3 is mechanically coupled to the piston 5 or the brake booster 4, this is automatically fed back to the driver as a decrease in the brake pedal reaction force, especially a dramatic decrease, when the brake pedal 3 is operated.

[0037] In the case of a brake-by-wire braking system where the brake pedal 3 is mechanically connected to a brake pedal force simulator, in step S5, the brake pedal reaction force is additionally reduced proportionally to the increase in hydraulic pressure by the brake pedal force simulator so that the driver also receives the tactile feedback described above.

[0038] Alternatively or in addition to this tactile feedback, in step S5, the driver is provided with visual (e.g., as a notification on the screen or by an optical signal in the dashboard of the vehicle 2), auditory (e.g., by a signal sound), and / or other tactile (e.g., by vibration of the pedal or steering wheel) confirmation.

[0039] This method ends with step S6, in which the hold function is deactivated when, for example, the driver's operation of the clutch pedal and / or accelerator pedal is recognized. In this case, the deactivation of the hold function is preferably carried out with a predetermined time delay or with a gradual release of hydraulic pressure, for example, to assist in the starting operation. [Explanation of Symbols]

[0040] 1. Brake equipment 2. Automobile 3. Brake pedal 4. Brake force booster 5 pistons 6. Main brake cylinder 7. Two-way arrow 8. Hydraulic liquid 9. Wheel brake system 10 wheels 11 Control device S1 Step S2 Step S3 Step S4 Step S5 Step S6 Step

Claims

1. A method for operating the brake equipment (1) of an automobile (2), wherein the brake equipment (1) It has a controllable brake force booster (4) and a brake pedal (3), The brake force booster (4) is controlled in response to the operation of the brake pedal (3). The operation of the rake equipment (1) is controlled to generate hydraulic pressure. The vehicle (2) is monitored for its stopped state. The operating stroke of the brake pedal (3) is monitored for exceeding a predetermined limit value. and When a stopped state and an exceedance of the limit value are recognized, the brake equipment (1) present Activate the hold function to maintain hydraulic pressure. In the method, Determine at least one state variable of the aforementioned automobile (2), The limit value is predetermined according to at least one of the state variables, and A method for operating the brake system of an automobile, characterized by determining, as the state variable, at least one braking characteristic value (CP value) that represents the ratio of the braking force to the required operating force of the wheel brake device (9) of the brake system (1).

2. The method according to claim 1, characterized in that the vehicle weight of the automobile (2) is determined as a state variable.

3. The method according to claim 2, characterized in that the distribution of the vehicle weight to each axle is determined.

4. The method according to any one of claims 1 to 3, characterized in that at least one braking characteristic value (CP value) indicating the wear state of the wheel brake device (9) of the brake equipment (1) is determined as the state variable.

5. The method according to any one of claims 1 to 3, characterized in that the inclination angle of the automobile (2) with respect to the horizontal is determined as a state variable.

6. The method according to claim 5, characterized in that the inclination angle is determined according to the map data of the navigation system of the automobile (2).

7. The method according to any one of claims 1 to 3, characterized in that, in order to adjust the hold function, the hydraulic pressure present in the brake equipment (1) when the hold function is activated is increased by a predetermined value by the brake force booster (4), and the increased hydraulic pressure is maintained.

8. The method according to any one of claims 1 to 3, characterized in that, after the activation of the hold function, the hydraulic pressure in the brake equipment (1) is kept constant when the operating stroke of the brake pedal (3) is further increased.

9. The method according to claim 8, characterized in that the brake pedal (3) is mechanically disconnected from the brake equipment (1), and the hydraulic pressure is kept constant by not considering a further increase in the operating stroke of the brake pedal (3) until the hold function is deactivated.

10. The method according to claim 8, characterized in that the brake pedal (3) is mechanically connected to the brake equipment (1) to adjust the hydraulic pressure, and the brake force booster (4) is operated to maintain a constant hydraulic pressure by controlling the operation to compensate for the hydraulic pressure changed by the operation of the brake pedal (3).

11. The method according to any one of claims 1 to 3, characterized in that, after the activation of the hold function, visual, auditory, and / or tactile confirmation is output on a display device facing the driver of the automobile (2).

12. A control device (11) for a brake system (1) of an automobile (2), wherein the control device (11) is configured in particular to carry out the method described in any one of claims 1 to 3.

13. A brake system (1) for an automobile comprising a controllable brake force booster (4) and a brake pedal (3), characterized by the control device (11) described in claim 12.

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