Title of Invention

SINGLE-PLUNGER INJECTION PUMP FOR A COMMON RAIL FUEL INJECTION SYSTEM

Abstract

ABSTRACT (IN/PCT/2002/02010/CHE) "SINGLE-PLUNGER INJECTION PUMP FOR A COMMON RAIL FUEL INJECTION SYSTEM" A single-plunger injection pump for high-speed internal combustion engines is proposed, which, due to its compact form of construction and high volumetric efficiency, in conjunction with a high oscillation frequency of the piston, has a feed quantity comparable to that of a multi-plunger injection pump, without the torque peaks during the drive of the single-plunger injection pump becoming inadmissibly high.

Full Text

Prior art The invention relates to an injection pump for a common-rail fuel injection system of an internal combustion engine, with a pump cylinder arranged in a housing, with a piston oscillating in the pump cylinder, the pressure of the fuel sucked into the cylinder from a fuel inflow being increased by the piston, and with a quantity control valve, the quantity control valve having a directly activated control piston integrated into the housing, the quantity control valve controlling the delivery stream of the piston into an outflow or into a high-pressure bore connected to a common rail. The injection pump known from DE-A 42 21 921 Al is suitable for use in internal combustion engines with more than one cylinder only when it has a number of pump cylinders corresponding to the number of cylinders. With the number of pump cylinders, the production costs also rise. In the case of what are known as common-rail fuel injection systems, there is, in principle, the possibility of uncoupling the number of cylinders of the internal combustion engine and the number of pump cylinders of the high-pressure fuel pump. On account of the large temporary delivery quantity and of the torque peak resulting from this, and also because of the hitherto unsolved filling of the pump cylinder in a very short time, single-plunger injection pumps have not been used hitherto for the fuel supply of common rails of internal combustion engines with more than one cylinder. The object on which the invention is based is to provide a single-plunger injection pump for internal combustion engines with more than one cylinder, which are equipped with a common-rail fuel injection system. This object is achieved, according to the invention, by means of an injection pump for a common-rail fuel injection system of an internal combustion engine, with a pump cylinder arranged in a housing, with a piston oscillating in the pump cylinder, the pressure of the fuel sucked into the pump cylinder from a fuel inflow being increased by the piston, and with a quantity control valve, the quantity control valve having a directly activated control piston integrated into the housing, the quantity control valve controlling the delivery stream of the piston into an outflow or into a high-pressure bore connected to a common rail, and the piston oscillating at a frequency higher than or equal to half the crankshaft rotational speed of the internal combustion engine. Alternatively, the single-plunger pump may also be controlled by means of a suction-throttle valve. Advantages of the invention By virtue of the compact form of construction of the injection pump according to the invention, the latter has a small dead volume, so that the efficiency of the injection pump is improved. Owing to the high efficiency of the injection pump, the piston can have small dimensioning, so that its oscillation is possible at a frequency higher than half the crankshaft rotational speed. It is thereby possible to arrange the non-uniformity of the delivery quantity over time so as to be in synchronism with injection. What can be achieved, moreover, for the same delivery capacity, is that the torque peaks for driving the injection pump according to the invention are reduced. On account of the small piston diameter, the leakage between the pump cylinder and the piston decreases, so that an improvement in volumetric efficiency and consequently also in overall efficiency is achieved. Moreover, because of the small surfaces, the housing is deformed only to a very slight extent by the pressure forces and by the thermally induced stresses, thus allowing a reduced cold-running play and therefore entailing a further improved efficiency of the injection pump according to the invention. Due to the combination according to the invention of a plurality of features, it became possible to provide an operable single-plunger injection pump [lacuna] internal combustion engines with a common-rail fuel injection system, the said pump having a very compact build owing to the advantages mentioned and also being capable of being produced cost-effectively because of the small number of components. In a variant of the invention, the piston is actuated by a camshaft or a cam disc with at least one cam, so that the oscillation frequency of the piston can be increased in a simple way. Depending on the shaft of the internal combustion engine (camshaft, balancing shaft, crankshaft) by which the injection pump according to the invention is driven, the number of cams can be selected as a function of the delivery requirement. In a further addition to the invention, the speed of the piston is lower during the suction stroke than during the delivery stroke, so that cavitation phenomena are as far as possible avoided during the suction stroke. In another embodiments [sic] of the invention, the pump cylinder is designed as a blind hole, so that the dead volume and the leakage losses are further reduced. The quantity regulation of the injection pump by means of the variation in the prestroke of the piston also contributes to reducing the dead volume. By means of this quantity regulation, the piston always delivers up to top dead centre (TDC) , so that the dead volume becomes minimal. In another embodiment of the invention, there is provision for the outflow to be capable of being sealed off by means of a sealing seat between the housing and the control piston, and for the diameter of