DE102012008508B4 - Generating an understeering torque when controlling brake pressures acting on braked wheels of a motor vehicle - Google Patents

Abstract

Method for controlling brake pressures (3) acting on braked wheels (HL, VR, VL, HR) of a motor vehicle (1), with: - determining a driving state variable describing a driving state of the motor vehicle (1), - determining a deceleration request (5 ) of a driver (7) of the motor vehicle (1) dependent default brake pressure (9), - Control of the brake pressures (3) acting on the wheels (HL, VR, VL, HR) depending on the default brake pressure (9), - Superimposed control of the brake pressures (3) to generate a brake pressure distribution of the brake pressures (3) which causes an understeer torque (11), as long as the driving state variable has the motor vehicle (1) cornering (13), - determining a drop (15) in the specified pressure (9), - time-delayed withdrawal of the superimposed control in response to the drop (15) in the specified pressure (9), so that after the braking has ended, an undesirable oversteering torque (23), which is reduced in accordance with a transient response of a suspension of the motor vehicle (1), is further compensated.

Description

The invention relates to a method and a hydraulic device for controlling brake pressures acting on braked wheels of a motor vehicle and to a motor vehicle according to the method and/or device.

To control brake pressures acting on braked wheels of a motor vehicle, it is known to influence the driving stability of the motor vehicle. Devices and methods that enable anti-lock braking control in a passive operating situation are known under the name “electronic stability program” (ESP). Furthermore, in a partially active case, such systems make it possible to increase a pressure specified by a driver of the motor vehicle in order to thereby have a stabilizing effect on the driving dynamics of the motor vehicle. In addition, such systems enable a fully active case in which pressure is generated to stabilize the motor vehicle without the driver of the motor vehicle entering a deceleration request, in particular without actuating the brake pedal.

From the disclosure document DE 10 2011 077 153 A1 a method for modifying a driving stability control of a vehicle is known, in which the input variables consisting of at least the steering angle and driving speed are converted into a setpoint of a yaw angular speed. Depending on the yaw angular velocity, a stabilization intervention with a driver-independent build-up of braking forces on one or more wheels is requested.

From the disclosure document DE 196 80 595 B4 is a vehicle dynamics controller for a vehicle known with a control unit that generates a braking force difference between the wheels to be braked to stabilize the vehicle movement in order to force a torque in the direction of the curve to the vehicle in the event of understeering driving behavior, or to impose a restoring torque against the direction of the curve on the vehicle in the event of oversteering driving behavior to impose.

From the disclosure document DE 100 57 297 A1 A method for regulating driving stability is known, in which pressures for the individual brakes are determined based on several input variables, so that the driving stability of the vehicle is increased by an ESP intervention.

The object of the invention is to better, in particular more completely, compensate for an oversteer torque that occurs due to a dynamic axle load distribution when braking while cornering.

The task is solved by a method according to claim 1. Advantageously, in a partially active case, a counter-torque can be built up during cornering, which counteracts an understeer moment that occurs during braking due to a dynamic axle load distribution of the vehicle. This advantageously allows neutral driving behavior to be achieved during braking. At one end of the braking, the superimposed control that generates the counter-torque will be withdrawn with a time delay, so that the counter-torque continues to have an effect in accordance with the time-delayed withdrawal. Advantageously, the time behavior of a corresponding brake system of the motor vehicle can be slowed down in such a way that it corresponds, or at least predominantly corresponds, to the time behavior of a suspension. In the event that braking ends, the dynamic axle load distribution is still present until the correspondingly compressed wheels, in particular a front wheel on the outside of the curve, finally rebound. Without the advantageous time-delayed withdrawal, as soon as the stabilizing measure suddenly disappears due to the control of the brake pressures, this would lead to an undesirable oversteer impulse. This is due to the fact that the advantageous understeer torque, which is set by controlling the brake pressures, is reduced more quickly than the undesirable oversteer torque that arises from the dynamic axle load distribution due to the shorter time response of the motor vehicle's brake system. The driver perceives this as a sudden onset of oversteer torque. According to the invention, it is precisely this sudden, sole occurrence of the oversteer torque that is compensated for by the advantageous superimposed control continuing to act to the same extent and for as long as the undesirable oversteer torque is still present. The undesirable oversteering torque is reduced in accordance with a transient response of the suspension of the motor vehicle and is advantageously further compensated for even after the braking has actually ended.

