System for controlling brakes

Abstract: In the brake control system (13), grounding loads on front (Wf) and rear (Wr) wheels are determined and a correction value for the braking of a predetermined wheel is computed based on the grounding loads thus determined. A braking force is determined inclusive of the computed correction value. A correction value for the braking of the front wheel (Wf) is computed based on the determined grounding loads. Thus, the optimum brake control can be made without being affected by a variation in the distribution of the loads of the front (Wf) and rear (Wr) wheels relative to the ground.

Description: The present invention relates to a system for controlling brakes. In a motorcycle, for example, an antilock control system is known in which an antilocking modulator is disposed between a master cylinder, for converting a brake operating instruction issued by operating a lever and a pedal by a driver into desired hydraulic pressure, and a caliper cylinder for causing brake disks of wheels to generate braking forces, and a control unit is supplied with signals indicative of front- and rear-wheel speeds, and a caliper pressure control signal is outputted to the modulator so as to brake each wheel based on a computed slip ratio and both an acceleration and a deceleration of each wheel, for example. When the braking of each wheel is carried out, the distribution of the grounding loads between the front and rear wheels tends to vary. In particular, the grounding load distribution in the front wheel tends to increase. It is therefore necessary for a driver to control the motorcycle in response to a variation in the ground load distribution in each of the front and rear wheels. EP-A-246790 discloses a vehicle braking system in which brake pressure is corrected based on the load on the front and rear axles of a vehicle, the load signals from the load sensors being modified to take account of weight transfer during braking. It is a principal object of the present invention to provide a system for controlling brakes attached to a vehicle wherein the optimum braking of each of front and rear wheels can be easily carried out without being affected by variations in the distribution of the grounding loads between the wheels. It is another principal object of the present invention to provide a system for controlling brakes attached to a vehicle which is capable of controlling braking forces without reducing the grounding load on a rear wheel in particular when the braking of a front wheel is made. The present invention provides a system for controlling brakes attached to a vehicle, comprising: deceleration detecting means for determining a rear-wheel deceleration; the system being characterised in that it includes: determining means for determining that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration falls within a preset range about zero during the operation of a front-wheel brake; and controlling means for reducing and controlling a braking force of the front-wheel brake based on said result of determination by said determining means. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. FIG. 1 is an overall side view showing a motorcycle on which a brake control system according to a first embodiment of the present invention has been mounted; FIG. 2 is a view illustrating the structure of the brake control system shown in FIG. 1; FIG. 3 is a view showing the structure of a control unit employed in the brake control system shown in FIG. 1; FIG. 4 is a flowchart for describing the operation of the brake control system shown in FIG. 1; FIG. 5 is a view for describing the relationship between the angular velocity of each wheel and the angular acceleration of each wheel; FIG. 6 is a view for describing the relationship between the angular velocity of each wheel and the angular acceleration of each wheel; FIG. 7 is a view for describing the operation of the brake control system shown in FIG. 1; and FIG. 8 is a view for describing the operation of a brake control system according to a second embodiment of the present invention. FIG. 1 is a side view showing the overall structure of a motorcycle X on which the brake control system 110 according to a first embodiment has been mounted. FIG. 2 is a view illustrating the structure of the brake control system 110. The brake control system 110 basically comprises a main body 114 disposed above a front fork 112, and a control unit 124 which is electrically connected to a motor controller 118 for driving and controlling a d.c. motor 116 coupled to the main body 114 and which is used to control the main body 114. In this case, the control unit 124 is activated to cause an encoder 122 (detecting means) attached to a rear wheel Wr to detect a wheel angular speed or velocity ω. Then, the control unit 124 performs an arithmetic operation on a wheel angular acceleration dω/dt [which will be hereinafter regarded as α (i.e., dω/dt=α )] based on a pulse signal indicative of the wheel angular velocity ω and supplies a signal indicative of the result of its computation to the motor controller 118. As illustrated in FIG. 3, the control unit 124 has an angular velocity computing device 123, an angular acceleration computing device 125 serving as a computing means, and a determining device 127 serving as a determining means. The signal detected from the encoder 122 is introduced into the angular velocity computing device 123 where the wheel angular velocity ω is calculated. Then, the angular acceleration computing device 125 calculates the wheel angular acceleration α based on the calculated wheel angular velocity ω. The determining device 127 makes a decision as to whether or not the wheel angular acceleration ∝ falls within a predetermined value range or below a predetermined value and supplies the result of determination to the motor controller 118. A front-wheel braking device has a master cylinder 132 which is driven by a brake lever 130 attached to a handle 128, and a caliper cylinder 134 used to brake a front wheel Wf. The master cylinder 132 and the caliper cylinder 134 are mutually connected to each other via the main body 114 disposed above the front fork 112. The master cylinder 132 