Fuel injector

Abstract

 A fuel injector comprises a nozzle defining a working chamber (38). Fuel is supplied to the working chamber (38) through an inlet, and an outlet is provided whereby fuel can escape from the working chamber (38). Electrodes (36, 40) are provided and arranged such that a voltage can be applied across the fuel within the working chamber (38). In one aspect of the invention, valve means (40, 42) controls fuel flow through the outlet.

Description

[0001] This invention relates to an injector for supplying fuel to a cylinder of an internal combustion engine. The injector is particularly suitable for use in supplying diesel fuel to an internal combustion engine.

[0002] In a known arrangement, a quantity of fuel is supplied at relatively low pressure to a working chamber provided in an injector nozzle. A plurality of small openings provide a restricted flow path between the working chamber and a cylinder to which fuel is to be supplied. An electrode extends into the working chamber, and an electrical power source is connected across the electrode and the housing defining the working chamber. In order to commence injection, a high voltage is applied across the electrode and the housing generating a pressure wave in the fuel in the working chamber. The pressure wave is of sufficiently high magnitude to cause fuel to escape from the working chamber through the small openings to the associated engine cylinder.

[0003] It is an object of the invention to provide an improved injector of this type.

[0004] According to a first aspect of the invention there is provided an injector comprising a nozzle defining a working chamber, an inlet whereby fuel is supplied to the working chamber, in use, an outlet whereby fuel can escape from the working chamber, in use, electrode means whereby a voltage can be applied across the fuel within the working chamber, and valve means controlling the flow of fuel through the outlet.

[0005] The valve means conveniently takes the form of a poppet valve.

[0006] According to a second aspect of the invention there is provided an injector comprising a nozzle defining a working chamber, an inlet whereby fuel is supplied to the working chamber, in use, an outlet whereby fuel can escape from the working chamber, in use, and electrode means whereby a voltage can be applied across the fuel within the working chamber, wherein the working chamber is defined, in part, by a surface of a piston, slidable within a bore, and biasing means associated with the piston, biasing the piston towards a first position.

[0007] The inlet may be defined by a small clearance between the piston and the surface of the bore.

[0008] The injector may further comprise valve means controlling the flow of fuel from the outlet.

[0009] According to a third aspect of the invention there is provided an injector comprising a nozzle defining a working chamber, an inlet whereby fuel is supplied to the working chamber, in use, an outlet whereby fuel can escape from the working chamber, in use, electrode means whereby a voltage can be applied across the fuel within the working chamber, and a resistive element associated with the electrode means.

[0010] The provision of such a resistive element is advantageous in that it enables ionization of some of the fuel, reducing its electrical resistance, thus enabling a reduction in the required spark discharge voltage.

[0011] Conveniently, the working chamber is defined, in part, by a surface of a piston slidable within a bore, the piston being resiliently biased towards a first position. The injector may further comprise valve means, for example a poppet valve, controlling the flow of fuel through the outlet.

[0012] According to a further aspect of the invention there is provided an electrical drive arrangement for a plurality of injectors, the drive arrangement comprising a high tension supply arranged to charge a capacitor and a control arrangement for controlling discharge of the capacitor to an injector.

[0013] The control arrangement may include a distributor arrangement for connecting a capacitor to more than one injector in turn.

[0014] The control arrangement may comprise at least one thyristor, and an arrangement for supplying a trigger signal to the or each thyristor to trigger discharge at an appropriate time.

[0015] Alternatively, the control arrangement may comprise a coil and at least one diode arranged in parallel with the coil, the coil being arranged, in use, to initiate discharge of the capacitor at an appropriate time, the main current flowing through the diode or diodes.

[0016] The invention will further be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a sectional view of an injector in accordance with an embodiment of the invention;

Figure 2 is an enlarged view of part of the injector of Figure 1;

Figure 3 is a side view of the part of the injector illustrated in Figure 2;

Figure 4 is an end view of the injector of Figures 1 to 3;

Figure 5 is a view similar to Figure 2 of a modification; and

Figures 6 and 7 illustrate electrical drive arrangements suitable for use with the injectors of Figures 1 to 5.

[0017] The injector illustrated in Figure 1 comprises a nozzle body 10 which is secured, for example by means of a screw thread to an end of a cylindrical nozzle holder 12. The end of the nozzle holder 12 remote from the nozzle body 10 is received within a connector unit 14 which includes an inlet 16 which is arranged to receive fuel at relatively low pressure from a suitable source, and an outlet 18 which is connected, in use, to a low pressure drain. The inlet 16 communicates through an annular chamber 20 with a supply passage 22 provided in the nozzle holder 12. The supply passage 22 communicates with a chamber 24 defined between the nozzle body 10 and the nozzle holder 12, the chamber 24 communicating with an axially extending bore provided in the nozzle body 10.

[0018] The nozzle holder 12 includes an axially extending bore within which an adjustment member 26 of an electrically insulating material is received in screw-threaded engagement. The adjustment member 26 includes an axially extending passage within which a connecting wire 28 is received, an end of the connecting wire 28 being connected to an electrical connector 30 carried by the adjustment member.

