SE534220C2 - Automatic friction estimation - Google Patents

Abstract

A coefficient of friction between the wheels of a motor vehicle and a ground on which the vehicle is driven is estimated. An input interface (210) here receives input signals (Min) representing one of an engine in the vehicle generated torque, angular velocities of the wheels of the vehicle and the longitudinal velocity of the vehicle. A calculation unit (200) calculates on the basis of the input signals (IVL) a longitudinal deceleration force (F), a normal force (N) acting on the vehicle from the ground (140) and a degree of slip (s) of the wheels of the vehicle. The calculation unit (200) also estimates an inclination (k) of an approximate linear relationship between a normalized longitudinal deceleration force (F / N) on the vehicle and the degree of slip (s). A storage unit (250) contains a look-up table, where slopes (k) are categorized into at least two different size categories of friction (plague). The calculation unit (200) consults the look-up table and indicates on the basis thereof and a current slope (k) an estimated friction (plague) as belonging to a certain category of the at least two size categories. (Fig. 2)

Description

534 220, the system comprising a storage unit. The storage unit contains a look-up table representing a categorization of slopes into at least two different size categories of friction. The calculation unit is further configured to indicate, on the basis of the slope and the look-up table, an estimated friction as belonging to a certain category of the at least two size categories.

Important advantages achieved by this system are the speed that the look-up table enables and that the resulting friction estimate can be used both as a basis for presenting information to the vehicle driver and for further processing in an Advanced Driver Assistance System (ADAS). , such as an emergency braking system or an automatic lane keeping system.

According to an embodiment of this aspect of the invention, the system comprises a first and a second calculation module. The first calculation module is configured to determine the normalized longitudinal deceleration force and the second calculation module is configured to determine the degree of slippage. The calculation modules can thus be tailored for the most efficient possible processing of the respective input signals.

According to another embodiment of this aspect of the invention, the system comprises a Kalman filter configured to estimate the slope of the normalized longitudinal deceleration force as a function of the degree of slippage based on the normalized longitudinal deceleration force and the degree of slippage. A Kalman filter is advantageous, as it offers good opportunities to model complicated relationships. In addition, the Kalman filter is suitably adaptive, so that its parameter values depend on the rate of change of the friction, and that a relatively fast estimate (i.e. high refresh rate) is obtained with relatively fast variation of the friction while a relatively stable estimate (with slightly lower refresh rate) is obtained. at relatively slow variation of the friction. In addition, a Kalman 10 15 20 25 30 534 220 man filter is comparatively easy to calibrate and tune in. The calculation unit is advantageously configured to in turn implement the Kalman filter and / or the above-mentioned calculation modules.

According to yet another embodiment of this aspect of the invention, the calculation unit is configured to receive a first additional signal representing a deceleration torque applied via a retarder on at least one wheel axle of the vehicle. The calculation unit is configured here to determine the slope on a further basis of the first additional signal. Thus, the estimated friction can be categorized with higher accuracy. Thus, for example, the number of size classes can be increased.

According to a further embodiment of this aspect of the invention, the calculation unit is configured to receive a second additional signal representing a deceleration torque applied via an exhaust brake to a drive shaft of the vehicle. The calculation unit is configured here to determine the slope on a further basis of the second additional signal. Assuming that the exhaust brake accounts for all deceleration contributions, this, together with the fact that the exhaust brake only attacks the vehicle's drive wheel, results in the estimated friction being categorized with even higher precision.

According to another embodiment of this aspect of the invention, the calculation unit is configured to receive a third additional signal representing a brake pressure applied in a braking system of the vehicle. Here, the calculation unit is configured to determine the slope on a further basis of the third additional signal. In analogy to the above, provided that the braking system is responsible for all deceleration contributions, this may result in improved accuracy in the categorization of the estimated friction.

