Method of and system for controlling brakes

Abstract: A method of and a system for controlling antilocking brakes (62, 66) employed in a vehicle (10) such as a motorcycle. The position of an expander piston (46) which constitutes an antilocking modulator (22) is detected and the torque of a rotative drive source (24) for actuating the expander piston is detected. A braking force used for each of the brakes is then computed from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position. Further, friction coefficients of a road surface are estimated from the braking force thus computed and a target slip ratio is estimated from the estimated friction coefficients so as to carry out the optimum braking. Accordingly, the optimum target slip ratio can be estimated depending on high and low µ roads, thereby making it possible to provide satisfactory braking.

Description: The present invention relates to a method of and a system for controlling antilocking brakes employed in a vehicle, a motorcycle, etc. A system for controlling antilocking brakes has been employed in a vehicle, a motorcycle, etc., for example. As a type of brake control system, there is known one (see, for example, EP 0 392 686 (General Motors)) in which a slip ratio of each wheel with respect to a road surface is computed based on the speed or velocity (Vc) of a running vehicle and the speed or velocity (Vw) of each wheel and the optimum braking is applied to the vehicle based on the computed slip ratio. Here, the slip ratio represents a value calculated from Vc-Vw/Vc. The relationship between the slip ratio of each wheel with respect to the road surface and a friction coefficient (µ) relative to the direction of rotation of each wheel is normally represented as shown in FIG. 1. The slip ratio vs. friction coefficient characteristic varies depending on the state of the road surface due to rain, snow or sand or the like. However, the µ value shows the peak in the slip ratio range of 10% to 20%. Therefore, the braking control can be carried out by causing the slip ratio to converge to a range in the vicinity of the slip ratio range of 10% to 20%. The relationship between a friction coefficient (µ) in the lateral or transverse direction (normal to the direction of the rotation) of each wheel and the slip ratio is then represented as shown in FIG. 2. In case of a road surface (hereinafter called a "low µ road") of a low friction coefficient, such as a frozen snow surface, the value of µ of the transverse direction of each wheel is reduced as compared with a road surface (hereinafter called a "high µ road") of a high friction coefficient, such as an asphalt road surface. It is therefore preferable to ensure the stability of the vehicle by setting a target slip ratio to a low value in the low µ road. On the other hand, both a lock speed and a return or reset speed of each wheel with respect to the caliper pressure also vary greatly depending on µ of the road surface. In case of the high µ road, the lock speed is slow and the reset speed is fast. In case of the low µ road to the contrary, the reset speed is slow and the lock speed is fast (see FIG. 3). Thus, when the braking control is made at the same operation speed in varying the caliper pressure (hereinafter called a "pressure increasing and reducing rate") in spite of the fact that a difference is developed between the lock speed and the reset speed of each wheel with respect to the road surface owing to a variation in µ, the optimum braking control cannot be attained for either a high µ road or a low µ road. It has been proposed therefore that the braking control be carried out by estimating µ from an actual vehicle deceleration and a wheel velocity or the like. However, the value of µ tends to vary greatly due to a variation in the state of braking of a front wheel and/or a rear wheel, for example. It has thus also been proposed that the caliper pressure is directly measured to more accurately estimate µ. However, an expensive and heavy hydraulic-pressure sensor is required, which will cause problems from the standpoint of the manufacturing cost and the weight. Therefore, this type of hydraulic-pressure sensor has not been conventionally used. With the foregoing problems in view, it is a general object of the present invention to provide a method of and a system for controlling brakes wherein µ can be easily and accurately estimated or computed, thereby making it possible to provide the optimum brake control. Viewed from one broad aspect the present invention provides a method of controlling brakes, comprising steps of detecting the position of an expander piston constituting an antilocking modulator, detecting the torque of a rotative drive source for driving the expander piston, computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, estimating friction coefficients of a road surface from the computed braking force, and carrying out the optimum braking by estimating a target slip ratio from the estimated friction coefficients. In a preferred arrangement a crank angle of a crank pin held in engagement with the expander piston is detected as the step of detecting the position of the