Injector apparatus

An injector apparatus (10) for injecting fluid under pressure into an associated chamber (32), the apparatus including a body (12), a first piston (14) moveable in the body, the first piston (14) defining a first working area facing an associated chamber (32), a high pressure piston (18, 118) defining a high pressure working area (182) facing a high pressure chamber (19, 119), the first working area being greater than the high pressure working area (182), the first piston (14) being operable to compress fluid in the high pressure chamber (19, 119), the first piston (14) further defining an injector orifice (76) through which the fluid can be injected into an associated chamber (32) from the high pressure chamber (19,119) and defining a valve seat (57), a valve member (92) selectively operable to engage the valve seat (57) to operably isolate the high pressure chamber (19, 119) from the injector orifice (76) and selectively operable to disengage the valve seat (57) to fluidly connect the high pressure chamber (19, 119) with the injector orifice (76).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/EP2020/085341, filed on Dec. 9, 2020, which claims priority to British Patent Application No. 1917998.5, filed on Dec. 9, 2019. The entire disclosures of the above applications are expressly incorporated by reference herein.

The present invention relates to an injector apparatus and to internal combustion engines comprising such injector apparatuses.

Although the present invention is described with reference to fuel injectors used in internal combustion engines, it is applicable to any injector apparatus for injecting a fluid under pressure into an associated chamber.

Fuel injectors used in internal combustion engines, including both spark ignition and compression ignition (or diesel) engines, generally utilise an external pump for supplying the fuel under sufficient pressure to be injected into the engine cylinder. The timing of the injection point in the engine operating cycle is determined by external controlling of the operation of an injector valve by a mechanical or electrical means. One disadvantage of providing external pumping and the control is the need for the provision of servicing of such external systems.

According to a first aspect of the present invention, there is provided an injector apparatus for injecting fluid under pressure into an associated chamber, the apparatus includinga body,a first piston moveable in the body, the first piston defining a first working area facing an associated chamber,a high pressure piston defining a high pressure working area facing a high pressure chamber,the first working area being greater than the high pressure working area, the first piston being operable to compress fluid in the high pressure chamber using the high pressure piston,the first piston further defining an injector orifice through which the fluid can be injected into an associated chamber from the high pressure chamber and defining a valve seat,a valve member selectively operable to engage the valve seat to operably isolate the high pressure chamber from the injector orifice and selectively operable to disengage the valve seat to fluidly connect the high pressure chamber with the injector orifice. With this arrangement, the injector apparatus is operable to generate very high injection pressures using the pressure within the combustion chamber without the need for an external high pressure pump.

The valve member may be moveable relative to the body.

The first piston may be moveable relative to the body in a first direction and the valve member may be moveable relative to the body in the first direction.

The injector apparatus may have a first apparatus position wherein the first piston is in a piston first position, the valve member is ina first valve member position and the valve member is engaged with the valve seat,the injector apparatus having a second apparatus position whereinthe first piston is in a piston second position displaced in the first direction by a first distance from the piston first position, the valve member is in a second valve member position displaced in the first direction by the first distance from the first valve member positionand the valve member is engaged with the valve seat.

The injector apparatus may have a first intermediate apparatus position wherein the first piston is positioned between the piston first position and the piston second position, the valve member is positioned between the first valve member position and the second valve member positionand the valve member is disengaged from the valve seat.

The first piston may be moveable relative to the body in a second direction opposite to the first direction and the valve member is moveable relative to the body in the second direction.

The injector apparatus may have a second intermediate apparatus position wherein the first piston is positioned between the piston first position and piston second position, the valve member is positioned between the first valve member position and the second valve member positionand the valve member is engaged with the valve seat.

The valve member may have an elongate stem having a first end having a valve surface for selective engagement with the valve seat.

The injector apparatus may include a control chamber and movement of the first piston is selectively controllable by controlling the fluid in the control chamber.

The control chamber may be partially defined by the valve member.

