1. Field of the Invention
This invention relates generally to fluid injectors. More particularly, this invention relates to a proportional needle control fuel injector having a piezoelectric actuator and an actuator motion amplifying lever.
2. Description of Related Art
Accurate control of fuel injection rate shape requires accurate control of the injector needle valve motion. Highly accurate electronic control of an injector needle valve motion may be provided by using solid state actuators such as piezoelectric, electro-strictive, or magneto-strictive actuators to control the needle valve position. To provide a desired valve displacement, conventional solid state actuators require high values of applied current and/or voltage.
In an attempt to reduce the magnitude of the applied control current and/or voltage to the solid state actuators, and dimensions of the actuator, some fuel injectors include mechanical or hydraulic motion amplifiers. The use of a hydraulic amplifier requires that some fuel must be wasted to control the amplification. Hydraulic amplifier""s also allow undesirable oscillations of the controlled motion parts
A piezoelectric actuator stack is advantageous in that a piezoelectric actuator reacts approximately five to ten times faster than a solenoid controlled injector. Additionally, the amount of extension of the piezoelectric actuator is directly proportional to the amplitude of the control current/voltage, applied to the piezoelectric actuator. A proposed actuator with a lever system is also beneficial in that the injected fuel may be accurately controlled without the use of a spill valve circuit. Conventional spill valves maintain a desired pressure within a fuel injector by bleeding off fuel from the fuel passageway when the pressure within the fuel passageway exceeds a predetermined amount. The fuel that is spilled either returns to the fuel supply or is wasted. A spill valve circuit needle control system is inherently inefficient in that the energy that is used to pressurize the fuel is wasted when it is spilled from the fuel system. In addition to the energy expended in increasing the pressure of fuel, energy may also be expended in heating the fuel and this heat may also be lost in a spill valve circuit.
Solid state actuators provide such an accurate degree of needle positioning that variable geometry atomizing orifices may be effectively used. Variable geometry atomizing orifices enable high quality atomization for all operation conditions of the engine, and accurate control over the amount and rate of fuel being injected.
It is an object of the present invention to overcome the disadvantages of the prior art and to provide a proportional needle control injector that compensates for changes in fuel pressure.
It is another object of the present invention to provide a proportional needle control injector that compensates for changes in friction forces.
It is another object of the present invention to provide a proportional needle control injector that compensates for wearing.
It is yet another object of the present invention to provide a proportional needle control injector that compensates for manufacturing tolerances.
It is a further object of the present invention to provide a proportional needle control injector that improves injection rate shape control.
It is a still further object of the present invention to provide a proportional needle control injector with reduced requirements to control current and/or voltage.
It is still another object of the present invention to provide a proportional needle control injector that does not require a control flow.
It is yet another object of the present invention to provide a proportional needle control injector that saves deficit radial space.
It is another object of the present invention to provide a proportional needle control injector that is hydraulically compensated such that the amplitude of the control current/voltage to the actuator may be reduced and the strength of a spring biasing the needle valve closed may also be reduced.
These and other objects of the present invention are achieved by providing an injector body including an injection fuel inlet port, an injection fuel outlet port and a control fuel inlet port. The injector also includes a solid state actuator housed within the injector body, an actuator amplifying lever housed within the injector body and a needle valve housed within the injector body. The needle valve being moveable between a first position closing the injection fuel outlet port and a second position to open the injection fuel outlet port. The actuator amplifying lever is responsive to a dimensional change of the solid state actuator to permit movement of the needle valve from the first position to the second position. The distance between the first and second positions (needle valve travel/lift) is proportional to the applied voltage/current.
These and other objects of the present invention may also be achieved by providing a fuel injector having an injector body that includes an injection fuel inlet port and an injection fuel outlet port. The injector also includes within an injector body: a solid state actuator, an actuator amplifying lever, a control piston and a needle valve. The control piston is housed within a control fluid chamber within the injector body which is in fuel communication with the injection fuel inlet port and the injection fuel outlet port. The needle valve is moveable between a first position closing the injection fuel outlet port and a second position to open to injection fuel outlet port. The actuator amplifying lever is responsive to a dimensional change of the solid state actuator to permit movement of the needle valve from the first position to the second position.
These and other objects of the present invention may also be achieved by providing a fuel injector having an injector body that includes an injection fluid inlet port and an injection fluid outlet port. The injector body houses a solid state actuator, a needle valve, a biasing means and an actuator amplifying lever. The needle valve is moveable between a first position closing the injection fluid outlet port and a second position to open the injection fluid outlet port. The biasing means biases the needle valve toward the first position. The actuator amplifying lever is positioned between the biasing means and the needle valve and is responsive to a dimensional change of the solid state actuator to permit movement of the needle valve from the first position to the second position.
One exemplary embodiment of the present invention provides hydraulic compensation for clearances between the solid state actuator and the needle valve. This embodiment uses a fuel that compensates for wear and manufacturing tolerances.
In another exemplary embodiment of the present invention the amplitude of the required current and/or voltage for the solid state actuator may be reduced by using a separate control channel to control forces acting at the top of a control piston linked to a needle valve.
Yet another exemplary embodiment of the present invention may use a pusher pin to contact an amplifying lever and to minimize the size of the fuel injector.
An additional exemplary embodiment may include a mechanical amplifying lever for the solid state actuator that engages an integral needle valve and control piston.