WO2001023752A1 - High pressure pump - Google Patents

Abstract

A high pressure pump (1) for supplying fuel to an internal combustion engine injection system comprises a drive unit (4) for at least one piston (5, 6) which is axially displaceable in a cylinder (7, 8) and whose crown (10, 11) opposing the drive unit (4) defines the pumping volume (12, 13), itself connected to a fuel filled low pressure volume (14) and a high pressure line (15, 16). The drive unit (4) comprises at least one valve gear (37, 38), itself comprising a valve element (43, 44) which is axially displaceable in a bore (39, 40) within the valve body (41, 42). Said element (43, 44) cooperates with a seat (45, 46) in the valve body (41, 42) to open and close a pressurized medium inlet (47, 48) for hydraulically operating the pistons (5, 6). The valve element (43, 44) is controlled by an actuator (50) on a piezo-electric unit (51).

Description

high pressure pump

State of the art

The invention is based on a high-pressure pump for supplying high-pressure fuel in injection systems for internal combustion engines according to the preamble of patent claim 1.

Such a high-pressure pump is known for example from DE 197 16 242 and DE 197 44 577, the high-pressure fuel pumps described therein corresponding to the type of a radial piston pump which, in a pump housing, has a drive shaft which is eccentric or has cam-like elevations in the circumferential direction, and preferably has a plurality of pump pistons arranged radially with respect to the drive shaft in a respective cylinder chamber. When the drive shaft is turned around, the pump pistons can be moved back and forth in their cylinder space, and with their end faces facing away from the drive shaft they each limit a pump work space in the cylinder space, which alternates with one fuel-filled low-pressure chamber and can be connected to a high-pressure delivery line.

These known high pressure pumps each form the interface between the low and the high pressure part of a

Common Rail injection system and have the task of always providing sufficient compressed fuel in all operating areas of the vehicle. The high-pressure fuel pump permanently generates the system pressure for the high-pressure accumulator (rail). Very high fuel pressures of up to 2000 bar are built up in the pump work space during the high-pressure delivery phase, so that the mechanical load on the drive unit of the high-pressure fuel pump is very high. Since the high-pressure fuel pump is a separate component from the high-pressure storage unit, which is connected to the latter via a high-pressure delivery line, the effort in terms of construction and assembly, as well as the number of components and the sealing of the sealing points and bores under high pressure are very great.

From US-PS 5,738,075 a hydraulically oversized pump unit between a low-pressure area and a high-pressure area is known, which works with a three-position control valve. In this hydraulically operated fuel injection device, the mechanical pump elements are loaded only relatively slightly, but this pump unit with its complex structure is hardly suitable for driving pump pistons in a high-pressure fuel pump. Piezoelectric actuators, which are characterized by a high adjustment speed, are increasingly being used in the field of fuel injection as drive or adjusting devices.

An arrangement for a valve is known from EP 0 477 400, in which the deflection of a piezoelectric actuator is transmitted via a hydraulic chamber to an actuator to be controlled. In this known arrangement, the hydraulic chamber works as a so-called hydraulic ratio. The hydraulic chamber encloses a common compensation volume between two pistons delimiting it, of which one piston is designed with a smaller diameter and is connected to a valve member to be actuated and the other piston is designed with a larger diameter and is connected to the piezoelectric actuator. The valve member, the pistons and the piezoelectric actuator lie one behind the other on a common axis.

The hydraulic chamber is clamped between the two pistons in such a way that the actuating piston of the valve member, which is held in its rest position by means of one or more springs relative to a predetermined position, makes a stroke increased by the ratio of the piston diameter when the larger piston is moved by the piezoelectric Actuator is moved by a certain distance. The compensating volume of the hydraulic chamber enables tolerances due to temperature gradients in the component or different temperature expansion coefficients of the materials used, as well as possible Setting effects can be compensated for without a change in the position of the valve element to be controlled thereby occurring.

However, the use of such a drive element in a drive unit of a high-pressure fuel pump is problematic due to the complex construction and with regard to the leakage losses that occur and the necessary refilling of the hydraulic chamber.

The object of the invention is to create a high-pressure pump for supplying high-pressure fuel to injection systems of internal combustion engines, in which, in particular, the drive unit is realized with a low mechanical load and with a simple structural design with as few components as possible and requiring little space.

