ANTILOCKING APPARATUS FOR VEHICLE

Abstract: An antilocking apparatus for a vehicle comprises a master cylinder (2), an inlet valve (40), an outlet valve (5), a damping reservoir (6), and a pump (7). The pump (7) draws working fluid stored in the damping reservoir (6), to deliver the same into a fluid path portion connecting the inlet valve (40) with a wheel brake (3). The inlet valve (40) is formed by a differential pressure conscious valve which is actuated by differential pressure between fluid pressure in the fluid path portion connecting the inlet valve (40) with the wheel brake (3) and that in a fluid path portion connecting the inlet valve (40) with the outlet valve (5).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an antilocking apparatus for performing antilocking operation for a wheel brake of a vehicle. Description of the Prior Art The simplest antilocking apparatus of this type is the so-called circulating type antilocking apparatus, such as that described in U.S. Patent No. 3,549,212. Fig. 7 is a hydraulic circuit diagram showing a well-known circulating type antilocking apparatus. An inlet valve 4 is provided in a fluid path between a master cylinder 2, which is adapted to convert operating physical force applied to a brake pedal 1 into fluid pressure, and a wheel brake 3. An outlet valve 5 can discharge working fluid from a fluid path portion connecting the inlet valve 4 with the wheel brake 3. The working fluid discharged through the outlet valve 5 is temporarily stored in a damping reservoir 6. A pump 7 draws the working fluid thus stored in the damping reservoir 6, to deliver the same into a fluid path portion connecting the master cylinder 2 with the inlet valve 4. A check valve 8 is adapted to allow only a unidirectional flow of the fluid. In this well-known antilocking apparatus, the working fluid temporarily stored in the damping reservoir 6 and drawn by the pump 7 is forced toward the master cylinder 2. Thus, the brake pedal 1 is pushed back against the driver's pedal force. This is the so-called kick-back against the brake pedal 1, which causes inferior pedal feeling. Some proposals have been made in order to solve the aforementioned problem. One of such proposals is disclosed in U.S. Patent No. 4,453,782, in relation to an antilocking apparatus. Fig. 8 is a hydraulic circuit diagram showing this apparatus. In the antilocking apparatus shown in Fig. 8, a differential pressure conscious valve 9 and a high-pressure accumulator 10 are added to the structure of Fig. 7. The differential pressure conscious valve 9 is provided between a master cylinder 2 and an inlet valve 4. Working fluid discharged from a pump 7 is introduced into a fluid path portion provided between the differential pressure conscious valve 9 and the inlet valve 4. Thus, the working fluid discharged from the pump 7 can be prevented from a back flow to the master cylinder 2, by such interposition of the differential pressure conscious valve 9. The working fluid thus discharged from the pump 7 and prevented from a back flow to the master cylinder 2 is stored in the high-pressure accumulator 10. The problem of kick-back against the brake pedal is thus solved by the antilocking apparatus shown in Fig. 8. However, this apparatus is disadvantageous in weight, space and cost due to employment of the high-pressure accumulator 10. Namely, the high-pressure accumulator 10 has a back-up spring which is extremely larger in size than that of the damping reservoir 6 of low pressure, although the former is identical in storage volume of working fluid to the latter. From DE-A1-35 42 689 an antilocking apparatus for performing antilocking operation for a wheel brake of a vehicle is known. Said antilocking apparatus comprises a master cylinder, an inlet valve provided in a fluid path connecting said master cylinder with said wheel brake to allow cut off communication between said master cylinder and said wheel brake through said fluid path, an electrically switch-controlled outlet valve, capable of discharging working fluid from a fluid path portion connecting said inlet valve with said wheel brake, a damping reservoir for temporarily storing said working fluid discharged through said outlet valve, and a pump for drawing said working fluid stored in said damping reservoir to deliver the same into said fluid path portion connecting said inlet valve with said wheel brake. A similar device is known from G-A-2 195 724. This document discloses an antilocking apparatus for performing antilocking operation for a wheel brake of a vehicle, said antilocking apparatus