WO1999008914A1

WO1999008914A1 - Method and device for determining the reference speed in an vehicle

Info

Publication number: WO1999008914A1
Application number: PCT/EP1998/005085
Authority: WO
Inventors: Andreas Herp
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 1997-08-16
Filing date: 1998-08-11
Publication date: 1999-02-25
Also published as: DE19735562B4; DE19735562A1; EP1005423A1; JP2001514992A

Abstract

The invention relates to a method and device for determining a reference speed in a vehicle. The aim is to provide an economical method and device which will enable the reference speed of a vehicle to be determined accurately and reliably. To this end, the wheel speeds of at least two wheels (111, 121) of the vehicle are measured (112, 122). The wheel speeds of at least two wheels are then taken into account in calculating the reference speed (113). The invention can be used in both vehicle traction control systems or anti-slip systems and anti-locking systems, especially in an all-wheel drive passenger vehicle, for example a four-wheel drive passenger vehicle.

Description

Method and device for determining the reference speed in a motor vehicle

The present invention relates to a method and a device for determining a reference speed in a motor vehicle, in particular in a four-wheel drive passenger car, for example in a four-wheel drive passenger car. The present invention can be used both in traction control systems or in anti-slip systems and in anti-lock braking systems in a motor vehicle.

With traction control or traction slip systems, it is necessary to regulate the driving forces acting on each driven wheel so that no driven wheel overturns, that is to say that the tangential speed of the outer wheel circumference of the driven wheel is as close as possible to the actual speed of the vehicle in the direction of travel. This ensures optimal vehicle acceleration.

With anti-lock braking systems, it is necessary to regulate the braking forces acting on each braked wheel so that none braked wheel is braked and thus tends to lock, that is, the tangential speed of the outer wheel circumference of the braked wheel is as close as possible to the actual speed of the vehicle. This ensures an optimal deceleration of the vehicle.

For these two tasks, it is necessary to determine the tangential speed of the outer wheel circumference of the driven or braked wheel of the vehicle. For this purpose, a corresponding sensor is attached to each wheel, which detects the number of revolutions of the respective wheel per unit of time. The circumferential speed of the respective wheel is calculated from this using the known radius of the wheel.

In addition, for these two tasks it is necessary to determine the reference speed, that is the actual speed of the vehicle in the direction of travel.

With non-all-wheel drive vehicles, the determination of the reference speed in the

Acceleration occurs relatively easily and reliably based on the tangential speed of the outer wheel circumference of a non-driven wheel, which is not affected by a drive torque. However, even in the case of non-all-wheel drive vehicles, the reference speed is no longer so easy to determine when braking, since even with multi-circuit braking systems, braking forces always act on each wheel of the vehicle in normal operation.

In known methods and devices, acceleration sensors are used to determine the reference speed. A disadvantage of this is that the acceleration sensors in question are expensive and significantly increase the costs for the overall system.

In other known methods, the tangential speed of the outer wheel circumference of the slowest rotating wheel is used as the reference speed of the vehicle in the event of acceleration. In the event of a delay, the

Tangential speed of the outer wheel circumference of the fastest rotating wheel is used as the reference speed of the vehicle. This method has the disadvantage that it allows an inaccurate and under certain conditions very unreliable determination of the reference speed.

US Pat. No. 4,969,100 describes a device for determining the reference speed in an automobile, which has a speed sensor on each wheel and in which for determining the reference speed one of the wheels or the Speed of one of the wheels is selected by selection means, and the reference speed of the automobile is determined based on the speed of that one selected wheel by performing a calculation.

This method also has the disadvantage that it allows an inaccurate and, under certain conditions, very unreliable determination of the reference speed.

The invention ^'is therefore based on the problem to provide a method and a device which allow a precise and reliable determination of the reference speed of a motor vehicle; in addition, the method and the device should be able to be implemented inexpensively.

The method and the device should also allow an accurate and reliable determination of the reference speed of a motor vehicle both for the acceleration case and for the deceleration case.