A further exemplary embodiment is carried out according to claim 2. When the default brake pressure falls, in a normal operating state, a brake pressure acting on the wheels of the motor vehicle can be reduced via the opened inlet valve. A check valve is advantageously connected in parallel with the inlet valve, which opens coming from the wheel brake cylinder in the direction of a master brake cylinder of the motor vehicle. Advantageously, the brake pressure on the corresponding wheel can be reduced via the check valve even when the inlet valve is closed. Advantage In this way, a time behavior of the pressure reduction can be positively influenced in such a way that the pressure reduction corresponds at least approximately to the time behavior of a corresponding rebound process and/or passive leveling process of a body of the motor vehicle. Advantageously, the controlled understeer torque can be reduced so slowly that the undesired oversteer pulse at the end of the brake can be completely compensated for or at least reduced to a tolerable level.

A further preferred embodiment is carried out according to claim 3. This effect can advantageously also be generated by only partially closing the inlet valve, depending on the time behavior of the motor vehicle's suspension. Advantageously, an overpressure, i.e. a flow through the inlet valve to the corresponding wheel brake cylinder, can also take place at any time, so that new braking can be initiated at any time by the driver of the motor vehicle.

A further preferred embodiment is carried out according to claim 4. In a normal operating state, brake pressure is reduced via an open high-pressure switching valve. Through targeted control, the superimposed control can advantageously be withdrawn with a time delay.

A further preferred embodiment is carried out according to claim 5. The high-pressure switching valve can advantageously set a medium brake pressure by simple pulsed switching, and can particularly advantageously control the time-delayed withdrawal.

A further preferred embodiment is carried out according to claim 6. According to a preferred embodiment, the high-pressure switching valve is designed as a proportional valve and/or as a pressure control valve and can therefore be partially closed by means of a corresponding control. The clocking and/or the complete closing can advantageously be dispensed with, so that a particularly precise and time-delayed withdrawal of the superimposed control following any curve can advantageously take place.

A further preferred embodiment is carried out according to claim 7. Advantageously, the high-pressure switching valve can initially be completely closed, so that brake pressure built up downstream of the high-pressure switching valve cannot be reduced. The time-delayed withdrawal of the superimposed control is then advantageously carried out analogously to an anti-lock braking control by appropriately controlling the exhaust valve, which is connected between a buffer and the corresponding wheel brake cylinder. Control can advantageously be either clocked and/or proportional, with the outlet valve being designed as a proportional valve and/or pressure control valve.

A further preferred embodiment is carried out according to claim 8. Depending on the design and/or axle load distribution and/or driving dynamics of the motor vehicle, it is sufficient if only the rear wheel of the motor vehicle applies the understeer torque remaining to eliminate the undesirable oversteer impulse by means of the time-delayed withdrawal of the superimposed steering. Advantageously, only the rear wheel needs to be controlled, which basically represents less effort and also a gentle intervention in the driving dynamics of the motor vehicle that is more appropriate to the situation.

The task is also solved by a hydraulic device according to claim 9. The hydraulic device is in particular set up, designed and/or constructed to carry out a method described above and/or has software suitable for this purpose. The advantages described above arise.

The task is also achieved by a motor vehicle with a hydraulic device described above. The advantages described above arise.

Further advantages, features and details emerge from the following description, in which at least one exemplary embodiment is described in detail - if necessary with reference to the drawing. Described and/or illustrated features form the subject matter of the invention on their own or in any meaningful combination, possibly also independently of the claims, and in particular can also be the subject of one or more separate applications. Identical, similar and/or functionally identical parts are provided with the same reference numerals.

• 1 eine schematische Draufsicht eines Kraftfahrzeugs während einer Kurvenfahrt und einer Bremsung;
• 2 ein Schaltschema einer Hydraulikvorrichtung zum Steuern von auf gebremste Räder des in 1 dargestellten Kraftfahrzeugs wirkenden Bremsdrücken; und
• 3 ein Messdiagramm verschiedener während der in 1 gezeigten Bremsung und Kurvenfahrt auftretender Größen.

Show it:

• 1 a schematic top view of a motor vehicle while cornering and braking;
• 2 a circuit diagram of a hydraulic device for controlling braked wheels of the in 1 brake pressures acting on the motor vehicle shown; and
• 3 a measurement chart of various during the in 1 shown during braking and cornering.

