Logic valve

Abstract: A main poppet body (44) of a logic valve receives inlet pressure (P IN ) at first and second ends. A flow-restricting orifice (77) between the first and second ends produces a differential pressure between the two ends when inlet fluid is permitted to flow from the second end. The main poppet body (44) is normally resiliently seated against a seat (52). A pilot poppet body (46), movable in the main poppet body (44), seats against a seat (71) in the main poppet body (44). The pilot poppet body (46), when sealed to its seat (71), seals the fluid at the second end of the main poppet body (44) from flowing. Thus, equal pressures exist at opposed ends of the main poppet body (44), and the main poppet body (44) remains in its sealing position. An external source of controllable pilot pressure (P i ) acts on the pilot poppet body (46) to unseal it from its seat (71). This permits a flow of inlet fluid from the second end of the main poppet body (44), and produces a pressure reduction at the second end. The differential pressure between the first and second ends of the main poppet body (44) tends to move the main poppet body (44) out of its sealing position, and consequently of permit an inlet flow past the seat (52) of the main poppet body (44). This inlet fluid flows to a drain (T₁). The position of the main poppet body (44) varies in substantially linear relationship to the pilot pressure (P i ) applied to the pilot poppet body (46).

Description: This invention relates to a logic valve which controls the volumetric flow of oil to a hydraulic valve used for construction and similar machines. In DE-A-2 309 345, there is disclosed a valve comprising a housing having a loading pressure inlet port, a drain port, and a valve seat functionally disposed between the inlet port and the drain port; a logic poppet valve body slidably disposed in the housing; a spring located in a spring chamber in the housing and arranged to urge the valve body against the valve seat; said inlet port being in communication with the spring chamber by a passage including a flow restricting orifice; a pilot spool slidably mounted in a part of the poppet valve body constituting a bleed passage connecting the spring chamber to the exterior of the valve. Hydraulic fluid is provided by a pump to a three position valve. In one position fluid is returned to a reservoir. In another position, fluid is supplied the logic valve. The valve is used alternately to supply hydraulic fluid under pressure to a cylinder and to control the return of fluid therefrom. For this purpose pump pressure and a reservoir are alternately connected to two parts via a changeover valve. The operation of the pilot valve is controlled indirectly by the pump pressure when the changeover valve is set to allow controlled drainage of the cylinder to the reservoir. A logic valve in accordance with the invention is characterised by a pressure chamber in the poppet valve body for controlling movement of the pilot spool by means of an external source of pilot pressure connected to a pilot pressure inlet port in the housing and in communication with the pressure chamber. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a cross-section of an embodiment of a logic valve according to the present invention; and Figure 2 is a schematic diagram of the logic valve of Figure 1. A logic valve has a logic valve poppet body 44 slidably fitted inside a housing 41. A loading pressure inlet port P IN at one end of logic valve poppet body 44 leads to a control device 96. A logic valve spring chamber 55, containing a spring 56, is disposed at the other end of logic valve poppet body 44. Spring 56 urges logic valve poppet body 44 against a seat 52 between loading pressure inlet port P IN and a drain port T₁. Loading pressure inlet port P IN is connected through an orifice 77 to logic valve spring chamber 55. A pilot spool 46, controlled by external pilot pressure, is installed in the bleed passage from logic valve spring chamber 55 to the outside. The pilot spool 46 is slidably fitted in logic valve poppet body 44. A pilot pressure inlet port P i is connected through passage 84, a groove 83, passage 82, a surrounding groove 81, and passage 80 to pressure chamber 66 for controlling the pilot spools. Groove 81 has a width at least as great as the sliding distance of logic valve poppet body 44. The pilot pressure bleed path leads outside