DE102005049368A1 - Method and arrangement for braking on surface creating different levels of friction for left and right wheels, comprise use of information about steering angle to be expected - Google Patents

Abstract

The rotation speed of the wheels (2,3,4,5) is determined with several sensors (16,17,18,19) and transmitted to a control unit (15) as well as the position of the electronically supported steering wheel (6,8) and the yaw factor (21). The course of the road is monitored by a camera (10) and the friction level, which can be different for the left (2,4) and the right wheels (3,5), is also determined. When the brake system (23) has to be activated in a situation with a mu -split condition the steering angle is automatically corrected. An independent claim is given for an arrangement for braking on a surface creating a different level of friction for the left and the right wheels.

Description

The The invention relates to a method and a device for braking a two-lane motor vehicle with different friction conditions the vehicle tracks according to the preamble of claims 1 and 10th

Becomes a two - lane vehicle braked in a driving situation, in the different on the two vehicle tracks or even the individual vehicle wheels friction conditions present, one speaks of a so-called μ-split braking. Since on the Side with the higher Coefficient of friction higher Transmit braking forces can be than on the side with lower coefficient of friction, this imbalance can when braking a turn of the car towards the grippier Effect page. To keep the vehicle straight ahead in the lane to stop and prevent the vehicle from breaking away must be Stabilization of the vehicle counter-steered towards the smoother side become. The bigger there the brake force difference between right and left is the faster and stronger must be responded to, which quickly becomes one for the driver only hard manageable driving situation lead can.

Around to mitigate the tendency to turn the vehicle during braking and not to overwhelm the driver, It is known to design ABS brake systems so that on the handy Page less braked than the adhesion with the road surface would actually allow. On This way, however, valuable meters of braking distance are given away.

Of Furthermore, systems for vehicle stabilization are already known, which during braking in μ-split situations automatically provide an active steering intervention. It is the Impact of the front wheels independent of the situation depending on the situation Driver increased at short notice either or decreased, causing the steering automatically compensatory maneuvers in unstable Driving situations supported. However, these systems are usually up to date by the driver orient the steering angle adjusted on the steering and depending on whose the intensity The active steering intervention can be controlled with such systems but only on a straight route and with certain Restrictions on Constant cornering achieved satisfactory results become. However, if the driver takes rapid changes when braking the steering angle, as for example during retraction or extension is necessary in a curve, these systems fail because a meaningful Regulation of the additional Steering intervention on the current steering angle due to this faster temporal change no longer possible in real time is. Usually Thus, such systems become inactive for the prevention of misregistration switched as soon as the driver automatically changes the current steering angle makes, as is the case for example when cornering.

Of Further, lane keeping systems are also known which provide an active steering intervention provide to prevent inadvertent lane departure. For example, cameras or infrared sensors are used, which detect the lane markings or side strips. threatens the vehicle thereby leaving the lane, performs an active control Vehicle by means of a steering intervention automatically on the safe Roadway back. However, such a tracking system can in the case of μ-split braking not enough cause the stabilization of the vehicle, since the vehicle then usually when threatened to pass the lane markings is already set in rotation so that a counter-steering too late would come, to return it to the roadway respectively, and a spin is inevitable.

Of the The invention is therefore based on the technical problem, an improved Method and an improved device for braking a two-lane Vehicle at different friction conditions of the vehicle tracks to accomplish. In particular, the effectiveness and mode of action should such devices and methods in Kurveneingangs- or -ausgangsbremsungen in μ-split situations as well as in μ-split braking in changing curves be improved.

The solution the technical problem results according to the invention by things the claims 1 and 10. Further advantageous embodiments of the invention result from the dependent claims.