According to yet another embodiment of this aspect of the invention, the calculation unit is configured to receive a fourth additional signal which indicates a geographical position of the vehicle. The calculation unit is also configured to determine the degree of slippage on a further basis of the fourth additional signal. With the support of the position indications, the speed of the vehicle can be determined with high precision and thus a more reliable determination of the degree of slip is possible. Specifically, this means, for example, that if two or more deceleration systems included in the vehicle are activated at the same time, a more fair slip value for the non-driving wheels can be obtained.

According to an embodiment of this aspect of the invention, therefore, the calculation unit is configured to, when mixing two or more deceleration systems, calculate a specified longitudinal deceleration force on a set of drive wheels of the vehicle based on the second auxiliary signal and at least one of the third and fourth auxiliary signals. The calculation unit is further configured to determine the slope on the basis of the specified longitudinal deceleration force, which offers increased precision in the friction estimation.

According to a further embodiment of this aspect of the invention, the calculation unit is configured to receive at least one additional signal indicating a windscreen wiper frequency, a detected rain intensity and / or an air temperature. On a further basis of the at least one auxiliary signal, the calculation unit is configured to categorize the estimated friction. Thus, the accuracy can be improved even more.

According to another aspect of the invention, the object is achieved by the method described in the introduction, the method comprising matching the slope of the normalized longitudinal deceleration force as a function of the degree of slippage against a look-up table representing a categorization of degrees of friction of at least two different size categories. An estimated friction is then determined as belonging to a certain category of the mentioned at least two size categories. The advantages of this method, as well as with the preferred embodiments thereof, will become apparent from the discussion above with reference to the proposed system.

According to a further aspect of the invention, the object is achieved through a computer program directly downloadable to the internal memory of a computer, comprising software for controlling the steps according to the method proposed above when said program is run on a computer.

According to another aspect of the invention, the object is achieved by a computer-readable medium with a program stored thereon, the program being adapted to cause a computer to control the steps according to the method proposed above.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained in more detail by means of embodiments, which are described by way of example, and with reference to the accompanying drawings. shows a schematic view of a motor vehicle illustrating the basic forces used according to the invention, Figure 1 Figure 2 shows a block diagram of a system according to an embodiment of the invention, Figure 3 shows a graph which exemplifies a relationship between a normalized longitudinal deceleration force and the degree of slippage of the wheels, Figure 4 illustrates an example of how different slopes of the normalized longitudinal deceleration force as a function of the degree of slippage are proposed to be divided into different size categories of friction degree, and shows a flow chart illustrating the general method according to the invention. .

Figure 5 10 15 20 25 30 534 220 DESCRIPTION OF EMBODIMENTS OF THE INVENTION We first refer to Figures 1 and 2. Figure 1 shows a schematic view of a motor vehicle 100 in which the basic forces F and N used according to the invention are illustrated. Figure 2 shows a bio diagram of the system according to an embodiment of the invention.

The proposed system is intended to estimate a coefficient of friction between the wheels 110, 120 and 130, respectively, of the vehicle 100 and a base 140 on which the vehicle 100 is driven. The system includes an input interface 210, a computing unit 200 and a storage unit 250. In addition, the system advantageously includes calculation modules 220 'and 230 and a Kalman filter 240, one or more of which may be included in the computing unit 200. In addition, it is advantageous if the system includes, or is on otherwise associated with, a memory module 260 comprising software for controlling the system to perform the procedure which will be described below. The input interface 210 is configured to receive input signals Mm representing parameters describing how the vehicle 100 is driven on the ground 140. The input signals Min can thus indicate a torque generated by an engine in the vehicle 100, angular velocities w of one or more of the vehicle 100 wheels 110, 120 or 130 and the longitudinal speed v of the vehicle 100. In the case of engine braking, however, one or more of the input signals Mm may instead indicate a deceleration torque generated by the engine. The input interface 210 may be connected to a bus system for data registration and control of various types of devices and processes in the vehicle 100. For example, the bus system may be adapted according to the CAN standard (CAN = Controller Area Network) or one of the following standards: Time Triggered CAN (TTCAN), FlexRay, Media Oriented System Transport (MOST) or ByteFlight.

