Method and device for operating a brake booster

Abstract

Method for operating a vacuum brake booster (2) with a vacuum pump (11) in a motor vehicle, comprising the following steps: - Determining a change in the position of a position indicator of a brake request device; - Determining a pressure value via a pressure in a chamber (7, 8) of the brake booster (2), depending on the determined change in position; and - Activation of the vacuum pump (11) depending on the specified pressure, characterized in that the change in position is determined as the difference between a position of the brake request device (3) determined in the current detection cycle and a position of the brake request device (3) determined in a previous detection cycle.

Description

Technical field

[0001] The present invention relates to brake boosters with electrically operated vacuum pumps. State of the art

[0002] Motor vehicles are primarily equipped with vacuum brake boosters to amplify the braking force applied by the driver via the brake pedal. In conventional gasoline engines, this is achieved by utilizing a pressure differential between the intake manifold of the combustion engine and the external environment.

[0003] Vacuum brake boosters typically consist of two chambers: a vacuum chamber and a normal pressure chamber, separated by a movable diaphragm. The chambers are connected via an intermediate chamber valve. In gasoline engines, the vacuum chamber is connected to the engine's intake manifold and is thus subjected to a vacuum created in the intake manifold. When the brake pedal is not depressed, the intermediate chamber valve is open, creating the corresponding vacuum in both chambers. When the brake pedal is depressed, an outside air valve opens to the normal pressure chamber, and simultaneously the intermediate chamber valve closes, creating a pressure differential across a diaphragm. The force exerted on the diaphragm by this pressure differential is coupled to the brake pedal, thus assisting the braking force applied to the pedal.When the brake pedal is released, the intermediate chamber valve is reopened and the external air valve is closed, allowing pressure equalization between the chambers.

[0004] In the event that the vacuum supplied to the vacuum chamber when using the intake manifold of the combustion engine is insufficient, alternative measures can be provided that are triggered depending on a measured or calculated pressure in the vacuum chamber. The vacuum in the vacuum chamber is calculated based on an air mass flow balance, the air mass flow in the brake booster, the hydraulic brake pressure of the brake system connected to the brake booster, and an incoming air mass flow component.

[0005] Alternatively, the vacuum required to operate the vacuum brake booster can also be provided by an electric vacuum pump. However, the vacuum pump must be operated in such a way that a vacuum level greater than a predetermined pressure threshold is maintained in a vacuum chamber of the brake booster. Electric vacuum pumps are particularly necessary in hybrid or electric vehicles, as they lack a permanent vacuum source, such as the intake manifold of a gasoline engine.

[0006] To provide sufficient vacuum in the vacuum chamber using an electric vacuum pump, it is necessary to determine the atmospheric pressure within the chamber. This can be done, for example, with a pressure sensor. However, using pressure sensors in brake boosters is complex, and it is therefore desirable to be able to operate a brake booster without one. Furthermore, using a pressure sensor has the disadvantage of being prone to failure, and for safety reasons, it must be ensured that the brake booster can function properly even if the pressure sensor is not working.

[0007] From DE 10 2012 205 713 A1, a method for operating a braking system with a brake booster is known. The brake booster is divided by at least one movable partition into at least one vacuum chamber and at least one working chamber. A sensor is provided that detects at least one quantity, such as the displacement and / or angle and / or force of a brake pedal actuation and / or a brake pressure, which is built up in at least one master brake cylinder connected to the brake booster according to a brake pedal actuation. The remaining vacuum in at least one vacuum chamber is estimated by considering previously performed actuations based on at least one of the detected quantities.

[0008] A brake pressure boosting device for road vehicles is known from DE 10 2004 052 781 A1.

[0009] From DE 699 20 579 T2 a brake control method with estimation of the maximum gain and the pedal force is known. Disclosure of the invention

[0010] According to the invention, a method for operating a brake booster with a vacuum pump according to claim 1, as well as the device, the brake booster system and the computer program product according to the dependent claims are provided.

[0011] Further advantageous embodiments of the present invention are specified in the dependent claims.

[0012] According to a first aspect, a method for operating a vacuum brake booster with a vacuum pump, in particular an electric one, in a motor vehicle is provided, comprising the following steps: - Determining a change in the position of a position indicator of a brake request device, in particular a brake pedal; - Determining a pressure value based on the pressure in a chamber of the brake booster, depending on the measured change in position; and - Activating the vacuum pump depending on the specified pressure.

[0013] Furthermore, the vacuum pump can be activated if the pressure determined by the pressure specification exceeds a predetermined pressure threshold, or if the pressure determined by the pressure specification, as relative pressure, in particular as negative pressure, falls below a predetermined pressure threshold.

