JP2001514992A - Method and apparatus for determining a reference speed of a motor vehicle - Google Patents

Abstract

The present invention relates to a method and an apparatus for determining a reference speed of a motor vehicle. It is an object of the present invention to provide a method and a device which enable an accurate and reliable determination of the reference speed of a motor vehicle. Furthermore, the method and apparatus should be able to be implemented at low cost. The problem is that in a method for determining a reference speed of a vehicle, according to the invention, the wheel speeds of at least two wheels (111, 121) of the vehicle are measured (112, 122) and the at least two wheels (111) are determined. , 121) to calculate the reference speed in consideration of the wheel speed (131). The invention is applicable to traction control systems or anti-slip and anti-lock systems for motor vehicles, especially all-wheel drive passenger vehicles, for example four-wheel drive passenger vehicles.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method and a device for determining the reference speed of a motor vehicle, in particular an all-wheel drive passenger vehicle, for example a four-wheel drive passenger vehicle. The present invention is applicable to a traction slip control system or an anti-slip system or an anti-lock system of an automobile.

In the case of a traction slip control system or an anti-slip system, the driven wheels are not over-rotated, ie the tangential speed around the driven wheels is as close as possible to the actual speed of the vehicle in the direction of travel. It is necessary to control the driving force acting on each driven wheel. Thereby, optimal acceleration of the vehicle is achieved.

In the case of an anti-lock system, each braked wheel is braked in such a way that it does not become overbrake, ie the tangential speed of the circumference of the wheel being braked is as close as possible to the actual speed of the vehicle. It is necessary to control the braking force acting on the wheels. Thereby, an optimal deceleration of the vehicle is achieved.

[0004] For both of these problems, it is necessary to detect the tangential speed of the periphery of the driven or braked wheels of the vehicle. For this purpose, a sensor for measuring the rotation speed of each wheel per unit time is attached to each wheel. Then, using the known radius of the wheel, the peripheral speed of each wheel is calculated.

[0005] Both of these tasks require a further detection of the reference speed, ie the actual speed of the vehicle in the direction of travel.

In the case of vehicles without all-wheel drive, the detection of the reference speed is relatively simple in the case of acceleration, and is reliably performed on the basis of the tangential speed of the outer periphery of the undriven wheel on which no driving torque acts.

Of course, even in the case of an automobile that is not all-wheel drive, the reference speed cannot be easily detected during braking. This is because, in the case of a multi-circuit brake system, a braking force always acts on each wheel of the motor vehicle during normal driving.

In known methods and devices, an acceleration sensor is used to detect a reference speed. In this case, the acceleration sensor is expensive and has a disadvantage that the cost of the entire system is greatly increased.

In another known method, when accelerating, the tangential speed around the circumference of the slowest rotating wheel is used as the reference speed of the motor vehicle. At the time of deceleration, the tangential speed on the outer periphery of the rapidly rotating wheel is used as the reference speed of the vehicle. This method has the disadvantage that the determination of the reference speed is inaccurate and is not reliable under certain conditions.

US Pat. No. 4,969,100 describes a device for determining a reference speed in a motor vehicle. The apparatus comprises a speed sensor for each wheel, and a single wheel or a speed of one wheel is selected by a selection means to measure a reference speed, and the vehicle is selected based on the selected speed. Is determined by calculation.

This method also has the disadvantage that the determination of the reference speed is inaccurate and is very unreliable under certain conditions.

It is therefore an object of the present invention to provide a method and a device which enable an accurate and reliable determination of the reference speed of a motor vehicle. Furthermore, the method and apparatus should be able to be implemented at low cost.

[0013] The method and apparatus should further allow for an accurate and reliable determination of the reference speed of the vehicle both during acceleration and during deceleration.

This problem is solved by a method and a device as disclosed in the independent claims. Particular embodiments of the invention are set out in the dependent claims.

[0015] In the case of a method for determining a reference speed of a motor vehicle, the object is, according to the invention, to determine the wheel speeds of at least two wheels of the motor vehicle and to take into account the wheel speeds of the at least two wheels. The problem is solved by calculating the reference speed.

