Fuel injector

Known fuel injectors have a valve housing in which an actuator and an hydraulic coupler are arranged, an electrical plug being provided on the valve housing for contact with a voltage source. The cables running from the plug to the actuator must be guided around the coupler to the actuator. It is disadvantageous that the compensating movements put heavy mechanical stress on the cables, so that a cable fracture as a result of material fatigue occurs after a predefined service life of the fuel injector, or that the solder or welding points of the cables tear. This leads to malfunctioning of the fuel injector. In the present fuel injector, the service life is increased by the provision of connections without cables. The earth pole of the actuator is electrically connected to the ground terminal of the plug in a cable-less manner, and the positive pole of the actuator is electrically connected to the positive terminal in a cable-less manner.

BACKGROUND INFORMATION

A fuel injector having a valve housing in which a piezoelectric armature and an hydraulic coupler are arranged has already been proposed in German Patent Application No. 103 60 449, the piezoelectric actuator having a positive pole and an earth pole, an electrical plug with a positive terminal and a ground terminal being provided on the valve housing for the contacting with a voltage source. Via a cable in each case, the positive pole of the piezoelectric actuator is connected to the positive terminal of the plug, and the earth pole of the piezoelectric actuator is connected to the ground terminal of the plug. Since the hydraulic coupler between the valve housing and the actuator is arranged in a section of the fuel injector that faces the plug, the cables originating from the plug must be guided around the coupler to reach the actuator. Due to the fact that the hydraulic coupler executes thermally caused compensating movements, the cables cannot be taut, but must be non-tensioned by providing additional length. The cables are not allowed to be in contact with adjacent components, since the many compensating movements may otherwise cause them to fray over time. It is disadvantageous that the compensating movements put heavy mechanical stress on the cables, so that a cable fracture as a result of material fatigue will occur after a predefined service life of the fuel injector, or the solder or welding points of the cables will tear. This leads to malfunctioning of the fuel injector.

SUMMARY OF THE INVENTION

The fuel injector according to the present invention has the advantage that an improvement is achieved in a simple manner to the effect that the service life of the fuel injector is increased in that the earth pole of the actuator is electrically connected to the ground terminal of the plug, and the positive pole of the actuator is connected to the positive terminal in a cable-less manner. This prevents malfunctioning of the fuel injector due to a cable fracture. Since two cables are omitted, space is saved, so that the fuel injector is able to have a smaller design.

It is particularly advantageous if the earth pole of the actuator is electrically connected to the ground terminal of the plug via the valve housing and/or an actuator housing, since this utilizes an already existing electrically conductive connection in the fuel injector. Furthermore, the ground contacting of the actuator reduces electromagnetic interference radiation of the actuator.

In addition, it is advantageous if the positive pole of the actuator is electrically connected to the positive terminal by way of the hydraulic coupler, since in this way the current supply to the actuator is implemented via an existing electrically conductive connection.

According to an advantageous further development, the actuator is prestressed for compression in an actuator sleeve between an actuator top and an actuator base, and the earth pole of the actuator is electrically contacted to the actuator top, the actuator top being electrically connected to the actuator base via the actuator sleeve. The actuator base is electrically connected to the valve housing and/or the actuator housing via a valve needle, a shoulder of the valve needle and a restoring spring cooperating with the valve needle.

Furthermore, it is advantageous if the positive terminal of the plug is electrically connected to a head part of the hydraulic coupler, and the positive pole of the actuator is electrically connected to a foot part of the hydraulic coupler, the head part and the foot part of the hydraulic coupler in turn being interconnected in an electrically conducting manner via an elastic sealing element. This allows the current to be supplied by way of the hydraulic coupler.

It is advantageous if a first electrical insulation is provided between the hydraulic coupler and the actuator, and a second electrical insulation is provided between the hydraulic coupler and the valve housing since this prevents a short circuit.

DETAILED DESCRIPTION

The fuel injector is used in the so-called direct injection, for instance, and injects fuel such as gasoline or diesel into a combustion chamber of an internal combustion engine.

The fuel injector has a valve housing1with an input port2for the fuel. The valve housing includes a housing component1.1in the shape of a cup, for instance, and a housing lid1.2sealing cup-shaped housing component1.1. Input port2is provided in housing lid1.2, for example.

A schematically illustrated actuator3such as a piezoelectric or magneto-restrictive actuator is arranged in valve housing1for the axial adjustment of a valve needle4.

