DE102021205975A1 - Method for loading a linear actuator of a braking system, control device and braking system - Google Patents

Abstract

The invention relates to a method for charging a linear actuator of a brake system, with a circuit separating valve first being closed, which connects a first brake circuit to a second brake circuit, and then the linear actuator being charged. In this way, in particular, the effect of a leak in a sequence valve can be reduced. The invention also relates to an associated control device and an associated braking system.

Description

The invention relates to a method for charging a linear actuator of a braking system and an associated control device and an associated braking system.

Braking systems are typically used in motor vehicles in order to decelerate them in a targeted manner. Linear actuators are often used here, for example to increase an applied braking pressure or to generate it independently of the driver. Linear actuators typically work hydrostatically, i.e. they provide a pressure which acts in the respective wheel brakes, with a volume of brake fluid pushed out of the linear actuator reaching the wheel brakes directly. Since linear actuators typically operate intermittently, it is necessary to charge them periodically.

It is an object of the invention to provide a method for loading a linear actuator of a brake system, which is implemented alternatively or better than known designs. It is also an object of the invention to provide an associated control device and an associated braking system. According to the invention, this is achieved by a method, a control device and a braking system according to the respective main claims. Advantageous configurations can be found, for example, in the respective dependent claims. The content of the claims is made part of the content of the description by express reference.

• - Schließen eines Kreistrennventils, welches einen ersten Bremskreis mit einem zweiten Bremskreis verbindet, und dann
• - Laden des Linearaktuators.

The invention relates to a method for loading a linear actuator of a brake system, the method having the following steps:

• - Closing a circuit isolation valve connecting a first braking circuit to a second braking circuit, and then
• - Loading the linear actuator.

The method makes it possible to localize any leaks in valves with regard to their effect on the braking system, since the circuit separating valve remains closed and thus a part of the braking system which is arranged fluidically opposite the linear actuator with regard to the circuit separating valve is not affected by any leakage.

A circuit separating valve is, in particular, a valve which fluidly separates at least two brake circuits of a brake system from one another in a switchable manner. For example, a brake circuit can be assigned to a front axle and another brake circuit can be assigned to a rear axle. Likewise, each brake circuit can be assigned to diagonally opposite wheels.

The circuit separating valve can remain closed, in particular during charging. This ensures that the previously mentioned separation is maintained for the entire charging process.

A supply of fluid can take place, in particular during charging, in that the linear actuator has a connection to a brake fluid reservoir or another storage vessel. Typically, a reduction in pressure in a brake circuit due to charging should advantageously be prevented.

The method can be carried out in particular in response to a leak being detected in a sequence valve. In particular, the sequence valve can connect the linear actuator to a brake circuit. The switching valve typically serves to separate the linear actuator from the remaining fluidic part of the braking system, for example in the event that the linear actuator is charged. If the sequence valve is leaking, it can no longer be ensured that charging the linear actuator will not lead to a pressure drop in parts of the braking system. In such a case, therefore, the use of the method according to the invention is particularly advantageous.

In order to detect a leak, pressure can be built up, in particular in a part of a brake circuit which is opposite the linear actuator with respect to the connection valve, and the connection valve can then be closed. It can be detected whether the sequence valve is tight or not. In particular, a leak can be detected if a pressure loss is at least as great as a threshold value in the part of the brake circuit in which pressure has built up while the sequence valve is closed. This indicates a leak. A leak can also be detected if, while the sequence valve is closed, a piston of the linear actuator is moved by pressure from that part of the brake system in which pressure has built up. Such a movement can be detected, for example, by means of a piston position sensor. This indicates that the sequence valve is not tight despite being closed and that the piston is therefore moved by the pressure applied.

In particular, the sequence valve can connect the linear actuator to the second brake circuit. The second brake circuit can in particular be assigned to a rear axle. Such designs have proven to be typical applications proven beneficial. However, other designs are also possible here.

The loading can take place in particular by retracting a piston of the linear actuator. As a result, negative pressure is typically generated in the linear actuator, which is compensated for by the fact that fluid flows in. This is preferably done from a connected reservoir such as a brake fluid reservoir.