the sealing seat to be smaller than the diameter of the receiving bore in the housing for the control piston, so that the opening movement of the control piston is assisted by the movement of the fuel which is under pressure. Furthermore, it is possible for the opening movement of the quantity control valve to be assisted by a spring, so that a reduction in the opening times and an improved start-up behaviour of the internal combustion engine are achieved. Furthermore, in a variant, the pressure forces on the low-pressure side can be largely compensated by means of two piston surfaces which are of similar size. In further variants of the invention, the longitudinal axis of the control piston forms an angle of 90° with the longitudinal axis of the piston and/or a pressure relief space acting as a low-pressure accumulator is provided in the outflow, so that a particularly compact form of construction, along with a correspondingly small dead volume, is achieved, and so that the low-pressure accumulator assists the filling of the pump cylinder during the suction stroke. Cavitation is likewise prevented by means of this measure. By the use of ceramics for the piston and for a tappet roller which is possibly present, the inertia forces can be reduced and therefore the load on the injection pump can be reduced. Moreover, because of the good wearing and deformation behaviour of ceramic, the play between the piston and the cylinder can be reduced, so that a further increase in the volumetric efficiency is obtained. In a further embodiment of the invention, there is provision for a common rail to be integrated into the housing, so that the dead volume is further reduced. In a further addition to the invention, the delivery stroke of the injection pump is phase-shifted in relation to the injection point of the internal combustion engine in synchronism with injection. Depending on how high a phase shift is selected, pressure pulses possibly present in the high-pressure region of the injection pump can be utilized to build up as high an inj ection pressure as possible or injection takes place at a point in time at which pressure pulses are absent or are present only to a slight extent. In the second variant, the accuracy of metering of the fuel during injection is improved. Further advantages and advantageous embodiments of the invention may be gathered from the drawing, its description and the patent claims. Drawing In the drawing: Fig. 1 shows a first exemplary embodiment of a single-plunger injection pump according to the invention. Fig. 2 shows a second exemplary embodiment of a single-plunger injection pump according to the invention, and Fig. 3 shows a third exemplary embodiment of a single-plunger injection pump according to the invention. Description of the exemplary embodiments Fig. 1 shows a first exemplary embodiment of a single-plunger injection pump according to the invention. A piston 3 having a pump cylinder 5 is guided in a housing 1. The piston 3 is driven by a camshaft 7. An eccentric portion 9 of the camshaft 7 acts on the piston 3 via a tappet roller 11. The eccentric portion 9 is a cam according to the invention. However, the cams may also have geometries other than an eccentrically arranged circle. The piston 3 is pressed onto the tappet roller 11 via a return spring 13 illustrated merely as an indication. A control piston 15 of a quantity control valve 17 designed as a solenoid valve is arranged, at right angles to the longitudinal axis of the pump cylinder 5, in the housing 1 above the pump cylinder 5. The control piston 15 has a shoulder 19 which, together with a correspondingly designed step 21, form [sic] a sealing seat. When the quantity control valve 17 is closed, the shoulder 19 rests on the step 21 and the fuel conveyed by the piston 3 is conveyed into a high-pressure bore 23. This high-pressure bore 23 is connected, via a high-pressure line, not illustrated, to the common rail, likewise not illustrated, of the fuel injection system. A non-return valve 25 in the high-pressure bore 23 prevents fuel from flowing out of the common rail back into the injection pump. The piston surface 34 closes off the low-pressure space 29 and largely compensates the forces on the needle which are on the low-pressure side. With the quantity control valve 17 open, the piston 3 conveys fuel into the low-pressure space 29 or, during the suction stroke of the injection pump, sucks fuel out of the low-pressure space 29 into the pump cylinder 5 via the fuel inflow 27. When the quantity control valve 17 is closed during the delivery stroke, a pressure builds up in the pump cylinder 5, which leads to the opening of the non-return valve 25 and subsequently allows the conveyance of fuel out of the pump cylinder 5 into the common rail, not illustrated. The sooner the quantity control valve 17 closes, the larger is the fuel quantity conveyed into the common rail for each delivery stroke of the piston 3. By the selection of the closing point of the quantity control valve 17, the quantity conveyed per delivery stroke can be controlled between 0 and 100% of the pump stroke volume. By virtue of the extremely compact and rigid form of construction of the injection pump and the small dead volumes of the injection pump, the latter has a high efficiency. As a result, the piston 3 can have smaller dimensioning, thus further reducing the leakage loss between the pump cylinder 5 and the piston 3. Moreover, because of the small stroke volume of the piston 3, only a small fuel quantity has to be conveyed out of the fuel inflow 29 into the pump cylinder 5 during the suction stroke, thus reducing the occurrence of cavitation. The tendency to cavitation may be further reduced by means of an appropriate configuration of the eccentric portion 9, illustrated in Fig. 1, of the camshaft 7. If the speed of the piston 3 is lower during the suction stroke than during the delivery stroke, the tendency to cavitation during the suction of fuel decreases. On account of the small dimensions of the piston 3 and of its low mass, the