Patent Publication Number: US-6213093-B1

Title: Hydraulically actuated electronic fuel injection system

Description:
TECHNICAL FIELD 
     The present invention relates to a system and means for injecting fuel into internal combustion engines. 
     BACKGROUND ART 
     Some fuel injection systems have been designed as unit injectors which incorporate an hydraulically driven pressure intensifier with a stepped plunger for injecting fuel into an engine&#39;s cylinder where the fuel delivery and timing are controlled by an electronically controlled valve. The spray pattern of each injector is controlled by means of modulating the base oil pressure supplied to each unit injector. 
     It is known that in many diesel engines the optimum injection curve shapes vary depending on the engine&#39;s operating conditions. A pilot injection of a small amount of fuel separate from a main injection may be required at some operating conditions and a boot-shaped injection at other conditions, or a sharp leading front of an injection curve may be the best for another engine speed and load. The correlations between engine operating conditions and the optimum shapes of the injection curves are often complex. Therefore it is desirable for a diesel injection system to have the shape of an injection curve electronically controlled, so that an engine management system can set the optimum injection characteristics for a wider range of engine operating conditions. 
     Known unit injection system do not enable control of an injection curve shape independently from the actuating pressure due to the lack of a control channel which can be connected to a nozzle&#39;s locking chamber during certain stages of a plunger&#39;s metering and injection strokes. 
     The present invention concerns hydraulically actuated electronically controlled unit injection (HEUI) systems which are well known. The closest art known to the present invention is that of PCT/AU98/0073, the contents of which are incorporated herein by reference. 
     The difference between the injector and injection system of a first aspect of the present invention and that disclosed in PCT/AU98/0073 resides in the provision of an external groove on the plunger for connection of a plunger&#39;s compression chamber with a nozzle&#39;s locking chamber during an injection cut-off period. 
     A second aspect of the present invention resides in the inclusion of a control channel for stabilization and control of the pressure in the locking chamber during parts of the metering and injection strokes of a pressure intensifier, wherein this control channel and the locking chamber can be disconnected from each other by the plunger during an injection cut-off. The pressure in the control channel is typically controlled by an engine management system. When the control channel pressure is increased, the pressure in the compression chamber required to open the nozzle and begin the injection also increases, therefore the leading edge of the injection curve steepens. By means of varying the pressure in the control channel the shape of the leading edge of an injection curve can be controlled. 
     It is preferable to join the control channels of a set of unit injectors of an engine into a common control chamber with pressure in this chamber controlled by an engine management system. This ensures uniform injection timingmmon control chamber with pressure in this chamber controlled by an engine management system. This ensures uniform injection timing and shape of injection curves in the engine cylinders, simplifies the injection system design and helps keep the cost down as in this case only one pressure regulator is required and it can be mounted anywhere on an engine. 
     Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers. 
     DISCLOSURE OF INVENTION 
     In accordance with a first aspect of the present invention there is provided a fuel injector of an injection system for an internal combustion engine, said injector comprising an inlet port; a spill port; a pressure intensifier comprised of a piston forming a working chamber and a spill chamber and a plunger forming a compression chamber, said spill chamber being connected to the spill port via a spill channel, said plunger having a control edge adapted to vary the flow area of said spill channel and close it off in dependence upon the plunger position; a nozzle with a needle, a locking chamber, means biasing the needle to close the nozzle and an outlet chamber connected to the compression chamber; a non-return valve, the inlet of the non-return valve being connected to the inlet port and the outlet of the non-return valve being connected to the compression chamber; an hydraulically controlled differential valve (HDV) comprising an HDV control chamber and having a valve located between the inlet port and the working chamber and opening into the working chamber upon opening, wherein said valve provides a throttling slot and a chamber connected to the HDV control chamber; resilient means biasing the HDV towards its closed position; a control valve installed between the HDV control chamber and the spill port; a cut-off channel connected to the locking chamber; a control channel connected to the spill port; said plunger having an external groove positioned so as to connect the cut-off channel to the compression chamber at an injection cut-off position of the plunger and adapted to connect the cut-off channel to the control channel at other positions. 
     In a preferred form of the first aspect, the valve located between the inlet port and the working chamber is a poppet with a seating face. 
     A fuel injection system for controlling an injector of the present invention comprises means for controlling the pressure in the control channel and means for detecting the start of injection comprising a pressure sensor installed in the control channel and an electronic conditioning unit. 
