Patent Application
20050103310
Both pressure-controlled and stroke-controlled injection systems can be used to supply fuel to combustion chambers of autoignition internal combustion engines. In addition to unit injectors and unit pumps, accumulator injection systems are also used as fuel injection systems. Accumulator (common rail) injection systems advantageously make it possible to adapt the injection pressure to the load and speed of the engine. Achieving high specific outputs and reducing emissions of the autoignition engine generally require the highest injection pressure possible.
For strength reasons, the achievable pressure level in accumulator injection systems currently in use is limited to approximately 1600 bar at this time. Pressure boosters are employed to further increase the pressure in accumulator injection systems.
EP 0 562 046 B1 has disclosed an actuator/valve apparatus with damping for an electronically controlled injection unit. The actuator/valve apparatus for a hydraulic unit has an electrically excitable electromagnet with a fixed stator and a moving armature. The armature has a first and second surface. The first and second surface of the armature delimit a first and second cavity, the first surface of the armature being oriented toward the stator. A valve is provided, which is connected to the armature. The valve is in a position to convey a hydraulic actuation fluid from a sump to the injection device. A damping fluid can either be collected in one of the cavities of the electromagnet device or drained from it. A region of a valve that protrudes into a central bore can selectively open and close the flow connection of the damping fluid in proportion to its viscosity.
DE 101 23 910.6 relates to a fuel injection apparatus used in an internal combustion engine. Fuel injectors supply fuel to the combustion chambers of the engine. The fuel injectors are acted on by means of a high-pressure source; the fuel injection according to DE 101 23 910.6 also includes a pressure booster that has a moving pressure booster piston, which divides a chamber that can be connected to the high-pressure source from a high-pressure chamber connected to the fuel injector. The fuel pressure in the high-pressure chamber can be varied by filling a return chamber of the pressure booster with fuel or by emptying fuel from this return chamber.
The fuel injector has a moving closing piston for opening and closing the injection openings that are oriented toward the combustion chamber. The closing piston protrudes into a closing pressure chamber so that it can be acted on with fuel pressure. This generates a force that acts on the closing piston in the closing direction. The closing pressure chamber and an additional chamber constitute a common working chamber; all of the partial regions of the working chamber are permanently connected to each other to permit the exchange of fuel.
With this design, triggering the pressure booster via the return chamber makes it possible to keep the triggering losses in the high-pressure fuel system low in comparison to a triggering by means of a working chamber that is intermittently connected to the high-pressure fuel shaft. In addition, the high-pressure chamber can only be pressure-relieved down to the pressure level of the high-pressure accumulator and not down to the leakage pressure level. On the one hand, this improves the hydraulic efficiency and on the other hand, permits a more rapid pressure increase up to the system pressure level so that the time intervals between injection phases can be reduced.
Pressure-controlled common rail injection systems with pressure boosters have the problem of not assuring the stability of the injection quantities to be injected into the combustion chamber, in particular the production of very small injection quantities of the kind required in preinjections. This is primarily due to the fact that the nozzle needle opens very quickly in pressure-controlled injection systems. As a result, very small variations in the triggering duration of the control valve can have powerful effects on the fuel quantity. Attempts have been made to remedy this problem by providing a separate needle stroke damper piston that delimits a damping chamber and must be guided in a high-pressure-tight clearance fit. This design does in fact permit a reduction of the needle opening speed, but on the other hand, it sharply increases the structural complexity and therefore the costs of the injection system.
In view of the ever-increasing standards regarding emissions and noise generation in autoignition internal combustion engines, further steps must be taken in the injection system in order to meet the stricter limit values to be expected in the near future.
In order to achieve the most flexible injection possible, systems with two solenoid valves have been developed. But since using two solenoid valves is complex and expensive, it would be desirable to use only one solenoid valve per injector/pressure booster combination. So far, a system of this kind has been controlled by means of a 3/2-way valve in order to produce multiple injections. These valves are complex in design and are difficult to manufacture with the required precision in series production because of the strict tolerances required.
