DE102017214135A1 - Method for testing a brake system - Google Patents

Abstract

The present invention relates to a method for testing a brake system (100), which is characterized in that in an operating step, an electric motor (M) driving a return pump (RP) of the brake system (100) is operated to supply brake fluid to a proportional valve (10). UPS) of the brake system (100), in a step of setting a valve position of the proportional valve (UPS) is set to set a flow resistance for the brake fluid, and in a step of comparing a detected on the electric motor (M) current flow with one of Valve position associated expected value is compared.

Description

Field of the invention

The invention relates to a method for testing a brake system.

State of the art

In a brake system, a secure pressure supply is required. Components of the brake system can age and thus influence flow rates or pressure build-up. The changes in the brake system can be detected, for example, by an external test device in the workshop and corrected if necessary.

Disclosure of the invention

Against this background, a method for testing a brake system and a corresponding computer program product according to the independent claims are presented with the approach presented here. Advantageous developments and improvements of the approach presented here are described in the dependent claims.

Advantages of the invention

Embodiments of the present invention may advantageously enable to verify components of a brake system when installed by detecting, without the aid of external means, the pressure on a proportional valve using known quantities and being correlated with a set valve position.

A method of testing a brake system is proposed, which is characterized in that in a step of operating a motor driving a return pump of the brake system is driven to promote brake fluid to a proportional valve of the brake system, in a step of setting a valve position of the proportional valve is set to set a flow resistance for the brake fluid, and in a step of comparing a current detected at the electric motor current flow is compared with an expected value associated with the valve position.

Ideas for embodiments of the present invention may be considered, inter alia, as being based on the thoughts and findings described below.

A proportional valve has different flow cross-sections depending on a valve position. By changing the valve position so a fluid flow can be changed by the proportional valve. The flow cross section resulting from a valve position may change over time. If multiple proportional valves are used in parallel to control brake devices of a brake system, such a change can lead to an asymmetric pressure distribution on braking devices of the brake system. Likewise, other components of the braking system may have altered characteristics over time. Due to the changed properties of the components, a functionality of the brake system may be limited.

In the approach presented here, the brake system is checked under approximate real conditions without a test device. For this purpose, a return pump of the brake system is driven to circulate brake fluid in the brake system. A proportional valve of the brake system is activated in order to build up pressure in a pressure range of the hydraulic system. Since the pressure can not be measured directly, it is indirectly closed to pressure using a current flow through an electric motor driving the return pump.

Due to the build-up of pressure, a required pumping power of the return pump increases. To provide the pumping power, a higher torque is required for the return pump. The electric motor draws at the increased torque increased current flow. There is a direct correlation between the current flow and the pressure.

The actual current flow is compared to a current flow expected at the valve position. The expected current flow can be determined, for example, for one type of brake system under laboratory conditions. The expected current flow is stored in a memory.

If the actual current flow deviates by more than a tolerance from the expected current flow, an action is triggered.

The electric motor can be operated speed controlled. The current flow can be compared with an expected value associated with the valve position and / or a rotational speed of the electric motor. The engine power is a product of torque and speed. The expected value can therefore be speed-dependent.

The electric motor can be operated in the following regulated to at least a second speed. Alternatively or additionally, at least one second valve position of the proportional valve can be provided. At least a second current flow on the electric motor can with one of the second Valve position and alternatively or additionally the second speed associated second expected value to be compared. The brake system can be tested in various operating states. In this way any changes can be detected more reliably.

In a subsequent step of setting, the valve position may be changed if the current flow deviates from the expected value by more than a tolerance. Alternatively or additionally, in the subsequent step of setting a warning message can be provided if a changed valve position is outside a tolerance range of the valve position. The valve position can be changed to reach the expected value. The changed valve position can be saved. Thus, the braking system can be operated as intended with slightly different components. If the valve position needs to be changed too much to reach the expected value, it can be warned. By warning the brake system can be repaired or maintained before a total failure. The alert message may also activate an alternative operating mode for the braking system and / or the vehicle. For example, functions can be deactivated and / or limits set for the vehicle.

A warning message may be provided if the current flow deviates from the expected value by more than a warning tolerance. A large deviation indicates a functional restriction in the brake system. The brake system can be repaired or repaired in good time.

