GB2260584A

GB2260584A - Vehicle body speed estimating method in an anti-lock control system for a vehicle

Info

Publication number: GB2260584A
Application number: GB9221671A
Authority: GB
Inventors: Toshio Yahagi; Takeshi Kojima
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1991-10-18
Filing date: 1992-10-15
Publication date: 1993-04-21
Anticipated expiration: 2012-10-15
Also published as: DE4234819A1; GB9221671D0; JP2620998B2; DE4234819C2; JPH05105056A; GB2260584B

Abstract

The method comprises the steps of: calculating a first vehicle body speed VRFL1 etc. on the basis of the wheel rotational speeds detected by the speed sensors SFL, etc.; determining, for every object wheel, a maximum difference in speed between inner and outer wheels supposing that a minimum turning radius is determined by the vehicle travel speed; correcting the maximum difference in speed between the inner and outer wheels with a ratio corresponding to an actual turning amount value corresponding to a maximum turning amount using a second index representative of the vehicle speed, to obtain for every object wheel, an estimated difference in speed between the inner and outer wheels; correcting the largest value of the wheel speeds from all the speed sensors using this estimated difference to calculate a second vehicle body speed for every object wheel; and selecting the higher of the first and second vehicle body speeds for use in an anti-lock control. <IMAGE>

Description

2 1 - -, n 4 - ' - j VEHICLE BODY SPEED ESTIMATING METHOD IN AN ANTI-LOCK

CONTROL SYSTEM FOR VEHICLE The present invention relates to a method for estimating a vehicle body speed, on which a slip rate is based, for an anti-lock control system for a vehicle. The anti-lock control system operates to control the braking pressure for vehicle wheels by estimating a vehicle body speed based on wheel rotational speeds detected by speed sensors and by determining the slip rate of each wheel based on the estimated vehicle body speed.

Conventionally, anti-lock control is effected to an object wheel by estimating a vehicle body speed from a rotational speed of the object wheel and by determining a slip rate from a comparison of the rotational speed of the object wheel with a reference wheel rotational speed determined by the estimated vehicle body speed. Such a conventional system has been disclosed in Japanese Patent Application Laid-open Nos.41237/82 and 60984/82.

During braking in a vehicle provided with an anti-lock control system when travelling on a straight road, the highest wheel rotational speed among the wheel rotational speeds of four front and rear wheels becomes a value closest to a vehicle body speed, during both anti-lock control and non-anti-lock control. During braking when the vehicle is turning, however, a large speed difference is produced between the highest one of the four wheel rotational speeds and the others due to the inner and outer wheel speed difference generated between left and right wheels. Hence, if the vehicle body speed is estimated on the basis of the highest speed, the reference wheel rotational speed determined from the estimated vehicle body speed for setting the slip rate becomes higher than necessary. As a result, anti-lock control may be carried out even though such control is not required.

In view of this, there is another prior art (Japanese Patent

Application Laid-open No.28044/90), in which the vehicle body speed can substantially accurately be estimated by employing, as the estimated vehicle body speed, the higher one of two values, i.e., a vehicle body speed estimated based on the wheel rotational speeds detected by the speed sensors, and a value obtained by correcting the highest value among all of the wheel rotoational speeds with the inner and outer wheel speed difference during turning of the vehicle.

In this prior art (Japanese Patent Application Laid-open No. 28044/90), the maximum inner and outer wheel speed difference during turning of the vehicle in accordance with an index representative of a vehicle travel speed is determined as a correcting value on the supposition that a minimum radius of turning of the vehicle is determined by the vehicle travel speed, and the highest value among all of the wheel rotational speeds is corrected with this correcting value. However, an actual inner and outer wheel speed difference is varied by the radius of turning of the vehicle. Therefore, when the maximum difference in speed between the inner and outer wheels is employed as the correcting value as in this prior art, the accuracy in the control is not sufficient.

Accordingly, it is an object of the present invention to provide a 5 method for estimating a vehicle body speed in an anti-lock control system for a vehicle, in which a more accurate estimation of the vehicle body speed during the turning of the vehicle can be done.