The invention is based on the finding that information about the expected steering angle can be made available in advance by means of an optical sensor to a brake control or vehicle stability system with active steering intervention by the forward-looking detection of the road course in advance of the vehicle Regulating the intensity of the necessary steering intervention can be used. This means that the vehicle in a μ-split braking not only on the straights, but also with changing road course, especially when cornering, stabilized and an imminent rotation of the vehicle by Überla tion of a compensation angle at the vehicle steering can be compensated. This is achieved according to the invention by proposing a method and a device for braking a two-lane motor vehicle at different friction ratios of the vehicle lanes, wherein the friction conditions are determined at least for each vehicle lane, from a current steering angle α taken at a vehicle steering system determines a directional target value is determined and in the case of braking in a first operating mode depending on the difference in the friction conditions of the vehicle tracks a compensation angle γ to maintain the driveability of the vehicle and the current steering angle α is superimposed in the direction of the smoother vehicle lane, and wherein detected by means of an optical sensor Roadway course an expected steering angle β is determined and at least with changes in time of the current steering angle α of the expected steering angle β in a second mode of operation at least ens is used in addition to determining the direction of travel target size. The steering angle β determined by the optical sensor corresponds to a road course predicted by the system. By delivering a steering recommendation in the direction of the smooth road surface can thus be significantly shortened even when cornering, especially when Kurveneinstritt- and -austritt, the braking distance. The first mode of operation corresponds essentially to a generic μ-split brake control, as it is already known from the prior art for use in μ-split braking on a straight line. The local friction conditions of the road surface are preferably detected by means of sensors on possibly different wheel speeds. Although the friction conditions are preferably determined for each vehicle lane, it is also conceivable that the determination of the friction conditions for each individual wheel takes place. A "vehicle lane" is to be understood as the entirety of all wheels on each side of the vehicle, which are aligned with one another and have the same direction of rotation in the respective axial plan view critical situations, such as changes in the current steering angle by the driver, does not have to be turned off, but is switched to a second operating mode and where appropriate, despite the steering movements of the driver continue to regulate and provide a compensation angle to the vehicle steering available Normally, the steering angle compensation is switched inactive when the steering angle is changed, this is not necessary in the method and the associated device according to the invention. Rather, in the case of a roadway lane detected by means of the optical sensor on a permanent activation of a superposition angle regardless of the change of the current steering angle by the driver possible.

In an advantageous embodiment occurs at a detected by the optical sensor curve input and / or output the determination of the direction of travel target size exclusively in dependence the expected steering angle β determined with the aid of the optical sensor. To this Way can be particularly critical especially in control technology Driving situations, such as curve entry and / or exit, the expected steering angle β determined by the optical sensor irrespective of which steering angle is set manually by the driver, directly and directly as a target angle for the μ-split braking be used.

In a further advantageous embodiment takes place at a detected by the optical sensor straight line the determination of Direction of travel target size exclusively in dependence the current steering angle α. As with straight driving the control quality of the first operating mode usually sufficient and the second mode of operation, which the Compensation angle γ on Base of the optical sensor controls, especially when cornering can be used advantageously, by the optional restriction a controlled only on the current steering angle compensation angle γ straight Distance the calculation speed and the control effort be reduced in these situations. That way the available system resources used particularly effectively.

In A further advantageous embodiment takes place in the second Operating mode the determination of the direction of travel desired value exclusively in dependence the expected steering angle β determined with the aid of the optical sensor. To this Way can be particularly critical especially in control technology Driving situations in which, for example, the driver changes the steering angle makes and the system due to the second Switches operating mode, which determined by means of the optical sensor expected steering angle β regardless of which steering angle is set manually by the driver, directly and directly as a target angle for the μ-split braking be used.