Intake valves of a brake circuit of the brake system may be closed and exhaust valves may be opened to allow pressure buildup by the return pump and the proportional valve in the brake circuit. Alternatively or additionally, a high-pressure switching valve of the brake circuit can be opened. Closing the intake valves does not pressurize the brake devices. The inlet valves are also proportional valves that can be tested with the approach presented here. By closing the other valves on the pressure side of the return pump, the flow rate of the return pump flows only through the Asked proportional valve. The pressure can be determined more easily. By opening the switching valves, the brake fluid flowing through the proportional valve can flow back to the suction side of the return pump. In addition, by opening the exhaust valves, the recirculation pump can also suck brake fluid from the brake devices. By opening the high-pressure switching valve, the return pump can suck in brake fluid from the reservoir on the master cylinder.

Further intake valves and further exhaust valves of a further brake circuit of the brake system can be opened. Alternatively or additionally, a further proportional valve and a further high-pressure switching valve of the further brake circuit can be opened in order to prevent pressure build-up in the further brake circuit. By opening the valves in the other brake circuit, the torque of the electric motor can be used essentially at the return pump in the brake circuit to be tested. Frictional losses are constant and not relevant for the approach presented here.

Another return pump of a further brake circuit of the brake system can be operated by the electric motor to promote brake fluid to a further proportional valve of the further brake circuit. Another valve position of the further proportional valve can be provided in order to set a further flow resistance for the brake fluid. Another current flow through the electric motor can be compared with a further expected value associated with the further valve position. The approach presented here can also be applied in other supplied by the electric motor brake circuits. As a result, brake circuits of the brake system can be checked one after the other.

Also of advantage is a computer program product or computer program with program code which can be stored on a machine-readable medium and used to carry out, implement and / or control the steps of one of the methods described above.

list of figures

• 1 zeigt eine Darstellung eines Schaltplans eines Bremssystems eines Fahrzeugs.

Embodiments of the invention will now be described with reference to the accompanying drawings, wherein neither the drawings nor the description are to be construed as limiting the invention.

• 1 shows a representation of a circuit diagram of a brake system of a vehicle.

The figure is merely schematic and not to scale.

Embodiments of the invention

1 shows a representation of a hydraulic circuit of a brake system 100 of a vehicle. The brake system 100 includes a transmitter unit 102 , a brake control unit 104 and braking devices 106 at the wheels of the vehicle. The transmitter unit 102 consists of one over one Rod with a brake pedal coupled brake booster and a master cylinder MC. On the master cylinder MC is a reservoir 108 arranged for brake fluid or brake fluid. The transmitter unit 102 is executed in two circles. In the master cylinder MC are arranged two simultaneously by the brake pedal or the brake booster moving piston. Each piston acts on its own volume. A first master cylinder chamber MC1 is with a first brake circuit 110 the brake control unit 104 fluidly connected. The second master cylinder chamber MC2 is with a second brake circuit 112 the brake control unit 104 connected. Every brake circuit 110 . 112 supplies two of the brake devices 106 , Here X-brake circuits are shown. Each of the brake circuits 110 . 112 each supplies a front wheel and a diagonally opposite rear wheel. The first brake circuit 110 thus supplies the braking device 106 of the left front wheel LV and the braking device 106 the right rear wheel RH , The second brake circuit 112 provides the braking device 106 the right front wheel RV and the braking device 106 the left rear wheel LH ,

Both brake circuits 110 . 112 are the same. Therefore, here is just one of the brake circuits 110 . 112 described. Components of the first brake circuit 110 are marked with the number one. Components of the second brake circuit 112 are marked with the number two. Components that are clearly assigned to a wheel are marked with the abbreviation of the wheel.

The respective output of the master cylinder MC is connected to the inputs of a proportional valve UPS and a switching valve HSV connected. The proportional valve UPS can be referred to as a changeover valve. The switching valve HSV can be referred to as a high pressure switching valve. Both valves are electromagnetically actuated. The proportional valve UPS is normally open. The switching valve HSV is normally closed. The switching valve HSV has only two switching positions, open or closed. The proportional valve UPS can take a variety of valve positions. A flow cross-section of the proportional valve UPS depends on the valve position. In the first brake circuit 110 is between the output of the master cylinder MC1 and the inputs of the proportional valve UPS1 and the switching valve HSV1 a pressure sensor 114 arranged.

An output of the proportional valve UPS is with the braking devices 106 connected. Between the proportional valve UPS and the braking devices 106 is ever another proportional valve EV arranged. The other proportional valves EV may be referred to as intake valves. The other proportional valves EV are also electromagnetically operated and normally open. The other proportional valves EV can be throttled. In de-energized state of the proportional valve UPS and the other proportional valves EV there is a direct fluidic connection between the master cylinder MC and the braking devices 106 ,

Between the input and the output of the proportional valve UPS a check valve is arranged. At a higher inlet pressure than at the outlet, brake fluid may be present at the proportional valve UPS flow past. The brake fluid can thus at any time of the master cylinder MC in the direction of the braking devices 106 stream.

