Method for operating a piston pump in brake systems without suction throttling

Abstract

The invention relates to a method for controlling a hydraulic brake system having at least one pressure supply device for delivering braking fluid into at least one wheel brake. In order to adjust the target pressure in the at least one wheel brake, a required braking fluid volume is determined, and the pressure supply device is actuated in order to deliver the braking fluid volume. In order to quickly and precisely adjust the target pressure, the discharge behavior of the pressure supply device is taken into account in that a threshold rotational speed is determined which delivers an overrun volume when the motor of the pressure supply device is deactivated, said overrun volume corresponding to the required brake fluid volume, and the rotational speed of the brake supply device is limited to the threshold rotational speed or the threshold rotational speed is requested by the pressure supply device.

Description

[0001] Method for operating a piston pump in brake systems without suction throttling

[0002] The invention relates to a method for controlling a hydraulic brake system having at least one pressure supply device for supplying brake fluid to at least one wheel brake. To set a target pressure in the at least one wheel brake, a required brake fluid volume is determined, and the pressure supply device is controlled to supply the brake fluid volume. The invention also relates to such a brake system.

[0003] Such braking systems have long been known for their ability to build up brake pressure independently of the driver using a pressure supply device. The target pressure is usually to be reached very quickly, which requires high flow rates and thus high speeds of the motors of the pressure supply device. Since these speeds do not drop suddenly to zero, brake fluid continues to be pumped even after the target pressure is reached, thus delivering a follow-up volume. This can lead to a significant overshoot of the pressure and thus to overbraking. This results in both a loss of comfort and safety.

[0004] It is therefore an object of the invention to provide a method for such braking systems which avoids the above disadvantages.

[0005] The object is achieved according to the invention by taking into account the run-out behavior of the pressure supply device when the pressure is set. For this purpose, a limiting speed is calculated which, when the motor of the pressure supply device is switched off, would deliver a follow-up volume that corresponds to the required brake fluid volume. This means that if the pressure supply device is running at the limiting speed and is switched off, exactly the required brake fluid volume is still pumped in its follow-up. The determined limiting speed is specified as a limit to the pressure supply device, or the limiting speed is simply requested directly from the pressure supply device. This means that the requirement for a speed known from the prior art can be expanded by means of such a limit, and only then can the limited speed requirement be requested from the pressure supply device.Alternatively, the limit speed determined according to the invention is requested directly. This generally initially exceeds the range of speeds physically achievable by the pressure supply device. Thus, the pressure supply device runs at its maximum speed, or rather, the maximum permissible speed. Only when the actual pressure approaches the target pressure and thus the volume of brake fluid still to be delivered, i.e., required, decreases, does the limit speed drop to a range that limits the actual speed of the pressure supply device. Thus, the pump runs down after being switched off, and the target pressure is reached precisely by the pressure supply device running on.

[0006] 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 while maintaining manageable component costs. By combining such a pump with the method according to the invention, a target pressure can be achieved particularly quickly and precisely.

[0007] In a further preferred embodiment of the invention, the braking system is a redundant braking system with an additional second pressure supply device, in particular a linear actuator. Such redundant braking systems can be used for highly automated driving, in which the driver is the last fallback.

[0008] In a particularly preferred embodiment of the invention, the piston pump has no suction throttling, in particular no switchable valve on a suction side, and is in particular directly connected to a pressure-free brake fluid reservoir. Thus, the cost of this additional component can be eliminated while still preventing excessive pressure.

[0009] In a further preferred embodiment of the invention, a pressure difference prevailing at the pressure supply device is taken into account when determining the limiting speed, in particular by using a run-down characteristic curve that specifies a speed gradient and / or a run-down time for a given pressure. Generally, the greater the backpressure, the shorter the run-down time. In an alternative embodiment, other characteristic curves or maps can also be used, each relating the run-down volume to the current speed of the pump and the prevailing pressure, so that the limiting speed can be determined for a given state of the braking system.

[0010] An analytical consideration according to the law of conservation of energy shows that friction can also be added to the determination:

[0011] J: Mass moment of inertia of the motor w: Angular frequency / speed of the motor Pi, P2, P: Pressure R: Friction coefficient N: Number of revolutions a: Volume per revolution

[0012] If we solve this equation for the number of revolutions N and compare it with the experimentally found solution shown below: n: speed pi: parameter 1

[0013] P2: Parameter 2 particularly shows the quadratic speed dependence. Parameters p1 and p2 can therefore be determined either experimentally or using the quantities from the analytical analysis.

[0014] In a further preferred embodiment of the invention, the power supply of the motor of the pressure supply device is short-circuited when the motor is switched off. This leads to a braking electromagnetic force via induction and thus to a faster deceleration of the pump. This results in a lower follow-up delivery volume for a given speed and differential pressure across the pump. The pump can thus be operated at high speed for longer, whereby the target pressure or volume is reached more quickly without pressure overshoot occurring.