In a further advantageous embodiment, the expected steering angle .beta. Is compared with the current steering angle .alpha. By means of an evaluation unit, and one of the two is determined as a function of at least one property of the optical sensor Steering angle α or β selected to determine the direction of travel target size. Since the quality of a forward-looking detection of the road course in advance of the vehicle with the aid of an optical sensor usually depends on various external parameters, which are reflected for example in properties of the optical sensor, it may be useful to use the determined from the optical sensor roadway to Control of the compensation angle γ on the existence of such properties, such as a sufficient signal quality to make dependent. This is particularly relevant when the current steering angle α and the expected from the optical sensor steering angle β have different values and accordingly must be decided by the system, which of the two values for the control of the compensation angle γ should be used. In this case, it is preferable to perform a balance between the two angle values. With the same value of the current steering angle α and the expected from the optical sensor to be expected steering angle β, it is conceivable that either always a certain of the two, ie, for example, always the expected steering angle β, or any of two angles for the control of the compensation angle γ is used.

In In a further advantageous embodiment, the property the optical sensor whose signal quality and / or sensor availability, where at high signal quality and / or sensor availability excluding the expected steering angles α and at low signal quality and / or sensor availability exclusively the current steering angle α is selected. That way to ensure that the control of the compensation angle γ with insufficient signal quality or availability of the optical sensor as needed and for safety reasons not in the second, but in the first mode of operation. This can be, for example be the case if the lane markings are poorly recognizable or not at all present, the optical sensor temporarily inactive is or unfavorable Light or contrast ratios prevail in the run-up to the roadway.

In In a further advantageous embodiment, the compensation angle γ is determined by a automatically applied to the vehicle steering additional steering torque set. This can be done, for example, by an electromechanical Steering or any other active steering system (Electric Power Steering or similar) respectively. This relieves the driver of the need to in the context of μ-split control Calculated calculated necessary steering torque manually apply. It It is also conceivable that the automatic steering intervention thereby also completely without driver intervention, d. H. "Freehand", can be done, if this e.g. in certain circumstances is no longer able to provide the necessary moment for the corrective Steering yourself to raise.

In a further advantageous embodiment, the additional Steering torque as needed by the driver of the motor vehicle Overcome counter steering become. This offers the advantage that the driver then despite a present automatic steering intervention by the control system according to as before, "Mr. of the procedure "remains and even decides if he actually has the extra steering torque the steering effect or whether he takes control in the hand and the additional steering torque manually controlled "overruled." It is at the additional Steering moment then just a "steering recommendation" to the driver additional However, steering torque must then be present in an order of magnitude which it allows the driver without much effort to counteract. The extra Steering torque is preferably for example between 3-5 Nm. In this case can the driver, for example, by applying a manual steering torque of at least approx. 6 Nm overrule the regulation. Further preferably he can thereby the μ-split brake control at least in the first operating mode also override or - if the ratios allow this - that Switch over to the second operating mode. The countersteering of the driver Thus, it is preferably used as a termination criterion for the μ-split brake control in the first operating mode.

In a further advantageous embodiment is the optical Sensor designed as LDW camera. LDW, i. Lane Departure Warning cameras are on known camera systems for lane detection, in which by a forward looking camera the course of the road ahead is detected for the purpose of tracking. Is such a "lane keeping" feature already Already present in the vehicle, it can easily for the inventive method and the associated Device used as an optical sensor in the context of μ-split brake control become.

The Invention will be described below with reference to a preferred embodiment explained in more detail. In the associated Drawings show

1 a schematic representation of a preferred embodiment of a device for braking a two-lane motor vehicle at different friction conditions of the vehicle lanes and

2 a schematic representation of the Travel of a two-lane motor vehicle with a device according to the invention.

