JPH04224447A - How to monitor the frictional coupling between the roadway and the tires of the wheels of a driving vehicle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for monitoring the frictional coupling between the tires of a driven wheel and the road.

0002

BACKGROUND OF THE INVENTION The frictional connection between the tires of motor vehicle wheels and the road is of critical importance to safe vehicle guidance. This is because any dynamic process, i.e. accelerating a vehicle by operating the accelerator pedal and/or slowing this vehicle by operating the brake pedal, results in a corresponding force transmission between the tires and the road. This is because it is necessary. In this case, if the maximum possible frictional connection is exceeded, an unstable or safety-related situation arises.

To stop the driven wheels when decelerating a vehicle and/or to prevent the wheels from spinning when accelerating the vehicle, antiskid control devices or drive antiskid control devices are already known. ing. In these devices, wheel sensors detect the circumferential speed and/or the acceleration/deceleration of the rotation of the wheels, and from these values, if necessary, along with other measured values, wheel slippage, etc. is calculated in an electronic evaluation control. If there is a risk that the wheels may stop or spin, an appropriate drive device applies brake pressure or starts the engine.

[0004] These known anti-slip control devices and drive slip control devices are designed to measure the maximum value of the respective characteristic curves of a known μ/s graph (friction coefficient/slip) or a known K/s graph (circling force/slip). It operates near (maximum friction coefficient μmax, maximum circulating force Kmax). These known devices are activated only when there is an imminent danger that a driven wheel will spin, or if there is an imminent danger that a braked wheel will stop. In this case, relatively large wheel forces generally act.

[0005] Before initiating a control that can be felt, for example, by a corresponding pedal reaction, the driver of the vehicle has no information regarding the state of the roadway or the friction conditions between the tires of the wheels and the road. I haven't gotten it.

[0006] However, devices for monitoring the degree of utilization of the road friction coefficient that prevails at that time are already known (for example,
German Patent No. 37 05 983). With this device, the driver of the vehicle receives information about the friction between the tires and the road, or the current frictional capacity, each time he brakes, starts or accelerates. In other words, information is obtained as to how far the vehicle's wheels are from stopping or from spinning.

[0007] This known monitoring device essentially includes an electronic evaluation device and a control device which includes a storage unit and a calculation unit. The slip characteristic curve (deceleration/acceleration of the vehicle as a function of the slip coefficient of each wheel) is memorized, and when accelerating or decelerating this vehicle, the acceleration or deceleration detected later as a function of driving and the friction of the wheels are stored. is based on comparing the value of ? with the stored characteristic curve described above. In this method, a rough slip characteristic curve that best matches the current roadway situation is searched from a stored characteristic curve field. From this quasi-recognized slip characteristic curve, the maximum possible deceleration of the vehicle, and thus also the then prevailing friction coefficient μmax or the maximum transmissible wheel circumferential force, is then deduced, so that the wheels of the vehicle can stop. It can be inferred how far from or how close it is from idling (ability of frictional contact).

An important prerequisite for the well-described mode of functioning of the known monitoring device is that the specific slip characteristic curves of the vehicle for the various typical road conditions are memorized with sufficient precision;
In particular, in order to obtain the above-mentioned slip characteristic curves for each vehicle, it is necessary to carry out corresponding preliminary tests in such typical road conditions. The cost of constructing this known monitoring device is initially very high. Furthermore, the driver of the vehicle receives information from this known monitoring device regarding the current roadway situation only occasionally during normal driving, i.e. when braking and when accelerating the vehicle sufficiently strongly. Information is given. When driving on highways and in comparable driving conditions, you are often driven at approximately the same speed over long driving stretches;
Only when the driver of the vehicle consciously interrupts this steady or quasi-steady driving state by applying the brakes or accelerating the vehicle sufficiently strongly does he gain information about the current roadway situation.

[0009]

[Problem to be Solved by the Invention] It is an object of the present invention to provide a method that is simpler than these known methods and yet reliable for monitoring the frictional coupling between the tires of the driving wheels and the road. The object of the present invention is to provide an apparatus capable of carrying out this method.