housing 41 through a surrounding groove 93 having a width at least as great as the sliding distance of logic valve poppet body 44. Logic valve poppet body 44 is slidably fitted inside housing 41 with a sleeve 43 therebetween. Surrounding groove 81 introduces external pilot pressure and surrounding groove 93 of pilot pressure bleed path is formed in the inner surface of sleeve 43. One end of pilot spool 46 faces pilot spool spring chamber 69. A spring 70, installed inside pilot spool spring chamber 69, at the other end of pilot spool 46, urges the pilot spool 46 against seat 71 connected to logic valve spring chamber 55. A pilot spool spring chamber 69 is connected, through an inner hole 88 of pilot spool 46, to a bleed chamber 89 formed at the pressure exhaust side of seat 71. A pressure chamber 66 for external pilot pressure is situated between pilot spool spring chamber 69 and bleed chamber 89. Pilot pressure is pressure chamber 66 urges pilot spool 46 in the axial direction against the resisting the force of spring 70 in the pilot spool spring chamber. A sub spool 47 is slidably fitted in logic valve poppet body 44, in order convey, in the same direction as the force of spring 70 in the pilot spool spring chamber, pressure at loading pressure inlet port P IN to pilot spool 46. The length of surrounding groove 81 ensures that, regardless of location of logic valve poppet body 44, pilot pressure at outside pilot pressure inlet port P i is always fed to pressure chamber 66 for controlling the pilot spool 46. Similarly internal exhaust pressure is bled out of housing 41 through surrounding groove 93. External pilot pressure is conducted to pilot spool 46 through surrounding groove 81 of sleeve 43 and internal exhaust pressure is bled to the outside through surrounding groove 93 of sleeve 43. Although the logic valve of the present invention does not eliminate a leak at the diametrical space between logic valve poppet body 44 and sub spool 47 or a leak at the diametrical space around logic valve poppet body 44, the configuration of having pilot spool spring chamber 69 connected to bleed chamber 89, at both sides of pressure chamber 66, other leaks are eliminated. This permits pilot pressure from the outside to prevent the internal pressure of logic valve spring chamber 55, (i.e. higher pressure) from working upon the pressure in pressure chamber 66 of the pilot pressure (lower pressure). The location of pilot spool 46 is determined by the balance between the force of pressure conducted from logic valve spring chamber 55 to pilot spool 46, the force of pilot pressure conducted from outside into pressure chamber 66, the force of spring 70 in pilot spool spring chamber 69, which works in the opposite direction to the above two forces, and the force applied from sub spool 47 to pilot spool 46. In Figure 1, numerals 41 and 42 denote housings of a metering type logic valve. Housing 41 includes a sleeve 43 fitted therein and stopped by housing 42. Logic valve poppet body 44 is slidably fitted into sleeve 43. Logic valve poppet body 44a is installed in logic valve poppet body 44, comprising a part thereof, and fixed to logic valve poppet body 44 by means of a snap ring 45. Pilot spool 46 and sub spool 47 are slidably fitted in logic valve poppet body 44a and logic valve poppet body 44, respectively. A spring receiver 44b is fitted in the opening of logic valve poppet body 44, and spring 56, which will be described hereunder, is attached to spring receiver 44b. Housing 41 includes loading pressure inlet port P IN located at the inlet side of logic valve poppet body 44. Housing 41 is sectioned to form a drain oil chamber 53 and pressure oil chamber 54, which are connected to the tank through a drainport T₁ by means of seat 52 facing a tapered portion 51 of logic valve poppet body 44. Housing 42 contains logic valve spring chamber 55 located opposite loading pressure inlet port P IN logic valve poppet body 44. Spring 56, in valve spring chamber 55 urged tapered portion 51 against seat 52. Spring chamber 55 is connected to pressure chamber 63 through a path 61 bored in spring receiver 44b and a threaded hole 62 bored through sleeve 44a in the logic valve poppet body for the purposes of disassembly. Loading pressure inlet port P IN is also connected through an orifice 65 to a pressure chamber 64, which is located opposite pressure chamber 63 with pilot spool 46 and sub spool 47 