1 schematically shows a preferred embodiment of a device 1 for braking a two-lane motor vehicle with different friction conditions of the vehicle lanes. The device 1 is part of the two-lane motor vehicle and includes front left, front right, rear left and right rear respectively a vehicle wheel 2 . 3 . 4 . 5 , At each of the vehicle wheels 2 . 3 . 4 . 5 is each a wheel speed sensor 16 . 17 . 18 . 19 arranged, which is the wheel speed n _{i of} each individual vehicle wheel 2 . 3 . 4 . 5 measures and sends to a control device 15 transmitted, which also has an evaluation unit. The device 1 further includes an electromechanical steering 8th with which, for example by means of an electric servomotor (not shown), the front vehicle wheels 2 . 3 can be deflected to the left or right. The electromechanical steering 8th can be controlled by the driver via a steering wheel 6 operate and will be via the control device 15 driven. The rash of electromechanical steering 8th , ie a current steering angle α, is via a steering angle sensor (not shown), for example, arranged on the steering shaft 7 measurable and to the controller 15 transmittable. The driver can also have a brake 23 , which also with the control device 15 connected to initiate a braking operation to decelerate the vehicle. The control device 15 is also preferably designed to detect and process further vehicle parameters, for example by means of a vehicle speed sensor 20 determined driving speed v and by means of a yaw sensor 21 determined yaw rate ω. These can be in a known from the prior art system for electronic vehicle stabilization by individually braking the vehicle wheels 2 . 3 . 4 . 5 Find application, which may preferably be combined with the device according to the invention. However, the driving speed v can be determined in the same way from the wheel speeds n _i . Furthermore, the device comprises a camera 10 trained, looking forward in the direction of travel optical sensor for lane detection, with the help of the course of the roadway in the run-up, among other things, for the purpose of tracking can be detected. The local friction conditions of the road surface become while driving with the help of wheel speed sensors 16 . 17 . 18 . 19 possibly detected different wheel speeds n _i . It is therefore preferably a determination of the friction conditions for each individual vehicle 2 . 3 . 4 . 5 , where the vehicle wheel front left 2 and the vehicle wheel at the rear left 4 the left vehicle lane form, while the vehicle wheel front right 3 and the vehicle wheel at the back right 5 form the right vehicle lane. This is preferably done continuously during the entire drive operation. However, it is also conceivable that the evaluation of the friction conditions only with actuation of the brake 23 is started. The determined values are evaluated in particular as to whether different friction conditions (μ-split) are present at the wheels of one axle. From the on the electromechanical steering 8th taken current steering angle α is with the help of the control device 15 determines a direction of travel target size. This corresponds to the desired value of the direction in which the motor vehicle should move according to the wishes of the driver. In the case of braking, a compensation angle γ (see FIG. 2 ) is determined to maintain the tracking stability of the vehicle and superimposed on the current steering angle α in the direction of the smoother vehicle lane. On the basis of the camera 10 detected lane course is also an expected steering angle β determined. In a second operating mode, the expected steering angle β with temporal changes of the current steering angle α can be used at least in addition to determining the direction of travel desired value. The one from the camera 10 determined steering angle β corresponds to a predicted by the system road course. By means of the control device 15 the expected steering angle β is compared with the current steering angle α and carried out a comparison between the two angle values α and β. It is first checked whether the current steering angle α and the camera 10 determined expected steering angle β have different values and then one of the two steering angle α or β selected to determine the direction of travel target size. The adjustment is carried out depending on at least one property of the camera 10 , It is from the controller 15 in particular, checks whether from the camera 10 ever a signal is delivered. If this is the case, it is checked whether the signal quality is sufficient, that of the camera 10 determined course of the road to control the compensation angle γ can be used. The signal quality can be limited, for example, if the lane markings are poorly recognizable or even absent, or unfavorable light or contrast conditions prevail in the run-up to the lane. With high signal quality and / or sensor availability is then by the controller 15 Preferably, only the expected steering angle β is selected for controlling the compensation angle γ, while with low signal quality and / or sensor availability, exclusively the current steering angle α is selected for this purpose. The compensation angle γ is then by the controller 15 through one on the steering wheel 6 or on the steering shaft applied additional steering torque by means of the electromechanical steering 8th automatically set. This additional steering torque corresponds to the delivery of a steering recommendation to the driver in the form of a torque on the steering wheel in the direction of the smooth road surface. It can if necessary be overcome by the driver of the motor vehicle by countersteering, ie by applying a larger manual steering torque in the opposite direction, if he decides that he wants to take the control itself in hand and thus manually "overruled" the additional steering torque Trap so he leaves the additional steering torque, which is controlled on the compensation angle γ, not on the front vehicle wheels 2 . 3 Act. In this way, the driver can override the μ-split brake control of the first mode of operation and, if the camera conditions allow, cause the switch to the second mode of operation. The countersteering of the driver thus serves as a termination criterion for the μ-split brake control in the first operating mode. If there is no counter-steering of the driver in the first operating mode, then the steering recommendation in the form of the additional steering torque in the direction of the compensation angle γ is maintained for a period of several seconds, preferably for about 5 seconds, until either the braking is stopped, the vehicle comes to a standstill has come or the direction of travel, ie the current steering angle α, is changed.