The reference speed is understood to be the actual speed in the direction of travel of the vehicle. Wheel speed is the speed in the tangential direction around the wheel. The wheel speed is determined from the rotational frequency of the wheel, taking into account the wheel diameter and possibly the speed-dependent wheel diameter. For detecting the rotational frequency of the wheels, various pickups are known in the state of the art, for example pickups having a mechanical, electrical, optical or magnetic pickup principle.

Considering the wheel speed of at least two wheels, very accurate and reliable,
The advantage is that the determination of the reference speed of the motor vehicle is guaranteed. Further, the method and apparatus can be implemented at low cost. This is because no costly acceleration sensor is required.

It is a further advantage that the method and the device ensure an accurate and reliable determination of the reference speed of the vehicle both during acceleration and during deceleration.

In a special embodiment of the invention, the wheel speeds of all the wheels of the motor vehicle are measured, and the calculation of the reference speed takes into account the wheel speeds of all the wheels. This has the advantage that an accurate, reliable and low-cost determination of the reference speed of the vehicle is guaranteed for both two-wheel drive and all-wheel drive vehicles.

In another particular embodiment of the invention, the reference speed is calculated at a discontinuity at a sufficiently high repetition frequency using a recursive formula.

This has the advantage that a digital electronic circuit can be used for this operation, whereby a high operation speed and high operation accuracy can be achieved at low cost and with low energy consumption by the associated operation means. Having.

It is further advantageous if the input quantity is simply filtered for the operation and undergoes a static processing operation, for example a floating average calculation operation. Thereby, the accuracy of the calculated reference speed further increases.

In another particular embodiment of the invention, the reference speed v _ref (t _{n + 1} ) is at time t _{n + 1} , and from the reference speed v _ref (t _n ) at time t _n , It is calculated according to the following equation: v _ref (t _{n + 1} ) = v _ref (t _n ) + w (t _n ) · a _mot (t _n ) · Δt, where w is an average weight determined empirically. a coefficient, a _{mo t} is the maximum acceleration derived from the engine torque, and Δt is the time difference between the time point t _n and t _{n + 1.} In this case, preferably, the weighting factor w depends on the speed, acceleration and slip of the wheels of the motor vehicle and is determined from an electronically stored table,
Furthermore, the maximum acceleration a _mot derived in particular from the engine torque is corrected in view of the effective braking torque M _brems . The acceleration and slip of the wheels of the motor vehicle can be determined by comparing the rotational speed over time with a reference speed.

This means that the reference speed can be calculated very quickly and at a high repetition frequency and at the same time with a high degree of accuracy and, in the case of extreme conditions, for example in vehicles such as ice, snow, wet asphalt and dry asphalt. Has the advantage that it is possible to quickly and reliably determine a reference speed which guarantees a stable and safe driving operation in connection with the anti-slip device or anti-lock device of the vehicle, even in different road conditions for all four wheels. . Determining the weighting factor from an electronically stored table allows the weighting factor in the form of a programmable memory (PROM, EPROM or EEPROM) to be stored in the vehicle control unit, and for different types of vehicles of different manufacturers. Alternatively, it has the advantage that it can be stored and / or replaced at a service station or a local repair shop for different fields of use of the motor vehicle.

In another particular embodiment of the invention, the vehicle is provided with an acceleration sensor, the vehicle speed being determined by the acceleration sensor, for example by integrating the output signal of the acceleration sensor over time, and determined by the acceleration sensor. The vehicle speed is compared to a reference speed.

This is by comparing the two speeds when using an inertial based acceleration sensor, which always detects the gravitational acceleration and thus the output signal depends on the direction of the acceleration sensor with respect to the horizontal and thus on the direction of the vehicle. Advantageously, it can be determined whether the vehicle is currently traveling uphill or downhill. This additional information can be used for other control of the vehicle, i.e. for safety.

