EP1379779A2

EP1379779A2 - Seat/sliding valve comprising a pressure compensation pin

Info

Publication number: EP1379779A2
Application number: EP02727211A
Authority: EP
Inventors: Nestor Rodriguez-Amaya; Achim Brenk; Wolfgang Klenk; Uwe Gordon; Manfred Mack; Hubert Greif
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-03-13
Filing date: 2002-03-12
Publication date: 2004-01-14
Also published as: US20030172978A1; US6837451B2; DE10111929A1; JP2004518875A; WO2002073028A3; WO2002073028A2

Abstract

The invention relates to a 3/2-directional control valve for controlling the injection of motor fuel in a common-rail-injection system in an internal combustion engine. Said valve has a first position wherein an injection nozzle is joined to a fuel return pipe, and a second position wherein the injection nozzle in connected to a high pressure fuel accumulator. The aim of the invention is to improve the function and the quality of the injection. As a result said 3/2-directional control valve comprises a force compensated control piston (44) whereby the control edge of the control piston (44) is pressure compensated by a pocket hole (50).

Description

Seat / slide valve m t pressure compensation pin

State of the art

The invention relates to a 3/2 way valve for controlling the injection of fuel in a common rail injection system of an internal combustion engine, with a control piston guided in a valve body, the control piston releasing a hydraulic connection between the injector and a fuel return in a first switching position and wherein the control piston releases a hydraulic connection between the injector and a high-pressure fuel accumulator in a second switching position.

Such a 3/2-way valve is known, for example, from DE 197 24 637 AI. In common-rail injection systems, a high-pressure pump supplies the fuel to the central high-pressure accumulator, which is referred to as a common rail. High-pressure lines lead from the rail to the individual injectors that are assigned to the engine cylinders. The injectors are individually controlled by the engine electronics. When the control valve opens, high-pressure fuel passes the nozzle needle, which is raised against the preload force of a nozzle spring, and into the combustion chamber. The object of the invention is to improve the function and the quality of the injection. In addition, the control valve according to the invention should be simple and inexpensive to manufacture.

The task is for a 3/2-way valve for controlling the injection of fuel in a common rail injection system of an internal combustion engine, with a control piston guided in a valve body, the control piston releasing a hydraulic connection between the injector and a fuel return in a first switching position , wherein the control piston in a second switching position releases a hydraulic connection between the injector and a high-pressure fuel accumulator according to the invention in that the control piston is force-balanced.

Advantages of the invention

Due to the complete or partial pressure equalization of the control piston, the smallest forces are sufficient for a control movement of the corresponding control piston, so that the control piston can be controlled directly. All valve surfaces that are in direct connection with the injection nozzle are designed so that they cannot exert any undesirable pressure surges on the control piston. The forces acting on the control pistons during operation come either from springs or from pressure surfaces that do not experience any force jumps or uncontrolled pressure changes during the movement phase of the control pistons. The size of the metering or discharge cross section can be of any size.

In a variant of the invention it is provided that the control piston has two guides with a larger guide diameter and a smaller guide diameter, and that the control piston has one with the smaller one Control diameter cooperating control edge that a blind hole is formed in the end of the control piston facing away from the control edge, that the blind hole can be pressurized via a bore, and that a throttle is provided in the bore. The pressure prevailing in the blind hole generates a force which acts in the closing direction of the control piston. This force ensures pressure equalization on the control piston after opening. The size of the force depends on the diameter of the blind hole. If the effective cross-sectional area of the blind hole corresponds to the ring area delimited by the larger guide diameter and the smaller guide diameter, the control piston is easily completely pressure-balanced.

In a further addition to the invention, an additional piston is guided in the blind hole, so that the leakage flow is reduced and the pressure equalization is accelerated.

In another embodiment of the invention, a circumferential groove is formed on the control piston, which is arranged in the assembled state of the 3/2-way valve in the region of at least one fuel return opening, so that the underside of the control piston remains unpressurized and there are pressure peaks on the control piston during the control can be avoided, which can have a favorable effect on the movement of the control piston, in particular in the opening and closing phase. The circumferential groove can also be subjected to any pressure from an external pressure source in order to specifically influence the movement of the control piston during operation. In addition, the circumferential groove reduces throttling, so that the pressure relief is accelerated.

A special embodiment of the invention is characterized in that the control piston has two guides has a larger guide diameter and a smaller guide diameter, and that the control piston has a valve seat edge, the diameter of which corresponds to the larger guide diameter. As a result, the spool is fully pressure balanced when opened. The control piston can be actuated, for example, by an energized magnet. When the solenoid is energized, only the spring preload force of the closing spring has to be overcome to lift the control piston.