Advantages of the invention

The high-pressure pump according to the invention for supplying high-pressure fuel in injection systems of internal combustion engines with the characterizing features of patent claim 1 has the advantage that the mechanical loading of the pump elements is kept low by the hydraulic translation, a high reaction speed being ensured by the control with a piezoelectric unit.

In a very advantageous embodiment of the invention it can be provided that the piezoelectric unit is arranged at right angles to the axial direction of movement of the valve member with respect to its direction of action, and can be acted upon with electrical current such that the piezoelectric unit exerts a tilting movement on the actuator serving as a lever arm, which is in operative connection with the valve member. In addition to a simple actuation of the valve member by the actuator, there is the advantage that an integrated tolerance compensation for temperature-related elongation tolerances of the piezoelectric unit is realized without an additional tolerance compensation element.

In such an embodiment of the high-pressure pump according to the invention, the actuator serving as a lever arm is connected to the piezoelectric unit in such a way that when only one piezoelectric actuator is electrically acted upon, the resulting elongation causes the actuator to be tilted with respect to its longitudinal direction. Depending on the tilting direction of the actuator, the valve member interacting with it is moved in its bore. The valve member thus executes a lifting movement, as a result of which the valve is brought into the closed or open position.

Due to temperature changes, the two piezoelectric actuators expand approximately the same, so that the actuator advantageously does not bring about any lifting movement of the valve member. Thus, temperature-related elongation tolerances in particular have no influence on the control of the valve member. In an embodiment of the invention of this type, it is particularly advantageous if two valve devices, each with a valve member, are provided, the valve members being arranged symmetrically with respect to one another and driving mutually actuated and reciprocally actuated pump pistons. Both pump pistons can be controlled with a single piezoelectric unit and its actuator, whereby the number of components and the design effort can be significantly reduced, since there is no need for two separate actuators, which are to be electrically synchronized accordingly. In addition, the electrical power for the overall system is advantageously halved.

In this embodiment of the invention in the manner of a two-pump ram system with high-frequency control by the piezoelectric unit, the pump pistons can be actuated alternately in such a way that permanent delivery takes place without dead time. In this way, pressure overshoots in the area of the high-pressure delivery line are avoided and high-quality smoothing of the applied high pressure is achieved.

Further advantages and advantageous embodiments of the subject matter of the invention are the description of

Drawing and the other claims can be found.

drawing An exemplary embodiment of the high-pressure pump according to the invention is shown in the drawing and is explained in more detail in the following description.

The single figure of the drawing shows a highly schematic, partial representation of an embodiment of the invention in a common rail injection system in partial section.

Description of the embodiment

The exemplary embodiment shown in the drawing shows in simplified form a high-pressure pump 1 for supplying high-pressure fuel in a common-rail injection system with a high-pressure storage space 2, the high-pressure pump 1 and a housing 3 of the high-pressure storage space 2 forming a structural unit.

The high-pressure pump 1 has a drive unit 4 for two hydraulically translated pump pistons 5, 6, each of which is axially displaceably guided in a simple manner in a cylinder space 7 or 8, which is in each case incorporated directly into a divided pump housing 9. The pump pistons 5, 6 each delimit a pump working space 12, 13 with their end face 10, 11 facing away from the drive unit 4.

The pump work chamber 12 or 13 is alternating with a fuel-filled low pressure chamber 14 which is only shown schematically and with a high pressure delivery line 15 or

16 connectable, the respective high-pressure delivery line 15, 16 opens into the high-pressure storage space (common rail) 2, from which in turn discharge injection lines to injection valves (not shown) which project into the combustion chamber of the internal combustion engine to be supplied.

A pressure valve 17, 18, which opens in the direction of the high-pressure storage chamber 2, is used in each high-pressure delivery line 15, 16, which in the present exemplary embodiment is designed as a check valve with a spherical valve member 19, 20. This valve ball 19, 20 is held on a conical valve seat via a valve spring 21, 22, the valve spring 21, 22 being supported on a counter-stop 23, 24 in the pump housing 9.

In a similar design, a filling valve 27, 28 is arranged in a respective fuel line 25, 26 between the low-pressure chamber 14 and the pump work chamber 12 or 13, in which a valve ball 29, 30 in the direction of the pump work chamber 12, 13 against the force of a valve spring 31, 32 opens.

