BACKGROUND  
       [0001]    The present invention relates to diesel engine fuel injectors of the type wherein a solenoid valve controls the pressure in a chamber acting on a needle injection valve. 
         [0002]    In these types of injectors, the control valve acts as a normally closed valve in a control chamber to separate fuel in a needle control chamber and associated passages at high pressure from a region of low pressure. A spring or the like on the solenoid armature or stem, urges a shaped pintle or the like against a commensurately shaped control chamber seat. The injection event is initiated by energizing the solenoid, which lifts the control valve off its seat, thereby connecting the high pressure fuel in the needle control chamber and passage to the low pressure region or sump and in a known manner lifts the injection needle off its seat at the bottom of the injector body. The lifting needle exposes injection orifices at the tip of the body to high pressure fuel, and thereby starts the injection event. 
         [0003]    If changes occur in the control valve, such as valve stroke change or seat leakage, fuel delivery to the engine will change. Changes in fuel delivery result in changes to engine power and exhaust. This undesirable effect can cause the engine to become overloaded by excess fuel and out of compliance with emission regulations. All injector control valve seats will exhibit some wear over the life of the injector. The control valve seat is exposed to high velocity fluid and high contact stresses when the control valve shuts against the control valve seat. 
         [0004]    To operate at very high injection pressures associated with common rail fuel systems, the pintle of the injector control valve must be pushed into its seat by a high enough spring load to assure that it seals. Such spring load accelerates the control valve into the seat. The resulting contact stresses can be very high when the valve closes onto the seat. Higher injector seat stresses produce accelerated wear, resulting in increased seat leakage which eventually requires replacement of the entire injector. 
         [0005]    High injector pressures also increase the risk of cavitation damage to the valve seat and in other fluid passages of the injector upstream of the control seat. Rapid reduction of upstream fluid pressure occurs when the control valve opens, producing bubbles. Upon re-pressurization after the control valve closes, such bubbles collapse. Collapsing bubbles focus streams of fuel onto the metal surfaces in the injector with enough energy to implode on the metal surface, causing damage. 
         [0006]    The present invention addresses these problems. 
       SUMMARY  
       [0007]    One improvement to the injector is focused on slowing the closing velocity of the control valve. This reduces seat stresses and significantly increases seat life. This improvement comprises means for resisting fuel flow in the closing direction through the control valve seat as the control valve closes. The control valve can be slowed by means downstream of the control valve seat, acting on the pintle, for resisting the closing action of the control valve spring, thereby reducing the impact of the control valve. 
         [0008]    The means for producing the desired resistance can be fixed, such as an orifice, or active, such as a pressure regulator, which act to regulate the pressure in a fluid volume against which the control valve acts during closure. This pressure regulation can be considered as a form of fluid back pressure against the control valve. 
         [0009]    The pressure regulator can be in the form of a pressure regulating valve in a low pressure chamber in fluid communication between the pressure regulated volume and the low pressure sump. This regulating valve opens to permit flow from the control valve chamber through the pressure regulated chamber to the low pressure sump in response to rising fluid pressure from the lifting of the control valve and closes to prevent flow from the control chamber through the regulated chamber to the low pressure sump in response to decreasing fluid pressure below the valve seat, from the closing of the control valve. The regulating valve opens after the control valve opens and the regulating valve closes after the control valve closes, thereby providing a diminishing back pressure on the control valve as the valve closes against its seat. 
         [0010]    A second improvement is to provide a restriction downstream of the control valve seat sufficient to prevent cavitation from occurring upstream of the control valve seat. Maintaining higher pressure upstream of the control valve seat prevents vapor bubbles from forming while the control valve is open, so no bubbles can collapse and cause damage upon re-pressurization when the control valve closes. An annular flow collar or the like can be tuned to achieve enough throttling of flow as the control valve opens to avoid upstream vapor bubble formation but not so much throttling that the time interval to end of injection is excessively slowed. 
         [0011]    Providing a collar on an extension or nose of the control valve pintle downstream of the control valve seat is one technique for achieving a predictable and constant throttling effect over the life of the control valve. This directs and throttles flow through an annular flow path between the collar and the surrounding passage wall. Such technique is passive, in the sense that there are no moving parts other than the normal reciprocation of the control valve. 
         [0012]    Although providing a pressure regulated volume downstream of the control valve for slowing down the control valve closure rate can also help reduce cavitation upstream of the control valve seat and providing a throttle for maintaining backpressure upstream of the control valve seat when the control valve opens can also help slow down the closure rate, optimum performance is achievable by using a combination of the two techniques. 