     In a second aspect the present invention consists in a fuel injector of a fuel injection system for an internal combustion engine, said injector comprising an inlet port; a spill port; a pressure intensifier comprised of a piston forming a working chamber and a spill chamber and a plunger forming a compression chamber, said spill chamber being connected to the spill port via a spill channel; said plunger having a control edge adapted to vary the flow area of said spill channel and close it off in dependence upon the position of the plunger; a nozzle with a needle, means biasing the needle to close the nozzle, an outlet chamber connected to the compression chamber and a locking chamber; a non-return valve, the inlet of the non-return valve being connected to the inlet port and the outlet of the non-return valve being connected to the compression chamber; an hydraulically controlled differential valve (HDV) comprising an HDV control chamber and having a valve located between the inlet port and the working chamber and opening into the working chamber upon opening; resilient means biasing the HDV towards its closed position; a control valve installed between the HDV control chamber and the spill port and adapted to connect said HDV control chamber with the spill port upon command from an engine management system; a cut-off channel connected to the nozzle locking chamber; a control channel connected to the cut-off channel; an additional control valve installed between the control channel and the spill port; said plunger having an external groove positioned so as to connect the compression chamber to the cut-off channel during an injection cut-off position of the plunger. 
     In a preferred embodiment of the second aspect of the invention, the valve located between the inlet port and the working chamber is a poppet with a seating face. 
     The present invention is related to unit injectors but includes features which enable electronic control to be applied to the shape of the injection curve of a unit injector independently of the base fluid pressure. In another aspect of the present invention the stability of fuel delivery in consecutive cycles of injections and between the unit injectors of a multi-cylinder engine can be facilitated. Differing embodiments of this invention enable simplification of a unit injector&#39;s design, reduce it&#39;s dimensions and the noise of it&#39;s operation. 
     Fuel injection systems according to embodiments of the present invention can be designed to provide an ability to markedly vary the shape of an injection curve as well as a wide range of fuel injection pressures, high maximum injection pressure, sharp injection cut-off which is necessary at all engine operating conditions, improved fuel delivery control accuracy and reduced noise of fuel system operation. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The present invention will now be described by way of example with reference to the accompanying drawings, in which: 
     FIGS. 1 and 2 are longitudinal cross sectional views through an hydraulically actuated unit injector in accordance with a first embodiment of the present invention at different stages of operation; 
     FIG. 3 is a longitudinal view of a second embodiment of the present invention; 
     FIG. 4 is a cross sectional view of a third embodiment of the present invention; 
     FIG. 5 is a cross sectional view of a fourth embodiment of the present invention; 
     FIG. 6 is a schematic of an electronic conditioning unit in a system of detection of the start of an injection; 
     FIG. 7 is a graphical representation of a boot-shaped injection; and 
     FIG. 8 is a graphical representation of outlet chamber pressure relative to injection pressure. 
    
    
     BEST MODES 
     The embodiment of FIG. 1 shows a source of fuel pressure  1 , inlet port  2 , spill port  3 , hydraulically controlled differential valve (HDV)  4 , HDV control chamber  5 , a pressure intensifier which is comprised of piston  6  and plunger  7  with the external groove  8  and the edge  9 , working chamber  10 , spill chamber  11  and compression chamber  12 , spill channel  13 , nozzle  14 , needle  15 , spring  16 , locking chamber  17  and outlet chamber  18 , non-return valve  19  the inlet of which is connected to the inlet port  2  and the outlet of which is connected to the compression chamber  12 , cut-off channel  20 , solenoid valve  21  installed between the HDV control chamber  5  and the spill port  3 , control channel  22 , the system  23  for controlling the pressure in the control channel  22  and the system  24  for detecting the start of injection consisting of a pressure sensor  25  installed in the control channel  22  and an electronic conditioning unit  26 . The HDV  4  controls the flow area from the inlet port  2  to the working chamber  10  and opens towards the working chamber. The HDV  4  has the poppet  27  with seating face  28  and forms poppet chamber  29  and throttling slot  30 . The poppet chamber  29  is connected to the HDV control chamber  5  via bypass channel  31 . The HDV  4  is biased towards its closed position by the spring  32 . The compression chamber  12  is connected with the outlet chamber  18 . The compression chamber  12  may also be connected with the cut-off channel  20  through the external groove  8  of the plunger  7  depending on the plunger&#39;s position. The cut-off channel  20  may be connected to the control channel  22  through groove  8  of the plunger  7  depending on the plunger&#39;s position. The spill channel  13  may be connected to spill chamber  11  depending on the plunger&#39;s position. 
