Injector apparatus

An injector apparatus (310) for injecting fluid under pressure into an associated chamber (332) is provided. The injector apparatus (310) includes a first piston (314) defining a first working area facing an associated chamber (332), a high pressure piston (318) defining a high pressure working area facing a high pressure chamber (319), and a control piston (317) defining a control piston working area facing a control chamber (315). The first piston (314) is moveable with a body of the injector apparatus (310) to compress fluid in the high pressure chamber (319) using the high pressure piston (318), while movement of the first piston (314) is selectively controllable by controlling the fluid in the control chamber (315). The first working area is larger than the control piston working area and the control piston (317) working area is larger than the high pressure working area.

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/EP2020/085352, filed on Dec. 9, 2020, which claims priority to British Patent Application No. 1918005.8, 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 injector fluid under pressure into an associated chamber, the apparatus including: a 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, and a control piston defining a control piston working area facing a control chamber, wherein movement of the first piston is selectively controllable by controlling the fluid in the control chamber, wherein the first working area is larger than the control pressure working area and the control pressure working area is larger than the high pressure working area.

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. Further, the first piston can be hydraulically locked using fluid in a control chamber which is pressurised by the control piston and can be hydraulically unlocked by venting the control chamber without the need to vent the high pressure chamber. By providing a control piston with a working area which is larger than the high pressure working area and smaller than the first piston working area, the fluid pressure in the control chamber is higher than the pressure in the associated chamber. This means that the amount of fluid that must be vented to initiate injection during each injection cycle can be reduced. This can reduce the time taken to vent the injector prior to injection and can reduce the number and capacity of vent valves required.

The first piston may define at least a part of the high pressure chamber. The high pressure chamber may be defined by the body of the injector. In such embodiments, the first piston may define at least a part of the high pressure piston which faces the high pressure chamber.

The first piston may define a high pressure bore of the high pressure chamber within which the high pressure piston is positioned.

The high pressure piston may be fixed relative to the body.

The high pressure piston may be moveable relative to the body.

The first piston may comprise the control piston. The control piston may be unitary with the first piston. In other embodiments, the control piston may be distinct from the first piston and connected to it by one or more intermediate elements.

The control piston may be annular. The control piston may be cylindrical. The control piston may have any other suitable cross-sectional shape, including but not limited to oval, elliptical, triangular, square, rectangular, pentagonal, hexagonal, or other regular or irregular polygonal shape.

The control piston working area may be annular. The control piston working area may be circular. The control piston working area may have any other suitable shape, including but not limited to oval, elliptical, triangular, square, rectangular, pentagonal, hexagonal, or other regular or irregular polygonal shape.

The control chamber may define a control chamber bore within which the control piston is positioned. The control chamber bore may be fixed relative to the body. In other embodiments, the control piston may be positioned in a further chamber in fluid communication with the control chamber.

The first piston may include an injector orifice through which fluid can be injected into an associated chamber from the high pressure chamber. In other examples, the injector orifice may be provided as part of one or more other components of the injector apparatus. For example, the injector orifice may be provided as part of an injector nozzle forming part of the injector apparatus. The injector nozzle may be connected to the first piston.

The injector apparatus may further include a first valve, or “control chamber vent valve”, operable to vent the control chamber to a lower pressure region. Alternatively, or in addition, the injector apparatus may further include a second valve, or “high pressure chamber vent valve”, operable to vent the high pressure chamber to a low pressure region.

The lower pressure region may be a tank or reservoir. The lower pressure region may be configured to store fluid to be injected. The lower pressure region may contain fluid to be injected. The lower pressure region may be open to the atmosphere.

The injector apparatus may further include a low pressure chamber at least partially defined by the first piston and a bore of the body and configured to displace fluid to a low pressure region during injection.

The control chamber may be fluidly connected to the low pressure chamber via a first passage in which a control chamber vent valve is located, the control chamber vent valve being operable to vent the control chamber to the low pressure chamber. For example, the control chamber vent valve may be operable to vent the control chamber to the low pressure chamber in order to initiate fluid injection.

The control chamber vent valve may be operable to permit the supply of fluid to the control chamber from the low pressure chamber via the first passage. For example, the control chamber vent valve may be operable to permit the supply of fluid to the control chamber from the low pressure chamber in order to fill the control chamber with fluid prior to injection.