In another particular embodiment of the invention, a stable wheel is provided, taking into account the speed, acceleration and slippage of each wheel and assuming that each wheel is not currently energized with braking force. One of the wheels is selected as, and this stable wheel speed is compared with the detected reference speed, and especially when the comparison results in a difference, the reference speed is adjusted to the stable wheel speed.

This means that the calculated reference speed can be checked with the parameters already detected, and in some cases the reference speed can be adapted, thereby further increasing the reliability of the determination of the reference speed. There are advantages.

The invention further comprises determining a reference speed of a motor vehicle implementing a method of the type described above, comprising a sensor for sensing wheel speed, electronic storage means and electronic arithmetic means. Including a device for performing

The invention further comprises a data carrier for storing an arithmetic program and / or associated data. In this case, the arithmetic program implements a method of the aforementioned kind or prepares data related to this method, or the arithmetic program controls a device of the aforementioned kind or prepares data related to the control of this apparatus. I do.

This is a programmable memory (PROM, EPROM or EEPROM)
The operating program and / or the associated data in the form of an OM) can be stored in the vehicle control unit, and for different types of vehicles of the manufacturer or for different fields of use of the vehicle, individually for service stations or field repairs. It has the advantage that it can be stored and / or replaced at the factory.

Next, one embodiment for carrying out the claimed invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows a method for determining a reference speed of a motor vehicle and the incorporation of this method into the control circuit of an anti-slip or anti-lock device of a motor vehicle.

At the first wheel 111, the wheel speed v of the first wheel 111₁Is the measurement value pickup.
Is detected through the loop 112. In the second wheel 121, the wheel of the second wheel 121
Speed v_TwoIs detected via the measurement value pickup 122. Both wheel speed v₁, V _Two From the reference speed v_refIs calculated. Reference speed v_ref Is, in particular, a function v of the time course of the two wheel speeds.₁(t), v_TwoIt is calculated as (t).

By comparing 141 the reference speed v _ref with the two wheel speeds v ₁ , v ₂ , each wheel 1 within the range of the vehicle's anti-slip or anti-lock device.
The operation or release of the brakes 114, 124 of the 11, 121 is controlled via suitable control channels 113, 123, for example electrical, optical, mechanical, pneumatic or hydraulic control channels.

For example, in the case of anti-slip control, if the result of the comparison is that the wheel speed v ₁ of the wheel 111 is significantly higher than the calculated reference speed v _ref , the brake 114 of the wheel 111 will Operated by closing or opening hydraulic valves in the brake system.

In the case of the anti-lock control, as a result of the comparison, if the wheel speed v ₂ of the wheel 121 is significantly lower than the calculated reference speed v _ref , the brake 124 of the wheel 121
Is operated via the control channel 123, for example, by opening or closing a hydraulic valve in the brake system.

FIG. 2 shows a special implementation of the method shown in FIG. In this embodiment, the wheel speeds v _i (i = 1) of the four wheels 211, 212, 213, 214 of the vehicle
, 2, 3, 4) are detected via a suitable measured value pick-up 210. From the temporal course of the wheel speed v _i, the wheel acceleration a _{i (i} = 1,2,3,4) of the four wheels 211, 212, 213, and 214 is calculated. Further, the slip s _i (i = 1, 2, 3, 4) of each of the four wheels 211, 212, 213, 214 is calculated from the wheel speed v _i and each of the effective reference speeds v _ref .

For each of the four wheels 211, 212, 213, 214, the parameter v_i , A_i, S_iFrom the weighting factor w_i(I = 1, 2, 3, 4) is determined (220)
Moreover, this weighting factor is stored in the electronically stored table 221 or at least
Read from a child readable table. Each of these tables is for a given speed range
And within this speed range, the slip / acceleration pair (s_i/ A _i ) For the weighting factor w_iAssign exactly. An example of such a table is shown in FIG.
I have. Next, this table will be described in detail. Weighting factor w_i(I = 1, 2,
By calculating the average value from (3, 4) (221), the average weight coefficient is calculated.
You. This average weighting factor is used for subsequent calculations of the reference speed.

In determining the average value, a statistical method can be applied in order to obtain an average value that is as reliable as possible and to eliminate, for example, “outliers” of the weighting factors.