     A second embodiment of the invention is shown in FIG. 3 which is identical to that shown in FIG. 1 except that there is a non-return valve  33  installed in the spill channel  13 , the inlet of the non-return valve is connected to the spill port  3  and the outlet of the non-return valve is connected to the spill chamber  11 . There is also a bypass spill channel  34  connecting the inlet of the non-return valve  33  to it&#39;s outlet. 
     A third embodiment of the invention is shown in FIG. 4 which is identical to that shown in FIG. 1 except that the control channel  35  is connected to the cut-off channel  20  and there is an additional solenoid valve  36  controlling the pressure in the control channel  35 . 
     A fourth embodiment of the invention is shown in FIG. 5, which is identical to that shown in FIG. 4 except that there is a link channel  37  connecting the inlet port  2  to the locking chamber  17  through a non-return valve  38  the inlet of which is connected to inlet port  2 . 
     FIG. 6 is a schematic of an electronic conditioning unit which generates a trigger on its output  39  used by an engine management system (not shown) as a start of injection mark. It comprises an input  40  from the pressure sensor  25  (Ref. FIG.  1 ), an input  41  (Ref. FIG. 6) from the engine management system, a comparator  42 , a counter  43  and a filter  44 . 
     A fuel injection system of the depicted embodiments works as follows: 
     Referring to FIG. 1, in the initial position the solenoid valve  21  is inert and closes off the connection between HDV control chamber  5  and spill port  3 . The HDV  4  is closed, the piston  6  and plunger  7  are kept in the bottom position by the fuel pressure in the working chamber  10 , the locking chamber  17  is connected via the cut-off channel  20  and the plunger&#39;s external groove  8  with compression chamber  12 , the nozzle  14  is closed by the needle  15 . The spill chamber  11  is connected to the spill port  3  via spill channel  13 . 
     Referring to FIG. 2, when electric current is supplied to the solenoid valve  21  it opens and allows the fuel to flow from the working chamber  10  through the throttling slot  30  to poppet chamber  29 , further through bypass channel  31  to HDV control chamber  5  and out through spill port  3 . The flow area of the throttling slot  30  is such that said flow through it causes the hydraulic force to act on the HDV  4  in the direction of the flow which holds the HDV closed with the additional assistance of the force exerted by the spring  32 . When pressure in the working chamber  10  has decreased to a certain level piston  6  and plunger  7  move up under the pressure in the compression chamber  12 , the fuel pressure being transmitted through the non-return valve  19 . At a certain point in the travel of the plunger its groove  8  closes the connection between compression chamber  12  and the cut-off channel  20  and whilst at or beyond this point it isolates cut-off channel  20  and thereby the locking chamber  17  from the compression chamber  12 . At a certain point of further upward movement of the plunger its groove  8  opens the connection between the cut-off channel  20  and the control channel  22  thereby connecting the locking chamber  17  with control channel  22  and whilst at or beyond this point it keeps locking chamber  17  and control channel  22  connected with each other. By this means the pressure in the locking chamber  17  equalizes with the pressure in the control channel  22  which is set by the system  23 . Also, at the certain point in the travel of the plunger its edge  9  closes off the connection between spill chamber  11  and spill port  3  and whilst at or beyond this point the spill port  3  and spill chamber  11  remain disconnected from each other. The period of time during which piston  6  and plunger  7  move up is determined by the duration of opening of the solenoid valve  21  which is in turn determined by the duration of the current supplied by the engine management system (not shown). When piston  6  and plunger  7  have reached the required position which is determined by the fuel delivery required at that instant, the current is switched off by the engine management system and the solenoid valve  21  closes thereby isolating the HDV control chamber  5  and spill port  3 . As a result, the fuel flow via the throttling slot  30  stops and the hydraulic force holding the HDV  4  closed ceases to act. The fuel pressure in the inlet port  2  acting on the differential spot in the HDV overcomes the force of spring  32  and provides an initial opening of the HDV. This allows fuel to flow through the inlet port  2  to the poppet chamber  29  and via the throttling slot  30  to working chamber  10  and via the bypass channel  31  to HDV control chamber  5 . This fuel flow increases the pressure in poppet chamber  29  and HDV control chamber  5  and forces HDV  4  to fully open. The pressure in the working chamber  10  rises and causes the piston  6  and the plunger  7  to move down thereby compressing the fuel in the compression chamber  12  and closing the non-return valve  19 . 