comprises a master cylinder, an inlet valve provided in a fluid path connecting said master cylinder with said wheel brake to allow cut off communication between said master cylinder and said wheel brake through said fluid path. The apparatus further comprises an electrically switch-controlled outlet valve, capable of discharging working fluid from a fluid path portion connecting said inlet valve with said wheel brake, a damping reservoir to deliver the same into said fluid path portion connecting said inlet valve with said wheel brake. As both references disclose to use electromagnetic valves, complicated electronic circuits are required. Further the weight of such a device is high. If such electronic circuits are employed, the costs are increased, while operational reliability is reduced. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an antilocking apparatus which can solve the problem of kick-back against a brake pedal without employing a high-pressure accumulator. In particular, the present invention is directed to an antilocking apparatus having high operational reliability, which is advantageous in cost. Provided according to the present invention is an antilocking apparatus for performing antilocking operation for a wheel brake of a vehicle. As known from the state of the art the apparatus comprises a master cylinder, an inlet valve provided in a fluid path connecting the master cylinder with the wheel brake to allow/cut off communication between the master cylinder and the wheel brake through the fluid path, an electrically switch-controlled outlet valve which can discharge working fluid from a fluid path portion connecting the inlet valve with the wheel brake, a damping reservoir for temporarily storing the working fluid discharged through the outlet valve, and a pump for drawing the working fluid stored in the damping reservoir to deliver the same into the fluid path portion connecting the inlet valve with the wheel brake. According to the invention the inlet valve is formed by a differential pressure conscious valve which is actuated by differential pressure between fluid pressure in the fluid path portion connecting the inlet valve with the wheel brake and that in a fluid path portion connecting the inlet valve with the outlet valve. In the conventional reflux type antilocking apparatus, the fluid discharged from the pump is introduced into the fluid path portion connecting the master cylinder with the inlet valve. In the present invention, on the other hand, the working fluid discharged from the pump is introduced into the fluid path portion connecting the inlet valve with the wheel brake, extremely dissimilarly to the conventional apparatus. Since the inlet valve is provided between the master cylinder and a port for introducing the working fluid discharged from the pump into the fluid path portion communicating with the wheel brake, the working fluid is prevented from a back flow to the master cylinder. Thus, according to the present invention, kick-back against the brake pedal can be prevented with no employment of a large-sized, heavy-weight and high-priced high-pressure accumulator. Further, the inlet valve employed in the present invention is formed by a differential pressure conscious valve which is actuated by differential pressure between fluid pressure in the fluid path portion connecting the inlet valve with the wheel brake and that in the fluid path portion connecting the inlet valve with the outlet valve. Therefore, no electronic circuit is required for the inlet valve, to provide a highly reliable antilocking apparatus which is advantageous in cost. 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 circuit diagram showing an antilocking apparatus for a vehicle, which can solve the problem of kick-back against a brake pedal; Fig. 2 is a hydraulic circuit diagram showing an embodiment of the present invention; Fig. 3 is a sectional view schematically illustrating concrete structure of a differential pressure conscious valve 40 shown in Fig. 2; Fig. 4 is a sectional view schematically showing leftward movement of a spool from the state shown in Fig. 3; Fig. 5 is a sectional view showing slight rightward movement of the spool from the state shown in Fig. 4; Fig. 6 is a sectional view schematically showing a flow regulating valve which is added to an outlet valve; Fig. 7 is a hydraulic circuit diagram showing a well-known reflux type antilocking apparatus; and Fig. 8 is a hydraulic circuit diagram of an antilocking apparatus disclosed in U.S. Patent No. 4,453,782. DESCRIPTION OF THE PREFERRED EMBODIMENTS As