DE19950029A1 - Method and equipment for controlling motor vehicle braking power differentiates between normal stopping and acceleration conditions - Google Patents

Abstract

The method involves controlling the level of hydraulic or pneumatic power applied according to the specific operational conditions. The parameters on which the control is based are the wheel speed (Vrad) and the degree to which the accelerator is depressed (P), e.g. under normal stopping conditions the brake power is reduced (decided by wheel speed) whilst over the range of pedal depression is amplified as a function of that depression

Description

State of the art

The invention relates to a method and a device for brake booster in a vehicle.

DE 195 01 760 A1 (US Pat. No. 5,727,852) describes it a method or a device which make it possible the vacuum brake booster of the brake system, which the Braking force of the driver increased, in whole or in part by a brake booster generated hydraulically to replace. The hydraulic brake booster kung by targeted control of at least one brake forces on the valve arrangement influencing the wheel brakes and / or at least one egg which causes the pressure to build up direction, e.g. B. reached a pump. Through the hydraulic Depending on the version, the brake booster becomes the vacuum brake booster completely or, among other things Comfort reasons, partially replaced. With the latter solution in a first braking area, in which a variety of Braking events take place through a brake booster causes a vacuum brake booster while outside this range (e.g. at ABS pressure level) instead of pneumatic a hydraulic brake booster  to be led. The vacuum brake achieves this power amplifier no or no appreciable gain.

In both solutions, i. H. both in a so-called hy drastic braking power support, in which to brake power boost from a transfer point from the vacuum brake power booster to a hydraulic brake booster is transferred, as well as with the full hydrauli brake booster without vacuum brake booster there are operating situations in which the driver has a Motor vehicle brakes, d. H. an unnecessarily high brake applies pressure to the wheel brakes. This is especially true in The vehicle comes to a standstill. In such a case drive situation, the mechanics of the brake system becomes excessive charged. This also applies to pure pneumatic Amplifier. There are also use cases in which the Driver irregularities in a pressure control, e.g. B. for Adjustment of the brake booster, feels so that an un Comfortable pedal feel arises.

It is an object of the invention to provide measures which the operation of a brake system with brake booster ver improve. This is due to the characteristics of the independent Pa Tent claims achieved.

Advantages of the invention

By controlling the brake depending on the operating situation Force amplification is advantageously an improvement ter operation of the brake system, especially an improved one Work of the systems controlling the brake booster (hydraulic and / or pneumatic brake booster), achieved, usually with a constant braking force amplification is operated.  

Depending on the application, at least in selected Be drive situations, the mechanics of the brake system less stress continuously, with hydraulic or pneumatic systems with we less pressure and thus with lower energy consumption The possibility of a strong overbraking by the Limited driver and / or improved pedal feel.

A reduction takes place in a particularly advantageous manner the brake booster under certain conditions instead, especially if at least one wheel speed below a predetermined minimum value. In addition, is to ensure braking in silence the gain was reduced when the driver conducted braking force magnitude below a given threshold worth lies. This is preferably zero, so that a verrin only when the vehicle is stationary, if the driver has released the brake pedal at least once.

With a hydraulic brake power assist, in which in a first area of brake pedal actuation a pneuma table vacuum brake booster is active at altitude pedal values within the framework of a transfer point towards one hydraulic brake booster at least partially exceeded the brake booster is reduced in addition, if the transfer point is undershot, d. H. the system is in the field of pneumatic reinforcement has found. Here too, when the pedal is pressed again in the hydraulic reinforcement area Standstill reduces the gain.

The application of this procedure is also advantageous for pneumatic amplifiers with adjustable amplification.  

Advantageously, the brake boost is immediate brought back to normal gain when the standstill area of the vehicle is left.

This will further improve ease of use achieved that the transition from the normal Bremskraftver Fluid flow to reduced brake force boost (e.g. using filters or a ramp-shaped control) is so that there is no jump in the gain. The driver does not feel the change in gain or only to a small extent.