The fuel injector with pressure booster proposed according to the invention makes it possible to execute multiple injections into the combustion chamber of an autoignition internal combustion engine by means of control sections provided on a pressure booster piston. These, in combination with a 2/2-way valve for actuating the pressure booster, i.e. in order to increase pressure in a compression chamber and relieve pressure in a control chamber, make it possible to execute multiple injections at a high pressure level. It is thus possible to eliminate the use of a 3/2-way valve, which is rather unsuited to the mass production of injector components, is difficult to produce within the required tolerances, and involves high costs.
Control sections on a rotationally symmetrical component such as a pressure booster piston can be produced inexpensively in terms of the precision requirements; moreover, the 2/2-way valve used in the pressure boosted fuel injector has a relatively simple design that is not susceptible to malfunction.
In order to produce extremely small preinjection quantities to be injected into the combustion chamber of the internal combustion engine during a preinjection phase, the control sections provided on the pressure booster piston can be embodied as very narrow in terms of their axial length, i.e. in the stroke direction of the pressure booster piston. The geometry of the control sections can be used to produce another preinjection phase that, depending on the design of the control sections, can be shorter or longer than a preceding first preinjection phase, for example. Instead of an additional preinjection phase that follows a first preinjection phase, a corresponding design of the control sections can also inexpensively achieve a longer main injection phase into the combustion chamber of the internal combustion engine.
The invention will be explained in detail below in conjunction with the drawing.
The sole FIGURE shows the hydraulic connection diagram of a fuel injector embodied according to the invention, in which the working chamber of a pressure booster connected upstream can be acted on with highly pressurized fuel by means of a high-pressure accumulator (common rail).
The FIGURE shows a device for injecting fuel, with a fuel injector that has a pressure booster connected upstream of it and can be actuated by means of a metering valve embodied in the form of a 2/2-way valve.
According to the hydraulic connection diagram of a fuel injector 1 shown in
A supply line 9 branches from the high-pressure accumulator 2 (common rail) and has an inlet 42 to a working chamber 10 of the pressure booster 5. In addition to the working chamber 10, the pressure booster 5 has a control chamber 11. The working chamber 10 of the pressure booster 5 is divided from the control chamber 11 of the pressure booster 5 by a piston 12, which in the embodiment variant according to
The second piston part 14 of the piston 12 inside the pressure booster 5 is acted on by a spring element 17 preferably embodied in the form of a coil spring, which is supported at one end against the bottom of the control chamber 11 of the pressure booster 5 and is supported at the other end against a spring stop 18 in the upper region of the first piston part 14. The pressure booster 5 also has a stop, e.g. embodied in the form of a support ring 16, for the upper end surface of the first piston part 13 of the piston 12.
The control chamber 11 of the pressure booster 5 communicates via a control line 26 with the metering valve 6 preferably embodied in the form of a 2/2-way valve; when it is switched from the closed position shown in
The hydraulic chamber 31 contains a spring element 33 embodied in the form of a coil spring that is supported at one end against the top of the hydraulic chamber 31 and is supported at the other end against the end surface 35 of the injection valve element 34. The nozzle chamber 28 encompassing the injection valve element 34 in the region of a pressure shoulder 38 has an inlet embodied in the form of an annular gap 26 extending from it in the direction of the needle tip 37. A seat of the injection valve element 34, which is disposed at the combustion chamber end, is provided at the needle tip 37 of the injection valve element 34. This seat at the needle tip 37 of the injection valve element 34, which is embodied for example in the form of a conical seat, opens and closes injection openings 39 that feed into a combustion chamber 7 of an autoignition internal combustion engine, which openings can be embodied as double rows of openings or as a single row of openings arranged in a circular pattern and serve to atomize the fuel as it enters the combustion chamber 7 of the autoignition internal combustion engine.