Valve needle4is provided in valve housing1so as to be axially displaceable, and has, for instance, a needle shaft7facing actuator3, and a valve-closure member8facing away from actuator3. Actuator3transmits its movement to needle shaft7of valve needle4, which causes valve-closure member8cooperating with a valve seat9to open or close the fuel injector. The fuel injector is a so-called outwardly opening valve, for instance, valve needle4executing a lift in the direction of a combustion chamber10. When the fuel injector is closed, the entire circumference of valve-closure member8rests sealingly against valve seat9with line and surface contact, forming a sealing seat11.

Piezoelectric actuator3is made up of a multitude of piezo-ceramic layers, which expand in the axial direction when an electrical voltage is applied. In the process, the so-called inverse piezoelectric effect is utilized in which electrical energy is converted into mechanical energy. The expansion of the piezo-ceramic layers caused by the application of the electrical voltage is transmitted to valve needle4, valve needle4executing a lift of 40 to 50 micrometer, for instance. After the valve has been opened, actuator3shortens in response to the electrical voltage being switched off, and restoring spring14moves valve needle4back again in the direction of valve seat9, closing the fuel injector.

To protect piezoelectric actuator3from tensile and bending stresses, it is arranged in an actuator sleeve12between an actuator top (head)16and an actuator base17, actuator sleeve12being designed as so-called tube spring and made from a metal such as steel.

Actuator top16is arranged on a front-side end of actuator sleeve12facing away from valve needle4and integrally and/or frictionally connected to actuator sleeve12, for instance by welding. Actuator base17is disposed at a front-side end, facing valve needle4, of actuator sleeve12and likewise integrally and/or frictionally connected to actuator sleeve12, for instance by welding.

Needle shaft7of valve needle4has a shoulder18against which restoring spring14rests by one end so as to press needle shaft7of valve needle4against actuator base17of actuator sleeve12and to press valve-closure member8in the direction of valve seat9.

Since actuator3and the other components of the fuel injector such as valve housing1expand to different degrees in response to temperature changes because of different thermal expansion coefficients, an hydraulic coupler15is provided, which compensates for the differences in the various linear expansions in order to ensure that the fuel injector with valve needle4will always implement the same lift regardless of the individual temperature of the fuel injector. No lift losses at which the lift of actuator3is not fully transmitted to valve needle4must occur, so that the lift of valve needle4is smaller than the lift of actuator3.

Hydraulic coupler15includes a cup-shaped cylinder21, for example, and a piston22which is axially displaceable in cup-shaped cylinder21. A so-called coupler gap23is present between cup-shaped cylinder21and piston22. Starting from cup-shaped cylinder21, an elastic sealing element24, which is configured as convoluted bellows and made of metal, extends up to piston22. Elastic sealing element24encloses a coupler volume25, which is connected to coupler gap23via the fluid by way of a throttle element28. Coupler volume25and coupler gap23are filled with a fluid such as fuel or a second medium such as silicon oil, for instance. The pressure in the fluid of coupler volume25is increased with the aid of a spring element26, for example, in that spring element26exerts a pressure force on elastic sealing element24from the outside, or is provided within elastic sealing element24, for instance in piston22, and exerts a pressure force on the fluid of coupler volume25. For instance, piston22has a cavity which is connected to coupler gap23via throttle element28, and which is connected to the circumference of piston22via a flow opening.

In displacement processes acting rapidly on hydraulic coupler15, for instance the expansion of actuator3in response to an electrical voltage supply, hydraulic coupler15reacts as extremely rigid component since barely any fluid is able to flow out of coupler gap23through throttle element28into coupler volume25within the short period of time. Since coupler gap23thus remains constant in this situation, the lift of actuator3is transmitted to valve needle4in its entirety.

In displacement processes that act slowly on hydraulic coupler15, such as the expansion in response to temperature changes, coupler gap23becomes smaller or larger since the fluid has enough time to flow out of or into coupler gap23via throttle element28.

Cylinder21of hydraulic coupler15faces actuator3, for instance, and piston22of hydraulic coupler15faces housing lid1.1, or vice versa. The part of hydraulic coupler15facing housing lid1.1forms a head part29, and the part facing actuator3forms a foot part30of hydraulic coupler15.

Hydraulic coupler15, actuator3with actuator sleeve12, and valve needle4are arranged concentrically with respect to a valve axis27, for instance.

Actuator sleeve12and hydraulic coupler15are, for instance, centered and fixed relative to one another, for example with the aid of an extrusion coat36, which begins at actuator top16and extends to foot part30of hydraulic coupler15.