A special embodiment of the invention is characterized in that the end face of a control piston is acted upon by the prestressing force of a compression spring. The pretensioning force of the compression spring ensures that the associated control piston is held in a switch position of the 3/2-way valve with its valve seat edge in contact with the associated valve seat surface.

Another special embodiment of the invention is characterized in that the control piston is actuated via a piezo actuator. The use of the piezo actuator enables faster switching times than with conventional valves.

3/2 way valve according to one of the preceding claims, characterized in that it is provided for use with an injection nozzle or a nozzle holder combination, so that the advantages of the 3/2-way valve according to the invention not only benefit common rail injection systems.

Further advantages, features and details of the invention result from the following description, in which various exemplary embodiments of the invention are described in detail with reference to the drawing are. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

Basically, the 3/2-way valves according to the invention can be made in one part or two parts. The control can take place directly via a solenoid valve or a piezo actuator or via a servo circuit. Exemplary embodiments of the possible combinations of these features are shown in FIGS. 2 to 5 and are described below. The other possible combinations, although not shown for reasons of clarity, are also part of the invention which is to be protected.

drawing

The drawing shows:

Figure 1 is a schematic representation of a common rail injection system, ^■

Figure 2 shows a first embodiment of a 3/2-way valve according to the invention with one-piece control piston, which is controlled directly via a solenoid valve, in longitudinal section;

Figure 3 shows a second embodiment of a 3/2 way valve according to the invention with one-piece control piston, which is controlled directly via a piezo actuator, in longitudinal section;

Figure 4 shows a particularly advantageous pressure relief of a 3/2 way valve according to the invention in longitudinal section and Figure 5 is an enlarged view of section VII in Figure 4.

Description of the embodiments

A common rail injection system is shown schematically in FIG. From a fuel tank 1 Kraf is made with the help of a pump unit 2 in one

High-pressure fuel reservoir 3 promoted and pressurized with high pressure. The fuel pressurized with high pressure is then allocated to the individual cylinders of the internal combustion engine to be supplied as required. The high-pressure fuel is injected by injectors 4, 5, 6 and 7. ■

For reasons of clarity, only the injector 7 is shown in FIG. The injector 7 is supplied with fuel via a metering valve 8. The metering valve 8 can be designed as an independent assembly, regardless of the selected embodiment. This makes it possible to place the valve anywhere between the high-pressure fuel reservoir 3 and an injector 7 or the like. to grow, whereby there is a free choice of line lengths between the high-pressure fuel reservoir 3 and metering valve 8 and between metering valve 8 and injector 7.

The metering valve 8 is a 3/2-way valve that is actuated electromagnetically. In the switch position shown in FIG. 1, the connection between the high-pressure fuel reservoir 3 and a high-pressure connection 10 of the injector 7 is interrupted. The high-pressure connection 10 of the injector 7 is connected to a fuel return 9 in the switching position of the metering valve 8 shown in FIG.

When the metering valve 8 is actuated, the second switching position, not shown in Figure 1, switched. In the second switching position, the high-pressure connection 10 of the injector 7 is connected directly to the high-pressure fuel reservoir 3. In this switching position, high-pressure fuel flows from the high-pressure fuel reservoir 3 via the high-pressure connection 10 into a pressure chamber 11 which is formed in the injector 7. When the pressure in the pressure chamber 11 exceeds a certain value, a nozzle needle 12, which is biased against a nozzle spring 13, lifts off its seat and high-pressure fuel is injected into the combustion chamber 14 of the internal combustion engine to be supplied.

The metering valve 8 can be designed as a so-called seat slide valve. In the case of a seat slide valve, one sealing surface is designed as a line seal and the other sealing surface is designed as a slide seal. The metering valve 8 can also be designed seat-seat valve with two valve seats.

In known seat-seat valves, it has been found in the context of the present invention that the load on the control piston with very high pressure forces is unfavorable. Even slight changes in the size of the pressure areas show strong influences on the speed of the control piston and thus also significant influences on the function of the 3/2-way valve.

FIG. 2 shows metering valve 8 designed as a seat / slide valve with only one control piston 44. The movement of the control piston 44 is controlled directly by an electromagnet. However, direct control of the movement of the control piston is only possible if the required magnetic forces can be kept within certain limits. For this purpose uss the Control piston 44 in the opening and closing phase be as completely pressure-balanced as possible.

In the switching position of the metering valve 8 shown in FIG. 2, a connection between a fuel inlet 40 and a connection 41 for the injector 7 (not shown) is interrupted. At the same time, a connection between the connection 41 and a fuel return 42 is opened. In the switching position shown in FIG. 2, the control piston 44 is pressed against its valve seat 46 by means of a compression spring 45. In this switching position, the pressure at the injector can be reduced via flats 48 in the opened slide seal, which are formed on the circumference of the control piston 44. A central blind hole 50 is recessed in the end of the control piston 44 facing the compression spring 45. The blind hole 50 is connected via a bore 51 to a longitudinal bore 49, in which the control piston 44 is received so as to be able to move back and forth. A piston 52 is received in the blind hole 50 so that it can be moved back and forth. The piston 52 is supported on the valve housing. A desired throttling effect can be set via the diameter of the bore 51, which leads to a time delay in the pressure equalization.