The high pressure chamber may be fluidly connected to the low pressure chamber via a second passage in which a high pressure chamber vent valve is located, the high pressure chamber vent valve being operable to vent the high pressure chamber to the low pressure chamber. For example, the high pressure chamber vent valve may be operable to vent the high pressure chamber to the low pressure chamber in order to stop fluid injection.

The high pressure chamber vent valve may be operable to permit the supply of fluid to the high pressure chamber from the low pressure chamber via the second passage. For example, the high pressure chamber vent valve may be operable to permit the supply of fluid to the high pressure chamber from the low pressure chamber in order to fill the high pressure chamber with fluid prior to injection.

The low pressure chamber may be at least partly defined by an annular bore of the first piston. Where the first piston comprises the control piston, the low pressure chamber may be at least partly defined by an annular bore of the first piston extending around the control piston and located between an outer surface of the control piston and an outer wall of the first piston. The low pressure chamber may be at least partly defined by an annular bore in the body of the injector apparatus. The low pressure chamber may be defined by an annular bore of the first piston and by an annular bore in the body of the injector apparatus which are fluidly connected.

The injector apparatus may further comprise a return valve between the low pressure chamber and the low pressure region, wherein the return valve is operable to fluidly connect the low pressure chamber to the low pressure region. The return valve may be operable to fluidly connect the low pressure chamber to the low pressure region prior to injection in order to vent fluid from the low pressure chamber to the low pressure region prior to injection. The return valve may be operable to fluidly connect the low pressure chamber to the low pressure region during injection in order to vent fluid from the low pressure chamber to the low pressure region during injection.

The injector apparatus may further comprise a pump operable to supply fluid to the low pressure chamber from the low pressure region. The pump may be operable to supply fluid to the low pressure chamber from the low pressure region prior to injection.

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 a second aspect of the 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.1to5, there is shown an injector apparatus310having a body312, a first piston314, an injector nozzle316, a control piston317, and a high pressure piston318.

The injector apparatus further includes a control chamber vent valve320and a high pressure chamber vent valve321.

In use, the injector apparatus is attached to a cylinder head330(shown schematically) or the like with the nozzle316being configured to inject fluid into an associated chamber332, such as an internal combustion chamber.

The associated chamber332varies in volume as a piston334reciprocates within a cylinder336of an internal combustion engine338.

In use, a pump328may be connected to a tank T. The tank T may supply fluid to the pump328and may also receive fluid from the injector apparatus as will be further described below.

The body312has a first part340and a second part342. The second part342is secured to the first part340(details of which are not shown).

The second part342includes a bore346having an internal diameter D, in one example D=25 mm. The second part342has a shoulder348.

The first part340includes a passage349being associated with the control chamber vent valve320and a passage351associated with the high pressure chamber vent valve321. First part340further includes a fill line350(shown schematically) associated with a fill valve324and a return line352(shown schematically) associated with a return valve325.

As best seen inFIG.2, the first piston314has a piston wall354sized so that its outer surface354A is a close sliding fit within bore346of the second part342so as to essentially seal the wall354with the bore346. The first piston314includes a shoulder355and an end wall356having a bore357in which the injector nozzle316is secured. The bore357has a chamfer358at its lower end. The first piston314is slidable within the bore346and its lowermost position is defined by engagement of shoulder355with the shoulder348on the body312.

Unitarily formed with the first piston314is a control piston317. Control piston317depends upwardly from end wall356of the first piston314and has a cylindrical annular stem380with an outer surface380A, an inner surface380B and an end surface380C. Inner surface380B defines a high pressure bore380B′. End surface380C defines the control chamber working area, as will be further described below.

As best seen inFIG.3, the first part340of the injector body312is generally elongate and includes an outer surface340A, an inner surface340B, an end surface340C, and an upper wall340D. A high pressure piston318depends downwardly from the upper wall340D into a control chamber bore340B′ defined by the inner surface340B of the first part340. The high pressure piston318has an outer surface318A, an inner surface318B and an end surface318C. In this manner, the high pressure piston318is fixed relative to the body312. The inner surface318B defines a central passage351.

Referring again toFIG.1, the upper end of the control piston stem380extends into the control chamber bore340B′ defined by the inner surface340B of the first part340so that there is a clearance between the end surface380C of the control piston stem380and the upper wall340D. The lower end of the high pressure piston318extends into the upper end of the high pressure bore380B′ defined by the inner surface380B of the control piston stem380so that there is a clearance between the end surface318C of the high pressure piston318and the injector nozzle316at the lower end of the high pressure bore380B′.