The control chamber may be partially defined by an end surface of a second end of the elongate stem opposite the first end.

The injector apparatus may include a control chamber vent valve operable to vent the control chamber to a low pressure region.

The injector apparatus may be configured so that operating the control chamber vent valve to vent the control chamber to a low pressure region allows the valve member to disengage the valve seat.

The first piston may be unitary with the high pressure piston.

The high pressure piston may be annular.

At least a part of the elongate stem may be received in the high pressure piston.

The first piston may be concentric with the high pressure piston.

The control chamber may be partially defined by a wall of the body.

The surface of the body may define a wall of the body and the valve member is partially received within said wall of the body.

The valve member may be in sliding engagement with the wall of the body.

The control chamber may be partially defined by a wall of the first piston.

The valve member may be partially received within the wall of the first piston.

The valve member may be in sliding engagement with the wall of the first piston.

The wall of the first piston may be an inside wall and the control chamber is fluidly connected to an outside wall of the first piston via a first fluid path, the outside wall being in sliding engagement with a bore of the body, the bore of the body including a second fluid path.

The outside wall and/or the bore of the body may have a recess to fluidly connect the first fluid path with the second fluid path.

The recess may be a groove.

The first piston may be separate from the high pressure piston.

The high pressure piston may be cylindrical.

The first piston may not be concentric with the high pressure piston.

The high pressure piston may be defined by a plurality of high pressure pistons and the high pressure chamber is defined by a corresponding plurality of high pressure chambers and the high pressure working area is defined by the plurality of high pressure pistons facing the corresponding high pressure chambers.

The injector apparatus may have just two high pressure pistons and just two corresponding high pressure chambers, or having just three high pressure pistons and just three corresponding high pressure chambers, or having just four high pressure pistons and just four corresponding high pressure chambers.

The injector apparatus may include return spring configured to bias the first piston towards the associated chamber during use.

The first piston may be freely moveable relative to the body. In such embodiments, the first piston is moved towards and away from the associated chamber during use due to pressure imbalances above and below the first piston. Alternatively, the injector apparatus may further comprise a return spring configured to bias the first piston towards the associated chamber during use. In this manner, it can be possible to supply the injector apparatus with fluid even when the pressure in the combustion chamber is higher than on the opposite side of the first piston. This can provide greater flexibility in the amount and timing of a flow of low pressure fluid into the injector apparatus for cooling during operation.

According to an aspect of the present invention there is provided a reciprocating internal combustion engine comprising at least one combustion chamber and at least one injector apparatus according to the first aspect, the at least one injector apparatus being configured to inject fluid under pressure into the at least one combustion chamber.

With reference toFIGS.1to5there is shown an injector apparatus10having a body12, a first piston14, an injector nozzle16, and a second piston18.

The injector apparatus further includes a control volume vent valve20.

In use, the injector apparatus is attached to a cylinder head30(shown schematically) or the like with the nozzle being configured to inject fluid into an associated chamber32, such as an internal combustion chamber. The associated chamber32varies in volume as a piston34reciprocates within a cylinder36of an internal combustion engine38.

In use, a pump28may be connected to a low pressure region, in this case to a tank T. The tank T may supply fluid to the pump28and may also receive fluid from the injector apparatus as will be further described below.

The body12has a first part40and a second part42. The second part42is secured to the first part40(details of which are not shown).

The second part42includes a bore46having an internal diameter D, in one example D=25 mm. The second part42has a shoulder48.

The first part40includes a passage49being associated with the control volume vent valve20. First part40includes a passage50(shown schematically) associated with a check valve24.

As best seen inFIG.4, the first piston14has a piston wall54sized to be a close sliding fit within bore46of the second part42so as to essentially seal the wall54with the bore46. The first piston14includes a shoulder55and an end wall56having injector nozzle16. The end wall56defines a valve seat57.

The injector nozzle16includes a plurality of injector orifices76.

