EP3490854A1

EP3490854A1 - Determining a maximum adhesion limit

Info

Publication number: EP3490854A1
Application number: EP17739894.8A
Authority: EP
Inventors: Robert Zdych; Heinz-Joachim Gilsdorf; Volker Wagner; Matthias Schlegel; Lara Ruth TURNER; Julian KING
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 2016-07-29
Filing date: 2017-06-27
Publication date: 2019-06-05
Also published as: JP2019525178A; CN109476289A; US20190161064A1; WO2018019505A1; DE102016214065A1

Abstract

A tyre (100) runs on an underlying surface (105). A method for determining a traction limit (μ_max) between the tyre (100) and the underlying surface (105) in the longitudinal direction (120) of the tyre (100) comprises steps of detecting an instantaneous slip (125) of the tyre (100); detecting an instantaneous longitudinal force on the tyre (100); determining an instantaneous coefficient of adhesion (210); forming a tuple from the detected slip (125) and the instantaneous coefficient of adhesion; and determining the maximum adhesion limit (μ_max). Therein, the maximum adhesion limit (μ_max) is determined on the basis of the gradient (m_u) of a straight line (240) from the origin through the tuple if the slip (125) is below a first predetermined threshold value (230), or on the basis of a tangent gradient (m_t) through the tuple if the slip (125) is between the first threshold value (230) and the second threshold value (235), or directly on the basis of the instantaneous coefficient of adhesion (210) if the slip (125) is above the second predetermined threshold value (235).

Description

Determination of a maximum traction limit

The invention relates to the determination of a maximum adhesion limit _ma x, which indicates a maximum transferable force between a tire and a substrate.

A motor vehicle with four tires drives on a surface. If a longitudinal force, in particular an acceleration or a braking force, acts between one of the tires and the ground, then the peripheral speed of the tire usually deviates from the speed of movement of the motor vehicle and there is a slip. If a lateral force acts on the tire, for example when the motor vehicle is turning, the plane of rotation of the tire does not coincide with the direction of movement of the tire and there is a non-zero slip angle. The lateral force can act in both directions and the

Slip angle can occur on a steered or unguided tire.

Slip and slip angle can be summarized as λ-value. A maximum transferable between the tire and the ground force is called adhesion limit and generally depends on the λ value and the maximum possible adhesion coefficient max. In this case, the relationship between λ value and adhesion coefficient μ is generally linear only in a subarea. If the force to be transmitted between the tire and the ground exceeds the limit of traction, there is a risk of loss of control over the tire

Motor vehicle.

DE 10 2012 217 772 A1 proposes to determine the maximum adhesion limit with respect to two different regions for the λ value. If the λ value is small, then the slope of an origin straight line is to be based on a tuple from the current λ value and the current adhesion coefficient μ of the determination of the maximum adhesion limit max. On the other hand, if the λ-value is large, then the determination of the maximum adhesion limit max on the basis of the tuple current λ-value u. Slope of a tangent. An object underlying the present invention is

Supplements u. to provide an improved technique for the reliable determination of the maximum traction limit. The object is solved by the subject matters of the independent claims. Subclaims give preferred

Embodiments again.

Disclosure of the invention

A tire rolls on a surface. A first method for determining a traction limit between the tire and the ground, in the longitudinal direction of the tire, comprises steps of detecting a momentary slip of the tire; determining a current coefficient of adhesion; forming a tuple from the detected slip and the current traction coefficient; and determining the maximum traction limit thereof. In this case, the maximum adhesion limit is determined on the basis of the slope of an original straight line by the tuple if the slip is below a first predetermined first

Threshold, or based on a tangent slope through the tuple, if the slip is between the first and second threshold, or directly based on the current traction coefficient, if the slip is above the second predetermined threshold.

It was recognized that after a certain slip a characteristic of the

Coefficient of adhesion over the slip has a negligible slope. The determination of the maximum adhesion limit can therefore be carried out in a simplified manner in this area. In contrast to the known state of the art, a tripartite division can be undertaken instead of a division of the characteristic of the adhesion coefficient over the slip. Thus, a direct further development of the proposals published in DE 10 2012 217 772 A1 can be realized. The present invention should be understood as an immediate further development of this publication.