Check valves are also arranged between the inputs and the outputs of the further proportional valves EV. At a higher pressure at the outlet than at the inlet, brake fluid may be present at the respective further proportional valve UPS flow past. Brake fluid can therefore at any time from the brake devices 106 stream away.

An output of the switching valve HSV is connected to a suction side of a return pump RP connected. The return pump is via the switching valve HSV RP So with the reservoir 108 on the master cylinder MC connected. A pressure side of the return pump RP is connected to the output of the proportional valve UPS and the inputs of the further proportional valves EV connected.

The return pumps RP1 . RP2 both brake circuits 110 . 112 are using a common electronically commutated electric motor M coupled. The electric motor M Here is a brushless DC motor and is powered by an engine control unit 116 provided. The engine control unit 116 has among other things an inverter 118 for providing a polyphase, in particular rectangular AC voltage for windings of the electric motor M , a current detection device 120 for detecting the resulting current flows through the windings and a position detecting device 122 for detecting a rotor position and rotational speed of a rotor of the electric motor M via a rotor position sensor.

When connected to the windings of the electric motor M a voltage signal is applied, rotate the rotor and coupled to it pump rotors of the return pumps RP1 . RP2 , The current flows through the windings are adjusted according to a torque required for rotating the pump rotors. One from a return pump RP delivered volume is dependent on a pump speed of the pump rotor. The pump speed is in a fixed ratio to the speed of the rotor of the electric motor M , Here are the pump rotors without intermediate gearbox with the rotor coupled, therefore, the pump speed corresponds to the speed.

If the pressure on the pressure side of the return pump RP increases, also increases the required torque. With the torque, the current flows increase. Since the torque can be calculated via the current flows and the pressure can be calculated via the torque, the pressure can be calculated using the current flows. The current flows can also lead to a resulting current flow at the electric motor M be summarized.

The suction side of the return pump RP is also with the braking devices 106 connected. Between the return pump RP and the braking devices 106 is ever another switching valve AV arranged. The other switching valves AV may be referred to as exhaust valves. The other switching valves AV are electromagnetically operated and normally closed. The other switching valves AV can be throttled. Between the outputs of the other switching valves AV and the suction side of the return pump RP is a low pressure accumulator A arranged. The low pressure accumulator A is designed as a cylinder with a spring-loaded piston therein. Between the low pressure accumulator A and the suction side of the return pump RP is a spring-loaded check valve RVR arranged to reduce a suction pressure of the return pump RP.

All valves of the brake control unit 104 are controlled by electrical signals. The switching valves HSR and other switching valves AV each have an open or a closed switch position without intermediate positions. The proportional valves UPS and the other proportional valves EV also have intermediate positions as a function of a signal value of the triggering electrical signal. A flow cross-section of the proportional valves UPS and further proportional valves EV depends on the valve position.

It is a method for assessing the operability of the pressure supply of a brake system 100 presented.

Safety-relevant systems are becoming increasingly demanding in terms of reliability and function monitoring. So far, only parts of the chain of action are tested, for example, that the engine M turns that the valves UPS, HSV . EV . AV are electrically controllable, etc. For automated driving higher demands on the monitoring depth are expected.

The method proposed here allows a review of the pressure supply chain in the brake system 100 , so malfunctions in the engine M the return pump RP , Pump elements, high pressure switching valve HSV , Proportional valve UPS , Inlet valves EV and can be detected in parts of the hydraulic lines.

The proposed method uses the measured motor current as information about the motor torque. The torque is used for a pressure estimation and compared to the expected pressure provided by the energizing of the proportional valves UPS. This evaluates the pressure supply circuit. In case of strong deviations, a fault is detected.

For example, at the end of production, a calibration is performed. One or more operating points of the pressure supply are activated. A speed of the eccentric pump and a pressure are set via the proportional valve UPS. The measured values of motor current and current values provided to the proportional valve UPS are stored in a table (e.g., EEPROM). These values form future expectation values.

To check the pressure supply, the valves are switched so that a pressure build-up is possible when the vehicle is stationary. In this case, the proportional valve UPS in the tested brake circuit 110 . 112 as energized as during the calibration at the end of production. The motor M is brought to the same speed, as measured during the calibration and the motor current. The measured motor current is compared with the stored value and rated as good or bad.

Too low current indicates a power loss in the pressure supply circuit.