Unitarily formed with the first piston14is a high pressure piston18. High pressure piston18depends upwardly from end wall56of the first piston14and is cylindrical having a stem80with an outer surface80A, an inner surface80B and an end surface80C. End surface80C is annular and defines the high pressure working area, as will be further described below.

First part40is generally elongate and includes an outer surface40A, an inner surface40B and an end surface40C.

A valve element92is generally elongate and includes a first end92C and a second end92D. The diameter of the first end92C is smaller than the diameter of the second end92D.

First end92C defines a valve surface93selectively engageable with and selectively disengageable from the valve seat57, as will be further described below.

Second end92D is received in a bore40B′ defined by inner surface40B. The sizing of the second end92D and bore40B′ is such that the valve element92is a sliding fit within the bore40B′, the sizing being such as to allow a small amount of fluid to pass from the high pressure chamber19to the control chamber15(as will be further discussed below). Thus, the valve element92can slide axially relative to the bore40B′.

Outer surface80A is received in bore40B″ defined by inner surface40B. The sizing of outer surface80A and bore40B″ in such as to create a close sliding fit so as to essentially seal outer surface80A with the bore40B″.

As best seen inFIG.1, the second end92D is positioned part way along bore40B′ thereby defining a control volume15above second end92D and a high pressure chamber19generally below the second end92D.

The control chamber15is generally cylindrical and is defined by end surface94of second end92D and part of inner surface40B. At an end of the control chamber15opposite end surface94is passage49which fluidly connects control chamber15to the control volume vent valve20.

The high pressure chamber19is connected via a passage51to the check valve24. Passage50is connected to the “upstream” side of check valve24.

A solenoid20′ can be used to open the control volume vent valve20thereby connecting passage49to passage49′ which in turn is connected to tank T. Deactivation of the solenoid20′ causes the control volume vent valve20to close thereby isolating passage49from passage from49′.

The first end92C of the valve element92is sized so as to create a clearance between the first end92C and the inner surface80B thereby allowing fluid from the high pressure chamber19to pass through the centre of the high pressure piston18to the injection orifices76and into the combustion chamber or the like as will be further described below.

As best seen inFIG.1, a portion of outer surface40A proximate end surface40C is received within an upper portion of the first piston14. However, as can be seen, there is a clearance between lower portion of outer surface40A and the first piston14.

The first piston defines a region60. The first part40and second part42of the body define a region61. Region61is fluidly connected to tank T (shown schematically). As such, region60is also fluidly connected to tank via region61.

Operation of the injector apparatus is as follows:—

Prior to injection the control chamber15, high pressure chamber19, region60, region61are all primed with fluid supplied via pump28. The fluid is at relatively low pressure (e.g. 3-5 bar). The first piston14is in its lowermost position (when consideringFIG.1) such that shoulder55of the first piston14is in engagement with shoulder48of the body. The valve element92is also in its lowermost position such that valve surface93is in engagement with valve seat57thereby isolating the orifices76from the high pressure chamber19. Control volume vent valve20is closed. Check valve24is closed.

As the piston34ascends within cylinder36during the compression stroke of the internal combustion engine38, pressure is developed within the combustion chamber32. This increasing pressure acts on the first working area of the first piston i.e. the area defined by diameter D of the first piston, i.e. an area equal to piD/42. Thus the increase in pressure within the combustion chamber32creates a force on the first piston14in the direction of arrow A. However, the first piston does not move in the direction of arrow A because the upward force on piston14is resisted by fluid within the high pressure chamber19being hydraulically locked (by virtue of check valve24) and hence causing a reaction force in direction B on the end surface80C of stem80of the high pressure piston18. The effective area of the high pressure piston is therefore the area of the end surface80C, i.e. pi (outer surface80A diameter—inner surface80B diameter)2/4. The upward force on piston14also resisted by fluid within the control chamber15being hydraulically locked (by virtue of control volume vent valve20being closed) and hence causing a reaction force in direction B on end surface94of the valve member92which in turn acts on valve seat57via valve surface93. Note that since regions60and61are connected to tank, no reaction force can be provided by fluid within these regions of the injector apparatus.