The problem is solved by the methods and devices disclosed in the independent patent claims. Particular embodiments of the invention are disclosed in the subclaims. In a method for determining a reference speed of a motor vehicle, the problem is solved according to the invention in that wheel speeds are measured on at least two wheels of the motor vehicle and the reference speed is calculated taking into account the wheel speeds of at least two wheels.

The reference speed is the actual speed in the direction of travel of the vehicle. The wheel speed is the tangential speed of the outer wheel circumference; it is determined from the frequency of rotation of the wheel, taking into account the wheel diameter, possibly also taking into account the speed-dependent wheel diameter. Various sensors are known from the prior art for determining the rotational frequency of the wheel, for example those with a mechanical, electrical, optical or magnetic sensor principle.

Taking into account the wheel speeds of at least two wheels has the advantage that an accurate and reliable determination of the reference speed of the motor vehicle is ensured; in addition, the method and the associated device can be implemented inexpensively, since the need for a cost-intensive acceleration sensor is eliminated. It is also advantageous that the method and the associated device ensure an accurate and reliable determination of the reference speed of a motor vehicle both for the acceleration case and for the deceleration case.

In a special embodiment of the invention, the wheel speeds are measured on all wheels of the motor vehicle and the reference speed is calculated taking into account the wheel speeds of all wheels. This has the advantage that an accurate, reliable and inexpensive determination of the reference speed of the motor vehicle is ensured both in two-wheel drive vehicles and in all-wheel drive vehicles.

In a further special embodiment of the invention, the reference speed is calculated at discrete times with a sufficiently high repetition frequency using a recursive calculation rule.

This has the advantage that digital electronic circuits can also be used for the calculation, as a result of which a high computing speed and high computing accuracy can be achieved with low costs and low energy consumption for the associated computing means. It is also advantageous that the input variables for the calculation can be simply filtered and subjected to statistical processing, for example a moving averaging, which further increases the accuracy of the calculated reference speed.

In a further special embodiment of the invention, the reference speed v _ref (t _{n + 1} ) is calculated at the time t _{n + 1} from the reference speed v _ref (t _n ) at the ^* time t _n according to the recursive calculation rule

V _re _ (t _{n +} _) = v _{re £} (t _n ) + w (t _n ) ^■ a _mot (t _n ) ^■ Δt

where w is a weighting factor that is determined empirically, a _{mot is} a maximum possible acceleration derived from the engine torque, and Δt is the time difference between the times t _n and t _{n + 1} , and preferably the weighting factor w is dependent on the speed that Acceleration and the slip of the wheels of the motor vehicle, and is taken from electronically stored tables, and further preferably the maximum possible acceleration a _mot derived from the engine torque is corrected taking into account an effective braking torque. The acceleration and the slip of the wheels of the motor vehicle can be determined from the time course of the speed of rotation in comparison with the reference speed. This has the advantage that the reference speed can be calculated very quickly and with a high repetition frequency and at the same time with high accuracy, and that even in critical driving situations, such as in different road conditions under all four wheels of a vehicle, for example ice, snow, wet and dry asphalt, a quick and reliable determination of the reference speed is possible, which in combination with an anti-slip or anti-lock device of the vehicle ensures stable and safe driving. The removal of the weighting factors from electronically stored tables has the advantage that the corresponding weighting factors, for example in the form of a programmable memory (PROM, EPROM or EEPROM) in the vehicle control system individually for different vehicle types of a manufacturer or for different areas of application of a vehicle, also by the Customer service or the workshop on site, can be plugged in and / or exchanged.

In a further special embodiment of the invention, the motor vehicle has an acceleration sensor and the vehicle speed is also determined by means of the acceleration sensor, for example by integrating the output signal of the acceleration sensor over time, and the vehicle speed determined by the acceleration sensor is determined by the Reference speed compared. This has the advantage that when using an inertial-based acceleration sensor that always detects the acceleration due to gravity, and whose output signal is therefore dependent on the orientation of the acceleration sensor and thus of the motor vehicle in relation to the horizontal, it can be determined by comparing the two speeds. whether the vehicle is currently driving uphill or downhill. This additional information can be used for other, also safety-specific, controls of the vehicle.

