Method for operating piston pump without suction throttle in brake system

Abstract

The invention relates to a method for controlling a hydraulic brake system having at least one pressure supply device for supplying brake fluid into at least one wheel brake, a required brake fluid volume being determined in order to set a target pressure in the at least one wheel brake, the pressure supply device is controlled to convey a brake fluid volume. In order to quickly and accurately set the target pressure, according to the invention, the idle operation behavior of the pressure supply device is observed by determining a threshold rotational speed, which causes a subsequent volume corresponding to the required brake fluid volume to be conveyed when the motor of the pressure supply device is turned off, the rotational speed of the pressure supply device is limited to a threshold rotational speed, or the threshold rotational speed is requested by the pressure supply device.

Description

[0001] The invention relates to a method for controlling a hydraulic brake system having at least one pressure supply device for delivering brake fluid to at least one wheel brake, wherein a required brake fluid volume is determined in order to set a target pressure in the at least one wheel brake, and the pressure supply device is controlled to deliver the brake fluid volume. The invention also relates to such a brake system.

[0002] It is known that such brake systems are able to build up the brake pressure independently of the driver by means of a pressure supply. In most cases, a target pressure is to be achieved very quickly, for which purpose a large volume flow and therefore a high rotational speed of the motor of the pressure supply is required. However, since these rotational speeds do not drop suddenly to zero, brake fluid is pumped even after the target pressure has been reached, thereby delivering a subsequent volume. This can lead to a large overshoot of the pressure and thus to overbraking. This creates comfort and safety problems.

[0003] It is therefore an object of the present invention to provide a method for such a braking system which avoids the above-mentioned disadvantages.

[0004] According to the present invention, this purpose is achieved by observing the inertial operation / inertial operation behavior of the pressure supply device when setting the pressure. For this purpose, a threshold speed is calculated, which will deliver a subsequent volume corresponding to the required brake fluid volume when the motor of the pressure supply device is turned off. This means that when the pressure supply device is running at the threshold speed and is turned off, the required brake fluid volume is still pumped accurately with its subsequent flow. The determined threshold speed is assigned to the pressure supply device as a restriction, or the threshold speed is simply requested directly by the pressure supply device. This means that the speed requirements known from the prior art can be extended by this type of restriction, and the pressure supply device can only request a limited speed requirement. Alternatively, the threshold speed determined according to the present invention is directly requested. This usually exceeds the speed range that can be physically realized by the pressure supply device at the beginning. Therefore, the pressure supply device runs with its maximum speed or maximum allowable speed. Only when the actual pressure approaches the target pressure and the required volume of the brake fluid that is still to be delivered is reduced, the threshold speed drops to the range of the actual speed of the pressure supply device. This means that the pump stops running after being turned off, and the target pressure is accurately achieved by the pressure supply device that continues to run.

[0005] In a preferred embodiment of the invention, the pressure supply device is a piston pump. Such a pump can deliver high volume flows and achieve high final pressures at manageable component costs. By combining such a pump with the method according to the invention, the target pressure can therefore be achieved particularly quickly and accurately.

[0006] In another preferred embodiment of the present invention, the brake system is a redundant brake system with an additional second pressure supply device, in particular a linear actuator. Such a redundant brake system can be used for highly automated driving, in which the driver is not used as the last backup level.

[0007] In a particularly preferred embodiment of the invention, the piston pump is not provided with a suction throttle, in particular a switchable valve, on the suction side and is in particular directly connected to a pressureless brake fluid reservoir. This means that the costs of such additional components can be saved and pressure overshoots are still prevented.

[0008] In another preferred embodiment of the invention, the pressure difference present at the pressure supply is taken into account when determining the threshold speed, in particular by using a coasting characteristic curve which specifies a speed gradient and / or a coasting time for a given pressure. In general, the greater the counterpressure, the shorter the coasting time. In alternative embodiments, other characteristic curves or diagrams can also be used which in each case relate the subsequent volume at the current speed of the pump to the prevailing pressure, so that the threshold speed can be determined for a given state of the brake system.