hereinabove described, an antilocking apparatus according to the present invention is different from the conventional apparatus in such a point that working fluid discharged from a pump is introduced into a fluid path portion connecting an inlet valve with a wheel brake. Therefore, specific modifications must be applied to the configuration of the inlet valve, control modes, setting of pump discharge ability and the like as compared with the conventional apparatus. Further, the inlet valve is different in function from that of the conventional apparatus. Description is now made on an improved antilocking apparatus for a vehicle, which can solve the problem of kick-back against a brake pedal caused in the conventional apparatus, and thereafter an embodiment of the present invention will be described. Fig. 1 is a sectional view showing an antilocking apparatus, which comprises an inlet valve 4 provided in a fluid path between a master cylinder 2 and a wheel brake 3, an outlet valve 5 which can discharge working fluid from a fluid path portion connecting the inlet valve 4 with the wheel brake 3, a damping reservoir 6 for temporarily storing the working fluid discharged through the outlet valve 6 and a pump 7 for drawing the working fluid stored in the damping reservoir 6, similarly to the conventional apparatus shown in Fig. 7. While the working fluid discharged by the pump 7 is introduced into the fluid path portion between the master cylinder 2 and the inlet valve 4 in the conventional apparatus shown in Fig. 7, the working fluid discharged from the pump 7 of the apparatus shown in Fig. 1 is introduced into a fluid path portion connecting the inlet valve 4 with the wheel brake 3. The inlet valve 4 shown in Fig. 1 is formed by an electrically switch-controlled two-port two-position directional control valve. In a non-energized state shown in Fig. 1, the inlet valve 4 is in a first valve position to allow a fluid flow through the valve 4. Upon energization, the inlet valve 4 is switched to a second valve position, to cut off the fluid flow through the valve 4. The outlet valve 5 shown in Fig. 1 is also formed by an electrically switch-controlled two-port two-position directional control valve. In the non-energized state shown in Fig. 1, the outlet valve 5 is in a first valve position to cut off a fluid flow through the valve 5. Upon energization, the outlet valve 5 is switched to a second valve position to allow the fluid flow through the valve 5. Dissimilarly to the conventional apparatus shown in Fig. 7, the working fluid discharged from the pump 7 is introduced into the fluid path portion between the inlet valve 4 and the wheel brake 3 in the apparatus shown in Fig. 1, whereby the working fluid can be prevented from a back flow to the master cylinder 2. Thus, no kick-back is caused against the brake pedal 1. The conventional apparatus shown in Fig. 7 can be switched to three modes, i.e., step-up, holding and step-down modes, with respect to the wheel brake 3, by appropriate control of the inlet valve 4 and the outlet valve 5. In more concrete terms, the apparatus enters the step-up mode when both of the inlet valve 4 and the outlet valve 5 are brought into non-energized states, while the apparatus is switched to the step-down mode when both of the inlet valve 4 and the outlet valve 5 are energized. When the inlet valve 4 is energized and the outlet valve 5 is in a non-energized state, the apparatus enters the holding mode. In the apparatus shown in Fig. 1, on the other hand, both of the inlet valve 4 and the outlet valve 5 are energized upon initiation of antilocking operation. In such a state, the inlet valve 4 cuts off the fluid flow, while the outlet valve 5 allows the fluid flow. Thereafter control is performed only through operation of the outlet valve 5, so that the apparatus is switched between step-up and step-down modes. Namely, the apparatus enters the step-up mode when the outlet valve 5 is brought into the non-energized state as shown in Fig. 1, while the apparatus is switched to the step-down mode when the outlet valve 5 is energized. In this case, the step-up speed is determined by discharge ability of the pump 7. Slow re-pressurization to a wheel brake is requisite in an aspect of antilocking control. The well-known three-mode type apparatus achieves such slow re-pressurization by appropriately introducing the step-up mode into the holding mode. In the two-mode type apparatus shown in Fig. 1, on the other hand, time allocations for the step-up mode and the step-down mode are appropriately selected, thereby to achieve slow