Patent Application
20170059057
This invention claims the benefit of Japanese Patent Application No. 2015-167474 which is hereby incorporated by reference.
The present invention relates to a system using an electromagnetic proportional control valve which performs spool position control using an electromagnetic force.
As one of directional control valves, a three position directional control valve, which performs switching control for fluid supply in three directions (a fluid supply position in a forward direction, a supply suspension position, and a fluid supply position in a backward direction), is publicly known. As this type of directional control valves, there is one which merely performs three ON/OFF position switching, however, there is also one which performs proportional control of amount of supplying fluid in response to amount of a spool stroke from the supply suspension position (a neutral position). Regarded to this proportional control concerned, in addition to direct control valve by manual, there are also well-known proportionally controlled valves as using a pilot pressure or operatively controlled electric (operatively controlled electromagnetic force) (for example, refer to Patent Document 1).
In order to perform position control of the three position proportional control valve 100, that is, spool position control, a command signal is transmitted to the electromagnetic pressure reducing valve 111 or 112, and pilot pressure depending on the command signal is applied on an end of the spool. For example, in order to move the spool leftward, pilot pressure is applied on the right end of the spool by the right electromagnetic proportional pressure reducing valve 112. This makes the spool pressed to stroke to leftward direction until the force generated with pilot pressure balances with the spring force of the left spring 102a so that the spool is settled on the rightward activated position 101b with the stroke corresponding to the above mentioned command signal.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2015-98936(A)
In the system configured above, there exists a problem of a large spring size because of the necessity of a relatively large spring force led when taking such factors into account as working range and control accuracy of the electromagnetic proportional pressure reducing valve, area of the end of the spool on which the pilot pressure is applied, a force necessary to restrain an influence due to such external factors as fluid force by flow, frictional force, etc. generated on the spool when it moves, and necessary force for the spool to return surely to the neutral position. Furthermore, although it is preferable that the electromagnetic proportional control valve is integrally installed into the chamber storing the spring, however, there arises a space problem around the end parts of the spool of the three position proportional control valve, and this is likely to expand to the space problem of total valve system.
The present invention is derived in view of such a problem, and aims to provide an electromagnetic proportional control valve system with reduced spring force, enabling to obtain a predetermined control characteristic with a possibility for downsizing.
In order to achieve the object, an electromagnetic proportional control valve system according to an aspect of the present invention is configured to comprise a three position proportional control valve, and left and right position control apparatuses which are provided on both ends of a main spool in the three position proportional control valve for stroke control of the main spool. The left and right position control apparatuses respectively comprises a compressible position feedback spring which confronts with the main spool end, a pilot control valve disposed so as to confront to the side of the position feedback spring opposed to the main spool end across the position feedback spring, and a proportional solenoid providing an electromagnetic expanding force applicable to the opposite side of pilot spool in the pilot control valve against the position feedback spring. The concerned pilot spool is configured to be moved in response to compression force of the position feedback spring and electromagnetic force of the proportional solenoid in order to control the pilot control valve operatively, with its output pressure applied on the both ends of the pilot spool additionally, so that control is performed to generate the output pressure with a negative characteristic against the electromagnetic force of the proportional solenoid.
In the electromagnetic proportional control valve system, it is preferable that when the main spool is moved either leftward or rightward from the neutral position, the position feedback spring in the moving direction side is compressed by the main spool, and on the other hand, in the side oppose to moving direction the main spool is configured to step away from the position feedback spring in the side oppose to moving direction.
In the electromagnetic proportional control valve system, it is preferable that in the position control apparatus oppose to the moving direction, output pressure, by the pilot control valve, generated in response to an electromagnetic force of the proportional solenoid shows a negative characteristic, and the position control apparatus works as an electromagnetic proportional pressure reducing valve.
In the electromagnetic proportional control valve system, it is preferable that in the position control apparatus in the moving direction side, spring force by the position feedback spring which varies in response to compression by stroke of the main spool is applied on the pilot spool to play as a feedback to the electromagnetic force of the proportional solenoid in order to establish closed loop position control.
In the electromagnetic proportional control valve system, it is preferable that adjusting means by adjusting compression force are provided in parallel with the proportional solenoid respectively in the left and right position control apparatuses. Compression force adjusted by the adjusting means is configured to work onto an end of the pilot spool in opposition to the end confronted by the position feedback spring, to be combined together with electromagnetic force generated by the proportional solenoid.
According to the electromagnetic proportional control valve system set forth in the present invention, it is possible to make the position feedback spring small, and by integrating it into the pilot control valve, it is possible to realize the compact structure.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.