In determining the average value, depending on the number of open differential gears of the motor vehicle, the weighting factors of all wheels should be taken into account or, for example, when the differential is open between axles, 1 Only the smallest weighting factor of the wheels of the axle should be taken into account.

In parallel with the determination of the weighting factor w _i , the maximum acceleration a _mot 230 of the vehicle is derived from the driving torque M _mot 231 supplied from the engine, taking into account the effective braking torque M _brems 232. Drive torque M _mot 231 supplied from the engine
, As well as the effective brake torque M _brems 232, are generally information buses for vehicles,
For example, it is taken out from the CAN bus. The maximum acceleration a _mot 230 of the motor vehicle is derived from these torques, taking into account vehicle-specific quantities, such as, for example, mass and air resistance, and current driving conditions, such as, for example, speed and gear.

From the parameters prepared in this way, in a calculation step 240, the reference speed v _ref (t _{n + 1} ) is at time t _{n + 1} , and from the reference speed v _ref (t _n ) at time t _n , The calculation is performed according to the following inductive (recursive) operation expression: v _ref (t _{n + 1} ) = v _ref (t _n ) + w (t _n ) · a _mot (t _n ) · Δt Here, w is an average weighting factor, a _mot maximum acceleration and Delta] t, derived from the engine torque and braking torque is the time difference between the time point t _n and t _{n + 1.}

Reference speed v_refIn parallel with the calculation 240, the vehicle speed v_sensOutput signal in time
Integral vehicle acceleration sensors can be detected in additional ways. Always heavy
Force acceleration is detected, and the output signal is
In the case of an inertial-based acceleration sensor that depends on the direction of the car,_refAnd v _sens By comparing 250 the vehicle is traveling uphill or downhill
It can be detected whether the vehicle is traveling on a slope.

For example, when the speed detected by the acceleration sensor is lower than the reference speed for a long time, it is known that the vehicle is traveling on an uphill.

On the other hand, when the speed detected by the acceleration sensor is higher than the reference speed for a long time, it is known that the vehicle is traveling on a downhill.

As a whole, according to the method according to the invention, the input variables engine speed, gear position, sensor acceleration, maximum acceleration derived from engine torque, wheel acceleration,
From the wheel slip and the wheel speed, a reference speed which is an output amount, an uphill inclination angle in a traveling direction, and a wheel friction coefficient are determined.

Furthermore, at least one so-called “stable” wheel is selected 261 in view of the wheel weighting factor w _i .

A stable wheel is understood to be a wheel whose wheel speed is very close to the actual speed of the vehicle in the direction of travel. The associated weighting factor w _i is 100%; the wheel brake pressure is lower than a set value for a predetermined time, for example lower than 3 to 5 bar; Not, and-when the wheel is recognized as stable already before the predetermined time, the wheel is recognized as stable.

The operation of the reference speed v _ref is checked for validity by comparing 260 the stable wheel reference speed v _ref and the wheel speed v _sens . If the difference between the two speeds v _ref and v _sens is large in this comparison 260, the reference speed v _ref is adapted to the stable wheel speed v _stabil .

The speed v and _stabil stable wheel slower than the reference speed v _ref is recognized, the reference speed of the point in time _{t n + 1 v ref (t} n + 1) the reference speed of the point in time t _n v _ref (t from _n), recursive arithmetic _{expression, v ref (t n + 1} ) = v ref (t n) + w stabil (t n) is calculated according to · a _neg · Δt. In this case, w _stabil stable weighting factors of the wheels, a _neg maximum deceleration, and Δt is the time difference between the time point t _n and t _{n + 1.} The stable wheel weighting factor w _stabil is determined from the table, depends on the slip and brake pressure of each wheel and is determined empirically.

[0052] velocity v the _stabil stable wheel faster than the reference speed v _ref is recognized, the reference speed at the time _{t n + 1 v ref (t} n + 1) the reference speed of the time t _n v _ref (t _n ) is determined according to the recursive operation formula: v _ref (t _{n + 1} ) = v _ref (t _n ) + (v _stabil (t _n ) −v _ref (t _n )) = v _stabil (t _n ) You.

