DE102010039816B4 - Method for operating a brake system of a motor vehicle, associated brake system and motor vehicle - Google Patents

Abstract

Method for operating a brake system (100) of a motor vehicle, with an electric generator (146) and a first hydraulic and a second hydraulic brake circuit each with first and second hydraulic service brakes (158, 164), a tandem master cylinder (112), a reservoir (118 ) for brake fluid and a brake pedal (106), characterized in that when the driver actuates the brake pedal (106), the available braking force of the generator (146) is determined and an equivalent brake fluid volume is calculated from this, which is used for hydraulic braking of the motor vehicle corresponds to the same braking force, and that the equivalent volume of brake fluid from the second brake circuit is conducted into a volume unit (250) specially provided for this purpose connected to the second brake circuit, the volume discharged into the volume unit (250) being determined by the corresponding dimensioning of the volume unit (250) so limited is that the still available volume in the second brake circuit during a braking process and with simultaneous failure of the generator (146) and the first brake circuit, a predetermined maximum deceleration is achieved.

Description

The invention relates to a method for operating a brake system of a motor vehicle, with an electric generator and a first hydraulic and a second hydraulic brake circuit each with first and second hydraulic service brakes, a tandem master cylinder, a reservoir for brake fluid and a brake pedal. It also relates to an associated brake system and an associated motor vehicle.

Motor vehicles whose drive or braking systems include an electric generator are becoming increasingly important. Such a motor vehicle can for example be equipped with a hybrid system in which the motor vehicle is preferably driven electrically and - when the battery is empty - with an internal combustion engine. Alternatively, the internal combustion engine can also be used to recharge the battery. Another category of motor vehicle is purely electrically powered by an electric motor. These vehicles therefore only run on electrical energy. For example, they can be charged at the designated charging stations.

A current problem with electrically powered vehicles is their significantly shorter range compared to vehicles powered by combustion engines. For this reason, it is advantageous not only to charge the batteries of the motor vehicle when the vehicle is stationary, for example at the charging stations mentioned, but also to do this while the motor vehicle is in operation. Since the electric motor can also be operated as a generator for electrical energy, energy can be generated recuperatively when braking the motor vehicle. During the braking of the motor vehicle, the generation of energy by the generator leads to a deceleration torque or braking torque of the motor vehicle, since the kinetic energy or rotational energy of the axle connected to the electric motor or the wheels attached to it is converted into electrical energy.

Brake systems in which a deceleration torque is generated by the electric motor operated in generator mode have additional braking means. These additional braking means, which are usually implemented in two legally prescribed brake circuits, include, for example, electromechanical, hydraulic and / or electrohydraulic brakes. The problem with conventional brake systems of this type is that either the maximum possible deceleration torque of the generator cannot be used, or that when switching between the braking deceleration of the generator and the other braking means, a gap arises in which the vehicle cannot be decelerated with an optimized braking force distribution. Furthermore, the decoupling of the regenerative braking by the generator from the brake pedal can give the driver an unusual pedal feel, so that he can poorly assess the braking effect achieved by him.

In addition, if the generator is connected to the rear axle of the vehicle, there is a risk that the vehicle will become unstable due to simultaneous deceleration by the generator and the rear wheel brakes.

From the WO2004101308 A1 it is known to discharge braking medium into the low-pressure accumulator of the ABS system in a brake system with a hydraulic service brake and an electric generator when braking by means of the electric generator.

From the DE 10 2009 009 647 A1 It is also known to provide a separating cylinder in a brake system with a hydraulic service brake and an electric generator, which has two chambers separated by a separating piston, a first chamber being connected to the master cylinder and the second chamber being connected to the low-pressure accumulator of the ABS system.

The invention is therefore based on the object of specifying a method for operating a braking system of a motor vehicle that allows maximum utilization of the braking torque available from the generator and at the same time - with the usual pedal feel - ensures an optimized braking force distribution and thus a stable state of the motor vehicle. Furthermore, an associated brake system and an associated motor vehicle are to be provided.

The object is achieved by the subject matter of claims 1, 7 and 8. With regard to the method, the above object is achieved in that when the driver presses the brake pedal, the available braking force of the generator is determined and an equivalent brake fluid volume is calculated therefrom which corresponds to the same braking force before hydraulic braking of the motor vehicle, and that the equivalent volume of brake fluid from the second brake circuit is passed into a volume unit specially provided for this purpose connected to the second brake circuit, the volume discharged into the volume unit by corresponding dimensioning of the volume unit is limited in such a way that a predetermined maximum deceleration is achieved by the volume still available in the second brake circuit during a braking process and when the generator and the first brake circuit fail at the same time.

