BRAKE PRESSURE CONTROL DEVICE FOR VEHICLES

Abstract: A brake pressure control device for vehicles is provided in a pipeline connecting a master cylinder (22) and a wheel brake (23) with an electromagnetic directional control valve (24) which is switched in a plurality of valve positions by electromagnetic force. The electromagnetic directional control valve (24) is switched between a first valve position and a second valve position. Bidirectional flow of fluid is allowed when the electromagnetic directional control valve is in the first valve position. Unidirectional flow of the fluid is allowed but reverse flow of the fluid is prevented when the electromagnetic directional control valve is in the second valve position.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a brake pressure control device for vehicles, which is adapted to perform brake pressure control such as antilocking control, traction control, automatic brake control for vehicle-to-vehicle distance control, automatic brake control for obstacle avoidance, etc. Description of the Prior Art As the simplest method of controlling brake pressure for antilocking control, traction control, automatic brake control for vehicle-to-vehicle distance control, automatic brake control for obstacle avoidance etc., it is well known to provide an electromagnetic directional control valve, which is switched in a plurality of positions by electromagnetic force, in a pipeline connecting a master cylinder and a wheel brake. A typical brake pressure control device for antilocking control is disclosed in U.S. Patent No. 3,617,098, for example. Fig. 1 is a hydraulic pressure circuit diagram of the brake pressure control device as disclosed in U.S. Patent No. 3,617,098. Referring to Fig. 1, an electromagnetic directional control valve 4, which is switched between two positions by electromagnetic force, is provided in a pipeline connecting a master cylinder 2 for converting operating force of a brake pedal 1 into hydraulic pressure and a wheel brake 3. An auxiliary power circuit 5 is provided in parallel with the electromagnetic directional control valve 4. A pump 7 is provided in the auxiliary power circuit 5, to be driven by a motor 6. An electromagnetic directional control valve 8, which is switched between two positions by electromagnetic force, and a reservoir 9 are further provided in the auxiliary power circuit 5, as shown in Fig. 1. A check valve 10 is provided in a circuit 11 which is in parallel with the electromagnetic directional control valve 4. The check valve 10 allows flow of fluid from the wheel brake 3 to the master cylinder 2, while preventing reverse flow of the fluid. It is assumed here that an antilocking signal is generated when the brake pedal 1 is worked in the hydraulic pressure circuit as shown in Fig. 1. The positions of the electromagnetic directional control valves 4 and 8 are suitably switched by the signal. Pressure against the wheel brake 3 is reduced when both of the electromagnetic directional control valves 4 and 8 are fed with electricity and retained when only the electromagnetic directional control valve 4 is fed with electricity, while being increased when the electromagnetic directional control valves 4 and 8 are fed with no electricity. Under such antilocking control, the pressure against the wheel brake 3 is controlled to be lower than that of the master cylinder 2. However, when the driver relaxes operating force against the brake pedal 1 for relaxing braking force during the control, the brake pressure must be lowered responsively. The check valve 10 is provided in order to satisfy such requirement. If, for example, the operating force against the brake pedal 1 is relaxed when the electromagnetic directional control valve 4 is fed with electricity, the pressure of the master cylinder 2 becomes lower than that against the wheel brake 3, whereby the fluid passes through the check valve 10 to flow toward the master cylinder 2. Thus, the brake pressure against the wheel brake 3 is also lowered in response to relaxation of the operating force by the brake pedal 1. Also in case where the brake pedal 1 is not worked in automatic brake control for traction control or vehicle-to-vehicle distance control, for example, the pressure against the wheel brake 3 must be increased when the driver works the brake pedal 1 so that the pressure against the wheel brake 3 is higher than automatic control pressure. Such operation is required in quick braking during start control in traction control, for example. In order to satisfy such requirement, it is necessary to provide another check valve, which is directed reverse to the check valve 10, in the hydraulic pressure circuit as shown in Fig. 1. The newly provided check valve is adapted to allow flow of the fluid from the master cylinder 2 to the wheel brake 3 while preventing reverse flow. When the brake pedal 1 is worked in such circuit structure, the pressure against the wheel brake 3 is also increased responsively. A device employing no check valve is also proposed in the art as a system for varying pressure against a wheel brake with change in operating force of a brake pedal during antilocking control or traction control. In U.S. Patent No. 4,462,642, hydraulic pressure sensors are provided in front and at the back of a cutoff valve, which is provided in a pipeline connecting a master cylinder and a wheel brake, to compare hydraulic pressure levels on both sides of the cutoff valve with each other, thereby to control operation of the cutoff valve in response to the hydraulic pressure levels. In the brake pressure control device as shown in Fig. 1, the check valve 10 must be provided in parallel with the electromagnetic directional control valve 4. Thus, the circuit structure and pipe arrangement are complicated, leading to economic loss and reduced reliability. Japanese Patent Laying-Open Gazette No. 202142/1983 also discloses a brake pressure control device having a check valve which is provided in parallel with an electromagnetic directional control valve. This brake pressure control device is also complicated in circuit structure, similarly to the brake pressure control device of U.S. Patent No. 3,617,098 as shown in Fig. 1. In particular, considerably complicated circuit structure is required in order to vary the pressure against the wheel brake with change in operating force of the brake pedal in both of antilocking control performed with the brake pedal being worked and traction control performed with no working of the brake pedal. Further, when hydraulic pressure sensors are provided on both sides of a cutoff valve as in the brake pressure control device disclosed in U.S. Patent No. 4,462,642, the entire device is increased in cost since the hydraulic sensors etc. are high-priced. SUMMARY OF THE INVENTION The present invention has been proposed in view of such circumstances, and an object thereof is to provide a brake pressure control device of simple circuit structure, in which brake pressure against a wheel brake can be changed with change in hydraulic pressure of a master cylinder