DE102019215344A1 - Method and electronic control device for operating a braking system - Google Patents

Abstract

The invention relates to a method, an electronic control unit, a computer program and a machine-readable storage medium for operating a brake system comprising a hydraulic actuator (100) and two brake units (101, 102), wherein during a first phase (10) a pressure build-up in a first of the two brake units ( 101) a target pressure level (p1) prevails, and a lower pressure level (p2) compared to the target pressure level (p1) is present in a second of the two brake units (102). Starting from the lower pressure level (p2), a pressure increase to the target pressure level (p1) is carried out by means of the hydraulic actuator (100) in the second of the two brake units, and in a second phase (20) the pressure increase in the first brake unit (101) ) and continued in the second brake unit (102) by means of the hydraulic actuator (100).

Description

State of the art

The disclosure document DE 10 2008 004 201 relates to a brake system for a vehicle with a master cylinder which provides a pressure signal, a brake medium reservoir connected to the master cylinder, and a first brake circuit which is coupled with a first input to the master cylinder and a second input to the brake medium reservoir. The first brake circuit comprises at least one first wheel brake cylinder arranged on a first wheel in order to exert a force on the first wheel corresponding to the pressure signal, and an isolating valve arranged between the first input and the first wheel brake cylinder in order to forward the pressure signal upon receipt of a closing signal provided prevent, as well as a control valve arranged between the second input and the first wheel brake cylinder in order to control an inflow of a brake medium from the brake medium reservoir to the first wheel brake cylinder.

Disclosure of the invention

The invention relates to a method for operating a brake system comprising a hydraulic actuator and two brake units. During a first phase of a pressure build-up, a target pressure level is present in a first of the two brake units and, on the other hand, a lower pressure level compared to the target pressure level is present in a second of the two brake units. Starting from the lower pressure level, the hydraulic actuator in the second of the two brake units is used to increase the pressure to the target pressure level. In a second phase, the pressure increase is then continued in the first brake unit and in the second brake unit by means of the hydraulic actuator.

By means of the method, different pressure levels in brake systems can be compensated jointly in two brake units before a pressure increase is imminent. For example, the lower pressure axle (with wheel brake cylinders on which a lower pressure prevails) can be brought up to the higher pressure axle (with wheel brake cylinders on which the higher pressure is applied). Such an approach allows a controlled transition from the first phase of the pressure build-up to the second phase of the pressure build-up. A carefully controlled and / or regulated transition from the first phase of pressure build-up to the second phase of pressure build-up allows the driver of the motor vehicle to make such a transition unnoticed or with little awareness, since he perceives the operation of the hydraulic actuator to be essentially constant during pressure build-up.

In an advantageous embodiment of the method, when the pressure increases in the first phase, a first volume flow is generated by means of the hydraulic actuator, and when the transition from the first phase to the second phase a second volume flow is generated by means of the hydraulic actuator, which essentially corresponds to the first volume flow. This has the advantage that the hydraulic actuator can be operated with a constant load without being confronted at the transition with other, in particular with higher, load requirements. The hydraulic actuator does not have to be accelerated in this way, which would generally lead to load changes that the driver can perceive, for example in the form of vibration behavior and / or engine noises of the hydraulic actuator.

In a further embodiment, the first volume flow is generated by specifying a first setpoint pressure gradient for the hydraulic actuator. Thus, by using a simple reference variable in the form of the pressure gradient, a simple setting of the desired volume flow is feasible. The prevailing pressure gradient can easily be analyzed and used for regulation, since pressure sensors are provided at the appropriate points in the hydraulic system in order to regulate a pressure build-up by means of the hydraulic actuator.

Likewise, in an embodiment of the method, the second volume flow is generated by specifying a second setpoint pressure gradient for the hydraulic actuator. This also has the advantage of being easy to regulate.

In a further development of the method, the second target pressure gradient is smaller than the first target pressure gradient. In this way it can be achieved that - despite the increased volume uptake because two brake units are now to be supplied by the actuator - the prevailing volume flow is kept essentially constant and the actuator is not subjected to any other load.

In a further embodiment of the method, the pressure increase is carried out in such a way that in the second phase the pressure level in the first brake unit and in the second brake unit is raised to a further pressure level. By initially adjusting the pressure levels with subsequent continuation of the pressure build-up to a common target pressure level, a comfortable pressure setting is achieved on both brake units that is not perceived as annoying for the driver.