The pump pistons 5, 6, which are designed in a stepped manner with a larger pressure meter in the direction of the drive unit 4 and a smaller diameter in relation to the pump work chamber 12 or 13, are pressurized against a pressure in a drive-side pressure chamber 33, 34 of the cylinder chamber 7 or 8 Spring 35, 36 displaced in the direction of the pump work chamber 12 or 13, the fuel therein being compressed. The T drive unit 4 has two valve devices 37, 38, in each of which a valve member 43, 44 is displaceably arranged in a bore 39, 40 of a valve body 41, 42. The valve bodies 41, 42 are components of the pump housing 9 in the embodiment shown.

The valve members 43, 44 each cooperate with a seat 45, 46 formed on the valve body 41, 42 for opening and closing a pressure medium supply line 47, 48 which is connected to a feed pump 49 and is provided for pressurizing the pump piston 5 or 6 is. The valve members 43, 44 are each designed as a force-balanced 3/2 valve spool, both of which can be actuated by a single actuator 50 of a piezoelectric unit 51. In your

Bore 39 and 40, the symmetrically arranged valve members 43, 44 are displaceable between the actuator 50 of the piezoelectric unit 51 and a respective spring device 52, 53, the bore 39, 40 in the area of the actuating element 50 each being designed as a fluid chamber 54, 55 is. This fluid chamber 54, 55 each has an opening 56, 57 to the drive-side pressure chamber 33, 34, which from the valve member 43 or 44 in its connection between the pressure medium supply line 47, 48 and the pressure chamber 33, 34 of the pump piston 5, 6 releasing open position is at least approximately closable.

The valve member 43, 44 is each formed with a valve head 58, 59, which is in an expanded area. 60, 61 of the bore 39, 40 of the valve member 43, 44 is arranged, the expanded region 60, 61 being connected to the pressure chamber 33, 34 of the associated pump piston 5 or 6 via a pressure medium line 62, 63. In the area between the fluid chamber 54 and 55 and the area 60, 61 enlarged for the valve head 58, 59, the bore 39, 40 has the same diameter as in an area facing away from the actuator 50 between the pressure medium supply line 47, 48 and the spring device 52, 53 on.

The piezoelectric unit 51 is in terms of its

Effective direction essentially at right angles to the axial direction of movement of the valve members 43, 44 and can be acted upon with electric current such that the actuator 50 serving as a lever arm, which is in operative connection with the valve members 43, 44, exerts a tilting movement. In the embodiment shown, the piezoelectric unit 51 is essentially arranged in a recess 64 in the pump housing 9, but in an alternative embodiment the piezoelectric unit 51 can also be accommodated in a separate housing.

The piezoelectric unit 51 has two piezoelectric actuators 65, 66 arranged parallel to one another, which are arranged approximately at right angles to the direction of movement of the valve members 43, 44 in a piezo chamber 67. Of course, the number of piezoelectric actuators used can also easily deviate.

The piezoelectric actuators 65, 66 have a common piezo head 68, via which they are connected to the actuator 50. They are at their opposite ends Piezoelectric actuators 65, 66 on a support-like piezo foot 69, which has contacts 70 for the power supply of the piezoelectric actuators 65, 66.

In order to achieve the greatest possible stroke, the piezoelectric actuators 65, 66 are constructed in a known “multilayer” design from a plurality of thin layers lying parallel to one another. So that these layers do not separate from one another when the piezoelectric actuators 65, 66 are energized, these must be preloaded, whereby the force to be applied can be approximately 1000 N.

For this purpose, the piezoelectric actuators 65, 66 arranged between the piezo head 68 and the piezo foot 69 are pressed together by means of a pretensioning element 71, which in the embodiment shown represents a tension band. Alternatively, of course, other hydraulic, mechanical or similar prestressing elements can also be used.

Between the bore 39 and 40 of the valve members 43, 44 and the piezoelectric actuators 65, 66, a sealing device 72 is provided, which is designed as a membrane in the drawing. The sealing device 72 is intended to prevent fuel from coming into contact with the piezoelectric actuators 65, 66.