expander piston, a terminal current value of a d.c. motor is detected as the step of detecting the torque of the d.c. motor serving as the rotative drive source, and caliper pressure is computed as a driving force for each of the brakes from the crank angle and the terminal current value to thereby perform the optimum braking. Viewed from another aspect the present invention provides a method of controlling brakes, comprising steps of detecting the position of an expander piston constituting an antilocking modulator, detecting the torque of a rotative drive source for driving the expander piston, computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, estimating friction coefficients of a road surface from the computed braking force, and carrying out the optimum braking by estimating a pressure increasing and reducing rate from the estimated friction coefficients. Viewed from a further aspect the present invention provides a method of controlling brakes, comprising steps of detecting the position of an expander piston constituting an antilocking modulator, detecting the torque of a rotative drive source for driving the expander piston, computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, estimating friction coefficients of a road surface from the computed braking force, and carrying out the optimum braking by estimating a target slip ratio and a pressure increasing and reducing rate from the estimated friction coefficients. Viewed from another aspect the present invention provides a system for controlling brakes, comprising means for detecting the position of an expander piston constituting an antilocking modulator, means for detecting the torque of a rotative drive source for driving the expander piston, means for computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, and means for estimating friction coefficients of a road surface from the computed braking force and estimating a target slip ratio from the estimated friction coefficients. Viewed from another aspect the present invention provides a system for controlling brakes, comprising means for detecting the position of an expander piston constituting an antilocking modulator, means for detecting the torque of a rotative drive source for driving the expander piston, means for computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, and means for estimating friction coefficients of a road surface from the computed braking force and estimating a pressure increasing and reducing rate from the estimated friction coefficients. Viewed for a further aspect the present invention provides a system for controlling brakes, comprising means for detecting the position of an expander piston constituting an antilocking modulator, means for detecting the torque of a rotative drive source for driving the expander piston, means for computing a braking force for each of the brakes from the detected position of the expander piston and the detected torque of the rotative drive source at the detected position, and means for estimating friction coefficients of a road surface from the computed braking force and estimating a target slip ratio and a pressure increasing and reducing rate from the estimated friction coefficients. Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- FIG. 1 is a graph for describing normal µ-S curves corresponding to various states of a road surface; FIG. 2 is a graph for describing relationships between a wheel transverse friction coefficient (µ) and a slip ratio; FIG. 3 is a graph for describing relationships between return forces and decelerating forces at high and low µ roads; FIG. 4 is a view schematically showing the structure of a system for carrying out a brake control method according to a first embodiment of the present invention; FIG. 5 is a schematic exterior view showing a motorcycle in which the brake control system shown in FIG. 4 is to be provided; FIG. 6 is a graph for describing a relationship between initial pressure (P o ) and µ of a road surface; FIG. 7 is a graph for describing relationships between µ of a road surface, a target slip ratio and a pressure increasing and reducing rate; FIG. 5 is a schematic exterior view showing a motorcycle in which a system for controlling brakes according to a first embodiment of the present invention is incorporated. In the same drawing, reference numeral 10 indicates the motorcycle. The motorcycle 10 comprises a main body 12, a handle 14, a front wheel 16 and a rear wheel 18. The brake control system 20 according to the first embodiment is disposed in the motorcycle 10. As shown in FIG. 4, the brake control system 20 has an antilocking modulator 22. A pinion 26 is rotatably mounted to a d.c. motor (rotative drive source) 24 of the modulator 22 and maintained in meshing engagement with a gear 28. The gear 28 is supported by a crank shaft 30 to which one end of a crank pin 34 is eccentrically coupled via a crank arm 32. A potentiometer 38 serving as a means for detecting the position of an expander piston (to be described later) is attached to the other end of the crank pin 34 via another crank arm 36. A cam bearing 40 is rotatably mounted on the crank pin 34. The lower