Advantageous refinements of the invention are the subject matter of the subclaims.

The invention is based on the idea that a generator for regenerative recovery of energy is used in an optimized manner if the entire braking torque that is currently available from the generator is used for braking at least partially during braking processes. In this way, the batteries can be charged as effectively as possible in the shortest possible time. Full use of the regenerative braking torque by the generator means that no deceleration or braking torque is generated by the other braking means, for example the electrohydraulic or hydraulic brakes, during this phase of the braking process. On the other hand, in the case of target braking torques that exceed the braking torque currently available from the generator, additional braking torque should be generated immediately by the service brakes, the braking force distribution with respect to the vehicle axles should ensure a stable vehicle condition.

The invention is further based on the consideration that it is important for the driver during the entire braking process to have feedback with regard to the deceleration he has caused. Since, for example, in a hydraulic brake system, the braking effect of the generator is completely decoupled from the hydraulic brake circuits, it would be disadvantageous for the driver of the motor vehicle if the feedback that he experiences on the brake pedal when braking is significantly different than during braking, which, for example, take place hydraulically, for example when the batteries are fully charged.

As has now been recognized, the optimized regenerative use of the generator can be combined with a familiar pedal structure in which the driver actually shifts brake fluid during the braking process. However, this brake fluid is not fed into the brakes, but into a specially designed volume unit. So that the driver receives exactly the same feedback during a braking process from the electric generator as if he would hydraulically effect the same deceleration torque, the brake fluid volume moved by the driver should now correspond to the volume that would result in a deceleration with the same deceleration torque as it would from delivered to the generator. So, to a certain extent, an equivalent volume of brake fluid should be pushed into the volume unit or the volume reservoir. With the same braking torque, the braking process “feels” essentially the same for the driver, regardless of whether braking is being carried out by the generator or exclusively hydraulically or in a combination of both.

In the event that the driver would like to increase the deceleration torque beyond the deceleration torque available from the generator, the second brake circuit is advantageously separated from the tandem master cylinder by a separating valve. In this case, the separation prevents further brake fluid from being displaced into the volume unit, which would give the driver the feeling that he could further increase the braking torque. The checking of the respective delays or braking torques that can be called up by the generator is preferably carried out continuously.

In the event that the driver wishes to increase the deceleration torque beyond the deceleration torque available from the generator, the service brakes of the first brake circuit are actuated. This is preferably done electrohydraulically, for example by controlling a pump. In the event that the rear brake circuit is connected to the rear wheels or the rear wheel brakes in a motor vehicle, and the generator is connected to the rear axle, the brakes of the first brake circuit would correspond to the front wheel brakes. While recuperative braking is only used at the rear on the rear axle up to the moment up to which the generator can deliver braking torque, the braking force is now distributed to both axles, since the front wheel brakes are activated when another braking request is made. The entire braking force is therefore distributed between the front and rear brakes. If the hydraulic or electrohydraulic rear wheel brakes were activated in this case, this could result in overbraking and, for example, the rear of the vehicle breaking away. By activating the front wheel brakes, a much more stable vehicle condition can be achieved during the braking process.

In combination with the front wheel brakes, the service brakes of the second brake circuit can also be actuated in the case described above. This means that during the braking process, the generator and the service brakes can be used on the rear axle and the service brakes at the front can be used to brake. In this way, the braking torque on the rear axle can also be increased if necessary. In the phases of the braking process in which the generator can only deliver a negligible braking torque, the service brakes brake at the front and rear.

The braking force distribution on the two vehicle axles - essentially the distribution on Front and rear axles or on generator + rear service brakes and front service brakes - is preferably carried out on the basis of a predetermined characteristic curve for the target brake distribution. Such a curve indicates, for example, the respective target braking torque of the front wheel brakes as a function of the braking torque available from the generator and the overall required target braking torque.

