EP2414675B1 - High-pressure pump - Google Patents

Description

The present invention relates to a high-pressure pump for a fuel injection device of an internal combustion engine according to the preamble of claim 1.

State of the art

High-pressure pumps are used, for example, in common-rail systems of motor vehicles to provide or supply pressurized fuel to a high-pressure accumulator under all operating conditions. Such high-pressure diesel pumps usually have either eccentric drives or cam drives. The advantage of cam-driven high-pressure pumps is that in this case it is possible to design for a desired application a cam profile adapted thereto, which represents the piston stroke via a rotation angle of the drive shaft or the camshaft. For example, a slow delivery phase and a fast suction phase of the high pressure pump can be realized via an asymmetric cam profile, whereby an advantage is achieved by the resulting low maximum drive torque, which must apply the motor to drive the high pressure pump.

However, in order to reduce the variety of parts in the production, substantially symmetrical cam contours have been developed in the prior art, which have the same stroke course in the suction and delivery phase. A cam contour designed in this way can therefore also be used both for the right-handed and for the anti-clockwise rotation.

Although the symmetrically designed cam contours have the advantage described above that the variety of parts is kept small, they have the disadvantage that the principal differences that arise for the suction phase and the delivery phase of the high-pressure pump, are not taken into account or included.

In the case of high-pressure pumps known from the prior art, moreover, the cams used for their drive shafts were also optimized with regard to their cam contour only with regard to the delivery phase. The resulting cam contours, however, gave unfavorable properties for the filling behavior of the element space or the pump working space of the high-pressure pump in the suction phase.

Therefore, it is necessary to provide a high-pressure pump for fuel injectors and in particular for common-rail systems, which has a cam contour, which is also optimized in terms of the suction phase.

The EP 1 101 939 A2 shows a piston pump for fluid delivery with a plurality of preferably similar piston-cylinder units, in whose cylinder chamber in each case an associated displacer piston is arranged. Each piston performs an oscillation with a suction and delivery interval. The delivery interval occupies a larger part of the oscillation period than the suction interval.

From the US 2002/004704 A1 For example, a variable supply fuel supply device is known. This comprises a piston and a cylinder, wherein the pressure in a pressure chamber at a position which is set to a certain value before the top dead center is reached in the course of the exhaust stroke, in which the piston of the fuel pump is from the bottom dead center is moved to the top dead center, is drained.

Disclosure of the invention Advantages of the invention

According to the invention, a high-pressure pump is provided for a fuel injection device of an internal combustion engine, in particular for a common rail injection system, which has a cam engine in which the rotational movement of a camshaft is converted via at least one cam into a stroke movement of a pump piston of the high-pressure pump, wherein the at least one Cam has an asymmetric cam contour, wherein a cam contour of the cam is designed so that in a suction phase of the high-pressure pump in a range from a top dead center to a bottom dead center, in which fuel is sucked into a pump chamber, the piston stroke of the pump piston as a function of Cam rotation angle follows a sinusoidal course. Due to the sinusoidal design of the cam contour, the filling behavior of the element space or the pump working space of the high-pressure pump is improved in the suction phase, and strong variations in the fuel delivery rate as a function of the rotational speed are reduced. Furthermore, the range in pressure reduction after the top dead center of the cam is improved.
According to the invention, the cam contour is designed such that in a delivery phase of the high-pressure pump, in which the fuel is compressed in the pump working space and supplied to a delivery valve, an acceleration of the pump piston as a function of the cam rotation angle follows a course composed of sinusoidal and linear sections.
This asymmetric cam contour allows adaptation to special requirements, for example with regard to the suction phase and the delivery phase.