In a further particular embodiment of the invention, a wheel is selected as the stable wheel, taking into account the speed, the acceleration and the slip of the respective wheel, and provided that the respective wheel is not currently subjected to braking forces, the speed of the stable wheel compared with the determined reference speed, and preferably the reference speed is adjusted to the speed of the stable wheel if the comparison yields a difference.

This has the advantage that a check of the calculated reference speed and, if necessary, an adjustment is possible with the parameters already determined, whereby the reliability of the determination of the reference speed is further increased. The teaching of the present invention also includes a device for determining a reference speed in a motor vehicle, which has sensors for recording wheel speeds, electronic data storage means and electronic computing means, and which carries out a method of the type described above.

The teaching of the present invention also includes a data carrier which stores a computer program and / or associated data, the computer program executing a method of the type described above or providing the data associated with this method, or the computer program having a device of the type described above. controls described type or provides the data associated with the control of this device.

This has the advantage that the computer program and / or the associated data, for example in the form of a programmable memory (PROM, EPROM or EEPROM) in the vehicle control system individually for different vehicle types of a manufacturer or for different areas of application of a vehicle, also by customer service or the workshop can be plugged in and / or exchanged on site.

One way of carrying out the claimed invention is explained in detail below with reference to the drawings. Show it :

Figure 1 is a schematic representation of the method for determining a reference speed of a motor vehicle and the integration of this method in the control loop of an anti-slip or anti-lock device.

2 shows a special embodiment of the method according to FIG. 1.

Figure 3 is a table for assigning a weighting factor.

FIG. 1 shows a schematic illustration of a method for determining a reference speed of a motor vehicle and the integration of this method in the control loop of an anti-slip or anti-lock device of the motor vehicle.

At a first wheel 111, the wheel speed is over a corresponding transducer 112 _v. of the first wheel 111 determined. The wheel speed v _{2 of} the second wheel 121 is determined on a second wheel 121 via a corresponding measurement sensor 122. From the two wheel speeds! and v ₂ is in a calculation step 131 calculates the reference speed v _{re £} ; the reference speed v _ref in particular as a function of the time profile of the two wheel speeds _v. (t) and v ₂ (t) are calculated.

By comparing 141 the reference speed v _ref with the two wheel speeds v _γ and v ₂ , in the context of an anti-slip or anti-lock device of the motor vehicle, corresponding control channels 113, 123, for example electrical, optical, mechanical, pneumatic or hydraulic control channels, e ne actuation or release of the brakes 114, 124 on the respective wheels 111, 121 controlled.

If, for example in the case of an anti-slip control, the comparison reveals that the wheel speed v of the wheel 111 is significantly higher than the calculated reference speed v _{re £} , the brake 114 on the wheel 111 is actuated via the control channel 113, for example via the closing or Opening hydraulic valves within the brake system.

If, in the other case of an anti-lock control, the comparison shows that the wheel speed v _{2 of} the wheel 121 is significantly lower than the calculated reference speed v _{re £} , the brake 124 on the wheel 121 is released via the control channel 123, for example by opening or closing hydraulic valves within the braking system. FIG. 2 shows a special embodiment of the method according to FIG. 1. In this embodiment, the wheel speeds Vj are measured using appropriate sensors 210 _. (i = 1, 2, 3, 4) of the four wheels 211, 212, 213, 214 of a motor vehicle. The wheel accelerations a _x (i = 1, 2, 3, 4) of the four wheels 211, 212, 213, 214 are calculated from the time profile of the wheel speeds v. Furthermore, the respective slip s (i = 1, 2, 3, 4) of the four wheels 211, 212, 213, 214 is calculated from the wheel speeds v _x and the respectively valid reference speed v _{re £} .

Weighting factors w _^ (i = 1, 2, 3, 4) are determined (220) from the parameters v _{ι r} a and s _x for each of the four wheels 211, 212, 213, 214, and these weighting factors are stored electronically or at least read out tables 221 that can be read out electronically. Each of these tables is valid for a certain speed range and assigns exactly one weighting factor w _± to each slip / acceleration pair (s / a) of a wheel i within this speed range. An example of such a table is shown in FIG. 3 and is described in more detail below. From the weighting factors w (i = 1, 2, 3, 4), an average weighting factor w is formed by averaging 221, which is used for the further calculation of the reference speed. Statistical methods can also be used in averaging in order to achieve the most reliable averaging possible and, for example, to eliminate an "outlier" from the weighting factors.

