EP3059437B1 - Pump unit for a high-pressure pump - Google Patents

Description

The invention relates to a pump unit for a high-pressure pump.

High-pressure pumps are regularly used to deliver fluid for a storage injection system for internal combustion engines of motor vehicles. Memory injection systems for internal combustion engines of motor vehicles, for example in common rail systems, should be able to provide the necessary volume flow and the required fluid pressure. The high-pressure pump is intended to adapt an amount of fuel to be delivered to a consumption of the internal combustion engine at a corresponding load operating point.

EP 1 403 509 A2 describes various pressure limiting devices, which allow the integration of a pressure limiting valve in a fuel pump of a fuel injection system. In this case, short-term pressure peaks, which result in each delivery stroke of the fuel pump, reduced, and thus prevents unwanted opening of the pressure limiting device in normal operation of the fuel injection system via a compensation chamber. For example, a compensating piston is arranged in a pump piston, wherein both pistons are coupled directly hydraulically to a working space of the fuel pump. The balance piston is supported by a spring inside the pump piston. If the pressure in the working space is too great, the balance piston is pressed against the spring force in the interior of the pump piston, so that the volume of the compensation chamber increases and the formation of a pressure peak is prevented.

The object of the invention is to provide a pump unit for a high-pressure pump, which makes it possible to adapt a quantity of a working medium to be conveyed to predetermined requirements. At the same time, the pump unit should be inexpensive to produce and have good energy efficiency.

The object is solved by the features of the independent claim. Advantageous embodiments of the invention are characterized in the subclaims.

According to an aspect not belonging to the invention, a pump unit for a high-pressure pump comprises a pump housing with a low-pressure inlet and a high-pressure outlet. Via the low-pressure inlet, a working medium is supplied to a working space formed in the pump housing. The working medium is discharged from the working space via the high-pressure outlet. The pump unit comprises a pump piston channel formed in the pump housing with a longitudinal axis. Furthermore, the pump unit has a pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is coupled directly hydraulically to the working space. The pump unit includes a balance piston directly hydraulically coupled to the working space and movably disposed in a balance piston passage along a second axis which is the longitudinal axis, the balance piston passage being disposed opposite to the pump piston passage along the longitudinal axis. Furthermore, the pump unit has a spring element which is mechanically coupled to an end of the compensating piston facing away from the working space and which is designed to influence a position of the compensating piston as a function of a force acting on the spring element. This allows a very flexible solution, since the spring element instead of in the pump housing in other components of the high-pressure pump, for example in a pressure equalization vessel of the high pressure pump, can be arranged. For example, it is also possible that the spring element and the compensation piston channel are combined with the low-pressure inlet and / or high-pressure outlet. This has the advantage that, for example, already existing high-pressure pumps and / or high-pressure pump concepts can be retrofitted with such a compensation device, for example by replacing a low-pressure input module. Advantageously, the spring element causes that in the delivery stroke of the pump piston on reaching the desired pressure in the working space of the balance piston is moved out of the working space, and so the volume of the working space remains substantially constant in the continuation of the course of the delivery stroke of the pump piston.

The invention is characterized by a pump unit for a high-pressure pump. The pump unit includes a pump housing with a low pressure inlet and a high pressure outlet. Via the low-pressure inlet, a working medium is supplied to a working space formed in the pump housing. The working medium is discharged from the working space via the high-pressure outlet. Furthermore, the pump unit comprises a pump piston channel formed in the pump housing with a longitudinal axis. The pump unit has a first pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is hydraulically coupled to the working space. Furthermore, the pump unit has a second pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is coupled via a spring element to the first pump piston, wherein the spring element is formed, depending on a pressure in the working space a distance between the first and to adapt to the second pump piston. The spring element is formed in a delivery stroke of the second pump piston until reaching a predetermined pressure in the working space the Distance between the first and second pump piston to leave substantially unchanged and in the sense of keeping constant the pressure in the working space in the course of a continuation of the delivery stroke the distance.