when a brake pedal is worked in antilocking control etc. or when the brake pedal is not worked in traction control etc. More preferably, the present invention is directed to implement a brake pressure control device being applicable to both of antilocking control and traction control in simple structure, in which brake pressure against a wheel brake can be changed with change in hydraulic pressure of a master cylinder in both of antilocking control and traction control. The present invention is directed to a brake pressure control device for vehicles, which is provided with an electromagnetic directional control valve switchable in a plurality of valve positions by electromagnetic force in a pipeline connecting a master cylinder and a wheel brake. The feature of the present invention resides in that the said electromagnetic directional control valve has a valve position for allowing only unidirectional flow of fluid while preventing reverse flow. According to the present invention, a check valve is not fixedly provided in a pipeline as in the conventional case but selectively positioned in the pipeline or outside the pipeline by electromagnetic force, whereby the entire circuit structure and pipe arrangement are simplified to improve economical effects and reliability. When it is necessary to change brake pressure against a wheel brake following change in master cylinder pressure in antilocking control or traction control etc., an electromagnetic directional control valve may be driven to locate the check valve in the pipeline. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a hydraulic pressure circuit diagram of a brake pressure control device as shown in U.S. Patent No. 3,617,098; Fig. 2 is a hydraulic pressure circuit diagram of a first embodiment according to the present invention; Fig. 3 is a hydraulic pressure circuit diagram of a second embodiment according to the present invention; Fig. 4 is a hydraulic pressure circuit diagram of a third embodiment according to the present invention; Fig. 5 is a hydraulic pressure circuit diagram of a fourth embodiment according to the present invention; Fig. 6 is a hydraulic pressure diagram of a fifth embodiment according to the present invention; Fig. 7 is a hydraulic pressure circuit diagram of a sixth embodiment according to the present invention; Fig. 8 is a hydraulic pressure circuit diagram showing an example in which the present invention is applied to an FR car; Fig. 9 is a hydraulic pressure circuit diagram showing an example in which the present invention is applied to an FF car; Figs. 10A and 10B are sectional views showing the structure of an electromagnetic directional control valve 24 or 34 symbolically shown in Fig. 2 or 3, with Fig. 10A showing a state in which a coil is fed with no electricity and Fig. 10B showing a state in which the coil is fed with electricity; Fig. 11 is a sectional view showing another example of an electromagnetic directional control valve according to the present invention; and Fig. 12 is a partially enlarged sectional view of the electromagnetic directional control valve as shown in Fig. 11. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 2 is a hydraulic pressure circuit diagram showing a first embodiment of the present invention. An electromagnetic directional control valve 24 is provided in a pipeline connecting a master cylinder 22, which is adapted to convert operating force by a brake pedal 21 into hydraulic pressure, and a wheel brake 23. This electromagnetic directional control valve 24 is switched between a first valve position and a second valve position by electromagnetic force. Bidirectional flow of fluid is allowed when the electromagnetic directional control valve 24 is in the first valve position as shown in the figure. On the other hand, flow of the fluid from the wheel brake 23 to the master cylinder 22 is allowed but reverse flow is prevented when the electromagnetic directional control valve 24 is switched to the second valve position. An auxiliary power circuit 25, which is in parallel with the electromagnetic directional control valve 24, is provided therein with a pump 27 driven by a motor 26, an electromagnetic directional control valve 28 and a reservoir 29. In order to perform general brake operation by the brake pedal 21 or re-pressurization in antilocking control, the electromagnetic directional control valve 24 is brought into the first valve position as shown in Fig. 2. On the other hand, electricity is fed to the electromagnetic directional control valve 24 to bring the same into the second valve position, in order to reduce or retain brake pressure against the wheel brake 23 in antilocking control. In this case, operating force by the brake pedal 21 is so relaxed that hydraulic pressure of the master cylinder 22 is lower than the brake pressure against the wheel brake 23, whereby the fluid flows through the electromagnetic directional control valve 24. Namely, the brake pressure against the wheel brake 23 is lowered following reduction in hydraulic pressure of the master cylinder 22. Fig. 3 is a hydraulic pressure circuit diagram showing a second embodiment according to the present invention. An electromagnetic directional control valve 34 is provided in a pipeline connecting a master cylinder 32 for converting operating force by a brake pedal 31 into hydraulic pressure and a wheel brake 33. The electromagnetic directional control valve 34 is switched between first and second valve positions by electromagnetic force. Bidirectional flow of fluid is allowed when the electromagnetic directional control valve 34 is in the first valve position as shown in the figure. On the other hand, flow of the fluid from the master cylinder 32 to the wheel brake 33 is allowed but reverse flow is prevented when the electromagnetic directional control valve 34 is brought into the second valve position. An auxiliary power circuit 35 is provided in parallel with the electromagnetic directional control valve 34. The auxiliary power circuit 35 is provided therein with an electromagnetic directional control valve 36. A pump 40 provided in the auxiliary power circuit 34 sucks working fluid from a reservoir 39 to pressurize the same. As shown in Fig. 3, an electromagnetic directional control valve 38 is provided in a drain circuit 37 which communicates with the reservoir 39. In order to perform automatic brake control for traction control or stop retention, for example, the electromagnetic directional control valve 34 is brought into the second valve position. When a brake pedal 31 is worked in this state, hydraulic pressure of the master cylinder 32 exceeds brake pressure against the wheel brake 33, whereby the fluid flows through the electromagnetic directional control valve 34. Thus, when the brake pedal 31 is worked for traction control or automatic brake control, the brake pressure against the wheel brake 33 is increased responsively. Fig. 4 is a hydraulic pressure circuit diagram showing a third embodiment according to the present invention. Two electromagnetic directional control valves 44 and 45 are provided