Abstract:
A fast-acting valve includes a valve body and a spool slidably mounted within the valve body between first and second limit positions. Both the spool and the valve body have a flow passage which come into alignment with the valve spool at a position intermediate the first and second limit positions and spaced therefrom by a given distance. That given distance allows the spool member to accelerate in travel from the first and second limit positions to the valve open position so that the opening of the valve (and closing) occurs quite quickly. Reciprocating movement of the valve spool relative to the valve body can be provided by springs mounted in opposing ends of the valve body bore in cooperation with solenoids mounted on opposing sides of the valve body. The fast-acting valve may be modified into the form of poppet valve or a cartridge valve.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 09/316,088 filed May 21, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The principal utility of the invention is with valve and actuator applications where extremely fast response is very desirable. For example, a piston engine that needs to introduce fuel through direct injection within 30 degrees of crank rotation and that is running at 4000 rpm, has 1.25 milliseconds to open the fuel injection valve, inject the fuel and close the valve. The most apparent field of application is in internal-combustion engines for motor vehicles. 
     2. Description of the Prior Art 
     The growing utilization of automobiles has greatly added to the atmospheric concentration of various pollutants including oxides of nitrogen and greenhouse gases such as carbon dioxide. In a quest for approaches which could significantly improve the efficiency of fuel utilization for automotive powertrains, while still achieving low levels of NOx emissions, the need for fast valves and actuators became apparent and this invention was conceived. 
     Conventional “fast” valves begin a valving change from either an open or closed position. In the closed position the “movable component” of the valve has “sealed” (usually against a seat or, in a spool valve, by positioning the spool so that flow from the high pressure port is blocked). A command to open results in a force being applied to the movable component, and movement (i.e., acceleration) of the mass of the movable component begins according to the following equation:          F   M     =   a                          
     Where: 
     “F” is the force applied to the movable component 
     “M” is the mass of the movable component 
     “a” is the acceleration of the movable component that results 
     The time required to move the movable component from the closed position to the fully open position is the time needed for valve opening, and this time is dependent on the acceleration and the distance the movable component must cover from the closed position to the fully open position. Conventional “fast” valves maximize acceleration by applying a very large force, minimize the mass of the movable components and minimize the travel distance by valve design to the extent possible. Extremely fast valve action (e.g., less than 1 millisecond) is therefore very difficult to achieve with conventional designs. Conventional valve designs begin the opening stage with an initial speed of zero. The acceleration rate results in a maximum speed that occurs at the end of the opening process. The average speed is therefore determined by the initial speed (i.e., zero) and the final speed, and for a near constant acceleration rate the average speed is about one half the final speed. Since the time for opening a conventional valve is the distance needed for travel to fully open the flow ports divided by the average speed, starting the valve opening from zero speed severely constrains the ability to obtain very fast valve openings. 
     In a conventional spool valve the “OFF” position has the spool valve port slightly withdrawn from communication with the passage through the valve body in order to provide a seal against leakage. See, for example, U.S. Pat. No. 4,770,389 issued to Bodine. This conventional sealing distance is not intended to allow the valve spool to accelerate prior to starting to open and, in fact, acceleration through a sealing zone in a conventional valve is de minimus, i.e., to less than 10% of maximum spool velocity. 
     In some modern “fast acting valves”, the leading edge of the valve port and that of the valve body passage are “line-on-line” in the OFF position. In other words, the leading edges of the two ports are radially aligned with no sealing distance therebetween. In such valves some small amount of leakage is tolerated in order to provide a faster acting valve. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a valve mechanism which starts the valve port opening at a high initial speed and finishes the port opening near or above this high initial speed then goes through a deceleration zone, thus significantly reducing the time required for opening (and closing) the valve. 
     Another object of the present invention is to achieve the above-stated objective by a unique valve design which provides acceleration and deceleration zones to provide extremely fast valve opening and closing. 
     A third object of the present invention is provision of a unique, two-way spool valve incorporating the desired acceleration/deceleration features described above. 
     A fourth object of the present invention is provision of a unique, three-way spool valve incorporating the desired acceleration/deceleration features described above. 
     A fifth object of the present invention is provision of a unique control valve for a two-way actuator incorporating the desired acceleration/deceleration features. 
     A sixth object of the present invention is provision of a unique, two-way cartridge valve incorporating the desired acceleration/deceleration features. 