0010

[Means for Solving the Problems] According to the present invention, the above-mentioned problems are solved in the case of the monitoring method mentioned at the beginning: (a) wheel circumferential force (K) acting simultaneously with wheel slip (λ) of the drive wheel being monitored; are measured during steady and quasi-steady driving conditions, i.e. within a small region of the known wheel circumferential force/wheel slip characteristic curve field, in a fixed order, in which case the wheel slip (λ) is measured in the range 0/∞. b) memorize the pair of wheel orbiting force/wheel slip values determined on at least a generally dry roadway; c) the wheel slip (λ) is determined with an accuracy that is equal to the previously memorized wheel orbiting force/wheel A subsequently generated or detected wheel circumferential force/wheel slip value pair that is significantly greater than the wheel slip of the slip value pair is evaluated as an indication of a significant deterioration of the frictional coupling conditions and, if appropriate, a warning signal is issued. It is solved by using it for issuing or controlling access.

Furthermore, the above-mentioned problem can be solved by the present invention in the case of the monitoring device mentioned at the beginning.
The solution is to use an electronic evaluation and control device with a microprocessor known per se programmed to carry out the method according to any one of claims 1 to 10.

Further advantageous developments according to the invention are described in the dependent claims.

[0013]

Contrary to the opinion commonly held among experts, the invention provides a characteristic curve of the ratio of wheel orbiting force to wheel slip (K=f( λ)), it is possible to deduce the frictional coupling prevailing between the tire and the road already early, i.e. in the lower force region, i.e. in the small region of the characteristic curve field of the known ratio of wheel circumferential force to wheel slip. It is based on the knowledge that this can be done very well, especially if wheel slip can be measured or detected with sufficient accuracy. In this infinitesimal region of the characteristic curve field, the rise in the characteristic curves of the various friction coefficients, contrary to the generally held view, is not of equal magnitude, independent of the current friction coefficient μ, but its It can be seen that, contrary to the friction coefficients, which are different in each case, there is a rise in the characteristic curve of different magnitudes associated with the corresponding maximum value of the force of different magnitudes.

According to the invention, the wheel circumferential force of the monitored drive wheel, which acts simultaneously with the wheel slip λ, is detected continuously between static and quasi-static driving states in each case. In that case wheel slip is measured with an accuracy in the range 0/∞. The circumferential force generated therein is on the order of about 60 to 120 Newtons, as is necessary for overcoming rolling resistance, for example, in a golf class vehicle. In terms of measurement technology, this wheel circumferential force is such that it is no longer possible to distinguish it with respect to the main coefficient of friction according to the hitherto held view.

According to the invention, the wheel rotation force/wheel slip value pairs detected in the above-mentioned method on an at least approximately dry roadway are stored in each case in a storage unit of the electronic evaluation and control device in a generally good manner. The road condition is stored as a reference for specific road conditions. In the characteristic curve field of virtual wheel rotation force/wheel slip,
As a result, an at least approximately straight lower part of the dry road slip characteristic curve is formed.

During other driving operations of the vehicle, the circumferential force of the wheels/
If a pair of values of wheel slip occurs or is detected and the wheel slip λ is significantly greater than the wheel slip of a prestored pair of values with the same magnitude of wheel rotation force K, this can be monitored. It is evaluated as an obvious deterioration of the friction conditions between the tires of the drive wheels and the road. In a simple manner, a detected significant deterioration of the friction conditions is then communicated, for example to the vehicle driver, with a suitable warning signal or, if appropriate, used for appropriate control access.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below with reference to drawings showing embodiments.