The spring element causes that in the delivery stroke of the second pump piston on reaching the desired pressure in the working space of the first pump piston substantially comes to a standstill and thus no further amount of the working fluid is conveyed into the working space. Until the desired pressure is reached in the working space, the first pump piston and the second pump piston form a unit which operates in substantially the same way as a one-part pump piston known from the prior art.

In an advantageous embodiment of the invention, the pressure in the working space by means of the second pump piston is limited to a maximum value of about 250 bar.

According to an aspect not belonging to the invention, a pump unit for a high-pressure pump comprises a pump housing with a low-pressure inlet and a high-pressure outlet. Via the low-pressure inlet, a working medium is supplied to a working space formed in the pump housing. The working medium is discharged from the working space via the high-pressure outlet. Furthermore, the pump unit comprises a pump piston channel formed in the pump housing with a longitudinal axis. The pump unit has a first pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is hydraulically coupled to the working space. Furthermore, the pump unit has a second pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is hydraulically coupled via a compensation volume to the first pump piston, wherein the compensation volume is hydraulically coupled to a compensation unit, which is formed depending on a pressure in the working space to adjust the compensation volume.

This advantageously makes it possible to regulate the volume flow of the working medium, preferably a fuel, with a reduced number of components and can contribute to ensuring that the pump unit and thus the high-pressure pump can have good energy efficiency. The saving of components enables cost-effective production. This has the advantage that a separate between a fuel tank and the pump unit electromagnetic flow control valve is not required and / or adjusting the flow rate, for example, a current fuel consumption of the internal combustion engine by throttling an inlet flow and / or by driving off an unneeded, compressed fuel amount is not required , For example, by controlling the unnecessary amount of fuel with a pressure relief valve, the energy efficiency can deteriorate remarkably.

The compensation unit is designed to leave the compensation volume substantially unchanged during a delivery stroke of the second pump piston until a predetermined pressure in the working space is reached and to adjust the compensation volume in the course of a continuation of the delivery stroke in order to keep the pressure in the working space constant. The compensation unit has the effect that during a delivery stroke of the second pump piston when the desired pressure in the working space is reached, the first pump piston essentially comes to a standstill and thus no further quantity of the working fluid is conveyed into the working space. Until the desired pressure is reached in the working space, the first pump piston and the second pump piston form a unit which operates in substantially the same way as a one-part pump piston known from the prior art. According to an aspect not belonging to the invention, a pump unit for a high-pressure pump comprises a pump housing with a low-pressure inlet and a high-pressure outlet. Via the low-pressure inlet, a working medium is supplied to a working space formed in the pump housing. The working medium is discharged from the working space via the high-pressure outlet. The pump unit comprises a pump piston channel formed in the pump housing with a longitudinal axis. Furthermore, the pump unit has a pump piston, which is arranged movably in the pump piston channel along the longitudinal axis and which is coupled directly hydraulically to the working space. The pump unit comprises a balancing piston which is directly hydraulically coupled to the working space and which is movably arranged in a balancing piston channel along a further axis. Furthermore, the pump unit has a spring element which is mechanically coupled to an end of the compensating piston facing away from the working space and which is designed to influence a position of the compensating piston as a function of a force acting on the spring element. The balance piston comprises an inlet valve.

In an advantageous embodiment of the invention, the spring element has a spring characteristic with a degressive course. For example, the spring element may have a plate spring.

In a further advantageous embodiment of the invention, the spring element has a predetermined bias.

Embodiments are explained below with reference to the schematic drawings.

Figur 1

eine schematische Ansicht eines ersten, nicht erfindungsgemäßen Ausführungsbeispiels einer Pumpeneinheit,

Figur 2

eine schematische Ansicht eines zweiten, nicht erfindungsgemäßen Ausführungsbeispiels der Pumpeneinheit,

Figur 3

eine schematische Ansicht eines dritten, nicht erfindungsgemäßen Ausführungsbeispiels der Pumpeneinheit,

Figur 4

eine schematische Ansicht eines erfindungsgemäßen Ausführungsbeispiels der Pumpeneinheit,

Figur 5

eine schematische Ansicht eines weiteren, nicht erfindungsgemäßen Ausführungsbeispiels der Pumpeneinheit,

Figur 6

eine schematische Ansicht eines Speichereinspritzsystems mit der Pumpeneinheit,

Figur 7

eine schematische Ansicht der funktionalen Abhängigkeit des Hubs eines Ausgleichskolbens der Pumpeneinheit von einem Druck der Pumpeneinheit, und

Figuren

8a, 8b und 8c Darstellungen des Drucks und der Einspritzmenge der Pumpeneinheit in Abhängigkeit von einer Drehzahl der Pumpeneinheit.