In particular, inlet valves of the brake circuits can be closed during charging. Inlet valves are to be understood in particular as valves which connect the remainder of a brake circuit directly to wheel brakes. Inlet valves thus typically control the pressure which is metered from a pressurized part of the brake circuit to wheel brakes in order to generate a braking effect. In particular, each inlet valve can connect a respective wheel connection to the remaining part of the respective brake circuit.

According to a development, the loading can already take place when a piston of the linear actuator has reached a predetermined position, which lies between a completely loaded and a completely emptied position. Typically, when loading, a linear actuator moves to the fully loaded position. If pressure is then required, it moves towards the fully deflated position. Although charging earlier increases the number of charging cycles, it can be ensured that in the event of a leak, especially in a sequence valve, an acting pressure cannot push the piston back so far and thus the leakage cannot be influenced by volume dissipation in the linear actuator is reduced.

The circuit separating valve can in particular be connected in such a way that it has a better closing effect against a volume flow pointing in the direction of the linear actuator than against a volume flow pointing away from the linear actuator. As a result, the effect in terms of the method described herein can be improved, since a higher blocking effect is achieved when the linear actuator is loaded. The asymmetry in the blocking effect is typically caused by the type of valves used, so it is not brought about intentionally for a specific fluidic purpose within the brake system.

The invention further relates to a control device configured to carry out a method described herein. With regard to the method, all of the versions and variants described herein can be used.

The invention also relates to a braking system for a motor vehicle, the braking system having a linear actuator, a circuit separating valve and a control device according to the invention. With regard to the control device and in particular with regard to the method implemented therein, all the embodiments and variants described herein can be used.

In other words, it is common, for example, that if leaks are detected in a sequence valve, volume-consuming functions such as ABS and EBD are switched off and a driver is warned by a warning lamp. An unattractive ABS regulation can also be accepted, with the violation of safety goals being able to be prevented even in the event of a leak. It is advantageous if the robustness against possible leaks increases. For this purpose, for example, if a leak is detected, the linear actuator can be reloaded, also referred to as a refill cycle (RFC), with the circuit separating valve closed. Depending on the size of the leak, the linear actuator can also suck volume out of a rear axle, for example. Since the intake valves are typically closed during recharging, only volume would be able to be sucked in through the linear actuator via check valves on the rear axle. In principle, a significant drop in pressure can occur on both axes. By closing a circuit separating valve, a pressure can be maintained, for example, on the front axle or on an axle. The release of the brakes on the other axis is limited in time and manageable. The deceleration capability of the unaffected axis is typically not impaired.

In particular in the case of a very strong leakage of the sequence valve, it is basically also conceivable that a hydraulic fallback level is influenced if a piston of the linear actuator is parked too far forward. In fact, this piston could be pushed back under manual pressure, which would reduce the pressure on the wheel brakes. To counteract this, the reload can be performed earlier so that the linear actuator piston does not have to travel as far forward. The reload cycles would then be shorter, but more frequent. Because of the shorter return travel, the pressure drops on the affected axle would also be lower.

The drop in pressure on an axle, such as the rear axle, can depend in particular on the leakage size of the switching valve and also on the ratio of this leakage to the check valves of the inlet valves on the rear axle. Due to the aperture size of the refill check Valves in relation to the check valves of the inlet valves in typical designs when the linear actuator is loaded, the largest part of the volume will be sucked out of the reservoir. In addition, even less is sucked out of the wheels in the event of a partial leakage of the sequence valve.

A circuit separating valve typically closes more poorly when there is a volume flow towards the front axle. However, the use of the circuit separating valve during a charging process fits from the requirements point of view. When loading, the linear actuator sucks and leads to a delta volume flow via the circuit separating valve in the direction of the rear axle.

In the case of adapted loading with leakage from the sequence valve, the hydraulic pressure model can always recalculate the wheel pressures of the rear axle (pre-pressure Psys sensor, previous wheel pressure, aperture factor of the check valve and PV behavior of the wheel). Thus, the wheel pressure control is not negatively influenced during and after loading. Typically, in the embodiment described herein, a warning can be omitted.