end of the cam bearing 40 is always pressed toward the upper limit position under the action of return springs 44 held in a spring holder 42. The expander piston 46 is brought into abutment against the upper end of the cam bearing 40 and displaced in upward and downward directions in response to an up-and-down movement of the cam bearing 40 so as to open and close a cup valve 48. A cup valve holder 50 having the cup valve 48 incorporated therein is disposed in the upper part of the expander piston 46. A master cylinder 56 is coupled via a passage 54 to an input port 52 of the cut valve holder 50. On the other hand, a wheel braking caliper cylinder 62 is coupled via a passage 60 to an output port 58 of the cup valve holder 50. The master cylinder 56 and the caliper cylinder 62 are interconnected with each other via the passage 54, the modulator 22 and the passage 60. This path is filled with oil for the hydraulic pressure. The master cylinder 56 is actuated to adjust the hydraulic pressure under the action of a brake lever 64 so as to cause the cut valve 48 to actuate the caliper cylinder 62, thereby applying a braking force to a disk plate 66 disposed in the front wheel 16 and/or the rear wheel 18. A motor controller 70 is electrically connected to the potentiometer 38 and the d.c. motor 24. The motor controller 70 is activated to supply information about the angular position of the crank pin 34, which has been detected by the potentiometer 38, i.e., information about the position of the expander piston 46 and a terminal current value of the d.c. motor 24 to a control unit 72. The control unit 72 has a function for computing caliper pressure (braking forces for brakes) based on the motor torque obtained from the terminal current value of the d.c. motor 24 and the position of the expander piston 46. Further, the control unit 72 also has a memory 74 in which a first table (to be described later) for predicting or estimating a friction coefficient (µ) of a road surface based on the initial pressure obtained from the computed caliper pressure and a second table (to be described later) for estimating a target slip ratio and/or a pressure increasing and reducing rate from the estimated friction coefficient (µ) have been stored as data. A sensor 76 for detecting a wheel speed, which is attached to the disk plate 66, is electrically connected to the control unit 72. The operation of the brake control system 20 constructed as described above will now be described below in connection with the brake control method according to the first embodiment of the present invention. Upon normal braking, the crank pin 34 is maintained at a predetermined upper limit position by resilient forces of the return springs 44 to thereby cause the cam bearing 40 mounted on the crank pin 34 to hold the expander piston 46 in a forced-up state. Thus, the cut valve 48 is forced up by the expander piston 46 so as to cause the input port 52 to communicate with the output port 58. When the brake lever 64 is gripped, the master cylinder 56 is actuated in such a manner that brake hydraulic pressure generated by the master cylinder 56 is transmitted to the caliper cylinder 62 through the passage 54, the input port 52, the output port 58 and the passage 60 in that order, thereby applying a braking force to the disk plate 66. When the control unit 72 then supplies a drive signal to the motor controller 70 to control a desired brake, the motor controller 70 controls the direction and amount of rotation of the d.c. motor 24. Therefore, the pinion 26 mounted on an unillustrated rotatable shaft is rotated to turn both the gear 28 held in meshing engagement with the pinion 26 and the crank arm 32 fixedly mounted to the gear 28 via the crank shaft 30, thereby displacing the crank pin 34 mounted to the crank arm 32 from the upper limit position to the lower limit position. Thus, the cam bearing 40 is lowered under the displacement action of the crank pin 34, so that the brake hydraulic pressure which acts on the expander piston 46 is added to the torque of the d.c. motor 24. Therefore, the expander piston 46 is pressed against the cam bearing 40 so as to be promptly lowered. When the expander piston 46 is lowered a predetermined amount, the cup valve 48 is seated to thereby block the communication between the input port 52 and the output port 58. Thus, when the expander piston 46 is further lowered singly, the volume on the output port 58 side increases so as to decrease the hydraulic pressure applied to the caliper cylinder 62, thereby reducing a braking force applied to the front wheel 16, for example. Now, the position of the expander piston 46 is detected by the potentiometer 38 as a crank angle in accordance with the displacement of the crank pin 34. A value outputted from the potentiometer 38 is introduced into the motor controller 70 as data. Afterwards, the motor controller 70 supplies the output value of the potentiometer 38 and the terminal current value of the d.c. motor 24 to the control unit 72. In the control unit 72, the motor torque (TM) of the d.c. motor 24 is first computed based on the terminal current value and the caliper pressure (PC) is