Depending on the number of open differentials in the motor vehicle, the weighting factors of all wheels have to be taken into account when averaging or, for example, only the minimum weighting factors of the wheels of an axle if the differentials between the axles are open.

In parallel with the determination of the weighting factors w, a maximum possible acceleration of the motor vehicle a _mot 230 is derived from the drive torque M _mot 231 provided by the engine, taking into account an effective braking torque Λf _rems 232. The drive torque M _mot 231 supplied by the motor, like the effective braking torque M _brakes 232, can generally be found in the information bus of the motor vehicle, for example a CAN bus. The maximum possible acceleration of the motor vehicle a _mot 230 can be derived from these moments, taking into account vehicle-specific variables, such as mass and drag coefficient, and the current driving state, such as speed and gear. In a calculation step 240, the parameters provided in this way become the reference speed v _{re £} (t _{n + 1} ) at the time t _{n + 1} from the reference speed v _ref (t _n ) at the time t _{n in} accordance with the recursive calculation rule

V _r βf (t _{n +} _) = v _zet (t _a ) + w (t _n ) ^■ a _mot (t _n ) ^■ Δt

calculated, where w is the average weighting factor, a _{mot is} the maximum possible acceleration derived from the engine and braking torque, and Δt is the time difference between the times t _n and t _{n + 1} .

In parallel to the calculation 240 of the reference speed v _{re £} , the vehicle speed v _{sens can be determined} in an additional manner 251 by means of an acceleration sensor in the motor vehicle, the output signal of which is integrated over time. In the case of an inertia-based acceleration sensor which always detects gravitational acceleration and whose output signal is therefore dependent on the orientation of the acceleration sensor and thus of the motor vehicle with respect to the horizontal, a comparison of the two speeds v _{re £} and v _sens can be used to determine whether the vehicle is currently driving uphill or downhill.

For example, when driving uphill it is recognized if the speed determined by the acceleration sensor is lower than the reference speed for a longer period of time. In the other case, when driving downhill, it is recognized if the speed determined by the acceleration sensor is greater than the reference speed for a longer period of time.

Overall, the method according to the invention turns the output variables from the input variables engine speed, gear stage, sensor acceleration, maximum acceleration, wheel acceleration, wheel slip and wheel speed derived from the engine torque

Reference speed, pitch angle in the direction of travel and wheel friction coefficient determined.

In addition, taking into account the weighting factors w of the wheels, at least one so-called “stable” wheel is selected 261.

A stable wheel is to be understood as a wheel whose wheel speed is very close to the actual speed of the motor vehicle in the direction of travel. A wheel is then recognized as a stable wheel if the associated weighting factor w is 100%, the wheel brake pressure is below a predetermined value for a certain period of time, for example less than 3 to 5 bar, no pressure build-up phase is recognized for the wheel, and that Wheel has been recognized as stable for a certain period of time. The calculation of the reference speed v _ref is checked for its plausibility by a comparison 260 of the reference speed v _{re £} and the wheel speed v _{stable of} the stable wheel. If this comparison 260 shows a significant deviation of the two speeds v _ref and v _stabι i, then the reference speed v _{re £ is} matched to the speed of the stable wheel v _sta bιi-

If a stable wheel is detected whose speed v _{stab is} below the reference speed v _{re £} , then the reference speed v _{re £} (t _{n + 1} ) at the time t _{n + 1} from the reference speed v _{re £} ( t _n ) at time t _n according to the recursive calculation rule

V _ref (t _{n + 1} ) = V _rβf (t ")" W _βtabll (t _n ) 'a _neg ^■ Δt

calculated, where w _{stabll is} the weighting factor of the stable wheel, a _{neg is} a maximum possible deceleration, and Δt is the time difference between the times t _n and t _{n + 1} . The weighting factor w _{stabll of} the stable wheel is taken from a table, depends on the slip and the brake pressure on the respective wheel and is determined empirically. If a stable wheel is detected, whose speed v _{stab is} above the reference speed v _{re £} , the reference speed v _{re £} (t _{n + 1} ) at time t _{n + 1 is} derived from the reference speed v _{re £} ( t _n ) at time t _n according to the recursive calculation rule

V _re (t _{n + 1} ) = v _ref (t _n ) + (v _stab (t _n ) - v _re _ (t _n )) = v _{Btab- 1} ( _n )

determined.