The line 9 communicates the pressure prevailing inside the high-pressure accumulator 2 to the working chamber 10 of the pressure booster. In the normal state of the fuel injector 1 according to the invention, i.e. the idle state, the metering valve 6 preferably embodied in the form of a 2/2-way valve is not actuated and no injection occurs. In this state, the pressure prevailing in the high-pressure accumulator 2 (common rail) and in the working chamber 10 of the pressure booster 5 communicates with the metering valve 6 via the working chamber 10, a throttle restriction 40 in the first piston part 13, the control chamber 11, and the control line 26. The pressure prevailing inside the high-pressure accumulator 2 also prevails in the control chamber 11 of the pressure booster 5 via the throttle restriction 40 in the first piston part 13. The pressure prevailing inside the high-pressure accumulator 2 is also communicated to the nozzle chamber 28 of the injector body 4 via the fuel inlet 27 and via a check valve 43 provided in the supply line 9; the hydraulic chamber 31 acting on the end surface 35 of the injection valve element 34 is supplied with the pressure prevailing in the high-pressure accumulator 2 via the supply line 9, the check valve 43, the inlet 29 to the compression chamber 15, and the line connection branching from it that contains the throttle restriction 30. The compression chamber 15 of the pressure booster is filled with highly pressurized fuel via the inlet 29 that branches off from the supply line 9 downstream of the check valve 43 in terms of the fuel flow direction.
In the normal state of the fuel injector proposed according to the invention, i.e. the idle state shown in
The rail pressure prevailing in the hydraulic chamber 31 in the nozzle body 4 exerts a hydraulic closing force on the end surface 35 of the injection valve element 34, which is preferably embodied in the form of a nozzle needle. In addition to this, a spring force acts on the end surface 35 of the injection valve element 34 in the closing direction, exerted by the spring element 33 embodied for example as a coil spring contained in the hydraulic chamber 31. Therefore the pressure prevailing inside the high-pressure accumulator 2 (rail pressure) can always be present in the nozzle chamber 28 encompassing the injection valve element 34 in the form of a ring in the region of a pressure shoulder 38, without the injection valve element 34 moving vertically into the hydraulic chamber 31 and thus unintentionally opening the injection openings 35 into the combustion chamber 7 of the autoignition internal combustion engine.
If the pressure booster 5 is triggered, then there is an increase in the pressure prevailing in the compression chamber 15, the nozzle chamber 28, and the hydraulic chamber 31 since the pressure prevailing in the control chamber 11 of the pressure booster 5 decreases because the triggering of the metering valve 6 connects the control line 26 to the low-pressure return 8 and the control volume contained in the control chamber 11 flows into this return 8. However, this does not lead to the opening of the injection valve element 34 inside the nozzle body 4, which valve element is preferably embodied as a nozzle needle, because the pressure difference between the nozzle chamber 28 and the hydraulic chamber 31 is not yet of sufficient magnitude. Only when there is an active pressure relief of the hydraulic chamber 31 does the injection valve element 34 open, i.e. its end surface 35 travels into the hydraulic chamber 31 in the upper region of the nozzle body 4 of the fuel injector 1.
In order to produce an active pressure relief of the hydraulic chamber 31 in the upper region of the nozzle body 4 of the fuel injector 1, control sections 19 and 21 are embodied at the end of the second piston part 14 of the piston 12 oriented toward the compression chamber 15 of the pressure booster 5. In the embodiment variant shown in
At the collar on the first piston part 14, the control section 19 is delimited by a control edge 20, whereas on the other side of the collar at the outer circumference of the first piston part 14, a second control edge 22 delimits the additional control section 21.
Instead of the two control sections 19 and 21 disposed one after the other in the stroke direction of the first piston part 14 shown in
The junction points 24 of the overflow line 41 to the control chamber 11 of the pressure booster 5 and the branching point 25 of the connecting line 32 that connects the compression chamber 15 to the hydraulic chamber 31 are disposed opposite each other in the compression chamber 15.