According to a first aspect of the present invention, there is provided a method for estimating a vehicle body speed in an anti-lock control system for a vehicle in which the braking pressure for wheels is controlled by estimating the vehicle body speed on the basis of wheel rotational speeds detected by speed sensors and judging a slip rate of the wheels on the basis of the estimated vehicle body speed, the method comprising the steps of: calculating a first vehicle body speed on the basis of the wheel rotational speeds detected by the speed sensors; determining, for every object wheel in the wheels, a maximum difference in speed between inner and outer wheels in accordance with a first index representative of a vehicle travel speed and a turning direction of the vehicle on the supposition that a minimum radius of turning of the vehicle is determined by the vehicle travel speed; correcting the maximum difference in speed between the inner and outer wheels with a ratio of a value corresponding to an actual turning amount to a value corresponding to a maximum turning amount which is determined in accordance with a second index representative of the vehicle travel 1 1 1 speed, thereby to calculate, for the every object wheel, an estimated difference in speed between the inner and outer wheels during turning of the vehicle correcting the largest value of speeds based on the wheel rotational speeds detected by the speed sensors for all of the wheels, with the estimated difference in speed between the inner and outer wheels to calculate a second vehicle body speed for the every object wheel; and selecting a higher one of the first and second vehicle body speeds as an estimated vehicle body speed for use in an anti-lock control for the object wheel. With this method, it is possible to correct the vehicle body speed during turning of the vehicle in correspondance with the turning amount with high accuracy and thus the vehicle body speed can be estimated more accurately.

In a preferred method in accordance with the invention the vehicle wheels include a left wheel and a right wheel for which the brake pressure is controlled collectively, the method further comprising the steps of: determining a maximum difference in speed between the left and right wheels as the value corresponding to the maximum turning amount by using, as the second index, a higher one of speeds based on the wheel rotational speeds detected by the speed sensors for the left and right wheels; and determining, as the value corresponding to the actual turning amount, a difference in speed between the left and right wheels based on their wheel rotational speeds detected by the speed sensors. This method unnecessitates a sensor for detecting the turning amount of - 4 the vehicle, and it is possible to detect and correct the turning amount of the vehicle with high accuracy while avoiding any increase in the number of parts.

In a preferred embodiment the method further comprises s the step of: correcting the wheel rotational speed detected by the speed sensor for the object wheel with predetermined acceleration and deceleration, thereby obtaining the first vehicle body speed so as to have its largest acceleration and deceleration set equal to the predetermined acceleration and deceleration. With this method, it is possible to stably estimate the vehicle body speed without being influenced by suddenly variable factors such as a locking tendency in the wheel.

An ei-t,bodiitient of tihe Invention will now be describad by way of example only and with reference to the accompanying drawings wherein:

Fig.1 to 3 illustrate one embodiment of the present invention, wherein Fig.1 is a block diagram illustrating an arrangement for estimating a vehicle body speed; Fig.2 is a graph illustrating a relationship between the wheel rotational speed and the first vehicle body speed; and Fig.3 is a block diagram illustrating an arrangement of turning correction means.

The present invention will now be described by way of a preferred embodiment in connection with the accompanying drawings.

The embodiment of the present invention is shown as being applied to an anti-lock control system for a front wheel drive vehicle, which is designed to independently control the braking pressures for front wheels and to collectively control the braking pressures for rear wheels.

Referring Fig.1 a speed sensor S FL is mounted on the left front wheel of a front wheel drive vehicle; a speed sensor SFR is mouunted on the right front wheel; a speed sensor S RL is mounted on the left rear wheel, and speed sensor SRR is mounted on the right rear wheel. Wheel rotational speeds VWFL s V WFR s V WRL and V WRR detected through the speed sensors SFLi S FRS S RL and SRR are supplied to speed arithmetic circuits 1FLi 1 FRS 1 RL and JRR corresponding to the left and right front wheels and the left and right rear wheels.