The drawing shows, in principle, in FIG. 1, ie, not to scale, the normal slip characteristic curve in the form of the wheel circumferential force K as a function of the wheel slip λ, and the friction coefficient μ as a parameter.
It is shown with In this case, .mu.1 is, for example, the coefficient of friction associated with a completely frozen road, and .mu.n is the coefficient of friction associated with a well-dried road. In the small region indicated by M, that is to say in the region of relatively small wheel orbiting force and small wheel slip, the characteristic curve is shown extremely strongly enlarged. In this small range, the individual characteristic curves, which are at least approximately straight, have clearly different curve slopes dK/dλ. Therefore, when using correspondingly precise measuring devices or sensor devices and/or adopting correspondingly precise measuring methods, the various characteristic curves or the frictional conditions prevailing between the tires of the wheels to be monitored and the road This makes it possible to make reliable distinctions with sufficient accuracy for practical use.

In the drawing of FIG. 2, the minute area M shown in FIG.
An enlarged cutout is shown. The method according to the invention will be explained by way of example on the basis of this cutout. As already explained, during static or quasi-static driving conditions at the driven wheels of the vehicle to be monitored, only relatively small circling forces are available here to overcome rolling resistance, etc. , the wheel slip λ and the simultaneously acting wheel orbiting force K are detected in successive order. In this case, the value pairs of wheel circumferential force/wheel slippage, which are detected at least in the case of approximately dry roads, are stored. In Fig. 2, in the case of a dry road (friction coefficient μn), wheel slippage λm1' with the associated wheel orbiting force K1 is detected, and it is assumed that a certain variation range actually occurs with respect to the detected value. be done. This is indicated by the corresponding box in FIG. Since the wheel circumferential forces acting on the driven wheels are not constant even in static or quasi-static driving conditions, it is thus possible (in each case with the above-mentioned constant dispersion) to obtain exactly the effective slip characteristic curve. Various such wheel circumferential force/wheel slip value pairs (here with a friction coefficient μn) are automatically detected. In FIG. 2, a pair of two such values with wheel orbiting forces K2 and K3 is shown in dashed lines. Knowing such a pair of two values, which are sufficiently spaced from each other, it is easy to understand that the rise of the effective slip characteristic curve, the so-called slope of the circling force, can also be understood.

In the course of the running motion, as shown in the left part of FIG. 2, an unexpected wheel rotation force/wheel slip value pair, for example K1/λm1'', is detected, in which case each wheel slip value is If is significantly larger than the previously examined and memorized pair of values with wheel rotation forces of approximately the same magnitude, this situation indicates that the friction between the tires of the drive wheels being monitored and the road is significantly worse. This reliably indicates that the vehicle is not traveling on a well-dry roadway during that time, but on a muddy or completely icy roadway. This significant change can be easily utilized by the electronic evaluation and control circuit to output a signal to communicate or warn the driver of the vehicle.This can therefore be used to adapt the vehicle's driving style and speed to the deteriorating situation. Therefore, there is no need to be surprised if the vehicle loses friction when driving around curves and/or when applying the brakes.

[0021] Knowledge of the increase in wheel rotation force, that is, knowledge of the increase in the curve of the slip characteristic curve that is effective at that time, includes at least the magnitude of the effective coefficient of friction (μmax) or the maximum possible wheel rotation force in this roadway condition. It is easy to see that knowledge about Kmax is relevant. Because,
This is because there is a constant relationship between the slope of the slip curve and the maximum value of the curve. On the other hand, the maximum possible wheel rotation force Kmax determined from the increase in the effective wheel rotation force,
On the other hand, the instantaneous wheel rotation force that actually acts (for example, K
1) By knowing the above, the electronic evaluation and control circuit can provide an expression regarding the magnitude of the frictional capacity at that time, that is, an indication of how far the actual wheel orbiting force K is approximately from the maximum possible wheel orbiting force Kmax. I can do it.

[0022] Knowing at least the magnitude of the maximum possible wheel turning force Kmax at that time allows the electronic circuit of the vehicle to determine, for example, the safety state, curve speed limit, maximum speed, braking force characteristics, etc., for example, in the future vehicle guidance system. It is important to find out within the framework of

In the case of known anti-skid control devices and/or driving anti-skid control devices that operate during unstable driving conditions (deceleration and/or acceleration), the monitoring, ie deceleration or drive The instantaneous slip of a vehicle wheel is generally calculated from the rotational speed or rotational speed of the monitored vehicle wheel on the one hand and the freely rotating vehicle wheel on the other hand. In order to determine the rotational speed of the wheels, digital wheel sensors are used which generally have pulse wheels with slits, holes or teeth that generate signal pulses.