The high pressure pump 1 shown in the drawing operates in the manner described below. First of all, fuel is conveyed from the low-pressure chamber 14, which is preferably a fuel storage tank, via the fuel lines 25, 26 and the filling valves 27, 28 into the pump working chambers 12, 13 by means of a pre-delivery pump, not shown

Filling valves 27, 28 work as suction valves. By mutual energization of the piezoelectric actuators 65, 66 of the piezoelectric unit 51, the pump pistons 5, 6, which are arranged parallel to one another, are alternately shifted up and down. During the upward suction stroke movement of the pump pistons 5, 6, a negative pressure is created in the respective pump working chamber 12 or 13, so that the fuel pressure present at the valve ball 29 or 30 of the filling valve 27 or 28 working as a suction valve is sufficient, the valve member from the valve seat to lift off and thus to release the fuel passage cross section in the pump work space 12 or 13.

After passing through an upper dead center, the respective pump piston 5, 6 is then displaced in the opposite direction against a lower dead center, this pump piston stroke movement corresponding to the delivery stroke. The fuel in the pump work chamber 12, 13 is compressed to a very high fuel pressure of up to 2000 bar and thereby opens the pressure valve 17 or 18 arranged in the high-pressure delivery line 15 or 16, so that the fuel under high pressure is at high pressure - Storage space 2 can flow out.

After passing through the bottom dead center of the pump piston movement, the pump piston 5 or 6 moves up again shifted, the pressure in the respective pump work space 12, 13 drops below a certain opening pressure and the associated pressure valve 17, 18 closes again.

In order to bring about a pump piston movement, the pressure chamber 33, 34 of the cylinder spaces 7, 8 of the pump pistons 5, 6 on the drive side is pressurized or relieved. The actuator 50 of the piezoelectric unit 51 actuates the valve members 43, 44 alternately such that one of the valve members 43, 44 is in the open position and thereby releases a pressure medium flow from the pressure medium supply line 47, 48 into the pressure chamber 33, 34 and one Venting to the fluid chamber 54, 55 in the area of the actuator 50 closes at least approximately. The valve member 43 or 44 of the other valve device 37 or 38 is in the flow position.

In order to achieve permanent delivery without dead times, the valve members 43, 44 are actuated alternately at high frequency by the actuator 50 of the piezoelectric unit 51. The piezoelectric actuators 65, 66 arranged parallel to one another are alternately acted upon by electric current in such a way that the piezoelectric actuators 65, 66 experience an abrupt expansion transversely to the direction of movement of the valve members 43, 44, the piezoelectric actuators 65, 66 opening up support the piezo foot 69. Elongation of one of the actuators 65, 66 causes the actuator 50 to operate like a rocker arm, the actuator 50 being tilted such that it displaces the valve members 43, 44 in the bore 39, 40 receiving them. In the figure, a state is shown in which the piezoelectric actuator 66 is energized. As a result of its elongation, the piezo head 68 is tilted and the actuator 50 transmits this tilting movement to the valve member 43, which is displaced in / against its seat 45 and thus assumes a closed position. The valve member 44 is lifted from its seat 46 by the spring device 53, whereby a pressurization of the pressure chamber 34 of the pump piston 6 is possible, which is displaced against its bottom dead center.

The piezoelectric actuators 65, 66 arranged transversely to the direction of movement of the valve members 43, 44 are both stretched or shrunk evenly in the event of temperature-related changes in length, so that the actuator 50 does not perform a tilting movement in the event of temperature fluctuations. By arranging the actuator 50 in the holes 39, 40 forming a spatial unit transversely to the direction of movement of the valve members 43, 44, it is sufficient to realize the tolerance compensation that the actuator 50 has sufficient axial freedom of movement, which may be due to an additional groove can still be enlarged in the pump housing 9.

This advantageously also ensures that the temperature-related changes in length of the piezoelectric actuators 65, 66 have no effects on the position of the valve members 43, 44 and thus the pump pistons 5, 6 and the fuel delivery into the high-pressure storage space 2.