permissible Hertzian stress between the tappet roller 11 and the eccentric portion 9 of the camshaft 7 is not exceeded during the delivery stroke, even in the event of high accelerations of the piston 3 and high pressures. In the exemplary embodiment shown in Fig. 1, the control piston 15 is assisted by a compression spring 31 which is supported against a cover 33 of the housing 1. In the second exemplary embodiment according to Fig. 2, there is no compression spring 31 and Che cover 33 is designed partially as a diaphragm. Directly behind the sealing seat formed from the shoulder 19 and step 21, there is in the housing 1 a recess 35 which, together with the correspondingly configured cover 33, forms a pressure relief space 3 7. The pressure energy stored in the pressure relief space 37 during the predelivery stroke assists the suction of fuel out of the fuel inflow 2 9 into the pump cylinder 5 and thus reduces the tendency to cavitation during the suction stroke. If the diameter of the sealing seat is smaller than the diameter of a receiving bore 3 9 in the housing 1 for the control piston 15, the opening movement of the control piston 15 is additionally assisted by the hydraulic forces. Due to the high oscillation frequency of the piston 3, the average flow velocity of the fuel during the suction stroke is lower than when the same fuel quantity is sucked in for every two crankshaft revolutions during a suction stroke. Fig. 3 illustrates a third exemplary embodiment of an injection pump according to the invention. As in the second exemplary embodiment, too, identical components are given the same reference symbols and what was said above applies accordingly. In this injection pump, the camshaft 7 is part of the internal combustion engine and the housing 1 is inserted directly into a corresponding clearance 41 of the internal combustion engine. This results in a highly compact form of construction. Moreover, when the camshaft 7 is part of a shaft which is present in any case on the internal combustion engine, the outlay in manufacturing terms is reduced and therefore costs are avoided. This injection pump does not require any independent camshaft with mounting and drive, thus having a positive effect on the production costs. All the features disclosed in the drawing, its description and the patent claims may be essential to the invention both individually and in any combination with one another. WE CLAIM: 1. An injection pump for a common rail fuel injection system of an internal combustion engine, the pump comprising a pump cylinder (5), disposed in a housing (1); a piston (3) oscillating in the pump cylinder (5), wherein the pressure of the fuel aspirated from a fuel inlet chamber (29) into the pump cylinder (5) is increased by the piston (3); a quantity control valve (17), wherein the quantity control valve (17) has a directly triggered control piston (15) integrated with the housing (1); the quantity control valve (17) controlling the pumping flow of the piston (3) into a fuel inlet (27) or into a high-pressure bore (23) communicating with a common rail; and the piston (3) oscillating at a frequency greater than or equal to half the crankshaft rpm of the engine during operation; characterized in that said injection pump comprises a sealing seat between the housing (1) and the control piston (15) sealing off the communication between the fuel inlet (27) and the pump cylinder (5), the diameter of the sealing seat being less than the diameter of a receiving bore (39) in the housing (1) for the control piston (15). 2. The injection pump according to claim 1, wherein the piston (3) is actuated by a camshaft (7) or by a cam disk having at least one cam. 3. The injection pump according to claim 2, wherein the speed of the piston (3) during the intake stroke is less than during the pumping stroke. 4. The injection pump according to claim 1, wherein the pump cylinder (5) is embodied as a blind bore. 5. The injection pump according to claim 1, wherein the quantity regulation of the injection pump is effected by varying the pre-stroke of the piston (3). 6. The injection pump according to claim 1, comprising a compression spring (31) reinforcing the opening motion of the quantity control valve (17). 7. The injection pump according to claim 1, wherein the longitudinal axis of the control piston (15) forms an angle of 90° with the longitudinal axis of the piston (3). 8. The injection pump according to claim 1, comprising a pressure relief chamber (37) acting as a low-pressure reservoir in the fuel inlet (27). 9. The injection pump according to claim 1, wherein the piston (3) and if present a tappet roller (11) are made from ceramic. 10. The injection pump according to claim I, comprising a common rail integrated with the housing (1). 11. The injection pump according to claim 1, wherein the pumping stroke of the injection pump is phase-offset in a way synchronized with injection to the instant of injection of the engine. 12. The injection pump according to claim 1, wherein the quantity control valve (17) is embodied as a magnet valve that is open when without current. 13. The injection pump according to claim 2, wherein the camshaft (7) or the cam disk is part of the engine. 14. The injection pump according to claim 1, comprising an intake throttle regulator regulating the pumping quantity.

Documents:

in-pct-2002-2010-che abstract-duplicate.pdf

in-pct-2002-2010-che abstract.jpg

in-pct-2002-2010-che abstract.pdf

in-pct-2002-2010-che claims-duplicate.pdf

in-pct-2002-2010-che claims.pdf

in-pct-2002-2010-che correspondence-others.pdf

in-pct-2002-2010-che correspondence-po.pdf

in-pct-2002-2010-che description (complete)-duplicate.pdf

in-pct-2002-2010-che description (complete).pdf

in-pct-2002-2010-che drawings-duplicate.pdf

in-pct-2002-2010-che drawings.pdf

in-pct-2002-2010-che form-1.pdf

in-pct-2002-2010-che form-18.pdf

in-pct-2002-2010-che form-26.pdf

in-pct-2002-2010-che form-3.pdf

in-pct-2002-2010-che form-5.pdf

in-pct-2002-2010-che pct.pdf

in-pct-2002-2010-che petition.pdf