According to a further preferred embodiment, the sinusoidal curve in the suction phase corresponds to a falling edge of a sinusoidal function, which starts at a top dead center of the cam and ends at a bottom dead center of the cam. By the "half sinus cam" with z. B. 2 x 6 mm stroke according to the embodiment, significant increases in production compared to conventional cams with z. B. 2 x 6 mm stroke can be achieved. The delivery rate, for example, increases from 160 l / h when using a conventional cam to 178 l / h when the "half-sine cam" according to the embodiment is used. In addition, this can reduce flow rate fluctuations over the speed, for example, a two-piston pump and the Abspringverhalten the plunger assembly of the high-pressure pump is improved in the suction phase. A correction or compensation of flow rate fluctuations over the speed and reduced flow rates by increasing the piston stroke is no longer necessary, which improves the durability of the high-pressure pump. In particular, by the configuration described above, a high load on the plunger spring, a high drive torque of the high-pressure pump and high Umpumpverluste what leads to an increased consumption of the high-pressure pump avoided.

It is particularly preferred if the falling edge is formed from a sum of harmonic functions. In forming the falling edge of the cam profile from a sum of harmonic functions, the performance of the high pressure pump is further optimized. In particular, the lift-off properties of the plunger body of the high-pressure pump are improved, and depending on the acceleration curve of the rising flank in the delivery phase, larger acceleration stages in the transition region to the suction phase are avoided. In particular, this refinement improves the speed and acceleration profile of the pump piston as well as the Hertzian pressure.

According to yet another preferred embodiment, the sinusoidal curve in the suction phase at the top dead center of the cam corresponds to a maximum delivery stroke of the pump piston. By this configuration, the suction phase is further optimized, the course or the cam contour of which takes place before the suction phase promotion phase is irrelevant and can follow an already optimized cam contour. The sinusoidal characteristic is characterized by a slow and harmonic decrease or increase in the piston stroke, the piston speed and the piston acceleration after and before the dead centers. The high piston speed in the mid-range of the delivery phase was previously the reason for high drive torques of the high-pressure pump and was not enforceable in the requirements previously placed on the high-pressure pumps in the prior art. However, the slow, harmonic decay after top dead center results in an improved suction phase and lower negative torques during pressure build-up. Due to the slow approach to the bottom dead center, the suction valve of the high-pressure pump can begin earlier with its closing operation and delivery losses due to a late closing of the suction valve are significantly reduced.

According to yet another preferred embodiment, the sinusoidal curve in the suction phase at the bottom dead center of the cam corresponds to a minimum delivery stroke of the pump piston.

Preferably, the cam contour is designed so that in the suction phase of the high-pressure pump, the piston speed of the pump piston performing a downward movement follows a sinusoidal course as a function of the cam rotation angle.

Brief description of the drawings

Fig. 1

einen Schnitt durch eine Hochdruckpumpe gemäß dem Stand der Technik;

Fig. 2

ein Diagramm, welches die Förderrate in Abhängigkeit von der Drehzahl eines Nockens gemäß dem Stand der Technik und eines Nockens gemäß einer Ausführungsform darstellt;

Fig. 3

ein Diagramm des Verlaufs des Kolbenhubs in Abhängigkeit von dem Nockendrehwinkel;

Fig. 4

ein Diagramm des Verlaufs der Kolbengeschwindigkeit in Abhängigkeit von dem Nockendrehwinkel; und

Fig. 5

ein Diagramm des Verlaufs der Kolbenbeschleunigung in Abhängigkeit von dem Nockendrehwinkel.

Hereinafter, embodiments of the invention will be described in more detail with reference to the accompanying drawings. It shows:

Fig. 1

a section through a high pressure pump according to the prior art;

Fig. 2

a diagram illustrating the delivery rate in dependence on the rotational speed of a cam according to the prior art and a cam according to an embodiment;

Fig. 3

a diagram of the course of the piston stroke in dependence on the cam rotation angle;

Fig. 4

a diagram of the curve of the piston speed in dependence on the cam rotation angle; and

Fig. 5

a diagram of the course of the piston acceleration in dependence on the cam rotation angle.