adjusts the hydraulic pressure under the action of the brake lever 130 and transmits the adjusted hydraulic pressure to a cut valve 156 to be described later. On the other hand, the caliper cylinder 134 serves to apply braking to a disk plate 120 based on the hydraulic pressure controlled by the cut valve 156. As shown in FIG. 2, the brake control system 110 includes the d.c. motor 116 serving as a drive source, which has a drive shaft connected with a pinion 136 which is maintained in meshing engagement with a gear 138. A crank shaft 140 is fixedly mounted in the center of the gear 138. One end of a crank pin 144 is coupled via a crank arm 142 to the crank shaft 140. A crank arm 146 is coupled to the other end of the crank pin 144, and a potentiometer 148 for detecting a displacement angle of the crank pin 144 is coupled to the crank arm 146. A cam bearing 150 is rotatably mounted on the outer peripheral surface of the crank pin 144. The cam bearing 150 is pressed upward by return springs 152. An expander piston 154, which is moved upward and downward under the displacement action of the cam bearing 150, is abutted against the upper surface of the cam bearing 150. Thus, the cut valve 156 is opened and closed under an up-and-down movement of the expander piston 154. The cut valve 156 is disposed in a cut valve holder 158 so that it can be moved in upward and downward directions. An input port 160, which communicates with the master cylinder 132, is defined above the surface of the cut valve 156, whereas an output port 162, which communicates with the caliper cylinder 134, is defined in a continuous or connecting portion between the cut valve holder 158 and the expander piston 154. The input port 160 and the output port 162 communicate with each other through a communication hole 164 defined in the outer peripheral surface of the cut valve 156. The brake control system 110 according to the first embodiment is constructed as described above. The operation of the brake control system 110 will now be described below. Upon normal braking, the cam bearing 150 is maintained at the top dead center by resilient forces of the return springs 152 to thereby hold the expander piston 154 in a forced-up state. Thus, the cut valve 156 is forced up by the expander piston 154 so as to be forcibly brought into an open state. Then, when the brake lever 130 is gripped, braking hydraulic pressure generated by the master cylinder 132 is transmitted to the caliper cylinder 134 through a passage 166, the input port 160, the communication hole 164, the output port 162 and a passage 168 in that order. A description will now be made, with reference to a flowchart shown in FIG. 4, to a case in which the braking of the front wheel Wf is made while the motorcycle X is running at a desired wheel angular velocity ω, and the grounding load of the rear wheel Wr, which is reduced by decelerating the wheel angular velocity ω, is detected in this condition. It is first necessary to reduce the body velocity of the motorcycle X to a given set value or below in order to reduce the grounding load of the rear wheel Wr and set it to a limit grounding load (hereinafter called a "W LiM ") which makes it hard to receive information fed back from a road surface. Then, the angular acceleration α (hereinafter called "front-wheel angular acceleration α f ) of the front wheel Wf is compared with a set value α L/V to thereby detect the result of its comparison (Step S1). Incidentally, the front-wheel angular velocity α f is regarded as -α f because it becomes a negative value due to the above deceleration, whereas the set value α L/V is taken as a positive value. The set value α L/V represents a value at the time that the grounding load of the rear wheel Wr, which is preset based on the dimensions and test data of the vehicle body, reaches W LiM . In this case, the signal detected from the encoder 122 attached to the rear wheel Wr is supplied via the angular velocity computing device 123 to the angular acceleration computing device 125 where the front-wheel angular acceleration α f is computed. Then, the determining device 127 makes a decision as to whether or not the front-wheel angular acceleration -α f outputted from the angular acceleration computing device 125 is larger than the set value α L/V . In order to reduce or decelerate the body velocity of the motorcycle X, the following two cases are known in which only the braking device of the front wheel Wf is actuated at a time t 1 as shown in FIG. 5 (see Steps S2 through S4) and the braking devices of the front and rear wheels Wf and Wr are simultaneously actuated at a time t 1 as illustrated in FIG. 6 (see Steps S6 and S7). In the former case, as indicated by a wheel angular velocity curve A1 in FIG. 5, the angular velocity ω of the rear wheel Wr reaches a substantially constant value at a time t 2 when a predetermined time interval has elapsed from the time t 1 . When the wheel angular velocity curve A1 is associated with a wheel angular acceleration curve A2, the wheel angular acceleration curve A2 indicative of a wheel angular acceleration α (hereinafter called "a rear-wheel angular acceleration α r ) of the rear wheel Wr falls within the range between a wheel angular acceleration α 0 (α>0) preset to 0 and a wheel angular acceleration -α 0 while the wheel angular velocity curve A1 is continuously maintained at a substantially constant value. When the time for holding this state exceeds a preset time T L/V (Steps S2 and S4), it can be determined that the grounding load of the rear wheel Wr has been reduced (Steps S3 and S7). This is based on the following reason. That is, since the rear wheel Wr is reduced in the grounding load and rotated in a substantially free state, the wheel angular velocity curve A1 does not fall and is maintained at a substantially constant value. In addition, the wheel angular acceleration curve A2 corresponding to such a wheel angular velocity curve A1 is also held at a value near to 0. In the latter case, on the other hand, the angular velocity ω of the rear wheel Wr is rapidly reduced as indicated by a wheel angular velocity curve B1 in FIG. 6 at a time t 2 when a predetermined time interval has elapsed from a