The calculation unit 200 is configured to calculate, on the basis of the inputs Min, a longitudinal deceleration force F, a normal force N acting on the vehicle 100 from the ground 140 and a degree of slip s of the wheels 100, 120 and / or 130 of the vehicle 100. .

The calculation unit 200 is also configured to estimate a slope k of an approximate linear relationship between a normalized longitudinal deceleration force F / N on the vehicle 100 and the degree of slip s.

We now refer to Figure 3, where a graph of a typical relationship between the normalized longitudinal deceleration force F / N and the slip degree s is shown in a diagram for different coefficients of friction: u = 0.1, u = 0.3, u = 0 , 5, u = 0.7 and u = 1, respectively. Along the horizontal axis of the diagram, the degree of slip is stated in percent.

The degree of slip s is defined according to SAE (Society of Automotive Engineers) as: szv-mg v [1] where v is the longitudinal velocity of the wheel center (essentially the speed of the vehicle 100), co is the angular velocity of the wheel, and re is the effective radius of the wheel.

The degree of slip s is thus a dimensionless quantity within the interval 0 s s s 1. Usually, however, the degree of slip s is expressed in terms of percent [0% - 100%].

The ratio between the longitudinal deceleration force F and the normal force N on the vehicle 100, i.e. the normalized longitudinal deceleration force FIN, is also a dimensionless quantity. However, although the diagram in Figure 3 shows an interval 0 s F / N s 1, the magnitude is not in principle limited to this interval. The normal force N is derived from sub-forces L1, L2 and L3, which in turn can be measured via position sensors and sensors in the vehicle's 100 wheel system. The longitudinal deceleration force F is determined, for example, by means of position sensors in the vehicle 100.

As can be seen from Figure 3, the slope k of the normalized longitudinal deceleration force F / N as a function of the slippage degree s is approximately linear for relatively small values of s (say up to s = 2% for the illustrated the example when p = 0.7). This means that the following relationship applies: -Eeksi-m [2] where k is the above-mentioned slope, and m is a constant (eg m = 0 for very small s).

For example, by linear regression, current slopes k are plotted against different coefficients of friction u for a set of data points in a vehicle 100, which data points have been registered on different surfaces (asphalt, concrete, cobblestones, gravel, etc.) and / or substrate conditions (dry, wet, snow, ice, etc.). The images between the slopes k and the coefficients of friction u are stored according to the invention in a storage unit 250 in the form of a look-up table, so that the slopes k are categorized into at least two different size categories of degree of friction.

Figure 4 shows a diagram of the normalized longitudinal deceleration force F / N as a function of the degree of slippage s, which illustrates an example of such a categorization, where the slope k has been divided into three different size categories, namely VS corresponding to "very high", RS corresponding to “relatively content” and NS corresponding to “not content”.

According to the invention, the calculation unit 200 is configured to indicate, on the basis of the slope k and the look-up table, an estimated friction plague as belonging to a certain category of the at least two size categories, for example VS, RS and NS.

The estimated friction value nes, can advantageously be transmitted to the above-mentioned bus system for further automatic processing in an ADAS and / or presentation to the driver of the vehicle.

According to an embodiment of the invention, the system comprises a first and a second calculation module 220 and 230, respectively. The first calculation module 220 is configured to receive a predetermined set of the input signals Min, and on the basis thereof determine it normalized longitudinal deceleration force F / N.

The second calculation module 230 is configured to receive a second set of the input signals Mm, and on this basis determine the degree of slippage s. The first and the second set of the input signals Min may overlap in whole or in part, so that one or more input signals are received by both the first calculation module 220 and the second calculation module 230. One or both calculation modules 220 and 230 can be implemented by the calculation unit 200. In any case, the calculation modules are advantageous because they can be tailored for the most efficient possible processing of the respective input signals.