[0015] In a further preferred embodiment of the invention, the required brake fluid volume is determined from a pressure-volume characteristic curve. This makes it particularly easy to establish a relationship between the target pressure and the required brake fluid volume.

[0016] In a further preferred embodiment of the invention, as soon as the actual speed of the pressure supply device is greater than or equal to the limit speed, the target speed of the pressure supply device is set to zero. Thus, the electrical power supplied to the pump is also reduced to zero, and the pump runs down. The method according to the invention thus precisely establishes the target pressure without any additional power supply to the motor.

[0017] The object is further achieved by a hydraulic motor vehicle brake system comprising at least one pressure supply device and a control unit for regulating the pressure supply device, wherein the control unit is configured to execute the above-mentioned method. The object is further achieved by a computer program product configured to execute one of the methods when executed in a control device.

[0018] The problem is also solved by a data carrier signal that transmits such a computer program product. A redundant braking system having several pressure or volume sources: a linear actuator (LAC) and a piston pump

[0019] Further features, advantages, and possible applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, both individually and in any combination, are part of the subject matter of the invention, regardless of their summary in the claims or their references.

[0020] Fig. 1 shows schematically a braking system according to the invention,

[0021] Fig. 2 shows a diagram with an exemplary run-out characteristic curve;

[0022] Fig. 1 shows a redundant hydraulic braking system for motor vehicles. For example, the braking system is designed to actuate four hydraulically actuated wheel brakes 8; expansion to more wheel brakes is easily possible. For example, the wheel brakes (HL, HR) are assigned to the rear axle and the wheel brakes (VL, VR) to the front axle of the vehicle.

[0023] The brake system comprises a first structural unit, which is designed, for example, as a first electro-hydraulic brake control unit with a valve block and a first electronic control device, and a second structural unit, which is designed, for example, as a second electro-hydraulic brake control unit with a valve block and a second electronic control device.

[0024] A pressure medium reservoir 4 with three chambers is arranged on the first structural unit, wherein a first reservoir connection is assigned to the first chamber, a second reservoir connection is assigned to the second chamber and a third reservoir connection is assigned to the third chamber.

[0025] A first electrically actuated pressure source 5 is arranged in the first structural unit.

[0026] In the second structural unit, a second electrically actuated pressure source 2 and wheel-individual brake pressure modulation valves are arranged, which are designed as an electrically actuated inlet valve 6 and an electrically actuated outlet valve 7 for each wheel brake 8.

[0027] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line to which the four inlet valves 6 are connected. Thus, all four wheel brakes 8 can be actuated by the first pressure source 5 or by the second pressure source 2.

[0028] An electrically actuated circuit isolation valve 40 is arranged in the brake supply line, so that when the circuit isolation valve 40 is closed, the brake supply line is separated into a first line section, to which the inlet valves 6 or the wheel brakes 8 of the rear axle are connected, and a second line section, to which the inlet valves 6 or the wheel brakes 8 of the front axle are connected. 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.In the first brake circuit I, the pressure source 2 (via the first line section) is connected only to the wheel brakes 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 (via the second line section) is connected only to the wheel brakes.

[0029] 8 of the front axle. The circuit isolation valve 40 is advantageously designed to be open when de-energized.

[0030] As already mentioned, the braking system comprises an inlet valve 6 and an outlet valve 7 for each hydraulically actuated wheel brake 8, which are hydraulically interconnected in pairs via central connections and each connected to a hydraulic wheel connection of the second structural unit to which the corresponding wheel brake 8 is connected. A check valve opening towards the brake supply line is connected in parallel to each of the inlet valves 6. The output connections of the outlet valves 7 are connected to the pressure fluid reservoir 4 or its second chamber via a common return line. The input connections of all inlet valves 6 can be supplied with a pressure provided by the first pressure source 5 or, for example, if the first pressure source 5 fails, by the second pressure source 2.

[0031] The first electrically controllable pressure source 5 of the valve block is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electro-hydraulic actuator (linear actuator)), the pistons of which are driven by a schematically indicated electric motor with the interposition of a likewise schematically shown rotation-translation _, The electric motor is actuated by a gear, in particular, it can be moved forward and backward to build up and reduce pressure in a pressure chamber. The piston defines the pressure chamber of the pressure source 5. A rotor position sensor, indicated only schematically, is provided to control the electric motor.

[0032] A system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. By means of the line section, the pressure source 5 or its pressure chamber is connected to a hydraulic connection of the first structural unit, which is connected to a hydraulic connection 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 and second structural units. It is a hydraulic connection for transmitting brake pressure for actuating the wheel brakes 8.

