Method and device for controlling a switching valve

Abstract

Method for controlling the switching valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, in which - the vehicle is detected to be stationary (502) and as long as the driver applies the brakes while stationary (501), - during a first phase the switching valve is controlled with a first, non-zero current (iUSV1) (503) and - during a subsequent second phase, the switching valve is controlled with a second current (iUSV2) that is different from zero and different from the first current (iUSV1) (505), - the first current (iUSV1) is chosen such that the switching valve just closes at this current and - the second current (iUSV2) is selected such that the changeover valve is reliably closed at this current, where - the switching valve is a normally open valve and - the second current (iUSV2) is greater than the first current (iUSV1) and the transition to the second phase then takes place when the driver reduces the intensity of the braking action (504).

Description

State of the art

[0001] Hill Hold Control (HHC) is now a standard feature in many ESP systems (ESP = Electronic Stability Program). This function makes starting on an incline easier. It does this by maintaining brake pressure for up to approximately 2 seconds after the brake is released. During this time, the driver can perform a roll-free start.

[0002] From DE 103 43 985 A1 a method for preventing a vehicle from rolling away on an incline is known, in which an analogized, normally open isolating valve is controlled to maintain a brake actuation pressure.

[0003] This document discloses a method for controlling the changeover valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, in which the standstill of the vehicle is detected and, as long as the driver operates the brake during the standstill, the changeover valve is controlled with a first current strength, which is not zero, during a first phase and, during a subsequent second phase, the changeover valve is controlled with a second current strength, which is not zero and differs from the first current strength, wherein the changeover valve is a normally open valve. Disclosure of the invention

[0004] The invention relates to a method for controlling the switching valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, in which - the vehicle's standstill is detected and as long as the driver applies the brakes while stationary, - during a first phase the switching valve is controlled with a first current intensity that is not zero and - during a subsequent second phase, the switching valve is controlled with a second current that is different from zero and different from the first current, - the first current strength is chosen such that the switching valve just closes at this current strength and - the second current strength is chosen such that the switching valve is reliably closed at this current strength, whereby - the switching valve is a normally open valve and - the second current is greater than the first current and the transition to the second phase then takes place when the driver reduces the intensity of the braking.

[0005] Reducing brake actuation creates a pressure differential at the UPS. The transition to the second phase ensures that the UPS remains closed even against this pressure differential. This makes it possible to implement a hill-hold function in an energy-efficient and therefore thermally uncritical manner.

[0006] An advantageous embodiment of the invention is characterized in that the first current intensity is selected such that the switching valve just closes at a predetermined pressure difference applied to it.

[0007] An advantageous embodiment of the invention is characterized in that the specified pressure difference is a small pressure difference.

[0008] An advantageous embodiment of the invention is characterized in that the specified pressure difference is a pressure difference between 2 and 8 bar, in particular 5 bar.

[0009] An advantageous embodiment of the invention is characterized in that the brake circuit is a hydraulic brake circuit.

[0010] The invention further relates to a device for controlling the switching valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, comprising - Stationary detection devices by means of which the stationary state of the vehicle is detected, - Brake actuation detection device, by means of which the actuation of the brake by the driver is detected - Power supply means by which the changeover valve is energized, wherein the power supply means are designed such that as long as the driver applies the brake while stationary, - during a first phase the switching valve is controlled with a first current intensity that is not zero and - during a subsequent second phase, the switching valve is controlled with a second current that is different from zero and different from the first current, - the first current (iUSV1) is chosen so that the switching valve just closes at this current and - the second current (iUSV2) is selected so that the changeover valve is reliably closed at this current, where - the switching valve is a normally open valve and - the second current (iUSV2) is greater than the first current (iUSV1) and - the transition to the second phase then takes place when the driver reduces the intensity of the braking action (504).

[0011] The advantageous embodiments of the method according to the invention naturally also manifest themselves as advantageous embodiments of the device according to the invention, and vice versa.