[0009] Analysis based on the law of conservation of energy shows that friction can also be added to this determination:

[0010]

[0011] J: Mass moment of inertia / rotational inertia of the motor

[0012] ω: angular velocity / rotational speed of the motor

[0013] P1, P2, P: Pressure

[0014] R: Friction coefficient

[0015] N: Number of revolutions

[0016] a: volume per revolution

[0017] Solve this equation for the number of revolutions N and compare it with the following solution found experimentally:

[0018]

[0019] n: speed

[0020] p1: parameter 1

[0021] p2: parameter 2

[0022] In particular, a speed squared dependency is demonstrated. The parameters p1 and p2 can therefore be determined experimentally or with the aid of analytically analyzed variables.

[0023] In another preferred embodiment of the invention, the power supply terminals of the motor of the pressure supply device are short-circuited when the motor is turned off. This results in a decelerating electromagnetic force being generated via induction, thereby causing the inertial operation of the pump to be faster. For a given speed and pressure difference across the pump, this results in a lower replenishment volume. As a result, the pump can be run at a high speed for a longer time, which means that the target pressure or target volume can be reached faster without pressure overshoot.

[0024] In another preferred embodiment of the invention, the required brake fluid volume is determined by a pressure / volume characteristic curve. This makes it particularly easy to establish a correlation between the target pressure and the required brake fluid volume.

[0025] In another preferred embodiment of the invention, once the actual speed of the pressure supply device is greater than or equal to the threshold speed, the target speed of the pressure supply device is set to zero. This also reduces the electrical output supplied to the pump to zero, and the pump will run out. Due to the method according to the invention, the target pressure is accurately set without continuing to supply current to the motor.

[0026] Furthermore, the object is achieved by a motor vehicle hydraulic brake system having at least one pressure supply device and a control unit for controlling the pressure supply device, wherein the control unit is designated for carrying out the above-described method.

[0027] The object is also achieved by a computer program product which is designed in such a way that one of the methods is performed when the computer program product is executed in a control device.

[0028] Furthermore, the object is achieved by a data carrier signal transmitting such a computer program product.

[0029] A redundant brake system having multiple pressure or volume sources: a linear actuator (LAC) and a piston pump.

[0030] Other features, advantages and possible applications of the invention are also derived from the following description of exemplary embodiments and the accompanying drawings. All features described and / or illustrated are associated with the subject matter of the invention individually and in any combination, independently of their combination in the claims or their reverse references.

[0031] Figure 1 A braking system according to the invention is schematically shown,

[0032] Figure 2 A diagram with an exemplary coasting characteristic curve is shown.

[0033] Figure 1 A redundant hydraulic brake system for a motor vehicle is shown. According to the example, the brake system is designed for actuating four hydraulically actuable wheel brakes 8; it can be easily upgraded to more wheel brakes. According to the example, wheel brakes (HL, HR) are assigned to the rear axle and wheel brakes (VL, VR) are assigned to the front axle of the vehicle.

[0034] The brake system comprises a first structural unit, which is configured as a first hydraulic electronic brake control unit having a valve block and a first electronic control device according to an example; and a second structural unit, which is configured as a second hydraulic electronic brake control unit having a valve block and a second electronic control device according to an example.

[0035] A pressure medium reservoir 4 having three chambers is arranged on the first structural unit, wherein a first reservoir port is assigned to a first chamber, a second reservoir port is assigned to a second chamber, and a third reservoir port is assigned to a third chamber.

[0036] A first electrically actuatable pressure source 5 is arranged in the first structural unit.

[0037] A second electrically actuatable pressure source 2 and wheel-specific brake pressure regulating valves, which are designed as electrically actuatable inlet valves 6 and electrically actuatable outlet valves 7 for each wheel brake 8 , are provided in the second component.

[0038] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line, to which four inlet valves 6 are connected. All four wheel brakes 8 can thus be actuated by the first pressure source 5 or by the second pressure source 2 .