In the area above the second threshold, the maximum

Frictional limit, in particular the current adhesion coefficient be equated. This allows an approximation that is sufficiently accurate for most purposes and that can be performed quickly and efficiently. Inaccuracies that could arise in the determination of the slope of the curve in this area on the basis of a tangential slope, are avoided, the reliability of the friction coefficient statement is thereby increased overall.

The instantaneous adhesion coefficient can be determined as the quotient of a directly measured tire tangential force and a directly measured tire normal force. The direct measurement of the tangential force acting on the tire or the normal force acting on the tire is usually inexpensive and may be already implemented on the motor vehicle for other reasons.

In another embodiment, the currently acting adhesion coefficient can also be determined on the basis of a model. In particular, the model may comprise a calculation model based on a yaw rate of the

Motor vehicle, a tire speed of the tire or other tire or on the basis of accelerations works. The variables mentioned can be recorded or determined on a conventional motor vehicle by means of an already existing sensor, so that the momentarily acting

Adhesion coefficient can be determined easily and accurately.

In a further embodiment, a longitudinal force acting momentarily on the tire is determined and the coefficient of adhesion is calculated as the quotient of

Longitudinal force and a normal force determined.

The first method can also be applied to a lateral force on the tire. A second method for determining a maximum traction limit between the tire and the ground, in the transverse direction of the tire, comprises steps of detecting a current slip angle of the tire; determining a current coefficient of adhesion; forming a tuple from the detected skew angle and the determined, currently acting traction coefficient; and determining the maximum traction limit. This is the maximum Frictional limit determined on the basis of the slope of a straight line of origin by the tuple, if the slip angle below a first predetermined

Threshold, or based on a tangent slope through the tuple, if the slip angle is between the first and second threshold, or directly based on the currently acting adhesion coefficient, if the slip angle is above the second predetermined threshold.

The procedure of the second method essentially corresponds to the first method described above, so that variants or embodiments can be exchanged directly or appropriately between the two methods. A method may also be provided for the universal determination of the longitudinal and / or transverse forces on the tire or successively on a plurality of tires of a motor vehicle.

In one embodiment, a longitudinal force currently acting on the tire is determined and the adhesion coefficient is determined as the quotient of the longitudinal force and a normal force.

A first device for determining a maximum traction limit between a tire and a ground on which the tire rolls, in

Longitudinal direction of the tire, comprises a first interface for detecting a current slip of the tire; a second interface for determining a current coefficient of adhesion; and a processing device configured to collect a tuple from the detected slip and the determined one

To form a coefficient of adhesion and to determine the maximum traction limit. The traction limit is determined on the basis of the slope of an original straight line by the tuple if the slip is below a first predetermined threshold, on the basis of a tangent slope through the tuple if the slip is between the first and second threshold, or directly on the basis of the currently acting adhesion coefficient if the slip is above the second predetermined threshold. Preferably, a further interface for providing the specific adhesion limit is provided. A second device for determining a traction limit between a tire and a ground on which the tire rolls, in the transverse direction of the tire, comprises a first interface for detecting a current slip angle of the tire; a determination device for determining a momentary adhesion coefficient; and a processing device configured to collect a tuple from the detected skew angle and the determined one

Form a coefficient of adhesion; and to determine the maximum traction limit. In this case, the maximum traction limit is determined based on the slope of an origin straight through the tuple if the skew angle is below a first predetermined threshold, based on a tangent slope through the tuple if the skew angle is between the first and second threshold, or directly based on the currently acting one

Adhesion coefficient if the slip angle is above the second predetermined threshold. Preferably, a further interface for providing the specific adhesion limit is provided.

The two devices essentially correspond to each other so that variants or embodiments can be exchanged directly or appropriately between the devices. It is also possible to provide a device for the universal determination of the longitudinal and / or transverse forces on the tire or successively on a plurality of tires of a motor vehicle.

The interfaces can each be realized, for example, as an electrical, electronic, computer or logical interface. The embodiments and features that apply to the methods may also be applied in a transferred manner to the devices and vice versa. The

Processing device of one of the devices may in particular comprise a programmable microcomputer, which is preferably adapted to perform at least a part of one of the described methods. For this purpose, the respective method can be present as a computer program product.