It should be mentioned that, in principle, the method described here can be used on brake systems that have a hydraulic fallback level, but also on those that do not have a hydraulic fallback level. A hydraulic fallback level is typically an operating mode that also works in the event of a total power failure and ensures that a driver can manually build up pressure, which is immediately used in the brakes. If such a power failure is reliably prevented by other mechanisms provided, this hydraulic fallback level can be dispensed with.

• 1: ein Bremssystem.

The person skilled in the art will derive further features and advantages from the exemplary embodiment described below with reference to the attached drawing. It shows:

• 1 : a braking system.

1 shows purely schematically a brake system 10 according to an embodiment of the invention. The brake system 10 has a master brake cylinder 20 with a piston 22 located therein, which can be actuated manually via a brake pedal 24 . Brake system 10 has a simulator 30 which is connected to master brake cylinder 20 via a simulator valve SV. A pressure applied thereto can be measured by means of a pressure sensor U/p. A position of the piston 22 can be measured using a position sensor U/s.

Master brake cylinder 20 and simulator 30 are connected to a first brake circuit BK1 via an isolating valve TV. This acts on a first wheel brake B1 and a second wheel brake B2 via a first inlet valve E1 and a second inlet valve E2. These are typically associated with a front axle. A second brake circuit BK2 is also connected via a circuit separating valve KTV and acts on a third wheel brake B3 and a fourth wheel brake B4 via a third inlet valve E3 and a fourth inlet valve E4. These are typically associated with a rear axle. On the wheel brakes B1, B2, B3, B4, respective outlet valves A1, A2, A3, A4 are connected for the purposeful release of pressure. The wheel brakes B1, B2, B3, B4 are connected to respective wheel connections of the brake system 10, which are not designated separately.

The brake system 10 also has a linear actuator 40, in which a piston 42 is located, which can be actuated by a motor M. Motor M is an electric motor and is monitored by a rotation angle sensor U/δ. The linear actuator 40 is connected to the second brake circuit BK2 via a sequence valve ZV. When the circuit separating valve KTV is closed, the linear actuator 40 can thus supply the second brake circuit BK2 with pressure when the connection valve ZV is open. When the circuit separating valve KTV is open, it can also supply pressure to the first brake circuit BK1.

In normal braking operation, the circuit separating valve KTV is open, the separating valve TV is closed and the simulator valve SV is open. A driver thus feels a force which is generated by the simulator 30, and a pressure in the brake circuits BK1, BK2 is generated exclusively by the linear actuator 40. Should a power failure occur, all valves switch in such a way that the sequence valve ZV and the simulator valve SV are closed and the isolating valve TV and the inlet valves E1, E2, E3, E4 are opened. A pressure generated by the driver using the brake pedal 24 is thus passed directly to the wheel brakes B1, B2, B3, B4.

The brake system 10 also has a brake fluid reservoir 50 to which the outlet valves A1, A2, A3, A4 are fluidically connected. Fluid drained from the brakes B1, B2, B3, B4 is thus routed to the brake fluid reservoir 50. The linear actuator 40 is also connected to the brake fluid reservoir 50 via a check valve R and an intake line AL and can thus suck in brake fluid from the brake fluid reservoir 50 .

For control, the brake system 10 has a purely schematically illustrated control device 60, which is all shown electrically controllable components can control. It is configured to carry out a method according to an embodiment of the invention.

The pressure in the second brake circuit BK2 can also be monitored using a pressure sensor U/p. In order to check the tightness of the switching valve ZV, a pressure can be generated by means of the linear actuator 40, for example, while the circuit separating valve KTV and the third and fourth inlet valves E3, E4 are closed. The sequence valve ZV is then closed and a check is made as to whether the pressure in the second brake circuit BK2 is dropping. If the pressure in the second brake circuit BK2 falls more quickly than would be expected if the valve was functioning properly, it is assumed that the sequence valve ZV is leaking. In this case, the circuit separating valve KTV can advantageously be closed each time before the linear actuator 40 reloads. Such reloading usually takes place when the sequence valve ZV is closed, and this can also be closed when a leak is detected. In this case, however, it can no longer be assumed that it closes completely tightly. Any undesired pressure reduction in the second brake circuit BK2 that may occur due to the leakage of the switching valve ZV remains localized to this second brake circuit BK2 due to the closing of the circuit separating valve KTV and does not affect the first brake circuit BK1. This can significantly reduce the effect of such a leak.

