Abstract:
A solenoid operated pressure biased spool valve for controlling flow between a pressure inlet port and a valving chamber ported to a control signal port. The spool also controls bleed flow from the valving chamber to an exhaust port. The solenoid armature is connected to an operating rod biased for end-to-end contact with the spool. An adjustment screw is provided in a pole piece and is adjusted at calibration to limit armature and operating rod travel when the exhaust port is fully open at maximum coil current and the pressure bias on the spool tends to zero. Upon de-energization, impulse contact of the operating rod and spool does not occur and pressure transients are thus eliminated.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to control valves of the type which control a pressure signal to a control outlet from a source of pressurized fluid and particularly hydraulic fluid by bleeding off fluid to an exhaust port typically connected to a sump or pump return for the system to be controlled. Valves of this type have found widespread usage in automotive applications for controlling the pressure of the fluid for an hydraulically assisted power steering system and also for controlling the shifting actuators in an automatic power transmission.  
           [0002]    Typically such valves are of the spool type operated by an electromagnetic solenoid with the moveable armature of the solenoid operatively connected for causing the desired movement of the spool to control the flow from the pressurized inlet to a valving chamber connected to the control signal outlet port and also to control flow from the valving chamber to an exhaust or sump return outlet port.  
           [0003]    Solenoid operated spool valves of the aforesaid type have been provided with a pressure balanced spool or a spool arranged such that the pressure forces acting on the spool produce a desired relatively slight bias force tending to move the spool in a direction to reduce the pressure to the control signal outlet port. In such pressure force biased solenoid operated spool valves, it has been found that where the pressure in the valving chamber approaches zero, as the valve reduces the flow from the high pressure inlet port to the valving chamber as a result of the exhaust port being opened, the pressure bias forces on the valve spool tend also to zero. In certain designs the pressure bias forces are relied upon to maintain the spool and actuator in contact with the armature to ensure accurate control of the movement of the spool in response to electrical energization.  
           [0004]    However, as the solenoid energization is increased and the spool is moved to a position reducing the pressure in the control signal output and opening the exhaust port, and the bias forces on the spool tends to zero the spool stops moving even though the armature continues its movement. Upon increasing energization of the solenoid, the armature can move away from the spool and its actuating member and thus cause lash to occur between the armature and the spool. Upon de-energization a relative velocity is developed between the armature and the spool and the armature gains momentum and contacts the spool with an impulse thereby producing transients or perturbations in the hydraulic system to be controlled.  
           [0005]    Accordingly, it has been desired to provide a way or means of preventing lash from occurring in a solenoid operated spool type pressure control valve as the pressure in the pressure control port and valving chamber tends to zero upon opening of the exhaust port and pressure force bias on the spool is eliminated. It has further been desired to provide such a solenoid operated pressure control valve which is not subject to perturbations in the system to be controlled due to armature impulse on the spool at zero control pressure. It has further been desired to provide such a valve which is relatively low in manufacturing cost and easy to assemble and calibrate. It has been particularly desired to provide such a solenoid operated pressure control valve which is suitable for low voltage, low current energization for motor vehicle applications.  
           [0006]    Referring to FIG. 3, a plot of control signal output port pressure (P 2 ) as a function of coil energization current is shown for a Prior Art valve wherein as the pressure (P 2 ) approaches zero at high levels of solenoid coil current. In the Prior Art valve plot shown in FIG. 3, it is seen that upon decreasing the current from the maximum level of energization, substantial perturbations or oscillations of the control pressure (P 2 ) occur as evidenced by the pressure excursions near zero current level.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a solenoid operated spool-type pressure control valve for controlling flow at a desired pressure to a signal output or control port adapted for connection to a hydraulic system to be controlled from a valving chamber which is connected to a pressurized source of fluid; and, the valving chamber is also connected to an exhaust outlet port through which flow is controlled by the spool for discharge to a sump or pump return.  