therebetween. Pilot spool 46 has pressure receiving surfaces 67 and 68 facing pressure chamber 63 and pressure chamber 66, respectively. Receiving surface 67 is urged against seat 71 by spring 70 in pilot spool spring chamber 69. Sub spool 47 is maintained in contact with pilot spool 46 by oil hydraulic pressure in pressure chamber 64. Loading pressure inlet port P IN and spring chamber 55 are interconnected through a hole 73 bored in a cylindrical portion 72, which slides in loading pressure inlet port P IN of logic valve poppet body 44, a surrounding groove 74 and a path 75 in housing 41, a path 76 in housing 42, and an orifice 77 in a path 76. Pressure chamber 66 surrounding pilot spool 46 is connected to the outlet side of an external oil pressure pilot valve (pressure reducing valve) 85 through a hole 78 bored in sleeve 44a in the logic valve poppet body surrounding groove 79, a hole 80 bored in body 44 surrounding groove 81, a hole 84 bored in housing 41, and external pilot pressure inlet P i . An oil pressure pilot pump 86 and a relief valve 87 are connected to the inlet side of oil pressure pilot valve 85. Oil in spring chamber 69 is connected through inner hole 88 bored through pilot spool 46, bleed chamber 89, a hole 90 in logic valve poppet body 44a, surrounding groove 91, hole 92 in logic valve poppet body 44, surrounding groove 93, a hole 94 bored in sleeve 43, surrounding groove 95 and drain port T₂ in housing 41. A head end 97 of control device 96, upon which load W acts, is connected to loading pressure inlet port P IN . Surrounding groove 81 in the passage to conduct pilot pressure and surrounding groove 93 in the bleed passage have a width in the axial direction at least as great as the axial movement of holes 80 and 92 bored in logic valve poppet body 44. With the above configuration, loading pressure at leading pressure inlet P IN is conducted into pressure chamber 64 of sub spool 47 through orifice 65. Pressure in spring chamber 55 is conducted into pressure chamber 63 of pilot spool 46 through path 61. Valve-outlet pressure of external oil pressure pilot valve (pressure reduction valve) 85 is conducted from external pilot pressure inlet port P i , to pressure chamber 66 to act upon ring-shaped pressure receiving surface 68 of pilot spool 46. Pilot spool 46 is urged into contact with seat 71 by spring 70, in the normal condition, when valve-outlet pressure from oil pressure pilot valve 85 is not present. Sub spool 47 is urged against pilot spool 46 by pressure through orifice 65 in pressure chamber 64. Fig. 2 is a schematic drawing of the logic valve shown in Fig. 1 with the same numerals identifying corresponding parts. The schematic diagram will aid in understanding the following. When the operation lever of external oil pressure pilot valve 85 is placed in its middle position, no valve-outlet pressure is produced. Therefore, the pressure in pressure chamber 66 is equal to that in the tank. At this time, the pressure at loading pressure inlet port P IN acts via paths 75 and 76, orifice 77, spring chamber 55, path 61 and pressure chamber 63 upon pilot spool 46. The pressure also acts on sub spool 47 via pressure chamber 64. As the pressure-applied area of pilot spool 46 against pressure chamber 63 is equal to the pressure-receiving area of sub spool 47 against pressure chamber 64, a balance is maintained in which pilot spool 46 is pushed against seat 71 by the force of the spring 70. When the operation lever of external oil pressure pilot valve 85 is operated, the force of valve-outlet pressure of pilot valve 85 multiplied by the pressure-receiving area of ring-shaped pressure receiving surface 68 is balanced by a preset load of spring 70. When the operation lever is further fine-adjusted, the force generated by the outlet pressure of external pilot valve 85 becomes somewhat more than the preset load of spring 70. Consequently, pilot spool 46 is moved out of contact with seat 71. Pressurized oil in spring chamber 55 flows to bleed chamber 89 through path 61, pressure chamber 63 and seat 71. At that time, pressurized oil flows into spring chamber 55 through orifice 77. Because of the restriction resistance of orifice 77, the pressure in spring chamber 55 is lower than the pressure at loading pressure inlet port P IN , pilot spool 46 becomes balanced at a position slightly away from seat 71. The distance the pilot spool is thus moved is normally very small