As will be appreciated, the effective area of the high pressure piston is significantly smaller than the effective area of the first piston14, and as such the pressure within the high pressure chamber will be greater than the pressure created in the combustion chamber32of the internal combustion engine. This allows extremely high injection pressures e.g. above 3000 bar.

In order to start injection, a control system (not shown) causes the control volume vent valve20to open e.g. by powering the solenoid20′. This fluidly connects passage49to passage49′, and hence fluidly connects the control chamber15to tank T. Thus, the pressure in the control chamber falls but the pressure in the high pressure chamber remains relatively high thereby causing the valve member92to move in the direction of arrow A, i.e. upwardly when viewingFIG.1so as to disengage the valve surface93from the valve seat57thereby fluidly connecting the high pressure chamber19with the injector orifices76. This allows the fluid within the high pressure chamber to be injected through the orifices76into the internal combustion chamber, thereby initiating combustion. As fluid is injected, the first piston progressively moves in the direction of arrow A, i.e. rises when viewingFIG.1. However, because pressure in the high pressure chamber is higher than pressure in the control chamber, the valve element92can continue to rise as fluid from the control chamber is vented to tank. In this manner, during injection, it is possible to ensure that the valve surface93of the valve element92remains disengaged from the valve seat57of the first piston.

In order to stop injection the control volume vent valve20is closed thereby isolating passage49from passage49′ and hence isolating the control chamber from tank T. The control chamber is then hydraulically locked. This prevents any further upward movement of the valve element92. However, continued movement of first piston upwardly will cause the valve seat57of the first piston to move into engagement with the now stationary valve surface93of the valve element92thereby isolating the injector orifices from the high pressure chamber19whereupon injection ceases.

Note that even though injection has stopped, the high pressure chamber remains pressurised by virtue of the pressure within the combustion chamber32. Injection typically occurs towards the end of a compression stroke and/or at the start of a combustion (expansion) stroke. Because the high pressure chamber remains pressurised at the end of injection, further injection is possible during the particular compression/combustion stroke. Such “double” injection is referred to as “double strike” injection. As will be appreciated, the present invention allows for two or more distinct injections (i.e. multi-strike injection) to occur during a single compression/combustion stroke.

Once injection for a particular compression/combustion stroke has finally stopped, the pressure within the combustion chamber will fall significantly, typically when an exhaust valve or valves are opened, and consequently the pressure within the high pressure chamber19will also fall significantly. The pressure within the combustion chamber32will remain at a relatively low pressure during an exhaust stroke and during an inlet stroke. At some time during the time period when the pressure in the combustion chamber is relatively low the injector apparatus will be reprimed with fuel in time for the next injection event which will occur at the next compression/combustion stroke.

Thus, the control volume vent valve20is closed and the pump28provides pressurised fluid (e.g. at around 3-5 bar) which flows past the check valve24, through passage51and into the high pressure chamber19. As mentioned above, the sizing of the second end92D and bore40B′ is such as to allow some fuel to pass from the high pressure chamber19to the control chamber15, thereby allowing the pressure in the control chamber to equalise with the pressure in the high pressure chamber. This causes the valve member92to be biased downwards in the direction of arrow B which in turn causes the first piston to be biased downwards via virtue of engagement between valve surface93and valve seat57. Note the sizing of the second end92D and bore40B′ is such as to create a restrictive orifice which allows the above mentioned repriming of the injector, but does not significantly affect the injection of fuel from the high pressure chamber through the injector orifice76into the combustion chamber. In further embodiments the restrictive orifice could be created by an alternative arrangement.

With reference toFIGS.6to9there is shown an injector apparatus110having a body112, a first piston114, an injector nozzle116, and second pistons118.

The injector apparatus further includes a control volume vent valve120.