In the speed arithmetic circuits 1 FLs 1 FRS 1 RL and IRR, first vehicle body speeds V RFLIs V RFRIs V RRL, and VRRR, are calculated on the basis of the received wheel rotational speeds VWFL 9 V WFR z V WRL and V wRR S a predetermined vehicle acceleration GG RA) and a predetermined deceleration ( -G RD). Specifically, in the speed arithmetic circuit 1 FL S a first vehicle body speed V RFL10%) is calculated, depending upon whether an acceleration or deceleration ((V RFL1 (n-1) - VWFL (.)) / AT) obtained from a value resulting from subtraction of a current wheel rotational speed V WFL(n) from the last value V RFLI(n-O of the first vehicle body speed V RFLI of the last time divided by a time AT of a calculating cycle is within a range determined by the predetermined given acceleration GG RA) and deceleration (-G RD).

That range is -G RD < (V RIFL 1 (n- 1) - VWFL /AT < +G RA, where VRFL 1 (n) "-- V RFL 1 (n- 1) - (V RFL 1 (n-1) - VWFL (n)) V WFL (n) In addition, the range encompasses URFL1 (n-O - VWFL(n) M AT t5-- -G RD. where VRFL1 (n) V RFLI (n-,)- G RD X AT.

Further, the range includes +G RA;SURFL1 (n-1) - VWFL(,,))/AT, where VRFL1 (n) - V RFL1 + GRA X AT.

This provides a first vehicle body speed V RFLI which is varied as shown in Fig.2 with respect to the wheel rotational speed V WFLI.

In the other speed arithmetic circuits IFR, 1 RL and IRR, a calculation similar to that in the above-described speed arithmetic circuit 1 FL is carried out, thereby providing first vehicle body speeds V RFRIs V RRL, and VRRRI, respectively.

The first vehicle body speeds VRFLIs V RFR1i V RRL, and VRRRI provided in the speed arithmetic circuits 1FL) 1 FR) 1RL and 1RR are supplied to the high select circuit 2, where the largest value of these first vehicle body speeds VRFLIs V RFRI9 V RRL, and VRRRI is selected as a first index representative of vehicle travel speeds.

The first vehicle body speeds VRRL, and YRRRI9 provided in the speed arithmetic--- circuits 1 RL and 1RR corresponding to the left and right wheels which are driven or follower wheels, are also supplied to a subtraction circuit 3 and a high select circuit 5.

In the subtraction circuit 3, a subtraction according to URRLI- V RRRI) AV is carried out. The value AV is a difference in speed between the first vehicle body speeds VRRL, and VRRRi, based on the wheel rotational speeds V WRL and V WRR Of the left and right rear wheels and is used as a value corresponding to a turning amount during the turning of the vehicle. The braking pressures for the left and right rear wheels are collectively controlled, and the wheel rotational speeds V WRL and V wRR of the left and right rear wheels are varied synchronously, during both anti-lock control and non-anti-lock control.

It is possible to provide a speed difference value substantially correctly as a value representative of the vehicle turning amount.

The speed difference AV as a turning amount-corresponding value provided in the arithmetic circuit 3 is supplied to a turning-direction judgement circuit 4. In the turning-direction jedgement circuit 4, it is jedged whether the vehicle has turned toward the right or left on the basis of the speed difference AV being positive or negative.

The high select circuit 5 selects the higher one of the vehicle body speeds VRRLI, and V RRR, received therein and delivers the higher value of the vehicle body speeds VRRL, and VRRR, as a second index representative of the vehicle travel speeds YRRa, which is received into a maximum turning-amount determination circuit 6.

In the maximum turning-amount determination circuit 6, a maximum speed difference- AV RH, between the left and right wheel speeds is determined as a maximum turning-amount corresponding value in accordance with the second index V RRH on the basis of a minimum radius of turning of the vehicle being determined by the vehicle travel speed.

The maximum speed difference A V Rm as a maximum turning-amount corresponding value from the maximum turningamount determination circuit 6 and the speed difference A V as a turning-amount corresponding value from the subtraction circuit 3 are received into a division circuit 7 where a ratio C =( AV/AV Rm) of an actual turning- amount corresponding value AV to the maximum speed difference AV RM is calculated.