re-pressurization to the wheel brake. Assuming that Vave represents average step-up/step-down speed, Vi represents step-up speed, Vd represents step-down speed, Ti represents step-up time and Td represents step-down time, the following relation is obtained: Vave = ( Vi x Ti + Vd x Td )/( Ti + Td ) Namely, it is necessary to properly select discharge ability of the pump 7 in response to rigidity of the brake system in the apparatus shown in Fig. 1. In the well-known apparatus, on the other hand, discharge ability of the pump 7 may only be larger than a constant limit. In the apparatus shown in Fig. 7, however, kick-back against the brake pedal 1 is increased with increase in discharge ability of the pump 7. Incidentally, the friction coefficient of road surface may be so increased during antilocking control that higher brake fluid pressure is preferably applied. In such case, the brake pressure is unlimitedly continuously increased by continuously increasing the time allocation for an opening state of the inlet valve 4 in the conventional apparatus which introduces the working fluid discharged from the pump 7 into an upstream side of the inlet valve 4, so far as pedal force to the pedal is sufficiently high. In the apparatus shown in Fig. 1, however, the inlet valve 4 must be brought into an opening state, i.e., a non-energized state if required brake pressure is larger than that upon initiation of antilocking control. In the apparatus shown in Fig. 1, therefore, the inlet valve 4 remains in a closed state in a locking tendency when judgement on dumping of brake pressure, i.e., judgement on the opening state of the outlet valve 5 is generated at appropriate intervals. If a subsequent locking tendency is delayed over a constant limit, the inlet valve 4 is brought into an opening state for an appropriate period (with appropriate continuation time and interval) similarly to the well-known apparatus. Thus, when the apparatus shown in Fig. 1 is employed, slight modifications are required in the control system and design of pump discharge ability. Such modifications are not particularly difficult but can be arbitrarily applied within the range of design capacity of those skilled in the art. In the apparatus shown in Fig. 1, however, the inlet valve 4 is different in function from that of the well-known apparatus. If the inlet valve 4 is formed by an electromagnetic valve, a complicated electronic circuit will be required. If such an electronic circuit is employed, the cost is increased as a matter of course, while operational reliability is reduced. According to the present invention, therefore, the inlet valve 4 is formed by a differential pressure conscious valve, which is lower in cost and higher in operational reliability than an electromagnetic valve. Fig. 2 is a hydraulic circuit diagram showing an embodiment of the present invention. While the inlet valve 4 is formed by an electromagnetic valve in the apparatus shown in Fig. 1, an inlet valve 40 of this embodiment is formed by a differential pressure conscious valve, which is actuated by differential pressure between fluid pressure in a fluid path portion connecting the inlet valve 40 with a wheel brake 3 and that in a fluid path portion connecting the inlet valve 40 with an outlet valve 5. Fig. 3 illustrates concrete structure of such a differential pressure conscious valve 40. The differential pressure conscious valve 40 comprises a case 48, a spool 41 which is slidable along the inner surface of the case 48 and having a first end facing a fluid path portion communicating with the wheel brake 3 and a second end facing a fluid path portion communicating with the outlet valve 5, and a spring 42 for urging the spool 41 toward its first end. The spool 41 is provided with an orifice 47 which connects the fluid path portion communicating with the wheel brake 3 and that communicating with the outlet valve 5. The case 48 has a plurality of ports. Configurations of the case 48 and the spool 41 and positional relation therebetween are so selected as to implement three operating states. Fig. 3 shows a first operating state and Fig. 4 shows a second operating state, while Fig. 5 shows a third operating state. In the first operating state shown in Fig. 3, a master cylinder 2 communicates with the wheel brake 3 through a large passage. The master cylinder 2 further communicates with the outlet valve 5 through the orifice 47. The wheel brake 3 communicates with the outlet valve 5 through the orifice 47. In the second operating state shown in Fig. 4, communication between the master cylinder 2 and