1 shows a schematic top view of a motor vehicle 1 at two points in time during braking and cornering 13. The motor vehicle 1 approaches a curve at high speed and drives through it while braking. Due to a dynamic axle load distribution that occurs during braking, an undesirable oversteer torque 23 occurs on the motor vehicle. By means of an active control of brake pressures 3 acting on the wheels of the motor vehicle 1, an understeer torque 11 that counteracts the undesirable understeer torque 23 can advantageously be generated during braking.
2 shows a circuit diagram of a hydraulic device 19 in 1 shown motor vehicle 1.

The hydraulic device 19 has a master brake cylinder HZ, which converts a deceleration request 5 of a driver 7 of the motor vehicle 1 into a specified brake pressure 9. The default brake pressure 9 can be determined using a measuring point or pressure sensor of the hydraulic device 19.

The default brake pressure 9 is distributed into a first brake circuit B1 and a second brake circuit B2. The first brake circuit B1 acts on a rear left wheel HL and a front right wheel VR. The second brake circuit B2 acts on a front left wheel VL and a rear right wheel HR of the in 1 shown motor vehicle 1.

Each of the wheels HL, VR, VL, HR of the motor vehicle 1 is assigned a wheel brake cylinder RZ that acts on the brakes. The wheel brake cylinders control braking torques acting on the wheels HL, VR, VL, HR depending on brake pressures 3.

The brake circuits B1 and B2 are constructed symmetrically according to a so-called X-connection, with each of the brake circuits having a braking effect on wheels arranged diagonally to one another in the motor vehicle 1. Only the brake circuit B1 is described in more detail below, although the description also applies to the brake circuit B2.

The brake circuit B1 has a total of six valves, which are designed as spring-returning, electromagnetically operated 2/2-way valves. According to one aspect of the invention, individual or all valves can be designed as proportional valves and/or pressure control valves. A high-pressure switching valve HSV and a switching valve USV are connected downstream of the master brake cylinder HZ. The high-pressure switching valve HSV is closed in a de-energized state. The UPS switching valve is open in a de-energized state. In a de-energized state, the hydraulic device 19 can be used passively, whereby the default brake pressure 9 can be passed on to the wheel cylinders without further control measures.

The high-pressure switching valve HSV and the switching valve USV are part of a hydraulic valve arrangement 21 of the hydraulic device 19 of the motor vehicle 1. The hydraulic valve arrangement 21 has a total of the six valves of the first brake circuit and six further valves of the second brake circuit, i.e. twelve valves.

There are two inlet valves EV connected downstream of the USV switching valve, which are also open in a de-energized state. The inlet valves EV are each connected upstream of one of the wheel cylinders RZ. In the de-energized state, the specified pressure 9 can be passed on directly to the wheel cylinder RZ via the switching valve USV and the two inlet valves EV.

An exhaust valve AV is connected downstream of the wheel cylinders RZ. The outlet valves AV are closed in a de-energized state, thus preventing a brake fluid from flowing back during the passive operation of the hydraulic device 19.

A low-pressure accumulator AC for temporarily storing the brake fluid is connected downstream of the outlet valves AV. In addition, the two outlet valves AV have a spring-loaded check valve 17. The check valve 17 is spring-loaded, so it has an opening pressure and opens in the direction of a return pump PE connected downstream of it. The return pump PE is designed as a self-priming pump and can in particular overcome the opening pressure of the spring-loaded check valve 17.

The return pump PE delivers in the direction of the switching valve USV and the two inlet valves EV.

Advantageously, when the switching valve USV is closed and the high-pressure switching valve HSV is open, the default brake pressure 9 can first be directed to a suction side of the return pump PE. The spring-loaded check valve closes in this operating state, so that the specified brake pressure 9 can be advantageously increased by building up pressure using the return pump PE.

In this operating state, which is also referred to as a partially active case, the specified brake pressure 9 can be actively increased. From outlet valves AV are closed and/or regulate the corresponding brake pressure 3 of the corresponding upstream wheel cylinder RZ.

This operating case can be advantageous for generating the in 1 Understeer torque 11 shown can be used to thereby compensate for the undesirable oversteer torque 23. Specifically, at least on the wheel brake cylinder RZ acting on the rear wheel HR or on this and on the wheel brake cylinder RZ acting on the front wheel VR, the default brake pressure 9 is increased as long as cornering 13 continues.