[0014] One idea behind the above method is to activate a vacuum pump to provide a vacuum for a vacuum brake booster only when, for example, a modeled pressure value for the pressure in the brake booster's vacuum chamber (which may represent an absolute pressure) exceeds a predefined pressure threshold, or falls below a predefined pressure threshold if the pressure value represents a vacuum. This allows the operating time of the vacuum pump to be limited to what is necessary, thus increasing its service life and preventing thermal overload.

[0015] The pressure value in the vacuum chamber is modeled as a pressure reading depending on the position of the brake request device or on a pressure change in the vacuum chamber triggered by a change in the position of the brake request device. The rationale behind this modeling is that when the brake request device is actuated, the diaphragm between the vacuum chamber and the normal pressure chamber in the brake booster moves, thus reducing the volume of the vacuum chamber and increasing the pressure of the air within it. When the brake pedal is released, the pressure in the vacuum chamber also increases due to air flowing from the normal pressure chamber through the opening of a corresponding intermediate chamber valve.

[0016] It was found that the pressure increase both when releasing and when applying the brake pedal also depends on the change in position of the brake pedal, so that with a corresponding change in the position of the brake pedal, a resulting pressure change in the vacuum chamber can be determined depending on the magnitude of the corresponding change in position.

[0017] It may be planned that the vacuum pump is activated for a predetermined period of time.

[0018] According to the invention, the change in position is determined as the difference between a position indication of the brake request device determined in the current detection cycle and a position indication of the brake request device determined in a previous detection cycle.

[0019] Furthermore, the pressure determined by the pressure specification can be reset to a predetermined reference pressure value at a specific time, whereby the reset is carried out immediately after the vacuum pump has stopped.

[0020] It may be provided that the pressure in the chamber of the brake booster, determined by the pressure specification, is determined using a predefined air chamber model.

[0021] In the given air chamber model, the change in position of the brake request device can be taken into account using a factor, where the factor is either constant or dependent on the sign of the change in position. The factor can be determined, in particular, by the design of the brake booster.

[0022] According to another aspect, a device for operating a vacuum brake booster with a vacuum pump in a motor vehicle is provided, wherein the device is designed to: - to determine a change in the position of a position indicator of a brake request device, in particular a brake pedal; - to determine a pressure reading for the pressure in a chamber of the brake booster, depending on the measured change in position; and - to activate the vacuum pump depending on the specific pressure.

[0023] According to another aspect, a brake booster system is provided with a vacuum brake booster, a vacuum pump and the above device.

[0024] According to another aspect, a computer program product is provided which contains program code which, when executed on the above device or computing device, performs the above procedure. Brief description of the drawings

[0025] Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1. A schematic representation of a vacuum brake booster with an electric vacuum pump; and Fig. 2. A flowchart illustrating a procedure for operating the brake booster system of the Fig. 1. Description of embodiments

[0026] With reference to Fig. 1 describes a brake booster system for connection to a hydraulic brake system for use in motor vehicles.

[0027] The brake booster system 1 comprises a brake booster 2, which is coupled to a brake pedal 3 as a brake request device. The brake pedal 3 is connected to a piston rod 4 that penetrates the brake booster 2 and is connected to a piston 5 of a hydraulic brake cylinder 6. The brake cylinder 6 is hydraulically connected to the hydraulic brake system of a motor vehicle and serves to transmit a braking force to corresponding brake devices (not shown) at the wheels of the motor vehicle.

[0028] The brake booster 2 has a vacuum chamber 7 and a normal pressure chamber 8 through which the piston rod 4 passes. The vacuum chamber 7 and the normal pressure chamber 8 are essentially pressure-tightly separated from each other by a flexibly movable diaphragm 9. The diaphragm 9 is rigidly connected to the piston rod 4, so that any movement of the diaphragm 9 is transmitted to the piston rod 4. A return spring 10 is provided in the vacuum chamber 7, which is tensioned between a housing of the brake booster 2 and the piston rod 4 such that when the brake pedal 3 is released (not actuated), it returns the pedal to its initial position with a restoring force.

[0029] When the brake pedal 3 is actuated, the piston rod 4 is moved in the direction of the brake cylinder 6, thereby tensioning the return spring 10.

[0030] The vacuum chamber 7 is connected to an electrically or otherwise controllable vacuum pump 11, so that a vacuum can be generated in the vacuum chamber 7 when the vacuum pump 11 is operated. In the initial position shown, with the brake pedal 3 not depressed, the same pressure prevails in the vacuum chamber 7 and in the normal pressure chamber 8.