In other words, in the method presented here for checking the brake system 100 the return pump RP is driven by the electric motor and builds up pressure between the return pump RP and one of the proportional valves UPS. In this case, the intake valves EV of the brake circuit to be tested 110 . 112 closed. The valves in the other brake circuit are open so as not to build up pressure. During pressure buildup, the current flow at the electric motor M is measured to estimate the pressure. The measured current flow is compared with an expected current flow for the set valve position. If the current flow is lower than expected, less pressure is built up before the proportional valve UPS than expected. If the current flow is higher than expected, more pressure will be built up on the proportional valve UPS than expected. Both can indicate a defect in the proportional valve UPS. However, a too low current flow can also indicate a defect at the inlet valves EV.

The current flow can be detected and compared for different valve positions of the proportional valve UPS. If the expected current flow is not achieved, the valve position can be changed until the current flow is within a tolerance again. Alternatively or additionally, it can be warned that the expected current flow or expected pressure is not reached.

The components of the braking system 100 are controlled via electrical control signals of one or more control units. The control unit has electronic components for providing the control signals. The components are driven in accordance with a stored in a memory of the controller computer program product. The computer program product is designed to implement and execute the steps of the method presented here or of the methods presented here.

The control device may comprise an electrical device having at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, and at least one interface and / or a communication interface for reading in or outputting data embedded in a communication protocol, be. The arithmetic unit can be, for example, a signal processor, a so-called system ASIC or a microcontroller for processing sensor signals and outputting data signals as a function of the sensor signals. The storage unit may be, for example, a flash memory, an EPROM or a magnetic storage unit. The interface can be used as a sensor interface for reading the sensor signals from, for example, the current detection device 120 and / or the position detection device 122 and as an actuator interface for outputting control signals for, for example, the inverter 118 be educated. The communication interface can be designed to read in or output the data wirelessly and / or by cable. The interfaces may also be software modules that are present, for example, on a microcontroller in addition to other software modules.

Finally, it should be noted that terms such as "comprising," "comprising," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a multitude. Reference signs in the claims are not to be considered as limiting.

Claims (11)

Method for testing a brake system (100), characterized in that, in a step of operation, an electric motor (M) driving a return pump (RP) of the brake system (100) is operated to supply brake fluid to a proportional valve (UPS) of the brake system (100). in a step of setting, a valve position of the proportional valve (UPS) is set to set a flow resistance for the brake fluid, and in a step of comparing a detected at the electric motor (M) current flow is compared with an expected value associated with the valve position. Method according to Claim 1 in which in the step of operating the electric motor (M) is operated speed-controlled, and wherein in the step of comparing the current flow with one of the valve position and / or a rotational speed of the electric motor (M) associated with expected value is compared. Method according to Claim 2 in which in the step of operating the electric motor (M) is operated regulated to at least a second speed and / or in the step of setting at least a second valve position of the proportional valve (UPS) is provided, and in the step of comparing a second current flow to the electric motor ( M) is compared with a second expected value associated with the second valve position and / or the second speed. Method according to one of the preceding claims, wherein in a subsequent step of setting the valve position is changed when the current flow deviates from the expected value by more than a tolerance. Method according to Claim 4 in which in the subsequent step of setting a warning message is provided when a changed valve position is outside a tolerance range of the valve position. A method according to any one of the preceding claims, wherein in the step of comparing, a warning message is provided when the current flow deviates from the expected value by more than a warning tolerance. Method according to one of the preceding claims, in which, in the setting step, further inlet valves (EV) of a brake circuit (110) of the brake system (100) are closed and exhaust valves (AV) are opened in order to establish a pressure build-up by the return pump (RP) and the proportional valve ( UPS) in the brake circuit (110) and / or a high-pressure switching valve (HSV) of the brake circuit (110) is opened. Method according to Claim 7 in which further exhaust valves (AV) and inlet valves (EV) of a further brake circuit (112) of the brake system (100) are also opened in the step of setting are, and / or another proportional valve (USV2) and another high-pressure switching valve (HSV2) of the further brake circuit (112) is opened to prevent pressure build-up in the further brake circuit (112). Method according to one of the preceding claims, wherein in the step of operating a further return pump (RP2) of another brake circuit (112) of the brake system (100) by the electric motor (M) is operated to brake fluid to another proportional valve (USV2) further To promote brake circuit (112), in the step of setting another valve position of the further proportional valve (USV2) is set to set a further flow resistance for the brake fluid, and in the step of comparing a further current flow through the electric motor (M) with one of the other Valve position associated further expected value is compared. Computer program product adapted to perform the method according to any one of Claims 1 to 9 execute, implement and / or control. Machine readable storage medium carrying the computer program product according to Claim 10 is stored.

Images