DE102019208459A1 - Determination of a coefficient of friction - Google Patents

Abstract

A two-lane vehicle (305) comprises at least one wheel (315). A method (400) for determining a coefficient of friction (210) between a road surface (105) and the wheel (315) comprises steps of exerting a first torque on the wheel (315) in order to prevent slip (150) between the wheel (315) and effect the roadway (105); simultaneously changing a steering angle (345) of one of the wheels (315) of the vehicle (305) in order to compensate for a change in direction of travel caused by the torque; and determining the coefficient of friction (210) on the basis of the slip (150).

Description

The invention relates to controlling a vehicle. In particular, the invention relates to determining a coefficient of friction that indicates a transferable force between a tire of the vehicle and a roadway.

A vehicle has multiple wheels that roll on a roadway while the vehicle is traveling. A force that can be transmitted between one of the wheels and the roadway is limited and can be determined on the basis of a coefficient of friction prevailing between the wheel and the roadway. The coefficient of friction depends in particular on a characteristic of the wheel or a tire it encompasses and a condition of the roadway. The condition of the road can often be difficult to assess, especially when it is raining, snow, ice or objects lying on the road such as leaves.

To determine the coefficient of friction, the wheel can be braked specifically until it slips onto the road. The coefficient of friction with respect to a predetermined tire characteristic can be determined on the basis of a braking force required for this. However, this procedure is usually only used on a straight route if a possible lateral breakout of the vehicle does not have to be feared or can be accepted. However, the coefficient of friction can be of interest in particular for driving through a curve, in particular to control the vehicle in the curve.

DE 10 2012 217 772 A1 relates to a technique for determining a maximum coefficient of friction between a vehicle tire and a road surface.

DE 10 2016 009 257 A1 suggests using fuzzy methods to estimate a current adhesion value between the wheel and a road surface on the basis of a braking force on a wheel.

An object of the present invention is to provide an improved technique for determining the coefficient of friction between a wheel of a vehicle and a roadway. The present invention achieves this object by means of the subjects of the independent claims. Sub-claims reproduce preferred embodiments.

A two-lane vehicle comprises at least one left and at least one right wheel. According to a first aspect of the invention, a method for determining a coefficient of friction between a roadway and one of the wheels comprises steps of exerting a first torque on the wheel to prevent slip between the wheel and effect the roadway; simultaneously changing a steering angle of one of the wheels of the vehicle in order to compensate for a change in direction of travel caused by the torque; and determining the coefficient of friction based on the slip.

By exerting a torque on the wheel until it slips, a torque can occur about a vertical axis of the vehicle, so that the vehicle can deviate from a desired course. By changing the steering angle at the same time, the torque about the vertical axis can be compensated so that the vehicle can continue on the desired course. The compensation can take place in such a way that a driver remains largely unaffected by the determination of the coefficient of friction. Ideally, the driver does not even notice the determination.

The coefficient of friction, which can also be called the coefficient of friction, coefficient of friction or friction coefficient, is a dimensionless measure of the frictional force in relation to the contact force between two bodies and is generally referred to with the formula letter µ. In one embodiment, a current coefficient of friction is determined, in another a maximum coefficient of friction. The determined coefficient of friction can be used to control the vehicle. In particular, a cornering speed of the vehicle can be selected such that the vehicle can be safely controlled, accelerated and / or braked.

While the first torque is being applied, a second torque can be applied to another wheel of the vehicle in order to compensate for a change in an acceleration or speed of the vehicle caused by the first torque. If, for example, the first wheel is slipped by means of a braking device, the other wheel can be driven by means of a drive motor. The reverse procedure is also possible. When determining the second torque, a position of the wheel on the motor vehicle must be taken into account in order to influence the yaw torque with the correct sign.

The second torque can have an influence on a direction of travel of the vehicle, so that the second torque can be determined as a function of the change in the steering angle or vice versa, in order to compensate for the influence of the direction of travel and the acceleration or deceleration of the vehicle by determining the coefficient of friction.

The method can in particular be carried out while the vehicle is driving through a curve. The wheel can go so far into the Slip can be performed until the vehicle begins to turn around its vertical axis. The steering angle can be changed as a function of a rotation taking place and / or in a predictive manner as a function of the torque exerted on the wheel.

The coefficient of friction can be determined in different ways. In a preferred embodiment, a determination is made with regard to a predetermined characteristic of the wheel on the basis of the torque and optionally a slip angle of the wheel.