In use, the injector apparatus is attached to a cylinder head130(shown schematically) or the like with the nozzle being configured to inject fluid into an associated chamber132, such as an internal combustion chamber. The associated chamber132varies in volume as a piston34reciprocates within a cylinder136of an internal combustion engine38.

In use, a pump128may be connected to a tank T. The tank T may supply fluid to the pump128and may also receive fluid from the injector apparatus as will be further described below.

The body112has a first part140and a second part142. The second part142is secured to the first part140.

The second part142includes a bore146having an internal diameter D, in one example D=25 mm. The second part142has a shoulder148.

The first part140includes a passage149being associated with the control volume vent valve120. First part140includes a passage150(shown schematically) associated with a check valve124.

The first piston114has a piston wall154sized to be a close sliding fit within bore146of the second part142so as to essentially seal the wall154with the bore46. The first piston114includes a shoulder155and an end wall156having injector nozzle116. The end wall156defines a valve seat157.

The injector nozzle16includes a plurality of injector orifices176.

In this case there are three high pressure pistons118(each having an axis F), only two of which can be seen inFIG.6. The three high pressure pistons are equi-spaced around an axis C of the injector apparatus110and are identical. Each high pressure piston is elongate having a diameter E (which defines a surface185), a first end surface181and a second end surface182. Each high pressure piston is slideable within a corresponding bore141of the first part140. The sizing of diameter E and associated bore141is such as to create a close sliding fit so as to essentially seal surface185with bore141. Each end surface181engages a surface158of the first piston114. Each second end surface182and associated bore141define a high pressure chamber119. Collectively the three second end surfaces182define the high pressure working area as will be described below.

First part140includes an outer surface140A, an inner surface140B and an end surface140C.

Attached to first piston114is a stem180which depends upwardly when viewingFIG.6. The stem180is cylindrical with an outer surface180A and inner surface180B defining a bore180B′ The outer surface180A includes a circular groove183A and a circular groove183B. Passage183A′ fluidly connects groove183A to inner surface180B and passage183B′ fluidly connects groove183B to inner surface180B.

A valve element192is generally elongate and includes a first end192C and a second end192D. The diameter of the first end192C is smaller than the diameter of the second end192D.

First end192C defines a valve surface193selectively engageable with and selectively disengageable from the valve seat157, as will be further described below.

Second end192D is received in a bore180B′ defined by inner surface180B. The sizing of the second end192D and bore180B′ is such that the valve element192is a sliding fit within the bore180B′, the sizing being such as to allow a small amount of fluid to pass from region184to the control chamber115. Thus, the valve element192can slide axially relative to the bore180B′.

As best seen inFIG.6, the second end192D is positioned part way along bore180B′ thereby defining a control volume115above second end192D and a region184generally below the second end192D.

The control chamber115is generally cylindrical and is defined by end surface194of second end192D and part of inner surface180B. At an end of the control chamber115opposite end surface194is passage149which fluidly connects control chamber115to the control volume vent valve120.

Each high pressure piston faces a check valve124(only one of which is shown). Passages150are connected to the “upstream” side of check valves124.

A solenoid120′ can be used to open the control volume vent valve120thereby connecting passage149to passage149′ which in turn is connected to tank T. Deactivation of the solenoid120′ causes the control volume vent valve120to close thereby isolating passage149from passage from149′.

The first end192C of the valve element192is sized so as to create a clearance between the first end192C and the inner surface180B thereby allowing fluid from each high pressure chamber119to pass through corresponding passages151, circular groove183B, passages183B′, region184to the injection orifices176and into the combustion chamber or the like as will be further described below.

As best seen inFIG.6, a portion of outer surface140A proximate end surface140C is received within an upper portion of the first piston114. However, as can be seen, there is a clearance between lower portion of outer surface140A and the first piston114.

The first piston defines a region160. Region160is fluidly connected to tank T (shown schematically).