The speed V RH as the first index provided in the high select circuit 2, a turning-direction judgement result provided in the turning direction judgement circuit 4 and the ratio C provided in the division circuit 7 are received into the turning correction means 8FL, 8 FR s 8RL and 8RR individually corresponding to the left and right front wheels and the left and right rear wheels. 20 The turning correction means 8 FL which corresponds to the left front wheel and is arranged as shown in Fig. 3 and comprises a maximum inner and outer wheel speed difference determination circuit 10, a speed difference estimating circuit 11 and a correction circuit 12. The speed VRH as the first index from the high select circuit 2 and the turningdirection judgement result provided in the turning direction jedgement circuit 4 are received into the maximum inner and outer wheel speed difference determination circuit 10 which determines a maximum inner and outer wheel speed difference AV Rm' in accordance with the first index representative of the travel speeds and the turning direction, on the basis of the minimum radius of turning of the vehicle being determined by the vehicle travel speed.

The nkixiffi= inner and outer wheel speed difference AV Rm' provided in the maximum inner and outer wheel speed difference determination circuit 10 and the ratio C provided in the division circuit 7 are received into a speed difference estimation circuit 11 which executes a calculation comprising a product of the maximum inner and outer wheel speed difference AV Rm' with the ratio C to produce an estimated inner and outer wheel speed difference AV= ( AV Rm' X C) as a calculation resul t.

The speed VRH provided in the high select circuit 2 and the estimated inner and outer wheel speed difference AV' provided in the speed difference estimation circuit 11 are received into the correction circuit 12. This circuit 12 executes a correction comprising a subtraction of the estimated inner and outer wheel speed difference AV' from the speed V RH to produce a second vehicle body speed V RFLZ(VRH AV) as a calculation result.

The turning correction means 8 FRY 8 RL and 8RR corresponding to the right front wheel and the left and right rear wheels respectively are arranged in a similar manner to the arrangement of the turning correction means 8 FL corresponding to the left front wheel. Second - 1 0 - vehicle body speeds YRFL2. V RFRZi V RRLz and VRRR2 corresponding to the respective wheels are delivered from the turning correction means 8 FL 2 8FR) 8 RL and 8RR, respectively.

The first vehicle body speeds VRFLI 9 V RFRI i V RRL, and VRRRI provided in the speed arithmetic circuits 1FL, 1 FR s 1RL and 1RR corresponding to the respeective wheels as well as the second vehicle body speeds YRFL2, V RFRZ7 V RRLz and VRRRz provided in the correction circuits 12 of the turning correction means 8 FL i 8FR) 8 RL and 8RR corresponding to the respective wheels are received into high select circuits 9FL, 9 FR j 9RL and 9RR corresponding to the wheels, respectively. Each of the high select circuits 9FI, 9 FR s 9RL and 9RR selects the higher one of the first vehicle body speed V RFLIs V RFRIs V RRLI or V RRRI, and the second vehicle body speed V RFL2Y V RFR2s V RR L2 or V RRR z as an estimated vehicle body speed VRFL j V RFR s V RRL or VRRR for use in the anti-lock control of a corresponding wheel, respectively.

The operation of this embodiment will be described below. A higher selected value of the first vehicle body speeds V RFL1i V RFRI3 V RRLI or V RRR, based on the wheel rotational speeds V WFL v V WFR 3 V WRL or NRR detected in the speed sensors S FL 3 SFR3 S RL or S RR and the second vehicle body speeds V RFL2s V RFRZ9 V RRL2 or V RRR z provided by the turning correction of the highest value of the wheel rotational speed V WFL s V WFR 9 V wRL and V wRR detected in the corresponding speed sensors S FL i SFRi S RL and SRR is used as the estimated vehicle body speed VRFL v V RFR 9 V WRL or V RRR for use in the anti-lock - 1 1 - control of a corresponding wheel, respectively. Therefore, even if a locking tendency is produced in an object wheel, resulting in a reduction tendency in the first vehicle body speed V RFLI3 V RFRIs V RR LI or V RRRIs it is possible to provide an increase in the accuracy of estimation of the vehicle body speed by using, as the estimated vehicle body speeds VRFL 3 V RFR 3 V WRL 3 V RRR. the second vehicle body speeds V RFL23 V RFRZ3 V RRL2s V RRRZ which are based on the rotational speeds of the corresponding wheels having a non-locking tendency other than the object wheel and which are provided by the correction of the turning.