     A seventh object of the present invention is provision of a unique fuel injection (or fluid control) system utilizing two valves, having the desired acceleration/deceleration characteristics, for each injector and an appropriately sized high pressure fuel supply line, or line with a flow restrictor such as an orifice. 
     An eighth object of the present invention is provision of a unique gas flow control valve which a control valve having the desired acceleration/deceleration characteristics, a fast, hydraulic actuator and, integrated with the hydraulic actuator, a poppet valve also having the acceleration/deceleration characteristics of the present invention. 
     A ninth object of the present invention is provision of a new means for utilizing multiple solenoids in series to maximize and maintain the accelerating force on the movable component (valve member). 
     A tenth object of the present invention is provision of a unique solenoid actuated valve providing the acceleration/deceleration characteristics of the present invention. 
     The unique design and operation of this new valve are based on utilization of acceleration and deceleration zones to achieve very fast valve response. The valve provides a zone (i.e., distance) wherein the movable component can be accelerated to a high speed of at least 30% of its maximum velocity before the movable component starts the valve port opening. Therefore, the valve port opening occurs in the shortest time possible. A second zone (i.e., distance) is provided for deceleration of the movable component and this second “deceleration” zone also serves as the acceleration zone for the reverse action of the valve (i.e., closing). 
     More specifically, in one embodiment the present invention provides a fast-acting valve including a valve body and a valve spool slidably mounted in a bore within the valve body for reciprocating movement in a linear path between first and second limit (rest) positions, i.e. between fully closed and fully open positions. The valve body and the valve spool both have at least one flow passage which align in the valve open position. The flow passage through the valve body is spaced from the one spool fluid flow passage with the valve spool in the fully closed position by a distance including an acceleration zone and a deceleration zone. The acceleration zone may be defined as the distance through which the valve spool accelerates before the one spool fluid flow passage reaches a position initiating fluid communication between it and the one valve body flow passage, i.e. a position where the leading edge of valve spool flow passage enters the one valve body flow passage, whereby the flow passage is very quickly opened. This acceleration zone is significantly longer than the distance required for sealing. The deceleration zone is the distance through which the valve spool decelerates before coming to rest in the fully open position. The fact acting valve of the present invention further includes first and second acceleration/deceleration means for alternately accelerating and decelerating the valve spool in travel between the fully open and fully closed rest positions. An additional drive means is provided in several embodiments for imparting the reciprocating movement to the valve spool. In one preferred embodiment springs or elastic members are mounted within opposing ends of the valve body bore and are compressed by the valve spool at the first and second limit positions, respectively. In this preferred embodiment, the acceleration and deceleration zones are equal in length to the distance a spring extends between a compressed state with the valve spool bearing against it in one of the fully closed and fully open positions and a relatively relaxed state with the valve spool in the other of the fully closed and fully open positions. This embodiment requires a separate motive means or actuator for driving the valve spool with the reciprocating movement and for holding the valve spool against the spring (or other elastic member) in its compressed state. An electromagnetic actuator would include at least one solenoid mounted at each end, surrounding the bore of the valve body. 
     Preferably, the acceleration zone will be a length through which the spool accelerates to a velocity at least 30% and, more preferably, at least 50% of maximum spool velocity. 
     In a further preferred embodiment at least two solenoids are mounted at opposing ends of the valve body, surrounding ends of the bore. In this embodiment the solenoids at one end would be energized in succession to accelerate the valve spool while the solenoids at the opposite end would be energized in succession to decelerate the valve spool. 
     The path through which the valve spool travels may include a gap between acceleration and deceleration zones. Toward this end the diameter of the valve body flow passage may be significantly larger than that of the flow passage through the valve spool. 
     In one preferred embodiment the valve body is further provided with a balancing chamber open to the valve spool at a position where the valve spool is diametrically opposed to the valve body inlet so that the force of the inlet pressure, tending to push the valve spool against one side of the bore is offset by pressure within the balancing chamber to negate the force at the valve body inlet. A conduit provides for fluid communication between the inlet to the valve body and the balancing chamber. 
     In other preferred embodiments the valve spool and the valve body are each provided with plural fluid passages which are selectively opened and closed as the valve spool slides relative to the valve body. 