According to a second aspect of the invention, a device for determining a coefficient of friction between a roadway and a wheel of a two-lane vehicle comprises a first interface for connection to an acceleration or deceleration device acting on the wheel; a second interface for connection to a device for controlling a steering angle of one of the wheels of the vehicle; and a processing device. The processing device is designed to exert a torque on the wheel in order to cause a slip between the wheel and the roadway; and at the same time to change a steering angle of one of the wheels of the vehicle in order to compensate for a change in direction of travel caused by the torque. In addition, the processing device can determine the coefficient of friction on the basis of the slip.

The processing device can be set up to carry out a method described herein in whole or in part. For this purpose, the processing device can comprise a programmable microcomputer or microcontroller and the method can be in the form of a computer program product with program code means. The computer program product can also be stored on a computer-readable data carrier. Features or advantages of the method can be transferred to the device or vice versa.

The device acting on the wheel can be a deceleration device, the first interface being set up for connection to the deceleration device of the vehicle. The deceleration device can also be activated by means of a brake system which, for example, performs an anti-lock function or an anti-slip control, and the first interface can be connected to the brake system.

The device acting on the wheel can also be a drive device, the first interface being set up for connection to the drive device of the vehicle. Here, too, the drive device can be controlled by means of a control system, and the first interface can be connected to the control system.

In a particularly preferred embodiment, the drive device is assigned individually to the wheel. In this case, the drive device can in particular comprise an electric motor, which can be designed, for example, as a hub motor on the wheel. Several wheels can be driven by means of several, each wheel-specific drive devices. In a further embodiment, a torque of a drive motor can be dynamically divided between several wheels.

According to yet another aspect of the present invention, a system comprises a device described herein and a vehicle described herein, in particular a motor vehicle, more preferably a passenger car. The motor vehicle can in particular be implemented as an electric vehicle with two or more radio-specific electric drive motors.

• 1 ein Rad auf einer Fahrbahn;
• 2 ein Reifendiagramm;
• 3 ein System; und
• 4 ein Ablaufdiagramm eines Verfahrens

darstellt.The invention will now be described in more detail with reference to the accompanying figures, in which:

• 1 a wheel on a roadway;
• 2 a tire diagram;
• 3 a system; and
• 4th a flow chart of a method

represents.

1A shows a wheel 100 on a roadway 105 in a side view and 1B a top view. The wheel 100 usually includes a rim and a tire. In the side view are a peripheral speed 110 and a longitudinal speed 115 offered. The longitudinal speed 115 runs in a longitudinal direction 120 perpendicular to an axis of rotation of the wheel 100 and usually parallel to the roadway 105 runs. A difference between the speeds 110 and 115 creates a longitudinal slip 125 .

In the top view are a plane of rotation 130 and a direction of movement 135 of the wheel 100 offered. The plane of rotation 130 stands perpendicular to a transverse direction 140 that are parallel to the axis of rotation of the wheel 100 extends. The cross direction 140 runs parallel to an axis of rotation of the wheel 100 and preferably coincides with this. Between the plane of rotation 130 and the direction of movement 135 there is a slip angle 145 .

With regard to a coefficient of friction µ between the wheel 100 and the roadway 105 the longitudinal slip behaves 125 that of a lengthways 120 acting force is dependent, similar to the Slip angle 145 that of one in the transverse direction 140 acting force is dependent. For the following explanations, there is therefore a slip 150 as a generic term for the longitudinal slip 125 and the slip angle 145 used and denoted by λ.

2 shows a tire diagram 200 with a number of exemplary tire characteristics 205 , each showing a relationship between a vertically plotted coefficient of friction 210 (µ) and a horizontal slip 150 (A) describe. Which of the tire characteristics 205 applicable can result from circumstances such as a tire used, a prevailing temperature or an applicable air pressure. Alternatively, an applicable tire characteristic 205 based on several specific slips 150 to be determined. The coefficient of friction 210 increases from a slip 150 from zero initially and quickly reaches a maximum value before continuing with increasing slip 150 falls off again.

3 shows a system 300 that is a vehicle 305 comprises, which is preferably designed as a motor vehicle, and a control device 310 on board the vehicle 305 . The vehicle 305 includes several wheels 315 that are arranged in more than one lane. A wheel 315 can the wheel 100 of 1 correspond. The wheels 315 are usually on the ground 105 and roll on this while the vehicle 300 moves.

There are four wheels in the representation chosen 315 provided, two of which are exemplary in a left lane 320 and two of a right lane 325 assigned. The traces 320 , 325 are on different sides of a longitudinal axis 330 that by a focus 335 of the vehicle. An embodiment with more than two tracks 320 , 325 or more or less than four wheels 315 is also possible, but every track should 320 , 325 at least one bike 315 be assigned.