time t 1 . When a rear-wheel angular acceleration α r is less than or equal to a preset lower-limit wheel angular acceleration α min in accordance with the decrease in the angular velocity ω of the rear wheel Wr, it can be determined that the grounding load of the rear wheel Wr has been reduced (Step S6). This is because when the grounding load of the rear wheel Wr is reduced, the rear wheel Wr rapidly stops rotating under the action of the braking device and the angular acceleration α r of the rear wheel Wr assumes a large negative value. FIG. 7 is a view for describing the logic of the determining device 127 in the control unit 124. If the angular acceleration α r of the rear wheel Wr falls within an allowable range near zero, i.e., ±α 0 (Step S3) or α r is less than or equal to the lower-limit wheel angular acceleration α min (Step S6) in FIG. 7, it is then determined that the grounding load of the rear wheel Wr has been reduced (Step S7). If it is determined in the control unit 124 that the grounding load of the rear wheel Wr has been reduced, then the control unit 124 is activated to cause the motor controller 118 to energize and de-energize the d.c. motor 116. When the d.c. motor 116 is energized, a rotatable shaft (not shown) of the d.c. motor 116 is rotatably driven to rotate the pinion 136 coupled to the rotatable shaft thereof. Then, the crank pin 144 is rotated in response to the rotation of the pinion 136 through the gear 138 held in meshing engagement with the pinion 136, and the crank shaft 140 and the crank arm 142 both coupled to the gear 138. The cam bearing 150 is moved away from the top dead center under the rotation of the crank pin 144 so as to lower the expander piston 154. As a result, the cut valve 156 is closed to stop the supply of the braking hydraulic pressure to the caliper cylinder 134 of the front wheel Wf. When the expander piston 154 is further lowered from this condition, the braking hydraulic pressure to be supplied to the caliper cylinder 134 is reduced to increase the angular velocity ω of the front wheel Wf. As a result, a reduction in the grounding load of the rear wheel Wr can be avoided. FIG. 8 is a view for describing other logic of a determining device 127 in a brake control system 110 according to a second embodiment of the present invention. It is determined in the determining device 127 whether or not the angular acceleration α r of the rear wheel Wr is less than or equal to the lower-limit wheel angular acceleration α min while the main body 114 is in operation. Alternatively, it is determined whether or not the absolute value of the angular acceleration α r of the rear wheel Wr falls within the allowable range α 0 during the operation of the main body 114. As a result, a decision can be made as to whether or not the grounding load of the rear wheel Wr has been reduced. The above judgments may be carried out during the operation of the braking device of the front wheel Wf as an alternative to during the operation of the main body 114. Further, the second embodiment has shown a case in which the brake control system 110 has been attached to the front wheel Wf. It is however needless to say that the brake control system 110 may be attached to either the rear wheel Wr or both wheels Wf, Wr. As an alternative to the angular velocity computing device 123 and the angular acceleration computing device 125, a device for directly measuring a deceleration of the rear wheel Wr using an acceleration sensor or the like can also be provided, thereby making it possible to detect the grounding load of the rear wheel Wr based on the measured output. Further, the pressure of brake fluid supplied to the caliper cylinder 134 can also be measured by a pressure sensor or the like so as to detect the grounding load of the rear wheel Wr under certain pressure or above. The present embodiment has shown a case in which a sensor is attached to the rear wheel Wr and a means for controlling a brake disposed on the front wheel Wf side is provided. However, the control similar to that performed in the present embodiment can be carried out even in the case where both of a sensor and a brake control means are mounted to the front and rear wheels respectively or even in the other case. In the brake control method according to the present invention, after the grounding loads of respective wheels at the time of running of a vehicle such as a motorcycle have been determined, a predetermined correction value for the braking of each wheel is computed as data based on the determined ground loads. Further, the data about the computed correction value is electrically processed together with other data so as to obtain a braking signal. Therefore, the most suitable braking force can be obtained according to a variation in the grounding load distribution of the front and rear wheels. Particularly, the grounding load distribution on the front wheel can be prevented from increasing upon braking. It is thus possible to easily improve the control feeling at the time that the braking is applied to the vehicle. Further, in the brake control system according to the present invention, the modulator may be controlled by providing a target angle of the crank pin 114 to the motor controller 118, the target angle being based on for example front and rear wheel speeds, and a value for correcting the target angle of a crank member may be computed based on the determined grounding loads to thereby correct the target angle based on the computed correction value. Therefore, the optimum brake control can be effected without being affected by a variation in the grounding load distribution between the front and rear wheels. Furthermore, in the brake control system according to the present invention, a reduction in the grounding load on the rear wheel can be judged from the deceleration of the rear wheel. A further reduction in the grounding load on the rear wheel can be reliably avoided by reducing and controlling the braking force of the front wheel based on the result of judgment. As a result, the front and rear wheels can be maintained at a suitable grounding state at all times. It is also possible to apply the brakes in a comfortable feeling at all times.