In particular, if a particularly high level of leakage is detected, the linear actuator 40 can already be loaded when the piston 42 has only traveled a certain part of its maximum possible travel to the right (in the illustration in FIG 1 ) drove. In the case of a hydraulic fallback level, this prevents the piston 42 from being able to travel too far, which compensates for a pressure build-up due to the driver's actuation of the brake pedal 24 . If the sequence valve ZV is leaking, a pressure generated by the driver would act on the piston 42 and thus push it to the left. The less travel distance that is available, the smaller the negative influence of the piston 42 in connection with the leakage of the sequence valve ZV on the pressure build-up. This can further increase security.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be executed in a different order, as far as this is technically reasonable. In one of its implementations, for example with a specific combination of steps, the method according to the invention can be carried out in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, including those which are not mentioned.

It should be noted that in the claims and in the description features can be described in combination, for example to facilitate understanding, although they can also be used separately. The person skilled in the art recognizes that such features can also be combined independently of one another with other features or combinations of features.

Back-references in dependent claims can identify preferred combinations of the respective features, but do not exclude other combinations of features.

reference list

10

braking system

20

master cylinder

22

Pistons

24

brake pedal

30

simulator

40

linear actuator

42

Pistons

50

Brake fluid reservoir

60

control device

SV

simulator valve

tv

isolation valve

ZV

sequence valve

KTV

circuit isolation valve

R

check valve

AL

intake line

BK1

first brake circuit

BK2

second brake circuit

B

wheel brakes

E

intake valves

A

exhaust valves

Claims (15)

Method for loading a linear actuator (40) of a brake system, the method having the following steps: - Closing a circuit separating valve (KTV) which has a first brake circuit (BK1) with a second Brake circuit (BK2) connects, and then - loading the linear actuator (40). procedure after claim 1 , - with the circuit separating valve (KTV) remaining closed during charging. Method according to one of the preceding claims, - Which is carried out in response to a detection of a leak in a sequence valve (ZV), - Wherein the sequence valve (ZV) connects the linear actuator (40) to a brake circuit (BK). procedure after claim 3 - Wherein to detect a leak in a part of a brake circuit (BK) that is opposite the linear actuator (40) with respect to the switching valve (ZV), pressure is built up and the switching valve (ZV) is then closed. procedure after claim 4 - wherein a leak is detected when in the part of the brake circuit (BK) in which pressure has been built up while the sequence valve (ZV) is closed, a pressure loss is at least as great as a threshold value. Procedure according to one of Claims 4 or 5 - wherein a leak is detected when, while the sequence valve (ZV) is closed, a piston (42) of the linear actuator (40) is moved by pressure from that part of the brake circuit (BK) in which pressure has built up. Procedure according to one of claims 3 until 6 - Wherein the sequence valve (ZV) connects the linear actuator (40) to the second brake circuit (BK2). procedure after claim 7 - Wherein the second brake circuit (BK2) is assigned to a rear axle. Method according to one of the preceding claims, - wherein the loading takes place by retracting a piston (42) of the linear actuator (40). Method according to one of the preceding claims, - With the inlet valves (E) of the brake circuits (BK) being closed during loading. procedure after claim 10 , - wherein each inlet valve (E) connects a respective wheel port to the remaining part of the respective brake circuit (BK). Method according to one of the preceding claims, - The loading already takes place when a piston (42) of the linear actuator (40) has reached a predetermined position which lies between a fully loaded and a fully emptied position. Method according to one of the preceding claims, - The circuit separating valve (KTV) being connected in such a way that it has a better closing effect in relation to a volume flow pointing in the direction of the linear actuator (40) than in relation to a volume flow pointing away from the linear actuator (40). Control device (60) configured to carry out a method according to any one of the preceding claims. Brake system (10) for a motor vehicle, comprising - a linear actuator (40), - a circuit separating valve (KTV), and - a control device (60). Claim 14 .

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