The present invention relates to an inlet valve assembly of a high pressure fuel pump, said assembly having a piezo-controlled direct acting valve member.
A direct injection equipment comprises a high pressure pump in which fuel received from a low pressure tank is pressurised prior to be delivered to a common rail and to injectors. The fuel in pressurised in a compression chamber which inlet is controlled by an inlet valve member that opens or closes under the influence of pressure difference between the upstream inlet conduit and said downstream compression chamber. Digital inlet valve (DIV) are added to limit the fuel entry in the compression chamber to the necessary volume demanded to be pressurised by the engine. A solenoid actuator may be added so that a magnetic armature cooperates with the valve member either to fully control the operation of the valve member or simply to speed-up the opening or to retard the closing, the valve member remaining generally passive. Such electro-valve, as disclosed in
Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a pumping head of a fuel injection equipment high pressure pump, said pumping head comprising a body provided with a main bore extending along a main axis from a lower opening to an upper end partially defining a compression chamber wherein are arranged an outlet opening and an inlet opening forming an axial guiding bore extending through said body from a seat face surrounding the inlet opening in the bore to a top face of the body.
Advantageously, the pumping head further comprises an inlet valve assembly controlling said inlet opening an comprising an inlet valve body fixed atop the pumping head body thus defining an inner space, an inlet valve member having a head member defining a closing face cooperating with said seat face and, a stem member axially guided in said guiding bore and extending from said head member to an upper end protruding in said inner space and, a piezoceramic actuator fixed in said body and to said stem upper end.
Also, said piezoceramic actuator is a disc-like member provided with a central orifice, the outer edge of said disc-like member being fixed in the inlet valve body and, the stem upper end being fixed into the central orifice, so that when energized the disc deforms and centrally balloons, the outer edge of the disc remaining pinched.
The pumping head further comprises a stem upper end cap member arranged atop the stem upper end and inside the central orifice of the piezoceramic member. It also comprises a flexible sealing membrane arranged in the inlet body inner space and preventing, in use, fuel to contact the piezoceramic disc.
Also, said membrane has an outer edge pinched between a face of the inlet valve body and the outer edge of the piezoceramic disc and, a central opening pinched between the stem upper end cap member and the piezoceramic disc.
Also, the inlet valve body comprises an annular member fixed on the pumping head body and defining the peripheral wall of the inner space and, a valve body cap member fixed on said annular member and closing said inner space.
Also, the disc membrane is arranged so its outer edge is against a top annular face of the annular member and the outer edge of said piezoceramic disc-like member, the valve body cap member covering the piezoceramic disc and being firmly tightened to the body annular member, thus pinching the piezoceramic disc and the membrane between the cover and the annular body member.
The pumping head further comprises electrical wires connected to the piezoceramic disc and extending outside the inlet valve body so that, in use, command signals may be sent from a command unit to said piezoceramic actuator.
The invention also extends to a high pressure fuel pump comprising a cambox and a pumping head as described above and wherein, in use, a camshaft rotates in the cambox imparting reciprocal displacements to a plunger guided in the main bore and varying the volume of the compression chamber.
It also extend to a fuel injection equipment comprising a high pressure pump as here above mentioned and a command unit connected to the inlet valve piezoceramic disc and adapted to send command signal for operating the inlet valve member.
The invention also extends to a method of controlling such fuel injection equipment, the method comprising the step of:
The present invention is now described by way of example with reference to the accompanying drawing in which
A fuel injection equipment comprises a high pressure pump 10 that receives fuel at low pressure, pressurises it and delivers it to a common rail. The pump 10 has a pumping head 12 fixed on a cambox, not shown, the head 12 having a body 14 provided with a blind bore 16 which extends along a pumping axis X and in which, in use, reciprocates a plunger, not shown, that cooperates with a camshaft rotating in the cambox. Said bore 16 is open at a lower end of the head 12 to enable the plunger to extend in the cambox and, at the upper blind end, said bore 16 partially defines a compression chamber 18 in which radially opens an outlet channel 20 controlled by an outlet check valve 22 and, axially opens an inlet valve guiding bore 24 controlled by an inlet valve assembly 26. In the example embodiment of the figure, the inlet valve guiding bore 24 is coaxial to the bore 16 and it upwardly extends from a lower end opening in the blind end of the bore 16, said lower opening being surrounded by a seat face 28 defined on said end face of the bore to, an upper end opening on a top face 30 of the head body. From said pumping head top face 30 upwardly protrudes a cylindrical wall 32 having a right-angled triangle wall section defining an cylindrical outer face 34 and, a frustoconical inner face 36 downwardly pointing toward the head body 14, said cylindrical wall 32 axially extending about the pumping axis X. The pumping head top face 30 further comprises a conical member 38 axially upwardly protruding in the middle of said cylindrical wall 32, the inlet valve guiding bore 24 axially extending in said conical member 38 and opening at the top of it. The pumping head body 14 is further provided with a fuel inlet channel 40 drilled in said conical member 38 and extending from the top face 30 of the pumping head, in an area close to the base of said conical member 38, to an annular chamber defined in the inlet valve guiding bore 24 above said seat face 28.