The clearance between the end surface380C of the control piston stem380and the upper wall340D defines a control chamber315which is bounded by the inner surface340B of the first part340, the outer surface318A of the high pressure piston318, the upper wall340D and the annular end surface380C of the control piston317. The clearance between the end surface318C of the high pressure piston318and the injector nozzle316defines a high pressure chamber319which is bounded by the inner surface380B of the control piston stem380, the injector nozzle316and the end surface318C of the high pressure piston318. In this manner, the first piston314defines at least part of the high pressure chamber319. In particular, the control piston317, which forms part of the first piston314, defines the high pressure bore380B′ of the high pressure chamber319.

The control piston stem380is sized so that the outer surface380A of the stem380forms a close sliding fit within the control chamber bore340B′ of the first part340so as to essentially seal outer surface380A with the bore340B′. The control piston stem380is also sized so that the outer surface318A of the high pressure piston318forms a close sliding fit within the high pressure bore380B′ of the control piston stem380so as to essentially seal the outer surface318A with the high pressure bore380B′ defined by the inner surface380B of the control piston stem380. The close sliding fit between the stem380and the adjacent components allows the control piston317to slide axially relative to the first part340and the high pressure piston318to vary the volumes of the control chamber315and the high pressure chamber319.

The first piston314defines an annular region360between the inner surface354B of the piston wall354and the outer surface380A of the stem380. The first part340and second part342of the body define an annular region361between the outer surface340A of the first part340and an inner surface342B of the second part342which surrounds the first part340. Region361is fluidly connected to region360. Together region360and region361form a low pressure chamber322.

The control chamber315is generally cylindrical and annular. At an end of the control chamber315opposite control piston317, is a passage349which fluidly connects control chamber315to a control chamber vent valve320. The opposite side of the control chamber vent valve320is fluidly connected to the low pressure chamber322by a passage349′. The control chamber vent valve320is operated by a solenoid320′. When the control chamber vent valve320is open, the control chamber315is connected to the low pressure chamber322via passages349and349′. When the control chamber vent valve320is closed, passage349is isolated from passage349′ and fluid communication between the control chamber315and the low pressure chamber322is prevented.

The high pressure chamber319is generally cylindrical and is connected to a high pressure chamber vent valve321via the central passage351in the high pressure piston318. The opposite side of the high pressure chamber vent valve321is fluidly connected to the low pressure chamber322by a passage351′. The high pressure chamber vent valve321is operated by a solenoid321′. When the high pressure chamber vent valve321is open, the high pressure chamber319is connected to the low pressure chamber322via passages351and351′. When the high pressure chamber vent valve321is closed, passage351is isolated from passage351′ and fluid communication between the high pressure chamber319and the low pressure chamber322is prevented.

The low pressure chamber322is generally annular and is fluidly connected to pump328(shown schematically) via fill valve324and fill line350, and is fluidly connected to tank T (shown schematically) via return valve325and return line352. When the fill valve324is open, the low pressure chamber322is in fluid communication with the fill line350and fluid can be pumped into the low pressure chamber322by the pump328, provided the output pressure from pump328is higher than the pressure in the low pressure chamber322. When the fill valve324is closed, the low pressure chamber322is isolated from the fill line350and from the pump328. When the return valve325is closed, the low pressure chamber322is in fluid communication with the return line352and fluid can be vented from the low pressure chamber322to the tank T via the return line352. When the return valve325is closed, the low pressure chamber322is isolated from the return line352.

As best seen inFIGS.4and5, the injector nozzle316includes a stem362having an outer surface362A, sized to be a close fit or a press fit in the bore357in the end surface356of the first piston314. The stem362also has an external thread362B on its outer surface362A and a bore363defined by a bore wall364, an internal thread365and a shoulder366. In one example the bore363has a diameter d of 3.5 mm. The bore363in the injector nozzle316is smaller than the diameter of the bore357in the end surface356of the first piston314. The injector nozzle316also includes an end wall367having a flange368. The flange368has a flange surface368A. Cross-drilling369fluidly couples the bore363to the outer surface362A of the stem362in a region near the flange368.

Located within the bore363of the injector nozzle316is a valve391which is retained by the internal thread365. The valve391has a valve body391A which defines a central bore391B. The upper end of the central bore391B is open to the bore363of the stem362. The lower end of the central bore391B defines a valve seat391C. The valve391also includes a moveable valve element392inside the central bore391B which is biased towards the closed position and has a valve surface393which selectively engages and disengages with the valve seat391C to open and close the valve391.