     As the fuel pressure in the compression chamber  12  increases, the pressure in the nozzle&#39;s outlet chamber  18  also increases and opens the nozzle  14 , overcoming the force of spring  16  and pressure in the locking chamber  17  and lifting needle  15  off its seat. The moment of nozzle opening and correspondingly the pressure developed in the compression chamber  12  at the moment of nozzle opening depends on the pressure in the locking chamber  17  which is equal to the pressure in the control channel  22  set by the system  23 . At the moment of nozzle opening the needle  15  displaces portion of the fuel from the locking chamber  17  through cut-off channel  20 , groove  8  and control channel  22  to the system  23 , causing a pressure surge in the control channel  22  which is detected by the pressure sensor  25 . The amplitude of said pressure surge can be adjusted by well known means of restricting the flow area of the control channel downstream of the pressure sensor. During an injection stroke of the piston  6  and the plunger  7  fuel is injected through opened nozzle  14 . At a final stage of an injection stroke the groove  8  disconnects the cut-off channel  20  from the control channel  22  and then opens the connection between the compression chamber  12  and the cut-off channel  20 . Also, at a final stage of an injection stroke the edge  9  opens the connection between the spill chamber  11  and spill port  3 . With the cut-off channel  20  and compression chamber  12  connected to each other the pressures in locking chamber  17  and compression chamber  12  equalise and the needle  15  closes nozzle  14  and the piston  6  and the plunger  7  stay at the bottom of the stroke. When the piston is stationary there is no fuel flow through the HDV  4  and the pressures in the working chamber  10 , poppet chamber  29  and HDV control chamber  5  equalise with the pressure in the inlet port  2  and the spring  32  moves the HDV up and closes it. Thus the system returns to the initial position as shown in FIG.  1 . 
     In FIG. 3 the fuel injection system works in the same way. When the piston  6  and the plunger  7  travel upwards from the bottom position to a certain point where the edge  9  closes off the connection between spill chamber  11  and spill port  3 , the non-return valve  33  opens and allows an unrestricted flow of fuel through the spill channel  13  from spill port  3  to spill chamber  11 . During an injection stroke, when piston  6  and plunger  7  move down from the point where the edge  9  opens the connection between the spill chamber  11  and the spill channel  13 , the non-return valve  33  is closed and the fuel flows from spill chamber  11  to spill port  3  through the bypass spill channel  34 . The flow area of the bypass spill channel  34  is chosen such that it provides sufficient restriction to the fuel flow to raise the pressure in the spill chamber  11  to a level when the hydraulic cushion in the spill chamber provides smooth deceleration of the piston  6  at the end of an injection stroke. 
     In FIG. 4 the fuel injection system works in the same way. When a smoother leading edge of an injection curve is required the additional solenoid valve  36  connects the control channel  35  to spill port  3  prior to an injection start relieving the pressure from the locking chamber  17  and thereby allowing the needle  15  to open nozzle  14  earlier during an injection stroke of the plunger at a lower pressure in the outlet chamber  18 . When a so-called “boot-shaped” injection is required, as exemplified by the graphical plot of FIG. 7, a relatively weak spring  16  is used, so that when the additional solenoid valve  36  opens during an upward travel of the plunger  7  a relatively low pressure in the outlet chamber  18  lifts the needle  15  and opens the nozzle  14 , and fuel gets delivered to an engine&#39;s cylinder at a relatively low rate from the inlet port  2  via non-return valve  19  until an injection stroke of the plunger takes place and the remainder of an injection occurs the usual way described earlier. The amount of fuel delivered during the boot-phase of injection is controlled by adjustment of a time period between the opening of the additional solenoid valve  36  and the closing of the solenoid valve  21 . 
     In FIG. 5 the fuel injection system works in the same way, but has the ability to provide a separate pilot injection during an upward movement of the pressure intensifier. In this embodiment the maximum flow area of the additional solenoid valve  36  and the flow area of link channel  37  are chosen in such a way that when the additional solenoid valve opens during an upward movement of the pressure intensifier the flow rate through it from the control channel  35  is greater than the flow rate via the link channel  37  from the inlet port  2 , which causes a drop of pressure in the locking chamber  17  sufficient for the pressure in the outlet chamber  18  to lift the needle  15  and start a pilot injection. When the additional solenoid valve  36  closes before the main injection, the flow of fuel through it stops and pressure in the locking chamber  17  equalises with pressure in the inlet port  2 , the fuel from inlet port entering the locking chamber through link channel  37  and non-return valve  38 . With pressure in the locking chamber equal to the pressure in the outlet chamber the spring  16  closes the nozzle  14  and the pilot injection stops. In this embodiment of the present invention the amounts of fuel and timing of pilot and main injections are controlled separately by the additional solenoid valve  36  and the solenoid valve  21  respectively. 