As already explained, during steady or quasi-steady driving conditions, the values of the wheel slip that can be evaluated and the differentiation of the significant wheel slip values can only be determined using high-precision measuring devices and/or in the measuring direction. be measured. These high demands are not really met by the digital wheel sensors and electronic evaluation and control circuits for generating signal pulses used in known anti-skid control devices and/or drive anti-skid control devices.

Nevertheless, the method according to the invention for monitoring the slippage of the wheels of a driven motor vehicle between the tires and the roadway is proven in practice and has a relatively low cost due to mass production. Known digital wheel sensors can be used. This means that the wheel slip of the vehicle being monitored is not measured as an instantaneous amount, but as a time interval of a constant length.
For example, over an interval of 1 to 2 seconds or over a certain distance section, the sum of the slip amounts or the average wheel slip value λm is expressed by the relational expression λm = (SA - SN )/SN
It is found according to. Here, SA means the sum of signal pulses generated by the wheel sensors of the driven wheels monitored during a fixed time interval or distance interval, and SN means the sum of the signal pulses generated by the wheel sensors of the driven wheels during a fixed time interval or distance interval, and SN means the sum of the signal pulses of the wheels of the vehicle that are not driven, i.e. free-rotating. It means the sum of signal pulses generated simultaneously by the wheel sensors.

With these methods, larger pulses are used. A sufficiently high measurement accuracy is therefore obtained for the method according to the invention.

A further improvement in measurement accuracy is achieved by not simply counting the teeth or holes or slits of a rotating pulse wheel or disc that pass close to the actual sensor;
This is achieved when teeth, holes, etc. are scanned at a high frequency in each case. In this way, the minimum error is no longer "tooth" or "
It is determined not by the smallest units of holes or slits, but by very small individual pulses scanned at high frequencies.

The relational expression λm = (SA −SN
)/SN applies without restriction as long as the wheel sizes of the driven and undriven vehicle wheels, ie, the free-spinning "reference" wheels, are of the same size.

In order to obtain as accurate a result as possible, in particular with respect to the duration, it is therefore possible to detect any wheel size differences that occur during the driving period (therefore, without any particular action on the part of the driver). It is advantageous if electronic evaluation and control circuits are repeatedly balanced and calibrated to take into account differences in performance (which may occur at any time). This situation can easily occur during periods of operation of a non-driving vehicle. During this period, the vehicle runs without any driving force (
For example, if the vehicle gradually comes to a stop or changes gears). In the case of a vehicle that is coasting without a drive, no orbital forces are transmitted to the wheels of the vehicle that is being driven, as long as normal roll resistance forces are ignored. In such conditions, the wheel slip that occurs is normally equal to zero. The difference between the sum of the two signal pulses generated by the wheel sensors of the monitored drive wheel and the essentially free-rotating non-drive wheel that occurs during such a drive leg has a different effect. It only represents the "apparent slippage" caused by the size of the wheels. When examining wheel slippage, this apparent slippage is
It is easily calculated by the calibration factor k=SNO/SAO. Here, SNO is the sum of signal pulses generated by the wheel sensors of the non-driven wheels of the vehicle during a time interval of a certain length or a certain distance interval, and SAO is the sum of signal pulses generated by the wheel sensors of the non-driven wheels of a vehicle during a time interval of a certain length or a certain distance represents the sum of signal pulses produced by the wheel sensors of a vehicle wheel that has been driven and monitored during a distance interval of , but is now free rotating. The average wheel slippage value λm is determined by the relational expression λm = (SA k-
SN)/SN.