In an advantageous embodiment, the pressure increase in the first phase and the pressure increase in the second phase set a hydraulic braking torque corresponding to the further pressure level, which compensates for a falling and / or decreasing regenerative braking torque. In this way, a pressure build-up in regenerative braking systems can be used easily and conveniently, without disturbing influences for the driver during load changes, in which adaptation of the hydraulic braking effects is often required because the braking torque produced by the generator fluctuates, for example due to the prevailing vehicle speed or the Fill level of an electrical energy storage device.

The invention further comprises a computer program which is set up to carry out all steps of the method, as well as a machine-readable storage medium on which the computer program is stored.

The invention also relates to an electronic control unit which is set up to carry out all steps of the method.

• 1 zeigt schematisch ein Bremssystem eines Fahrzeugs mit einem Aktor, zwei hydraulischen Bremseinheiten für jeweils eine Primärachse und eine Sekundärachse und jeweils zugeordneten Radbremsen.
• 2 zeigt Druckverläufe an den Radbremsen der Primärachse und der Sekundärachse in unterschiedlichen Phasen sowie eine Stellgröße eine Bremsdruckerzeugers.
• 3 zeigt einen Ablauf eines Verfahrens zum Betreiben eines Bremssystems.

An embodiment of the invention is described below with reference to figures.

• 1 shows schematically a brake system of a vehicle with an actuator, two hydraulic brake units for each a primary axle and a secondary axle and respectively assigned wheel brakes.
• 2 shows pressure curves at the wheel brakes of the primary axle and the secondary axle in different phases as well as a manipulated variable of a brake pressure generator.
• 3 shows a sequence of a method for operating a brake system.

Embodiments of the invention

1 shows schematically a braking system 1 of a vehicle. The components shown relate to the hydraulic part of a braking system for a vehicle. In addition to the components shown, the brake system can also include a regenerative brake system which, through energy recovery - for example when charging an energy store - can also cause a vehicle to be braked using a regenerative braking torque.

A brake actuator 100 is hydraulic via hydraulic connections 111 and 112 with two hydraulic partial braking units 101 and 102 a hydraulic braking system 1 connected. The partial braking units 101 and 102 are two hydraulic wheel brakes each 103 , 104 as 105 , 106 assigned, which are located in pairs on a primary axle and on a secondary axle of a vehicle. The hydraulic wheel brakes 103 , 104 , 105 , 106 are via hydraulic connections 113 , 114 as 115 , 116 with the brake units 101 , 102 connected.

The braking units 101 , 102 are known to include valve devices (not shown) by means of which the hydraulic connection between the brake actuator 100 and the respective wheel brakes 103 , 104 , 105 , 106 can be produced for individual, in pairs, three or for all wheel brakes.

The brake actuator 100 can for example be a pump, a plunger or a controllable brake booster, for example an electromechanical brake booster. Becomes an adjusting element of the brake actuator 100 when a force is applied, a hydraulic fluid can be subjected to pressure via the actuating element. This hydraulic pressure is via the hydraulic connections established between the brake actuator 100 and the brake units 101 , 102 the wheel brakes 103-106 selectively feedable. A hydraulic pressure in the wheel brakes 103-106 leads in a known manner - for example on brake disks - to a braking effect when brake linings are pressed against assigned brake disks by means of the hydraulic pressure.

The braking system also includes 1 an electronic control unit 150 that are used for signal processing of sensor signals, for example the brake units 101 , 102 is designed. Furthermore, by means of the control unit 150 Data are kept available, for example characteristic curves for controlling the hydraulic actuator. Likewise, by means of the control unit 150 a control of components of the brake system 1 take place, for example of the actuator or for example of sub-units of the brake units 101 , 102 as from valves.

In the case of cooperative operation of the hydraulic brake system described with a regenerative brake system, it may be necessary to maintain hydraulic pressure only in a first part of the hydraulic brake system and not to provide a second part with pressure, or only with a lower pressure. This may be necessary if, for example, wheels that are assigned to the wheel brakes of the second part are braked as a generator and the braking effect is not, or not only, caused by the hydraulic wheel brakes.

If a regenerative braking effect on the wheels that are assigned to the second part of the hydraulic brake system is eliminated or reduced, the hydraulic braking effect on the corresponding wheel brakes must be built up / increased.

Likewise, the regenerative braking effect can be applied to those wheels that are assigned to the first part of the hydraulic brake system and then reduced, although the hydraulic braking effect on the wheels that are assigned to the second part of the hydraulic brake system is adapted, in particular built up or increased.