The control piston 44 has two guides. Since the diameter of the valve seat 46 corresponds to the upper diameter of the control piston 44, the control piston 44 is completely pressure-balanced when opened. When the solenoid valve is energized to raise the control piston 44, only the forces of the compression spring 45 have to be overcome. After lifting the control piston 44 and thus opening the valve seat 46, the valve fills with the fuel under high pressure via the fuel inlet 40. A pressure wave runs at the speed of sound through port 41 to the injector and injection begins.

Since the control piston 44 has two guides, it is no longer pressure-balanced after opening. Additional hydraulic forces act in the opening direction, which act on the resulting annular surface between the lower and upper guide of the control piston. These forces must be balanced, since they act against the compression spring 45 and prevent the control piston 44 from closing. The pressure equalization is made possible through the blind hole 50. The bore 51 ensures that the hydraulic pressure acts in the blind hole 50 and generates forces in the closing direction of the control piston 44. These forces depend on the diameter of the blind hole 50, the surface of the connecting bore 51 having to be subtracted. If the pressure area in the blind hole 50 is as large as the circular area between the upper and lower guide, then the control piston 44 is completely pressure-balanced. The diameter of the blind hole 50 can, however, also be larger than the pressure area on the control piston 44. As a result, additional forces can be generated which enable accelerated closing. However, the additional closing forces should remain so low that the balance of forces is not shifted too much.

The piston 52 guided in the blind hole 50 prevents fuel under pressure from flowing permanently from the compensation space into the leak oil return. The space of the blind hole 50 left free by the piston 52 is referred to as the compensation space. The volume of the compensation space is decisive for the time after which the pressure equalization takes place after opening the valve seat 46. With a large volume, the time to inflow and build up pressure is longer. As usually small pre-injection quantities are to be realized and after The volume should be kept as low as possible in the pre-injection to close the valve.

In the pressure-controlled common rail system shown in FIG. 1, fuel pressure is only present at the injector (not shown) when the injection is to be carried out.

A metering valve 8 is shown in FIG. 3, in which a control piston 56 is activated with the aid of a piezoceramic.

The metering valve shown in FIG. 3 comprises a valve body 53 in which a control piston 56, which is biased by a spring 64, is accommodated so that it can be moved back and forth. The control piston 56 can be moved back and forth between two positions via a hydraulic booster piston 60, which can be actuated via a piezo actuator. In the position of the control piston 56 shown in FIG. 3, a sealing seat 57 is closed. When the sealing seat 57 is closed, the connection between a fuel inlet 54 and a connection 55 for a connection to the injector (not shown) is interrupted. At the same time, a connection between the connection 55 and a fuel return 58 is opened. In this way, the injector (not shown) can be relieved of pressure as long as no injection takes place. When the control piston 56 lifts off its sealing seat 57, the connection between the connection 55 and the fuel return 58 is interrupted at the same time. In this second position, not shown in FIG. 3, of the control piston 56, fuel subjected to high pressure passes from the fuel inlet 54 via the connection 55 to the injector, from which the injection takes place.

During the opening movement of the control piston 56, a hydraulic medium contained in a coupling space 59, for example Fuel displaced by a booster piston 60. The translation piston 60 is actuated by a piezo actuator 69.

In the end of the control piston 56 facing away from the coupling space 59, a central blind hole 62 is recessed, in which a pressure compensation piston 61 is accommodated so that it can move back and forth. The pressure compensation piston 61 is supported on the housing by a screw plug. The blind hole 62 is connected to the interior of the valve body 53 via a bore 63.

The control piston 56 has two guides. Since the diameter of the high-pressure sealing seat 57 corresponds to the upper guide diameter of the control piston 56, the control piston 56 is pressure-balanced when opened and can therefore be opened with little force. When the control piston 56 is lifted off its sealing seat 57, additional forces act in the opening direction since the lower guide of the control piston 56 has a smaller diameter than the sealing seat 57. These additional forces act against the closing spring 64 of the control piston 56 and must be compensated for.

