Flow control mechanism for power steering

Abstract: A mechanism for a power steering device of automobile is disclosed. Particularly, a flow control mechanism for power steering is disclosed in which there is formed a combination consisting of: a valve for controlling the amount of the hydraulic fluid to be supplied to the power steering device by a pump (which is driven by the engine); and a valve installed for protecting the hydraulic circuit and a stable operation of the pump. The flow control mechanism for a power steering, includes a valve directly connected to a pressure port (1) of said pump; a cylindrical spool hole (18) formed within an inlet port of said valve and within a valve housing; a main spool (6) inserted into said spool hole (18); a sub-spool (5) inserted into said main spool (6); and orifices (3) formed in said sub-spool (5); whereby the required amount of the hydraulic fluid is sent to a power steering device through a combined action of said main spool (6) and said sub-spool (5), and the surplus flow amount over the required flow amount is bypassed by pressure differences formed between the front and rear of said orifices of said sub-spool (5) so as to obtain a stabilized steering.

Description: FIELD OF THE INVENTION The present invention relates to a mechanism for a power steering device of automobiles. Particularly,the present invention relates to a flow control mechanism for power steering in which there is formed a combination consisting of: a valve for controlling the flow amount of the hydraulic fluid to be supplied to the power steering device by a pump (which is driven by the engine); and a valve installed for protecting the hydraulic circuit and for a stable operation of the pump. BACKGROUND OF THE INVENTION Generally,a vane pump is widely used as the power steering pump, and this pump is driven by an internal combustion engine which is installed on the automobile. The hydraulic fluid is sucked by the pump so as to produce a pressure,and,by utilizing this pressure,the manual steering torque is controlled. In the power steering device, when the vehicle runs slow or is stopped, a sufficient steering force is required, because the ground contact resistance acts in a high degree. However,during a fast running in which the ground contact resistance is low ( in this case, the revolution speed of the internal combustion engine is very high, and therefore, the power steering pump supplies a large amount of hydraulic fluid), a large steering force is not required. Therefore, if the hydraulic power is used as it is, then a problem occurs in the stability of the steering. Therefore,if the hydraulic power source which is increased proportionately to the engine speed is applied to the power steering without any adjustment, it becomes undesirable. Therefore,in the usual cases,a hydraulic control mechanism (pressure compensating hydraulic control valve + pressure control valve) having a hydraulic characteristics as shown in FIG. 1B is used. As shown in FIG. 1B, in a low speed region in which a large steering force is required, a certain amount of hydraulic fluid Q1 is supplied. On the other hand, in a high speed region in which a large steering force is not required, the hydraulic fluid amount is reduced to Q 2 proportionately to the velocity of the automobile. This method is called a flow down method. FIG. 1A is a sectional view showing a conventional apparatus of the type shown in JP-A-61 64583. Referring to this drawing,the hydraulic fluid which is discharged by a pump passes through an inlet fluid path 1, a main orifice 2,a first orifice 3 formed in a sub-spool 5 and a second orifice 4 to be supplied to an actuator. The control of the hydraulic fluid which is supplied to the actuator is done in such a manner that the sub-spool 5 move to the left owing to the pressure difference produced between the front and the rear of the first orifice 3 and the second orifice 4, and that the sectional area is reduced owing to the movement of the sub-spool 5. The extra discharge amount from the pump is bypassed, because a main spool 6 moves to the left by the elastic force of a spring 8 which supports the main spool 6. During a low speed revolution of the engine, small pressure differences are produced between the front and the rear of the first orifice 3 and the second orifice 4, because the discharge amount of the pump is small.Therefore,the hydraulic fluid is supplied to the actuator proportionately to the revolution speed of the internal combustion engine.However,when the discharge amount of the pump increases,pressure differences begin to be produced between the front and the rear of the first orifice 3 and the second orifice 4, and the main spool 6 moves to the right against the elastic force of the spring 8 supporting the main spool 6,so that the hydraulic fluid would be bypassed proportionately to the aperture of the main spool and the pressure difference.Consequently,the flow amount Q1 is supplied to the actuator as shown in FIG. 1B. When the revolution speed of the internal combustion engine increases,and thus,if the discharge amount of the pump increases, the pressure differences between the front and