Operation of the injector apparatus is as follows:—

Prior to injection the control chamber115, high pressure chambers119, and region160, are all primed with fluid supplied via pump28. The fluid is at relatively low pressure (e.g. 3-5 bar). The first piston114is in its lowermost position (when consideringFIG.6) such that shoulder155of the first piston114is in engagement with shoulder148of the body. The valve element192is also in its lowermost position such that valve surface193is in engagement with valve seat157thereby isolating the orifices176from the high pressure chambers119. Control volume vent valve120is closed. Check valves124are all closed.

As the piston134ascends within cylinder136during the compression stroke of the internal combustion engine138, pressure is developed within the combustion chamber132. This increasing pressure acts on the first working area of the first piston i.e. the area defined by diameter D of the first piston, i.e. an area equal to piD2/4. Thus the increase in pressure within the combustion chamber132creates a force on the first piston114in the direction of arrow A. However, the first piston does not move in the direction of arrow A because the upward force on piston114is resisted by fluid within the three high pressure chambers119being hydraulically locked (by virtue of check valves124) and hence causing a reaction force in direction B on the shoulder158of the first piston. The collective effective area of the three high pressure piston is therefore the total area of the second end surfaces182i.e. 3piE2/4. Note that since the control chamber is defined by components that are fixed relative to the first piston no reaction force is provided by fluid in the control chamber. Note that since regions160and161are connected to tank, no reaction force can be provided by fluid within these regions of the injector apparatus.

As will be appreciated, the collective effective area of the three high pressure piston is significantly smaller than the effective area of the first piston114, and as such the pressure within the high pressure chambers will be greater than the pressure created in the combustion chamber132of the internal combustion engine. This allows extremely high injection pressures e.g. above 3000 bar.

In order to start injection, a control system (not shown) causes the control volume vent valve120to open e.g. by powering the solenoid120′. This fluidly connects passage149to passage149′, and hence fluidly connects the control chamber115to tank T. Thus, the pressure in the control chamber falls but the pressure in the high pressure chamber remains relatively high thereby causing the valve member92to move in the direction of arrow A, i.e. upwardly when viewingFIG.6so as to disengage the valve surface193from the valve seat157thereby fluidly connecting the high pressure chamber119with the injector orifices176. This allows the fluid within the high pressure chambers to be injected through the orifices176into the internal combustion chamber, thereby initiating combustion. As fluid is injected, the first piston progressively moves in the direction of arrow A, i.e. rises when viewingFIG.6. Because the valve surface193has disengaged the valve seat157and because as the first piston moves upwardly the control chamber also moves upwardly then it is not necessary to continue to vent the control chamber during injection. In this manner, during injection, it is possible to ensure that the valve surface193of the valve element192remains disengaged from the valve seat157of the first piston.

In order to stop injection the control volume vent valve120is closed thereby isolating passage149from passage149′ and hence isolating the control chamber from tank T. The pressure in the control chamber is thenequalised with the pressure in region184(and hence equalised with the pressure in the high pressure chamber119) by virtue of fluid passing from region184past end192D into the control chamber115. This causes the valve member to move in the direction of arrow B relative to the first piston thereby causing the valve surface93to engage the valve seat and isolate the high pressure chambers119from the injector orifices176whereupon injection ceases.

Note that even though injection has stopped, the high pressure chamber remains pressurised by virtue of the pressure within the combustion chamber132. Injection typically occurs towards the end of a compression stroke and/or at the start of a combustion (expansion) stroke. Because the high pressure chamber remains pressurised at the end of injection, further injection is possible during the particular compression/combustion stroke. Such “double” injection is referred to as “double strike” injection. As will be appreciated, the present invention allows for two or more distinct injections (i.e. multi-strike injection) to occur during a single compression/combustion stroke.