Show it:

FIG. 1

FIG. 2 is a schematic view of a first embodiment of a pump unit not according to the invention; FIG.

FIG. 2

a schematic view of a second, non-inventive embodiment of the pump unit,

FIG. 3

a schematic view of a third, non-inventive embodiment of the pump unit,

FIG. 4

a schematic view of an embodiment of the invention of the pump unit,

FIG. 5

a schematic view of another, not inventive embodiment of the pump unit,

FIG. 6

a schematic view of a storage injection system with the pump unit,

FIG. 7

a schematic view of the functional dependence of the stroke of a balance piston of the pump unit of a pressure of the pump unit, and

characters

8a, 8b and 8c show the pressure and the injection quantity of the pump unit as a function of a rotational speed of the pump unit.

FIG. 6 shows a hydraulic diagram of a storage injection system 200 for internal combustion engines. The accumulator injection system 200 has a prefeed pump 210 for delivering fuel from a Fuel tank (not shown). Downstream of the feed pump 210, a filter and damping unit 212 is arranged. Downstream of the prefeed pump 210 and the filter and damping unit 212, a high pressure pump 214 with at least one pump unit 10 is further arranged. The pump unit 10 has an inlet valve 216 and an outlet valve 218. The inlet valve 216 is preferably designed as a digital inlet valve, by means of which the volume flow is controlled at the inlet of the pump unit 10. By means of the high-pressure pump 214, the fuel is conveyed to a fuel reservoir 220 in order to get from there to (not shown) injection valves.

FIG. 1 shows a first, not inventive embodiment of the pump unit 10 of the high-pressure pump 214. The high-pressure pump 214 may be formed, for example, as a radial piston pump. For example, the high pressure pump 214 may be provided for fueling a high pressure accumulator injection system, such as a common rail injection system.

The pump unit 10 comprises a pump housing 15 with a low-pressure inlet 17 and a high-pressure outlet 19. In order to be able to fill a working space 20, which is arranged in the pump housing 15, with a working medium, in particular a fluid, the low-pressure inlet 17 has, for example, a feed line. which is preferably hydraulically coupled to the working space 20 by means of an inlet valve. The inlet valve serves to prevent a backflow into the supply line, in particular when filling and compressing the working medium.

The high-pressure outlet 19 has a drain line and an outlet valve which is preferably arranged in this outlet. The outlet valve is designed, for example, as a high-pressure valve, which allows only from a predetermined fluid pressure in the working chamber 20 an ejection of the working fluid from the working space 20 in the drain line. The outlet valve prevents backflow of the working medium, for example from a rail, into the pump unit 10.

The pump unit 10 further comprises a pump piston 30, which is arranged in a pump piston channel 36 formed in the pump housing 15. The pump piston channel 36 has a longitudinal axis L1 along which the pump piston 30 is movably arranged. The pump piston 30 is hydraulically coupled directly to the working space 20.

During a suction stroke, that is to say during a movement of the pumping piston 30 away from the working space 20, the working medium, for example the fuel, is conveyed from the supply line via the inlet valve into the working space 20, the outlet valve being closed. During a delivery stroke, that is to say during a movement of the pump piston 30 directed toward the working space 20, the working medium located in the working space 20 is compressed or discharged via the outlet valve under high pressure to the discharge line, the inlet valve being closed.