         [0013]    As a further preference, the pressure regulating valve can open against a low pressure of, for example 5 psi, provided by a valve in a drain line upstream of the sump, which has the beneficial effect of limiting the amplitude of fluid pressure pulsations in the injector. 
         [0014]    In an additional preference, an orifice is located in fluid communication between the pressure regulated volume and one of the low pressure chamber or low pressure sump, thereby providing a path for relieving residual pressure in the regulated volume when the regulating valve closes after the control valve closes. Preferably, the pressure is regulated to a pre-determined pressure using a spring-loaded sealing member (plate or ball) which also includes a small orifice leading from the pressure regulated volume to the drain. The orifice can be located in the sealing member or can be drilled through the seat block in the pressure regulating chamber to a drain return passage to the fuel tank. The pressure is maintained at a pre-selected pressure which is higher than the drain return pressure only when the control valve has been activated into the open position to allow flow past the control valve seat into the pressure regulated volume. 
         [0015]    As described generally above, when the control valve is activated with current, the control valve lifts off its seat and flow enters the pressure regulated volume. According to one aspect of the invention, the pressure in the pressure regulated volume acts on the bottom of the control valve with a force which biases the control valve to lift off its seat more rapidly when the control valve is activated. When the current is stopped, the valve begins to close but is slowed due to the pressure in the pressure regulated volume. The reduced closing velocity in turn reduces contact stresses on the seat. The components can be selected and configured to achieve an optimum closing velocity that best meets the trade-off between durability and the ability of the injector to open and close quickly. 
         [0016]    Once the control valve seats, flow no longer reaches the downstream pressure regulated volume and the pressure therein decays via flow through the orifice to the drain. With the pressure decayed to the drain return pressure (which has lower pressure than in the pressure regulated chamber), the spring force closing the valve is subject to little counteracting pressure pushing the control valve off its seat. The only lifting force is from the low pressure contained in the drain. The orifice allows the pressure to decay after the control valve seats. This allows the spring load to succeed at sealing the valve to the maximum amount possible without the loss of sealing that would occur if the set regulation pressure were to remain in the pressure regulated volume. 
         [0017]    The actual pressure maintained in the pressure regulated volume is determined by the amount of spring load pushing against the regulator plate (or ball), in combination with the orifice hole size, and also depends on the operating pressure fed to the common rail injector. The higher the pressure in the common rail, the higher the flow past the control valve into the pressure regulated volume when the control valve is actuated open. 
         [0018]    Simply increasing the pressure in the injector drain circuit would not provide the advantages as disclosed herein. This approach would not drop the pressure at the nose of the control valve between injection events. At high pressures it is desirable to have the full spring force acting through the sealing surface of the pintle on the control valve seat to assure maximum sealing. If the pressure did not decay in the pressure regulated volume when injection ended, the valve seat would not succeed at sealing at higher injection pressures due to the lifting force in the pressure regulated volume. The orifice in combination with the pressure regulator is thus an important preferred feature. 
         [0019]    The sizing of the orifice and the regulating valve spring needs to assure that sufficient flow restriction occurs at the lowest injection pressure operating condition. The regulated pressure should be high enough to avoid excessive seat closing velocity and also high enough to avoid the development of cavitation in the fluid in the control valve seat area and upstream fluid passages. If the orifice is made too small, then the time to drain off pressure between injections could become too slow and seat leakage would be more likely to occur between injections when the current is turned off. 
         [0020]    Whereas regulation of the pressure downstream of the control valve seat for slowing down the valve closure rate is beneficial at all fuel pressure operating conditions, cavitation is not a problem at low fuel system pressure, so the throttling of flow past the control valve seat can be optimized for operation at high fuel system pressure. 
         [0021]    The addition of the throttling feature on the nose of the control valve facilitates optimization by permitting design of the throttle primarily for cavitation control with secondary effect on slowing down valve closure, and design of the pressure regulator primarily for slowing down valve closure with secondary effect on cavitation control. 