2 shows schematically the track of a two-lane motor vehicle with a device according to the invention. It can be seen how a merely indicated two-lane vehicle turns from a straight line into a curve, where on the surface of the left lane ice, ie, a small coefficient of friction μ, and on the right lane side asphalt, ie a larger coefficient of friction μ, is present. The vehicle thus moves at this time in a μ-split situation. In the lower part of 2 the vehicle is shown before entering the curve and before initiating a braking operation, ie a μ-split braking, while in the upper part of 2 just during braking within the curve input. Since higher braking forces can be transmitted on the right-hand side of the road with the higher coefficient of friction μ than on the left side with lower coefficient of friction μ, this imbalance during braking can cause the motor vehicle to rotate in the direction of the grippier side, ie to the right. In order to keep the vehicle still in the designated lane and to prevent breakage, to stabilize the vehicle during braking in the direction of the smoother side, ie to the left, must be counter-steered. According to the invention, this takes place both on the straight line, as well as when entering, exiting or driving in or from curves by an active steering intervention of the device 1 , From the on the electromechanical vehicle steering 8th chosen current steering angle is first determined a direction of travel target size. If the driver now initiates braking, then in the first operating mode, depending on the difference in the friction conditions of the vehicle lanes, a compensation angle γ is determined for maintaining the lane stability of the vehicle and superimposed on the current steering angle α in the direction of the smoother vehicle lane (not shown). Captures the camera 10 In this case, only a straight line in the run, so preferably the determination of the direction of travel target size exclusively in dependence of the current steering angle α, since the straight line the control quality of the first operating mode is usually sufficient. However, if the motor vehicle drives directly towards a curve ( 2 below) or straight into a curve ( 2 above), ie the driver changes the current steering angle α, so is the control device 15 by means of the camera 10 detected roadway course of the expected steering angle β determined and used in the second mode of operation at least in addition to determining the direction of travel target size or to control the compensation angle γ. The compensation angle γ is then by the controller 15 through one on the steering wheel 8th (or the steering shaft) applied additional steering torque in the direction of the smooth road surface by means of electromechanical steering 8th automatically set. In this case, the determination of the direction of travel desired value in the second operating mode preferably takes place exclusively as a function of the camera 10 determined expected steering angle β. In the second operating mode, in particular in control-technically particularly critical driving situations, provided that the driver does not undertake a self-sufficient tracking steering compensation within a predefined period of time or completely independent of which steering angle is set manually by the driver, by means of the camera 10 determined expected steering angle β directly and directly be used as a target angle for the μ-split braking.

1

contraption

2

vehicle Left in the front

3

vehicle front right

4

vehicle back left

5

vehicle back right

6

steering wheel

7

Steering angle sensor

8th

electromechanical steering

10

camera

15

control device

16

Wheel speed sensor to wheel 2

17

Wheel speed sensor to wheel 3

18

Wheel speed sensor to wheel 4

19

Wheel speed sensor to wheel 5

20

Vehicle speed sensor

21

yaw sensor

23

brake

_i

wheel speed

v

driving speed

α

current steering angle

β

to expected steering angle

γ

compensation angle

μ

friction

ω

yaw rate

Claims (18)