Embodiments of the invention

In Fig. 1 is a section through a high-pressure pump 1 for a fuel injection device of an internal combustion engine shown, as is known in the prior art. The high-pressure pump 1 has a multipart pump housing 2 in which a drive shaft or camshaft 3 driven in rotation by the internal combustion engine is arranged. The camshaft 3 is rotatably supported, for example, via two bearing points spaced apart from one another in the direction of the axis of rotation 4 of the camshaft 3. The bearings can be arranged in different parts of the pump housing 2, for example, a first bearing point in a base body 5 of the pump housing 2 and a second bearing point can be arranged in a connected to the base body 5 flange 6.

In a region lying between the bearing points, the camshaft 3 has a cam 7, which may also be designed as a multiple cam. The high pressure pump 1 has at least one or more arranged in the housing 2 pump elements 8, each with a pump piston 9 which is driven by the cam 7 of the camshaft 3 in a lifting movement in at least approximately radial direction to the axis of rotation 4 of the camshaft 3. Upon rotation of the cam 7, the pump piston 9 is set in a reciprocating or upward and downward movement. This results in a cyclical change in the volume of a pump working chamber 14 bounded by the pump piston 9. In the region of each pump element 8, there is provided a pump housing part 10 which is connected to the main body 5 and which is designed as a cylinder head. The pump housing part 10 has a voltage applied to an outer side of the main body 5 flange 11 and a through an opening in the base body 5 to the camshaft 3 out, at least approximately cylindrical projection 12 with respect to the flange 11 of smaller diameter. The pump piston 9 is guided tightly displaceably in a neck 12 formed in the cylinder bore 13 in the pump housing part 10 and limited with its side facing away from the camshaft 3 end face in the cylinder bore 13 the pump chamber 14. The cylinder bore 13 may extend into the flange 11, in the then the pump working space 14 is arranged. The pump working chamber 14 has a connection with a fuel feed, for example a feed pump (not shown), via a fuel feed channel 15 running in the pump housing 2. At the mouth of the fuel inlet channel 15 in the pump chamber 14 is a in the pump working space 14 opening inlet valve 16 is arranged. The pump working chamber 14 also has, via a fuel outlet channel 17 running in the pump housing 2, a connection to an outlet, which is connected to a high-pressure accumulator 18, for example. One or more injectors 19 arranged on cylinders of the internal combustion engine are connected to the high-pressure accumulator 18, through which fuel is injected into the cylinders of the internal combustion engine. At the mouth of the fuel outlet channel 17 into the pump working chamber 14, an outlet valve or delivery valve 20 opening out of the pump working chamber 14 is arranged.

During the suction stroke of the pump piston 9 or in the suction phase, in which the pump piston 9 moves radially inward, the pump working chamber 14 is filled with fuel through the fuel inlet channel 15 with open inlet valve 16, which acts as a suction valve, wherein the delivery valve 20 is closed , During the delivery stroke of the pump piston 9 or in the delivery phase in which the pump piston 9 moves radially outward, fuel is conveyed under high pressure through the pump piston 9 through the fuel outlet channel 17 with open delivery valve 20 to the high-pressure accumulator 18, wherein the inlet valve 16 is closed.

Between the pump piston 9 and the cam 7 of the camshaft 3, a plunger 21 is arranged, via which the pump piston 9 is at least indirectly supported on the cam 7 of the camshaft 3. The plunger 21 is hollow cylindrical with a round outer cross-section and is guided in a bore 22 of the main body 5 of the pump housing 2 in the direction of the longitudinal axis 23 of the pump piston 20 slidably. The longitudinal axis of the plunger 21 is thus at least substantially identical to the longitudinal axis 23 of the pump piston 9. In the plunger 21 in the camshaft 3 end facing a support member 24 is inserted, in which a roller 25 is rotatably mounted on the cam 7 of Camshaft 3 rolls off. The axis of rotation 26 of the roller 25 is at least approximately parallel to the axis of rotation 4 of the camshaft 3. The support member 24 has on its side facing the camshaft 3 a recess 27 in which the roller 25 is rotatably mounted. The support member 24 and the plunger 21 may also be integrally formed.