The preferable embodiments are now described with reference to drawings. The electromagnetic proportional control valve system according to the present embodiment controls to supply, as shown in
Specifically, hydraulic supply to the actuator 18 from the hydraulic pump 15 is stopped by setting to the neutral position 10c, hydraulic oil from the hydraulic pump 15 is supplied to a left oil chamber (bottom side oil chamber) of the actuator 18 and hydraulic oil in a right oil chamber (rod side oil chamber) is discharged to the tank 16 by setting to the left activated position 10a(placing the left activated position 10a to a location illustrated as the neutral position 10c), and the hydraulic oil from the hydraulic pump 15 is supplied to the right oil chamber of the actuator 18 and the hydraulic oil in the left oil chamber is discharged to the tank 16 by setting the right activated position 10b. Note that when setting to the left activated position 10a or the right activated position 10b, oil flow supplied to the actuator 18 from the hydraulic pump 15 is controlled (proportionally controlled) in response to amount of stroke of the main spool 11.
As shown the configuration in
Furthermore, left and right pilot control valve 21 and 31 are respectively provided outside the chamber 12a or 12b so that they respectively confront the position feedback spring 25 or 35. An inner end of a pilot spool of these left and right pilot control valve 21 or 31 confronts and contacts the position feedback spring 25 or 35 via pushpin 25c or 35c and outside support plate 25a or 35a respectively, and an outer end of the pilot spool confronts and contacts the proportional solenoid 27 or 37 respectively. Accordingly, the pilot spool of the pilot control valve 21 or 31 receives compression force of the position feedback spring 25 or 35 from inside respectively, and receive expanding force of the proportional solenoid 27 or 37 from outside respectively. The proportional solenoid 27 and 37 are respectively coupled to controller 29 or 39 via control line 29a or 39a, and are activated in response to control signal from the controller 29 or 39. Note that the controller 29 is integrated with the controller 39.
Pilot pressure line 23a or 33a from pilot supply source 23 or 33, tank line 24a or 34a reaching tank 24 or 34, and outlet line 22 or 32 are coupled to the left or right pilot control valve 21 or 31 respectively. The outlet line 22 or 32 has first outlet line 22a or 32a coupled to outlet port of the left or right pilot control valve 21 or 31, and second outlet line 22b or 32b and third outlet line 22c or 32c branched leftward or rightward from the first outlet line 22a or 32a respectively. The second outlet line 22b and 32b are respectively coupled to the outer end oil chamber of the pilot control valve 21 or 31, and the third outlet line 22c and 32c are respectively coupled to the left or right chamber 12a or 12b. Accordingly, internal pressure in the left or right chamber 12a or 12b is applied on an inner end of the pilot spool via the pushpin 25c or 35c respectively, and same pressure as this internal pressure is applied on an outer end of the pilot spool. As illustrated in the drawing that the diameter of the pushpin is smaller than that of the pilot spool, the pressure-receiving area of the inner end is smaller than that of the outer end. Note that the pilot supply source 23 is structurally identical with the pilot supply source 33, thus they respectively supply the same pilot pressure. It is appreciated that the tanks 24 is integrated with the tank 34.
The pilot control valve 21 and 31 are configured to be set to the neutral position 21c or 31c, the outer activated position 21a or 31a, and the inner activated position 21b or 31b respectively in response to movement of the pilot spool. When set to the neutral position 21c or 31c, a connection between the pilot pressure line 23a or 33a and the tank line 24a or 34a, and the outlet line 22 or 32 is severed. When set to the inner activated position 21b or 31b, the pilot pressure line 23a or 33a is coupled with the outlet line 22 or 32, thus pilot pressure is supplied to the outlet line 22 or 32 from the pilot pressure supply source 23 or 33. On the other hand, when set to the outer activated position 21a or 31a, the tank line 24a or 34a is coupled with the outlet line 22 or 32, thus oil is discharged to the tank 24 or 34 from the outlet line 22 or 32.
Way of controlling hydraulic oil supply to the actuator 18 from the hydraulic pump 15 by using the electromagnetic proportional control valve system as configured above is described as follows.
(Math 1)
Pb*(A(R)y−A(R)z)+F(R)sol+F(R)ad=F(R)fb (1)
Based on the conditional expression (1), hydraulic pressure Pb in the right chamber 12b, that is, right control pressure Pb which is pressure of the outlet line 32 adjusted by the right pilot control valve 31, is defined by the conditional expression (2).
