DE19955094A1 - Motor vehicle braking control method - Google Patents

Abstract

A braking control method for a motor vehicle during a braking phase, where the braking pressure for at least one rear wheel is determined via the wheel response/behaviour at at least one front wheel. For the at least one rear wheel, a braking force is specifically determined from the braking force prevailing during incursion of wheel-slip and/or from the front wheel acceleration values via specified control parameters, such that the braking force corresponds approximately to the maximum transferable braking force at the, at least one, rear wheel.

Description

The present invention relates to a method for braking success of a motor vehicle during a braking phase in particular with a slip inlet and an ar according to this procedure brake device for a motor vehicle.

With the known methods for brake control of motor vehicles The aim is to testify to over-braking - that is, over increased slip between the wheels of the car and the driver web surface - to prevent. The technological background In this context, the reason must be briefly stated that the so-called "slip" in the wheel arch of a motor vehicle everyone - even less - power transmission occurs. So lie about 10% slip when the rotation measured on the rim number when braking at a speed of 90 km / h speaks, but the vehicle is actually at 100 km / h emotional.

Conventional tires now initially transmit forces such as grow linearly with the slip, as elastic deformations tire without sliding the tread rubber to one Slip. With increasing slip at first only get Parts of the tire contact patch start to slide, as the Conditions within the footprint are inhomogeneous because different surface sections, for example a un have different contact pressure. The transferred After all, forces no longer increase linearly, but ver wrestle again after passing a maximum until finally over the entire contact area in sliding friction has gone. The optimum slip is included depending on the type of tire approx. 7 to 15% slip.  

Under "Schlupfeinlauf" is now exceeded this Op timums understood, with the tire also its lateral feel loses properties. A wheel not braked now makes it easier to determine a vehicle Reference speed, which is a basis for driving dynamics Mic control and the ABS control of the vehicle.

Among the known brake control methods, the anti Blocking system control (ABS control) and as a subsystem of which the so-called electronic brake force distribution (EBV) call.

From the outset we should say to simplify the terminology be synonymous with the term "braking force" synonymous "Brake pressure" can be understood.

With ABS control, the braking behavior of the rear wheels mainly by the so-called select-low method This applies the braking force of a rear wheel to that adapted to the other rear wheel, in which slip first was found. The first named rear wheel is consequently "braked" - d. H. its transmitted braking torque is on due to the adaptation to the braking force of the other rear wheel lower than its maximum with optimal slip transferable res braking torque. This has a particularly disadvantageous effect Cornering from where high lateral accelerations occur to step. Here the outside wheel is braked because on inner wheel only a lower braking torque because of the lower contact pressure of the wheel can be transferred to the road is.

In order to provide a solution to this problem, the so-called cornering brake control (CBC) method was developed in particular for hydraulic brake systems, which is based on the principle that a brake pressure difference on different wheels (decaying) is retained. However, the CBC process only partially overcomes the above-mentioned disadvantage in that at high lateral accelerations (approx. 5 m / s ² ) no brake pressure is built up on the inside wheel between the start of braking and the entry into the ABS control. When entering the ABS control, the same valve position is used in the hydraulic system on the inside of the curve as on the outside wheel. The pressure difference prevailing before the ABS control has an advantageous effect, which remains for a certain time until the initial pressure difference is compensated for due to the hydraulic inertia.

The application of the CBC procedure has further effects on the driving behavior. Due to the uneven braking force distribution between the left and right side of the vehicle when braking sen - that is, before the ABS campaign begins - has an external effect directed torque on the vehicle that the otherwise prevailing tendency towards so-called "screwing in", i. H. to oversteer with skidding counteracts. This The procedure is based on electromechanical brake systems the rest only partially transferable, since they are of the typi behavior of a hydraulic brake system.

With an EBV regulation, certain values are exceeded Slip and / or acceleration thresholds the braking force Wheels no longer raised, but on a constant Ni kept veau. So no braking force is released so that slip enemas can occur.