[0039] An electrically operable circuit isolation valve 40 is provided in the brake supply line, so that when the circuit isolation valve 40 is closed, the brake supply line is divided into a first line section, the inlet valve 6 and / or the wheel brake 8 of the rear axle is connected to the first line section, and the inlet valve 6 and / or the wheel brake 8 of the front axle is connected to the second line section. The second pressure source 2 is hydraulically connected to the first line section, and the first pressure source 5 is hydraulically connected to the second line section. When the circuit isolation valve 40 is closed, the brake system is thus separated or divided into two hydraulic brake circuits I and II. Here, in the first brake circuit I, the pressure source 2 is still connected (via the first line section) only to the wheel brake 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 is still connected (via the second line section) only to the wheel brake 8 of the front axle. The circuit isolation valve 40 is advantageously embodied as normally open when not energized.

[0040] As already mentioned, for each hydraulically actuatable wheel brake 8, the brake system comprises an inlet valve 6 and an outlet valve 7, which are hydraulically connected to one another in pairs via a central port and are each connected to a hydraulic wheel port of a second structural unit to which the corresponding wheel brake 8 is connected. A non-return valve opening in the direction of the brake supply line is connected in parallel to each inlet valve 6. The output port of the outlet valve 7 is connected to the pressure medium reservoir 4 or its second chamber via a common return line. The input ports of all inlet valves 6 can be supplied with the pressure provided by the first pressure source 5 via the brake supply line (i.e. when the circuit isolation valve 40 is open) or, for example, with the pressure provided by the second pressure source 2 in the event of a failure of the first pressure source 5.

[0041] The first electrically controllable pressure source 5 of the valve block is designed as a hydraulic cylinder piston device (or a single-circuit hydraulic electric actuator (linear actuator)), the piston of which can be actuated, in particular advanced and retracted, by a schematically shown electric motor with an interposed rotary-translational transmission also schematically shown, in order to build up and relieve pressure in a pressure chamber. The piston delimits the pressure chamber of the pressure source 5. A rotor position sensor is provided for actuating the electric motor, which detects the rotor position of the electric motor and is indicated only schematically.

[0042] The system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. Via the line section, the pressure source 5 or its pressure chamber is connected to a hydraulic port of the first structural unit, which is connected to a hydraulic port of the second structural unit via a hydraulic connecting element. This connection represents the only hydraulic pressure connection, in particular the only hydraulic connection, between the first structural unit and the second structural unit. This is the hydraulic connection for transmitting the brake pressure to actuate the wheel brakes 8.

[0043] The pressure chamber is connected to the pressure medium reservoir 4 via a (replenishing) line, independently of the actuation state of the piston. A non-return valve 53 is arranged in the line, which is connected to the second chamber and closes in the direction of the pressure medium reservoir 4. The electrically switchable valve 23 forms a further connection to the first reservoir chamber, which is also connected and connected jointly to the output connection of the linear actuator 5. The cylinder-piston arrangement 5 does not have any compensation / balancing bores, for example.

[0044] The second electrically controllable pressure source 2 of the second structural unit is designed, for example, as a double-piston pump, the two pressure sides of which are interconnected. The suction side is connected to the return line and thus to the pressure medium reservoir 4. The pressure side is connected to the first line section of the brake supply line.

[0045] According to the example, in addition to the pressure source 2 and the brake pressure regulating valves 6, 7, an electrically actuatable isolating valve 26, which is advantageously normally open when not energized, is provided in the second structural unit. The isolating valve 26 is hydraulically arranged between the port and the second line section of the brake supply line. Thus, the first pressure source 5 is detachably connected to the second line section or the brake supply line via the isolating valve 26.

[0046] According to the example, the brake system comprises a pressure sensor in brake circuit I, which is therefore assigned to the second pressure source 2. This is advantageous for preventing blowouts when the circuits are separated, that is to say when the circuit isolation valve 40 is closed. However, a pressure sensor can also be provided in brake circuit II, or a second pressure sensor can be provided, so that each of the two brake circuits I and II can be monitored directly by means of a pressure sensor.

[0047] According to the example, for monitoring leakages, the brake system comprises a level measuring device for determining the pressure medium level in the pressure medium reservoir 4 .

[0048] Each valve block is assigned an electronic control device. Each electronic control device includes electrical and / or electronic components (e.g., microcontroller, power module, valve driver, other electronic components, etc.) for controlling the electrically actuatable components of the associated valve block and optionally the associated sensors. The valve blocks and the electronic control devices are advantageously implemented as hydraulic electronic units in a known manner.