Moreover, in correcting the turning, a difference AV between the vehicle body speeds based on the left and right rear wheel speeds is found, and the maximum inner and outer wheel speed difference AV Rm' determined on the basis of the speed V RH as the first index representative of the vehicle travel speeds and the turning direction is corrected by the ratio C of the speed difference AV to the maximum turning amount AV Rm determined using the second index VRR ii representative of the vehicle travel speeds. This provides an estimated speed difference AV', and further, the speed V RH is corrected by the estimated speed difference AV' so as to provide the second vehicle body speeds VRFL2, V RFRZs V RRLz and V RRR2. Therefore, a sensor for detecting the vehicle turning amount is not required, and it is possible to provide a highly accurate correction of the turning and a higher accuracy estimation of the vehicle body speeds.

Further, the wheel rotational speeds V WFL i V WFR s V WRL and V WR - 1 2 - R detected in the corresponding speed sensors S FL j S FR i S RL and S R it are corrected by the predetermined acceleration ( +G RA) and deceleration (-G-RD) so as to provide the first vehicle body speeds V R FL19 V RFR1i V RRL, and V RRRI. Therefore, it is possible to provide a stable vehicle speed which is not governed by a rapid variation factor such a locking tendency of each wheel.

In another alternative embodiment, it is possible to use an output from the high select circuit 5 rather than use the output from the high select circuit 2 as the first index representative of the vehicle speeds.

- 1 3 -

Claims

CLAIMS:

1. A method for estimating a vehicle body speed in an anti-lock control system for a vehicle in which the braking pressure for wheels is controlled by estimating the vehicle body speed on the basis of wheel rotational speeds detected by speed sensors and judging a slip rate of the wheels on the basis of the estimated vehicle body speed, said method comprising the steps of: calculating a first vehicle body speed on the basis of the wheel rotational speeds detected by the speed sensors; determining, for every object wheel in the wheels, a maximum difference in speed between inner and outer wheels in accordance with a first index representative of a vehicle travel speed and a turning direction of the vehicle on the supposition that a minimum radius of turning of the vehicle is determined by the vehicle travel speed; correcting said maximum difference in speed between the inner and outer wheels with a ratio of a value corresponding to an actual turning amount to a value corresponding to a maximum turning amount which is determined in accordance with a second index representative of the vehicle travel speed, thereby to calculate, for said every object wheel, an estimated difference in speed between the inner and outer wheels during turning of the vehicle; correcting the largest value of speeds based on the wheel rotational speeds detected by the speed sensors for all of the wheels, with said estimated difference in speed between the inner and outer 25 wheels to calculate a second vehicle body speed for said every object - 1 4 - wheel; and selecting a higher one of said first and second vehicle body speeds as an estimated vehicle body speed for use in an anti-lock control for the object wheel.

2. A method for estimating a vehicle body speed in an anti-lock control system according to claim 1, wherein the vehicle wheels include a left wheel and a right wheel for which the brake pressure is controlled collectively, said method further comprising the steps of: determining a maximum difference in speed between said left and right wheels as said value corresponding to the maximum turning amount by using, as said second index, a higher one of speeds based on the wheel rotational speeds detected by the speed sensors for the left and right wheels; and determining, as said value corresponding to the actual turning amount, a difference in speed between the left and right wheels based on their wheel rotational speeds detected by the speed sensors.

3. A method for estimating a vehicle body speed in an antilock control system according to claim 1 or 2, said method further comprising the step of:

correcting the wheel rotational speed detected by the speed sensor for the object wheel with predetermined acceleration and deceleration, thereby obtaining the first vehicle body speed so as to have its largest acceleration and deceleration set equal to said predetermined acceleration and deceleration.

4. A method for estimating a vehicle body speed in an anti-lock 11 1 - 1 5 - control system substantia accompanying drawings.

lly as described herein with reference to the - 1 6