     In another preferred embodiment the fast-acting valve of the present invention is in the form of a poppet valve for mounting in the head of a combustion chamber to control inlet of a fuel/air mixture or outlet of an exhaust gas. 
     In yet another preferred embodiment the fast-acting valve of the present invention is a cartridge valve which may be utilized in series with a fuel injection nozzle to form a fuel injection system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1A is a cross-sectional view of a valve according to a first embodiment of the present invention in its “OFF” (closed) position; and FIG. 1B is a cross-sectional view of the valve of FIG. 1A in its “ON” (open) position; 
     FIG. 2 is a cross-sectional view of a valve according to a second embodiment of the present invention in its closed position; 
     FIG. 3 is a cross-sectional view of a valve according to a third embodiment of the present invention in its open position; 
     FIG. 4A is a cross-sectional view of a valve according to a fourth embodiment of the present invention in its “OFF” (closed) position; and FIG. 4B is a cross-sectional view of the valve of FIG. 4A in its “ON” (open) position; 
     FIG. 5A is a cross-sectional view of a valve according to a fifth embodiment of the present invention in its “OFF” (closed) position; and FIG. 5B is a cross-sectional view of the valve of FIG. 5A in its “ON” (open) position; 
     FIG. 6A is a cross-sectional view of a valve according to a sixth embodiment of the present invention in its “OFF” (closed) position; and FIG. 6B is a cross-sectional view of the valve of FIG. 6A in its “ON” (open) position; 
     FIG. 7A is a cross-sectional view of a valve according to the seventh embodiment of the present invention in its “OFF” (closed) position; and FIG. 7B is a cross-sectional view of the valve of FIG. 7A in its “ON” (open) position; 
     FIG. 8 is a cross-sectional view of a valve according to the eighth embodiment shown in FIGS. 7A and 7B; 
     FIG. 9A is a cross-sectional view of a valve according to a ninth embodiment of the present invention; and FIG. 9B is a schematic diagram of a fuel injection system including two valves in accordance with the ninth embodiment illustrated in FIG.  9 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A and 1B illustrate a first embodiment of the present invention. As shown in FIGS. 1A and 1B, the major components of the acceleration/deceleration spool valve  10  are the valve block  12  having an axial bore  12   a,  the slidable valve spool  2 , solenoids  3   a  and  3   b,  fluid supply port  4 , fluid discharge port  6 , spool flow passage  9  and energy absorbing springs  7   a  and  7   b.    
     FIG. 1A shows the spool  2  in its no-flow (“OFF”) position. Pressurized fluid is present in fluid supply port  4  but is unable to flow to fluid discharge port  6  because flow passage  8  is blocked by the spool  2 . Solenoid  3   a  is holding spool  2  in this position to offset the force of compressed spring  7   a.  When a command to open the valve is given, solenoid  3   a  terminates its holding force; solenoid  3   b  is activated to generate a force on the spool  2  and, in combination with the force being applied by spring  7   a,  initiates acceleration of the spool  2  from its leftmost position to the right. The spool  2  is accelerated through the first zone  14  which serves as an acceleration zone in movement toward opening and through which the spool accelerates to at least 30% of its maximum velocity and, more preferably to at least 50% of maximum velocity. In experimental tests spool speeds of over 90%, even 98% and 99%, maximum have been achieved prior to start of valve opening. Thus, the spool flow passage  9  reaches the leading edge of flow passage  8  traveling at a high speed and the valve opening event occurs very quickly. As spool  2  continues traveling to the right, it engages the energy absorbing spring  7   b  and begins its deceleration as the leading edge of flow passage  9  enters deceleration zone  15 . Movement of spool  2  terminates as the leading edge of spool flow passage  9  reaches the trailing edge of flow passage  8 , at the position shown in FIG.  1 B. To terminate fluid flow, the reverse process is employed. Solenoid  3   b  is disengaged, solenoid  3   a  is engaged and the spool  2  begins acceleration from the rightmost position shown in FIG. 1B to the leftmost position shown in FIG.  1 A. The acceleration zone to terminate fluid flow is zone  16  in FIG.  1 B. 