[0012] The drawing includes the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5. Fig. Figure 1 shows the topological structure of a brake circuit suitable for a hillhold function according to the state of the art. Fig. Figure 2 shows the time course of various quantities in a first embodiment for controlling the switching valve (UPS). Fig. Figure 3 shows the time course of various quantities in a second embodiment for controlling the switching valve (UPS). Fig. Figure 4 shows the time course of various quantities in a third embodiment for controlling the switching valve (UPS). Fig. Figure 5 shows the process of the inventive method in a flowchart.

[0013] In Fig. Figure 1 schematically depicts the braking system of a vehicle equipped with a vehicle dynamics control system, in accordance with the state of the art. All parts not essential for understanding have been omitted. A braking system with two brake circuits is considered: Brake circuit 1 is the left branch in Fig. Brake circuit 1 (also known as the floating circuit) is the first branch (also known as brake circuit 2, or rod circuit 1). Brake circuit 1 covers the rear wheels, and brake circuit 2 covers the front wheels. This configuration is also called a II-distribution. Of course, other configurations are also possible.

[0014] (Details can be found, for example, in "Kraftfahrtechnisches Taschenbuch, 23rd edition, ISBN No. 3-528-03876-4, pp. 654-655)

[0015] Before discussing the processes in the braking system, the individual blocks should first be briefly introduced: 300 Hydraulic brake pressure control device 301 Master brake cylinder 302 HSV1 (= High-pressure switching valve of brake circuit 1) 303 UPS1 (= Switching valve of brake circuit 1) 306 RFP1 (= Return pump of brake circuit 1) 308 EVHL (= Inlet valve rear left, i.e. at the brake of the left rear wheel) 309 AVHL (= rear left exhaust valve) 311 EVHR (= rear right intake valve) 310 AVHR (= rear right exhaust valve) 316 Wheel brake of the left rear wheel 317 Wheel brake of the right rear wheel 305 HSV2 (= High-pressure switching valve of brake circuit 2) 304 UPS2 (= Switching valve of brake circuit 2) 307 RFP2 (= Return pump of brake circuit 2) 312 EVVL (= front left inlet valve) 313 AVVL (= front left exhaust valve) 315 EVVR (= front right inlet valve) 314 AVVR (= front right exhaust valve) 318 Wheel brake of the left front wheel 319 Wheel brake of the right front wheel

[0016] The two return pumps are driven by a common motor, meaning they are operated in parallel.

[0017] Two lines run from the master brake cylinder 301 to the brake pressure control unit 300. Within this unit, a branch leads to the high-pressure switching valves 302 and 305 and to the changeover valves 303 and 304. The high-pressure switching valve 302 is connected to the outlet valves 309 and 310 and the suction side of the return pump 306. The changeover valve 303 is connected to the inlet valves 308 and 311 and the delivery side of the return pump 306. The outlet side of the inlet valve 308 and the inlet side of the outlet valve 309 are connected to the wheel brake 316, as are the inlet valve 311 and the outlet valve 310 to the wheel brake 317.

[0018] The high-pressure switching valve 305 is connected to the outlet valves 313 and 314 and the suction side of the return pump 307. The changeover valve 304 is connected to the inlet valves 312 and 315 and the delivery side of the return pump 307. The outlet side of the inlet valve 312 and the inlet side of the outlet valve 313 are connected to the wheel brake 318, as are the inlet valve 315 and the outlet valve 314 to the wheel brake 319.

[0019] The return pump 306 is located between the switching valve 303 (supply side) and the outlet valve 310 (suction side), the return pump 307 is located between the switching valve 304 (supply side) and the outlet valve 313 (suction side).

[0020] In a first embodiment, the switching valves 303 and 304 are closed with the required set current as soon as the vehicle is stationary and the driver presses the brake pedal.

[0021] In Fig. Figure 2 shows time t plotted on the x-axis. The changeover valves are closed with the required set current iUSV as soon as the vehicle is stationary (v_Fzg = 0) and the driver depresses the brake pedal. After the driver releases the brakes, the UPS continues to receive current for up to 2 seconds. This results in a time delay between the falling edge of p_HZ (p_HZ is the hydraulic pressure in the master cylinder) and the falling edge of p_Rad (p_Rad is the hydraulic pressure in the wheel cylinder). This design completely prevents the vehicle from rolling backward and is very convenient. However, the potentially very long current flow to the changeover valves can be a disadvantage, leading to thermal problems and thus requiring complex heat dissipation measures.