the wheel brake 3 is cut off. Communication between the master cylinder 2 and the outlet valve 5 is also cut off. The wheel brake 3 communicates with the outlet valve 5 through the large passage. In the third operating state shown in Fig. 5, communication between the master cylinder 2 and the wheel brake 3 is cut off. Communication between the master cylinder 2 and the outlet valve 5 is also cut off. The wheel brake 3 communicates with the outlet valve 5 through the orifice 47. In general, the spool 41 is urged by the spring 42, having weak urging force, into the first operating state as shown in Fig. 3. In this state, the master cylinder 2 communicates with the wheel brake 3 through a passage 45. When the outlet valve 5 is energized to open its passage upon initiation of antilocking operation, pressure in a chamber 43, which is positioned on the left side of the spool 41 in Fig. 3, is reduced. Pressure in the fluid path portion communicating with the wheel brake 3 acts on another chamber 44, which is positioned on the right side of the spool 41 in Fig. 3. When pressure in the chamber 43 is thus reduced, the spool 41 is leftwardly moved in Fig. 3 against urging force of the spring 42. Therefore, communication between the passage 45 to the master cylinder 2 and the chamber 44 communicating with the wheel brake 3 is cut off. This is the third operating state shown in Fig. 5. When an opening state of the outlet valve 5 is sustained, the spool 41 is further leftwardly moved from the state shown in Fig. 5, whereby the chamber 44 communicates with the chamber 43 through a bypass 46. This is the second operating state shown in Fig. 4. Since the flow rate in the opening state of the outlet valve 5 is set to be larger than the discharge of the pump 7, pressure applied to the wheel brake 3 is continuously lowered even if the pump 7 is in a discharging state, so far as the outlet valve 5 is open. When the outlet valve 5 is brought into a non-energized state to be closed in the step-up mode, pressure applied to the wheel brake 3 is increased in proportion to the discharge from the pump 7. Since the chamber 44 communicates with the chamber 43 through the orifice 47 which is provided in the spool 41, the spool 41 is urged by the spring 42 to sequentially rightwardly return to its original position from the state shown in Fig. 4. With such movement of the spool 41, a fluid flow is caused to pass through the orifice 47. Differential pressure between the chambers 44 and 43 is defined by the storing 42. The return speed of the spool 41 is determined by the rate of the flow caused by the differential pressure to pass through the orifice 47. Thus, the return time of the spool 41 is determined by the distance between closure of the bypass 46 and opening of the passage 45 communicating with the master cylinder 2 and the aforementioned return speed. After a lapse of this return time from final closure of the outlet valve 5, the master cylinder 2 again communicates with the wheel brake 3. The above return time is chosen by desired balance between smoothness of control and quickness in response to change in friction coefficient of the road surface. The aforementioned return time is important also in view of safety upon opening of the outlet valve 5 in failure of the pump 7. If the pump 7 is not actuated after pressure to the wheel brake 3 is reduced by opening of the outlet valve 5, pressure in wheels becomes lower than optimum pressure which is responsive to the current state of the road surface. Therefore, deceleration is rendered lower than possible maximum deceleration of the road surface, although a locking state is avoided. When the prescribed return time elapses in this state, the master cylinder 2 is automatically coupled with the wheel brake 3 again, whereby brake force is re-increased. Movement of the spool 41 is independent of change in master cylinder pressure. Therefore, a check valve 8 is required in order to reduce brake pressure in response to the master cylinder pressure in an interval shorter than the aforementioned return time when the brake pedal 1 is abruptly loosened after opening of the outlet valve 5. In another embodiment of the present invention, a flow regulating valve 11 can be added to an outlet valve 5, as shown in Fig. 6. The flow regulating valve 11 comprises a case 12, a spool 13 which is slidable along the inner surface of the case 12 and a spring 15 for unidirectionally urging the spool 13. The spool 13 is provided with an orifice 14. When the outlet valve 5 is opened in the state shown in Fig. 6, differential pressure is caused across the orifice 14. Thus, the spool 13 is leftwardly moved in Fig. 6 against urging force of the spring 15. The spool 13 is held in a constant position when urging force of the spring 15 is balanced with the differential pressure across the orifice 14. Namely, fluid passing through the outlet valve 5 is allowed to pass through the flow regulating valve 11 only at a constant rate which is determined by the differential pressure across the orifice 14. Thus, the flow regulating valve 11 is adapted to discharge the fluid at a constant discharge speed when the outlet valve 5 is open, with no regard to the level of brake pressure. 