     In a second embodiment, as depicted in FIG. 2, multiple solenoids  3   c ,  3   d ,  3   e ,  3   f  are used in series, with  3   c  and  3   d  at one end  3   e  and  3   f  at the other, to maximize the accelerating force on the spool through its entire acceleration zone. In this second embodiment, to accelerate spool  2  to the right, solenoid  3   e  is energized and acts on that part  2   a  of spool  2  which responds to the magnetic force. Solenoid  3   d  may also be energized to maximize the initial force on the spool as it acts on part  2   b  of spool  2 . As the rightmost end of spool  2  passes solenoid  3   e  and its accelerating force is diminished, current to solenoid  3   e  is terminated (and current to solenoid  3   d  is also terminated), and solenoid  3   f  is energized to continue force on spool  2  through the entire acceleration zone. As the valve spool clears the acceleration zone, the opposing solenoids can be energized to create a reverse force on the valve spool, thereby decelerating the valve spool as it approaches the rest position. Thus, in this embodiment, if the current to the solenoids is reversible, the solenoids can be used both to accelerate and decelerate, thus dispensing with need for separate acceleration/deceleration means, e.g. springs. To reverse the movement of spool  2  from its rightmost position to its leftmost position, the reverse process is employed. Current to solenoid  3   f  is terminated and solenoids  3   e  and  3   d  are energized. As the leftmost end of spool  2  passes solenoid  3   d , current to solenoids  3   d  and  3   e  is terminated, and solenoid  3   c  is energized until spool  2  reaches its leftmost position. 
     Another modification would be to use means other than solenoids to provide the primary forces to accelerate the spool (or movable component in other embodiments). For example, FIG. 3 shows a third embodiment which utilizes hydraulic pressure to provide force for acceleration of spool  2 . Spool  2  is shown in its rightmost position. To accelerate spool  2  to the left, valve  23  opens high pressure line  24  to spool port  25  while disconnecting low pressure line  26  from spool port  25 . Valve  22  at the same time closes high pressure line  27  from spool port  28  while connecting low pressure line  27  to spool port  28 . The high pressure hydraulic fluid acts on the right end of the spool  2 , accelerating it to the left while fluid in the volume left of spool  2  flows from spool port  28  through valve  22  to low pressure line  29 . To accelerate spool  2  from its leftmost position to the right, the reverse process is employed. 
     In yet another modification the springs would be deleted to minimize the “hold” force required of the solenoids (especially for applications where the valve will be in either the on or off position for an extended time) and other means would be used to decelerate the spool, such as, “hydraulic stops”. 
     A fourth embodiment of the invention employs hydraulic force balancing on the spool to minimize the friction opposing movement of the spool. FIGS. 4A and 4B show one means of providing hydraulic balance for the valve described in FIG.  1 . In the off position, (FIG. 4A) fluid from the high pressure fluid supply port  4  acts on a bottom portion of the cylindrical surface of the spool  2  which increases the force of a top portion of the spool on the valve block  12  which increases friction when movement of the spool occurs, since the fluid discharge port  5  is likely to be at much lower pressure. By providing fluid at the same pressure as the fluid in the fluid supply port  4  to an area of the top portion of the spool that is equal to the area exposed to the bottom face of the spool through the fluid supply port  4 , hydraulic balancing results. Accordingly, a fluid passage  18  connects the fluid supply port  4  to spool flow passage  9  in the valve off position. Fluid at the high pressure within port  4  is thereby provided to balancing port  20  to provide hydraulic balance. As the spool accelerates, the spool flow passage  9  moves beyond balancing port  20  and pressure begins to dissipate in balancing port  20  because it no longer is in direct communication with fluid supply port  4  and some leakage inherently will occur. As the spool flow passage  9  enters flow passage  8 , high pressure fluid from fluid supply port  4  comes into direct communication with fluid discharge port  6  and hydraulic balance resumes. The surface area of spool  2  exposed to balancing port  20  is approximately equal to the surface area of spool  2  exposed to flow passage  8  on the side of inlet port  4  when the valve is in the off position shown in FIG.  4 A. 
     A fifth embodiment of the invention is shown in FIGS. 5A and 5B. The operation of this valve will be described as it could be applied to the control of fuel (i.e., fluid) injection directly into the cylinder of an internal combustion piston engine. 
     Fluid supply port  30  is supplied with high pressure fuel. Fuel discharge port  31  is connected to a pressure-actuated fuel injector (not shown). Fuel vent port  32  is connected to fuel discharge port  31 , or is connected to the line (not shown) connecting the fuel discharge port  31  to the fuel injector, or is connected directly to the fuel injector. Fuel return port  33  returns vented fuel to the fuel tank (not shown). 