It is also an advantage if the system includes a Kalman filter 240, which is configured to estimate the slope k on the basis of the normalized longitudinal deceleration force F / N and the degree of slip s. The Kalman filter 240 offers good possibilities for modeling complicated relationships in real time. According to one embodiment of the invention, the Kalman filter 240 is adaptive. This may mean, for example, that the parameter values of the filter 240 depend on the rate of change of the estimated friction value plague, so that a relatively fast estimate (i.e. a high refresh rate) is obtained with relatively rapid variation of the estimated friction value plague. Since, on the other hand, the estimated friction value plague varies relatively slowly, the estimation can take place with a slightly lower update frequency, but with relatively good stability. A Kalman filter is also advantageous as it is relatively easy to calibrate and tune in.

Like the calculation modules 220 and 230, the Kalman filter 240 can also be implemented by the calculation unit 200.

According to an embodiment of the invention, the calculation unit 200 is configured to receive, in addition to the above-mentioned signals F / N and s, a first additional signal DRET representing a deceleration torque applied via a retarder to at least one wheel axle of the vehicle 100, for example the rear axles on which the wheels 120 ~ and 130 are mounted. The calculation unit 200 is here configured to determine the slope k on a further basis of the first additional signal DRET. Thus, the estimated friction value can be given, categorized with higher accuracy. Consequently, the number of size classes in the look-up table can be increased.

The calculation unit 200 is advantageously also configured to receive a second additional signal DEXB representing a deceleration torque applied via an exhaust brake to a drive shaft of the vehicle 100, for example the shaft on which the wheels 120 are mounted. The calculation unit 200 is here configured to determine the slope k on a further basis of the second additional signal DEXB, which offers a further improved precision in the estimation of the friction value plague. This is especially true if the calculation unit 200 is configured to also receive a third additional signal DBR representing a brake pressure applied to a brake system of the vehicle 100, and the calculation unit 200 is configured to determine the slope k on a further basis of the third additional signal DBR. The braking pressure represented by the third additional signal DBR normally applies a deceleration torque to all wheel axles of the vehicle 100, i.e. the axles on which the wheels 110, 120 and 130 are mounted.

The exhaust brake, on the other hand, applies only one deceleration torque to the drive shaft of the vehicle 100 and any retarder can apply a deceleration torque to a further set of wheel axles, for example the axles on which the wheels 120 and 130 are mounted. It can thus be a relatively complex task to calculate the contribution of each deceleration system to the overall longitudinal deceleration force F.

According to an embodiment of the invention, therefore, the calculation unit 200 is configured to, when mixing two or more deceleration systems included in the vehicle 100, calculate a specified longitudinal deceleration force F on a set of drive wheels 120 of the vehicle 100 based on the second additional signal DEXB and the third the additional signal DBR and / or the fourth additional signal and Dpos, respectively, depending on which signals occur in the case in question. The calculation unit 200 is then configured to determine the slope k on the basis of the specified longitudinal deceleration force F.

In addition, the computing unit 200 according to an embodiment of the invention is configured to receive a fourth additional signal Dpos. This signal indicates with high accuracy a geographical position of the vehicle 100. The calculation unit 200 is here configured to determine the degree of slip s on a further basis of the fourth additional signal Dpos. More specifically, the calculation unit 200 uses the position data transmitted via the fourth additional signal Dpos to determine the speed v of the vehicle with high precision. This speed v then forms the basis for the determination of the degree of slippage s, for example according to equation [1].

The calculation unit 200 is advantageously configured to additionally receive at least one additional signal DEXT, which indicates a windscreen wiper frequency, a detected precipitation intensity and / or an air temperature. The calculation unit 200 here categorizes the estimated friction plague on a wider basis of the at least one auxiliary signal DEXT. By considering factors such as the amount and type of precipitation, the precision in estimating the friction value of plague can be further improved.

In order to summarize, the general method according to the invention for estimating a coefficient of friction between the wheels of a vehicle 100 and the base 140 on which the vehicle 100 is driven will now be described with reference to the flow chart in Figure 5.