The following is based on a driving situation in which a brake pressure p1 in the first braking unit 101 for the wheel brakes 103 , 104 - assigned to the primary axis - is available. In the second braking unit 102 can for example be a brake pressure p2 = 0 on the wheel brakes 105 , 106 must be set - i.e. assigned to the secondary axis. Likewise, a compared to the brake pressure p1 in the first braking unit 101 lower brake pressure p2 <p1 can be maintained.

When the regenerative braking effect decreases or ceases to exist, the brake pressure should be used p2 in the second braking unit 102 and thus on the wheel brakes 105 , 106 be increased first.

A brake pressure can be set both in the first brake unit 101 as well as in the second brake unit 102 by the brake actuator 100 respectively.

An increase in the brake pressure p2 in the second braking unit 102 can be done in such a way that the brake pressure p2 the second braking unit 102 to the brake pressure of the first brake unit 101 is introduced. After applying the brake pressure p2 to the brake pressure p1 the first braking unit 101 there is a continuation of the increase in the brake pressure in both brake units 101 and 102 by means of the brake actuator 100 .

The course of such an increase in pressure p2 on the wheel brakes of the second brake unit 102 by means of the brake actuator 100 and continuing to pressurize the pressure p1 on the first brake unit 101 and the pressure p2 on the second brake unit 102 by means of the brake actuator 100 is explained below using 2 described.

In the lower part of 2 are time courses of the brake pressure p1 the first braking unit 101 and the brake pressure p2 the second braking unit 102 shown.

The first braking unit 101 points ahead of the time t0 a pressure p1 (t <t0). On the wheel brakes of the brake unit 102 is before the point in time t0 a pressure p2 (t <t0), the smaller one p1 (t <t0). The pressure p2 (t <t0) can also be zero.

In a first phase 10 from the point in time t0 should the pressure p2 in the second braking unit 102 on the print p1 (t <t0) of the first braking unit 101 to be brought.

der sich durch den Druckunterschied der Drücke p1 und p2 der Bremseinheiten 101 und 102 zum Zeitpunkt t0 - also zu Beginn der ersten Phase - und durch die Dauer der ersten Phase 10 ergibt.The pressure increase in the first phase 10 that is between the points in time t0 and t1 extends, takes place with a pressure gradient 2 $$\text{dp}2/\text{German}=\left[\text{p}1\left(\text{t}0\right)-\text{p}2\left(\text{t}0\right)\right]/\left[\text{t}1-\text{t}0\right],$$

which is characterized by the pressure difference of the pressures p1 and p2 the braking units 101 and 102 at the time t0 - i.e. at the beginning of the first phase - and through the duration of the first phase 10 results.

The pressure gradient 2 can be specified on the vehicle side or stored in a map. The pressure gradient can also 2 be parameterizable. For example, the pressure gradient 2 depending on the prevailing pressure difference p1 ( t0 ) - p2 ( t0 ) parameterized, or depending on the time required for the pressure build-up. Likewise, empirical values, such as a fixed pressure gradient or pressure gradient as a function of the pV relationship of the brake units used, can also be used 101 , 102 stored in a control unit in the vehicle.

At the end of the first phase 10 - so at the time t1 - are the pressures p1 ( t1 ) and p2 ( t1 ) adjusted.

The pressure increase in phase 1 in the second braking unit 102 takes place with a volume flow Q2 that by means of the actuator 100 the displaced volume V per unit of time, i.e. dV / dt.

Because in the first braking unit 101 no pressure build-up should take place, and there the pressure p1 is held, all of the volume V of hydraulic fluid delivered by the actuator is fed into the second brake unit 102 with volume flow Q2 promoted.

From the point in time t1 - so in the second phase 20th - will both pressures p1 and p2 further raised. Compared to the first phase 10 will be from the date t1 both brake units 101 and 102 by the actuator 100 filled, which means an increased volume requirement compared to the first phase 10 goes hand in hand.

At the transition point t1 between first phase 10 and second phase 20th the volume flow of the actuator should be kept essentially constant, i.e. dV / dt = constant.

also dass der Volumenstrom Q2(t1) zum Ende der ersten Phase 10 am Zeitpunkt t1 der Summe der Volumenströme Q1 in der ersten Bremseinheit 101 und Q2 in der zweiten Bremseinheit 102 zum Zeitpunkt t>t1 ist, im Folgenden auch als Q12 bezeichnet.In other words: $$\text{Q}2\left(\text{t}1\right)=\text{Q}1\left(\text{t}>\text{t}1\right)+\text{Q}2\left(\text{t}>\text{t}1\right)=\text{Q}\mathrm{12th}\left(\text{t}>\text{t}1\right),$$

so that the volume flow Q2 (t1) at the end of the first phase 10 at the time t1 the sum of the volume flows Q1 in the first braking unit 101 and Q2 in the second braking unit 102 at time t> t1, hereinafter also referred to as Q12.