     FIG. 5A shows the valve in the “off” position. When a command is given to inject fuel, solenoid  3   a  is disengaged, and solenoid  3   b  is engaged. Acceleration occurs as previously described in connection with FIG.  1 A. Spool flow passage  35  passes beyond valve block flow passage  38  as spool flow passage  36  begins to enter valve block flow passage  39  and fuel is quickly supplied to the injector through fuel discharge port  31 . Deceleration occurs as described in connection with FIG.  1 A. FIG.  5 B shows the spool  37  at rest in the valve “on” position. When a command is given to terminate the injection of fuel, solenoid  3   b  is disengaged, and solenoid  3   a  is engaged. As spool flow passage  36  passes beyond fuel valve block flow passage  39 , spool flow passage  35  enters valve block flow passage  38 , and the injector pressure is quickly vented, providing a clean, quick termination of the injection event. 
     A sixth embodiment of the invention is shown in FIGS. 6A and 6B. FIGS. 7A and 7B show, as a seventh embodiment, an acceleration/deceleration gas flow valve that includes a fast actuator  60  which would be controlled by the valve of FIGS. 6A and 6B. 
     FIG. 6A shows the control valve spool  48  in the position which will result in the gas flow valve of FIG. 7A being in the closed position. Considering FIGS. 6A and 7A together, high-pressure fluid is supplied to ports  41  and  42 . With the spool flow passage  49  providing fluid communication between port  42  and port  43 , and port  43  connected to port  61  of the fast actuator  60 , high-pressure fluid has acted on hydraulic piston  62  to move the poppet valve  63  against its seat  64 , formed in cylinder head  65  closing a combustion chamber formed in an engine block (not shown). With poppet valve  63  seated in seat  64  the flow of gas between gas ports  66  and port  67  formed in cylinder head  65  is blocked. In order for the hydraulic piston  62  to travel to its lowermost position as shown in FIG. 7A, hydraulic fluid on the bottom side of hydraulic piston  62  flows out port  68  and, with port  68  connected to port  47 , discharge fluid flows through spool flow passage  50  to port  46  which is connected to a low-pressure fluid storage tank (not shown). 
     When a command is given for the gas flow valve of FIG. 7A to open, solenoid  3   b  is disengaged, solenoid  3   a  is engaged, and the control valve spool  48  is first accelerated, and then decelerated to a stop in the position shown in FIG. 6B in the manner previously described in connection with FIG.  1 B. As spool flow passage  49  enters valve block flow passage  51  it comes into communication with high-pressure fluid supply port  41 , high-pressure fluid flows to port  40  and, with port  40  connected to port  69 , high-pressure fluid acts on the bottom side of hydraulic piston  62  which, with the assistance of energy-absorbing spring  70 , begins acceleration of poppet valve  63 . Poppet valve  63  reaches a high speed as it approaches gas ports  66  and thus provides rapid opening. With ports  68  and  61  unable to permit the flow of fluid through the control valve, fluid on the top side of the hydraulic piston  62  must flow from port  72  to port  44  through spool flow passage  50  to port  45  which, like port  46 , is connected to a low-pressure fluid storage tank (not shown). As the hydraulic piston  62  reaches energy absorbing spring  74 , poppet valve  63  has passed to a position above gas ports  66 , and deceleration can begin. As hydraulic piston  62  compresses energy absorbing spring  74  and begins to close port  72 , it rapidly decelerates until it stops at a position (FIG. 7B) where it has closed port  72 , and fluid can no longer flow. The poppet valve  63  acting in the manner of the acceleration/deceleration spool valve of FIGS. 1A and 1B, provides very fast initiation of gas flow during opening and very fast termination of gas flow during closing. The pressure/port arrangement described above for the acceleration/deceleration control valve of FIGS. 6A and 6B provides hydraulic balancing of the control valve. 
     The eighth embodiment shown in FIG. 8 is modification of the seventh embodiment wherein the poppet valve  63  shown in FIGS. 7A and 7B is replaced by a conventional poppet valve actuated hydraulically and controlled by the acceleration/deceleration valve of FIGS. 6A and 6B, in the same manner described for the valve of FIGS. 7A and 7B, but without the acceleration/deceleration features of the gas flow control valve of FIGS. 7A and 7B. 
