Brake control device in an antilock brake system

Abstract: A brake control device in an antilock brake system for a motorcycle is disclosed for automatically adjusting a valve provided in a brake fluid lines for front and rear wheels of the motorcycle to reduce a fluid pressure in a brake cylinder for eliminating symptoms of brake locking independently in said front and rear wheels. The brake control device comprises means for detecting a vehicle deceleration (VCEL); means for determining whether or not an antilock brake control is being applied to either one of said front and rear wheels; vehicle deceleration amplification means for amplifying said detected vehicle deceleration by a predetermined amount when it is determined by said determining means that antilock brake control is being applied to one of said front and rear wheels; and antilock brake control means for applying antilock brake control to said one wheel based on said amplified vehicle deceleration.

Description: The present application is divided from European Patent application 90 104 719.1 filed on the 13th March, 1990. The present invention relates to a brake control device in an antilock brake system for a motorcycle for automatically adjusting a valve provided in a brake fluid lines for front and rear wheels of the motorcycle to reduce a fluid pressure in a brake cylinder for eliminating symptoms of brake locking independently in said front and rear wheels, said brake control device comprising: means for detecting a vehicle deceleration; and means of determining whether or not an antilock brake control is being applied to either one of said front and rear wheels. Such a brake control device in an antilock brake system is disclosed in GB-A-2 134 200. An antilock brake system is a brake control system which automatically reduces the brake cylinder fluid pressure (hereinafter "brake fluid pressure") to lower the brake pressure and cancel wheel locking when the brakes are applied and the wheels lock and begin to slip on the road surface; when this antilock control is applied it overrides the operation of the brakes by the driver. In Fig. 1 is shown a conventional brake pressure control system. When the brake pedal is pressed, the fluid pressure inside the brake cylinder 2 rises, and the brakes 4 are applied by means of the intake solenoid valve 3. If the wheels lock because the brakes are excessively applied, the antilock control system functions: the intake solenoid valve 3 is displaced to the pressure rise buffer position and the exhaust solenoid valve 6 is displaced to the conductivity position for the calculated time period ΔT. The fluid pressure applied to the brakes 4 is thus lowered, the brake 4 pressure decreases, and the wheels can be released from the locked state. In general, brake fluid pressure characteristics vary non-linearly as shown in Fig. 2(a). As a result, the higher the brake fluid pressure is when pressure reduction is first applied, the wider pressure reduction band ΔP becomes for the same time period ΔT. Thus, in order to obtain a given pressure reduction band, the time period ΔT must vary according to the brake fluid pressure. However, since conventional devices do not compensate the pressure reduction time according to the actual or estimated brake fluid pressure, antilock control begins at a low brake fluid pressure on frozen roads, snow-covered roads, and other road surfaces with a low coefficient of friction µ ("low µ surfaces"); this results in excessive tire slipping, as well as reduced steering control on front wheel drive vehicles, and reduced vehicle stability on rear wheel drive vehicles due to insufficient reduction of the brake fluid pressure. Furthermore, on asphalt and other road surfaces with a high coefficient of friction µ ("high µ surfaces"), antilock control begins at a high brake fluid pressure, resulting in excessive brake fluid pressure reduction which may cause vehicle deceleration to fluctuate and the required braking distance to increase. The present invention has been developed with a view to substantially solving the above described disadvantages and has for its essential object to provide an improved brake control device in a motorcycle antilock brake system. According to the invention, there is provided an antilock brake system as initially defined characterized by: vehicle deceleration amplification means for amplifying said detected vehicle deceleration by a predetermined amount when it is determined by said determining means that antilock brake control is being applied to one of said front and rear wheels; and antilock brake control means for applying antilock brake control to said one wheel based on said amplified vehicle deceleration. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings in which: Fig. 1 is a block diagram of a known brake fluid pressure system; Fig 2(a) is a graph showing the change in brake fluid pressure; Fig 2(b) is a graph showing the brake fluid pressure reduction signal K; Fig. 3 is a block diagram showing the brake control device in an antilock brake control system according to a first realization which is not an embodiment of the invention but is nevertheless included for background understanding and forms the subject of European parent application 90104719.1; Fig. 4 is a block diagram showing a modification of the device shown in Fig. 3; Fig. 5 is a flow chart of brake fluid pressure control according to the first realisation; Fig 6 is a graph showing the relationship between compensation value α and vehicle deceleration; Fig. 7 is a graph showing control on asphalt roads and snow-covered roads; Fig. 8 is a block diagram showing the brake control device in a motorcycle antilock brake control system according to a first embodiment of the present invention; Fig. 9 is a block diagram showing a modification of the device shown in Fig. 8; and Figs. 10a and 10b, taken together as shown in Fig. 10 show a flow chart of brake fluid pressure control for the system of Fig. 8. Referring to Fig. 3, a block diagram of the brake control device in an antilock brake control system not according to the present invention is shown. In this figure, S0, S1, S2 and S3 are the wheel speed sensors which detect the speed of each wheel; CAL is the calculator which computes the wheel deceleration and estimated vehicle deceleration from the wheel speed; L0, L1, L2 and L3 are the lock symptom detectors which detect the locking symptoms for each wheel; T0, T1, T2 and T3 are pressure reduction time setters to which are input the brake pressure for each wheel from the fluid pressure detectors P0, P1, P2, and P3, and which set the pressure reduction time required to apply antilock brake control to each wheel. OUT0, OUT1, OUT2 and OUT3 are solenoid command output devices which output a drive command to the solenoid of the solenoid valve according to the pressure reduction time; and ACT0, ACT1, ACT2 and ACT3 are pressure reduction controllers which include an intake solenoid valve and exhaust solenoid valve. In the above construction, it is preferable that the calculator, lock symptom detector, pressure reduction time setter, and solenoid command output device be comprised of a microcomputer for processing. It is to be noted that the fluid pressure. detectors need not necessarily be provided at all four wheels, and it is sufficient to provide one on only one of the right wheels and one on only one of the left wheels. In addition, the fluid pressure detectors may be hydraulic pickups which directly detect the brake fluid pressure, but vehicle deceleration sensors may also be used because the brake fluid pressure and the vehicle deceleration have a proportional relationship. In this case, a pressure signal may be sent from one of the vehicle deceleration sensors to the pressure reduction time setters T0, T1, T2, T3. Also, as shown in Fig. 4, instead of providing an independent fluid pressure detector, the estimated vehicle deceleration may also be computed from the wheel speed by the calculator CAL and the fluid pressure signal output based on this result. The operation of the brake control device in this antilock brake control is described herein below with reference to the flow chart in Fig. 5. It is to be noted this flow chart describes the process for only one wheel, but the same control operation is also executed for the other wheels. At step #1, the wheel speed, wheel deceleration, estimated vehicle deceleration and compensation value α are calculated. Note that the method of calculating the estimated vehicle deceleration may be that described, for example, in U.S. Patent application Serial Number 07/291650, or any other known method. The value obtained from the graph shown in Fig. 6 according to the estimated vehicle deceleration is output as compensation value α. At step #2, it is detected whether there are any symptoms of brake locking. Brake locking may be detected by determining that the wheel deceleration is below a predefined wheel deceleration threshold Dt when the wheel speed is also below a predefined wheel speed threshold St, or by another method of common knowledge. When brake locking symptoms are detected, a flag is set at step #3 and the antilock timer is cleared; when locking symptoms are not detected, a flag is reset at step #4, and the antilock timer is incremented. At step #5, it is detected whether the flag is set or not; if it is not, when the antilock timer is greater than a predefined value, e.g., 128, antilock control is not applied and the operation of the brake pedal is transmitted directly to the brakes. However, if the antilock timer value is less than the predefined value, antilock control is still being applied and the brake fluid pressure is gradually increased. On the other hand, antilock control is required if at step #5 the flag is set, and at step #6 pressure reduction signal K is set for the desired pressure reduction rate R, i.e., desired pressure reduction ΔW per unit time Δt is set (Fig. 2(b)). The pressure reduction signal K may be obtained from, for example, the equation: K = ¦DECEL¦ where DECEL is the wheel deceleration. The desired pressure reduction rate R may be more gradual than the average slope of the normal pressure reduction curve for the brake fluid pressure as shown in Fig. 2(b). When antilock brake control is applied, the pressure does not drop suddenly but intermittently. How this may be achieved is described with reference to Fig. 1. When intermittent pressure reduction is required, the intake solenoid valve 3 is first set to the pressurization buffer state and the exhaust solenoid valve 6 is then intermittently set to the conductive state. The solenoid opening coefficient J which causes the exhaust solenoid valve 6 to open and close intermittently is computed in step #8, but because the duty ratio determining intermittent operation is dependent upon the current brake fluid pressure, it is obtained by the relationship with the brake fluid