the rear of the first orifice 3 and the second orifice 4 are increased. Proportionately to this,the sub-spool 5 moves to the left against the elastic force of a sub-spring 9 which supports the sub-spool 5. Meanwhile,the main spool 6 moves to the right against the elastic force of the spring 8, so that the hydraulic fluid would be bypassed proportionately to the aperture of the main spool 6 and the pressure difference. Thus as shown in FIG. lB,the flow amount Q2 is supplied to the actuator,thereby assuring a stability during the steering. However,in the above described hydraulic control mechanism,a tapered portion 12c and projected portions 12a and 12b which are formed on the sub-spool 5 may cause a variation of the aperture area. Consequently, an imbalance is caused in the orifice characteristics, so that the characteristics of the sub-spool 5 may be affected, and that the hydraulic fluid supplied to the actuator would become unstable. Consequently,the stability of the power steering is adversely affected.The aperture area of the main orifice 2 is varied in a linear form over a certain region,but if the region is departed,the variation becomes non-linear,with the result that an accurate hydraulic control becomes difficult.Further,the pressure pulse of the pump can be transmitted to the actuator. US-A-2 748 711 discloses a flow control mechanism, with a valve body having a cylindrical spool hole, an inlet port, a drain port and an outlet port; a main spool slidably disposed within the cylindrical spool hole of the valve body and having a main bore, and a sub-spool slidably disposed within the main bore of the main spool. The sub-spool is movable to discharge fluid from the inlet port to the drain port in case of extrememy high pressure conditions. The main spool is movable to direct fluid from the inlet port to the outlet port or to the drain port, and thus control the required amount of flow to the outlet port. US-A-4 361 166 discloses a flow control mechanism of the type described in reference to figure 1A, where two spools are slidably mounted inside of the same bore of the mechanism. Summary of the invention. The present invention is intended to overcome the above described disadvantages of the conventional techniques. Therefore it is the object of the invention to provide a flow control mechanism for power steering, in which a sub-spool is inserted into a main spool, so that the control of hydraulic fluid would be possible in a wider range, and that the control may be carried out in an accurate manner. BRIEF DESCRIPTION OF THE DRAWINGS The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which: FIG. 1 illustrates the conventional mechanism, in which: FIG. 1A is a sectional view of the conventional apparatus; and FIG. 1B is a graphical illustration showing the flow amount characteristics; FIG. 2 is a sectional view showing a preferred embodiment of the present invention, in which: FIG. 2A is a plan view of the mechanism of the present invention; and FIG. 2B is a frontal view of the mechanism of the present invention; FIG. 3 illustrates the hydraulic circuit for activating the control valves; FIG. 4 illustrates the flow amount characteristics for the preferred embodiment of the present invention; FIG. 5 illustrates the actuating state of the spool for the control valve; in which: FIG. 5A illustrates a first switched state; FIG. 5B illustrates a second switched state; and FIG. 5C illustrates a third switched state; and FIG. 6 is a sectional view showing a second embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the conventional mechanism, in which: FIG. 1A is a sectional view of the conventional apparatus; and FIG. 1B is a graphical illustration showing the flow amount characteristics. The overall constitution of the present invention will be described referring to FIG. 2. The flow control mechanism for the power steering device includes a pump and a valve body which are integrally formed.The valve body is provided with an accommodating hole 18 for accommodating a main spool 6 into which a sub-spool 5 is inserted.Thus the overall bulk is reduced, and the energy saving characteristics becomes superior.Further, a relief valve 21 which is for protecting the circuit is exposed to the outside,so that its set pressure can be tested even in the assembled state. FIG. 3 illustrates a hydraulic circuit for activating the control valve. FIG. 4 illustrates the flow amount characteristics for the preferred embodiment of the present invention.FIG. 5 illustrates the actuating state of the spool for the control valve. In describing the present invention,the same reference codes are assigned to avoid the confusion with the conventional mechanism.However, the present invention is quite different from the conventional mechanism,and therefore, only the portions which corresponds to the general hydraulic circuit will be skipped. Therefore, descriptions will be made on the main spool 6, the sub-spool 5 and the hydraulic circuit and the actuation state of the relief valve 21. The hydraulic fluid which is discharged by the pump passes through an inlet fluid path 1 and a main orifice 2 to be supplied to a first orifice 3 and a second