         [0022]    It can thus be appreciated that when all preferred features are combined, the control valve pintle extends downstream of the valve seat and forms a throttling collar; a pressure regulated volume is provided downstream of the throttle, with the regulation achieved by a regulating valve in a low pressure chamber downstream of and biased toward the regulated volume; and an orifice is provided in the regulating valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0023]      FIG. 1  is a schematic view of a fuel injector that embodies preferred aspects of the present invention, including a nose on the control valve pintle extending into the pressure regulated volume, a biased plate valve acting on the pressure regulated volume, and an orifice in the plate valve; 
           [0024]      FIG. 2  is a detail view of how the preferred aspects of  FIG. 1  can be implemented; 
           [0025]      FIG. 3  is a schematic view of an alternative embodiment; 
           [0026]      FIG. 4  is a view similar to  FIG. 1 , showing another embodiment in which the pressure regulating valve is offset from the axis of the control valve; 
           [0027]      FIG. 5  shows a variation of the embodiment of  FIG. 4 ; 
           [0028]      FIG. 6  shows another embodiment in which the pressure regulation is provided only by a biased plate valve with orifice; 
           [0029]      FIG. 7  shows another embodiment in which the pressure regulation is provided by the profile on the extended nose of the control valve pintle, without a plate valve; 
           [0030]      FIG. 8  shows another embodiment similar to  FIG. 4 , but with a ball type pressure regulating valve; 
           [0031]      FIG. 9  shows four schematics of a fuel system in a Base design according to the prior art and three embodiments according to the present disclosure; 
           [0032]      FIG. 10  is a Table showing the fuel pressure at various locations in the fuel system according to the schematics of  FIG. 9 ; 
           [0033]      FIG. 11  is a graph showing the relationship between throttle flow area and pressure drop across the control valve seat, for a common rail pressure of 2000 bar. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIGS. 1 and 2  show one embodiment of an injector  100  having a needle valve  102  with tip  104  that engages a seat  106  in the injector body during a closed condition between injection events. In this closed condition, a needle control chamber  108  is supplied with high pressure fuel  110  from a high pressure supply pump (not shown) and likewise the same high pressure fuel  110  is supplied to an annular surface  128  at an intermediate position on the needle. Due to the area differences, the fluid pressure force on the injection needle is substantially higher at the control chamber  108  at the upper end of the needle. The needle is held against the seat  106  as a result of this net downward hydraulic force as supplemented by the spring  112  in the chamber  108 . 
         [0035]    A fluid path  114   a,b  connects the high pressure needle control chamber  108  with a control valve chamber  116 . The control valve  118  has a stem-like pintle with a generally conical sealing area which when seated at  124  separates the high pressure existing in  108 ,  114 , and  116 , from a low pressure sump, e.g., via pump inlet or return line  122 . Preferably, a low pressure chamber  120  can be provided between the seat  124  and the return line  122 . 
         [0036]    Flow restrictors or orifices “Z” can be provided in the high pressure line  110  leading to the needle control chamber  108  and “A” between the passages  114   a,b  from the needle control chamber  108  to the control valve chamber  116 . 
         [0037]    A solenoid actuated armature  126  selectively lifts the pintle portion of control valve  118  off seat  124  thereby exposing the chamber  108  to the low pressure sump  122  via path  114 ,  116 , and  120 . The reduced pressure in chamber  108  enables the continued presence of the high pressure at the lower surface  128  of needle  102  to overcome the spring  112  and thereby lift the nose  104  from seat  106  and inject high pressure fuel that surrounds the lower portion of the needle. 
         [0038]    According to  FIGS. 1 and 2 , flow resistance or restricting means  130  are provided downstream of the seat  124  of the control chamber  116 , to control the time dependent pressure in a pressure regulated volume  132  immediately downstream of the seat  124 . The restriction produces sufficient back pressure to slow down the engagement of the control valve  118  against seat  124 , while keeping this back pressure low enough so as not to unduly resist the prompt re-seating of the control valve  118  onto seat  124 . This objective is difficult to achieve because of the need to accommodate a range of high pressure fuel in the common rail (and thus a range of differential pressure between chamber  116  and chamber  132 ) as well as a range of injection frequencies (i.e., injection events per unit time). The pressure regulated volume  132  preferably has a cross sectional area approximately that of the outlet of the control chamber  116  at seat  124  and is provided immediately upstream of low pressure chamber  120  (considering flow direction from chamber  116  toward return or drain line  122 ). 
         [0039]    In a target operating context, the fuel pressure in needle control chamber  108 , passages  114   a,b  and control chamber  116  can be in the high range of 2000-3000 bar down to a low range of 200-300 bar, with steady state pressure typically at least 1200 bar. With the present invention, fuel flow past seat  124  to substantially ambient pressure at  120  during operation in the high pressure range is resisted so that the upstream pressure in chamber  116  and passages  114   a,b  is maintained well over 100 bar. The restriction is designed so that fuel flow past the seat  124  during operation in the low pressure range will result in maintaining a pressure in upstream passages well above 50 bar without adversely affecting the reseating of pintle  118 . 
