Solenoid operated, three way, normally closed, high flow, pressure compensated proportional pilot valve

A pilot valve having a sleeve with a central hole therethrough and a first undercut region in an exterior surface thereof which includes a further passageway. A spool is reciprocally mounted in the further passageway for movement between first and second positions. A first end of the spool and a second undercut region thereon has a radially outwardly extending flange larger in diameter than a diameter of the central hole. A spring is provided for continually urging the flange toward a first position thereof in engagement with a first end of the sleeve to effect a closing off of the communication between the second undercut region and the passageway. A second end of the spool defines a nozzle orifice and opposes an end of the armature member configured to selectively move toward and away from the nozzle orifice to control a level of pressure at the control port.

DETAILED DESCRIPTION In FIGS. 2 and 3 , the electro-mechanical or solenoid portion 10 of the solenoid operated valve 11 A is identical to the configuration illustrated in FIG. 1 . The primary difference between the structure illustrated in FIG. 1 and the structure illustrated in FIGS. 2 and 3 is the structure of the liquid control valve 31 A oriented at the right end of the housing 29 which houses the aforesaid armature 12 and annular coil 13 . The central bore 32 A in the valve 31 A is of a uniform diameter throughout its length. A sleeve-like member 51 is provided in the central bore 32 A. More specifically, the sleeve-like member 51 is generally cylindrical in configuration and has an undercut region 52 provided in the exterior surface thereof communicating with the supply port 33 . Axially spaced lands 53 and 54 are oriented at the axial ends of the undercut region 52 and sealingly engage the interior facing wall 56 of the central bore 32 A. In this particular embodiment, the radially outer dimension of the lands 53 and 54 are sized to the internal diameter of the central bore 32 A so as to facilitate a forced fit relation between the sleeve-like member 51 and the central bore 32 A holding the sleeve-like member 51 fixed in the central bore 32 A. The axially facing right end surface 57 of the sleeve-like member 51 is planar and is oriented in a plane perpendicular to the longitudinal axis of the sleeve-like member 51 . A plurality of passageways 58 are provided in the undercut region 52 of the sleeve-like member 51 to provide communication between the undercut region 52 and a central hole 59 through the sleeve-like member 51 . In this particular embodiment, the lands 53 and 54 are oriented on opposite sides of the supply port 33 . A spool 61 is sealingly, slidingly reciprocally mounted within the central hole 59 . The spool 61 includes a length that is greater than the overall length of the sleeve-like member 51 . As a result, the opposite axial ends of the spool 61 project outwardly from the central hole 59 of the sleeve-like member 51 . The spool 61 has a central bore 62 therethrough. An external surface of the spool 61 has an undercut region 63 therein communicating with the passageway 58 . The undercut region 63 terminates at one end thereof in a radially outwardly extending flange 64 also oriented at an axial end of the spool 61 . The radially outer diameter of the flange 64 is greater than the diameter of the central hole 59 in the sleeve-like member 51 . The left axially facing surface 66 on the flange 64 is conformed to the axial end face 57 so that when the surface 66 engages the surface 57 , fluid communication between the undercut regions 63 and the control port 34 is blocked. The end of the spool 61 opposite the flange 64 is configured into an annular surface 67 oriented in a plane preferably perpendicular to the longitudinal axis of the spool 61 as well as in a plane parallel to the opposing surface 42 of the button 39 . An elastically yieldable member 68 in the form of a compression spring is provided between an annular surface 69 encircling the control port 34 and the radially outwardly extending flange 64 so as to continually urge the spool 61 to the position illustrated in FIG. 2 , namely, wherein the surface 66 on the flange 64 is in engagement with the surface 57 on the sleeve-like member 51 . In operation, the solenoid portion 10 can be energized with an analog input signal or a pulse width modulated (PWM) input signal. For purposes of the following discussion, the description will resort to the provision of an analog input signal. In the de-energized state (see FIG. 2 ), the spool is biased by the spring 68 in a direction that seals off the communication between the undercut region 63 and the control port 34 by reason of the surface to surface engagement between the surface 66 on the flange 64 and the