At least one of the bikes 315 is steerable. The present is a steering device 330 for controlling a steering angle 345 the front wheels 315 intended. The steering angle 345 can change the steering angle 145 in 1 correspond. In a further variant, the rear wheels can additionally or alternatively 315 by means of an assigned steering device 330 be steered. The steering device 330 can in particular comprise an electrical or hydraulic actuator for exerting a steering force.

To drive the vehicle 300 can be a drive motor 350 be provided, which is designed in the present example as an electric motor, but can also be implemented as an internal combustion engine in another embodiment. The present is the drive motor 350 set up for this on the rear wheels 315 to act; in another embodiment, the drive motor 350 but also on the front wheels 315 Act. The drive motor 350 can also be used on more than two of the wheels 315 Act. It is preferred that one be driven by the drive motor 350 provided torque can be controlled individually for each wheel. Also a wheel-specific drive motor 350 that is just one of the wheels 315 assigned can be used. In one embodiment, each of the four wheels 315 a drive motor 350 assigned, the drive motors 350 can be designed in particular as electric wheel hub motors. A drive motor 350 is usually used to provide the vehicle 305 accelerating torque set up, but he can also a the vehicle 305 Provide braking torque.

At least one of the wheels is preferred 315 a delay device 355 , also called braking device, provided to a torque 315 exercise on the wheel that the vehicle 305 delayed. They are usually delay devices 355 on all wheels 315 of the vehicle 305 provided and can be controlled in concert to the vehicle 305 to decelerate and stabilize at the same time, or at least to counteract a loss of driving stability. The operation of a delay device 355 can depending on an actuation of the drive motor 350 controlled or vice versa.

The control device 310 preferably comprises a processing device 360 with a first interface 365 for connection to the drive motor 350 and / or the delay device 355 and more preferably a second interface 370 for connection to the steering device 340 . It is proposed that the processing device 360 be set up to determine a coefficient of friction 210 between one of the wheels 315 and the underground 105 to be determined by applying an accelerating or decelerating torque to the wheel 315 exercises until this in slip 150 device. The steering device should 340 be controlled in order to compensate for a change in the direction of travel of the vehicle caused by the torque. The stronger the torque exerted, the stronger the steering angle can be 345 can be changed to an intended course of the vehicle 305 to be observed. The course can follow a straight line or any curve. In other words, the steering angle 345 already be nonzero before the slip 150 is effected.

On the basis of the determined slip 150 and as a function of the torque exerted, the coefficient of friction 210 between the wheel 315 and the underground 105 to be determined. Further Parameters such as air pressure, temperature or speed of the vehicle 305 can also be taken into account. Depending on the coefficient of friction 210 can then control the vehicle 305 or a signal that affects the coefficient of friction 210 indicates can be sent to a driver of the vehicle 305 are issued. In particular, the signal can indicate a difference between a current and a maximum coefficient of friction 210 notify the driver of the vehicle 305 can control so that the maximum coefficient of friction 210 is not exceeded if possible.

4th shows a flow chart of a method 400 to determine a coefficient of friction 210 between a wheel 315 of a vehicle 305 and an underground 105 . In one step 405 can be a driving situation of the vehicle 305 to be determined. In particular, it can be determined whether the vehicle 305 while driving through a curve or a maneuver that differs from driving straight ahead. In addition, an upper and / or lower limit for an acceleration taking place can be predetermined. The procedure 400 is preferably only carried out if it can be determined in this step that the exercise does not pose a threat to the driving stability of the vehicle.

In one step 410 becomes a torque on one of the wheels 315 exercised. The affected wheel 315 can be selected as a function of the specific driving situation and, for example, an inside or outside front or rear wheel of the vehicle 305 affect. The torque exerted is usually increased at a predetermined speed during a rotational speed of the wheel 315 and a speed of the vehicle 305 compared to the ground 105 can be determined from which the slip 150 can be determined. The torque can be used as a braking torque by means of the deceleration device 355 be effected, the torque can be determined, for example, on the basis of an effected hydraulic brake pressure. The torque can also be used as drive torque by means of the drive motor 350 be effected. A slip caused in this step 150 on the selected bike 315 in one embodiment is a maximum of approx. 1% and the torque required for this can be built up over approx. 1 s. A brake pressure of a hydraulic brake device 355 can be at a maximum of approx. 30 bar.

In parallel, in one step 415 an acceleration or deceleration on at least one of the other wheels 315 of the vehicle 305 can be controlled to decelerate or accelerate the action by step 410 to compensate.