[0031] When the brake pedal 3 is actuated, an intermediate chamber valve 13 between the vacuum chamber 7 and the normal pressure chamber 8, specifically in the diaphragm 9, is closed by means of a valve actuator 12. This occurs, for example, when the brake pedal 3 is actuated and the valve actuator 12 is moved towards the diaphragm 9. Simultaneously, the movement of the valve actuator 12 opens an external valve 14, allowing ambient air to flow into the normal pressure chamber 8. This creates a pressure differential across the diaphragm 9. The pressure differential exerts a force on the piston rod 4 towards the brake cylinder 6. This force assists the force exerted by the driver on the brake pedal 3. When the brake pedal 3 is released, the intermediate chamber valve 13, located between the vacuum chamber 7 and the normal pressure chamber 8, opens, allowing the air in the normal pressure chamber 8 to flow into the vacuum chamber 7.At the same time, the external valve 14 is closed, so that pressure equalization takes place between the negative pressure chamber 7 and the normal pressure chamber 8.

[0032] The brake pedal 3 is also connected to a position sensor 16 to provide information about the position of the brake pedal 3.

[0033] Furthermore, to operate the brake booster system 1, it is equipped with a control unit 15 which receives information about the position of the brake pedal 3 from the position sensor 16 and activates or deactivates the vacuum pump 11 according to the following procedure in order to maintain the vacuum in the air chambers 7, 8.

[0034] Both when the brake pedal 3 is actuated and when it is released, the movement of the piston rod 4 and the valve functions of the brake booster 2 cause an increase in pressure in the vacuum chamber 7. When the brake pedal 3 is actuated, the movement of the piston rod 4 moves the diaphragm 9 towards the vacuum chamber 7, thus reducing its volume and thereby increasing the pressure within it. When the brake pedal 3 is released, the spring action of the return spring 10 causes the piston rod 4 to retract, but this opens the intermediate chamber valve 13, allowing air from the normal pressure chamber 8, which is under a higher pressure, particularly ambient pressure, to flow through the intermediate chamber valve 13 into the vacuum chamber 7.

[0035] To ensure a sufficient pressure differential between the vacuum chamber 7 and the normal pressure chamber 8 for subsequent braking operations, the pressure in the vacuum chamber 7, and also in the normal pressure chamber 8 when the brake pedal 3 is not depressed, must fall below a predetermined pressure threshold, or the vacuum in the vacuum chamber 7, and also in the normal pressure chamber 8 when the brake pedal 3 is not depressed, must exceed a predetermined pressure threshold. Typically, this pressure threshold for conventional brake booster systems is between 500 and 700 hPa as an absolute pressure.

[0036] The vacuum pump 11 serves to ensure that a sufficient vacuum is always available in the vacuum chamber 7 of the brake booster 2. It is therefore essential to ensure that the vacuum pump 11 is activated whenever the pressure in the vacuum chamber 7 exceeds the pressure threshold.

[0037] In particular, if a pressure sensor for determining the chamber pressure in the brake booster 2 is defective, or if no such pressure sensor is provided to reduce design complexity, it is necessary to provide a method for activating and deactivating the vacuum pump 11 to supply a vacuum in the vacuum chamber 7. It is therefore necessary to estimate a pressure value based on the pressure in the vacuum chamber 7, preferably using available system parameters.

[0038] For this purpose, a method for operating the brake booster 2 is provided, as described in conjunction with the flowchart of the Fig. 2 is described in detail.

[0039] In step S1, the position sensor 16 detects a position information for a position of the brake pedal 3.

[0040] In a subsequent query step S2, it is checked whether the position information has changed in a previous data entry cycle. For this purpose, the two most recently entered position information entries are temporarily stored. If this is not the case (alternative: No), the process continues with step S3.

[0041] In query step S3, it is checked whether the vacuum pump 11 has been inactive for more than a predefined period of time. If this is the case (alternative: Yes), the procedure continues with step S4. Otherwise (alternative: No), it jumps back to step S1.

[0042] In step S4, the vacuum pump 11 is activated for a predetermined duration, such as between 5 and 10 seconds, to create or increase a vacuum in the air chambers 7 and 8. After step S4 is completed, i.e., after the activation of the vacuum pump 11 has ended, the process returns to step S1. This step serves to compensate for any leaks in the brake booster's pressure system.

[0043] If a change in the position of the brake pedal 3 is detected in query step S2 (alternative: Yes), then in step S5 a pressure in the vacuum chamber 7 is determined according to an air chamber model.

[0044] In step S5, the modeled absolute pressure p in the air chambers 7, 8, in particular in the negative pressure chamber 7, is to be determined as follows: p(t+dt)=p(t)+K⋅|brk(t)−brk(t+dt)|, where p corresponds to the absolute pressure in the vacuum chamber 7 at time t or t + dt, brk to the position of the brake pedal 3 at time t or t + dt, t to a time point of a previous acquisition cycle, dt to the time difference between two acquisition cycles and K to a modeling factor.