One in 2 Control device, not shown, determines a driving state variable describing a driving state of the motor vehicle 1, in particular by means of corresponding sensor signals of the motor vehicle 1. In addition, the deceleration request 5 and / or the resulting default brake pressure 9 is determined. As long as the driving state variable has the cornering 13 and/or describes it accordingly, the advantageous increase in the brake pressures 3 takes place on the wheels on the outside of the curve, i.e. at least the rear right wheel HR and possibly the front right wheel VR.

Advantageously, the understeer torque 11 built up in this way is only reduced with a time delay by the superimposed control of the brake pressures 3, in particular by means of the amplification by the return pump PE after the braking has ended, although cornering is still ongoing. This can advantageously counteract an undesirable overcontrol impulse.

This advantageous relationship is shown using a measurement diagram 3 presented in more detail.

3 shows a diagram 25 of different individual variables occurring during cornering 13 of the motor vehicle 1. From top to bottom, a brake light switch signal 27, a vehicle deceleration 29, wheel speeds 31 of the wheels HL, VR, VL, HR, a steering wheel angle 33, a vehicle yaw rate 35, the default brake pressure 9 and the brake pressures 3 acting on the wheel brake cylinders RZ are shown in the diagram 25 drawn at a time. A time grid drawn using vertical lines is in particular 2 seconds.

An end of the deceleration request 5 of the driver 7 of the motor vehicle 1 is shown by means of a first dashed line 37. It can be seen that the brake light switch signal 27 drops at this point in time.

In response to the end of braking, the vehicle deceleration 29 decreases. In addition, the wheel speeds 31 have a bend at which a comparatively large negative slope changes into a smaller negative slope, which corresponds in particular to free rolling of the motor vehicle 1. This in 3 Driving maneuvers of the motor vehicle 1 shown therefore correspond to a comparatively strong braking of the motor vehicle 1 from a high speed, in particular from over 200 km/h, in particular approximately 220 km/h, to a medium speed, in particular > 140 km/h, in particular approximately 145 km /h during the in 1 cornering shown 13.

In addition, an oversteer pulse 39 of the vehicle yaw rate 35 can be seen in response to the end of braking. The overdrive pulse 39 is in by means of a circle 3 symbolized.

It can also be seen that at the end of braking, the default brake pressure 9 and the brake pressures 3 following this have a drop 15.

Advantageously, according to one aspect of the invention, the superimposed control of at least one of the brake pressures 3, i.e. the increase of at least one of the brake pressures 3, is reduced with a time delay, which in 3 is symbolized by a dash-dotted representation of the corresponding brake pressure 3.

The delayed withdrawal lasts until another point in time, which is in 3 is symbolized by a second line 41. The time between the first line 37 and the second line 41 corresponds to the duration of the occurrence of the undesired oversteer pulse 39. The graph of the vehicle yaw rate 35 is shown by means of a further dash-dotted line, as it results from the advantageous time-delayed withdrawal of the superimposed control. It can be seen that the overdrive pulse 39 can be advantageously compensated for in this way. Advantageously, the understeer torque 11, which counteracts the undesirable oversteer torque 23, can be at least partially maintained for the period of time remaining between the first line 37 and the second line 41. This advantageously takes place exactly to the extent that the undesired oversteering torque 23 still has an effect, in particular due to set spring damper forces and a mass inertia of a body of the motor vehicle 1.

The short-term oversteer impulse 39, which is unexpected for the driver 7 of the motor vehicle 1, can advantageously be compensated for or at least reduced to a tolerable level. A sudden collapse of an asym metric distribution of the brake pressures 3 can be avoided.

By slightly delaying the reduction in brake pressure 3 on the outside of the curve, the undesirable oversteer impulse 39 can advantageously be eliminated.

This can be achieved by closing the inlet valves EV of the wheels on the outside of the curve VR, HR in a timely manner using a suitable electrical current.

The brake fluid can therefore only flow back from the corresponding wheel brake cylinder RZ into the master brake cylinder HZ with a reduced volume flow via a bypass valve connected in parallel with the inlet valves EV.

In motor vehicles 1 with a comparatively low tendency to oversteer, it is conceivable according to one aspect of the invention to reduce the brake pressure drop, i.e. the time-delayed withdrawal of the superimposed control in response to the drop 15 in the default pressure 9, only on the rear axle, i.e. in the present one Embodiment to control the rear right wheel HR.

A renewed build-up of brake pressure by the driver 7 of the motor vehicle 1 can advantageously be counteracted by quickly opening the intake valves EV on the outside of the curve.