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: An antilocking apparatus for performing antilocking operation for a wheel brake (3) of a vehicle, said antilocking apparatus comprising: a master cylinder (2); an inlet valve (40) provided in a fluid path connecting said master cylinder (2) with said wheel brake (3) to allow/cut off communication between said master cylinder (2) and said wheel brake (3) through said fluid path; an electrically switch-controlled outlet valve (5) capable of discharging working fluid from a fluid path portion connecting said inlet valve (40) with said wheel brake (3), a damping reservoir (6) for temporarily storing said working fluid discharged through said outlet valve (5); and a pump (7) for drawing said working fluid stored in said damping reservoir (6) to deliver the same into said fluid path portion connecting said inlet valve (40) with said wheel brake (3), characterized in that said inlet valve (40) being formed by a differential pressure conscious valve actuated by differential pressure between fluid pressure in said fluid path portion connecting said inlet valve (40) with said wheel brake (3) and that in a fluid path portion connecting said inlet valve (40) with said outlet valve (5). An antilocking apparatus for a vehicle in accordance with claim 1, wherein said differential pressure conscious valve (40) cuts off communication between said master cylinder (2) and said wheel brake (3) through said fluid path upon initiation of operation for opening said outlet valve (5), and brings said master cylinder (2) and said wheel brake (3) into communication again through said fluid path after a lapse of a constant time upon completion of said operation for opening said outlet valve (5). An antilocking apparatus for a vehicle in accordance with claim 1, wherein said differential pressure conscious valve (40) comprises: a case (48), a spool (41) being slidable along the inner surface of said case (48) and having a first end facing a fluid path portion communicating with said wheel brake (3) and a second end facing a fluid path portion communicating with said outlet valve (5), and a spring (42) for urging said spool (41) toward said first end, said spool (41) being provided with an orifice (47) connecting said fluid path portion communicating with said wheel brake (3) and said fluid path portion communicating with said outlet valve (5). An antilocking apparatus for a vehicle in accordance with claim 3, wherein said case (48) has a plurality of ports, and configurations of said case (48) and said spool (41) and positional relation there between are selected to implement three states including: a first operating state of allowing communication between said master cylinder (2) and said wheel brake (3) through a large passage, communication between said master cylinder (2) and said outlet valve (5) through said orifice (47) and communication between said wheel brake (3) and said outlet valve (5) through said orifice (47), a second operating state of cutting off communication between said master cylinder (2) and said wheel brake (3) as well as communication between said master cylinder (2) and said outlet valve (5) and allowing communication between said wheel brake (3) and said outlet valve (5) through a large passage; and a third operating state of cutting off communication between said master cylinder (2) and said wheel brake (3) as well as communication between said master cylinder (2) and said outlet valve (5) and allowing communication between said wheel brake (3) and said outlet valve (5) through said orifice (47). An antilocking apparatus for a vehicle in accordance with claim 1, wherein said outlet valve (5) includes a flow regulating valve (11) for allowing passage of said working fluid through said outlet valve at a constant flow rate.

Inventors: TAKATA, KOJI
Applicants: SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1988
Main classification: B60T8
IPC codes: B60T8