The injector nozzle316further includes an annular nozzle ring370having a first surface371, a second surface372and a third surface373. The first surface includes a series of generally radially orientated grooves374. In this example, the first surface371is flat but it could be at an angle, for example it could be frustoconical. The second surface372is frustoconical. The third surface is cylindrical. The nozzle ring370also includes a chamfer375between the third surface373and the first surface371. When the injector nozzle316is assembled into the first piston314, the nozzle ring370is forced into the “wedge” shape defined between the chamfer375and the outer surface362A of the stem362. In this position, the first surface371is sealed against the flange surface368A, the second surface372is sealed against the chamfer358and the third surface373is sealed against the stem wall362A. When the first surface371of the nozzle ring is in engagement with the flange surface368A, the grooves374define a plurality of injector holes376.

Operation of the injector apparatus310is as follows:—

Prior to injection, for example at the start of the compression stroke of the piston334, the injector apparatus310is in the primed condition. In the primed condition, the control chamber315, high pressure chamber319and low pressure chamber322are all primed with fluid supplied from the tank T, via pump328and fill line350. The fluid is at relatively low pressure (e.g. 3-5 bar). The first piston314is in its lowermost position (when consideringFIG.1) such that shoulder355of the first piston314is in engagement with shoulder348of the body312. The valve element392is also in its uppermost position such that valve surface393is in engagement with valve seat391C thereby isolating the orifices376from the high pressure chamber319. Control chamber vent valve320is closed. High pressure chamber vent valve321is closed. Fill valve324is closed. Return valve325is open.

As the piston334ascends within cylinder336during the compression stroke of the internal combustion engine338, pressure is developed within the combustion chamber332. This increasing pressure (Pcomb) acts on the first working area (Afp) of the first piston314to generate a force (Ffp) in the direction of arrow A, which can be expressed as:
Ffp=Pcomb×Afp

Where the first piston314has a circular working area, as in this example, then Afpis equal to (π/4)D2. Thus, as the pressure Pcombwithin the combustion chamber332increases, so too does the force Ffpon the first piston314in the direction of arrow A. However, the first piston does not move in the direction of arrow A, because the upward force on piston314is resisted by fluid within the control chamber315being hydraulically locked by the fluid in the control chamber315(by virtue of control chamber vent valve320being closed). This hydraulic locking results in a reaction force (Rcp) in direction B on the end surface380C of stem380of the control piston317from the fluid in the control chamber315.

The effective area of the control piston317, or “control piston working area”, facing the control chamber315is equal to the area of the end surface380C. Where the end surface380C of the control piston317has a circular annular shape, as in this example, then the control piston working area (Acp)) equates to π×(outer surface380A diameter-inner surface380B diameter)2/4.

In order to start injection, a control system (not shown) causes the control chamber vent valve320to open, e.g. by powering the solenoid320′. This fluidly connects passage349to passage349′, and hence fluidly connects the control chamber315to the low pressure chamber322. The return valve325may also be opened by the control system to fluidly connect the low pressure chamber322to the tank T via the return line322. With the control chamber vent valve320open, fluid in the control chamber315vents to the low pressure chamber322. Thus, the control chamber315no longer provides a hydraulic lock. The pressure within the combustion chamber332acting on first piston314thereby moves first piston314upwardly as fluid is vented from the control chamber315through the control chamber vent valve320. Upward movement of the first piston314, i.e. in the direction of arrow A, causes the volume of the high pressure chamber to decrease, since the injector nozzle316ascends with the first piston314whereas the high pressure piston318remains in place. Thus, the pressure in the high pressure chamber319increases. This increases the force exerted on the valve391in the direction of arrow B, i.e. downwardly inFIG.1, by fluid in the high pressure chamber. Once pressure in the high pressure chamber319is sufficiently high to overcome the spring force on the valve element392, the valve surface393of valve element392is disengaged from the valve seat391C to open valve391and thereby fluidly connect the high pressure chamber319with the injector orifices376. Fuel passes from through cross-drillings369and out of the injector orifices376into the combustion chamber332thereby initiating combustion.