because the above flow rate is restricted by orifice 77. When the outlet pressure of external oil pressure pilot valve 85 (the pressure upon ring-shaped pressure-receiving surface 68 of pilot spool 46) is increased by further operation of the operation lever of external oil pressure pilot valve 85, pilot spool 46 moves further away from seat 71, differential pressure ΔP between the pressure at loading pressure inlet port P IN and the pressure in spring chamber 55 increases. When pilot spool 46 moves further away from seat 71 by the increasing outlet pressure of external oil pressure pilot valve 85, the force which is the product of the pressure-receiving section area A of logic valve poppet body 44 by the differential pressure ΔP between loading pressure inlet port P IN and spring chamber 55 balances preset load of spring 56. When the outlet pressure increases by further operation of the operation lever of oil pressure pilot valve 85, the differential pressure ΔP becomes larger. The force A·ΔP exceeds the preset load of spring 56, and consequently logic valve poppet body 44 starts to lift, and tapered portion 51 thereof moves away from seat 52. When the stroke of the operation lever of oil pressure pilot valve 85 increases even further, outlet pressure thereof is further increased, and differential pressure ΔP acting upon logic valve poppet body 44 is also increased. This moves tapered portion 51 further away from seat 52. As a result, holes 73a bored in cylindrical portion 72 begin to move into positions communicating with pressure oil chamber 54. When the stroke of the operation lever of external oil pressure pilot valve 85 is even further increased the differential pressure ΔP acting upon logic valve poppet body 44 increases proportionally. The lifting distance (stroke) of logic valve poppet body 44 also increases proportionally in the direction of increasing load on spring 56. Therefore, the aperture area of holes 73a opening into pressure oil chamber 54 also gradually increases. When a logic valve as above is used to control the flow rate for switching the operational direction of the actuator 96, as described above, differential pressure ΔP between loading pressure inlet port P IN and spring chamber 55 is principally controlled as a linear function of valve-outlet pressure of external pilot valve 85, and therefore the strokes of logic valve poppet body 44 can be very accurately controlled. Further, as it is not affected by absolute value of the loading pressure produced at loading pressure inlet port P IN , a logic valve according to the present invention can be used for the meter-out flow control circuit (a circuit to smooth operation of an actuator subject to variation of load) of cylinder actuator 96, which is expected to operate with consistent stability. Firstly, according to the logic valve shown in Figure 1, the stroke distance of logic valve poppet body 44 is determined by a balance between the pressure at loading pressure inlet port P IN , and the pressure in spring chamber 55, which act on pressure receiving areas at both right and left side of logic valve poppet body 44, (which are identical in case of the embodiment shown in Figure 1), and the force of spring 56. Logic valve poppet body 44 of the present logic valve has therein a mechanism (spools 46 and 47, spring 70, etc.), to linearly control the differential pressure between loading pressure inlet port P IN and spring chamber 56, which is the factor to determine the aforementioned balance, by means of external pilot pressure. Furthermore, with respect to a logic valve shown in Figure 1, leakage occurs at two locations: leak Q₁ at the diametrical space between logic valve poppet body 44 and sub spool 47; and leak Q₂ at the diametrical space between the other surface of logic valve poppet body 44 and the inlet surface of sleeve 43. It is possible to install a pilot spool 46 to control strokes of the logic valve poppet body 44 inside the logic valve poppet body, economizing on the space for the stroke control mechanism centering around the pilot spool, and thereby making the configuration of the logic valve compact and reducing the number of parts necessary for the logic valve. A surrounding groove for introducing external pilot pressure and a surrounding groove for a pilot pressure bleed passage, both necessary for having a pilot spool inside the valve, can be easily formed by means of a sleeve.