in series in a pipeline connecting a master cylinder 42 for converting operating force by a brake pedal 41 into hydraulic pressure and a wheel brake 43. The electromagnetic directional control valve 44 is switched between a first valve position for allowing bidirectional flow of fluid and a second valve position for allowing flow of the fluid from the wheel brake 43 to the master cylinder 42 while preventing reverse flow. The other electromagnetic directional control valve 45 is switched between a first valve position for allowing bidirectional flow of the fluid and a second valve position for allowing flow of the fluid from the master cylinder 42 to the wheel brake 43 while preventing reverse flow. An auxiliary power circuit 46, which sucks working fluid from a reservoir 50 to pressurize the same, is provided therein with an electromagnetic directional control valve 47. As shown in Fig. 4, an electromagnetic directional control valve 49 is provided in a drain circuit 48 which communicates with the reservoir 50. In order to perform general brake operation by the brake pedal 41, both of the electromagnetic directional control valves 44 and 45 are brought into the first valve positions as shown in the figure. In order to perform antilocking control with the brake pedal 41 being worked, electricity is fed to the electromagnetic directional control valve 44 to bring the same into the second valve position. In this case, the other electromagnetic directional control valve 45 is in the first valve position as shown in the figure. When the operating force by the brake pedal 41 is relaxed in this state, the fluid acting on the wheel brake 43 passes through the electromagnetic directional control valves 45 and 44 to flow toward the master cylinder 42. Thus, the brake pressure against the wheel brake 43 is reduced following relaxation of the operating force of the brake pedal 41. In order to perform traction control etc. in such a state that the brake pedal 41 is not worked, electricity is fed to the electromagnetic directional control valve 45 to bring the same into the second valve position. In this case, the electromagnetic directional control valve 44 is in the first valve position as shown in the figure. When the brake pedal 41 is worked in this state, the fluid delivered from the master cylinder 42 passes through the electromagnetic directional control valves 44 and 45 to flow toward the wheel brake 43. During such traction control etc., the brake pressure against the wheel brake 43 is increased following increase in hydraulic pressure of the master cylinder 42. Fig. 5 is a hydraulic pressure circuit diagram showing a fourth embodiment according to the present invention. An electromagnetic directional control valve 64, which is switched in three positions by electromagnetic force, is provided in a pipeline connecting a master cylinder 62 for converting operating force by a brake pedal 61 into hydraulic pressure and a wheel brake 63. Bidirectional flow of fluid is allowed when the electromagnetic directional control valve 64 is in a first valve position as shown in the figure. Flow of the fluid from the master cylinder 62 to the wheel brake 63 is allowed but reverse flow is prevented when the electromagnetic directional control valve 64 is brought into a second valve position. Further, flow of the fluid from the wheel brake 63 to the master cylinder 62 is allowed but reverse flow is prevented when the electromagnetic directional control valve 64 is switched to a third valve position. An auxiliary power circuit 65, which sucks working fluid from a reservoir 69 to pressurize the same, is provided therein with an electromagnetic directional control valve 66. An electromagnetic directional control valve 68 is provided in a drain circuit 67, which communicates with the reservoir 69. In order to perform general brake operation, the electromagnetic directional control valve 64 is brought into the first valve position as shown in the figure. In order to perform antilocking control in a state that the brake pedal 61 is worked, the electromagnetic directional control valve 64 is brought into the third valve position. When the operating force of the brake pedal 61 is relaxed in this state, the fluid acting on the wheel brake 63 passes through the electromagnetic directional control valve 64 to flow toward the master cylinder 62. Thus, the brake pressure against the wheel brake 63 is reduced following relaxation of the operating force of the brake pedal 61. In order to perform traction control etc. in a state that the brake pedal 61 is not worked, the electromagnetic directional control valve 64 is brought into the second valve position. When the brake pedal 61 is worked in this state, the fluid delivered from the master cylinder 62 passes through the electromagnetic directional control valve 64 to flow toward the wheel brake 63. When the brake pedal 61 is thus worked during the traction control etc., the brake pressure against the wheel brake 63 is increased responsively. Fig. 6 is a hydraulic pressure circuit diagram showing a fifth embodiment according to the present invention. An electromagnetic directional control valve 74, which is switched between first and second valve positions, is provided in a pipeline connecting a master cylinder 72 for converting operating force into hydraulic pressure and a wheel brake 73. Flow of fluid from the master cylinder 72 to the wheel brake 73 is allowed but reverse flow is prevented when the electromagnetic directional control valve 74 is in the first valve position as shown in the figure. On the other hand, flow of the fluid from the wheel brake 73 to the master cylinder 72 is allowed but reverse flow is prevented when the electromagnetic directional control valve 74 is brought into the second valve position. As shown in Fig. 6, a directional control valve 75, which is switched between two positions by electromagnetic force, is provided in parallel with the electromagnetic directional control valve 74. This directional control valve 75 allows bidirectional flow of the fluid when the same is in a first valve position as shown in the figure. The directional control valve 75 is brought into a second valve position to prevent the bidirectional flow of the fluid. An auxiliary power circuit 76, which sucks working fluid from a reservoir 80 to pressurize the same, is provided therein with an electromagnetic directional control valve 77. An electromagnetic directional control valve 79 is provided in a drain circuit 78, which communicates with the reservoir 80. In order to perform general brake operation, the electromagnetic directional control valve 74 is brought into the first valve position and the directional control valve 75 is also brought into the first valve position, as shown in Fig. 6. In order to perform antilocking control etc. in such a state that the brake pedal 71 is worked, the electromagnetic directional control valve 74 is brought into the second valve position and the directional control valve 75 is also brought into the second valve position. When the operating force by the brake