         [0040]    If a low pressure check or bypass valve  122 ′ is provided in the drain  122  to prevent the drain pressure from dropping below about 5 psi, the amplitude of the pressure pulses in the pressure regulated volume  132  and upstream passages  114   a,b  can be reduced considerably. One such valve  122 ′ can be located at the downstream end of a common drain in fluid communication with the low pressure chambers  120  from all the injectors. 
         [0041]    It can thus be understood that the pressure regulated volume  132  is situated in fluid communication between the valve seat  124  and the low pressure sump  122 . A pressure regulating valve  130  is located in low pressure chamber  120 , which regulating valve opens to permit flow from the control chamber  116  through the regulated volume  132  and low pressure chamber  120  to the low pressure sump  122  in response to rising fluid pressure from the lifting of the control valve  118  and closes to prevent flow from the control chamber  116  through the regulated chamber  132  to the low pressure sump in response to decreasing fluid pressure from the closing of the control valve  118 . The regulating valve  130  opens after the valve  118  opens and the regulating valve closes after the valve  118  closes, thereby providing a diminishing back pressure on the valve  118  as the valve closes against its seat  124 . 
         [0042]    As used herein, “pressure regulating valve” should be broadly understood as a device that is designed to hold a fluid pressure in an associated pressure regulated chamber or volume. 
         [0043]    In the embodiment shown in  FIG. 2 , the pressure regulating valve  130  is a plate valve having an upper disc-like portion  130   a  with a coil spring  130   b  seated on the plate  130   a  and against a recess in wall of chamber  120  at opposite end  130   c,  urging portion  130   a  against shoulder or similar seat  136  at the upstream face of the low pressure chamber  120 . The fluid in the regulated volume  132  can escape through orifice  134  in plate  130   a  and thereby relieve any residual pressure that may be present in the regulated volume  132  when the regulating valve  130  has re-seated at  136 . In  FIG. 2  the orifice  134  is shown as part of the plate valve  130   a,  but other restrictive flow paths could be provided, for example, through a wall of the pressure regulated chamber  132  or low pressure chamber  120 . 
         [0044]      FIG. 3  shows one such example in a more generalized embodiment in which the control chamber  116  and associated control valve  118  interact with the seat  124  and the regulated volume  132  is in fluid communication with the low pressure chamber  120  which in turn is in fluid communication with the low pressure sump  122 , but the difference relative to  FIG. 2 , is that the back pressure in regulated volume  132  can be provided only by an orifice  138  between the regulated volume  132  and the low pressure chamber  120 . Moreover, this orifice  138  also avoids residual pressure in the regulated volume  132  after the control valve  118  has closed. 
         [0045]    It should be understood that the advantage of the arrangement of  FIG. 2  relative to  FIG. 3 , is that the time dependent pressure profile in the regulated volume  132  as the control valve  118  closes, can be optimized through the selection of one or more of the rate of the coil spring  130   b,  the shape of the periphery of the plate  130   a,  and the profile immediately surrounding the seat  136 . This optimization can accommodate a wider range of high pressure fuel in passage  114 . 
         [0046]      FIGS. 1-3  show a further preference in which anti-cavitation throttle means  140  is provided on tip or nose at the seating end of the control valve pintle  118 . This feature  140  preferably extends below seat  124  into regulated volume  132  and can include a recess  142  (e.g., an in indented dome or a blind bore with or without a conical or frusto conical counterbore). This throttle means  140  substantially eliminates any cavitation and in the embodiment of  FIG. 2  allows the location of the regulator valve plate  130   a  to be optimized without affecting cavitation at the control valve seat  124 . The plate valve  130  and control valve throttle  140  preferably are used in combination to reduce the control valve seating velocity and reduce or eliminate cavitation damage. 
         [0047]    The exterior of nose  140  has a smooth or stepped frustoconical angle  144   a  at its upper end for sealing against seat  124  and a downstream cylindrical collar portion  144   b  below the valve seat  124 . This provides a reduction in flow area and can be considered a throttling collar  144   b  having a purposely designed clearance within the cylindrical bore wall above or defining the pressure regulated volume  132 . The throttling diameter allows pressure upstream of the throttle to be increased, which increase helps avoid upstream cavitation damage, such as in passages  114   a,b.  The throttle collar  144   b  can increase upstream pressure with less effect on slowing down of the control valve  118  than the pressure regulating valve  130  and as shown in  FIG. 3 , can be deployed without the regulating valve  130 . 