then computed in accordance with the following respective equations: Tm = KT·(IM - IO) TP = (Z·Z·JM + JC)·ω - TM + TS ± TF PC = 4·TP/(π·D·D·e·sin c ) where TM: motor torque IM: motor current TP: caliper pressure torque JM: motor inertial mass ω : crank angular acceleration TF: friction torque KT: motor torque constant IO: motor non-load current Z : reduction ratio JC: crank inertial mass TS: B/USPG torque D : diameter of expander piston e : eccentric amount of crank  c : crank angle After the caliper pressure (PC) has been estimated in this way, the initial pressure (P o ) is computed based on the caliper pressure (PC) and the crank angle at the time of its estimation. The initial pressure (P o ) represents the caliper pressure at the moment that the cup valve 48 has been seated. Then, µ of the road surface, which corresponds to the computed initial pressure (P o ), is estimated based on the first table (see FIG. 6), which has been stored as data in the memory 74 of the control unit 72. Further, the target slip ratio and/or the pressure increasing and reducing rate, which corresponds to the estimated µ, is estimated based on the second table (see FIG. 7) stored as data in the memory 74. Thus, the control unit 72 outputs a signal for controlling a braking force to the motor controller 70 based on the target slip ratio and/or the pressure increasing and reducing rate in such a manner that the motor controller 70 controls the direction and amount of rotation of the d.c. motor 24, thereby placing the expander piston 46 in a desired position. Consequently, the braking force of the front wheel 16 and/or the rear wheel 18 is controlled. In the first embodiment, the crank angle of the crank pin 34 is detected by the potentiometer 38. At the same time, the terminal current value of the d.c. motor 24 is also detected. Afterwards, the caliper pressure (PC) is computed from the detected crank angle and terminal current value. Further, the µ and the target slip ratio and/or the pressure increasing and reducing rate are estimated based on the first and second tables after the initial pressure (P o ) has been computed. Therefore, dedicated sensors such as a conventional expensive and heavy hydraulic sensor, etc. can be omitted, thereby making it possible to provide the brake control system 20 which is extremely economical and light in weight. By selecting a target slip ratio in accordance with a low µ road and a high µ road in particular, the optimum target slip ratio can be estimated based on the estimated µ. That is, the target slip ratio can be set to a low value so as to secure the stability of the vehicle under the low µ road. On the other hand, the target slip ratio can be set to a high value so as to secure a satisfactory deceleration under the high µ road. In addition, a µ-S curve itself can be computed based on the caliper pressure (PC) computed from the equations (1) through (3), a wheel acceleration/deceleration determined from the sensor 76 and the wheel slip ratio or the like. Thus, the µ can be more accurately estimated, thereby making it possible to estimate the target slip ratio with high accuracy. Incidentally, the first embodiment has shown a case in which the caliper pressure of the caliper cylinder 62 for applying the braking force to the disk plate 66 is computed so as to estimate the µ and the target slip ratio. However, the present embodiment can be applied even to a case where a braking force is applied to a drum brake. At this time, a brake shoe attached to the drum brake under pressure is used as the caliper cylinder 62. The caliper pressure (PC) corresponding to the degree of opening of the brake shoe is computed based on a crank angle and a terminal current value, thereby estimating µ and a target slip ratio based on the computed caliper pressure (PC). Further, the above-described embodiment has shown a case in which the front wheel 16 is controlled, as an illustrative example. However, the rear wheel 18 can also be controlled in the same manner as described above. In the method of and the system for controlling the brakes described above, a braking force for each of the brakes is computed based on the position of an expander piston of an antilocking modulator and the torque of a rotative drive source for driving the expander piston. Afterwards, a friction coefficient of a road surface is estimated from the computed braking force. In addition, a target slip ratio and/or a pressure increasing and reducing rate is estimated from the estimated friction coefficient to thereby carry out the optimum braking. Therefore, the optimum target slip ratio and/or pressure increasing and reducing rate can be estimated in association with high and low µ roads, thereby making it possible to provide satisfactory braking. It is also only necessary to detect the position of the expander piston and the torque of the rotative drive source. It is thus unnecessary to use a hydraulic-pressure sensor which is expensive and heavy in weight, thereby making it possible to provide the brake control method which can be efficiently carried out and the brake control system which is extremely economical and light in weight.