pedal 71 is relaxed in this state, the fluid acting on the wheel brake 73 passes through the electromagnetic directional control valve 74 to flow toward the master cylinder 72. When the operating force of the brake pedal 71 is thus relaxed in antilocking control etc., the brake pressure against the wheel brake 73 is reduced responsively. In order to perform traction control etc. in a state that the brake pedal 71 is not worked, the electromagnetic directional control valve 74 is brought into the first valve position and the directional control valve 75 is brought into the second valve position. When the brake pedal 71 is worked in this state, the fluid delivered from the master cylinder 72 passes through the electromagnetic directional control valve 74 to flow toward the wheel brake 73. Thus, the brake pressure against the wheel brake 73 is increased following increase in operating force of the brake pedal 71. Fig. 7 is a hydraulic pressure circuit diagram showing a sixth embodiment according to the present invention. Two electromagnetic directional control valves 84 and 85 are provided in parallel in a pipeline connecting a master cylinder 82 for converting operating force of a brake pedal 81 into hydraulic pressure and a wheel brake 83. The electromagnetic directional control valve 84 is switched between a first valve position for allowing flow of fluid from the master cylinder 82 to the wheel brake 83 while preventing reverse flow and a second valve position for preventing bidirectional flow of the fluid. The other electromagnetic directional control valve 85 is switched between a first valve position for allowing flow of the fluid from the wheel brake 83 to the master cylinder 82 while preventing reverse flow and a second valve position for preventing bidirectional flow of the fluid. An auxiliary power circuit 86, which sucks working fluid from a reservoir 90 to pressurize the same, is provided therein with an electromagnetic directional control valve 87. An electromagnetic directional control valve 89 is provided in a drain circuit 88, which communicates with the reservoir 90. In order to perform general brake operation, the electromagnetic directional control valve 84 is brought into the first valve position as shown in the figure, and the other electromagnetic directional control valve 85 is also brought into the first valve position as shown in the figure. In order to perform antilocking control, the electromagnetic directional control valve 84 is brought into the second valve position while the other electromagnetic directional control valve 85 is brought into the first valve position. When the operating force by the brake pedal 81 is relaxed in this state, the fluid acting on the wheel brake 83 flows through the electromagnetic directional control valve 85. Thus, the brake pressure against the wheel brake 83 is reduced following relaxation of the operating force of the brake pedal 81. In order to perform traction control etc., the electromagnetic directional control valve 84 is brought into the first valve position and the other electromagnetic directional control valve 85 is brought into the second valve position. When the brake pedal 81 is worked in this state, the fluid delivered from the master cylinder 82 flows through the electromagnetic directional control valve 84. Thus, the brake pressure against the wheel brake 83 is increased following increase in operating force of the brake pedal 81. Fig. 8 is a hydraulic pressure circuit diagram showing such an example that the present invention is applied to an FR car. A master cylinder 102 for converting operating force by a brake pedal 101 into hydraulic pressure is prepared by a tandem master cylinder. A first pressurized chamber of the master cylinder 102 communicates through a junction 103 with wheel brakes 104 and 105 for left and right rear wheels, which are driving wheels. A second pressurized chamber of the master cylinder 102 communicates through a junction 106 with wheel brakes 107 and 108 for left and right front wheels, which are driven wheels. An electromagnetic directional control valve 109, which is switched between a first valve position for allowing bidirectional flow of fluid and a second valve position for allowing flow of the fluid from the junction 103 to the master cylinder 102 while preventing reverse flow, is provided in a pipeline between the first pressurized chamber of the master cylinder 102 and the junction 103. Further, electromagnetic directional control valves 110 and 111, each of which is switched between a first valve position for allowing bidirectional flow of the fluid and a second position for allowing flow of the fluid from the junction 103 to the wheel brake 104 or 105 while preventing reverse flow, are provided in pipeline between the junction 103 and the wheel brakes 104 and 105 for the left and right rear wheels. Electromagnetic directional control valves 118 and 119, each of which is switched between a first valve position for allowing bidirectional flow of the fluid and a second position for allowing flow of the fluid from the wheel brake 107 or 108 to the junction 106 while preventing reverse flow, are provided in pipelines between the junction 106 and the wheel brakes 107 and 108 for the left and right front wheels. An auxiliary power circuit 113, which sucks working fluid from a reservoir 112 to pressurize the same, communicates with the respective wheel brakes 104, 105, 107 and 108, and electromagnetic directional control valves 114, 115, 116 and 117 are provided in pipelines connecting the auxiliary power circuit 113 with the respective wheel brakes 104, 105, 107 and 108. The electromagnetic directional control valves 114, 115, 116 and 117 communicate with the reservoir 112 through a drain circuit 120. In order to perform general brake operation by the brake pedal 101, the electromagnetic directional control valves 109, 110, 111, 118 and 119 are brought into the first valve positions as shown in the figure respectively. In order to perform antilocking control in a state that the brake pedal 101 is worked, the electromagnetic directional control valves 109, 118 and 119 are brought into the second valve positions while the remaining electromagnetic directional control valves 110 and 111 are brought into the first valve positions as shown in the figure. When the operating force of the brake pedal 101 is relaxed in this state, the fluid acting on the wheel brakes 104, 105, 107 and 108 flows toward the master cylinder 101. Consequently, the brake pressure acting upon each of the wheel brakes 104, 105, 107 and 108 is reduced. In order to perform traction control in a state that the brake pedal 101 is not worked, the electromagnetic directional control valves 109, 118 and 119 are brought into the first valve positions as shown in the figure, while the remaining electromagnetic directional control valves 110 and 111 are brought into the second valve positions. When the brake pedal 101 is worked in this state, brake pressure against the wheel brakes 104 and 105 for the left and right rear wheels, which are driving