     The electronic conditioning unit (ECU) shown in FIG. 6 works as follows. It receives on input  41  a stop trigger from an engine management system which is initiated by the cessation of a control pulse supplying an electric current to the solenoid valve  21  (Ref. FIG. 1) and transmits said stop trigger to the reset-start count input of the counter  43  (FIG.  6 ). The ECU also receives on the input  40  the signal from the pressure sensor  25  (Ref. FIG. 1) which is transmitted to the filter  44  (Ref. FIG. 6) and to one of the inputs of the comparator  42 . The filtered signal after filter  44  is transmitted to the other input of the comparator. The comparator generates a surge trigger when the difference between the two input values exceeds a predetermined threshold, said surge trigger is transmitted to the counts input of counter  43 . The counter is set to generate an output trigger when it overflows, and the maximum number of counts is set to zero, thus the counter transmits a trigger to the ECU output  39  when there is a pressure surge in the control channel  22  (Ref. FIG. 1) caused by the opening needle  15 . The ECU output remains unaffected by any pressure surges occurring outside the period between the stop trigger and the first pressure surge after the stop trigger. 
     The advantages of the embodiments of the present invention over known fuel injection systems are achieved mainly by the following means: 
     the provision of the external groove  8  on the plunger  7 ; 
     the provision of the control channel  22 , which may be connected to the cut-off channel  20  depending on the position of the plunger  7 , and the application of the system  23  which is connected to the control channel  22  and which can vary the pressure in the control channel according to an engine management system command; 
     the application of the pressure sensor  25  installed in the control channel  22  and feeding its signal to the electronic conditioning unit (ECU) which generates the start of an injection trigger; 
     the application of the additional solenoid valve  36  installed in the control channel  35  which is connected to the cut-off channel  20 ; 
     the application of the link channel  37  between the inlet port  2  and the locking chamber  17  and the non-return valve  38 , the input of which is connected to the inlet port and the output of which is connected to the locking chamber; 
     the application of the spill channel  13  connecting the spill chamber  11  to the spill port  3  which may be closed off by the edge  9  of the plunger  7  depending on the plunger&#39;s position; 
     the application of the non-return valve  33  the output of which is connected to the spill chamber  11  and the input of which is connected to the spill port  3 , and the application of the bypass spill channel  34  connecting the inlet and the outlet of the non-return valve  33 . 
     The application of the external groove  8  (FIG. 1) on the plunger  7  which is used to connect the compression chamber  12  to the cut-off channel  20  instead of a cut-off port in the plunger permanently connected to the compression chamber via a bore in the plunger as shown in PCT/AU98/0073 allows the use of a smaller diameter plunger. In the case of PCT/AU98/0073 a high pressure present in the bore of a plunger tends to expand it and in case of too small a diameter of the plunger this expansion can cause plunger seizure. In a fuel injection system according to an embodiment of the present invention there is no bore in the plunger  7  and the plunger diameter is not limited by the design of the groove  8 . 
     The application of the control channel  22 , which may be connected to the cut-off channel  20  depending on the position of the plunger  7 , and the application of the system  23  which is connected to the control channel  22  and which can vary the pressure in the control channel according to an engine management system command, allows an engine management system to control the shape of a leading edge of an injection curve. This is possible because during upward travel of piston  6  and plunger  7  the groove  8  firstly disconnects the cut-off channel  20  from the compression chamber  12  and then connects cut-off channel to control channel  22 . The cut-off channel is permanently connected to the locking chamber  17 , therefore the pressure in the locking chamber equalises with the pressure in the control channel before an injection takes place. When a slower rise of an injection pressure and rate is required in the beginning of an injection process the system  23  in response to the command of the engine management system decreases the pressure in the control channel  22  thereby decreasing the pressure in the locking chamber. It enables a lower pressure P F1  as indicated in FIG. 8 a,  in the outlet chamber to lift the needle  15  off its seat, therefore the nozzle opens earlier in the beginning of a plunger&#39;s injection stroke when the pressure in the compression  12  and outlet  18  chambers has not yet been built up to a higher level. The effect of this is a more gradual rise of the injection pressure in the beginning of the process, as shown in FIG. 8 b.  When a steep leading front of an injection curve is required, the system  23  increases the pressure in the control channel  22  and therefore in the locking chamber  17  at the beginning of an injection stroke, the nozzle starts to open later with higher pressure P F2  (FIG. 8 a ) in the compression  12  and outlet  18  chambers, which results in a sharp rise of injection pressure as shown in FIG. 8 c.    