Method for braking a two-lane motor vehicle at different friction conditions of the vehicle lanes, wherein the friction conditions are determined at least for each vehicle lane, from a current steering angle α taken at a vehicle steering a direction of travel target size is determined and in case of braking in a first operating mode depending the difference of the friction conditions of the vehicle lanes a compensation angle γ determined to maintain the tracking stability of the vehicle and the current steering angle α is superimposed in the direction of the smoother vehicle lane, characterized in that on the basis of a track detected by an optical sensor an expected steering angle β is determined and at least in the case of temporal changes of the current steering angle α, the expected steering angle β in a second operating mode at least in addition to determining the desired direction of travel is pulled. Method according to claim 1, characterized in that that at a detected by the optical sensor curve input and / or output the determination of the direction of travel target size exclusively in dependence of the determined using the optical sensor to be expected steering angle β. Method according to claim 1, characterized in that that at a detected by the optical sensor straight line the Determination of the direction of travel target size exclusively in dependence of the current steering angle α. Method according to one of the claims, characterized characterized in that in the second operating mode, the determination of Direction of travel target size exclusively in dependence of the determined using the optical sensor to be expected steering angle β. Method according to one of the claims, characterized characterized in that by means of an evaluation of the expected Steering angle β with the current steering angle α compared and depending of at least one property of the optical sensor of one of both steering angles α and β for determination the direction of travel desired size is selected. Method according to claim 5, characterized in that that the property of the optical sensor whose signal quality and / or sensor Availability is, with high signal quality and / or sensor availability exclusively the expected steering angle β and with low signal quality and / or sensor availability exclusively the current steering angle α is selected. Method according to one of the claims, characterized characterized in that the compensation angle γ by a at the vehicle steering applied additional Steering torque is set automatically. Method according to claim 7, characterized in that that extra Steering torque, if necessary, overcome by a driver of the motor vehicle by countersteering can be. Method according to one of the claims, characterized in that the optical sensor is designed as an LDW camera is. Device for braking a two-lane motor vehicle at different friction conditions of the vehicle tracks, where the friction conditions at least for each vehicle lane can be determined, from one to a vehicle steering taken current steering angle α a direction of travel target size determined is and in case of braking in a first operating mode depending the difference of the friction conditions of the vehicle tracks a compensation angle γ to Maintaining the tracking stability of the vehicle can be determined and the current steering angle α in the direction superimposed on the smoother vehicle lane is characterized in that by means of a an optical sensor detected road course expected Steering angle β can be determined is and at least in temporal changes of the current steering angle α of the expected Steering angle α in a second operating mode at least in addition to determining the direction of travel target size used becomes. Device according to claim 10, characterized in that that at a detected by the optical sensor curve input and / or output the determination of the direction of travel target size exclusively in dependence of the determined using the optical sensor to be expected steering angle β. Device according to claim 10, characterized in that that at a detected by the optical sensor straight line the Determination of the direction of travel target size exclusively in Dependence of current steering angle α. Device according to one of claims 10 to 12, characterized that in the second operating mode, the determination of the direction of travel desired value exclusively in dependence of the determined using the optical sensor to be expected steering angle β. Device according to one of claims 10 to 13, characterized that by means of an evaluation of the expected steering angle β with the current Steering angle α compared and depending of at least one property of the optical sensor of one of both steering angles α and β for determination the direction of travel desired size is selected. Device according to claim 14, characterized in that that the property of the optical sensor whose signal quality and / or sensor Availability is, with high signal quality and / or sensor availability exclusively the expected steering angle β and with low signal quality and / or sensor availability exclusively the current steering angle α is selected. Device according to one of claims 10 to 15, characterized that the compensation angle γ by an applied on the vehicle steering additional steering torque automatically adjustable is. Device according to claim 16, characterized in that that extra Steering torque as required by a driver of the motor vehicle Overcome counter-steering is. Device according to one of claims 10 to 17, characterized that the optical sensor is designed as an LDW camera.