The methods and the devices can be used to advantageously determine the respective maximum adhesion limit, so that a valuable Information for judging a driving condition or for controlling the motor vehicle may be available. For example, a warning may be issued if forces acting on the tire threaten to reach the maximum traction limit, such as when the forces are less than one

predetermined amount are smaller than the maximum traction limit. In another embodiment, in the same case, the motor vehicle may be controlled to avoid reaching the maximum traction limit, such as by braking or accelerating the tire or other tire, changing a steering angle, or taking some other measure.

A motor vehicle includes a tire and one of those described above

Devices. Usually the motor vehicle comprises several tires,

For example, two if it is a motorcycle, four if it is a passenger car or a light commercial vehicle, and four or more tires if it is a larger or heavier commercial vehicle.

Multiple tires that together form a wheel can be considered as a tire. The determination of the adhesion limit can be carried out on a tire-specific basis for all or some of the existing tires. As has been described, a determination of the adhesion limit in both the longitudinal direction and in

Transverse direction of the relevant tire possible.

Embodiments of the invention will now be described in more detail with reference to the accompanying figures, in which:

Figure 1 shows a tire on a substrate.

Fig. 2 shows a characteristic between a slip and a slip angle of a

Tire and its coefficient of adhesion;

3 is a flowchart of a method for determining a maximum

Coefficient of adhesion of a tire; and

Fig. 4 is a schematic representation of a device for determining the

represents maximum adhesion coefficient. Figure 1 shows a tire 100 on a substrate 105 in a side view and a plan view. The tire 100 is usually comprised of a wheel; in the present description, however, is mainly focused on the friction behavior between the tire 100 and the substrate 105, so that for

Considerations example of the driving behavior of a motor vehicle, the said tire 100 can be considered as a synonym for a wheel.

In the side view are a peripheral speed 1 10 and a

Longitudinal speed 1 15 applied. The longitudinal speed 15 runs in a longitudinal direction 120, which is perpendicular to an axis of rotation of the tire 100 and usually runs parallel to the base 105. A difference between the speeds 1 10 and 1 15 produces a slip 125 which may be referred to as s.

In plan view, a plane of rotation 130 and a direction of movement 135 are plotted. The plane of rotation 130 is perpendicular to a transverse direction 140 that extends parallel to the axis of rotation of the tire 100. Between the plane of rotation 130 and the direction of movement 135 is a slip angle 140, which can be designated α.

With respect to a coefficient of adhesion between the tire 100 and the substrate 105, the slip 125 acting on a longitudinal force 120 is similar to the slip force 145 depending on a transverse force 140. For the following explanations, therefore, a λ-value 150 is considered superordinate term for the slip 125 and the slip angle 145 used. The determination of a frictional limit on the basis of the currently acting adhesion coefficient can thus be carried out in an analogous manner with regard to the longitudinal and transverse forces.

FIG. 2 shows a diagram 200 with a characteristic curve 205 between a λ value 150 and a coefficient of adhesion 210, which is designated here by μ. The characteristic curve 205 can be connected to a first region 215, which adjoins the origin (λ = 0, μ = 0), a second area 220 and a third area 225 are distinguished. Between the first region 215 and the second region 220 there is a first threshold value 230 and between the second region 220 and the third region a second threshold value 235.

An adhesion limit can be determined as a function of a slope of the characteristic curve 205. This slope is in the three areas 215 to 225

differently. In the first region 215, the slope may be approximated by the slope of an origin straight line 240 that passes through the origin and a measurement point on the 205. This measurement point is a tuple with the right-hand value of a current λ value 150 and the high value of a current one

Coefficient of adhesion 210 given. In the second region 220, it is possible to improve the slope of a tangent 245 to the measuring point. It is also possible to consider several measuring points that are as close together as possible. In the third region 225, the slope can be approximated as a constant simplifying. In particular, the adhesion limit with the current

Coefficient of adhesion 210 are set equal.