Brake systems for motor vehicles in general, and in particular brake systems of the type shown above, must be equipped with what is known as a fall-back level. This means that in the event of a failure of components, e.g. B. the electrical system or individual brakes, the driver - usually by higher muscle power - can still generate a braking torque that meets the safety requirements. In the above-mentioned method for operating a brake system, this requirement is satisfied by the volume discharged into the volume unit being limited physically - by appropriate dimensioning of the volume unit - in such a way that the still available volume of brake fluid in the second brake circuit during a braking process if the generator, the electrohydraulic components of the second brake circuit and the brakes assigned to the first brake circuit fail at the same time, a predetermined delay is achieved. This predetermined delay is advantageously essentially 0.3 g.

With regard to the brake system for a motor vehicle, the above-mentioned object is achieved with an electric generator and a first hydraulic and a second hydraulic brake circuit each with first and second hydraulic service brakes, a tandem master cylinder, a reservoir for brake fluid and a brake pedal and with an electronic control unit , in which a method of the type mentioned above is implemented in software and / or hardware. In the control and regulation unit, for example, the characteristic curve for the braking force distribution to the generator, front wheel and rear wheel brakes can be stored.

In relation to the motor vehicle, the above-mentioned object is achieved with an above-mentioned brake system. In a preferred embodiment of the motor vehicle, the second brake circuit is assigned to the rear wheels and the first brake circuit is assigned to the front wheels. The generator is advantageously operated as an electric motor to drive the vehicle. This operating mode can be used in all-electric vehicles as well as in hybrid-powered vehicles.

The advantages of the invention are, in particular, that by using the generator to generate the braking torque and the conduction of an equivalent volume of brake fluid in a volume unit, the generator can be used in an optimized manner for braking during every driving situation of the motor vehicle, while the driver is using the usual feedback the brake pedal receives. The use of the service brakes of the first brake circuit in the event that the driver's braking request or the corresponding braking torque exceeds the braking torque available from the generator at this point in time prevents heavy loading of the rear axle or overbraking. In addition, the driver can instantly generate additional braking torque without any interruption or gap.

• 1 ein Flussdiagramm des Verfahrens in einer bevorzugten Ausführungsform,
• 2 ein Diagramm einer vorteilhaften Bremskraftverteilung zwischen Generator und hydraulischen Vorderradbremsen, und
• 3 ein hydraulisches Schaltbild eines Bremssystems in einer bevorzugten Ausführungsform.

An embodiment of the invention is explained in more detail with reference to a drawing. They show in a highly schematic representation:

• 1 a flow chart of the method in a preferred embodiment,
• 2 a diagram of an advantageous braking force distribution between generator and hydraulic front wheel brakes, and
• 3 a hydraulic circuit diagram of a braking system in a preferred embodiment.

The same parts are provided with the same reference symbols in all figures.

The process or the process sequence begins with the start 6th , which marks the point in time at which the driver expresses a braking request. In block 10 the driver's braking request is determined and a target braking torque of the motor vehicle is derived from this. In block 16 the currently maximum available generator braking torque is determined. The procedural steps 10 and 16 can also be performed essentially simultaneously. In the decision 22nd it is now tested whether the driver's braking request or the corresponding target braking torque is greater than the braking torque currently available from the generator. If this is not the case, that is, if the braking torque desired by the driver can be supplied in full by the generator, the method branches off from the decision 22nd to block 28 . In block 28 the motor vehicle is braked with the aid of the braking torque supplied by the generator. The process continues to stop 40 .

In the event that in the decision 22nd it has been determined that the driver's desired braking torque exceeds the braking torque that can be generated by the generator, the method branches to block 46 . In block 46 will depend on the The braking force distribution between the generator and the service brakes is determined by the desired total braking torque and the braking torque available from the generator. In the present case, the additional braking torque is supplied by the front wheel brakes. A discussion of braking force distribution is given below in connection with 2 .

After in block 46 the braking force distribution was determined is in block 52 the motor vehicle is braked by the generator and the front wheel brakes. The process branches on to stop 40 . The procedural steps between start 6th and stop 40 are carried out almost continuously during a braking process.

In both branches, in which the procedure from the decision 22nd branches, a brake fluid volume is equal to that in the block 16 certain generator braking torque is equivalent, passed into a volume unit. The braking process by the generator is thus mapped to a certain extent on a purely hydraulic braking process. It also follows from this that the driver during braking or the exclusive braking by the generator has the same or a very similar braking feeling as if he were braking purely hydraulically. When in decision 22nd If it is determined that the desired braking torque exceeds the braking torque that can be delivered by the generator, after the equivalent volume of brake fluid has been fed into the volume unit, a separating valve is closed, which prevents further brake fluid from being passed into the volume unit. The isolation valve is preferably closed only once during a braking process. The volume unit is also dimensioned in such a way that in the fallback mode or in the fallback level of the brake system, if the generator, the electrohydraulic components of the second brake circuit and the front wheel brakes fail, there is still enough brake fluid to achieve a deceleration of at least 0.3 g .