orifice 4 which are formed on the sub-spool 5.Then the hydraulic fluid which has passed through the orifices are supplied to the actuator, so that a steering force needed to the steering can be obtained. In the hydraulic circuit of FIG. 3,the hydraulic fluid which discharged from the hydraulic fluid source is easily supplied through the sub-spool 5 to the actuator.When the pressure differences between the front and the rear of the first and second orifices 3 and 4 are increased,the main spool 6 is opened, so that the hydraulic fluid to be supplied from the hydraulic fluid source to the actuator would be bypassed through the main spool 6.If the circuit pressure reaches a pre-set pressure, in order that the stabilities of the circuit and the pump can be maintained,the relief valve 21 is opened, so that the circuit pressure would not rise over the pre-set pressure. The pump which is connected to the engine of the automobile by means of a V belt discharges a flow amount proportionate to the revolution speed of the engine,so that the discharged flow amount would be supplied to the actuator. Under this condition,during a low speed region Nl,the pressure difference between a first pressure chamber 24 and a second pressure chamber 25 is small,and therefore, a flow amount proportionate to the revolution speed of the engine is supplied to the actuator. Then as shown in FIG. 5A,if the revolution speed rises (N0 - N1),then a pressure difference begins to be formed between the first pressure chamber 24 and the second pressure chamber 25,and there is generated a force equivalent to the pressure difference multiplied by the sectional area of the pressure receiving portion of the main spool. Owing to this force,the main spool moves as much as the spring force (spring constant x displacement) to the left so as to open a drain port, so that a part of the hydraulic fluid would be bypassed,thereby supplying a certain flow amount Q1. If the revolution speed is increased further (N1 - N2),then as shown in FIG. 5B,he pressure of the first pressure chamber 24 rises,so that the main spool 6 would overcome the elastic force of the supporting spring 8 so as to move to the left.At the same time,a force equivalent to the pressure difference multiplied by the pressure receiving sectional area of the sub-spool 5 is built up, so that the sub-spool 5 would be pushed to the left. Consequently, the aperture area of the second orifice is slowly reduced, with the result that the flow amounts Q1 - Q2 characteristics are formed. When the revolution speed further rises (N2), then as shown in FIG. 5C,a poppet portion 12 of the sub-spool 5 completely contacts to a seat portion 16 of the main spool. From this point,the force which reaches the sectional area of the pressure receiving portion of the sub-spool 5 acts on the main spool 6. Consequently,the aperture area of the drain port portion 7 is increased,and a flow amount which is proportionate to the pressure difference between the first pressure chamber and the drain port portion is bypassed, with the result that the flow amount supplied to the actuator attains to a certain amount Q2. Further,if the load of the steering is large,the circuit pressure rises over the pre-set pressure,and this over-pressure causes problems in the circuit stability. Therefore,in order to eliminate the circuit instability, the relief valve 21 is installed. If the circuit pressure rises over the pre-set pressure,the relief valve 21 is opened,and the hydraulic fluid of a guide fluid path 20 is drained through the drain port 7,so that a stabled operation would be possible. In the conventional mechanism, the spring 8 for supporting the main spool 6 and the spring 9 for supporting the sub-spool 5 are separately actuated, with the result that the control of the flow down is not sufficiently smooth. On the other hand,according to the present invention,the spring 8 for supporting the main spool and the spring 9 for supporting the sub-spool are serially constituted. Therefore, there can be adjusted the gradient by which the flow amount is subjected to a flow down from Q1 to Q2 under an arbitrary revolution speed of the engine (N1 - N2', or N1 -N2"). Therefore the control range is large,so that an accurate and comfortable steering characteristics can be obtained both in the low speed and high speed. Further,a large damping effect can be obtained compared with the conventional mechanisms,and therefore,the actuator is greatly freed from the influence of the pressure pulses.Further,only the spring constants for the springs 8 and 9 for supporting the main spool 6 and the sub-spool 5 are varied, and therefore, the variation of the controlled fluid due to the processing error can be adjusted. FIG. 6 is a sectional view showing a second embodiment of the present invention. The inlet fluid path 1 of the flow control mechanism according to the present invention is provided with main spool accommodating holes 13 in a symmetrical form.If one direction is blocked by using a plug,then the assembling can be made from any direction.Therefore, a flexibility is provided when changing the design and the installation space during its attachment on an automobile.