At the in FIG. 1 shown, not inventive embodiment of the pump unit 10, the pump unit 10 has a balance piston 40. The balance piston 40 is arranged in a balance piston channel 45. The compensation channel has a second axis A2 along which the compensating piston 40 is movably arranged in the compensation channel. The balancing piston 40 is also directly hydraulically coupled to the working space 20. Furthermore, the pump unit 10 comprises a spring element 50. The spring element 50 is on one of the Working chamber 20 facing away from the first end of the balance piston 40 mechanically coupled thereto. The spring element 50 is designed to influence a position of the compensation piston 40 as a function of a force acting on the spring element 50. The spring element 50 may in this case have, for example, a degressive spring characteristic.

• Durchmesser des Ausgleichskolbens 40: 10 mm
• Maximaler Hub des Ausgleichskolbens 40: 4,2 mm
• Masse des Ausgleichskolbens 40: 8 g
• Federelement 50: Federkonstante 20,3 N/mm, Vorspannung 1900 N

An advantageous design of the balance piston 40 and the spring element 50 in a pump piston 30 with a diameter of 10 mm and a stroke of 2 mm is:

• Diameter of balance piston 40: 10 mm
• Maximum stroke of the balance piston 40: 4.2 mm
• Mass of balance piston 40: 8 g
• Spring element 50: spring constant 20.3 N / mm, preload 1900 N

The balance piston 40 starts a movement only when the pressure in the working space 20 exceeds a predetermined value. Preferably, this predetermined pressure in the working space 20 is about 245 bar. The balance piston 40 stops its movement as soon as the pressure in the working space 20 exceeds another predetermined value. Preferably, this further predetermined pressure in the working space 20 is about 258 bar. It can thus be achieved that at a pressure in the working chamber 20 of about 245 bar, the compensating piston 40 compensates for the change in volume in the working space 20 by the pump piston 30, and so a further increase in pressure in the working space 20 can be avoided. Thus, the pressure in the working chamber 20 can be limited by means of the balancing piston 40 to a value of about 245 bar. This is especially shown in FIG. 7 with a schematic view of the functional dependence of the stroke of the balance piston 40 of the pump unit 10 of the pressure in the working space 20th

In addition, in the Figures 8a, 8b and 8c the pressure curves at the outlet of the pump unit 10 ( FIG. 8a ) and in the fuel storage 220 ( FIG. 8b ) as well as injector injection quantities as a function of a rotational speed of the pump unit 10 (FIG. FIG. 8c ). So is in particular in FIG. 8a shown that the pressure at the outlet of the pump unit 10 by means of the balance piston 40, in particular at higher speeds (here from about 4,800) can be limited to a value of about 245 bar (see boundary G between the dark and the lighter area).

The compensating piston 40 may for example be arranged in the pump housing 15 such that the longitudinal axis L1 of the pump piston channel 36 and the second axis A2 include a predetermined angle. In particular, the compensating piston channel 45 can also be arranged opposite the pump piston channel 36 along the longitudinal axis L1.

The spring element 50 can be arranged, for example, in a further vessel 60 of the pump unit 10. In the vessel 60, the spring element 50 may be arranged such that the spring element 50 has a bias voltage.

FIG. 2 shows a second, not inventive embodiment of the pump unit 10, in which the spring element 50 is arranged in a pressure equalization vessel 60 '. The spring element 50 can additionally be used to dampen pressure pulsations. This is in the in FIG. 2 shown, not inventive embodiment between the balance piston 40 and the spring element 50, a movable member 70, for example, a rolling diaphragm, clamped.

FIG. 3 shows a third, not inventive embodiment of the pump unit 10, wherein the pump unit 10th a combined arrangement of the balance piston 40 and the inlet valve. For example, the balance piston 40 may include the inlet valve.