[0049] The first electronic control device controls the first pressure source 5. According to the example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0050] The second electronic control device controls the second pressure source 2. According to the example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0051] According to the example, the first pressure source 5 can be controlled only by the first electronic control device or only by the first electronic control device, and the second pressure source 2 can be controlled only by the second electronic control device or only by the second electronic control device.

[0052] The brake system has a main pressure source 5 and a secondary pressure source 2, each of which is electrically operated by the ECU and has a suction port and a pressure port. Even in a power-off state, no brake fluid can flow into the pressure port of the secondary pressure source 2. The main pressure source 5 is preferably a linear actuator with a supplementary check valve 53, while the secondary pressure source 2 is a piston pump. The secondary pressure source 2 can preferably generate a higher pressure than the main pressure source 5.

[0053] The suction sides of the two pressure sources 2 , 5 are connected to a pressure medium reservoir 4 , preferably each to at least one of the individual chambers.

[0054] The pressure side of the main pressure source 5 is connected to the main circuit node via a solenoid valve 26 , also called a pressure switching valve or isolating valve.

[0055] The pressure side of the secondary pressure source 2 is connected directly—without providing an intermediate valve—to the secondary circuit node. The two circuit nodes are connected to one another via a solenoid valve 40 , also referred to as a circuit isolation valve.

[0056] In normal operation, the pressure in the wheel brake is built up by the main pressure source 5. The pressure to the main pressure source 5 is reduced. The pressure is regulated by the inlet and outlet valves as required specifically for the wheel. If necessary, the isolation valve 26 is closed so that the main pressure source 5 can introduce additional volume.

[0057] If a particularly high volume flow is required, both pressure sources 5 and 2 work in parallel at the same time. When a particularly high pressure is required, the isolation valve 26 is closed and the secondary pressure source 2 increases the pressure to exceed the pressure of the main pressure source 5. Outside of the braking operation, atmospheric pressure equalization can be permanently ensured via the isolation valve 23 and the isolation valve 26.

[0058] In the event of a leak in the brake system, the circuit isolation valve 40 is closed and the system is thus divided into two independent brake circuits I and II.

[0059] The isolation valve 26 is preferably actuated by the slave ECU.The following description of operation in the event of a fault relates to the described valve arrangement.

[0060] If an electrical fault occurs in the primary system, in particular the primary ECU or its power supply, the slave ECU closes the isolation valve 26 to build up pressure via the secondary pressure source 2. The pressure is unloaded via the isolation valve 26 or via the outlet valve 7. The inlet and outlet valves are preferably controlled by the slave ECU so that the pressure can be adjusted specifically for the wheels.

[0061] If an electrical fault occurs in a secondary system, in particular a secondary ECU or its voltage source, the pressure is built up and discharged via the main pressure source 5, as in normal operation. Wheel-specific pressure control must be abandoned, but a joint regulation of the wheel pressures is still possible to avoid vehicle instability due to wheel locking.

[0062] In the above operating mode, the piston pump 2 is therefore the pressure source for at least two wheel brakes. In this case, in addition to the inlet valve 6 of the wheel brake 8, the pressure side of the pump 2 is only partially connected to the closed valve, that is, the circuit isolation valve 40 or the connection valve 26.

[0063] The wheel pressure regulator (WPC) can prevent the higher pilot pressure from entering the wheel by closing the inlet valve. However, in this case, the pump pumps against the hydraulic rigidity, which can lead to high pressure peaks and thus damage the hydraulic components.

[0064] Therefore, the pump should be controlled so that the target pressure is set quickly and without overshoot. The difficulty here is that the pump delivers the fluid while the motor is rotating and cannot be throttled on the suction side.

[0065] In a preferred method according to the invention, on the one hand, once the target pressure is almost reached, the motor is electrically decelerated. This occurs by isolating the motor from the supply voltage by means of an electronic power driver module and short-circuiting the motor, thereby allowing the braking torque to be generated by the current generated by the generator's own voltage and the induced magnetic field.