Once injection for a particular compression/combustion stroke has finally stopped, the pressure within the combustion chamber will fall significantly, typically when an exhaust valve or valves are opened, and consequently the pressure within the high pressure chamber119and region184will also fall significantly. The pressure within the combustion chamber132will remain at a relatively low pressure during an exhaust stroke and during an inlet stroke. At some time during the time period when the pressure in the combustion chamber is relatively low, the injector apparatus will be reprimed with fuel in time for the next injection event which will occur at the next compression/combustion stroke.

Thus, the control volume vent valve120is closed and the pump128provides pressurised fluid (e.g. at around 3-5 bar) which flows past the check valve124, through passage151and into region184. As mentioned above, the sizing of the second end192D and bore180B′ is such as to allow some fuel to pass from region184to the control chamber115, thereby allowing the pressure in the control chamber to equalise with the pressure in region184and hence the pressure in the high pressure chamber119. This causes the valve member192to be biased downwards in the direction of arrow B which in turn causes the first piston114to be biased downwards via virtue of engagement between valve surface193and valve seat157. As the first piston114descends, then so do the high pressure pistons118and the high pressure chambers119are consequently refilled with fuel from pump128coming via check valve124.

Note the sizing of the second end192D and bore180B′ is such as to create a restrictive orifice which allows the above mentioned repriming of the injector apparatus110but not so as to significantly affect the injection of fuel from the high pressure chambers119through the injector orifice176into the combustion chamber132. In further embodiments the restrictive orifice could be created by an alternative arrangement.

FIGS.10A to10Cshows a variant of an injector assembly apparatus110′ which is the same as injector apparatus110except that associated with two of the high pressure chambers119′ and119″ are associated vent valves96′ and96″ (shown schematically) and associated check valves97′ and97″ (shown schematically).

Check valve97′ is positioned in passage151′ and check valve97″ is positioned in passage151″. Note there are no check valves in passage151′″. Check valve97′ and97″ allow fluid to flow from the high pressure chamber119′ and119″ to the region184but prevent reverse flow through passage151′ and151″.

Vent valves96′ and96″ can be selectively independently opened thereby connecting high pressure chambers119′ and119″ with tank T. Vent valves96′ and96″ can be selectively independently closed, thereby isolating the high pressure chamber119′ and119″ from tank.

The injector apparatus110′ allows the ratio of [the effective areas of the high pressure pistons] to [effective area of the first piston] to be varied.

In a first configuration vent valves96′ and96″ are closed. Under these circumstances the injector apparatus110′ operates as described above with respect to injector apparatus110. In particular the collective effective area of the three high pressure pistons is the total area of the second end surfaces182i.e. 3piE2/4.

In a second configuration, vent valve96′ is open and vent valve96″ is closed. As such, high pressure chamber119′ cannot generate any pressure and is therefore “disabled”. Under these circumstances the high pressure working area is reduced from 3piE2/4 down to 2piE2/4. As such, the pressure in the high pressure chambers119″ and119′″ is increased.

In a third configuration vent valve96′ and96″ are both opened and under these circumstances high pressure chambers119′ and119″ are unable to generate any pressure and hence are both “disabled”. As such, the high pressure working area is further reduced to piE2/4 and the pressure is high pressure chamber119′″ is increased.

Advantageously, by selectively enabling/disabling certain high pressure chambers enables fluid to be injected at different pressures and this is advantageous at certain operating conditions of the associated internal combustion engine.

As described above, the high pressure chambers119ofFIG.6all have the same diameter. Similarly, the high pressure chambers119′,119″ and119″ ofFIGS.10A to10Call have the same diameter. In a further embodiment having a plurality of high pressure pistons, the diameter of one of the pistons may differ from the diameter of another of the pistons. In particular, an injector apparatus may have just two high pressure pistons of different diameters, facing associated high pressure chambers. Enabling or disabling the high pressure chambers provides for three high pressure working areas:—

a) a first high pressure working area where both high pressure chambers are enabled,

b) a second high pressure working area where one of the high pressure chambers is enabled and the other is disabled, and

c) a third high pressure working area where said one of the high pressure chambers is disabled and said other of the high pressure chambers is enabled.