The effective area of the high pressure piston318, or “high pressure working area” facing the high pressure chamber319is equal to the area of the end surface318C. Where the end surface318C of the high pressure piston318has a circular annular shape, as in this example, and the high pressure vent valve321is closed, then the high pressure piston working area (Acp) equates to π×(outer surface318A diameter)2/4.

The pressure in the high pressure chamber is defined by the pressure in the combustion chamber332and the ratio of the working areas of the first piston314and the high pressure piston318, i.e.:
Php=Pcomb×(Afp/Ahp)

As fluid is injected, the first piston314progressively moves in the direction of arrow A, i.e. rises when viewingFIG.1. However, provided fluid pressure in the high pressure chamber319remains sufficient to keep the valve391open, the injector nozzle316can continue to inject fuel as fluid from the control chamber315is vented to tank.

As will be appreciated, the effective area of the high pressure piston318is significantly smaller than the effective area of the first piston314and as such the pressure within the high pressure chamber319will be greater than the pressure created in the combustion chamber332of the internal combustion engine. This allows extremely high injection pressures to be generated, e.g. above 3000 bar. As will also be appreciated, the effective area of the control piston317is smaller than the effective area of the first piston314and larger than the effective area of the high pressure piston318. Consequently, the pressure within the control chamber315will be greater than the pressure created in the combustion chamber332of the internal combustion engine338and will be less than the pressure in the high pressure chamber319.

In order to stop injection, there are two options:

The first option is to open the high pressure chamber vent valve321. This causes the high pressure chamber319to be vented to the tank T via the low pressure chamber322and return line352. The drop in pressure in the high pressure chamber319causes the valve391to close thereby preventing further injection. The first piston314will continue to move upwardly as the control chamber315and high pressure chamber319both vent to tank. Upward movement of first piston314will stop when the piston wall354comes into contact with the top end of region361.

The second option is to close the control chamber vent valve320. This isolates passage349from passage349′ and hence isolates the control chamber315from the low pressure chamber322and the tank T. The control chamber315is then hydraulically locked. This decelerates upward movement of the first piston314and allows the pressure in the high pressure chamber319to reduce to close the valve391thereby isolating the injector orifices376from the high pressure chamber319whereupon injection ceases. Note that even though injection has stopped, the high pressure chamber319remains pressurised by virtue of the pressure within the combustion chamber332. 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 by reopening the control chamber vent valve320. 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.

By hydraulically locking the first piston314using fluid in a control chamber315which is pressurised by the control piston317and has a smaller volume than the low pressure chamber322, the amount of fluid that must be vented during each injection cycle can be reduced relative to arrangements which require venting of the low pressure chamber.

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 chamber319will also fall significantly. The pressure within the combustion chamber332will 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 re-primed with fuel in time for the next injection event which will occur at the next compression/combustion stroke.

In order to re-fill or re-prime the injector, the return valve325is closed and the fill valve324, control chamber vent valve320, and high pressure chamber vent valve321are all opened when the pressure in the combustion chamber Pcombis less than the supply pressure from the pump328. For example, at or towards the end of the expansion stroke. The pump328provides pressurised fluid (e.g. at around 3-5 bar) which flows along fill line350into the low pressure chamber322to fill the control chamber315, high pressure chamber319and low pressure chamber322and push the first piston314to the start position in which the shoulder355of the first piston abuts the shoulder348on the body312.

Although the control piston317is illustrated as being unitary with the first piston314, this need not necessarily be the case. Instead, the control piston317could be positioned elsewhere in the injector apparatus. For example, the control piston could be fixed to the first part340of the injector body312and moveable within a bore defined in the first piston. Alternatively, the control piston and control chamber could be offset from the central axis of the injector. Similarly, although the high pressure piston319is illustrated as being unitary with the first part340, this need not necessarily be the case. Instead, the high pressure piston319could be positioned elsewhere in the injector apparatus. For example, the high pressure piston could be fixed to and moveable with the first piston314within a bore defined in the first part340. Alternatively, the high pressure piston and high pressure chamber could be offset from the central axis of the injector and connected to the injector nozzle by one or more passages.

Although a single high pressure piston and a single control piston are illustrated, the injector apparatus may comprise two or more high pressure pistons and/or two or more control pistons.

Further, although the high pressure chamber and the control chamber are illustrated as being re-primed via the low pressure chamber, one or both of the high pressure chamber and control chamber may be in fluid communication with the feed line via one or more passages which bypass the low pressure chamber.

Although the return line and feed line are schematically illustrated as separate lines, in practice, they may be provided as a single line.