Further advantages result from the following Be writing of exemplary embodiments or from the dependent ones Claims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. Fig. 1 shows the hydraulic circuit diagram of a controllable hy draulic brake system, as is known from the prior art, while in Fig. 2 a block diagram of a control unit for controlling the brake system is shown. FIG. 3 shows a flowchart which shows a program of the computer unit of the control unit of FIG. 2 and shows a preferred exemplary embodiment for the control of the brake booster depending on the operating situation. In Fig. 4, finally, the operation of the Bremskraftver gain control is illustrated on the basis of time diagrams.

Description of exemplary embodiments

Fig. 1 shows a hydraulic circuit diagram of a known controllable hydraulic brake system. With 10 , 11 , 12 and 13 wheel brake cylinders are each one wheel of a motor vehicle. The wheel brake cylinders 10 and 11 belong to a first and the wheel brake cylinders 12 and 13 to a second brake circuit. 40 with a brake pedal is referred to, in conjunction with a pneumatic brake booster 14 in a known manner pressure in a master cylinder 16 can be generated. The master brake cylinder 16 is connected to a brake fluid reservoir 15 in a known manner. Between the master cylinder 16 and the wheel brake cylinder 10 to 13 , a hydraulic unit 17 is scarfed, which comprises an arrangement of valves and in this case two pumps 25 , 25 '. The valve arrangement has in known manner for each brake circuit a switching valve USV1, USV2, a precharge or intake valve ASV1, ASV2 as well as an intake valve EV and an exhaust valve AV for each wheel brake cylinder. The designations HL, HR, VL and VR in connection with the intake and exhaust valves EV and AV indicate the assumed position of the respective wheel brake cylinder in the motor vehicle. HL rear left, VL front left, HR rear right and VR front right mean. Furthermore, the hydraulic unit includes 17 storage devices 30 , 30 ', 35 , 35 ', which are used in a known manner for receiving brake fluid. Furthermore, several non-return valves such as the valves 20 , 20 'are provided in a known manner. The function of the hydraulic unit 17 described is z. B. from the aforementioned prior art, so that a detailed explanation should be omitted here. In summary, it can be said that by suitable control of the switching valves USV1, USV2, the suction or Vorladeven tile ASV1, ASV2 and the pumps 25 , 25 'and the inlet and outlet valves both a pressure build-up and a pressure reduction, as well as a state the pressure maintenance in the wheel brake cylinders 10 to 13 can be generated. With the aid of the pumps 25 , 25 ', a higher pressure can be generated in the wheel brake cylinders 10 to 13 than is present in the master brake cylinder 16 . A pressure build-up is e.g. B. by closing the affected UPS and AV, opening the affected ASV and EV and actuating the pumps, a pressure reduction by opening the affected AV and UPS and closing the affected ASV and EV. With 60 a sensor is designated net, which generates information about the pedal position of the brake pedal 40 . 70 with a sensor is designated with which information regarding the brake pressure P _HZ in the main cylinder 16 can be generated. With 80 and 85 sensors are referred to, with which information about the brake pressures in the wheel brake cylinders 11 and 12 can be generated. In another exemplary embodiment, these sensors determine the pressure in the brake lines of the brake circuits and are therefore each installed between the UPS and the EV valves. With 50 a brake light switch is designated.

Fig. 2 shows a schematic representation of a Steuerein unit 200 for controlling the valves and pumps 25 , 25 'of the hydraulic unit 17th The signals from sensors 60 , 70 , 80 and 85 are fed to control unit 200 on the input side. The control unit 200 contains at least one computing unit and a storage unit which represent the facilities for carrying out the procedure described below. The computer unit in conjunction with the programs stored in the storage unit forms the output variables of the control unit 200 taking into account the input variables supplied by the corresponding measuring devices or estimation algorithms and evaluated for calculating the output variables.

The brake booster is shown in the brake system prepared by a vacuum brake booster poses. If a small brake booster is used, so acts its reinforcing effect only in the lower area of the Pedal movement. For this reason, systems are planned that are available at Nach let the brake booster through the vacuum brake brake booster by means of hydrauli Provide control. This is done in that by appropriate control of the valves and the Pumps causing pressure build-up reinforce between master cylinder pressure and brake system pressure through which the reinforcing effect of the Un terdruckbremskraftkrafters is continued. The About from vacuum brake booster to hydraulic brake power boost takes place at a transfer point, which, for example, from the change in the main brake cylinder derdrucks is derived. In other embodiments the vacuum brake booster is completely dispensed with and the brake booster only by means of the hydrauli control performed. In this case too the base, for example, the master cylinder pressure or the brake pedal actuation variable by valve and pump control set a wheel brake or brake circuit pressure, which compared to the pressure specified by the driver via egg is related to a given gain factor. Like this probably with the braking power support as well as with the hy drastic brake booster is for normal operation a gain factor is provided which a brake has the usual value.