In this respect, the known additional processes stop within the ABS control only in certain special cases the brake pressure construction on the rear wheels. However, there will be no advance notice conveniently recognized brake pressure set on the rear wheels, in particular, no pressure is released without significant slip builds. If the optimal adhesive value groove is exceeded tongue are also the cornering properties of the wheel and receiving the most accurate information possible about the Driving speed for any control tasks such. B. in connection with the ABS or driving dynamics control pro  blemish. In this respect, the core of the problem is lying invention in the prevention of deep slippage break in.

The known brake control methods are mainly used for hydraulic braking systems implemented because with these high Braking force gradients can be generated. A targeted one position of the braking force is, however, only with a certain Tolerance range possible. In contrast, z. B. electromecha systems specifically target certain braking forces Adjust the appropriate brake force sensors. However, it is recommended for such brake systems often a relative cost reasons slow actuator what the quick activation and Deactivation, as required by ABS control, is not without problems.

Based on the problem described above, it is open surrender of the invention, a method and an apparatus for To create brake control of a motor vehicle with which Braking behavior of the rear wheels of a motor vehicle against above the known brake regulations in particular on braking phases and also jumps in coefficient of friction is improved.

This task is due to the general technical Grundge thanked that the brake pressure for at least one rear wheel on the wheel behavior of at least one front wheel is true. The braking behavior of at least one front So rades is not just about ABS regulation on the concerned Front wheel used, but also for at least one Determine suitable brake control specifications for the rear wheel. On the se way it is z. B. possible with a sudden change of Coefficient of friction of the road surface - the mentioned coefficient of friction jump - the braking behavior of the rear wheels even before theirs To be able to adjust reaching the coefficient of friction, for what the known control methods are simply not able wa ren.  

The method according to the invention or the one according to the invention Braking devices are particularly useful with the use of a electromechanical brake device suitable, since already at Appropriate start of critical braking phases on the rear wheels Braking forces can be set. In addition, the exact setting a determined braking force value possible. Depending on Design and implementation of the basic idea according to the invention In a brake control system, it can be universally differentiated union driving situations, e.g. B. in curves, when braking improved braking behavior can be achieved. The beginning he In contrast, mentioned brake control procedures were usually more on mastering special situations - see e.g. B. the CBC process - tailored.

It is preferred to slip out at the front wheel prevailing braking force and / or the front wheel acceleration optimal values for the at least one rear wheel Braking force determined that corresponds to a braking torque that is transferable before slip entry. Whichever it can be advantageous, on the one hand, the one that can actually be applied Braking force less than or equal to the determined brake force to ensure that braking continues is guaranteed under optimal hatching conditions. Ande on the other hand, it can be advantageous to actually bring them up braking force slightly greater than the determined brake force, because this braking force is already very has approached meaningful values. With the subsequent hatching enema that is much weaker than without it procedure according to the invention, the ABS control can be used as usual enter the slip control.

Moments originating from the drive train can in principle according to their effect, but what is not mentioned and treated separately below. A particularly simple regulation is created in that the optimal braking force to be set directly from the straight  still transferable braking force before a slip in on the corresponding front wheel is determined.

In order to determine the optimal braking forces z. B. at to obtain a different transverse load on the vehicle, becomes the ratio of the braking forces of the pair of front wheels determined and transferred accordingly to the pair of rear wheels Different wheel loads, for example be taken into account. In addition to the different Querbela Stung is another case for a page by page difference braking ability the presence of pages under different coefficients of friction. These two cases could be caused by the inventive method and a corresponding implemen not be distinguished at first, which, however, to optimize driving behavior would make sense. To solve this problem, others can Driving and control parameters are used, such as. B. the Lateral force, yaw rate, wheel speed differences and / or steering wheel angle for curve detection.

When inferring from the braking force of the front wheel on the of the rear wheel, it is advantageous to determine the braking force to apply to the rear wheel with a time lag. This time ver sentence can vary mainly according to the speed of the force straighten vehicle. This ensures that at one abrupt jump in the coefficient of friction on the road surface for the Rear wheels the original braking force until it is reached of the transition area is maintained in order after the time delay the determined to the new coefficient of friction apply adjusted braking force.

It can also be advantageous in certain braking situations a linearly increasing or decreasing application of the Braking force immediately when a slip is detected to ensure fes on a front wheel.  