wheels, is increased. Fig. 9 is a hydraulic pressure circuit diagram showing such an example that the present invention is applied to diagonal split piping suitable for an FF car. In this example, a master cylinder 132 for converting operating force by a brake pedal 131 into hydraulic pressure is prepared by a tandem master cylinder. A first pressurized chamber of the master cylinder 132 communicates through a junction 133 with a wheel brake 134 for a left front wheel, which is a driving wheel, and a wheel brake 135 for a right rear wheel, which is a driven wheel. A second pressurized chamber of the master cylinder 132 communicates through a junction 136 with a wheel brake 137 for a right front wheel, which is a driving wheel, and a wheel brake 138 for a left rear wheel, which is a driven wheel. A pair of electromagnetic directional control valves 139 and 140 and another pair of electromagnetic directional control valves 141 and 142 are provided in series in pipelines between the junction 133 and the wheel brake 134 for the left front wheel and between the junction 136 and the wheel brake 137 for the right front wheel. Each of the electromagnetic directional control valves 139 and 141 is switched between a first valve position for allowing bidirectional flow of fluid and a second valve position for allowing flow of the fluid from the wheel brake 134 or 137 to the junction 133 or 136 while preventing reverse flow of the fluid. Each of the remaining electromagnetic directional control valves 140 and 142 is switched between a first valve position for allowing bidirectional flow of the fluid and a second valve position for allowing flow of the fluid from the junction 133 or 136 to the wheel brake 134 or 137 while preventing reverse flow. Electromagnetic directional control valves 144 and 143, each of which is switched between a first valve position for allowing bidirectional flow of the fluid and a second valve position for allowing flow of the fluid from the wheel brake 135 or 138 to the junction 133 or 136 while preventing reverse flow, are provided in pipelines between the junction 133 and the wheel brake 135 for the right rear wheel and between the junction 136 and the wheel brake 138 for the left rear wheel respectively. An auxiliary power circuit 146, which sucks working fluid from a reservoir 145 to pressurize the same, communicates with the respective wheel brakes 138, 135, 134 and 137, and electromagnetic directional control valves 147, 148, 149 and 150 are provided in pipelines connecting the auxiliary power circuit 146 with the wheel brakes 138, 135, 134 and 137 respectively. Electromagnetic directional control valves 154, 155, 152 and 153 are provided in a drain circuit 151, which connects the respective wheel brakes 134, 137, 138 and 135 with the reservoir 145. In order to perform general brake operation by the brake pedal 131, the electromagnetic directional control valves 139, 140, 141, 142, 143 and 144 are brought into the first valve positions as shown in the figure respectively. In order to perform antilocking control in such a state that the brake pedal 131 is worked, the electromagnetic directional control valves 139, 141, 143 and 144 are brought into the second valve positions and the electromagnetic directional control valves 140 and 142 are brought into the first valve positions as shown in the figure. When the operating force of the brake pedal 131 is relaxed in this state, brake pressure against each wheel brake is reduced. In order to perform traction control in a state that the brake pedal 131 is not worked, the electromagnetic directional control valves 140 and 142 are brought into the second valve positions and the electromagnetic directional control valves 139, 141, 143 and 144 are brought into the first valve positions as shown in the figure. When the brake pedal 131 is worked in this state, brake pressure against each wheel brake is increased. The electromagnetic directional control valve 64 as shown in Fig. 4 may be provided in the pipeline connecting the wheel brake for each driving wheel and the master cylinder, although the same is not shown in the figure. Further, the electromagnetic directional control valve 74 and the directional control valve 75 as shown in Fig. 6 may be provided in the pipeline connecting the wheel brake for each driving wheel and the master cylinder. Figs. 10A and 10B are illustrative of a concrete example of the electromagnetic directional control valve 24 as shown in Fig. 1 or the electromagnetic directional control valve 34 as shown in Fig. 2. An electromagnetic directional control valve 200 shown in these figures is provided with a frame 201 and a stator 202 which is fixedly engaged into the frame 201. The frame 201 has ports 203 and 204, and the stator 202 has a port 205. A guide ring 206 of non-magnetic material is fixedly mounted around an upper part of the stator 202. Liquid tightness is maintained between the guide ring 206 and the frame 201. A coil 207 is provided around the stator 206, as shown in the figures. A fixed valve seat 208 is press-fitted into the upper portion of the stator 202. An armature 211, which can be attracted toward the stator 202 by electromagnetic force, and a movable valve 210 are contained in a space between the stator 202 and the frame 201. The movable valve 210 is provided in its lower end portion with a globe valve portion 212, which is brought into contact with the fixed valve seat 208 to close a passage. As shown in the figures, a shim 209 of non-magnetic material is fixedly mounted on an upper end portion of the stator 202, to adjust a clearance between the stator 202 and the armature 211. A return spring 214 is provided between the fixed valve seat 208 and the armature 211. This return spring 214 continuously urges the armature 211 to upwardly move the same in the figures. A relief spring 213 is provided between the movable valve 210 and the frame 201, to continuously urge the movable valve 210 thereby to downwardly move the same in the figures. Spring force of the relief spring 213 is extremely small as compared with the return spring 214. Further, a movable distance ℓ₂ of the armature 211 is made larger than a movable distance ℓ₁ of the movable valve 210. Fig. 10A shows a state in which the coil 207 is fed with no electricity and Fig. 10B shows a state in which the coil 207 is fed with electricity. It is assumed here that the ports 203 and 204 of the frame 201 communicates with a master cylinder and the port 205 of the stator 202 communicates with a wheel brake. When the coil 207 is fed with no electricity as shown in Fig. 10A, the armature 211 is upwardly moved by the spring force of the return spring 214. The armature 211 is thus in contact with a flange portion of the movable valve 210 thereby to upwardly move the same. The armature 211 and the movable valve 210 are thus upwardly moved until an upper end portion of the movable valve 210 is brought into contact with the frame 201. In the state as shown in Fig. 10A, the globe valve portion 212 of the movable valve 210 is in a position separated from the fixed valve