A first step 510 calculates a longitudinal deceleration force F, a normal force N acting on the vehicle 100 from the ground 140 and a degree of slip s of the wheels 110, 120 and / or 130 of the vehicle 100. This calculation is performed on the basis of input signals Min, which represent one of a engine in the vehicle 100 generated torque, angular velocities m of the vehicle 100 wheels 110, 120, and / or 130 and the vehicle 100 longitudinal speed v. 10 15 20 25 30 35 534 220 12 A step 520 then produces a normalized longitudinal deceleration force F / N on the vehicle 100 (i.e., the ratio of the longitudinal deceleration force F to the normal force N), and linearly approximates a relationship between the normalized longitudinal deceleration force F / N and the degree of slip s. Then, a step 530 estimates a slope k of the in step 520 the approximation was linear.

A subsequent step 540 matches the slope k to a look-up table representing a Categorization of slopes k in degree of friction of at least two different size categories, for example VS, RS and NS according to Figure 4. Based on this, a step 550 then determines an estimated friction plague. , as belonging to a particular category of said at least two size categories.

The procedure then loops back to step 510 to update the calculated longitudinal deceleration force F, the normal force N and a slip degree s.

The method steps described with reference to Figure 5 can be controlled by means of a programmed computer apparatus. In addition, although the embodiments of the invention described above with reference to the figures include a computer and processes performed in a computer, the invention extends to computer programs, especially computer programs on or in a carrier adapted to practically implement the invention. The program may be in the form of source code, object code, a code which constitutes an intermediate between source and object code, such as in partially compiled form, or in any other form suitable for use in implementing the process according to the invention. can be any entity or device which is capable of carrying the program.

For example, the carrier may comprise a storage medium such as a flash memory, a ROM (Read Only Memory), for example a CD (Compact Disc) or a semiconductor ROM, EPROM (Electrically Programmable ROM), EEPROM (Erasable EPROM), or a magnetic recording medium, e.g. a floppy disk or hard disk. In addition, the carrier may be a transmitting carrier such as an electrical or optical signal, which may be conducted through an electrical or optical cable or via radio or otherwise.

When the program is formed by a signal which can be conducted directly by a cable or other device or means, the carrier can be constituted by such a cable, device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, where the integrated circuit is adapted to perform, or to be used in performing, the actual processes.

The invention is not limited to the embodiments described with reference to the figures but can be varied freely within the scope of the appended claims.

Claims (13)