[0066] Furthermore, a coasting characteristic curve is determined. This means that the dependence between the counterpressure and the gradient is determined as a function of the speed set during coasting. This characteristic curve can be learned once in advance and stored in the brake system. Alternatively or additionally, the characteristic curve can be learned and / or adjusted during operation by measuring the coasting behavior of the pump. Figure 2 This characteristic curve is shown in .

[0067] With this knowledge, conclusions can be drawn in normal operation regarding the coasting time T. The gradient G is formed from the interpolated parameters p1 and p2 (both < 0) and the pressure P (=system pressure (Psys)):

[0068] G=p1*P+p2

[0069] Because in Figure 1 In an exemplary brake system of , the suction side of the pump is connected to a pressureless reservoir, so that the system pressure on the pressure side of the pump corresponds to the pressure difference on both sides of the pump.

[0070] The inertia time T is obtained based on the current speed n and gradient G.

[0071]

[0072] Therefore the subsequent volume V, which is still delivered by these N rotations:

[0073] V=α*N

[0074] For pressure control, a known pressure / volume characteristic curve is used to determine a given volume requirement to meet the pressure requirement. This can be used to determine a threshold speed n*, which if set sets the target pressure precisely without overshooting in coasting.

[0075]

[0076] Where p1<0, p2<0

[0077] This threshold speed may then be used as a parameter or limit for the hydraulic pump.

[0078] In the case of operation with an LAC, this method can also be used advantageously by a controller, since the controller of the LAC simply requests the volume requirement that the piston pump should contribute in addition to the target pressure.

[0079] As the pressure continues to increase while the pump is coasting, various counterpressures are present at the piston pump, which have a corresponding effect on the coasting behavior. Figure 2 The linear coasting characteristic curve shown can be taken into account simply by taking the current actual pressure and the target pressure and forming the sum from them, which can also be weighted:

[0080]

[0081] Where b+c=1

[0082] In one variant, the motor controller can first be assigned a speed corresponding to the volume requirement. If the coasting speed n* is less than nVol or the actual speed n 实际 , the target speed is set to 0 and the motor sets the desired pressure during its coasting or stopping operation.

[0083] Thus, by means of the method of the invention, the pressure can be set quickly and precisely without any overshoot without additional hardware.

Claims

1. A method for controlling a hydraulic brake system having at least one pressure supply device for conveying brake fluid to at least one wheel brake, wherein: In order to set a target pressure in the at least one wheel brake, a required brake fluid volume is determined, and a pressure supply device is controlled to deliver this brake fluid volume, characterized in that the inertia of the pressure supply device is observed by determining a threshold speed, which allows a subsequent volume corresponding to the required brake fluid volume to be delivered when the motor of the pressure supply device is switched off, and the speed of the pressure supply device is limited to this threshold speed or the threshold speed is requested by the pressure supply device.

2. The method according to claim 1, characterized in that The pressure supply device is a piston pump.

3. The method according to claim 2, characterized in that The brake system is a redundant brake system having an additional second pressure supply, in particular a linear actuator.

4. The method according to claim 2 or 3, characterized in that The piston pump is not provided with a suction throttle, in particular with a switchable valve, on the suction side and is in particular connected directly to a pressureless brake fluid reservoir.

5. The method according to any one of the preceding claims, characterized in that In particular, the pressure difference present at the pressure supply device is taken into account when determining the threshold speed by using a coasting characteristic curve which specifies a speed gradient and / or a coasting time for a given pressure difference.

6. The method according to any one of the preceding claims, characterized in that The power supply input of the motor of the pressure supply device is short-circuited when the motor is switched off.

7. The method according to any one of the preceding claims, characterized in that The required brake fluid volume is determined from the pressure / volume characteristic curve.

8. The method according to any one of the preceding claims, characterized in that Once the actual rotational speed of the pressure supply device is greater than or equal to the threshold rotational speed, the target rotational speed of the pressure supply device is set to zero.

9. A motor vehicle hydraulic brake system having at least one pressure supply device and a control unit for controlling the pressure supply device, characterized in that: The control unit is configured to carry out the method as claimed in one of the preceding claims. 10 . A computer program product, which is designed such that, when it is executed in a control device, it carries out the method according to claim 1 .

11. A data carrier signal transmitting the computer program product according to claim 10.

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