However, there are operating situations, such as the The vehicle comes to a standstill in which the driver is over-braking  sen an unnecessarily high brake pressure by means of the reinforcement generated. This is due to the excessive load on the Mechanics undesirable. It also leads to comfort due to the high pressure specified by the driver regularities in the gain control can be felt nen. Therefore, to improve comfort and / or Reduction in mechanical stress in the least an operational situation the reinforcement upon detection of this at least one operating situation deviating from the normal value changed, preferably reduced. In the preferred embodiment Example is the operating situation the standstill of the vehicle. This is in an execution tion form based on at least one wheel speed speed signal and preferably one desired by the driver te brake force representative signal detected. It it is checked whether this signal has a predetermined smolder lenwert, preferably zero, falls below or reached Has. If the control system is a hydraulic one Brake booster without additional vacuum brake booster, the operating situation determined if the at least one wheel speed falls below a minimum threshold and preferably that Transfer point was under. The transfer point will be in the preferred embodiment by comparing the Change of master cylinder pressure to brake pedal actuation value determined. The minimum speed is like this set it to be the lowest calculated speed in the system or a predetermined limit in the range of a few km / h. The brake the driver wants force representative signal is depending on the version Master cylinder pressure, the brake circuit pressure, the brake actuation value (e.g. deflection), etc. Is one of these If the criteria are not met, the gain is restored Normal gain led or remains the normal gain receive. In the preferred embodiment is with a view  to protect the mechanics and / or improve the Comfort the gain factor compared to the normal value lowered, so the gain is reduced. The transition between The gain factors are fluid, at for example by means of ramps (time-dependent control) or Filters designed so that none compromise comfort Jump is noticeable.

In a preferred embodiment, the locking takes place the gain is reduced from the normal value to a predetermined value lower value if the relevant conditions are met. This value is chosen such that the driver in the Is able to brake the vehicle at a standstill build up kung. In another embodiment the gain after detection of the standstill depends on other operating parameters (e.g. road gradient, coefficients of friction, etc.) set to different values.

In the preferred exemplary embodiment, the function described is implemented by means of a computer program. The flow chart shown in FIG. 3 outlines a preferred exemplary embodiment for such a computer program. The program is started at specified times. Thereupon in the first step 100 at least one wheel speed variable Vrad, which represents the wheel speed of a selected wheel or a wheel speed variable calculated from at least two wheel speeds, as well as at least one variable P representing the brake pedal actuation by the driver. Depending on the embodiment, this size is the pressure in the brake master cylinder of the brake system, the pressure in a brake circuit of the brake system or in a selected wheel brake or a size derived therefrom or the actuation path or the deflection or the actuating force of the Brake pedals or a quantity derived from them. In the next step 102 , it is checked whether the wheel speed variable Vrad read is smaller than the predetermined minimum value Vmin. If this is not the case, ie if the vehicle is outside the standstill range, the brake booster factor BKV is set to its normal value or remains at its normal value in accordance with step 104 and the status mark ST described below is set to the value zero. The program is then ended and run through at the next point in time.

The amplification factor set in step 104 is then used in a program (not shown for reasons of clarity) for complete or partial control of the brake system, depending on the exemplary embodiment, by an actuation variable set by the driver (pedal travel, pedal force, master cylinder pressure, etc.) into a setpoint for the Brake pressure to be set is implemented, the gain factor being taken into account, so that a gain corresponding to the gain factor is effected between the set brake pressure size and the actuation size. In the preferred embodiment, the target pressure size is set in the context of a control loop taking into account the detected wheel brake or brake circuit pressures.