Also parallel to the step 410 is in one step 420 the steering angle 345 controlled in such a way that a change in the direction of travel of the vehicle 305 who step through that in 410 exerted torque is caused, is compensated if possible. It should be noted that the steering angle 345 prefers only the influence on the direction of travel of the vehicle 305 compensated, which is caused by the torque exerted. The steering angle 345 should in particular be controlled so that a predetermined course of the vehicle 305 , even if it concerns a curve or a predetermined change in a curve radius traveled through (turning in or out), is as unaffected as possible.

In one step 425 can be the coefficient of friction 210 on the basis of the slip 150 and the torque can be determined, for example as above with reference to FIG 1 and 2 is executed. A current and / or a maximum coefficient of friction can be used 210 to be determined.

In a further step 430 can the vehicle 305 depending on the specific coefficient of friction 210 to be controlled. In particular, a speed and / or a curve radius of a curve traveled through can be determined as a function of the determined coefficient of friction 210 be coordinated. In a further embodiment, a certain coefficient of friction 210 on one in front of the vehicle 305 lying terrain. For this purpose, for example, a camera or a radar sensor can be used to determine whether one is in front of the vehicle 305 lying section of the subsoil 105 the same conditions are likely to apply as under the vehicle 305 for which a coefficient of friction 210 has already been determined. Is a coefficient of friction, for example 210 known on a snow-covered road, and describes the road in front of the vehicle 305 a snow-covered curve, the specific coefficient of friction 210 used to drive around the curve. If, on the other hand, the curve is dry and free of snow, a higher coefficient of friction can occur 210 determined or estimated for this section of the subsurface.

Furthermore, a signal on board the vehicle 305 are output that is based on the specific coefficient of friction 210 indicates. In particular, there can be a difference between an actual and a maximum coefficient of friction 210 are issued.

List of reference symbols

100

wheel

105

roadway

110

Peripheral speed

115

Longitudinal speed

120

Longitudinal direction

125

Longitudinal slip

130

Turning plane

135

Direction of movement

140

Transverse direction

145

Slip angle

150

A value (slip)

200

Tire diagram

205

Tire characteristic

210

Tuple

300

system

305

vehicle

310

Control device

315

wheel

320

Left Lane

325

right lane

330

Longitudinal axis

335

main emphasis

340

Steering device

345

Steering angle

350

Drive motor

355

Deceleration device / braking device

400

Procedure

405

Determine driving situation

410

Exerting torque

415

Exercise acceleration / deceleration

420

Control steering angle

425

Determine coefficient of friction

430

Control vehicle / output signal

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102012217772 A1 [0004]
• DE 102016009257 A1 [0005]

Claims (9)

A method (400) for determining a coefficient of friction (210) between a roadway (105) and a wheel (315) of a two-lane vehicle (305), the method (400) comprising the following steps: exerting (410) a first torque on the wheel (315) to cause a slip (150) between the wheel (315) and the road surface (105); simultaneous changing (420) of a steering angle (345) of one of the wheels (315) of the vehicle (305) in order to compensate for a change in the direction of travel caused by the torque; and determining (430) the coefficient of friction (210) on the basis of the slip (150). Method (400) according to Claim 1 , further comprising simultaneously applying (420) a second torque to another wheel (315) of the vehicle (305) to compensate for a change in an acceleration of the vehicle (305) caused by the first torque. Method (400) according to Claim 1 or 2 wherein the method (400) is performed while the vehicle (305) is cornering. Method (400) according to one of the preceding claims, wherein the coefficient of friction (210) is determined with respect to a predetermined characteristic (205) of the wheel (315) on the basis of the torque and a slip angle of the wheel (315). Device (310) for determining a coefficient of friction (210) between a roadway (105) and a wheel (315) of a two-lane vehicle (305), the device (310) comprising: a first interface (365) for connection to a the wheel (315) acting acceleration (350) or deceleration device (355); a second interface (370) for connection to a device (340) for controlling a steering angle (345) of one of the wheels (315) of the vehicle (305); and a processing device (360) which is adapted to exert a torque on the wheel (315) in order to cause a slip (150) between the wheel (315) and the roadway (105); and at the same time changing a steering angle (345) of one of the wheels (315) of the vehicle (305) in order to compensate for a change in direction of travel caused by the torque; and also for determining the coefficient of friction (210) on the basis of the slip (150). Device (310) after Claim 5 wherein the first interface (356) is set up for connection to a delay device (355) of the vehicle (305). Device (310) after Claim 5 or 6th , wherein the first interface (365) is set up for connection to a drive device (350) of the vehicle (305). Device (310) after Claim 7 , wherein the drive device (350) is individually assigned to the wheel (315). System (300) comprising a device (310) according to one of Claims 5 to 8th and a vehicle (305).

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