[0045] The factor K represents the physical model of the brake booster 2 and can be chosen to be constant or dependent on the operating point. In particular, the factor K can be chosen depending on the sign of the change in the position signal, i.e., depending on sgn(brk (t) - brk (t + dt)).

[0046] As long as the position of the brake pedal 3 increases (position value increases from one detection cycle to the next), the factor K describes the effect of the movement of the piston rod 4 on the pressure difference between the vacuum chamber 7 and the normal pressure chamber 8, depending on the change in the position of the brake pedal 3. Therefore, for brk (t) < brk (t + dt), K = constant, since the volume of the vacuum chamber 7 changes approximately proportionally to the movement of the piston rod 4 or the brake pedal 3.

[0047] In contrast, brk (t) > brk (t + dt) corresponds to the case of releasing the brake pedal 3, whereby the opening of the intermediate chamber valve 13 results in pressure equalization between the vacuum chamber 7 and the normal pressure chamber 8 with the external valves 14 closed. A pressure equilibrium is established, which results from the amount of air in the two air chambers 7, 8 at the time of the change in the sign of the change in the position information and the predetermined total volume of the air chambers 7, 8.

[0048] In step S6, it is checked whether the modeled absolute pressure in the brake booster 2 exceeds a predefined pressure threshold. If this is the case (alternative: Yes), the vacuum pump 11 is activated in step S7 for a predefined duration, e.g., between 5 and 10 seconds, and then the process returns to step S1. Otherwise (alternative: No), the process returns directly to step S1. The predefined duration is chosen such that, in every operating condition, the pumping action achieves a vacuum or absolute pressure in the vacuum chamber that is greater or less than the predefined pressure threshold. In particular, the predefined duration is chosen such that, starting from an assumed ambient pressure in the vacuum chamber, a vacuum or absolute pressure is reached in the vacuum chamber that is greater or less than the predefined pressure threshold.

[0049] In a simplified model, factor K can be assumed to be a constant factor that represents a change in pressure in the vacuum chamber 7, i.e., a pressure increase, with every change in the position of the brake pedal 3, whether positive or negative. This model can be used to determine, in a simplified manner, the instantaneous pressure in the vacuum chamber 7 of the brake booster 2 and may be sufficient to define a condition for activating the vacuum pump 11.

[0050] In this case, however, it is desirable to regularly determine the absolute pressure in the air chambers 7 and 8 of the brake booster 2, or at least in the vacuum chamber 7. A preset pressure value can be defined, in particular, immediately after the vacuum pump 11 is switched off. In other words, it can be provided that when the vacuum pump 11 stops, the pressure value p is set or initialized to a predefined reference pressure value.

Claims

[1] Method for operating a vacuum brake booster (2) with a vacuum pump (11) in a motor vehicle, comprising the following steps: - Determining a change in the position of a position indicator of a brake request device; - Determining a pressure value via a pressure in a chamber (7, 8) of the brake booster (2), depending on the determined change in position; and - Activating the vacuum pump (11) depending on the specified pressure characterized by , that the change in position is determined as the difference between a position value of the brake request device (3) determined in the current detection cycle and a position value of the brake request device (3) determined in a previous detection cycle. [2] Method according to claim 1, wherein the vacuum pump (11) is activated when the pressure determined by the pressure specification as absolute pressure exceeds a predetermined pressure threshold value or when the pressure determined by the pressure specification as relative pressure falls below a predetermined pressure threshold value. [3] Method according to claim 1 or 2, wherein the vacuum pump (11) is activated for a predetermined period of time. [4] Method according to any one of claims 1 to 3, wherein the pressure determined by the pressure specification is reset to a predetermined reference pressure value at a specific time, wherein the reset is carried out immediately after the vacuum pump (11) is stopped. [5] Method according to any one of claims 1 to 4, wherein the pressure determined by the pressure specification in the chamber of the brake booster (2) is determined using a predetermined air chamber model. [6] Method according to claim 5, wherein the predetermined air chamber model takes into account the change in position of the position indicator of the brake request device with a factor (K), wherein the factor (K) is constant or dependent on a sign of the change in position. [7] Device for operating a vacuum brake booster (2) with a vacuum pump (11) in a motor vehicle, wherein the device is designed to: - to determine a change in position of a position indicator of a brake request device (3); - to determine a pressure value for a pressure in a chamber (7, 8) of the brake booster (2) depending on the determined change in position; - to activate the vacuum pump (11) depending on the pressure determined by the pressure specification; - to determine the change in position as the difference between a position value of the brake request device (3) determined in the current detection cycle and a position value of the brake request device (3) determined in a previous detection cycle. [8] Brake booster system (1) comprising a vacuum brake booster (2), a vacuum pump (11) and a device according to claim 7. [9] Computer program product containing program code which, when executed on the device according to claim 7 or on a computing device, performs the method according to any one of claims 1 to 6.

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