The pressure equalization required to compensate for the additional forces is made possible by the blind hole 62. When the control piston 56 is raised from its high-pressure sealing seat 57, there is a connection from the blind hole 62 via the bore 63 to the high pressure. The pressurization of the blind hole 62 generates forces in the closing direction of the control piston 56. The magnitude of the forces is determined by the cross-sectional area of the blind hole 62. If the pressure area of the blind hole 62 is as large as the circular area between the upper and lower control piston guide, then the control piston 56 is completely pressure-balanced and can by the forces of the Closing spring 64 can be easily closed. The diameter of the blind hole 62 can also be larger than the pressure area on the control piston 56. As a result, additional forces for accelerated closing of the control piston 56 can be generated. The pressure compensation piston 61 guided in the blind hole 62 prevents fuel from permanently flowing out of the pressure compensation space of the blind hole 62 into the fuel return.

The piezoceramic enables faster switching times than with conventional valves. The number of components used is also reduced. Another advantage is that the actuator unit can be made compact and short. Furthermore, the stroke curve of the piezo actuator can be regulated. By dispensing with a complex servo circuit, the manufacturing and testing effort is significantly reduced.

FIGS. 4 and 5 show a special form of pressure relief. This pressure relief can be used in all embodiments of the invention and is described below by way of example using a one-piece control piston.

In the embodiments of the invention shown in FIGS. 4 and 5, a valve housing 65 is equipped with a fuel inlet 66. In addition, a connection 67 to an injector (not shown) is provided in the valve housing 65. In addition, the valve housing 65 has a fuel return 68. In the valve housing 65, a control piston 70 is accommodated so that it can move back and forth.

As can best be seen in the partial enlargement of FIG. 5, a diameter widening 71 is formed on the control piston 70. The Diameter expansion 71 merges into a cylindrical / section 72 with a larger outer diameter. A circumferential groove 73 is formed in the cylindrical section 72 of the control piston 70 in the area of the fuel return 68. The relief stroke of the control piston 70 is designated 74.

Pressurization of the underside of the control piston 70 is avoided by the circumferential groove 73. Such pressurization would counteract the closing force of the control piston 70 and is therefore undesirable. Any pressure surges in the opening and closing phases could have an unfavorable effect on the movement of the control piston. In addition, throttles are avoided by the circumferential groove 73, so that a faster pressure relief is achieved. Due to the circumferential groove 73, the discharge quantity can be collected directly on the relief stroke and fed to the fuel return 68. As a result, the pressure on the rear side of the control piston 70 is decoupled from the pressure behind the relief stroke 74. This avoids pressure peaks on the control piston 70 during the shutdown.

By energizing a solenoid valve (not shown), the control space provided above the control piston 70 is relieved. The control piston 70 makes a stroke movement in this way and the connection between the fuel accumulator and the injection nozzle is established. The connection to the fuel return, which is still open until then, is interrupted by the further stroke movement, since the control edge on the control piston 70 dips into the valve housing 65.

The end of the injection is initiated by the energization of the solenoid valve, as a result of which the solenoid valve closes the flow restrictor. Thereby pressure builds up again in the control chamber through the inlet throttle in the control piston. This pressure pushes the control piston back into its seat. This opens the relief cross-section. The injection nozzle and pressure line are thus connected to the fuel return. The injection pressure drops quickly and the control piston closes.

Claims

Expectations

1. 3/2-way valve for controlling the injection of fuel in a common rail injection system of an internal combustion engine, with a control piston (44) guided in a housing (53), the control piston (44) in a first switching position having a hydraulic ' Releases connection between an injector (7) and a fuel return (42), the control piston (44) releasing a hydraulic connection between the injector (7) and a high-pressure fuel reservoir (3) in a second switching position, characterized in that the control piston (44, 70) is balanced.

2. 3/2-way valve according to claim 1, characterized in that the control piston (44, 70) has two guides with a larger guide diameter and a smaller guide diameter, that the control piston (44, 70) has a control edge cooperating with the smaller guide diameter that a blind hole (50, 62) is formed in the end of the control piston (44, 70) facing away from the control edge, that the blind hole (50, 62) can be pressurized via a bore (51), and that in the bore ( 51) a throttle is provided.

3. 3/2-way valve according to claim 2, characterized in that an additional piston (52) is guided in the blind hole (50, 62).

4. 3/2-way valve according to one of the preceding claims, characterized in that on the control piston

(70) a circumferential groove (73) is formed, which is arranged in the assembled state of the 3/2 way valve in the region of at least one fuel return opening (68).

5. 3/2-way valve according to one of the preceding claims, characterized in that the control piston

(44, 70) two guides with a larger one

Guide diameter and a smaller guide diameter that the control piston (44, 70) has a valve seat

(46), the diameter of which corresponds to the larger guide diameter.

6. 3/2-way valve according to one of the preceding claims, characterized in that the control piston

(44, 70) is biased by a closing spring (45).

7. 3/2-way valve according to one of the preceding claims, characterized in that the control piston

(44, 70) is actuated via a piezo actuator.

8. 3/2-way valve according to one of the preceding claims, characterized in that it is provided for use with an injection nozzle or a nozzle holder combination.