[0022] Another version of this function closes the UPS valves only when the driver brakes. This is in Fig. Figure 3 illustrates this. However, the UPS switching times can lead to a pressure drop (delta_p), which can then cause the vehicle to roll backward briefly but uncomfortablely during acceleration. The minimal thermal requirements of the solution are advantageous, as the valves are only energized for a maximum of 2 seconds.

[0023] Similar to the first-mentioned form, according to Fig. As proposed in section 4, the changeover valve should close immediately when the vehicle is stationary. Unlike the first described configuration, the UPS (Uninterruptible Power Supply) is only energized with a minimum current iUSV1 to ensure it remains closed without pressure. This minimum current can be selected so that the valve remains just closed against, for example, a differential pressure of 5 bar. This is sufficient because there is no pressure drop across the UPS when the driver is braking while stationary. Only when the driver releases the brakes is the current increased to the required target current iUSV2 to maintain pressure.

[0024] The process of the inventive method is described in Fig. 5 is shown. After starting in block 500, block 501 checks whether the driver is applying the brakes. This can be done, for example, by checking whether the brake pressure in the master cylinder exceeds a threshold value. If the answer is "no" (in Fig. (5 is always marked with "n"), then the path branches back to block 500.

[0025] If the answer is "yes" (in Fig. (5 always marked with "y"), then block 502 checks whether the vehicle is stationary. If the answer is "no", the program branches back to block 500. If the answer is "yes", then block 503 activates the changeover valve with an initial current iUSV1.

[0026] Block 504 then checks whether the driver is reducing the intensity of the brake pedal application. This can be determined, for example, by verifying whether there is a negative change in brake pressure in the master cylinder. If the answer is "no," the system branches back to block 503.

[0027] If the answer is "yes", then the changeover valve in block 505 is subsequently controlled with a second current, iUSV2. The second current is chosen so that the UPS closes more securely and reliably than with the first current.

[0028] The inventive method ends in block 506.

Claims

[1] Method for controlling the switching valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, in which - the vehicle is detected to be stationary (502) and as long as the driver applies the brakes while stationary (501), - during a first phase the switching valve is controlled with a first, non-zero current (iUSV1) (503) and - during a subsequent second phase, the switching valve is controlled with a second current (iUSV2) that is different from zero and different from the first current (iUSV1) (505), - the first current (iUSV1) is chosen such that the switching valve just closes at this current and - the second current (iUSV2) is selected such that the changeover valve is reliably closed at this current, where - the switching valve is a normally open valve and - the second current (iUSV2) is greater than the first current (iUSV1) and the transition to the second phase then takes place when the driver reduces the intensity of the braking action (504). [2] Method according to claim 1, characterized by , that the first current (iUSV1) is chosen such that the switching valve closes at a given pressure differential applied to it. [3] Method according to claim 2, characterized by that the specified pressure difference is a pressure difference between 2 and 8 bar, in particular 5 bar. [4] Method according to claim 1, characterized by that the brake circuit is a hydraulic brake circuit. [5] Device for controlling the switching valve of a brake circuit designed for driver-independent brake pressure build-up within the framework of a vehicle standstill holding function, comprising - Stationary detection devices by means of which the stationary state of the vehicle is detected, - Brake actuation detection means by which the actuation of the brake by the driver is detected, - Power supply means by which the changeover valve is energized, wherein the power supply means are designed such that as long as the driver applies the brake while stationary, - during a first phase the switching valve is controlled with a first, non-zero current (iUSV1) (503) and - during a subsequent second phase, the switching valve is controlled with a second current (iUSV2) that is different from zero and different from the first current (iUSV1) (505), - the first current (iUSV1) is chosen so that the switching valve just closes at this current and - the second current (iUSV2) is selected so that the changeover valve is reliably closed at this current, where - the switching valve is a normally open valve and - the second current (iUSV2) is greater than the first current (iUSV1) and - the transition to the second phase then takes place when the driver reduces the intensity of the braking action (504).

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