           [0008]    The valve of the present invention has the valving spool provided with a first annular valving land for controlling flow from the inlet port to the valving chamber; and, a second land controls flow from the valving chamber to the exhaust with the control pressure signal outlet port continuously connected to the valving chamber. The spool has the second valving land for the exhaust port formed of larger diameter than the first land to provide a greater annular area exposed to the valving chamber such that the pressure forces in the valving chamber provide a bias on the spool in the direction tending to open the exhaust port. The solenoid armature has an operated rod connected thereto which contacts the end of the spool; and, the armature and operating rod are spring biased to move the spool in a direction tending to close the exhaust port and to open the inlet port, thereby providing maximum pressure to the control pressure chamber and control signal outlet port. Upon energization, the armature is pulled in a direction tending to close a working gap with a pole piece and permitting the hydraulic bias to move the spool in a direction tending to close the inlet port and open the exhaust port. The maximum travel of the solenoid and operating rod are limited by an adjustable stop pin provided in the pole piece to prevent the armature from completely closing the working air gap and being moved away from the spool as the hydraulic bias on the spool approaches zero when the exhaust port is fully opened.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross-section of the valve assembly of the present invention taken through the axis of symmetry of the spool and armature;  
         [0010]    [0010]FIG. 2 is a graph of control signal outlet pressure (P 2 ) as a function of coil energization current; and,  
         [0011]    [0011]FIG. 3 is a plot similar to FIG. 2 of a valve of the known Prior Art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Referring to FIG. 1, the valve assembly of the present invention is indicated generally at  10  and includes a valve body  12  defining a valving chamber  14  therein which communicates with a first valving bore  16  at the upper end thereof and a second valving bore  18  of lesser diameter at the lower end thereof. The valve body  12  has an upper portion comprising an annular flux collector or pole segment  20  attached to upper end of the body  12  by any suitable expedient such as press fitting, weldment, adhesive bonding or threaded connection.  
         [0013]    Valve body  12  has at least one, and preferably a plurality of, control pressure outlet ports  22  formed therein and communicating with the valving chamber  14 . A plurality of inlet ports  24  disposed in body  12  in axially spaced arrangement from the ports  22 ; and, ports  24  are adapted to be connected to a source (not shown) of pressurized fluid as, for example, a hydraulic pump. As illustrated in FIG. 1, the ports  24  are preferably formed with a feathering notch  26  on one side thereof to provide decreased pressure sensitivity as the ports are closed as will hereinafter be described. A third set of ports  28  are disposed in axially spaced arrangement on the opposite sides of valving chamber  14  from the inlet ports  24 ; and, ports  28  are adapted for connection to a pump inlet (not shown) or sump (not shown) and are thus considered exhaust ports.  
         [0014]    A valving spool  30  is slidably disposed in valving chamber  14  with the spool having an upper annular valving land or surface  32  formed thereon which closely interfits the bore  16  in precision sliding engagement for limiting fluid leakage; and, a lower inlet valving land  34  is formed thereon which also closely interfits the bore  18  in precision sliding engagement in a manner which minimizes fluid leaking therebetween.  
         [0015]    It will be understood that valving lands  34  and  32  are of appropriate axial length so as to have land  32  covering exhaust ports  28  with inlet land  34  covering the inlet ports  24 . It will be understood that the lower annular axial face  36  of land  32  is located axially on spool  30  so as to provide opening and closing of the ports  28  with a relative limited movement in the axial direction. Similarly, the upper axial face  38  of land  34  is disposed to effect opening and closing of the inlet ports  24  including notches  26 .  
         [0016]    In the present practice of the invention for an automotive application providing low pressure control in the range 130 to zero PSIG (900 to zero kPa). It has been found satisfactory to have the full stroke movement of the spool in the axial direction in the range of 0.014 to 0.017 inches (0.35 to 0.43 mm) for maximum current energization of the electrical actuator as will hereinafter be described. It will be understood however, that the invention is not limited to the aforesaid pressure ranges and stroke arrangements and other valves may be employed in accordance with the needs of the fluid powered application in which the valve is used.  