pressure. Specifically, the solenoid opening coefficient J is obtained as J = K + α. As shown in Fig. 6, the compensation value α is a value obtained from the vehicle deceleration, which has a proportional relationship to the brake fluid pressure. Table 1 shows sample settings of solenoid opening coefficients J and the duty ratio turning the solenoid on/off. Open coef. J Duty ratio Off time On time J ≥ 72 0 (ms) ∞ (ms) 72 > J ≥ 48 6 24 48 > J ≥ 36 6 12 36 > J ≥ 24 6 6 24 > J ≥ 12 12 6 12 > J 24 6 J = 0 ∞ 0 The solenoid command is output in step #9 according to this duty ratio. Fig. 7 is the operation wave form during antilock brake control on asphalt roads and on snow-covered roads. The wheel speed is obtained from the wheel speed sensors, and the wheel deceleration is obtained with a single differentiation of the wheel speed. The flag is set when the wheel speed is less than a predefined threshold St and the wheel deceleration is also less than a predefined threshold Dt. The absolute value of the wheel deceleration when the flag is set is output as the pressure reduction signal K, and the compensation value α is obtained from the vehicle deceleration, the first differential of the estimated vehicle speed. It is to be noted that the estimated vehicle speed can be obtained from the wheel speed. Next, the pressure reduction signal K and compensation value α are added, the solenoid opening coefficient J is obtained, and the duty ratio is obtained from Table 1. Because the exhaust solenoid valve 6 is intermittently opened and closed based on this duty ratio at a speed appropriate to the brake fluid pressure at any given point, appropriate antilock brake control is possible. The case in which, for example, antilock brake control is necessary and the brake fluid pressure reduction signal K required for its execution is 30 is examined. If conditions requiring antilock brake control occur on an asphalt road, the brake fluid pressure shows a relatively high value, and thus the vehicle deceleration, which is proportional to the brake fluid pressure, is high and the compensation value α is either zero or nearly zero. Therefore, the solenoid opening coefficient J is approximately equal to the pressure reduction signal K, and is thus approximately 30. In other words, pressure reduction occurs with a solenoid on/off time of 6/6 msec. On the other hand, if conditions requiring antilock brake control occur on a snow-covered road, the brake fluid pressure shows a relatively low value, and thus the vehicle deceleration, which is proportional to the brake fluid pressure, is also low and the compensation value α is high, for example 20. Thus, the solenoid opening coefficient J is added to the pressure reduction signal K (=30), resulting in approximately 50, and pressure reduction occurs with a solenoid on/off time of 24/6 msec. In other words, because the brake fluid pressure is detected to be a low value on snow-covered roads, the solenoid on time percentage is longer, and the desired pressure reduction band can obtained. According to the present brake system, because the current brake fluid pressure is detected and the pressure reduction signal K is corrected accordingly, even if the same pressure reduction signal K command is output, the solenoid opening coefficient J is determined using a value approximately equal to pressure reduction signal K on asphalt and other high µ roads, while the solenoid opening coefficient J is determined using a value greater than the pressure reduction signal K on snow-covered roads and other low µ roads. Thus, even if the brake cylinder pressure is low, the valve opening time can be made longer, and the desired pressure reduction can be obtained. Therefore, according to the present brake system, even if antilock brake control is begun with a low brake fluid pressure, an unnecessary increase in wheel slipping due to insufficient pressure reduction, reduced steering control occurring with front wheel drive vehicles, and reduced vehicle stability occurring with rear wheel drive vehicles can be avoided. Furthermore, even if antilock brake control begins with a high brake fluid pressure, consistently stable antilock brake control occurs without fluctuating vehicle deceleration caused by excessive pressure reduction or such problems as, for example, increased braking distances. The first embodiment of the invention is directed to the brake control device in an antilock brake system for use in a motorcycle. When the antilock brake system is employed in a motorcycle, it is not possible to simply substitute the vehicle deceleration for the brake fluid pressure when the brakes are applied to a single wheel, because the brakes can be independently operated for the front and rear wheels on a motorcycle. If the vehicle deceleration is simply substituted for the brake fluid pressure when the brakes are applied to a single wheel, the following may occur. When the brakes are applied to both the front and rear wheels, the vehicle deceleration (hereinafter "two-wheel limit deceleration") when the locking symptoms begin to appear varies according to the coefficient of friction µ of the road surface. Furthermore, when the brakes are applied to either the front or the rear wheel, the vehicle deceleration (hereinafter "one-wheel limit deceleration") when the locking symptoms begin to appear varies according to the coefficient of friction µ of the road surface, but is less than the two-wheel limit deceleration by a predefined percentage. Since