FIG. 3 shows a table for the assignment of a weighting factor w as a function of the acceleration a _x and the slip s _{x of} a wheel i (i = 1, 2, 3, 4) within a speed range for the wheel speed v _x .

The acceleration a _x is specified in the unit g, whereby approximately 1 g = 10 ms ^-2 applies. The slip s is given in absolute values of the difference between the wheel speed and the vehicle speed in the unit kmlr ¹ . The numerical values for the weighting factors w are given in%.

The table given applies to a certain range of the wheel speed v _{x of} the wheel i, for example for the range 20 to 30 kmhX. In this speed range, for example, a wheel acceleration of 1.75 g and a slip of 5 kmh results in ^{" 1} a weighting factor of 20% for the wheel i. Generally it can be said that a high acceleration and / or a large slip result in a low weighting factor and vice versa. This is due to the connection, known from the literature, between the coefficient of adhesion, drive slip and vehicle speed.

Claims

claims

1. A method for determining a reference speed of a motor vehicle, comprising the steps:

Measuring (112, 122) a wheel speed on at least two wheels (111, 121) of the motor vehicle,

characterized by the step:

Calculate (131) the reference speed taking into account the wheel speeds of at least two wheels (111, 121).

2. The method according to claim 1, characterized by

Measuring (112, 122) the wheel speeds on all wheels of the motor vehicle, and

Calculate (131) the reference speed taking into account the wheel speeds of all wheels.

3. The method according to claim 1 or 2, characterized by calculating the reference speed at discrete times and with a sufficiently high repetition frequency, and using a recursive calculation rule for calculating the reference speed.

4. The method according to claim 3, characterized by calculating the reference speed v _{re £} (t _{n + 1} ) at the time t _{n + 1} from the reference speed v _{re £} (t _n ) at the time t _n according to the recursive calculation rule

v _ref (t _{n + 1} ) = v _ref (t _n ) + w (t _n ) ^■ a _mot (t _n ) ^■ Δt

where w is a weighting factor that is determined empirically,

a _{mot is} a maximum possible acceleration derived from the engine torque, and

Δt the time difference between the times t _n and tn + _l ISt.

5. The method according to claim 4, characterized in that the weighting factor w is dependent on the speed v, the acceleration a and the slip s of the wheels of the motor vehicle, and is taken from electronically stored tables (221).

6. The method according to claim 4 or 5, characterized in that the maximum possible acceleration a _mot derived from the engine torque is corrected taking into account an effective braking torque M _brakes .

7. The method according to any one of the preceding claims, wherein the motor vehicle has an acceleration sensor, characterized by

Determining (251) the vehicle speed by means of the acceleration sensor, and

Compare (250) the vehicle speed v _sens determined with the acceleration _sensor and the reference speed v _{re £} .

8. The method according to any one of the preceding claims, characterized by

Select (261) a wheel as a stable wheel

taking into account the speed, acceleration and slip of the respective wheel,

and provided that the respective wheel is not currently subjected to braking forces, and comparing (260) the speed of the stable wheel with the determined reference speed.

9. The method according to claim 8, characterized by adapting the reference speed to the speed of the stable wheel when the comparison (260) results in a difference.

10. The method according to any one of the preceding claims, characterized in that the vehicle is an all-wheel drive passenger car.

11. Device for determining a reference speed in a motor vehicle, the device comprising:

Sensors for recording wheel speeds, electronic data storage means and electronic

Computing means, characterized in that the device carries out a method according to one of the preceding claims.

12. A data carrier that stores a computer program and / or associated data, characterized in that the computer program executes a method according to one of claims 1 to 10 or provides the data associated with this method, or that the computer program controls a device according to claim 11 or provides the data associated with the control of this device.