         [0017]    The flux collector  20  has one end of a coil bobbin  40  received thereon and registered over an annular hub  43  which extends upwardly from the lower flux collector  20 . Bobbin  40  has a coil  44  wound thereon with the ends thereof (not shown) extending outwardly of the coil for external electrical connection thereto in a manner well known in the art.  
         [0018]    An outer casing or shell  42  is received over the coil  44  and the shell  42  has the lower end thereof mounted on the flux collector  20  and registered on annular shoulder  46  and retained thereon by any suitable expedient as, for example, press fit, staking, crimping or suitable adhesive. The casing  42  is formed of magnetically permeable material for completing a flux loop about the coil  44 .  
         [0019]    Flux collector  20  has a lower bearing  48  disposed therein with one end of an operating rod or actuating member  50  received therein in sliding arrangement. The lower end of member  50  contacts the upper end of spool  30 . The operating rod has attached thereover an annular armature  52  with the operating rod  50  having its upper end extending through the armature and through a second bearing  54  provided in an upper pole piece  56  which is attached to the upper end of casing  42  in a manner similar to the connection of the lower end of casing  42  to the flux collector  20 .  
         [0020]    The lower end of the spool  30  has the upper end of spring  58  registered thereagainst; and, the lower end of spring  58  is retained in bore  18  by a suitable plug secured to the lower end of the body  12 . A vent port  62  is formed through the plug  60  for venting the lower end of the spool to atmospheric or ambient pressure.  
         [0021]    The upper end of the armature  52  forms an annular preferably conically tapered working air gap denoted by reference numeral  64  with the upper pole piece  56 . A cap or plug  66  is threadedly received in the upper end of pole piece  56 ; and, plug  66  has a recess  68  formed in the lower end thereof which has received therein a spring  70  which registers against a bushing  71  provided on the upper end of the actuating member  50 . An adjustment pin  72  is threadedly engaged in the plug  66  for external adjustment therein; and, the pin  72  extends downwardly through the plug  66  and its lower end is adjustably positioned to contact the upper end of rod  50  and limit the upward travel of the rod and armature  52 .  
         [0022]    In operation, the spool is biased upwardly by the pressure forces in valving chamber  14  and the control pressure outlet port  22  acting on the differential area between the lower face of land  32  and the upper face of land  34 ; and, the upper end of the spool registers against the lower end of the operating rod  50 .  
         [0023]    In operation with the coil  44  in the de-energized condition, spring  70  maintains or pushes the operating rod  50  and armature  52  downwardly against the spool  30 . In the fully energized condition of the coil, that is with maximum current flowing therethrough, the armature is attracted upwardly minimizing air gap  64  until the upper end of the rod  50  registers against the lower end of pin  72 . It will be understood that the pin  72  is adjusted during calibration to prevent the air gap  64  from closing completely and thus prevents further movement of the armature and prevents the lower end of the rod  50  from being moved away from the upper end of spool  30 .  
         [0024]    With reference to FIG. 2, it will be seen from the graph that at maximum current flow in coil  44 , the pressure in chamber  14  and the control pressure (P 2 ) in the outlet ports  22  goes to zero. In this condition with zero pressure in chamber  14 , there is no effective hydraulic bias of the spool in the upward direction. Thus, the calibration of pin  72  prevents the armature and operating rod from being pulled further upward by the magnetic forces acting on the armature  52 ; and, the lower end of the operating rod is maintained in contact with the spool upper end. The pressure trace for the valve of the present invention shown in FIG. 2 illustrates the absence of pressure transients in the control pressure chamber  14  and the pressure outlet ports  22  which is present in the pressure plot for the Prior Art valves as shown in FIG. 3.  
         [0025]    The present invention thus provides a unique and novel solenoid operated pressure control valve which limits the upward travel of the armature at maximum current energization to prevent lash between the operating rod and the spool and upon de-energization eliminates impulse contact of the operating rod with spool and resultant transients in the control pressure outlet port which would be transmitted to the system to be controlled.  
         [0026]    Although the invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.