(Math 2)
Pb=[−F(R)sol+(F(R)fb−F(R)ad)]/(A(R)y−A(R)z) (2)
In the conditional expression (2), compression force F(R)fb of the right position feedback spring 35 and compression force F(R)ad by the right adjustment spring 38a are constant, and pressure-receiving area A(R)y and A(R)z are constant (however, A(R)y>A(R)z), the right control pressure Pb can be controlled by controlling the electromagnetic force F(R)sol of the right proportional solenoid 37. In the conditional expression (2), the right control pressure Pb has an inverse proportion relationship to the electromagnetic force F(R)sol, because the coefficient of electromagnetic force F(R)sol becomes a negative value. This relationship is shown in
Note that when the right control pressure Pb becomes high from a state shown in
Next, the left position control apparatus 20 in a state shown in
Firstly, a relationship of forces which act on the main spool 11 can be defined by the following conditional expression (3).
(Math 3)
Asp*Pa+F(L)fb=Asp*Pb (3)
Meanwhile, a relationship of forces which act on the main spool 11 when the left feedback spring 25 is in the neutral position (When X=0) can be defined by the following conditional expression (4). However, this denotes a relationship of forces at the position just before the main spool 11 contacts the right inner support plate 35b, that is, a relationship of forces at a starting position at which the main spool 11 starts to move leftward. Moreover, Pa0 denotes hydraulic pressure in the chamber 12a in this state.
(Math 4)
Asp*Pa0+F(L)fb0=Asp*Pb (4)
A relationship of forces which act on the left pilot spool of the left pilot control valve 21 is defined by the following conditional expression (5).
(Math 5)
F(L)sol+F(L)ad+Pa*A(L)y=F(L)fb+Pa*A(L)z (5)
On the other hand, a relationship of forces which act on the left pilot spool when the left position feedback spring 25 is in the neutral position (when X=0) is defined by the following conditional expression (6).
(Math 6)
Pa0*(A(L)y−A(L)z)+F(L)sol0+F(L)ad=F(L)fb0 (6)
Wrapping up the conditional expressions (3) to (6), the following conditional expression (7) is obtained.
(Math 7)
F(L)sol=(F(L)fb−F(L)fb0)*[1+(A(L)y−A(L)z)/Asp]+F(L)sol0 (7)
The following conditional expression (8) is satisfied based on a characteristic of the left position feedback spring 25.
(Math 8)
F(L)fb=K*X+F(L)fb0 (8)
The following conditional expression (9) is obtained based on the conditional expressions (7) and (8).
(Math 9)
F(L)sol=K*[1+(A(L)y−A(L)z)/Asp]*X+F(L)sol0 (9)
In the conditional expression (9), K*[1+(A(L)y−A(L)z)/Asp] and F(L)sol0 are also constant, thus it is understandable that expanding force of the left proportional solenoid 27 has a proportional relationship with a stroke X of the main spool 11. At this point, when increasing the electromagnetic force F(L)sol of the left proportional solenoid 27, the left pilot control valve 21 is set to the external activated position 21b by moving the pilot spool rightward, and the outlet line 22 is coupled to the tank. As a result, since the left control hydraulic pressure Pa in the left chamber 12a falls, the main spool 11 moves leftward, therefore the left position feedback spring 25 is compressed, and the pilot spool is returned back. This mechanism stops with the pilot spool balanced in a state in which a relationship of the above conditional expression (9) is satisfied. As mentioned above, the position of the main spool 11 is closed-loop controlled via the left position feedback spring 25 in response to the command (the electromagnetic force F(L)sol of the left proportional solenoid 27).
At this point, a case of a conventional three position proportional control valve 100 shown in
In the electromagnetic proportional control valve system according to the present invention above, in case that the diameter of the main spool is 28 mm and the maximum stroke in any one of rightward and leftward directions is 10 mm, an electromagnetic force of the proportional solenoid is set to 1.5 kgf at a maximum, a control pressure is 20 bar when the electromagnetic force is 0 kgf, a difference between pressure-receiving area inside and outside of the pilot spool (A(L)y−A(L)z above-mentioned) is set to 4.50 mm2, then it is possible to obtain the position feedback springs 25 and 35 having reduced values such as 0.9 kgf for initial setting force and 2.4 kgf for maximum force when stroke is maximum 10 mm. As mentioned above, this enables to reduce the maximum load to the spring down to 2.4 kgf from 160 kgf, hence, approximately 1/67.
According to the electromagnetic proportional control valve system set forth in the embodiment of the present application as described above, it is possible to downsize the position feedback springs 25 and 35, furthermore to have a compactly configured system by integrating the spring into the pilot control valves 21 and 31.
Moreover, the conventional electromagnetic proportional valve control system shown in
Furthermore, as shown in
Even if a command signal is severed due to an unexpected incident, the same operations as those of a conventional control system are guaranteed. For example, if control signals of both of the left and right proportional solenoids 27 and 37 are not available, the main spool 11 will return to the neutral position. When a control signal of the proportional solenoid in the position control system on a side shown in
The invention being thus described; it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-167474 | Aug 2015 | JP | national |