Claims

Expectations 1. High-pressure pump (1) for supplying high-pressure fuel in injection systems of internal combustion engines with a drive unit (4) for at least one pump piston (5, 6) which is arranged in a cylinder space (7, 8) and which is axially displaceable in the cylinder space (7, 8) is guided and with its end face (10, 11) facing away from the drive unit (4) delimits a pump work chamber (12, 13) which can be connected to a fuel-filled low pressure chamber (14) and to a high-pressure delivery line (15, 16) characterized in that the drive unit (4) has at least one valve device (37, 38) with a valve member (43, 44) which is axially displaceable in a bore (39, 40) of a valve body (41, 42) and which is connected to the valve body ( 41, 4.2) trained seat (45, 46) for opening and closing a pressure medium supply line (47, 48), which is provided to act on the hydraulically translated pump piston (5, 6), the valve The link (43, 44) can be actuated by means of an actuator (50) of a piezoelectric unit (51). 2. High-pressure pump according to claim 1, characterized in that the valve member (43, 44) is designed as a force-balanced 3/2 valve spool, which between the actuator (50) of the piezoelectric unit (51) and a spring device (52, 53) is movable. 3. High pressure pump according to claim 1 or 2, characterized in that the bore (39, 40) of the valve body (41, 42) in the region of the actuating element (50) as one Fluid chamber (54, 55) is formed, which has an opening (56, 57) to a drive-side pressure chamber (33, 34) of the pump piston (5, 6), which in its connection between the valve member (43, 44) Pressure medium supply line (47, 48) and the pressure chamber (33, 34) of the pump piston (5, 6) opening position is at least approximately closable. 4. High-pressure pump according to one of claims 1 to 3, characterized in that the valve member (43, 44) as a valve closing member has a valve head (58, 59) which in an enlarged area (60, 61) of the bore (39, 40) of the valve body (41, 42), which is connected to the drive-side pressure chamber (33, 34) of the pump piston (5, 6) via a pressure medium line (62, 63). 5. High-pressure pump according to one of claims 1 to 4, characterized in that the piezoelectric unit (51) with respect to their direction of action substantially at right angles to the axial direction of movement of the valve member (43, 44) is arranged, and electrical current can be applied in such a way that the piezoelectric unit (51) exerts a tilting movement on the actuator (50) which acts as a lever arm and is operatively connected to the valve member (43, 44) , 6. High-pressure pump according to one of claims 1 to 5, characterized in that the piezoelectric unit (51) has at least two piezoelectric actuators (65, 66) arranged parallel to one another, the piezoelectric actuators (65, 66) alternating with electrical current are acted upon. 7. High-pressure pump according to one of claims 1 to 6, characterized in that the actuator (50) simultaneously as Tolerance compensation element for compensating changes in length of the piezoelectric unit (51) transverse to: direction of movement of the valve member (43, 44) is provided. 8. High-pressure pump according to one of claims 6 or 7, characterized in that a first end of the actuator (50) cooperates with the valve member (43, 44) and a second end of the actuator (50) with a piezo head (68) of the piezoelectric actuators (65, 66) is connected. 9. High-pressure pump according to one of claims 6 to 8, characterized in that the piezoelectric actuators (65, 66) are held between the actuator (50) and a piezo foot (69), and that one with the piezo head (68) and the biasing element (71) connected to the piezo foot (69) is provided for the piezoelectric actuators (65, 66). 10. High-pressure pump according to claim 9, characterized in that the biasing element (71) is designed as a tension band. 11. High-pressure pump according to one of claims 1 to 10, characterized in that a sealing device (72) between the bore (39, 40) of the valve body (41, 42) and the piezoelectric unit (51) is provided. 12. High-pressure pump according to one of claims 1 to 11, characterized in that two valve devices (37, 38) are provided, each with a valve member (43, 44), the valve members (43, 44) being arranged symmetrically to one another and arranged parallel to one another and actuate reciprocally actuated pump pistons (5, 6). 13. High-pressure pump according to claim 12, characterized in that the actuator (50) of the piezoelectric unit (51) is operatively connected to both valve members (43, 44) such that when the piezoelectric unit (51) is energized alternately, the valve member (43, 44) of one of the valve devices (37, 38) in the open position and the valve member (43, 44) of the other valve device (37, 38) is in the closed position. 14. High-pressure pump according to one of claims 1 to 13, characterized in that the valve body (41, 42) is part of a pump housing (9). 15. High-pressure pump according to one of / claims 1 to 14, characterized by its use as part of a common rail injection system, the high-pressure pump (1) forming a structural unit with a housing (3) of a high-pressure storage space (2).