[0033] The pressure chamber is connected to the pressure fluid reservoir 4 via a (suction) line, regardless of the piston's actuation state. A check valve 53, closing toward the pressure fluid reservoir 4, is arranged in the line and connected to the second chamber. An electrically switchable valve 23 forms a further connection to the first reservoir chamber, which is also jointly connected to the output port of the linear actuator 5. The cylinder-piston assembly 5, for example, has no sniffing holes.

[0034] The second electrically controllable pressure source 2 of the second assembly is designed, for example, as a two-piston pump whose two pressure sides are interconnected. The suction sides are connected to the return line and thus to the pressure fluid reservoir 4. The pressure sides are connected to the first line section of the brake supply line.

[0035] In addition to the pressure source 2 and the brake pressure modulation valves 6, 7, an electrically actuated, preferably normally open, isolation valve 26 is arranged in the second structural unit, for example. Isolation valve 26 is hydraulically arranged between the connection 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 isolation valve 26.

[0036] The braking system, for example, includes a pressure sensor in brake circuit I, which is thus assigned to the second pressure source 2. This is advantageous for burst protection during active circuit separation, i.e., when the circuit separation valve 40 is closed. However, the pressure sensor can also be arranged 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 directly monitored by means of a pressure sensor.

[0037] For example, the brake system for leakage monitoring comprises a level measuring device for determining a pressure medium level in the pressure medium reservoir 4.

[0038] Each valve block is assigned an electronic control device. Each electronic control device comprises electrical and / or electronic elements (e.g., microcontrollers, power units, valve drivers, other electronic components, etc.) for controlling the electrically actuated components of the associated valve block and, if applicable, the associated sensors. The valve block and electronic control device are advantageously designed as an electrohydraulic unit, as is known in the art.

[0039] The first electronic control device controls the first pressure source 5. For example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0040] The second electronic control device controls the second pressure source 2. For example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0041] For example, the first pressure source 5 can be or is controlled exclusively by the first electronic control device and the second pressure source 2 can be or is controlled exclusively by the second electronic control device.

[0042] The braking system has a primary pressure source 5 and a secondary pressure source

[0043] 2, each of which is electrically operated by an ECU and has a suction port and a pressure port. No brake fluid can flow into the pressure port of the secondary pressure source 2, even when de-energized. Preferably, the primary pressure source 5 is a linear actuator with a suction check valve 53, and the secondary pressure source 2 is a piston pump. Preferably, the secondary pressure source 2 can generate a higher pressure than the primary pressure source 5.

[0044] The suction sides of the two pressure sources 2, 5 are connected to a pressure medium reservoir 4, preferably to at least one of the separate chambers.

[0045] The pressure side of the primary pressure source 5 is connected to a primary circuit node via an electromagnetic valve 26, also called a pressure connection valve or isolation valve.

[0046] The pressure side of secondary pressure source 2 is connected directly (without the interposition of a valve) to a secondary circuit node. The two circuit nodes are connected via an electromagnetic valve 40, also called a circuit dividing valve.

[0047] During normal operation, the pressure in the wheel brakes is built up by primary pressure source 5. The pressure is released into primary pressure source 5. The pressure is modulated for each wheel as needed by the inlet and outlet valves.

[0048] If necessary, the isolation valve 26 is closed so that the primary pressure source 5 can draw in additional volume.

[0049] If a particularly high flow rate is required, both pressure sources 5 and 2 operate in parallel. If a particularly high pressure is required, the isolation valve 26 is closed, and the secondary pressure source 2 increases the pressure above the pressure of the primary pressure source 5. Outside of braking situations, atmospheric pressure equalization can be permanently ensured via the isolation valve 23 and the isolation valve 26. In the event of a leak in the braking system, the circuit isolation valve 40 is closed, dividing the system into two independent brake circuits I and II.

[0050] Isolation valve 26 is preferably controlled by the secondary ECU. The following description of operation in the event of a fault refers to this valve assignment.

[0051] If the primary system fails electrically, specifically the primary ECU or its power supply, the secondary ECU closes the isolation valve 26 to build up pressure via the secondary pressure source 2. Pressure is released via the isolation valve 26 or via the exhaust valves 7. Preferably, the intake and exhaust valves are controlled by the secondary ECU so that the pressure can be modulated for each individual wheel.

[0052] If the secondary system fails electrically, specifically the secondary ECU or its voltage source, the pressure is increased and decreased via the primary pressure source 5, as in normal operation. Individual wheel pressure control is not required, but joint modulation of the wheel pressures remains possible to prevent the vehicle from being destabilized by locking wheels.

[0053] In the above operating modes, piston pump 2 is therefore the pressure source for at least two wheel brakes. In addition to the inlet valves 6 of the wheel brakes 8, the pressure side of pump 2 is partially connected to only one closed valve, circuit isolation valve 40 or connection valve 26.