     A ninth embodiment of the valve of the present invention is shown on FIG. 9A; and FIG. 9B shows how this valve could be used to create a unique fuel (or other fluid) injection system. The acceleration/deceleration control valve  80  shown in FIG. 9A is of the two-way cartridge type. High pressure fuel would be supplied to the supply port  81 . In its maximum down position, poppet valve  82  would remain seated against its seat  83 , preventing the flow of fuel. Spring  84  must be strong enough to hold poppet valve  82  in its maximum down position and must offset the force created by the high pressure fuel acting on the exposed face of poppet valve  82  at supply port  81 . When a command to open is given, solenoid  85  is engaged and acts on poppet valve piston  86  to accelerate poppet valve  82  in the upward direction. As poppet valve  82  begins to move, high pressure fuel flows in through supply port  81  and accesses the larger area of the bottom face  87  of poppet valve  82 . This additional force on valve  82  greatly increases its acceleration. As with the other embodiments of the acceleration/deceleration valve, a high speed is reached before the bottom face  87  of the poppet valve  82  crosses the exit ports  88 , located in the cartridge valve body  90 , thus providing a rapid opening of valve  80 . The valve block  92  then collects the fuel flow through exit ports  88  in flow passage  91  and allows fuel flow to continue through block port  93 . Poppet valve  82  begins deceleration after the bottom face  87  of the poppet valve  82  crosses the top of exit ports  88 , due to compression of spring  84  and the closing of vent ports  94  (as more fully described with reference to FIGS. 7A and 7B) by poppet valve  82 . Poppet valve  82  is held in its uppermost position by solenoid  85  and/or the force of the high pressure fuel on the exposed face of poppet valve  82 , and fuel flows to the injector. As will be described in greater detail with reference to FIG. 9B, when a command to stop fuel flow to the injector is given, the fuel pressure below the exposed face of poppet valve  82  is reduced, and solenoid  85  is disengaged. Spring  84  acting on poppet valve  82  then causes downward acceleration of poppet valve  82 , which first travels past and the closes exit ports  88  (and thus stops fuel flow) and then approaches seat  83 . As poppet valve  82  approaches its lowermost position, fuel flow past seat  83  is being restricted by poppet valve  82  thereby providing a hydraulic means for rapid deceleration to its lowermost position. 
     FIG. 9B shows a line  100  for supplying fuel at a high pressure from a supply source (not shown), two control valves  80  and  80 ′, as described in FIG. 9A, together with a pressure actuated fuel injector  95  and an orifice  97 , which in total are a unique fuel injection system. When a command to inject fuel is given, valve  80 ′ is opened very quickly in the manner described with reference to FIG. 9A, and fuel flows to injector  95 , providing a very rapid beginning of injection (a very highly desired characteristic in direct fuel injection systems). Because it is the objective of fuel injection systems to provide the maximum system pressure drop across the nozzle orifice(s)  96  so that the best possible fuel atomization can occur, orifice  97  must be sized so as to not represent a significant restriction to flow when fuel is to flow through orifice(s)  96 . When a command to terminate injection is given, the solenoid of valve  80 ′ is disengaged and the solenoid of valve  80  is engaged. As was described in reference to FIG. 9A, valve  80  opens very quickly and allows the high pressure fuel between orifice  97  and orifice(s)  96  to be vented through port  98  and returned to the fuel tank (not shown). Orifice  97  then restricts the flow of fuel because the flow passage of valve  80  has a much larger flow area than orifice  97 . This reduced line pressure: (1) causes very rapid and precisely controllable termination of flow across the injector orifice(s)  96  (very highly desired characteristics for direct fuel injection systems), and (2) allows valve  80 ′ to close quickly because of the reduced pressure on the face of poppet valve  82 , as described in reference to FIG.  9 A. As valve  80 ′ closes, the solenoid of valve  80  is disengaged so that valve  80  begins closing before fuel line pressure can be restored by flow through orifice  97 . Valve  80  will shut more slowly than valve  80 ′ because it will experience a relatively much higher pressure on the face of its poppet valve  82  than valve  80 ′ experiences. However, fuel injection has already terminated and a somewhat longer closing time for valve  80  has little undesirable consequence. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.