On the plunger 21 or on the pump piston 9 engages a prestressed spring 28, which is designed as a return spring, which is supported on the pump housing part 10. By the spring 28 of the pump piston 9 and the plunger 21 are applied to the cam 7 of the camshaft 3 down, so that the system of the roller 25 on the cam 7 and the camshaft 3 directed towards the suction stroke of the pump piston 9 and at high speed of the camshaft. 3 is ensured. The pump piston 9 may be coupled to the plunger 21, at least in the direction of its longitudinal axis 23. Alternatively, the pump piston 9 may not be connected to the plunger 21, then by the return spring 28, the system of the pump piston 9 is secured to the plunger 21. It can be provided that the return spring 28 engages, for example via a spring plate 29 on an enlarged diameter piston base of the pump piston 9, which is thereby held in contact with a on the plunger 21 by the jacket inwardly projecting flange, in turn, in contact with the support element 24 is held, so that the entire composite of pump piston 9, plunger 21 and support member 24 is acted upon with roller 25 to the cam 7 of the camshaft 3 out.

In the direction of the axis of rotation 26, a support 30 is arranged laterally next to the roller 25 for this purpose, which prevents the roller 25 from moving out of the support element 24 in the direction of its axis of rotation 26. The roller 25 may be convexly curved at its side facing the support 30 side surfaces, for example, curved at least approximately spherical. The side surfaces of the roller 25 facing surface of the support 30 may be formed at least approximately flat or curved. The support 30 may be formed as a ring surrounding the roller 25 or may be arranged only laterally adjacent to the side surfaces of the roller 25.

Fig. 2 shows a diagram representing the delivery rate of a high pressure pump 1 as a function of the rotational speed of a cam 7 on the one hand according to the prior art and another cam 7 on the other hand, according to an embodiment, which is determined according to a simulation. The simulation of the delivery rates or the comparison of the delivery rates was carried out on the basis of the conditions of a pressure of 1800 bar and a temperature of 40 ° C. Furthermore, on the one hand a radial piston pump according to the prior art with a conventional cam 7 with 2 x 6 mm stroke with a radial piston pump compared with a cam 7 according to an embodiment of the invention, which has a cam contour with respect to the suction phase, which follows a sinusoidal course. The cam 7 according to the embodiment is hereinafter referred to as a half-sine cam. As can be seen from the diagram, according to the simulation, the delivery rate of 160 l / h achieved by the conventional cam 7 increases to 178 l / h for the half-sine cam at a speed of about 5000 rpm.

Fig. 3 shows a diagram of the course of the piston stroke in dependence on the cam rotation angle. In this case, in the left half of the diagram, the delivery phase over a cam rotation angle range of 0 ° to 90 ° is shown, in which the curve is composed of linear, sinusoidal, tangential or arcuate acceleration regions. It is important, however, that in the suction phase, the cam contour follows a sinusoidal course in a cam rotation angle range of 90 ° to 180 °. Beginning at the top dead center of the cam 7 indicated by reference numeral 31 at a cam rotation angle of 90 °, the piston stroke smoothly drops until it approaches zero at a cam rotation angle of 180 ° at the bottom dead center of the cam 7 indicated by reference numeral 32 , Due to the slow, harmonic drop in the beginning of the flank after passing through top dead center 31 and a subsequent rapid suction phase, inter alia, an improved suction phase and lower negative torques are achieved during pressure reduction.

The falling edge 33 of the cam contour can also be formed from a non-pure sine function, the falling edge 33 of the cam contour is then obtained from a sum of harmonic functions, whereby a further optimization latitude in the cam design can be obtained.