In other words, the volume flow through the actuator 100 in the first phase 10 only for filling the second brake unit 102 was used in the second phase 20th the first braking unit 101 and the second brake unit 102 fill together. Set the volume flow when changing from the first phase 10 to the second phase 20th be kept constant, so the pressure gradient 4th showing the pressure increase in the first braking unit 101 and in the second brake unit 102 in the second phase 20th not identical to the pressure gradient 2 the first phase 10 be, but must be given less.

For the individual brake units 101 and 102 pressure-volume relationships, for example in the form of pV characteristics, are known and stored in the vehicle. A pressure-volume relationship of the first and second brake units is also known and stored 101 , 102 together. Corresponding characteristic curves can also be used for the pressure-volume relationships of the brake units 101 and 102 connected wheel brakes 103 - 106 include, as well as pressure-volume relationships of the associated hydraulic connections 113 - 116 . For the sake of simplicity, the following only refers to the braking units 101 , 102 Referenced.

Furthermore, there are the elasticities of the individual brake units 101 and 102 , i.e. the volume requirement per bar at the respective pressure operating point is known and stored in the vehicle. The volume requirement per bar at the pressure operating point can be determined by adding the two individual elasticities of the individual braking units 101 and 102 calculate.

This relationship indicates the volume requirement at a pressure operating point in order to achieve a corresponding pressure increase. By deriving the elasticity, it is possible to determine the volume flow for the desired pressure gradient at the pressure operating point.

Wobei hier dV1/dp der Druck-Volumen-Zusammenhang der ersten Bremseinheit 101 in beispielhaften Einheiten vom mm³/bar ist, dV2/dp der Druck-Volumen-Zusammenhang der zweiten Bremseinheit 102 in mm³/bar ist, jeweils ausgewertet am Druck p1(t=t1) = p2(t=t1) = p12(t=t1). Der Druckgradient pGrd in bar/s ist in 2 mit Bezugszeichen 4 angedeutet.The following applies: $$\begin{array}{l}\left(\text{dV}1/\text{dp}@\text{p}\mathrm{12th}\left[{\text{mm}}^3/\text{bar}\right]+\text{dV}2/\text{dp}@\text{p}\mathrm{12th}\left[{\text{mm}}^3/\text{bar}\right]\right)\times \text{pGrd}\left[\text{bar}/\text{s}\right]=\text{Q}\mathrm{12th}\left(\text{t}>\text{t}1\right)\\ \left[{\text{mm}}^3/\text{s}\right]\end{array}$$

Where here dV1 / dp is the pressure-volume relationship of the first braking unit 101 in exemplary units of mm ³ / bar, dV2 / dp is the pressure-volume relationship of the second braking unit 102 in mm ³ / bar, each evaluated at the pressure p1 (t = t1) = p2 (t = t1) = p12 (t = t1). The pressure gradient pGrd in bar / s is in 2 with reference numerals 4th indicated.

If one evaluates the relationship between volume flow Q12 (t> t1) and the associated pressure gradient pGrd 4 at pressure p2 (t = t1) = p1 (t = t1), taking into account the transition from phase 1 to phase 2 If the volume flow is to be kept constant, this results in the new pressure gradient to be set 4th . $$\begin{array}{l}\text{pGrd}\left[\text{bar}/\text{s}\right]=\text{Q}\mathrm{12th}\left(\text{t}>\text{t}1\right)\left[{\text{mm}}^3/\text{s}\right]/(\text{dV}1/\text{dp}@\text{p}\mathrm{12th}\left[{\text{mm}}^3/\text{bar}\right]+\text{dV}2/\text{dp}@\text{p}\mathrm{12th}\\ \left[{\text{mm}}^3/\text{bar}\right])\end{array}$$

Using the pressure gradient pGrd 4 as a new reference variable from the transition between phases 10 and phase 20th the pressure build-up is continued.

The common pressure increase in the first brake unit 101 and in the second brake unit 102 takes place until a target pressure p3 in both the first and the second brake unit 101 , 102 is reached.

In the upper part of 2 is the course over time 6th a manipulated variable of the brake actuator 100 shown. Such a manipulated variable can, for example, be an adjustment speed of a plunger of a plunger 100 , or an output piston of an electromechanical brake booster 100 or a pump speed of a hydraulic pump 100 be.

