Unit fuel injector

Details Unit fuel injector Unit fuel injector

1999-08-02

2001-06-05

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Charge forming device

With fuel pump

C239S091000, C239S093000

Reexamination Certificate

active

06240905

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a unit fuel injector for delivering fuel to a combustion chamber of direct-injection internal combustion engines, having a pump unit for building up an injection pressure and for injecting the fuel via an injection nozzle into the combustion chamber. The invention further includes a control unit with a control valve that is embodied as an outward-opening A-valve, and a valve actuation unit for controlling the pressure buildup in the pump unit.
BACKGROUND OF THE INVENTION
In an injection system of this kind, the pump unit and the injection nozzle form a unit. One unit fuel injector (UFI) per engine cylinder is incorporated into the cylinder head and driven by an engine cam shaft either directly via a tappet or indirectly via tilt levers.
In the unit fuel injectors known from the prior art, the control units are as a rule embodied as magnet valves. The valve actuation unit is embodied as an electromagnet that actuates the control valve. The magnet valve is open in the unexcited state. This provides a free flow from the pump unit to the low-pressure region of the system and thus enables filling of the pump chamber during the intake stroke of the pump piston as well as a return flow of fuel during the pumping stroke. Triggering the magnet valve during the pumping stroke of the pump piston closes this bypass. This leads to a pressure buildup in the high-pressure region and, after the opening pressure of the injection nozzle is exceeded, to the injection of fuel to the combustion chamber of the engine. The closing time of the magnet valve thus determines the onset of injection, and the closing duration of the magnet valve determines the injection quantity.
The UFI is a time-controlled injection system; that is, a mechanical connection between the onset of injection and the cam shaft position is lacking. The injection onset must therefore be associated as precisely as possible with a certain engine piston position or crank shaft position. To that end, an engine control unit is supplied with information on the engine piston position or crank shaft position. The electromagnet of the magnet valve is triggered for controlling the injection events in accordance with the chronological order stored in memory in the engine control unit and in accordance with the information obtained.
The known UFIs with control units embodied as magnet valves have the disadvantage, however, that typically magnet valves have a very long response time. The reason is that the magnet armature of a magnet valve, because of its mass, cannot be accelerated arbitrarily fast, since mass inertia forces are acting on it. In addition, the magnetic field must first be built up to generate the attraction force. Magnet valves are moreover relatively large in size and have a relatively large number of individual parts which must be assembled into the magnet valves in production. This is time-consuming and labor-intensive and makes the magnet valves quite expensive.
OBJECT AND SUMMARY OF THE INVENTION
In view of the above disadvantages of the prior art, it becomes an object of the present invention to create a unit fuel injector with a control unit that is simple in structure, small in size, and in particular has a short response time.
To attain this object, the invention, taking the unit fuel injector of the type defined at the outset as the point of departure, proposes that the valve actuation unit be embodied as a piezoelectric actuator.
So-called A-valves close outward, counter to the flow direction. In contrast to this, so-called I-valves close inward, in the flow direction.
The piezoelectric actuator comprises a crystal, for instance of barium titanate (BaTiO
3
) or lead titanate (PbTiO
3
) which can be polarized by compressive or tensile strain. The polarization creates surface charges of different signs on opposed surfaces (this is known as the piezoelectric effect).
In the piezoelectric actuator, the so-called reciprocal piezoelectric effect is utilized. In crystals of the above type, by applying an electrical field, a change in length can be brought about as a function of the polarity and direction of the field.
This change in length is utilized to actuate the control valve.
Since a piezoelectric actuator has no moving parts and instead the change in length is based slowly on a shift in the crystal lattice structure, it has especially short response times. Furthermore, piezoelectric actuators are not subject to any wear and are economical to make. Piezoelectric actuators are thus especially well suited for actuating the control valve of a unit fuel injector.
In an advantageous refinement of the invention, the control unit has means for deflecting the expansion motion of the piezoelectric actuator into a differently oriented valve actuation motion. This has the advantage that the piezoelectric actuator can be positioned virtually arbitrarily with respect to the control valve triggered by it. This advantageously leads to greater freedom in designing the control units of the invention.
In another advantageous refinement of the unit fuel injector of the invention, it is proposed that the control unit has means for stepping up the expansion motion of the piezoelectric actuator to a greater valve actuation motion. This has the advantage that in the UFI of the invention, especially small-sized piezoelectric actuators can be used. The maximum change in length of a piezoelectric actuator is dependent on its external dimensions. Small piezoelectric actuators accordingly have a lesser change in length than larger actuators. To enable certain, reliable actuation of the control valve despite the lesser expansion motion of a small-size piezoelectric actuator, the means for stepping up the expansion motion to a greater valve actuation motion are employed. Stepping up the expansion motion of the piezoelectric actuator necessarily leads to a reduction in the force of the stepped-up valve actuation motion. The outer dimensions of the piezoelectric actuator and the step-up ratio must therefore be selected such that on the one hand the length and on the other the force of the valve actuation motion are sufficient to actuate the control valve in a certain and reliable way.
In still another refinement of the invention, it is proposed that the control unit has means that act as a thermal compensation element between the piezoelectric actuator and the control valve. The expansion coefficient of the piezoelectric actuator, which is typically a crystal, differs from that of the control valve, which is typically of metal. Because of the different temperature coefficients, in a control unit with a piezoelectric actuator rigidly joined to the control valve, temperature fluctuations can cause unintended actuation of the control valve. To compensate for the effects of the different temperature coefficients and to prevent unintended actuation of the control valve, a compensation element is provided between the piezoelectric actuator and the control valve.
Advantageously, the means for deflecting and/or the means for stepping up the expansion motion of the piezoelectric actuator and/or the means for compensating for the effects of the different temperature coefficients of the piezoelectric actuator and control valve are embodied as a hydraulic step-up arrangement. A hydraulic step-up arrangement on the one hand represents a sufficiently rigid connection between the piezoelectric actuator and the control valve. On the other, by the hydraulic step-up arrangement, the expansion motion of the piezoelectric actuator can be deflected into a differently oriented valve actuation motion. Furthermore, the expansion motion of the piezoelectric actuator can thereby be stepped up to a greater valve actuation motion. Finally, the hydraulic step-up arrangement also acts as a thermal compensation element between the piezoelectric actuator and the control valve.
The present invention also relates to a control unit with a control valve that is embodied as an outward-opening A-valve, and having a valve actuati

Affiliated with

Also associated with

Rating

Unit fuel injector does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Unit fuel injector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Unit fuel injector will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2446694