         [0048]      FIG. 4  shows another embodiment, in which the pressure regulated volume  132 ′ includes a downstream low pressure fluid passage  146  to a restriction upstream of the low pressure return line  122 . As an analog to the embodiment of  FIG. 2 , the restriction is a plate valve  130 ′, biased with a spring to closure on the upstream face of a low pressure chamber  120 ′, with an orifice  134 ′. However, this restriction could be a simple orifice or a biased plate without orifice. 
         [0049]      FIG. 5  shows a variation of  FIG. 4 , incorporating a floating control valve seat which offers both improved alignment for the seat to the control valve and potentially improved manufacturability. The regulating valve  130 ′ and low pressure chamber  120 ′ downstream of passage  146  are similar to those shown and described with respect to  FIG. 4 . Optionally, the spring may be seated in a friction fit cup  150  or the like as a manufacturing convenience. The control valve chamber  116  has a floating control valve  152  with associated seat  154  at its upper internal edge. The floating seat  152  rests on ring  156 . The bore formed by the floating seat  152  and ring  156  extends from the seat  154  through to a port  164  in the upper surface  160  of plate  166 . Spring  162  in control chamber  116  bears on the top of seat  152 , whereby a downward biasing force is continuous applied to the seat  152  and ring  156 , such that the bottom of ring  156  seats against surface  160 . The control valve pintle including extended throttling nose are as described in  FIGS. 3 and 4  and relate to control seat  154  and pressure regulated chamber  158  in the same manner as described with respect to  FIGS. 3 and 4 . Although the seat  152  is biased by spring  162 , which acts to hold the seat against the plate  166 , the sealing is actually performed by the fluid pressure in control chamber  116  acting above the seat. Radial freedom is provided by radial clearance between the seat ring  156  and seat block  168 . Angular freedom is accomplished with a spherical contact between the seat ring  156  and floating seat  152 . 
         [0050]      FIG. 6  shows another embodiment  170 , in which the control valve  172  and control chamber  174  are generally conventional. The tip of the control valve pintle  172  is tapered to seal against seat  178 , but has no substantial extension into the pressure regulated volume  180 . The pressure regulating function is performed by valve assembly  182  with preferred orifice and low pressure chamber and drain, as shown in  FIG. 2 . 
         [0051]      FIG. 7  shows yet another embodiment  184 , where the pressure regulating function is performed only by the control valve  186 . Control chamber  188 , sealing surface  190 , and seat  192  are as shown at  174 ,  176 , and  178  in  FIG. 6 . However, the pintle  186  has nose  196  that extends into the cylindrical volume  194 , and cylindrical collar  198  is closely spaced from the cylindrical bore wall of volume  194 . The nose  198  extends with a bullet shaped tip  200  into a conical flow volume  202  that enlarges from the end of the cylindrical volume  194 . The shape of the tip also has an effect on the back pressure. As in previously described embodiments, when the control valve  186  lifts off seat  192 , the fluid flow is throttled into low pressure chambers  202 ,  204 , which in turn is in fluid communication with a sump at substantially ambient pressure. 
         [0052]    As described with respect to  FIG. 2 , the low pressure chambers such as  120 ,  120 ′, and  204  from each injector are connected to a common drain line and a low resistance valve between the drain line and the fuel tank provides a baseline pressure on the order of 3-10 psi in the low pressure chambers. In general, the drain includes a line from the injector to a fuel reservoir at ambient pressure and the drain line includes means for maintaining fuel at the injector drain outlet to the drain line, at a pressure of at least about 3 psi above the pressure in the reservoir. 
         [0053]      FIG. 8  presents another embodiment  206  which incorporates features from  FIGS. 4 and 7 , but has a different pressure regulating valve. Pintle  208  passes through control chamber  210  for sealing against seat  212  and has an extension with cylindrical throttle collar  214  in a cylindrical volume defined by wall  216 . The cylindrical portion of wall  216  immediately below the collar  214  is the operative volume of the pressure regulated volume. The cylindrical wall opens frustoconically  218  in a downstream direction where region  220  is in fluid communication with volume  224  on which the pressure regulating valve  226  directly operates. 