Claims: A logic valve comprising a housing having a loading pressure inlet port (P IN ), a drain port (T₁), and a valve seat (52) functionally disposed between the inlet port and the drain port; a logic poppet valve body (44, 44a) slidably disposed in the housing; a spring (56) located in a spring chamber (55) in the housing and arranged to urge the valve body (44, 44a) against the valve seat; said inlet port being in communication with the spring chamber (55) by a passage including a flow restricting orifice (77); a pilot spool (46) slidably mounted in a part of the poppet valve body constituting a bleed passage connecting the spring chamber (55) to the exterior of the valve (T₂), characterised by a pressure chamber (66) in the poppet valve body (44, 44a) for controlling movement of the pilot spool by means of an external source (85) of pilot pressure connected to a pilot pressure inlet port (Pi) in the housing and in communication with the pressure chamber (66). A logic valve as claimed in claim 1, characterised in that said pilot pressure inlet port (Pi) is in communication with a groove (81) surrounding the poppet body (44) and the width of the groove (81) being at least equal to the maximum displacement of the poppet body, and the groove (81) is in communication with the pressure chamber (66); and the bleed passage includes a groove (93) surrounding the poppet body and in communication with the exterior of the housing, said groove (93) having a width at least equal to the maximum displacement of the poppet body. A logic valve as claimed in claim 2, characterised in that the poppet body (44) is slidably mounted in a sleeve (43) disposed in the housing and said grooves (81) and (93) are formed in the wall of the sleeve adjacent the poppet body. A logic valve as claimed in any preceding claim, characterised in that the pilot spool (46) has one end urged against a seat (71) in the bleed passage by a spring (70) located in a spring chamber (69) and acting against the opposite end of the spool and the spring chamber (69) is in communication with a bleed chamber (89) at the pressure exhaust side of the seat (71) by way of a passage through the pilot spool. A logic valve as claimed in claim 4, characterised in that the pressure chamber (66) is located between the spring chamber (69) and the bleed chamber (89) and pressure applied to the chamber serves to bias the pilot spool against the action of the spring and a sub-spool (47) slidably mounted in the poppet body (44) serves to apply force to the pilot spool corresponding to pressure applied to the loading pressure inlet port (P IN ) to re-inforce the action of the spring. A logic valve as claimed in any preceding claim characterised by a pressure reducing surface (68) on said pilot poppet body (46); means for applying a controlled external oil pilot pressure (Pi) to said first pressure receiving surface; said controlled external oil pilot pressure (Pi) being in a direction to oppose said second means for resiliently urging, whereby said second tapered surface is moved out of sealing contact with said second seat (71); means for permitting a flow of said inlet fluid pressure (P IN ) at said second end of said main poppet body (44), past said second seat (71), whereby said flow-restricting orifice (77) reduces a pressure at said second end, and a differential pressure on said main poppet body (44) is produced; said differential pressure being in a direction to oppose said first means for resiliently urging, whereby said main poppet body (44) is moved in a direction to unseal said first tapered portion (51) from said first seat (52); means for permitting a controlled flow of said inlet fluid past said valve seat (52) is substantially proportional to linear motion of said poppet valve body (44), whereby said motion of said poppet valve body (44) is substantially linearly proportional to said controlled external oil pilot pressure (Pi). A logic valve according to claim 6, characterised in that said means for permitting a controlled flow includes a plurality of holes (73, 73a) exposed to said inlet fluid; and means for partially communicating said plurality of holes (73a) with a drain (T₁) in proportion to motion of said main poppet valve body (44). A logic valve according to claim 7, characterised in that said means for partially communicating includes a cylindrical portion (72) of said poppet valve body (44) and a cylinder in which said cylindrical portion (72) moves; at least one hole (73a) in one of said cylindrical portion (72) and said cylinder; said at least one hole (73a) being substantially sealed by fitting to the other of said cylindrical portion (72) and said cylinder when said poppet valve body (44) is in a position seating said first tapered portion (51) against said first seat (52); and said at least one hole (73a) becoming progressively unsealed as said poppet valve body (44) moves in a direction unsealing said first tapered portion (51) from said first seat (52).

Inventors: DOHKE NAOTAKA C O SHIN CATERPI, YOSHINO KAZUNORI C O SHIN CATE, DOHKE, NAOTAKA, C/O SHIN CATERPILLAR, YOSHINO, KAZUNORI, C/O SHIN CATERPILLAR
Applicants: CATERPILLAR MITSUBISHI LTD, SHIN CATERPILLAR MITSUBISHI LTD.
Application year: 1990
Main classification: F15B11
IPC codes: B65D25, G05D7, F15B11, F15B13