Especially when there is an abrupt braking phase, it is green the driving stability of the vehicle necessary that the Slip-in occurs first on the front wheels. To do this Ensure control engineering should the invention braking processes must be upstream, which ensures that slip enemas always go to the Front wheels occur.

The determination of a brake that ensures optimum slip power value for the rear wheels can be of a variety of Parameters based on measured quantities (or their temporal Derivation) from the ABS or vehicle dynamics control, such as. B. the actual braking force, the wheel acceleration, the blocking limit, the axle load, the vehicle mass including load, the strength ke of the fading effect (the weakening of the braking effect of the Brake system), the slip / slip angle, the lateral force, Yaw rate and so on can be made dependent. The above parameters can be in the invention Procedures may be included very easily, as they are in ver form of form that is already sensibly processed other vehicle safety systems, such as the ABS or the driving dynamics control can be derived again nen.

A very reliable braking force control is provided with a fik tive brake force approximation created. This corresponds to one approximately optimal braking force, which would be determined when the vehicle is fully loaded would. Because the braking force is usually too high a slip on the rear wheels can be observed, however lies before the rear wheels slip Braking force of the braking force that achieves optimal slip much closer than with the known brake controls without predictive braking force limitation. It also has this Procedure has the advantage that knowledge of braking parameters, such as for example the state of the brake system, the fading state, which is difficult to determine, are not required.  

During the subsequent slip run-in, the ABS control can enter the slip control as usual.

Further features, properties and advantages of the invention are based on the following description of preferred An application examples of the inventive method clearly.

1st example

In this application example, the invention supports the ABS regulation in determining the maximum braking torque that can be transmitted to the rear wheels In the event of an abrupt braking phase or in the event of a sudden jump Changes in road surface friction.

In order to make braking force predictions for a rear wheel, the maximum braking torque M _{Vmax applied} to the front wheel is determined shortly before the slip run-in, which is located equal to the rear wheel in question. The actual braking torque M _Vtat , which is effectively transmitted from the front wheel to the road surface, corresponds to the maximum braking torque M _Vmax minus the wheel acceleration torque M _R. The wheel acceleration torque M _{R is} calculated from the derivative of the wheel speed divided by the tire radius and multiplied by the tire moment of inertia. Finally, one obtains the approximately optimum braking torque M _Hmax on the rear wheel by _dividing the actually transmitted braking torque M _Vtat by the wheel load G _v on the front wheel and multiplying it by the wheel load G _H on the rear wheel. The wheel loads G _v and G _H can be determined either by geometric calculations from longitudinal and lateral acceleration, center of gravity and wheel / wheel bases or by a vehicle model that takes into account chassis influences and body movements. The load is also taken into account in the wheel loads.

The above-mentioned determination of the maximum braking torque before hatching is otherwise relatively accurate, because in this driving state, the not very precisely determinable Wheel accelerations are low and therefore no we significant contribution to the calculation of the moment balance deliver. The application of this method is problematic however, in the case of jumps in the coefficient of friction, since the method is only one Statement about the last one and not about the current one Friction coefficient. The monitoring of the transmitted braking torque. The transmitted braking torque drops ment during a slip run-in essential stronger than normal below the braking torque before slip run, there is a jump in the coefficient of friction. Detection and Be Suitable moments can then be calculated using the moments balance of the wheel.

The calculated braking force is applied when the brakes are applied abruptly spent directly on the rear wheels and for a maintain certain time, preferably 150 ms. The ABS can withstand this pressure when slip is detected humiliate even further.

In the event of a jump in the coefficient of friction, the braking force is reduced depending on the driving speed a bit delayed and / or in Ramp shape performed with linear change.

2nd example

In this application example of the method according to the invention rens will propose an improvement in the select-low procedure hit a rear wheel especially when cornering as low as possible below the one optimal To brake slipping braking torque.

The braking forces shortly before the slip run in are at the front wheels. From this the ratio of Braking forces on the front wheels determined. Subsequently  are the braking forces that achieve optimal slip determined on the rear wheels.

For example, the braking force level at the front right wheel 1.4 times as high as the braking force level on the left front wheel. In this case, after the Select-Low method brakes the right rear wheel. For Determination of the slip-free braking force on the right The rear wheel must have the braking force on the left rear wheel can be determined using the ABS control - d. H. the braking force at which slip entry detec is tiert. This determined braking force is then ßend imposed an additional force that 0.4 times the am Left rear wheel determined braking force corresponds.