[0019] A piston member 32 is also received within the bore of the nozzle holder 12, a spring 34 being engaged between the adjustment member 26 and a surface of the piston member 32. The piston member 32 includes an axially extending extension which is located within the bore of the nozzle body 10.

[0020] As shown in Figure 2, a clearance exists between the extension of the piston member 32 and the bore provided in the nozzle body 10. As this clearance communicates with the chamber 24, fuel at relatively low pressure from the inlet 16 is able to flow to a working chamber 38 defined between an end part of the nozzle body 10, the end of the extension of the piston member 32 and a poppet valve member 40 which is spring biased into engagement with an end of the bore provided in the nozzle body 10. As illustrated in Figures 3 and 4, the spring biasing of the poppet valve member 40 is achieved by means of a pair of convoluted high temperature spring members 42a, 42b, for example constructed of stainless steel or nimonic alloy.

[0021] The piston member 32 includes an axially extending passage within which an electrode 36 is provided, the electrode 36 being of tubular form and receiving, in sliding engagement, an end part of the wire 28. It will be appreciated, therefore, that the wire 28 provides an electrical connection between the connector 30 and the electrode 36. The piston member 32 is constructed of an electrically insulating material thus the electrode 36 is insulated from the nozzle body 10.

[0022] Starting from the position illustrated in Figures 1 and 2, the poppet valve member 40 is in engagement with the nozzle body 10 thus injection is not occurring. Fuel at relatively low pressure is supplied to the inlet 16, this fuel being able to flow through the supply passage 22 to the chamber 24, and from there through the clearance between the piston member 32 and nozzle body 10 to the working chamber 38. The fuel pressure within the working chamber 38 and chamber 24 act against surfaces of the piston member 32 to move the piston member 32 against the action of the spring 34 towards an equilibrium position which is determined by the prestressing of the spring 34 which in turn is determined by the axial position of the adjustment member 26 with respect to the nozzle holder 12, and upon the pressure of fuel applied to the inlet 16. Once the piston member 32 has reached this equilibrium position, no further fuel flows to the working chamber 38. As mentioned hereinbefore, the quantity of fuel supplied to the working chamber depends upon the supply pressure, and this can be controlled using an appropriate hydro-mechanical system or using an electrically driven regulator. If desired, the quantity of fuel within the working chamber 38 may be monitored by sensing the axial position of the piston member 32 using a suitable displacement transducer.

[0023] In order to commence injection, a high voltage is applied to the connector 30 and hence to the electrode 36, whilst the nozzle body 10 and poppet valve member 40 are held at low or zero potential. This potential difference is applied across the fuel within the working chamber 38 and is of sufficient magnitude to generate a high temperature/pressure wave within the fuel 38 sufficient to result in the valve member 40 being lifted from the end of the nozzle body 10 against the action of the springs 42a, 42b thus permitting fuel to escape from the nozzle body 10 to a cylinder of an associated engine. After the pressure wave has passed, the force applied to the valve member 40 is reduced, thus the valve member 40 returns into engagement with the nozzle body 10 under the action of the springs 42a, 42b.

[0024] It will be appreciated that the existence of the pressure wave within the working chamber 38 also applies a force to the end of the extension of the piston member 32, and the application of the force to the piston member 32 results in the piston member 32 moving against the action of the spring 34 by a small amount. The spring 34 is located within a spring chamber which communicates through a restricted connection 48 with the outlet 18. The movement of the piston member 32 compresses the fuel within the spring chamber, and as the fuel can only escape from the spring chamber at a restricted rate, the movement of the piston member 32 occurs at a relatively low rate. Further, a small quantity of fuel may escape from the working chamber 38 to the chamber 24 along the small clearance between the piston 32 and nozzle body 10, however this quantity of fuel is very small as the clearance therebetween is restricted. Fuel may also escape from the working chamber 38 between the electrode 36 and the wire 28, this fuel escaping to the outlet 18 and low pressure drain.

[0025] Figure 5 illustrates a modification to the arrangement illustrated in Figures 1 to 4. In the arrangement of Figure 5, an electrically resistive element 44 is secured to an end of the electrode 36, the resistive element 44 extending within the working chamber 38. The valve member 40 includes a recess 46 aligned with the resistive element 44. Operation of this arrangement is similar to that described hereinbefore, but the provision of the resistive element 44 enables injection to occur upon the application of a reduced voltage to the injector. As described hereinbefore, in order to commence injection, a voltage is applied to the connector 30 and hence through the wire 28 to the electrode 36. As the electrically resistive member 44 is secured to the electrode 36, the voltage is also applied to the resistive member 44. The path length between the resistive member 44 and the valve member 40 is relatively short, thus a relatively low voltage is required to cause ionization of the fuel therebetween. The ionized fuel is of reduced resistance, thus a reduced voltage is required to achieve discharge through the ionized fuel from the electrode 36 to the electrode defined by the valve member 40 and nozzle body 10 generating a high temperature/pressure wave as described hereinbefore. As this arrangement creates an ionized, relatively low resistance path though the fuel, the voltage necessary to generate a pressure wave of sufficient magnitude to commence injection can be reduced to approximately 20kV.