[0030] In any suitable non-driving periods that occur during driving, when carried out in this manner, it is advantageous to constantly activate the calibration factor k. Through constant activation of the calibration coefficients, which represents a type of driving process, even fairly significant changes are automatically detected and taken into account, for example when installing winter tires or parts of a vehicle's wheels. It is easy to see that the installation of new tires can be automatically detected and taken into account only when new tires are installed.

[0031]Changes that take place over a relatively short period of time compared to the size of the associated wheel, such as can occur, for example, due to changes in tire temperature, are not necessarily compensated to the desired extent by the calibration process. This is because non-driving periods suitable for this calibration occur only rarely during normal driving.

Therefore, with the aid of repeated measurements of the engine braking state during driving, it is possible to perform a zero point calibration of the average wheel slip value λm of the wheel in question being monitored or of the characteristic curve of wheel circumferential force/wheel slip. It's advantageous. Such engine braking periods occur relatively frequently during normal road driving by "off the gas pedal." The engine traction torque acting in this case is a relatively small and reproducible value. The resulting (negative) wheel rotation forces are therefore easily calculated and measured at the wheels of the vehicle being monitored.

Negative lap forces result from the zero point of the lap force/wheel slip characteristic curve of the tire in question. Since the slip characteristic curve is point symmetric with respect to the origin under uniform conditions,
In the case of a known (negative) wheel rotation force (calculated from the measured or known engine traction torque) and a negative wheel slip average value (measured by the wheel sensor), determine the zero point of the slip characteristic curve field. It can be inspected or operated repeatedly.

The wheel circumferential force K of the wheels of the vehicle being monitored cannot be determined purely numerically (from the engine traction torque) only during the above-mentioned calibration process or during the above-mentioned zero point determination. It is generally possible to determine each effective wheel rotation force purely numerically. This is because the engine characteristic data at that time is known. Furthermore, it is of course also possible to measure the wheel circumferential forces with the aid of known strain gauge devices.

Constant recalibration or zero-point checking or monitoring during periods of engine braking makes it especially easy to use particularly quantitative methods, such that a decrease in the friction coefficient value of about Y percent can be directly estimated from an increase in wheel slip of X percent. enable expression.

[0036] To carry out the monitoring method according to the present invention,
It is advantageous to use an electronic evaluation and control device equipped with a known microprocessor or the like. These microprocessors can be easily programmed according to individual needs. For example, in a main program, the measured or calculated wheel circumferential forces and the distance measurements or signal pulses supplied by the various wheel sensors are read repeatedly in the main program;
From these values, the sum of slips or the average wheel slip value λm
In addition, the wheel circumferential force and the wheel slip average value can be correlated and, if necessary, stored. In intermediate and/or post-connected lower level programs, etc.
On the one hand, it is necessary to form the calibration coefficients or to locate and operate the zero points of the slip characteristic curve field, and on the other hand to determine the wheel circumferential forces and to locate clearly "highly outlying values" or to eliminate the calculated values. , it is possible to newly obtain each time and compare the (average) values of the wheel orbiting force and wheel slip read with the stored values.

[0037]

[Effect of the invention] As explained above, with this invention,
A simple and yet reliable method is obtained compared to known methods for monitoring the frictional forces between the tires of the wheels of a driven motor vehicle and the road.

[Brief explanation of the drawing]

FIG. 1 is a graph of a slip characteristic curve in which the wheel circumferential force K is a function of the wheel slip λ and the friction coefficient μ is used as a parameter.

FIG. 2 is an enlarged view of a minute region M in FIG. 1.