To encapsulate actuator3and hydraulic coupler15with respect to fuel, an actuator housing31which hermetically surrounds actuator3and hydraulic coupler15and seals them from the fuel, is provided in valve housing1. Actuator housing31has a cylindrical design, for example, and divides the interior space of valve housing1into a pressure chamber32loaded with fuel and connected to input port2via the fluid, and an actuator chamber having actuator3and hydraulic coupler15. Actuator housing31is arranged in valve housing1in a concentric manner, for example, and rests against valve housing1at the front-side ends. For example, on the front side facing housing lid1.2, actuator housing31is connected to housing lid1.2in an integral and/or non-positive manner, for instance by soldering. Starting from actuator base17, needle shaft7of valve needle4extends in actuator chamber33in the direction facing away from actuator3and projects through actuator housing31into pressure chamber32through an opening34; opening34is sealed by an elastic seal35, so that no fuel is able to travel from pressure chamber32into actuator chamber33. Seal35is designed as elastic convoluted bellows, for instance, which is made of metal, for example, and extends in an annular manner from needle shaft7to actuator housing31.

Restoring spring14rests against shoulder18of valve needle4via its one end, and against actuator housing31by its other end.

Actuator3has a positive pole38and an earth pole39, which is the electrical negative pole. Provided on valve housing1, for instance on housing lid1.2, is a two-pole electrical plug40, for example, which has a positive terminal41and a ground terminal42for the contacting with an external voltage source43. Depending on the setting of a high-power switch44, either a high voltage of voltage source43or no voltage is applied at plug40. High-power switch44is connected to a positive pole of voltage source43. Voltage source43is a transformer, for example, which, for instance, raises a 12V on-board voltage of a vehicle to a high voltage.

According to the present invention, earth pole (39) of actuator (3) is electrically connected to ground terminal (42) of plug (40) in a cable-less manner, and positive pole (38) of actuator (3) is electrically connected to positive terminal (41) of plug40in a cable-less manner. Because of the cable-free connection, cable breaks, which would lead to malfunctioning of the fuel injector, are prevented.

According to an advantageous embodiment, earth pole39of actuator3is electrically connected to ground terminal42of plug40via actuator housing31and/or valve housing1. This reduces the electromagnetic interference radiation of actuator3.

Positive pole38of actuator3is electrically contacted by positive terminal41via hydraulic coupler15, for instance. According to this circuit arrangement, the current is fed from plug40to actuator3via hydraulic coupler15.

For example, earth pole39of actuator3is in electrical contact with actuator top16, actuator top16being connected to actuator base17by way of actuator sleeve12. Actuator base17in turn is electrically connected to actuator housing31via needle shaft7of valve needle4, shoulder18of valve needle4and restoring spring14resting against shoulder18.

Positive terminal41of plug40is electrically connected to head part29of hydraulic coupler15, for instance, and positive pole38of actuator3to a foot part30of hydraulic coupler15.

Head part29and foot part30of hydraulic coupler15are connected to one another in an electrically conducting manner by way of elastic sealing element24.

Provided between hydraulic coupler15and actuator3is a first electrical insulation46, and provided between hydraulic coupler15and valve housing1is a second electrical insulation47so as to prevent a short circuit between positive pole38and earth pole39of actuator3or between positive terminal41and ground terminal42of plug40. Insulations46,47are in the shape of disks, for example, and made of ceramic or some other electrically insulating material.

Positive pole38of actuator3extends, for instance, through a through hole50in actuator top16and projects through first electrical insulation46through a first opening48so as to provide contacting with foot part30of hydraulic coupler15. Positive terminal41of plug40runs through a connecting duct51in housing lid1.2and projects through second electrical insulation47, for instance through a second opening49, so as to provide contacting with head part29of hydraulic coupler15.

Second insulation47may also be embodied as piezo-ceramic for analyzing the power profile of actuator3and utilizing it to regulate the injection.

In valve housing1, the fuel is guided from input port2into pressure chamber32to valve-closure member8upstream from sealing seat11. When the fuel injector is opened, valve-closure member8lifts off from sealing seat11, thereby opening a connection to combustion chamber10of the internal combustion engine, so that fuel is flowing into combustion chamber10by way of an annular discharge gap52formed between valve-closure member8and valve seat9. The greater the lift of valve needle4in the opening direction, the larger discharge gap52becomes and the more fuel will be injected into combustion chamber10per time unit.