An opposite conclusion, that is, from the right one more heavily loaded rear wheel on the left, should by a properly working brake control procedure excluded be because a slip inlet on the heavier burden Rear wheel extremely negative on the driving stability of the Would affect the vehicle. Still exaggerated Slip on the more heavily loaded rear wheel, so can from this the braking force that ensures optimal slip the left rear wheel with the help of the right rear wheel determined braking force minus the braking force Difference can be determined, the amount of which is made up | (1 / 1.4-1) | about 0.29 times the braking force of the right rear wheel calculated.

With this procedure, the difficult to determine Pa parameters, such as fading, the dynamic axis load shifting from front to back etc. with consideration does. It should also be mentioned that the pressure to be set differences between the left and right side regarding their absolute values and the setting speed in addition from, for example, driving dynamics control knew situations such as cornering or the presence  of large differences in the coefficient of friction on the side web with a correspondingly low coefficient of friction can be.

Claims (14)

1. A method for brake control of a motor vehicle during a braking phase, characterized in that the brake pressure for at least one rear wheel is determined via the wheel behavior on at least one front wheel. 2. The method according to claim 1, characterized in net that a braking force for the at least one rear wheel from the brake prevailing on the front wheel during slip-in force and / or the front wheel acceleration values above given control parameters is determined so that they are close approximately the maximum transferable braking force on the minde least corresponds to a rear wheel. 3. The method according to claim 2, characterized in net that the actual braking force for that at least a rear wheel equal to or slightly less than that determined braking force is set. 4. The method according to any one of claims 2 or 3, characterized characterized in that the actual braking force for the at least one rear wheel slightly larger than that he average braking force is set. 5. The method according to any one of claims 2 to 4, characterized characterized in that for determining the braking force for the at least one rear wheel before and / or during of the slip inlet applied braking torque and / or Wheel acceleration on the front wheel is determined.   6. The method according to any one of claims 1 to 5, characterized characterized in that for the determination of the braking force the ratio of the brakes for the at least one rear wheel forces on the front wheels. 7. The method according to any one of claims 2 to 6, characterized characterized in that the determined braking force on a Rear wheel is applied after a time delay that preferably according to the speed of the motor vehicle judges. 8. The method according to any one of claims 2 to 6, characterized characterized in that the determined braking force for the at least one rear wheel immediately after detection nes slip inlet on the at least one front wheel linear applied with increasing or decreasing time. 9. The method according to any one of claims 1 to 8, characterized characterized in that a slip inlet by an ent speaking brake force distribution first on one of the two Front wheels generated and from the resulting wheel behavior ten determined the brake pressure on at least one rear wheel becomes. 10. The method according to any one of claims 1 to 9, characterized characterized in that for determining the brake pressure of the with at least one rear wheel braking parameter on the front wheel Slip run-in are used as the measured braking Actual force; Wheel acceleration, yaw rate, steering angle, Lateral force, engine torque, gear ratio or measured variable or derive from the ABS regulation, such as especially the wheel speed.   11. The method according to any one of claims 1 to 10, characterized characterized that the driving behavior of the vehicle flowing or descriptive parameters, such as in particular Wheel or axle load, the vehicle mass with any allowances the slip angle or specifications of other regulations, such as the vehicle dynamics control, for determination of the brake pressure for the at least one rear wheel be viewed. 12. The method according to any one of claims 2 to 11, characterized characterized in that the determined braking force of a fictitious braking force, which is approximately equal to the Braking force at slip in at least one rear rad when the vehicle is fully loaded. 13. Braking device for a motor vehicle, in particular corresponding to the method according to any one of claims 1 to 13 works, including a brake system for front and rear wheels and a control device that works with the braking system is coupled, characterized in that in a Braking phase with slip running in on at least one front wheel the braking system is turned on by the control device is that the brake pressure for the at least one Hin terrad about the wheel behavior on at least one front wheel is determined. 14. Braking device according to claim 13, characterized records that they have an electromechanical braking system sums up.