     The use of control channel  22  in the injectors and a system  23  which is common for a set of injectors of a multi-cylinder engine presents another advantage in that it improves the repeatability of injection timing in the consecutive injections and the uniformity of injection timing throughout the set of injectors, because it stabilizes the locking chamber pressures at a uniform level for every cycle of injection and for each injector, making it practically independent from the mechanical conditions of an injector such as a wear of the plunger. 
     The use of control channel  22  in the injectors and a system  23  which is common for a set of injectors of a multi-cylinder engine is also advantageous in terms of unit injector design simplicity as well as the injection system as a whole because only one pressure control system for the control channels is required and in some cases this system may be just a valve connecting the control channels either to spill port  3  or to inlet port  2 . Furthermore, only one pressure sensor  25  may be required because the injection timings of different injectors within the set are determined by a common source of pressure in the system  23  and therefore their correlations with the pressure in the control channel with the single sensor installed in it are identical. 
     The use of the pressure sensor  25  in the control channel  22  and the ECU providing the start of injection trigger allows for a more accurate control of fuel delivery as it enables a closed loop control of injection timing. 
     The use of the control channel  35  (FIG. 4) connected to the cut-off port  20  and the additional solenoid valve  36  in the control channel  35  allows control of the injection pressure of very-small fuel deliveries independently from the base pressure. It also allows a wider range of control of an injection curve. The pressure in the control channel  35  and therefore in the locking chamber  17  can be relieved immediately after the groove  8  disconnects cut-off channel  20  from compression chamber  12  during an upward travel of plunger  7 , making it possible to provide an additional control over the injection pressures of very small fuel deliveries. With such an embodiment of the present invention it is also possible to use a weaker spring  16  of the needle  15 , so that when the pressure in the locking chamber  17  is relieved to a certain level the base pressure in the outlet chamber  18  lifts the needle  15  and opens the nozzle  14 . By this means even greater control of the leading edge of an injection curve can be achieved because an injection can be started during an upward movement of the plunger  7  by opening the additional valve  36 . In this case the injection will be started with the base fuel pressure and after the solenoid valve  21  closes and the additional solenoid valve  36  closes the injection stroke of the plunger and the main injection will take place, which will be terminated in the way described earlier. It is also possible to control the rate of injection cut-off by opening additional solenoid valve  36  during an injection cut-off period which will reduce the pressure in the locking  17  and compression  12  chambers and will slow down the rate of nozzle closing. 
     The use of the link channel  37  and the non-return valve  38  as shown in FIG. 5 makes it possible to provide a pilot injection separately from the main injection performed by the injection stroke of the plunger  7  by opening and closing the additional solenoid valve  36  during an upward travel of the plunger and before the solenoid valve  21  closes. 
     The application of the spill channel  13  (FIG. 1) connecting the spill chamber  11  to the spill port  3  which may be closed off by the edge  9  of the plunger  7  depending on the plunger&#39;s position instead of a non-return valve as shown in a prior art simplifies the unit injector design while achieving the same goal of preventing the admission of fuel into the spill chamber  11  during an upward movement of piston  6  and plunger  7  which helps to keep the pressure in spill chamber  11  low during an injection stroke of the plunger. 
     The application of the non-return valve  33  (FIG. 3) the output of which is connected to the spill chamber  11  and the input of which is connected to the spill port  3 , and the application of the bypass spill channel  34  connecting the inlet and the outlet of the non-return valve  33  reduces the noise of the injector operation because during the initial stage of an upward movement of piston  6  and plunger  7 , when the spill channel  13  is still connected to the spill chamber  11 , the non-return valve opens and allows an increased volume of fuel to enter spill chamber  11  before the edge  9  closes spill channel  13 . During the final stages of an injection stroke this increased amount of fuel in the spill chamber provides greater deceleration of the piston  6  because when the edge  9  opens spill channel  13  the non-return valve  33  remains closed and fuel from spill chamber  11  is discharged to the spill port  3  through the bypass spill channel  34  which restricts the flow. The increased deceleration of the piston  6  reduces the impact speed of the piston when it comes to rest in the bottom position, reducing both mechanical noise and the noise of a hydraulic shock occurring during an abrupt stop of the piston. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.