FIG. 3 shows a flow chart of a method 300 for determining the

Frictional limit on a tire 100. In a step 305, one or more parameters are determined on the tire 100 or an associated motor vehicle. In one embodiment, at a time k, a current λ value 150, a normal force F _z , _k, and a tire longitudinal force F | _k or one

Tire sides force F _s , k are determined. In a step 310, the instantaneous coefficient of adhesion _k (210) is determined, for example as a quotient of the determined tangential force, ie the force previously sampled in the longitudinal direction 120 or transverse direction 140, and the normal force. In another embodiment, the adhesion coefficient 210 can also be determined in another way, for example by means of a calculation model. The calculation model may require a determination of the yaw rate of the motor vehicle, a tire speed of the tire 100, or another tire or accelerations. Subsequently, the determined λ value 150 is evaluated with respect to the threshold values 230 and 235. In a first case 315, the A value 150 lies in the first region 215, ie between the origin and the first threshold value 230. In a second case 320, the λ value 150 lies in the second region 220, ie between the first threshold value 230 and second threshold 235. In a third case 325, the λ-value 150 is above the second threshold 235. The range 225 may be bounded above by a third threshold 255, if desired. In which adjacent area 215-225 the A-value 150 falls, if it coincides with one of the thresholds 230, 235, can be appropriately defined.

For the three cases 315 to 325, the positions of the respective regions 215 to 225 with respect to the characteristic curve 205 and the determination of a gradient m are sketchy

specified. In the first case 315, a source line slope m _u is determined and the adhesion limit p _ma x is determined in a step 330 by a function f1 on the basis of the slope m _u. In the second case 320 becomes a

Tangent slope m _t determined and the adhesion limit p _ma x is determined in a step 335 by means of a function f2 on the basis of the slope m _t . In the third case 325, the slope can be assumed to be constant, so that a determination is not required. The adhesion limit p _ma x can be set equal to the instantaneous or current adhesion coefficient _k in a step 340.

In a concluding step 345, the determined adhesion limit _ma x may be provided, for example, to evaluate a consideration or evaluation of a driving state of a motor vehicle to which the tire 100 is connected, or a control of the motor vehicle or the tire 100

perform.

FIG. 4 shows a schematic representation of an exemplary device 400 for determining the adhesion limit _max on any tire 100 that is attached to a motor vehicle 405. The device 400 comprises a

Processor 410, which includes a programmable microcomputer, and in particular may be configured to fully process 300 or partially perform. Furthermore, the device 400 comprises a first

Interface 415 for receiving a first value, a second interface 420 for receiving a second value, and preferably a third interface 425 for providing a certain adhesion limit _ma x- Some of the interfaces 415, 420 and 425 may also coincide or be integrated with each other. In one embodiment, the two values for the interfaces 415 and 420 comprise a λ-value 150 and a coefficient of adhesion μ 210. In another embodiment, other values are taken, from which, as described above, the λ-value 150 and the adhesion coefficient μ 210 can be determined. The determination of the adhesion limit _ma x is preferably carried out as described above, taking into account in which of the three regions 215 to 225 the current λ value 150 falls.

REFERENCE CHARACTERS

100 tires

105 underground

1 10 peripheral speed

1 15 longitudinal speed

120 longitudinal direction

125 slip

130 plane of rotation

135 direction of movement

140 transverse direction

145 slip angle

150 λ value (slip or slip angle)

200 diagram

205 characteristic

210 adhesion coefficient

215 first area

220 second area

225 third area

230 first threshold

235 second threshold

240 straight line of origin

245 tangent

250 constant

255 third threshold (to limit 255, if needed)

300 procedures

305 Capture

310 determine the momentary coefficient of adhesion

315 λ lies in the 1. Area

320 λ is in the 2nd area

325 λ is in the 3rd area 330 max. Determine the coefficient of adhesion with respect to the slope of the straight line

335 max. Determine adhesion coefficient with regard to tangential slope

340 max. Determine adhesion coefficient with regard to maximum value

345 max. Provide coefficient of adhesion

400 device

405 motor vehicle

410 processing device

415 first interface

420 second interface

425 third interface

Claims

claims

1 . Method (300) for determining a traction limit (Mmax) between a tire (100) and a substrate (105) on which the tire (100) rolls, in the longitudinal direction (120) of the tire (100), the method (300) comprising the steps of: detecting (305) a current slip (125) of the tire (100); Determining (310) a current coefficient of adhesion (210); Forming (310) a tuple from the detected slip (125) and the current traction coefficient; Determining (330) the maximum traction limit (Mmax) based on the slope (m _u ) of an origin straight line (240) through the tuple if the slip (125) is below a first predetermined threshold (230) or (335) Base a tangent slope (m _t ) through the tuple if the slip (125) is between the first (230) and a second threshold (235); characterized in that the maximum traction limit (Mmax) is determined directly on the basis of the traction coefficient (210) if the slip (125) is above the second predetermined threshold (235).