Alternatively or additionally, a weak current supply to the corresponding inlet valves EV can take place, whereby it is advantageously possible for the driver 7 to overpress a valve force of the corresponding inlet valve EV at any time and thereby build up brake pressure 3 again on the corresponding wheel brake cylinder RZ.

Another possible alternative to delaying the brake pressure reduction is to switch the high-pressure switching valves HSV and to achieve the desired pressure reduction by supplying them with suitable, clocked current.

Likewise, in a further alternative, there is the possibility of displaying the desired delayed pressure reduction by switching the corresponding outlet valves AV of the control system or the hydraulic valve arrangement 21 of the hydraulic device 19 of the motor vehicle 1 when the high-pressure switching valves HSV are completely closed.

Reference symbol list

1

motor vehicle

3

Brake pressure

5

Request for delay

7

driver

9

Default brake pressure

11

Understeer torque

13

Cornering

15

Waste

17

check valve

19

Hydraulic device

21

Hydraulic valve assembly

23

Oversteer torque

25

graph

27

Brake light switch signal

29

Vehicle deceleration

31

Wheel speed

33

Steering wheel angle

35

Vehicle yaw rate

37

first line

39

Overdrive impulse

41

second line

HL, VR, VL, HR

Wheels

RZ

Wheel brake cylinder

EZ

Inlet valve

HZ

Brake master cylinder

HSV

High pressure switching valve

AV

outlet valve

B1

first brake circuit

B2

second brake circuit

UPS

changeover valve

AC

Low pressure accumulator

P.E

return pump

Claims (10)

Method for controlling brake pressures (3) acting on braked wheels (HL, VR, VL, HR) of a motor vehicle (1), with: - determining a driving state variable describing a driving state of the motor vehicle (1), - determining a deceleration request (5 ) a driver (7) of the motor vehicle (1) depending on the default brake pressure (9), - controlling the brake pressures (3) acting on the wheels (HL,VR,VL,HR) depending on the default brake pressure (9), - Superimposed control of the brake pressures (3) to generate a brake pressure distribution of the brake pressures (3) which causes an understeering torque (11), as long as the driving state variable involves cornering (13) of the motor vehicle (1), - Determining a drop (15) in the specified pressure (9 ), - time-delayed withdrawal of the superimposed control in response to the drop (15) in the specified pressure (9), so that after the braking has ended, an undesirable oversteering torque (23), which is reduced in accordance with a transient response of the suspension of the motor vehicle (1), is further compensated. Method according to the preceding claim, with: - Closing at least one inlet valve (EV) connected upstream of a wheel brake cylinder (RZ) on the outside of the curve in order to withdraw the superimposed control with a time delay. Method according to the preceding claim, with: - partially closing the at least one inlet valve (EV). Method according to one of the preceding claims, with: - Controlling a high-pressure switching valve (HSV) hydraulically connected downstream of a master brake cylinder (HZ) for the time-delayed withdrawal of the superimposed control. Method according to the preceding claim, with: - Clocked switching of the high-pressure switching valve (HSV) for a time-delayed withdrawal of the superimposed control. Method according to one of the preceding two claims, with: - Partial closing of the high-pressure switching valve (HSV) for a time-delayed withdrawal of the superimposed control. Method according to one of the preceding three claims, with: - Closing the high-pressure switching valve (HSV) for a time-delayed withdrawal of the superimposed control, - Controlling an outlet valve (AV) which is hydraulically connected downstream of the at least one wheel brake cylinder (RZ) on the outside of the curve for the time-delayed withdrawal of the superimposed control. Method according to one of the preceding Claims 2 - 7 , wherein the at least one wheel brake cylinder (RZ) has a braking effect on a rear wheel (HR) of the motor vehicle (1). Hydraulic device (19) for controlling brake pressures (3) acting on braked wheels (HL,VR,VL,HR) of a motor vehicle (1), with: - a master brake cylinder (HZ) for generating a default pressure (9), - a large number of wheel brake cylinders (RZ), which have a braking effect on the wheels (HL, VR, VL, HR) of the motor vehicle (1), - a hydraulic valve arrangement (21) connected hydraulically between the master brake cylinder (HZ) and the wheel brake cylinders (RZ) for controlling the brake pressures (3) acting on the wheel brake cylinders, set up, designed, constructed and/or equipped with software for carrying out a method according to one of the preceding claims. Motor vehicle (1) with a hydraulic device (19) according to the preceding claim.

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