If the falling edge 33 is composed of the sum of harmonic functions of different orders, then the piston stroke is given by the following equation: $$\begin{array}{l}\mathrm{stroke}=\mathrm{A}0+\mathrm{A}1*\sin \left(1*\left(\mathrm{\alpha }+{\mathrm{\alpha }}_0\right)\right)+\mathrm{A}2*\sin \left(2*\left(\mathrm{\alpha }+{\mathrm{\alpha }}_1\right)\right)+\mathrm{A}3*\sin \left(3*\left(\mathrm{\alpha }+{\mathrm{\alpha }}_2\right)\right)\\ +...\end{array}$$

For reasons of spring excitation, contributions from the 4th order may only be less than 1% of the 1st order A1.

Fig. 4 shows a further diagram, in which the curve of the piston speed in dependence on the cam rotation angle in a delivery phase and in the suction phase is shown. Again, the piston velocity in the suction phase again follows a sinusoidal course.

Finally shows Fig. 5 a diagram of the course of the piston acceleration in dependence on the cam rotation angle. Again, in the suction phase of the following a sinusoidal curve can be seen, while the course of the delivery phase of sinusoidal and linear regions is composed.

The sinusoidal piston acceleration results from the formula: $$\mathrm{b}={\mathrm{b}}_0*\sin \left({\mathrm{a}}_0*\left(\mathrm{\alpha }+{\mathrm{\alpha }}_0\right)\right)+\mathrm{c},$$

The piston speed and the piston stroke result from appropriate integration of the piston acceleration.

Overall, it is created with the high-pressure pump 1 according to the invention with an optimized suction phase, whereby the delivery rate can be increased and flow rate drops can be avoided.

Claims (6)

1. High-pressure pump (1) for a fuel injection device of an internal combustion engine, in particular for a common-rail system, which high-pressure pump has a cam drive mechanism in which the rotational movement of the camshaft (3) is converted by means of at least one cam (7) into a reciprocating movement of a pump piston (9) of the high-pressure pump (1), wherein the at least one cam (7) has an asymmetrical cam contour, wherein a cam contour of the cam (7) is designed such that, in a suction phase of the high-pressure pump (1) in a region from a top dead centre (31) to a bottom dead centre (32), in which fuel is drawn into a pump working chamber (14), the piston stroke of the pump piston (9) follows a sinusoidal profile as a function of the cam rotational angle,
   characterized in that
   the cam contour is configured such that, in a delivery phase of the high-pressure pump (1), in which the fuel in the pump working chamber (14) is compressed and fed to the delivery valve (20), the acceleration of the pump piston (9), as a function of the cam rotational angle, follows a profile made up of sinusoidal and linear sections.
2. High-pressure pump (1) according to Claim 1,
   characterized in that
   the sinusoidal profile corresponds, in the suction phase, to a falling flank (33) of a sine function, which flank begins at a top dead centre (31) of the cam (7) and ends at a bottom dead centre (32) of the cam (7).
3. High-pressure pump (1) according to Claim 2,
   characterized in that
   the falling flank (33) is formed from a sum of harmonic functions.
4. High-pressure pump (1) according to Claim 2 or 3,
   characterized in that
   the sinusoidal profile in the suction phase corresponds, at the top dead centre (31) of the cam (7), to a maximum delivery stroke of the pump piston (9) .
5. High-pressure pump (1) according to one or more of Claims 2 to 4,
   characterized in that
   the sinusoidal profile in the suction phase corresponds, at the bottom dead centre (32) of the cam (7), to a minimum delivery stroke of the pump piston (9).
6. High-pressure pump (1) according to one or more of Claims 1 to 5,
   characterized in that
   the cam contour is configured such that, in the suction phase of the high-pressure pump (1), the piston speed of the pump piston (9), which performs a reciprocating movement, follows a sinusoidal profile as a function of the cam rotational angle.

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