Looking at 2 the manipulated variable 5 of the actuator 100 so it can be seen that ahead of time t0 there is no activity as both the pressure p1 as well as the pressure p2 be kept constant.

From the time t1 the manipulated variable increases by the volume flow Q1 ensure in the first phase. The rise above a maximum to the plateau value 6th the manipulated variable is due to the actuator starting up. The volume flow Q2 , which should be kept constant, only results towards the end of the first phase 10 .

As soon as the target pressure p2 = p1 in the first braking unit 101 is reached, the first braking unit is also 101 with the actuator 100 connected and the volume to be filled changes as described above. By changing the target pressure gradient 4th to a value smaller than the previously existing setpoint pressure gradient 2 is achieved that the volume flow Q12 in the second phase 20th the volume flow Q2 in the first phase 10 corresponds to.

The adjustment of the second volume flow can be seen Q12 at the first volume flow Q1 also on the plateau 6th the manipulated variable 5 , indicated here by the line 7th .

The subsequent drop in the manipulated variable 5 takes place on the basis of the approach to the target value p3 in the braking units 101 and 102 is to be set. As soon as the target value p3 is reached - at the point in time t2 - the second phase ends 20th and the pressure p3 is held. The manipulated variable 5 goes back to the zero level 8th back, as no volume promotion is required any more.

3 shows a sequence of the method.

In a first step 110 becomes the gradient for the pressure build-up in the second brake unit 102 and the pressure build-up is carried out with this gradient as the pressure specification until the pressure p2 equal to the pressure p1 is that in the first braking unit 101 prevails.

In a subsequent step 120 becomes dependent on the existing volume flow Q2 at the end of the first phase 10 a new pressure gradient to be set 4th determined so that when operating the hydraulic actuator 100 with the new pressure gradient to be set 4th the volume flow Q2 from the first phase 10 also with the transition to the second phase 20th is retained.

In a further step 130 then the pressure in the first brake unit 101 and in the second brake unit 102 increased to a target value p3.

By increasing the brake pressure first in the second brake unit 102 , and then followed it in both brake units 101 and 102 A hydraulic braking torque is then generated to the value p3 in order to compensate for a falling or decreasing regenerative braking torque - caused by an electric motor in generator mode.

Furthermore, the brake system has a computer program which is set up to carry out all steps of the method described, a machine-readable storage medium on which the computer program is stored and an electronic control unit which is set up to carry out all steps of the method.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102008004201 [0001]

Claims (10)

Method for operating a brake system comprising a hydraulic actuator (100) and two brake units (101, 102), with a pressure build-up during a first phase (10) - A target pressure level (p1) prevails in a first of the two brake units (101) and a lower pressure level (p2) compared to the target pressure level (p1) is present in a second of the two brake units (102), - starting from the lower pressure level (p2) by means of the hydraulic actuator (100) in the second of the two brake units, a pressure increase to the target pressure level (p1) is carried out, and in a second phase (20) the pressure increase in the first brake unit (101) and in the second brake unit (102) by means of the hydraulic actuator (100). Procedure according to Claim 1 , characterized in that when the pressure increases in the first phase (10), a first volume flow (Q2) is generated by means of the hydraulic actuator (100), and that when the first phase (10) is passed into the second phase (20), a second Volume flow (Q12) is generated by means of the hydraulic actuator (100), which essentially corresponds to the first volume flow (Q2). Procedure according to Claim 2 , characterized in that the first volume flow (Q2) is generated by specifying a first setpoint pressure gradient (2) for the hydraulic actuator (100). Procedure according to Claim 3 , characterized in that the second volume flow (Q12) is generated by specifying a second target pressure gradient (4) for the hydraulic actuator. Procedure according to Claim 4 , characterized in that the second target pressure gradient (4) is smaller than the first target pressure gradient (2). Method according to one of the preceding claims, characterized in that the pressure increase in the second phase (20) raises the pressure level in the first braking unit (101) and in the second braking unit (102) to a further pressure level (p3). Procedure according to Claim 6 , characterized in that the pressure increase in the first phase (10) and the pressure increase in the second phase (20) set a hydraulic braking effect corresponding to the further pressure level (p3), which compensates for a missing and / or decreasing regenerative braking torque. Computer program which is set up, all steps of the method according to one of the Claims 1 to 7th to execute. Machine-readable storage medium on which the computer program is based Claim 8 is stored. Electronic control unit which is set up to carry out all the steps of the method according to one of the Claims 1 to 7th to execute.

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