seat 208. Therefore, flow of fluid from the master cylinder to the wheel brake is allowed and reverse flow, i.e., flow of the fluid from the wheel brake to the master cylinder, is also allowed. On the other hand, when the coil 207 is fed with electricity as shown in Fig. 10B, the armature 211 is attracted and moved toward the stator 202. This movement is performed until the armature 211 is in contact with the shim 209. The movement stroke of the armature 211 is rendered larger than that of the movable valve 210. Therefore, in such a state that the movable valve 210 is downwardly moved by the relief spring 213 so that the globe valve portion 212 is in contact with the fixed valve seat 208, a clearance d (=ℓ₂ - ℓ₁) is defined between the flange portions of the movable valve 210 and the armature 211. In the state as shown in Fig. 10B, flow of the fluid from the wheel brake to the master cylinder, i.e., flow of the fluid from the port 205 to the ports 203 and 204 is allowed since the spring force of the relief spring 213 is weak. On the other hand, reverse flow of the fluid, i.e., flow of the fluid from the ports 203 and 204 to the port 205 is prevented. A brake pressure control device employing such an electromagnetic directional control valve as shown in Figs. 10A and 10B is simplified in circuit structure and pipe arrangement. However, the electromagnetic directional control valve as shown in Figs. 10A and 10B can be further improved. When the electromagnetic directional control valve is fed with electricity and the fluid in the armature 211 side, i.e., the fluid in the ports 203 and 204 is higher in pressure than the fluid in the stator 202 side, i.e., the fluid in the port 205, the movable valve 210 is in contact with the fixed valve seat 208 to be held in a closed state. When the electromagnetic directional control valve is transited from the fed state to a non-fed state in the same fluid pressure relation, i.e., in the state that the fluid in the armature 211 side is retained at a high pressure level, the following conditions must be satisfied in order to separate the movable valve 210 from the fixed valve seat 208 thereby to open the same. The return spring 214 urges the movable valve 210 to a valve-opening direction. On the other hand, the relief spring 213, hydraulic pressure force acting on sealing effective areas of the movable valve 210 and the fixed valve seat 208 and residual magnetic force urge the movable valve 210 in a valve-closing direction. Therefore, even if the electromagnetic directional control valve is transited from the fed state to the non-fed state, the movable valve 210 is held in the closed state unless the force urging the movable valve 210 in the valve-opening direction exceeds the force urging the same in the valve-closing direction. Thus, a delay may be caused in valve opening when the electromagnetic directional control valve is transited from the fed state to the non-fed state. In order to reduce such valve opening delay in the aforementioned non-fed state, the spring force of the return spring 214 may be increased. In this case, however, a delay in valve opening is increased when the electromagnetic directional control valve is transited from the non-fed state to the fed state. Thus, it is difficult to attain quick response on both of the fed and non-fed states in the electromagnetic directional control valve as shown in Figs. 10A and 10B. Fig. 11 is a sectional view showing an electromagnetic directional control valve which is excellent in quick response in both of fed and non-fed states, and Fig. 12 is a partially enlarged sectional view thereof. This electromagnetic directional control valve 330 has a frame 331 and a stator 332 which is fixedly engaged into the frame 331. The frame 331 is provided with ports 333 and 334, and the stator 332 is provided with an axially extending passage 335. In exemplary application, the passage 335 of the stator 332 communicates with a master cylinder and the ports 333 and 334 of the frame 331 communicate with wheel brakes. A guide ring 337 of non-magnetic material is fixedly press-fitted around an upper portion of the stator 332. Liquid tightness is maintained between the guide ring 337 and the stator 332 as well as between the guide ring 337 and the frame 331. An electromagnetic coil 336 is provided around the stator 332, as shown in the figures. A valve seat 338 and a second spring 340 are provided in the passage 335 of the stator 332. The valve seat 338 has a passage 346 within the same and a sealing member 339 in its outer peripheral surface. The sealing member 339 is adapted to maintain liquid tightness between the valve seat 338 and the stator 332. The valve seat 338 is slidable within the passage 335 of the stator 332 while maintaining liquid tightness with respect to the stator 332. The second spring 340 urges the valve seat 338 upwardly in the figures. A retainer 341 of non-magnetic material is fixedly mounted on an upper end portion of the stator 332. Thus, the valve seat 338 is urged by the second spring 340 to be in contact with the retainer 341, whereby upward movement thereof is stopped. An armature 342, which can be attracted toward the stator 332 by electromagnetic force, and a movable valve 343 are contained in a space between the stator 332 and the frame 331. A flange portion 343a of the movable valve 343 is fixedly press-fitted with the armature 342, whereby the armature 342 and the movable valve 343 are integrally moved. The movable valve 343 has a globe valve portion 344 which is brought into contact with the valve seat 338 to close the passage 346. The armature 342 is guided to slide by a bore surface of the guide ring 337. A first spring 345 is provided between the flange portion 343a of the movable valve 343 and the retainer 341 which is fixed to the upper end portion of the stator 332. The first spring 345 urges the movable valve 343 and the armature 342 to separate the same from the stator 332. The distance of movement of the movable valve 343 to be in contact with the valve seat 338 in a fed state is made smaller than a distance of movement of the armature 342 which is attracted by the stator 332. Fig. 11 shows a state in which the coil 336 is fed with no electricity and Fig. 12 shows a state in which the coil 336 is fed with electricity. When the coil 336 is fed with no electricity as shown in Fig. 11, the movable valve 343 and the armature 342 are upwardly moved by spring force of the first spring 345. The movable valve 343 and the armature 342 are thus upwardly moved until the upper end portion of the movable valve 343 is brought into contact with the frame 331. In the state as shown in Fig. 11, the globe valve portion 344 of the movable valve 343 is in a position separate from the valve seat 338. Thus, in the non-fed state as shown in Fig. 11, flow of fluid from the master cylinder to each wheel brake is allowed and reverse flow, i.e., flow from each wheel to the master cylinder is also allowed. On the other hand, when the coil 336 is fed with electricity as shown in Fig. 12, the armature 342 is attracted and