Claims: A method of controlling brakes (62, 66), comprising steps of: detecting the position of an expander piston (46) constituting an antilocking modulator (22); detecting the torque of a rotative drive source (24) for driving said expander piston; computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; estimating friction coefficients of a road surface from said computed braking force; and carrying out the optimum braking by estimating a target slip ratio from said estimated friction coefficients. A method according to claim 1, wherein a crank angle of a crank pin (34) held in engagement with said expander piston (46) is detected as said step of detecting the position of said expander piston, a terminal current value of a d.c. motor (24) is detected as said step of detecting the torque of said d.c. motor serving as said rotative drive source, and caliper pressure is computed as a driving force for each of the brakes from said crank angle and said terminal current value to thereby carry out said step of the optimum braking. A method of controlling brakes, comprising steps of: detecting the position of an expander piston (46) constituting an antilocking modulator (22); detecting the torque of a rotative drive source (24) for driving said expander piston; computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; estimating friction coefficients of a road surface from said computed braking force; and carrying out the optimum braking by estimating a pressure increasing and reducing rate from said estimated friction coefficients. A method according to claim 3, wherein a crank angle of a crank pin (34) held in engagement with said expander piston (46) is detected as said step of detecting the position of said expander piston, a terminal current value of a d.c. motor (24) is detected as said step of detecting the toroque of said d.c. motor serving as said rotative drive source, and caliper pressure is computed as a driving force for each of said brakes from said crank angle and said terminal current value to thereby carry out said step of the optimum braking. A method of controlling brakes, comprising steps of: detecting the position of an expander piston (46) constituting an antilocking modulator (22); detecting the torque of a rotative drive source (24) for driving said expander piston; computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; estimating friction coefficients of a road surface from said computed braking force; and carrying out the optimum braking by estimating a target slip ratio and a pressure increasing and reducing rate from said estimated friction coefficients. A method according to claim 5, wherein a crank angle of a crank pin (34) held in engagement with said expander piston (46) is detected as said step of detecting the position of said expander piston, a terminal current value of a d.c. motor (24) is detected as said step of detecting the toroque of said d.c. motor serving as said rotative drive source, and caliper pressure is computed as a driving force for each of said brakes from said crank angle and said terminal current value to thereby carry out said step of the optimum braking. A system (20) for controlling brakes (62, 66), comprising: means (38) for detecting the position of an expander piston (46) constituting an antilocking modulator (22); means (72) for detecting the torque of a rotative drive source (24) for driving said expander piston; means (72) for computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; and means (72) for estimating friction coefficients of a road surface from said computed braking force and estimating a target slip ratio from said estimated friction coefficients. A system (100) for controlling brakes, comprising: means (38) for detecting the position of an expander piston constituting an antilocking modulator (22); means (72) for detecting the torque of a rotative drive source (24) for driving said expander piston; means (72) for computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; and means (72) for estimating friction coefficients of a road surface from said computed braking force and estimating a pressure increasing and reducing rate from said estimated friction coefficients. A system for controlling brakes, comprising: means (38) for detecting the position of an expander piston (46) constituting an antilocking modulator (22); means (72) for detecting the torque of a rotative drive source (24) for driving said expander piston; means (72) for computing a braking force for each of said brakes from said detected position of said expander piston and said detected torque of said rotative drive source at said detected position; and means for estimating friction coefficients of a road surface from said computed braking force and estimating a target slip ratio and a pressure increasing and reducing rate from said estimated friction coefficients.

Inventors: MATSUTO TAKUSHI, OTA ATSUO, SUZUKI OSAMU, MATSUTO, TAKUSHI, OTA, ATSUO, SUZUKI, OSAMU, MATSUTO, TAKUSHI, C/O KABUSHIKI KAISHA HONDA, OTA, ATSUO, C/O KABUSHIKI KAISHA HONDA, SUZUKI, OSAMU, C/O KABUSHIKI KAISHA HONDA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: B60T8
IPC codes: B60T8