antilock brake systems for motorcycles are normally designed on the premise that the brakes are applied to both the front and rear wheels, when the brakes are applied to only one wheel and the antilock brake system engages, vehicle deceleration is determined to be low, a higher compensation value α is obtained from the graph shown in Fig. 6, the pressure reduction signal (K+a) after compensation is thus higher, and the brake fluid pressure reduction time is longer than necessary. As a result, pressure reduction is excessive, and vehicle deceleration during antilock brake control varies and may be insufficient. Referring to Fig. 8 is a block diagram of the brake control device in a motorcycle antilock brake control according to the first embodiment of the present invention is shown. In this figure, S0 and S1 are the wheel speed sensors which detect, respectively, the speed of the front and rear wheels; STP0 and STP1 are the stop switches which turn the brake lights on when the brakes are applied, respectively, to the front and rear wheels; CAL is the calculator which computes the wheel deceleration, estimated vehicle speed, and estimated vehicle deceleration from the wheel speed; L0 and L1 are the lock symptom detectors which detect the locking symptoms for each wheel; T0 and T1 are pressure reduction time setters to which are input values proportional to the brake fluid pressure for each wheel from the vehicle deceleration sensor P, and which use this value to set the pressure reduction time required to apply antilock brake control to each wheel. OUT0 and OUT1 are solenoid command output devices which output a drive command to the solenoid valve solenoid according to the pressure reduction time; ACT0 and ACT1 are pressure reduction controllers which include the intake solenoid valve and exhaust solenoid valve. In the above construction, it is preferable that the calculator, lock symptom detector, pressure reduction time setter, and solenoid command output device be comprised of a microcomputer for processing. Furthermore, as shown in Fig. 9, the estimated vehicle deceleration may also be computed by the calculator CAL and the pressure reduction time set based on this result instead of providing a vehicle deceleration sensor. The operation of the brake control device in this antilock brake control is described herein below with reference to the flow chart in Figs 10a and 10b. It is to be noted this flow chart describes the process for only one wheel, but the same control operation is also executed for the other wheel. At step #41, the wheel speed, wheel deceleration, and estimated vehicle deceleration are calculated in the same manner as in step #1. At step #42, it is detected whether there are any symptoms of brake locking. Brake locking may be detected by determining that the wheel deceleration is below a predefined wheel deceleration threshold when the wheel speed is also below a predefined wheel speed threshold, or by another method of common knowledge. When brake locking symptoms are detected, a flag is set at step #43 and the antilock timer is cleared; when locking symptoms are not detected, a flag is reset at step #44, and the antilock timer is incremented. At step #45, it is detected whether the flag is set or not. If it is not, the antilock timer is compared with a predefined value, e.g., 128, and if the antilock timer value is greater, antilock control is not applied and the operation of the brake pedal or lever by the operator is transmitted directly to the brakes. However, if the antilock timer value is less than 128, antilock control is continued to buffer brake fluid pressurization. On the other hand, if at step #45 the flag is set, pressure red pressure reduction DW per unit time Dt is set, and pressure reduction signal K is set to achieve this level of pressure reduction (Fig. 2(b)). Steps #48 to #55 are the steps whereby the vehicle deceleration VCEL is corrected as shown in Table 2 below; the compensation value α is modified by these correction steps. Antilock control STP Vehicle deceleration correction FW RW FW RW VCEL'= X X - - VCEL O O - - VCEL O X - X VCEL x 1.5 O X - O VCEL x 1.25 X O X - VCEL x 2.5 X O O - VCEL x 1.75 (FW: Front Wheel, RW: Rear Wheel) As shown in Table 2, when antilock brake control is not applied to the front and rear wheels together, and when antilock brake control is applied to the front and rear wheels together, the value VCEL' after vehicle deceleration correction uses the same value VCEL before correction. However, if antilock brake control is being applied to the front wheel and is not applied to the rear wheel, the compensation value VCEL' will differ depending on whether the stop switch STP for the rear wheel is on or off; if it is off, VCEL' = VCEL x 1.5 , and if it is on, VCEL' = VCEL x 1.25 . Furthermore, if antilock brake control is not applied to the front wheel and is applied to the rear wheel, the compensation value VCEL' will differ depending on whether the stop switch STP for the front wheel is on or off; if it is off, VCEL' = VCEL x 2.5 , and if it is on, VCEL' = VCEL x 1.75 . In order to make the above determinations, step #48 at which it is determined whether the antilock brake control is applied to the other wheel, step #49 at which it is determined whether the stop switch STP for the other wheel is on or off, steps #50 and #51 at which it is determined whether the currently detected wheel is the front wheel for not, and steps #52, #53, #54, and #55 