2. Method (300) for Determining a Maximum Frictional Limit (Mmax)

between a tire (100) and a substrate (105) on which the tire (100) rolls, in the transverse direction (140) of the tire (100), the method (300) comprising the steps of: detecting (305) a current skew angle (145) the tire (100); Determining (310) a current one

Adhesion coefficient (210); Forming (310) a tuple from the detected one

Slip angle (145) and the momentary coefficient of adhesion (210);

Determining (330) the maximum traction limit (Mmax) based on the slope (m _u ) of an origin straight line (240) through the tuple if

Slip angle (145) is below a first predetermined threshold (230), or (335) based on a tangent slope (m _t ) through the tuple if the slip angle (145) between the first (230) and a second

Threshold (235) is; characterized in that the traction limit directly (Mmax) is determined (340) on the basis of the momentarily acting adhesion coefficient (210) if the slip angle (145) is greater than the second

predetermined threshold (235).

The method (300) according to claim 1 or 2, wherein the adhesion limit (Mmax) is set equal to the current adhesion coefficient (21 0) if the slip (1 25) is above the second predetermined threshold (235).

4. The method (300) according to one of the preceding claims, wherein the

Adhesion limit (Mmax) is equated to the momentary coefficient of adhesion (21 0) if the slip angle (1 45) is greater than the second

predetermined threshold (235).

5. The method (300) according to any one of the preceding claims, wherein a

currently acting on the tire (1 00) acting tangential force is determined and the momentary adhesion coefficient (21 0) as a quotient of the tangential force (1 40) and a normal force is determined.

The method (300) according to any one of claims 1 to 4, wherein the adhesion coefficient (21 0) is determined (31 0) on the basis of a model.

7. The method (300) according to any one of claims 1 to 4, wherein a momentarily on the

Tire (1 00) acting longitudinal force is determined and the current

Adhesion coefficient (21 0) as a quotient of the longitudinal force (1 20) and a

Normal force is determined.

8. A device (400) for determining a maximum adhesion limit (Mmax) between a tire (1 00) and a substrate (1 05) on which the tire (1 00) rolls, in the longitudinal direction (1 20) of the tire (1 00 ), the apparatus comprising: a first interface (41 5) for detecting a

instantaneous slip (1 25) of the tire (1 00); a second interface (420) for detecting a current coefficient of adhesion (21 0); a

Processing means (41 0) adapted to form a tuple of the detected slip (1 25) and the determined adhesion coefficient; and the adhesion limit (Mmax) based on the slope (m _u ) of a

Origin line (240) determined by the tuple, if the slip (1 25) is below a first predetermined threshold (230), the Force limit (Mmax) on the basis of a tangent slope (m _t ) to determine by the tuple, if the slip (1 25) between the first (230) and a second threshold (235), or the maximum traction limit (Mmax) directly the basis of the coefficient of adhesion (21 0) if the slip (1 25) is above the second predetermined threshold (235); and another interface (425) for providing the particular

Frictional limit (Mmax) -

9. Device (400) for determining a traction limit (Mmax) between

a tire (100) and a base (105) on which the tire (100) rolls, in the transverse direction (1 40) of the tire (100), the apparatus comprising: a first interface (41 5) for detecting a current slip angle (1 45) of the tire (1 00); a second interface (420) for detecting a current coefficient of adhesion (21 0); a processing device (41 0) which is adapted to form a tuple of the detected slip angle (1 45) and the determined adhesion coefficient (21 0); and determine the traction limit (max) based on the slope (m _u ) of an origin straight line (240) by the tuple if the skew angle (145) is below a first predetermined threshold (230), the traction limit (Mmax) on the basis a tangent slope (m _t ) to be determined by the tuple, if the slip angle (145) between the first (230) and a second

Threshold (235), or to determine the adhesion limit (Mmax) based on the adhesion coefficient (21 0) if the slip angle (1 45) is above the second predetermined threshold (235); and another

Interface (425) for providing the determined adhesion limit (Mmax) -

1 0. A motor vehicle (405) with a tire (1 00) and a device (400) according to claim 8 or 9.