moved toward the stator 332. The armature 342 is thus moved until the same is brought into contact with the retainer 341. A hereinabove described, the distance of movement of the movable valve 343 to be in contact with the valve seat 338 in the fed state is made smaller than the distance of movement of the armature 342 which is attracted by the stator 332. Thus, the movable valve 343 is first brought into contact with the valve seat 338 to close the passage 346 during movement of the armature 342. Upon further movement of the armature 342, the movable valve 343 urges the valve seat 338 downwardly in the figures against spring force of the second spring 340, while maintaining a valve-opening state. Thus, the valve seat 338 is separated from the retainer 341 by a distance Δℓ in the fed state as shown in Fig. 12. In the state as shown in Fig. 12, flow of the fluid from the passage 335 to the ports 333 and 334 is prevented. On the other hand, flow of the fluid from the ports 333 and 334 to the passage 335 is allowed when hydraulic pressure acting on sealing effective areas of the movable valve 343 and the valve seat 338 urges the valve seat 338 in a valve-opening direction and the hydraulic pressure exceeds the spring force of the second spring 340. Thus, the electromagnetic directional control valve 330 as shown in Figs. 11 and 12 allows bidirectional flow of the fluid in the non-fed state. Further, the same allows unidirectional flow of the fluid while preventing reverse flow of the fluid upon being switched to the non-fed state. Further, the electromagnetic directional control valve 330 as shown in Figs. 11 and 12 causes no such problem that has occurred in the electromagnetic directional control valve as shown in Figs. 10A and 10B. It is assumed here that the passage 335 side is at a high pressure level and the ports 333 and 334 are at low pressure levels in the fed state as shown in Fig. 12. In this case, fluid pressure acting on a sealing effective area between the movable valve 343 and the valve seat 338 urges the movable valve 343 in the valve-opening direction. Therefore, when the electromagnetic directional control valve 330 is switched from the fed state to the non-fed state, the movable valve 343 is subjected to urging force by the fluid pressure in addition to the spring force by the first spring 345, to be immediately moved to a valve-opening position. Thus, the electromagnetic directional control valve 330 as shown in Figs. 11 and 12 can attain quick response in conversion from the fed state to the non-fed state. Further, the spring force of the first spring 345 may not be increased to attain quick response in the non-fed state. Thus, quick response can be attained also in conversion of the electromagnetic directional control valve from the non-fed state to the fed state. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: 1. A brake pressure control device for vehicles being provided, in a pipeline connecting a master cylinder (22) and a wheel brake (23), with an electromagnetic directional control valve (24, 34, 44, 45, 64, 74, 75, 84, 85, 109, 110, 111, 118, 119, 139, 140, 141, 142, 143, 144) being switchable in a plurality of valve positions by electromagnetic force, said electromagnetic directional control valve having a valve position for allowing only unidirectional flow of fluid while preventing reverse flow of said fluid. 2. A brake pressure control device for vehicles in accordance with claim 1, wherein said electromagnetic directional control valve (24, 34, 44, 45, 109, 110, 111, 118, 119, 139, 140, 141, 142, 143, 144) is switched between a first valve position and a second valve position, bidirectional flow of said fluid is allowed when said electromagnetic directional control valve is in said first valve position, and unidirectional flow of said fluid is allowed but reverse flow of said fluid is prevented when said electromagnetic directional control valve is in said second valve position. 3. A brake pressure control device for vehicles in accordance with claim 2, wherein flow of said fluid from said wheel brake to said master cylinder is allowed when said electromagnetic directional control valve is in said second position. 4. A brake pressure control device for vehicles in accordance with claim 3, wherein said electromagnetic directional control valve is provided in a pipeline connecting said master cylinder with a wheel brake for a driven wheel. 5. A brake pressure control device for vehicles in accordance with claim 2, wherein flow of said fluid from said master cylinder to said wheel brake is allowed when said electromagnetic directional control valve is in said second valve position. 6. A brake pressure control device for vehicles in accordance with claim 1, wherein a pair of said electromagnetic directional control valves (44, 45, 109, 110, 111, 139, 140, 141, 142) are provided in series in a pipeline connecting said master cylinder and said wheel brake, one said electromagnetic directional control valve (44, 109, 139, 141) is switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from said wheel brake to said master cylinder while preventing reverse flow, and the other said electromagnetic directional control valve (45, 110, 111, 140, 142) is switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from said master cylinder to said wheel brake while preventing reverse flow. 7. A brake pressure control device for vehicles in accordance with claim 6, wherein said electromagnetic directional valves are provided in a pipeline connecting said master cylinder with a wheel brake for a driving wheel. 8. A brake pressure control device for vehicles in accordance with claim 1, wherein said electromagnetic directional control valve (64) is switched in a first valve position, a second valve position and a third valve position, bidirectional flow of said fluid is allowed when said electromagnetic directional control valve is in said first valve position, flow of said fluid from said master cylinder to said wheel brake is allowed but reverse flow of said fluid is prevented when said electromagnetic directional control valve is in said second valve position, and flow of said fluid from said wheel brake to said master cylinder is allowed but reverse flow of said fluid is prevented when said electromagnetic directional control valve is in said third valve position. 9. A brake pressure control device for vehicles in accordance with claim 8, wherein said electromagnetic directional control valve is provided in a pipeline connecting said master cylinder with a wheel brake for a driving wheel. 10. A brake pressure control device for vehicles in accordance with claim 1, wherein said electromagnetic directional control valve (74) is switched between a first valve position for allowing flow of said fluid from said master cylinder to said wheel brake while preventing reverse flow of said fluid and a second valve position for allowing flow of said fluid from said wheel brake to said master cylinder while preventing reverse flow of said fluid, a directional control valve (75) is provided in parallel with said electromagnetic directional control valve (74) in said pipeline connecting said master cylinder and said wheel brake, and said directional control valve (75) is switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for preventing said bidirectional flow of said fluid by electromagnetic force. 