[0054] A wheel pressure regulator (WPC) can keep a higher pre-pressure away from the wheel by closing the inlet valve. However, in this case, the pump pumps against a hydraulically stiff space, which can lead to large pressure peaks and thus damage to the hydraulic components.

[0055] The pump must therefore be controlled in such a way that a target pressure is set quickly and without overshoot. The difficulty here is that the pump delivers fluid while the motor is running and cannot be throttled on the suction side.

[0056] In the preferred method according to the invention, the motor is electrically braked as soon as the target pressure is almost reached. This is achieved by disconnecting it from the supply voltage using the electronic power driver components and short-circuiting it, thus allowing braking torque to be generated by the current generated by its own generator voltage and the induced magnetic field.

[0057] Next, a coasting characteristic curve is determined. This means determining the relationship between backpressure and the gradient with respect to the speed that occurs during coasting. This characteristic curve can be learned once in advance and stored in a braking system. Alternatively or additionally, the characteristic curve can be learned and / or adjusted during operation by measuring the coasting behavior of the pump. Such a characteristic curve is shown in Fig. 2.

[0058] With this knowledge, the run-down time T can then be determined during normal operation. The gradient G is formed from the parameters p1 and p2 (both < 0) of the interpolation and the pressure P (= Psys):

[0059] G = p * P + p2

[0060] Since in the exemplary brake system in Fig. 1 the suction side of the pump is connected to the pressure-free reservoir, the system pressure on the pressure side of the pump corresponds to the pressure difference across the pump.

[0061] The run-down time T, from the current speed n, and the gradient G.

[0062] And thus the after-run volume V that is still pumped by these N revolutions:

[0063] V=a*N For pressure control, the pressure requirement is calculated using the known

[0064] Pressure-volume characteristic curve determines the given volume requirement for satisfaction.

[0065] From this, a limit speed n* can be determined which, if set, precisely sets the target pressure without overshoot during run-out.

[0066] With p1 <0, p2<0

[0067] This limit speed can then be used either as a specification or as a limitation for the hydraulic pump.

[0068] In the case of operation with the LAC, this method can also be used advantageously by the controller for the LAC simply requesting the volume requirement that the piston pump should contribute in addition to the set pressure.

[0069] Since the pressure continues to rise as the pump decelerates, various backpressures exist at the piston pump, which accordingly affect the deceleration behavior. Assuming a linear deceleration characteristic curve as shown in Fig. 2, this can be easily accounted for by taking the current actual pressure and the target pressure and calculating a sum, which can also be weighted:

[0070] With b+c=1

[0071] In one variant, the motor controller can initially be set to a speed that matches the volume requirement. If the deceleration speed n* is lower than nVol or the actual speed nact, the target speed is set to 0, and the motor adjusts to the desired pressure during its deceleration or stopping process.

[0072] The method according to the invention thus makes it possible to set a pressure quickly and precisely without overshoot without additional hardware.

Claims

Patent claims 1 . Method for controlling a hydraulic brake system having at least one pressure supply device for conveying brake fluid into 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 the pressure supply device is controlled to convey the brake fluid volume, characterized in that a run-out behavior of the pressure supply device is taken into account by determining a limit speed which, when the motor of the pressure supply device is switched off, conveys a run-on volume which corresponds to the required brake fluid volume, and the speed of the pressure supply device is limited to the limit speed or the limit speed is requested by the pressure supply device.

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

3. Method according to claim 2, characterized in that the braking system is a redundant braking system with an additional second pressure supply device, in particular a linear actuator.

4. Method according to claim 2 or 3, characterized in that the piston pump has no suction throttling, in particular no switchable valve on a suction side and in particular is directly connected to a pressure-free brake fluid reservoir.

5. Method according to one of the preceding claims, characterized in that in determining the limit speed, a pressure difference prevailing at the pressure supply device is taken into account, in particular by using a run-out characteristic curve which is suitable for a A given pressure difference indicates a speed gradient and / or a run-down time. Method according to one of the preceding claims, characterized in that the voltage supply inputs of the motor of the pressure supply device are short-circuited when the motor is switched off. Method according to one of the preceding claims, characterized in that the required brake fluid volume is determined from a pressure-volume characteristic curve. Method according to one of the preceding claims, characterized in that as soon as the actual speed of the pressure supply device is greater than or equal to the limit speed, the target speed of the pressure supply device is set to zero.A hydraulic motor vehicle brake system comprising at least one pressure supply device and a control unit for regulating the pressure supply device, characterized in that the control unit is configured to execute a method according to one of the preceding claims. A computer program product configured to execute one of the methods according to claims 1 to 8 when executed in a control device. A data carrier signal transmitting a computer program product according to claim 10.

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