[0026] Figure 6 illustrates a circuit diagram of a drive arrangement suitable for use in controlling the operation of a series of injectors of the type described with reference to Figures 1 to 5. The circuit comprises a capacitor 50 arranged to be charged by a high tension supply 52. Discharge of the capacitor 50 is controlled by an arrangement comprising a plurality of thyristors 54 arranged in series, the thyristors being controlled by a common trigger arrangement 56, the output of the thyristors 54 being supplied to a distributor 58 which controls which of a plurality of injectors the voltage is to be applied to. Several thyristors are used in series rather than a single thyristor in order to avoid the voltage ratings of the thyristors 54 being exceeded. Capacitors 60 are connected to the gates of the thyristors 54 in order to permit simultaneous triggering of the thyristors in spite of the gates of the thyristors being at different potentials.

[0027] Figure 7 illustrates an alternative arrangement in which a capacitor 62 is arranged to be charged by a high tension supply 64. As in the arrangement illustrated in Figure 6, a distributor arrangement 66 is used to control which injector the voltage from the capacitor 62 is to be applied to. In order to control the timing of discharge, an ignition type coil arrangement 68 is used, a plurality of diodes connected in series being connected in parallel across the coil 68. In use, the coil is used to initiate discharge, and once discharge has commenced, the majority of the current flows through the diodes 70 to the distributor 66. This arrangement is particularly suitable for use in the injector illustrated in Figure 2 since in this arrangement the voltage generated in the coil is added to that stored in the capacitor, to give a higher ignition voltage. The voltage on the capacitor 62 is insufficient to cause dielectric breakdown of the diesel, but high enough to cause discharge once the diesel has been ionized.

[0028] In either of the circuits illustrated in Figures 6 and 7, the high tension supply may comprise the output of an inverter or an alternating current generator driving a step-up transformer and capacitor diode voltage multiplier.

[0029] Although the circuits shown in Figure 6 and Figure 7 show the use of distributor members 58 and 66 to switch the high tension voltage between injectors on the engine, it would of course be possible to use separate high tension circuits to supply power to each injector directly.

Claims

1. An injector comprising a nozzle defining a working chamber (38), an inlet whereby fuel is supplied to the working chamber (38), in use, an outlet whereby fuel can escape from the working chamber (38), in use, electrode means (36, 40) whereby a voltage can be applied across the fuel within the working chamber (38), and valve means (40, 42) controlling the flow of fuel through the outlet.

2. An injector as claimed in Claim 1, wherein the valve means comprises a poppet valve (40, 42).

3. An injector comprising a nozzle defining a working chamber (38), an inlet whereby fuel is supplied to the working chamber (38), in use, an outlet whereby fuel can escape from the working chamber (38), in use, and electrode means (36, 40) whereby a voltage can be applied across the fuel within the working chamber (38), wherein the working chamber (38) is defined, in part, by a surface of a piston (32), slidable within a bore, and biasing means (34) associated with the piston (32), biasing the piston (32) towards a first position.

4. An injector as claimed in Claim 3, wherein the inlet is defined by a small clearance between the piston (32) and the surface of the bore.

5. An injector as claimed in Claim 3 or Claim 4, further comprising valve means (40, 42) controlling the flow of fuel from the outlet.

6. An injector comprising a nozzle defining a working chamber (38), an inlet whereby fuel is supplied to the working chamber (38), in use, an outlet whereby fuel can escape from the working chamber (38), in use, electrode means (36, 40) whereby a voltage can be applied across the fuel within the working chamber (38), and a resistive element (44) associated with the electrode means (36, 40).

7. An injector as claimed in Claim 6, wherein the working chamber is defined, in part, by a surface of a piston (32) slidable within a bore, the piston (32) being resiliently biased towards a first position.

8. An injector as claimed in Claim 6 or Claim 7, further comprising valve means (40, 42) controlling the flow of fuel from the outlet.

9. An electrical drive arrangement for a plurality of injectors, the drive arrangement comprising a high tension supply (52, 64) arranged to charge a capacitor (50, 62) and a control arrangement for controlling discharge of the capacitor (50, 62) to an injector.

10. A drive arrangement as claimed in Claim 9, wherein the control arrangement includes a distributor arrangement (58, 66) for connecting said capacitor (50, 62) to the injectors, in turn.

11. A drive arrangement as claimed in Claim 9 or Claim 10, wherein the control arrangement includes at least one thyristor (54), and an arrangement (56, 60) for supplying a trigger signal to the or each thyristor (54) to trigger discharge at an appropriate time.

12. A drive arrangement as claimed in Claim 9 or Claim 10, wherein the control arrangement comprises a coil (68) and at least one diode (70) arranged in parallel with the coil (68), the coil (68) being arranged, in use, to initiate discharge of the capacitor (62) at an appropriate time, the main current flowing through the diode or diodes (70).

Drawing