surface 57 on the sleeve-like member 51 . Since the seat diameter and the spool diameter are the same, the spool is in essence pressure balanced in the undercut area 63 . The control port is connected to tank via the central bore 62 through the spool and the gap between the surface 42 on the button 39 and the end face 67 on the spool 61 . When the solenoid portion 10 is energized (see FIG. 3 ) to a position less than full on, the surface 42 on the button 39 is driven toward the surface 67 on the spool 61 to move the spool 61 slightly against the urging of the spring 68 to seal off or close the communication between the control port 34 and the tank port 36 . The button continues moving thereby urging the spool 61 so that a spacing occurs between the surfaces 66 and 57 thereby allowing liquid flow and pressure to be communicated between the supply port 33 and the control port 34 . The pressure in the control port 34 will rise until there is a sufficient load acting on the end face of the spool 61 facing the control port 34 plus the bias load of the spring 68 to equal the output load provided by the armature 12 effecting an urging of the surface 42 on the button 39 into engagement with the surface 67 on the spool 61 . At this time, if the pressure in the control port 34 tries to continue increasing, the increase in load applied to the spool 61 will push it back toward the surface 42 on the button 39 thereby also reducing the opening between the supply and control and thereby restricting the flow to effect a maintaining of a relatively constant control pressure. If the pressure continues to rise, the spool 61 will continue moving shutting off the opening between the supply port 33 and the control port 34 . The increased pressure will then push the surface 67 on the spool off from the button surface 42 venting fluid and pressure from the control port 34 thereby maintaining a relative constant pressure at the control port. Also during operation, if for some reason, the pressure in the control port tries to decrease, the reduced pressure (load) on the spool 61 allows the button 39 to push the spool 61 rightwardly, increasing the communication between the supply port and the control port thereby allowing more flow and pressure into the control unit until the spool load and the solenoid load balances thereby maintaining a relative constant control pressure. As a result, increasing and/or decreasing the solenoid input signal increases and decreases the solenoid (button) load respectively and changes the control pressure correspondingly, and it maintains that pressure as described above. When a fast response, changing from one pressure to another is to occur quickly, a command is given and the following description applies. When a quick increase in control pressure is desired, the input signal to the solenoid portion 10 is changed from an existing level to a higher level representing the desired control pressure. The solenoid button load increases, pushing the spool 61 against the bias of the spring 68 (or the spool 61 or solenoid armature 12 reach their respective maximum design stroke), this opens a large communication between the opposing surfaces 66 and 57 as well as between the supply port 33 and the control port 34 across the check seat allowing flow and pressure to be transmitted quickly to the control port 34 . As the pressure approaches the desired level, the increase in spool load plus the bias of the spring 68 moves the spool leftwardly against the surface 42 on the button 39 closing down the opening between the opposing surfaces 66 and 57 until the desired pressure is reached, at which time the solenoid load, the spool load and the bias of the spring are in balance as described above. When a quick reduction in control pressure is required, the input signal to the solenoid 10 is reduced to the desired level, thereby reducing the load on the button 39 and the spool 61 . The pressure load in the control port 34 plus the bias of the spring 68 push the spool leftwardly to bring the surfaces 66 and 57 closer together and eventually into engagement shutting off communication between the supply port 33 and the control port 34 . The control pressure load, pushing on the button 42 adjacent the surface 67 of the spool 61 pushes the surface 67 off from the button surface 42 allowing flow and pressure to pass from the control port 34 to the tank port 36 very quickly. As the pressure in the control port decreases to the desired level, the surface 67 of the spool 61 moves back to the button 39 moving the spool 61 to the left thereby closing communication between the surfaces 66 and 57 and, consequently, closing communication between the supply port 33 and the control port 34 if necessary until the proper pressure balance is obtained as described above. Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.