11. A brake pressure control device for vehicles in accordance with claim 10, wherein said electromagnetic directional control valve and said directional control valve are provided in series in a pipeline connecting said master cylinder with a wheel brake for a driving wheel. 12. A brake pressure control device for vehicles in accordance with claim 1, wherein a pair of said electromagnetic directional control valves (84, 85) are provided in series in said pipeline connecting said master cylinder and said wheel brake, one said electromagnetic directional control valve (84) is switched between a first valve position for allowing flow of said fluid from said master cylinder to said wheel brake while preventing reverse flow and a second valve position for preventing bidirectional flow of said fluid, and the other said electromagnetic directional control valve (85) is switched between a first valve position for allowing flow of said fluid from said wheel brake to said master cylinder while preventing reverse flow and a second valve position for preventing bidirectional flow of said fluid. 13. A brake pressure control device for vehicles in accordance with claim 1, wherein said master cylinder (102) is a tandem master cylinder, a first pressurized chamber of which communicates through a junction with wheel brakes (104, 105) for left and right rear wheels, being driving wheels, while a second pressurized chamber communicates with wheel brakes (107, 108) for left and right front wheels, being driven wheels, an electromagnetic directional control valve (109) is provided in a pipeline between said first pressurized chamber and said junction, said electromagnetic directional control valve being switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from said junction to said first pressurized chamber while preventing reverse flow of said fluid, and electromagnetic directional control valves (110, 111) are provided in pipelines between said junction and said wheel brakes for said left and right rear wheels, each of said electromagnetic directional control valves being switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from said junction to each said wheel brake while preventing reverse flow of said fluid. 14. A brake pressure control device for vehicles in accordance with claim 1, wherein said master cylinder (132) is a tandem master cylinder, a first pressurized chamber of which communicates through a first junction with a wheel brake (134) for a left front wheel, being a driving wheel of a four-wheel car, and with a wheel brake (135) for a right rear wheel, being a driven wheel, while a second pressurized chamber communicates through a second junction with a wheel brake (137) for a right front wheel, being a driving wheel, and with a wheel brake (138) for a left rear wheel, being a driven wheel, pairs of electromagnetic directional control valves (139, 140, 141, 142) are provided in series in a pipeline between said first junction and said wheel brake for said left front wheel and a pipeline between said second junction and said wheel brake for said right front wheel respectively, first ones (139, 141) of said pairs of electromagnetic directional control valves each being switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from each said wheel brake to each said junction while preventing reverse flow of said fluid, the other said electromagnetic directional control valves (140, 142) each being switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from each said junction to each said wheel brake while preventing reverse flow of said fluid, and electromagnetic directional control valves (143, 144) are provided in a pipeline between said first junction and said wheel brake for said right rear wheel and a pipeline between said second junction and said wheel brake for said left rear wheel respectively, each of said electromagnetic control valves being switched between a first valve position for allowing bidirectional flow of said fluid and a second valve position for allowing flow of said fluid from each said wheel brake to each said junction while preventing reverse flow of said fluid. 15. An electromagnetic directional control valve (200) being switched between two valve positions by electromagnetic force, said electromagnetic directional control valve comprising: a fixed valve seat (208) fixedly provided in a passage for fluid; a movable valve (210) being movable between a closing position being in contact with said fixed valve seat for closing said passage and an opening position separated from said fixed valve seat for opening said passage; a first spring (213) for continuously urging said movable valve toward said fixed valve seat; an armature (211) being brought into contact with said movable valve from a location of said fixed valve seat and moved to approach said fixed valve seat by electromagnetic force in feeding of electricity; and a second spring (214) for continuously urging said armature to separate the same from said fixed valve seat, spring force of said first spring being smaller than that of said second spring, the maximum distance of movement of said armature being larger than that of said movable valve. 16. An electromagnetic directional control valve (330) being switched between two valve positions by electromagnetic force, said electromagnetic directional control valve comprising: a stator (332) enclosed by an electromagnetic coil and having an axially extending passage in its interior; a valve seat (338) positioned in said passage of said stator to be slidable in said passage while maintaining liquid tightness between its outer peripheral portion and said stator and having a passage in its own interior; a movable valve (343) movable between a closing position being in contact with said valve seat for closing said passages and an opening position being separated from said valve seat for opening said passages; an armature (342) provided to be moved with said movable valve and attracted toward said stator by electromagnetic force in feeding of electricity; a first spring (345) for urging said armature to separate the same from said stator; a second spring (340) for urging said valve seat to allow the same approach said movable valve; and positioning means (341) fixed to said stator to be in contact with said valve seat urged by said second spring in a non-fed state thereby to position said valve seat, a distance of movement of said movable valve to be in contact with said valve seat in feeding of electricity being smaller than a distance of movement of said armature being attracted by said stator.

Inventors: HASHIDA, KOICHI C/O ITAMI WORKS, KOHNO, TERUHISA C/O ITAMI WORKS, TAKATA, KOJI C/O ITAMI WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1987
Main classification: B60T8
IPC codes: B60T8