The active pressure relief of the hydraulic chamber 31 in the nozzle body 4 of the fuel injector is executed by means of an insertion movement of the first piston part 14 into the compression chamber 15. If the second piston part 14 has traveled a certain stroke distance, then the additional control section 21, which can be embodied as an annular groove, connects a cross section between the hydraulic chamber 31 and the connecting line 32 on the one hand and the overflow line 41 into the control chamber 11 and the control line 26 to the low-pressure return 8 on the other. As a result, depending on the axial length 21.1 of the additional control section 21, the hydraulic chamber 31 can be set to low pressure, thus decreasing the force acting on the end surface 35 of the injection valve element 34 so that the injection valve element 34 can no longer be held in its closed position. Because of the hydraulic force prevailing in the nozzle chamber 28 and acting on the pressure shoulder 38 of the injection valve element 34, the injection valve element 34 opens and unblocks the injection openings 39 feeding into the combustion chamber 7 of the autoignition internal combustion engine. From the beginning, the injection pressure is higher than the pressure prevailing inside the high-pressure accumulator 2 (rail pressure). A higher injection pressure favorably affects a reduction of the emissions of an autoignition internal combustion engine as well as the production of higher specific outputs. This permits the best possible conversion of the energy inherent in the fuel.
In order to be able to produce a small preinjection quantity in the context of a multiple injection, the hydraulic chamber 31 that acts on the end surface 35 of the injection valve element 34 cannot be connected to the low-pressure return 8 for too long. The desired preinjection quantity can be influenced by means of the axial length 21.1 of the additional control section 21. In the embodiment variant shown in
In order to terminate the injection event, the pressure in the nozzle chamber 28 is reduced to the pressure level prevailing in the high-pressure accumulator 2. To this end, the metering valve 6 preferably embodied in the form of a 2/2-way valve disconnects the control chamber 11 of the pressure booster 5 from the low-pressure return 8. As a result, the control chamber 11 is acted on by the pressure level prevailing in the high-pressure accumulator 2 (common rail), which effectively prevails from the working chamber 10 to the control chamber 11 of the pressure booster 5 via the throttle restriction 40 provided in the first piston part 13 of the piston 12. As a result, the rail pressure level builds up in the control chamber 11 of the pressure booster 5 since it is no longer connected to the low-pressure return 8 via the control line 26. In this state, the metering valve 6 preferably embodied in the form of a 2/2-way valve is moved into its closed position shown in
After the pressure balancing, the action of the return spring 17, which acts on a stop 18 on the second piston part 14, moves the piston 12 of the pressure booster 5 back into the starting position; the compression chamber 15 is filled with fuel again via the inlet line 29 branching from the supply line 9. The hydraulic chamber 31 is refilled with fuel via the supply line 9, which can contain a check valve 43 that damps pressure pulsations, via the inlet 29 to the compression chamber 15, and via the line that branches from it and contains the throttle restriction 30.
In order to stabilize switching sequences with the fuel injector with pressure booster 5 proposed according to the invention, additional steps can be taken in order to damp the oscillations between the high-pressure accumulator 2 (common rail) and the fuel injector 1. The check valve 43 can be disposed directly downstream of or at the junction point into the high-pressure accumulator 2. Instead of a check valve 43, a throttle element can also be provided there. When the pressure booster 5 is actuated, the check valve 43 or a throttle element provided in its place disconnects the high-pressure accumulator 2 from the compression chamber 15, from the lines 29 and 27, and from the nozzle chamber 28.
The embodiment proposed according to the invention combines a simply designed 2/2-way valve, which is embodied as a metering valve 6, with a pressure booster piston part that is provided with several control sections disposed one after another in the stroke direction of the piston part. On the one hand, this makes it possible to avoid using a complex, expensive-to-produce 3/2-way valve and on the other hand, permits the simple production of preinjection phases, main injection phases, and secondary injections in the context of a discharge rate curve shaping process. Furthermore, instead of using two solenoid valves, the design according to the invention makes it possible to use a single metering valve 6. The control sections 19 and 21 in the lower region of the second piston part 12 of the pressure booster 5 are easy to produce.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 29 412.7 | Jun 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE03/01097 | 4/3/2003 | WO |