         [0054]    The pressure regulating valve  226  includes an upstream valve seat  228  with central passage and associated ball  230 . Ball counter seat  232  has a passage  234  leading into low pressure volume  236  where a coil spring  238  has a one bearing on seat  234  and another end bearing on a shoulder  240 . The low pressure volume  236  is in fluid communication through passage  242  with the low pressure sump. The seats  228  and  232  are slidable in the entry bore region of pressure regulating valve  226 . As in previously described embodiments, an orifice  244  is provided, in the upstream seat  228 , in fluid communication between volume  224  and the low pressure volume  236 . 
         [0055]      FIGS. 9 and 10  represent fuel systems, by which an integrated approach to pressure management according to embodiments of the present invention can be described and compared to a previously known base design.  FIG. 8  can be related to  FIGS. 2 and 3 , in that the common rail pressure P 2  is in high pressure passage  110 ; reduced pressure P 3  follows orifice Z, further reduced pressure P 4  follows orifice A and is the pressure at the control chamber  116 . It is known that orifice A provides flow restriction for pressure management associated with the control valve. 
         [0056]    In the Base design the pressure drops from P 4  to P 7  through the control valve seat  124 . In the Base design, there is no significant restriction between the control valve seat  124  and the sump (fuel tank), so the pressure immediately past the control valve seat  124  is P 7 , the same as or slightly above the sump pressure P 8 . The valve seat  124  experiences a flow velocity corresponding to the pressure drop and there is no back pressure to slow down the reseating of the control valve. 
         [0057]    However, with the present invention a flow restriction produces a pressure in the pressure regulated volume at P 5  or P 6 &gt;&gt;P 7  immediately past the control valve seat  124 . The Table of  FIG. 10  shows that with a low rail pressure of 300 bar (P 2 ) the pressure drop P 4  to P 7  in the base design is about 16 bar but the pressure at P 4  is only about 16 bar. In each of the three embodiments according to the present disclosure (Configurations  1 - 3 ), the pressure drop P 4  to P 5  or P 6  is in the range of about 10-15 bar (so the flow velocity over the valve seat is somewhat similar), but the pressure at P 4  remains much higher, i.e., in the range of about 26-65 bar, which helps reduce cavitation. With a high rail pressure of 2000 bar, the pressure at P 4  for Configurations  1 - 3  remains at least about 40 bar greater than in the Base design. 
         [0058]    The throttling feature at the pintle nose according to Configurations  2  and  3  when integrated into the Base design provides an increased operating pressure prior to pressure zone P 5  which raises pressure in the injector above the fluid vapor pressure to prevent cavitation at the valve seat and spherical area after the exit of orifice A. As a result, the valve seating velocity can be decreased by varying the throttle diameter to create differential lifting area/force. A slight increase in closing delay can be measured, which is evidence of the valve slowing down. 
         [0059]    The main advantage of the throttle feature is a net increase in zones P 2 -P 5  to pressures above vapor pressure and elimination of cavitation at the seat which is located in zone P 5 . Conventional injectors do not have a secondary restriction that is part of the control valve.  FIG. 11  (differential pressure vs. throttle area) shows that a small change in throttle flow area removes the restriction and the benefit of maintaining a high pressure P 5  relative to pressure P 6  is no longer achieved. 
         [0060]    The regulator plate in the low pressure chamber which raises pressure in zone P 6  (pressure regulated volume) for Configurations  1  and  3  is designed to reduce the closing velocity of the control valve. The slowing of the control valve reduces the impact velocity thus reducing the impact forces and stresses in the contact region. Zone P 6  is maintained at a pressure while the valve is open and the injector is delivering fuel to the cylinder. When the control valve is commanded to close the regulator maintains pressure while the control valve opening reduces to the point when the valve closes. At the point the control valve closes, the pressure in zone  6  reaches drain pressure (0-0.5 bar). The cycle then repeats again when the valve is open. The optimum pressure under the control valve and above the regulator plate in zone P 6  while the valve moves toward closure, is about 40 bar.
A needle type fuel injector has a needle control chamber at a pressure subject to a control valve in a control valve chamber which in an opening phase is lifted from its seat to expose the control valve chamber, connecting passages, and needle control chamber to a low pressure drain and in a closing phase is urged against the seat to isolate the control valve chamber, connecting passages, and needle control chamber from the drain. Resistance to the flow or displacement of fuel through the control valve seat is provided by a pressure regulating valve as the control valve rapidly closes against its seat, thereby reducing the rate of closure and thus the impact of the control valve on the seat.