Claims: A flow control mechanism comprising: a valve body (30) having a cylindrical spool hole (18), an inlet port, a drain port and an outlet port (11); a main spool (6) slidably disposed within the cylindrical spool hole (18) of the valve body and being movable in response to a pressure differential between the inlet port and the outlet port so as to by-pass an excess flow to the drain port, the main spool having a main bore (19) and an orifice (4) at one end of the main bore through which a fluid is communicated from the inlet port to the outlet port; and a sub-spool (5) slidably disposed within the main bore (19) of the main spool and having an orifice (3) at one end thereof, the sub-spool being movable relative to the main spool in response to a pressure differential between the inlet port and the outlet port so as to reduce the aperture area of the orifice of the main spool and control the required fluid flow from the inlet port to the outlet port. A flow control mechanism as claimed in claim 1, further comprising pressure relief means (21) for controlling the maximum pressure of the fluid flowing from the inlet port to the outlet port. A flow control mechanism as claimed in claim 1 or 2, wherein the valve body comprises a second opening independent from the cylindrical spool hole (18); and wherein the pressure relief means is disposed in the second opening. A flow control mechanism as claimed in claim 1, 2 or 3, further comprising means for limiting the movement of the sub-spool in a direction toward the orifice of the main spool. A flow control mechanism as claimed in claim 4, wherein the limiting means comprises a shoulder portion formed integrally with the main spool. A flow control mechanism as claimed in one of claims 1 to 5, further comprising a spring (9) disposed in the main bore (19) of the main spool (6) for biasing the sub-spool (5) in a direction away from the orifice (4) of the main spool. A flow control mechanism as claimed in one of claims 1 to 6, wherein the main bore (19) of the main spool (6) has first and second pressure chambers (24, 25), and wherein the main spool is movable in response to a pressure differential between the first and second pressure chambers. A flow control mechanism as claimed in one of claims 1 to 7, wherein the sub-spool has a pair of land portions (13, 14) having different cross-sectional areas. A fluid control mechanism as claimed in one of claims 1 to 8, wherein the sub-spool has a tapered portion (12) which extends into the orifice (4) of the main spool to form a variable orifice in cooperation with the orifice (4) of the main spool; and wherein the tapered portion of the sub-spool reduces the volume of the fluid passing through the orifice of the main spool when the sub-spool is moved outwardly of the main bore of the main spool in a direction toward the orifice of the main spool. A flow control mechanism as claimed in claim 9; further comprising pressure relief means (21) for controlling the pressure of the fluid flowing from the inlet port to the outlet port. A flow control mechanism as claimed in claim 9 or 10, wherein the valve body comprises a second opening independent from the cylindrical spool hole (18); and wherein the pressure relief means is disposed in the second opening. A flow control mechanism as claimed in one of claims 9 to 11, further comprising means for limiting the movement of the sub-spool in a direction toward the orifice of the main spool. A flow control mechanism as claimed in claim 12, wherein the limiting means comprises a shoulder portion formed integrally with the main spool. A flow control mechanism as claimed in one of claims 9 to 13, further comprising a spring (9) disposed in the main bore (19) of the main spool (6) for biasing the sub-spool (5) in a direction away from the orifice (4) of the main spool. A flow control mechanism as claimed in one of claims 9 to 14, wherein the main bore (19) of the main spool (6) has first and second pressure chambers (24, 25), and wherein the main spool is movable in response to a pressure differential between the first and second pressure chambers. A flow control mechanism as claimed in one of claims 9 to 15, wherein the sub-spool has a pair of land portions (13, 14) having different cross-sectional areas; and wherein the fluid flow is subjected to a stepwise flow down to reduce the flow proportionately to the pressure of the pump, in response to pressure differentials across the land portions. A fluid control mechanism as claimed in one of claims 9 to 16, wherein the sub-spool has a tapered portion (12) which extends into the orifice (4) of the main spool to form a variable orifice in cooperation with the orifice (4) of the main spool; and wherein the tapered portion of the sub-spool reduces the volume of the fluid passing through the orifice of the main spool when the sub-spool is moved outwardly of the main bore of the main spool in a direction toward the orifice of the main spool.

Inventors: KIM HYONG-EUI, MUN SEONG-DAE, YUN SO-NAM, KIM, HYONG-EUI, MUN, SEONG-DAE, YUN, SO-NAM
Applicants: KOREA MACHINERY & METAL INST, KOREA INSTITUTE OF MACHINERY & METALS
Application year: 1995
Main classification: F04C15
IPC codes: F04C14, B62D6, B62D5