In 2 is a synthetic braking force distribution between generator braking torque, which is plotted on the ordinate in units of g, where g denotes the acceleration due to gravity, and the braking force of the front wheel brakes, which is plotted on the abscissa, also in units of g.

Braking torques between 0 g and 0.15 g, which are on the ordinate between the zero point and the point P1 are completely supplied by the generator. If larger braking torques are to be generated, the front wheel brakes are activated in addition to the generator. Between the points P1 and P2 Both the braking torque generated by the generator and the braking torque generated by the front brakes increase linearly. For even greater braking torques between point P2 and point P3 As in the previous sections, the braking torque then results from the brake distribution 70 .

Depending on the strength of the available braking torque of the generator, the service brakes on the rear axle or on the rear wheels can also be used to generate the desired braking torque.

A recuperative, electro-hydraulic brake system 100 of a motor vehicle in a preferred embodiment is in 3 Shown as a Hyrdaulisches circuit diagram. The braking system 100 exhibits a brake pedal 106 , a tandem master cylinder 112 and a reservoir 118 for brake fluid. Via a pedal travel sensor 124 becomes the position of the brake pedal 106 definitely. The hydraulic line 140 connects the tandem master cylinder 112 with a first, the hydraulic line 130 with a second brake circuit. In the present case, the second brake circuit corresponds to the brake circuit of the rear wheels. A generator 146 is used for regenerative braking of the motor vehicle. An electronic control and regulation unit 152 is on the signal side with the generator 146 and the controllable components of the braking system 100 as well as connected to the sensors.

The wheel brakes are the first brake circuit 158 , the front wheel brakes, the second brake circuit the wheel brakes 164 , the rear brakes. Furthermore, the corresponding wheels are wheel speed sensors 170 assigned.

Each of the two brake circuits has a hydraulic pump 176 , a low pressure accumulator 182 , as well as various normally open or normally closed, electromagnetically actuated valves 188 , 190 , 192 , 194 , 196 , 198 , 200 , 202 on. The two brake circuits are (electromagnetically actuated) isolating valves 220 , 230 upstream. In some hydraulic lines of the braking system 100 are shut-off valves 236 , for example in the form of check valves, switched.

In the braking system 100 can in a known way brake fluid in the wheel brakes 158 , 164 or in the respective low pressure accumulator 182 be directed. From there it can, for example, with the help of the respective pump 176 be fed back to the respective brake circuit via the hydraulic lines.

The braking system 100 includes a unit of volume 250 , which can also be referred to as an e-gap. The unit of volume 250 includes a brake fluid-free area 256 , a memory area 262 for brake fluid and one Control fluid area 268 . It also includes three displaceable pistons 274 , 278 , 280 . There are also three feathers 286 , 292 , 298 intended. The storage volume 262 is limited in such a way that when this volume is completely filled with brake fluid, there is still enough brake fluid available in the second brake circuit to decelerate the motor vehicle in fallback mode with at least 0.3 g.

At the control connection 300 is the control fluid area 268 with the hydraulic line 310 between the pump 176 and a pressure-generating cascade diaphragm 316 connected. The tuning of the cascade panel 316 at the outlet of the pump 176 is selected in such a way that pressure pulsations can be mitigated, especially at high pump speeds and / or with high pressure build-up dynamics. The control fluid area 268 is used as a kind of damping chamber.

At the storage connection 320 can in the memory area 262 Brake fluid taken in and out or via the pump 176 be fed back into the brake circuit. Via a return channel 330 with a return valve 336 is a connection between control connection 300 and storage connection 320 created.

Both brake circuits are in the operating state of the motor vehicle - before the first braking process and if necessary after a braking process - by running the pump, that is, by activating the pump or pumps, pre-filled with brake fluid. For pressure build-up processes - for example when priming the brake circuits - the isolating valve 220 and the return valve 336 getting closed.