The inlet valve assembly 26 has a body 42 comprising a main member 44 and a cap member 46, said main member 44 having a base 48, fixed on the top face 30 of the pumping head body and, an annular tubular portion 50 axially protruding from said base 48 and adjusted onto the outer face 34 of the cylindrical wall. Said tubular portion 40 is covered by the cap member 46 having a transverse wall 52 closing the inlet body tubular portion 50 and a peripheral wall 54 internally threaded and complementary engaged and tightened onto a male thread provided on the outer face of the inlet body tubular portion 50. As visible on the figure, the inlet valve body 42 and the top face 30 of the pumping head together define an inner space S in which opens the inlet valve guiding bore 24 and the fuel inlet channel 40.
Said inlet valve assembly 26 further comprises a poppet inlet valve member 56 having a stem 58 axially guided in the guiding bore 24 and extending between an upper end 60 protruding in the inner space S and a lower end protruding in the compression chamber 18, said lower end enlarging to form a head member 62 defining a closing face adapted to cooperate with the seat face 28 to seal said blind end of the bore.
The upper end 60 of the stem is covered by a cap member 46 defining a closed cylindrical portion 66 wherein said stem upper end 60 is inserted and, a crimping annular member 68 enabling to crimp said cap member 46 on the stem. The stem upper end 60 covered by said closed portion 66 of the cap are inserted in an orifice 70 centrally provided in a disc-like piezoceramic member 72 that transversally extends parallel to the transverse wall 52 of the cap toward an outer circular edge 74 that is between said body cap member 46 and the inlet body tubular portion 50. Moreover, a sealing flexible membrane 76 adapted to prevent fuel contact to the piezoceramic disc 72 is arranged in the inner space S, lying against the under face of said disc member 72, the membrane 76 having a peripheral area sandwiched between the disc member 72 and the inlet body tubular portion 50. Centrally, the membrane 76 is holed and fixed to the crimping annular member 68.
Not shown, the pumping head 12 and the inlet valve assembly 26 further comprise a fuel inlet conduit opening in the inner space S and enabling, in use, fuel to flow from a low pressure tank and to fill said inner space S and, electrical connection means, such as cables, wires and connectors, enabling to electrically connect said piezoceramic disc member 72 to an external command unit that will deliver relevant electrical command signals.
The operation of said pumping head 12 is now described focusing mainly on the moves of the inlet valve member.
In a first step the piezoceramic disc 72 is not energised, it does not receive electrical signals, and it remains in a neutral planar position. In said neutral position the inlet valve member is upwardly pulled sealing the fluid communication between the inlet channel and the compression chamber 18.
In a subsequent second step, the piezoceramic disc 72 is energized and, upon receiving such electrical signal, the disc deforms and centrally balloons, the outer edge 74 of the disc remaining pinched. As the disc 72 balloons, the disc central area downwardly moves pushing the inlet valve member 56 in an open position where the closing face of the head lifts away from the seat face 28 of the bore, enabling fuel passage in and out the compression chamber.
Thanks to said piezoceramic actuation of the inlet valve member, the opening and closing of the inlet is directly controlled, therefore, the inlet valve member can be opened or closed, earlier or later than it would naturally do under the sole influence of the pressure differences in the inner space S and in the compression chamber 18, this to optimise the filling of the compression chamber to the necessary quantity demanded by an engine.
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