If step 102 has shown that the vehicle is in the standstill area, then in step 103 it is checked whether the status mark ST has the value 1. If this is not the case, it is checked in step 106 whether the pressure is less than a predetermined minimum pressure Pmin or, in another exemplary embodiment, whether the transfer point between pneumatic and hydraulic amplification is undershot, ie the system is in the area of pneumatic amplification . If this is not the case, step 104 follows. If this is the case, the status flag ST is set to the value 1 (step 105 ). The status mark therefore indicates that the driver has released the brake pedal after the vehicle has come to a standstill. In the subsequent step 108 , the gain factor BKV is reduced. If step 103 shows that the status mark has the value 1, step 108 follows. When the vehicle is at a standstill and the brake pedal is released after the pedal is released, the reduced amplification factor is effective. After step 108 , the program is ended and run through again at the next point in time.

For reasons of clarity, it is not shown in FIG. 3 that the transitions between the normal value and the reduced value of the amplification factor are smoothed, so that no jump can be felt.

The mode of operation of the function shown above is illustrated in FIG. 4 on the basis of time diagrams. Here, Fig 4a shows the time course of at least 4b 4c shows. Radge a speed V-rad Fig. The timing of the pressure variable P and Fig. The timing of the braking force gain BKV.

A situation is assumed in which the vehicle travels without braking. The wheel speed quantity Vrad is at a certain value ( FIG. 4a). The gain factor is according to FIG. 4c at its normal value NORM. At time T0, the driver operates the brake pedal, the pressure variable P increases accordingly ( Fig. 4b). As a result of the braking process, the wheel speed quantity is reduced until it falls below the intended minimum value Vmin at time T1. Since the print size is undiminished, the amplification factor remains at its standard value. After time T1, the pressure quantity P is reduced until it falls below its minimum value PMIN at time T2 ( FIG. 4b). Correspondingly, the gain factor is then ramped from the normal value to a reduced value BKVred from time T2 in accordance with FIG. 4c. This remains during the standstill phase of the vehicle. At time T3, the brake pedal is actuated again (see pressure curve in FIG. 4b), which acts with the reduced amplification factor. At the time T4 ( Fig. 4a), the Radgeschwin speed exceeds the minimum value, so that from the time T4 the gain factor is again performed according to a ramp to the normal value. At time T5, the driver actuates the brake, the pressure quantity P increases according to FIG. 4b. After the time T5, the wheel speed magnitude drops until the time falls below the minimum speed T6. If the pressure variable P also falls below its minimum value (time T7), the gain factor is reduced from its normal size to its reduced size.

The change in the gain factor also takes place in Verbin with a pneumatic brake booster, if its gain is controllable.

Claims (11)

1. A method for boosting the braking force in a vehicle, wherein there is a gain between a predetermined by the driver and the applied braking force, which is characterized by a gain factor, characterized in that this gain factor is changed in at least one operating situation. 2. The method according to claim 1, characterized in that the gain factor is reduced. 3. The method according to any one of the preceding claims, since characterized in that the at least one Betriebsi tuation is the standstill of the vehicle. 4. The method according to any one of the preceding claims characterized in that the operating situation then before is when a wheel speed size is less than one Is the minimum value. 5. The method according to claim 4, characterized in that the operating situation is when one of the Size ei representing driver's predetermined braking force has fallen below a predetermined threshold.   6. The method according to claim 4, characterized in that which is at least one situation when a Transfer point between pneumatic and hydraulic Brake force gain is undercut. 7. The method according to any one of the preceding claims characterized in that the transition from a first Gain factor is smoothed to a second. 8. The method according to any one of the preceding claims characterized in that the gain factor be depending on drive size, e.g. B. depending on road gradient and / or is dependent on the coefficient of friction. 9. The method according to any one of the preceding claims, since characterized in that when leaving the at least an operational situation the reinforcement back on their Normal value is maintained. 10. The method according to any one of the preceding claims characterized in that the gain factor means Control of valves and at least one pump hydraulic brake system is set. 11. Device for boosting braking force in a vehicle, with a control unit, which depends on the input size Output variables for setting a gain factor tors between the one specified by the driver and one out exerted braking force, characterized in that the control unit the presence of at least one Be recognizes the drive situation and if this is present drive situation changes the gain factor.