Claims: A system (110) for controlling brakes (120) attached to a vehicle (X), comprising: deceleration detecting means (122, 125) for determining the deceleration (αr) of a rear wheel the system being characterised in that it includes: determining means (127) for determining that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) falls within a preset range (±αo) about zero during the operation of a front-wheel brake (120); and controlling means (118) for reducing and controlling a braking force of the front-wheel brake (120) based on said result of determination by said determining means (127). A system for controlling brakes according to claim 1, wherein said determining means (127) determines that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) continuously falls within said preset range (±αo) about zero for a predetermined period of time (TL/V) or longer during the operation of said front-wheel brake (120). A system for controlling brakes according to claim 1 or 2, wherein said determining means (127) determines that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) is smaller than a predetermined value (αmin) while front-wheel and rear-wheel brakes are being operated. A system for controlling brakes according to claim 3, wherein said determining means (127)determines that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) is continuously smaller than said preset value (αmin) for a predetermined period of time or longer while said front-wheel and rear-wheel brakes are being operated. A system for controlling brakes according to any preceding claim, wherein said controlling means (118) is operable to prevent a front wheel (Wf) from being locked under the operation of said front-wheel brake (120); wherein said determining means (127) determines that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) falls within a preset range about zero (±αo) during the operation of said controlling means (118); and wherein said controlling means (118) is activated to reduce and control the braking force of said front-wheel brake (120) when said rear-wheel grounding load is less than or equal to said predetermined value. A system for controlling brakes according to any preceding claim, wherein said controlling means (118) is operable to prevent a front wheel (Wf) from being locked under the operation of said front-wheel brake (120); wherein said determining means (127) determines that a rear-wheel grounding load is less than or equal to a predetermined value when said deceleration (αr) is smaller than a preset value (αmin) during the operation of at least said controlling means (118); and wherein said controlling means (118) is activated to reduce and control the braking force of said front-wheel brake (120) when said rear-wheel grounding load is less than or equal to said predetermined value. A system for controlling brakes according to any preceding claim, further comprising: target angle computing means for computing a target angle of a crank member (144) abutted against an expander piston (154) which forms a modulator together with the crank member (144) and increases the volume of an output hydraulic chamber (162) when antilock braking is made; correction value computing means for computing a value for the correction of said target angle based on said detected grounding loads; and target angle correcting means for computing a corrected target angle based on said computed correction value and said target angle. A system according to any preceding claim, wherein the deceleration detecting means comprises: detecting means (122) for detecting the rotational speed of a rear wheel (Wr); and calculating means (125) for calculating a rear-wheel deceleration (αr) from said detected rotational speed. A system according to any preceding claim, further including hydraulic pressure detecting means for detecting caliper hydraulic pressure of the front-wheel brake and wherein said determining means determines that the grounding load of the rear wheel is less than or equal to a predetermined value when said caliper hydraulic pressure is larger than a predetermined hydraulic pressure value.

Inventors: MATSUTO TAKUSHI, OTA ATSUO, SUZUKI OSAMU, MATSUTO, TAKUSHI, OTA, ATSUO, SUZUKI, OSAMU, Matsuto, Takushi, c/o K.K Honda Gijyutsu Kenkyusho, Ota, Atsuo, c/o K.K. Honda Gijyutsu Kenkyusho, Suzuki, Osamu, c/o K.K. Honda Gijyutsu Kenkyusho
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: B60T8
IPC codes: B60T8, B60G17