at which the vehicle deceleration is amplified are provided. At step #56, compensation value α is obtained according to the corrected vehicle deceleration based on the graph shown in Fig. 6. For example, if the brakes are applied to the front wheel only and antilock brake control is applied, the one-wheel limit deceleration VCEL computed at step #55 is increased 1.5 times at step #55 and a value VCEL' equivalent to the two-wheel limit deceleration is obtained. If the vehicle deceleration VCEL was 0.4G at this time, the vehicle deceleration VCEL' after correction will be 0.6G. Thus, the value of compensation value α is corrected to a value from 5 - 0 (see Fig. 6). As thus described, when antilock brake control is applied to only one wheel, the vehicle deceleration VCEL is amplify-corrected to the two-wheel limit deceleration VCEL' which would be expected if antilock brake control were applied to both the front and rear wheels, and compensation value α based on the corrected vehicle deceleration VCEL' is obtained from the graph in Fig. 6. Because the correction ratio applied to VCEL will vary with the height of the center of gravity and the wheelbase length of the vehicle, these values may be set as desired for each vehicle. In other words, vehicle deceleration VCEL' after compensation is the value which would be obtained if antilock brake control were applied to both the front and rear wheels. It is to be noted that when the brakes are applied, load transfer to the front axle occurs, and since braking the front wheel produces a vehicle deceleration closer to that achieved during both wheel braking than when the brakes are applied to the rear wheel only, the compensation is set to be greatest (2.5 times) during single wheel braking of the rear wheel only due to the output of the stop switch STP. Next, the pressure reduction signal K obtained at step #46 and the compensation value α are added at step #56 to compute the solenoid opening coefficient J that intermittently opens the exhaust solenoid valve 6, and set the pressure reduction time, such as in the manner described above in connection with Table 1. A brake control device in an antilock brake control system for motorcycles according to the first embodiment of the present invention computes the vehicle deceleration VCEL' for the case in which antilock brake control is applied to both wheels even if antilock brake control is applied to one wheel, and thus obtains compensation value α; the brake fluid pressure reduction time is not therefore longer than necessary and excessive pressure reduction does not occur, and antilock brake control with an appropriate degree of pressure reduction can occur. Furthermore, because when antilock brake control is applied to one wheel it is determined whether the brakes are applied to the wheel to which antilock brake control is not applied and the vehicle deceleration VCEL' is computed, compensation value α can be obtained for more specific situations, and antilock brake control with an even more specific degree of pressure reduction can be applied. Therefore, stable antilock brake control can be provided without discriminating between single or dual wheel brake control.

Claims: A brake control device in an antilock brake system for a motorcycle for automatically adjusting a valve provided in a brake fluid line for front and rear wheels of the motorcycle to reduce a fluid pressure in a brake cylinder for eliminating symptoms of brake locking independently in said front and rear wheels, said brake control device comprising: means (step #41) for detecting a vehicle deceleration (VCEL); means (step #48) of determining whether or not an antilock brake control is being applied to either one of said front and rear wheels; characterised by: vehicle deceleration amplification means (steps #49 - #55) for amplifying said detected vehicle deceleration by a predetermined amount when it is determined by said determining means that antilock brake control is being applied to one of said front and rear wheels; and antilock brake control means (steps #56 - #58) for applying antilock brake control to said one wheel based on said amplified vehicle deceleration. A brake control device as claimed in claim 1, wherein said vehicle deceleration amplification means comprises means (step #49) for determining whether or not a brake is being applied to a wheel to which antilock brake control is not being applied. A brake control device as claimed in claim 1 or 2, wherein said vehicle deceleration amplification means comprises means (steps #50 and #51) for determining whether said one wheel is the front wheel or said one wheel is the rear wheel. A brake control device as claimed in claim 1, 2 or 3, wherein said vehicle deceleration amplification means comprises setting means for setting one of four amplification ratios for four different cases: when a brake is applied to said front wheel to which antilock brake control is not applied; when a brake is not applied to said front wheel to which antilock brake control is not applied; when a brake is applied to said rear wheel to which antilock brake control is not applied; and when a brake is not applied to said rear wheel to which antilock brake control is not applied.

Inventors: FUJIOKA HIDEAKI, KATAYAMA YOSHIO, FUJIOKA, HIDEAKI, KATAYAMA, YOSHIO, FUJIOKA, HIDEAKI, C/O ITAMI WORKS OF SUMITOMO, KATAYAMA, YOSHIO, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1990
Main classification: B60T8
IPC codes: B60T8