Piezoelectric valve system

Details Piezoelectric valve system Piezoelectric valve system

2003-01-23

2004-04-13

Look, Edward K. (Department: 3754)

Valves and valve actuation

Electrically actuated valve

Having element dimensionally responsive to field

C310S368000, C239S524000

Reexamination Certificate

active

06719266

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to valve systems for controlling a flow of fluid through a fluid passageway and, more particularly, to a valve system having a valve actuated by a piezoelectric device to control the flow of fluid through the valve system.
BACKGROUND
Valve systems have been designed in the past having a valve actuated by a solenoid, piezoelectric stack or magnetorestrictive rod to control the flow of fluid through the valve system. The valve system may comprise a common rail fuel injector, electrohydraulic actuator system, electronically-controlled fuel injector, gasoline port injector, fluid metering valve, relief valve, reducing valve, direct valve or direct-injection gasoline injector by way of example.
However, in solenoid-controlled valve systems, it is often difficult to accurately control movement and positioning of the valve through the control signals applied to the solenoids. This is especially true when intermediate positioning of a solenoid-controlled valve between two opposite, fixed positions is desired. Solenoid-controlled valves, by their very nature, are susceptible to variability in their operation due to inductive delays, eddy currents, spring preloads, solenoid force characteristics and varying fluid flow forces. Each of these factors must be considered and accounted for in a solenoid-controlled valve system design. Moreover, the response time of solenoids limits the minimum possible dwell times between valve actuations and makes the valve system generally more susceptible to various sources of variability.
While solenoids provide large forces and have long strokes, solenoids do have certain drawbacks. For example, first, during actuation, current must be continuously supplied to the solenoid in order to maintain the solenoid in its energized position. Further, to overcome the inertia of the armature and provide faster response times, a solenoid is driven by a stepped current waveform. A very large current is initially provided to switch the solenoid; and after the solenoid has changed state, the drive current is stepped down to a minimum value required to hold the solenoid in that state. Thus, a relatively complex and high power current driver is required.
In addition to requiring a relatively complex and high current power source, the requirement of continuous current flow to maintain the solenoid at its energized position leads to heating of the solenoid. The existence of such a heat source, as well as the ability to properly dissipate the heat, is often of concern depending on the environment in which the solenoid is used.
Additionally, the force produced by a solenoid is dependent on the air gap between the armature and stator and is not easily controlled by the input signal. This makes the solenoid difficult to use as a proportional actuator. Large proportional solenoids are common, but they operate near or at the saturation point and are very inefficient. Small, relatively fast acting non-proportional solenoids may have response times defined by the armature displacement as fast as 350 microseconds. However, this response time can be a significant limitation in some applications that require high repetition valve actuation rates or closely spaced events. Further, it is known that there is a substantial delay between the start of the current signal and the start of the armature motion. This is due to the inductive delay between the voltage and magnetic flux required to exert force on the armature. In valve systems, such delays lead to variability.
Electroactive actuators such as piezoelectric stacks and magnetorestrictive rods eliminate the response time and proportionality shortcomings of the solenoid. The piezoelectric stacks, due to their capacitive behavior, offer the benefit of drawing no power during “hold in”, where actuation is maintained for a long period of time. However, these actuators have shortcomings of their own. Piezoelectric stacks and magnetorestrictive actuators possess impressive force, but have very small stoke capabilities. The output of these actuators must then be mechanically or hydraulically amplified, limiting the response time and proportionality benefits that they offer. Because of their small strain capabilities, these actuators also tend to be large. Additionally, these actuators are uni-directional, i.e., they move in only one direction in response to a control signal. Therefore, any valve or mass moved by the actuator requires a return biasing force, such as by a return spring, to be applied to return the valve or mass to its original position. Often, the spring comprises a significant amount of the force required to move the valve or mass and represents another source of variability. Also, the beneficial response time of the actuator will have no impact on the return of the valve or mass, as it depends completely on the return spring.
Thus, the present invention is directed to overcoming one or more of the problems set forth above.
SUMMARY OF THE INVENTION
While the invention is described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with one embodiment of the present invention, a valve system, such as a common rail fuel injector by way of example, includes a valve body and a fluid chamber disposed within the valve body. The fluid chamber is adapted to communicate with a fluid source for containing fluid therein. A fluid orifice communicates with the fluid chamber. A valve member mounted within the valve body is movable between a closed position for closing the fluid orifice and an open position for opening the fluid orifice. A pre-stressed bender actuator operatively engages the valve member and is operable to selectively move the valve member to at least one of the closed and open positions to close and open the fluid orifice.
In accordance with another embodiment of the present invention, a valve system, such as a common rail fuel injector by way of example, includes a valve body and a fluid chamber disposed within the valve body. The fluid chamber is adapted to communicate with a fluid source for containing fluid therein. A fluid orifice communicates with the fluid chamber. A control fluid chamber is disposed within the valve body and is adapted to communicate with a fluid source for containing fluid therein. The control fluid chamber is also adapted to selectively communicate with a drain for draining fluid from the control fluid chamber. A valve member is mounted within the valve body and is movable between a closed position for closing the fluid orifice and an open position for opening the fluid orifice. The valve member moves between the open and close positions in response to a difference in fluid pressure in the fluid chamber and in the control fluid chamber. A control valve member is mounted within the valve body and is operable to move between a closed position for containing fluid within the control fluid chamber and an open position for draining fluid from the control fluid chamber. A pre-stressed bender actuator operatively engages the control valve member and is operable to selectively move the control valve member to at least one of the closed and open positions.
In accordance with yet another embodiment of the present invention, an apparatus is provided for adjusting a preload of a piezoelectric device having first and second opposed surfaces and a peripheral edge extending therebetween. The apparatus includes a clamping device configured to engage the first and second opposed surfaces of the piezoelectric device proximate the peripheral edge thereof. The clamping device is operable to apply a variable clamping force to the piezoelectric device. A load device operatively engages the clamping device and is operable to vary the applied clamping force to adjust the preload of the piezoelectric device.
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