[Explanation of symbols]

K Wheel rotation force Kmax Maximum possible wheel rotation force λ Wheel slippage λmax Average value of wheel slippage μ Friction coefficient μ1 Friction coefficient of frozen roadway μn
Friction coefficient M of a well-dried roadway Minuscule area SA of the slip characteristic curve Sum of signal pulses output from sensors on driving wheels during a certain period SN Sum of signal pulses output from sensors on non-driving wheels during a certain period k Calibration coefficient SNO Sum of signal pulses output from sensors on non-driving wheels during a certain period SAO Sum of signal pulses output from sensors on driving wheels during a certain period

Claims (11)

[Claims] 1. A method for monitoring a frictional coupling between a tire of a driven wheel and a road, comprising: a) a wheel orbiting force (K) acting simultaneously with a wheel slip (λ) of the driving wheel being monitored; and during quasi-steady driving conditions, i.e. measured in a constant sequence within a small area of the known wheel circumferential force/wheel slip characteristics curve field, in which case the measurement of wheel slip (λ) is in the range 0/∞. done with precision; b)
memorize the pair of wheel orbiting force/wheel slip values determined on at least a generally dry roadway; c) the wheel slip (λ) is greater than the wheel slip of the previously stored pair of wheel orbiting force/wheel slip values; Significantly large subsequently occurring or detected wheel rotation force/wheel slip value pairs are evaluated as an indication of a significant deterioration of the frictional coupling conditions and, if appropriate, are used to issue a warning signal or to access the control. A method characterized by using. 2. Using a digital wheel sensor that generates signal pulses that continuously measures the wheel rotational speed or wheel orbital speed of the drive wheel being monitored and at least one non-drive wheel, During a time interval or a certain distance interval, the relational expression λm = (SA - SN)
/ SN The average wheel slip value λm (sum of slips) is stored and evaluated as wheel slip each time, and in this case, SA and SN are each monitored during the fixed time interval or distance section. 2. A method as claimed in claim 1, characterized in that it is a sum of signal pulses originating from a wheel sensor of a driven wheel and from a wheel sensor of a non-driven wheel. 3. The average wheel slip value that is stored and evaluated as wheel slip is determined by the relation λm = (SA k - SN
)/SN, where k is formed by the ratio of the sum of the signal pulses SNO and SAO of the non-driven wheel and the driven wheel, respectively, which occur when the wheels are running freely. 3. The method according to claim 2. 4. The calibration coefficient k is constantly operated during a ratio drive operation period (for example, when gradually reducing speed or when changing gears) that occurs during a driving operation. the method of. 5. In order to take into account tire parameters, such as tire temperature, which change over a particularly short period of time during driving,
Perform a zero point calibration of the wheel slip mean value λm or the characteristic curve of wheel orbiting force/wheel slip for the wheel in question, which is monitored with the aid of repeated engine brake measurements, in which case a negative wheel slip mean value (-λm) is detected by the wheel sensor. The associated negative wheel rotation force (-K) can be measured or directly calculated from a reproducible and relatively small engine traction torque. The method according to any one of claims 1 to 4, characterized in that: 6. The wheel circumferential force (K) is determined in each case by a measurement technique using a strain gauge device or by calculation from the engine characteristic data at that time. Method described. 7. The rise of the wheel orbiting force, that is, the slope in the minute region of the characteristic curve K=f(λ, λm) attached to the pair of measured wheel orbiting force/wheel slippage values is determined, and from this value. The method according to any one of claims 1 to 6, characterized in that the magnitude of the dominant friction coefficient μmax or the maximum possible wheel rotation force Kmax under the current situation is estimated. [Claim 8] The rise of the determined wheel circumferential force and the determined wheel slip (λ) or wheel slip average value (λm
8. The method according to claim 7, wherein the actually usable frictional coupling capacity is estimated from the magnitude of ). 9. A pulse generator with a slotted, perforated or toothed pulse wheel or disc is used as a digital wheel sensor from the anti-slip control and the drive slip control. The method according to any one of claims 2 to 8, characterized in that: 10. Method according to claim 9, characterized in that the gaps between the teeth of the pulse wheel or the disk, or the webs and slits, etc. are scanned with high frequency. 11. A device for monitoring a frictional coupling between a tire of a wheel of a driven motor vehicle and a road, as claimed in claim 1.
Device characterized in that it uses an electronic evaluation and control device with a microprocessor known per se programmed to carry out the method according to any one of claims 1 to 10.