During a braking process in which the driver of the motor vehicle depresses the brake pedal 106 is actuated by the control and regulation unit 152 determines the required deceleration or braking torque. It then determines that from the generator 146 braking torque that can be generated. The control and regulating unit determines this determined braking torque 152 then an equivalent volume of brake fluid, which in the storage area 262 the unit of volume 250 is directed. When the pedal position reaches the same position as that of the generator 146 deliverable braking torque or the equivalent brake fluid volume, the isolating valve 220 closed. When the isolation valve 220 was closed during braking, it will not be reopened. Exceptions can be made if, for example, panic braking of the driver by the control and regulation unit 152 is recognized.

On the other hand, if the vehicle threatens to assume an unstable braking state due to the braking on the rear axle, the isolating valve is activated 220 closed and the front brakes 158 are activated to build up the desired braking torque.

The braking system 100 Also behaves particularly advantageously in situations in which the motor vehicle is only moved slowly, for example during parking maneuvers. In these situations the generator does not deliver any significant torque. However, the driver can build up pressure hydraulically directly via the front wheel brakes. In this way, (gradual) pressure on the rear axle is avoided and the motor vehicle can be braked completely using the front wheel brakes.

List of reference symbols

6th

begin

10, 16

block

22nd

decision

28

block

40

stop

46, 52

block

70

Brake force distribution

76

ordinate

82

abscissa

100

Braking system

106

Brake pedal

112

Tandem master cylinder

118

reservoir

124

Pedal travel sensor

130, 140

hydraulic pipe

146

generator

152

Control and regulation unit

158, 164

Wheel brake

170

Wheel speed sensor

176

pump

182

Low pressure accumulator

188

Valve

190

Valve

192

Valve

194

Valve

196

Valve

198

Valve

200

Valve

202

Valve

220, 230

Isolation valve

236

Check valve

242, 244

hydraulic pipe

250

Volume unit

256

Area

262

Storage area

268

Control fluid area

274

Pistons

278, 280

Pistons

286, 292

feather

298

feather

300

Control connection

310

hydraulic pipe

316

Cascade screen

320

Storage connection

330

Return duct

336

Return valve

P1

Point 1

P2

Point 2

P3

point 3

Claims (10)

Method for operating a brake system (100) of a motor vehicle, with an electric generator (146) and a first hydraulic and a second hydraulic brake circuit, each with first and second hydraulic service brakes (158, 164), a tandem master cylinder (112), a reservoir (118 ) for brake fluid and a brake pedal (106), characterized in that when the brake pedal (106) is actuated by the driver, the available braking force of the generator (146) is determined and an equivalent brake fluid volume is calculated from this, which is used for hydraulic braking of the motor vehicle corresponds to the same braking force, and that the equivalent volume of brake fluid from the second brake circuit is directed into a volume unit (250) specially provided for this purpose connected to the second brake circuit, the volume discharged into the volume unit (250) being determined by the corresponding dimensioning of the volume unit (250) so limited is that the still available volume in the second brake circuit during a braking process and with simultaneous failure of the generator (146) and the first brake circuit, a predetermined maximum deceleration is achieved. Procedure according to Claim 1 In the event that the driver wishes to increase the deceleration torque beyond the deceleration torque available from the generator (146), the second brake circuit is separated from the tandem master cylinder (112) by a separating valve (220). Procedure according to Claim 2 In the event that the driver wishes to increase the deceleration torque above the deceleration torque available from the generator (146), the service brakes (158) of the first brake circuit are actuated. Procedure according to Claim 3 , the service brakes (164) of the second brake circuit also being actuated if necessary. Procedure according to Claim 3 or 4th , wherein a braking force distribution (70) is carried out on the basis of a predetermined characteristic curve for the target braking force distribution. Method according to one of the preceding claims, wherein the predetermined delay is 0.3 g. Brake system (100) for a motor vehicle with an electric generator (146) and a first hydraulic and a second hydraulic brake circuit each with first and second hydraulic service brakes (158, 164), a tandem master cylinder (112), a reservoir (118) for brake fluid and a brake pedal (106) and with an electronic control unit (152), in which a method according to one of the Claims 1 until 6th is implemented in software and / or hardware. Motor vehicle with a braking system (100) according to Claim 7 . Motor vehicle after Claim 8 , wherein the second brake circuit is assigned to the rear wheels and the first brake circuit is assigned to the front wheels. Motor vehicle after Claim 8 or 9 , wherein the generator (146) is operated as an electric motor to drive the vehicle.

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