10 15 20 25 30 35 534 220 14 Patent claims A system for estimating a coefficient of friction between the wheels (110, 120, 130) of a motor vehicle (100) and a base (140) on which the vehicle (100) is driven, the system comprising: an input interface (210) configured to receive input nals (Mm) representing a torque generated by an engine in the vehicle (100), angular velocities (w) of the wheels (110, 120, 130) of the vehicle (100) and the longitudinal velocity (v) of the vehicle (100), a calculation unit (200) configured to calculate on the basis of the inputs (Min) a longitudinal deceleration force (F), a normal force (N) acting on the vehicle (100) from the ground (140) and a degree of slip (s) of the wheels of the vehicle (100) (110, 120, 130), and estimating an inclination (k) of an approximate linear relationship between a normalized longitudinal deceleration force (F / N) on the vehicle (100) and the degree of slippage (s), and a storage unit (250) containing a look-up table, characterized by representing the look-up table is a categorization of gradients (k) in degree of friction of at least two different size categories (VS, RS, NS) and the calculation unit (200) is configured to: on the basis of the slope (k) and the look-up table enter an estimated friction (plague) as belonging to a certain category of said at least two size categories (VS, RS, NS), receive at least one additional signal (DRET, DEXB, DHR) representing at least one of: a deceleration torque applied via a retarder to at least one wheel axle of the vehicle (100) , a deceleration torque applied via an exhaust brake to a drive shaft of the vehicle (100), and a brake pressure applied to a brake system of the vehicle (100), and determining the inclination (k) on a further basis of the at least one additional signal (DRET, DEXB, DBR) . The system of claim 1, wherein the system comprises: a first calculation module (220) configured to determine the normalized longitudinal deceleration force (F / N), and a second calculation module (230) configured to determine the normalized longitudinal deceleration force (F / N). ma degree of slip (s). The system of any of claims 1 or 2, wherein the system comprises a Kalman filter (240) configured to estimate the slope (k) based on the normalized longitudinal deceleration force (FIN) and the degree of slippage (s). The system of claim 3, wherein the computing unit (200) is configured to implement the Kalman filter (240). The system of claim 1, wherein the computing unit (200) is configured to receive a fourth additional signal (Dpos) indicating a geographical position of the vehicle (100), and the computing unit (200) is configured to determine the degree of slippage (s) on a further basis. of the fourth additional signal (Dpos). The system of claim 5, wherein the computing unit (200) is configured to, when mixing two or more deceleration systems included in the vehicle (100): calculate a specified longitudinal deceleration force (F) on a set of drive wheels (120) of the vehicle (100) on basis of the second additional signal (DEXB) and at least one of the third and fourth additional signals (DBR; Dpos), and determine the slope (k) on the basis of the specified longitudinal deceleration force (F). The system of any preceding claim, wherein the computing unit (200) is configured to: receive at least one additional signal (DEXT) indicating at least one of a windshield wiper frequency, a detected rain intensity and an air temperature, and categorize the estimated the friction (plague) on a further basis of the at least one extra signal (DEXT). 10 15 20 25 30 534 220 16 A method for estimating a coefficient of friction between the wheels (110, 120, 130) of a motor vehicle (100) and a base (140) on which the vehicle (100) is driven, the method comprising: calculating a longitudinal deceleration force (F), a normal force (N) acting from the ground (140) on the vehicle (100) and a degree of slip (s) of the wheels (110, 120, 130) of the vehicle (100) on the basis of input signals (Min) representing one of a engine in the vehicle (100) generated torque, angular velocities (co) of the vehicle's (100) wheels (110, 120, 130) and the longitudinal velocity (v) of the vehicle (100), linear approximation of a relationship between a normalized longitudinal deceleration force (F / N) on the vehicle (100) and the degree of slippage (s), and estimation of a slope (k) of the linearly approximated relationship, characterized by matching the slope (k) against a look-up table representing a Categorization of Slopes (s). k) in a degree of friction of at least two different size categories (VS, RS, NS), and on the basis thereof determining an estimated friction (pen) belonging to a certain category of said at least two size categories (VS, RS, NS), the slope (k) being determined on a further basis by at least one additional signal (DRET, DEXB, DBR) representing at least one of: a deceleration torque applied via a retarder to at least one wheel axle of the vehicle (100), a deceleration torque applied via an exhaust brake to a drive axle of the vehicle (100), and one in a brake system of the vehicle (100) applied brake pressure. The method of claim 8, comprising determining the degree of slip (s) on a further basis of a fourth additional signal (Dpos) indicating a geographical position of the vehicle (100). The method of any of claims 8 or 9, wherein the vehicle (100) is configured to decelerate by mixing two or more deceleration systems included in the vehicle (100), and the method of brake mixing comprises: calculating a specified longitudinal deceleration force (F) on a set of drive wheels (120) of the vehicle (100) based on the second additional signal (DEXB) and at least one of the third and fourth additional signals (DBR; Dpos), and determining the inclination (k) of basis of the specified longitudinal deceleration force (F). The method according to any one of claims 8 to 10, comprising categorizing the estimated friction (plague) on a further basis of at least one additional signal (DEXT) indicating at least one of a windscreen wiper frequency, a detected rain intensity and an air temperature. A computer program directly downloadable to the internal memory (260) of a computer, comprising software for controlling the steps of any of claims 8 to 11 when said program is run on the computer. A computer readable medium (260) having a program stored thereon, the program being adapted to cause a computer to control the steps of any of claims 8 to 11.