FIG. 4 shows an inventive embodiment of the pump unit 10. In contrast to the in FIG. 1 In the embodiment shown, the pump unit 10 has a first pump piston 32 and a second pump piston 34. The first pump piston 32 is movably arranged in the pump piston channel 36 along the longitudinal axis L1 and directly hydraulically coupled to the working space 20. The second pump piston 34 is also movably arranged in the pump piston channel 36 along the longitudinal axis L1 and is coupled via the spring element 50 with the first Pumping piston 32, wherein the spring element 50 is formed, depending on a pressure in the working space 20 to adjust a distance between the first 32 and the second pump piston 34. The spring element 50 is designed to leave the distance between the first 32 and second pump piston 34 substantially unchanged during a delivery stroke of the second pump piston 34 until a predetermined pressure in the working space 20 is reached, and to keep the pressure in the working space 20 constant in the process Course of a continuation of the delivery stroke of the second pump piston 34 to adjust the distance. The first pumping piston 32 has a recess 90 at a first end facing the second pumping piston 34. In the recess 90, the spring element 50 is arranged. Alternatively, the spring element may be arranged outside of the first pump piston. The second pump piston 34 has a plunger 80 at a first end facing the first pump piston 32. The plunger 80 is mechanically coupled to the spring element 50.

FIG. 5 shows a further, not inventive embodiment of the pump unit 10. In contrast to the in FIG. 4 the embodiment shown is the second pump piston 34 via a compensation volume 100 hydraulically coupled to the first pump piston 32, wherein the compensation volume 100 is hydraulically coupled to a compensation unit 110, which is designed to adjust the compensation volume 100 depending on a pressure in the working space 20. The compensation unit 110 is designed, for example, to leave the compensation volume 100 essentially unchanged during a delivery stroke of the pump piston until a predetermined pressure in the working space 20 is reached and in order to keep the pressure in the working space 20 constant in the course of a continuation of the delivery stroke, the compensation volume 100 adapt.

The compensation unit 110 includes, for example, a compensation chamber 120, which is arranged in the pump housing 15. Preferably, the compensation chamber has an opening, via which the compensation chamber is hydraulically coupled without resistance to a pump inlet. Furthermore, the compensation unit 110 comprises a further spring element 50 ', which is arranged in the compensation chamber 120. The compensation unit 110 further comprises a piston 130, which is arranged movably in the compensation chamber 120 along a third axis. The piston is mechanically coupled at a first end to the further spring element 50 'and at a second end directly hydraulically coupled to the working volume. The further spring element 50 'may have a spring characteristic with a degressive course. Further, the further spring element 50 'may be arranged and configured such that it has a predetermined bias voltage.

Claims (4)

1. Pump unit (10) for a high-pressure pump, comprising:

   - a pump housing (15) with a low-pressure inlet (17) via which a working medium is fed to a working chamber (20) which is formed in the pump housing (15), and a high-pressure outlet (19) via which the working medium is discharged from the working chamber (20),

   - a pump piston channel (36) which is formed in the pump housing (15) and has a longitudinal axis (L1),

   - a first pump piston (32) which is arranged movably along the longitudinal axis (L1) in the pump piston channel (36) and which is coupled hydraulically to the working chamber (20), and

   - a second pump piston (34) which is arranged movably along the longitudinal axis (L1) in the pump piston channel (36) and is coupled via a spring element (50) to the first pump piston (32), wherein the spring element (50) is configured to adapt a distance between the first pump piston (32) and the second pump piston (34) in a manner which is dependent on a pressure in the working chamber (20), wherein the spring element (50) is configured to allow the distance between the first pump piston (32) and the second pump piston (34) to be essentially unchanged during a delivery stroke of the second pump piston (34) until a specified pressure is reached in the working chamber (20) and to adapt the distance with the effect of keeping the pressure in the working chamber (20) constant over the course of a continuation of the delivery stroke,

   characterized in that the spring element (50) is configured such that, during the delivery stroke of the second pump piston (34), when the specified pressure is reached in the working chamber (20), the first pump piston (32) essentially comes to a standstill and therefore no further quantity of the working medium is delivered to the working chamber (20).
2. Pump unit (10) according to Claim 1, in which a pressure in the working chamber (20) is limited to a value of at maximum circa 250 bar by means of the second pump piston (34) .
3. Pump unit (10) according to either of the preceding claims, in which the spring element (50) has a spring characteristic with a decreasing profile.
4. Pump unit (10) according to one of the preceding claims, in which the spring element (50) has a specified pretension.

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