[0053] Figure 3 is a table for assigning a weighting factor w _i in dependence on the acceleration a _i and the slip s _i of the wheel i (i = 1,2,3,4) in the speed range of the wheel speed v _i Is shown.

The accelerations a _i are described in units g. In this case, approximately 1 g = 10 ms ⁻² applies. Slip s _i is described the absolute value of the difference between the wheel speed and the vehicle speed in units kmh ^-1. The numerical value of the weight coefficient w _i is described in%.

[0055] The described table, a predetermined range of the wheel speed v _i of the wheels i, for example 20~30km
h- ¹ . In this speed range, for example, when the wheel acceleration is 1.75 g and the slip is 5 kmh ⁻¹ , a weight coefficient of 20% is generated for the wheel i. In general, it can be said that a high acceleration and / or a large slip will result in a small weighting factor, and vice versa. The cause lies in the relationship between the coefficient of friction, traction slip and vehicle speed known from the literature.

[Brief description of the drawings]

1 schematically shows a method for determining a reference speed of a motor vehicle and the incorporation of this method into the control circuit of an anti-slip device and an anti-lock device.

FIG. 2 shows a special embodiment of the method of FIG. 1;

FIG. 3 is a diagram showing a table for assigning weight coefficients.

Claims (12)

[Claims] 1. A method for determining a reference speed of a motor vehicle, comprising the steps of measuring wheel speeds of at least two wheels (111, 121) of the motor vehicle. 111), a step (131) of calculating a reference speed taking into account the wheel speed. 2. The wheel speeds of all wheels of the vehicle are measured (112, 122).
The method according to claim 1, characterized in that the reference speed is calculated taking into account the wheel speeds of all wheels (131). 3. The method according to claim 1, wherein the reference speed is calculated at a point of discontinuity at a sufficiently high repetition frequency using a recursive calculation formula for calculating the reference speed. the method of. 4. The reference speed v _ref (t _{n + 1} ) is at time t _{n + 1} , and from the reference speed v _ref (t _n ) at time t _n , the following recursive operation expression, v _ref (t _{n + 1} ) = v _ref (t _n ) + w (t _n ) · a _mot (t _n ) · Δt, where w is an average weighting factor determined empirically, and a _mot is engine torque. the maximum acceleration derived from, and method of claim 3, wherein the Δt is the time difference between the time point t _n and t _{n + 1.} 5. The method as claimed in claim 4, wherein the weighting factor w depends on the speed v, acceleration a and slip s of the vehicle wheels and is determined from an electronically stored table. 6. The method according to claim 4, wherein the maximum acceleration a _mot derived from the engine torque is corrected in consideration of the effective braking torque M _brems . 7. The method according to claim 1, wherein the motor vehicle is provided with an acceleration sensor. The vehicle speed is determined by the acceleration sensor.
1) and comparing the vehicle speed v _sens determined by the acceleration sensor with the reference speed v _ref (250). 8. Considering the speed, acceleration and slip of each wheel,
And assuming that each wheel is not currently energized with braking force,
8. A wheel according to claim 1, wherein one wheel is selected as a stable wheel (261) and the speed of the stable wheel is compared with the detected reference speed (260). the method of. 9. The method according to claim 8, wherein the reference speed is adapted to a stable wheel speed when the comparison produces a difference. 10. The vehicle according to claim 1, wherein the wheels are all-wheel-drive passenger cars.
10. The method according to any one of claims 9 to 9. 11. A device for determining a reference speed of a motor vehicle, comprising a sensor for sensing wheel speed, electronic storage means, and electronic calculation means, the apparatus comprising: An apparatus for performing the method according to any one of the preceding claims. 12. A data carrier for storing an arithmetic program and / or associated data, wherein the arithmetic program implements a method according to claim 1 or obtains data relating to this method. 12. A data carrier, characterized in that the computing program controls the device according to claim 11 or makes data relevant to the control of the device available.