Fluid sprinkling – spraying – and diffusing – Processes – Of fuel injection
Reexamination Certificate
2000-02-11
2001-11-20
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Of fuel injection
C239S533200, C239S533140, C239S533150, C239S397500, C251S011000, C251S129010, C251S129060, C137S338000
Reexamination Certificate
active
06318641
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a small package shape memory alloy actuator for a fuel injector.
BACKGROUND OF THE INVENTION
Certain metals commonly referred to as shape memory alloys exhibit characteristic material properties that make them desirable for use in actuators. Shape memory alloy actuation provides greater force per volume than electromagnetic-type actuation, and is also less complex. These characteristics make shape memory alloy actuation highly desirable for use in fuel injectors, particularly automotive fuel injectors.
Shape memory alloys (hereinafter “SMAs”) undergo a temperature-related phase change which is characterized by the memory of any mechanical configuration imposed on the material in its austenitic crystalline phase. In particular, SMAs have two different crystal structures that are determined by temperature. In its low temperature state the material exhibits a martensitic crystal structure which has a relatively low modulus of elasticity, and which can be easily deformed. However, when the alloy is heated above a temperature threshold, the transition temperature, its crystal structure changes to austenite and the alloy returns to its original configuration.
This temperature-dependent memory characteristic is exploited in actuators for fuel injectors by providing a bias mechanism, for example a spring, to deform the SMA element while it is in the low temperature state, then raising the SMA element's temperature, for example by resistance heating, in order to induce a return to the element's original configuration. The return to the SMA element's original conformation thereby creates motion in the spring, which in conjunction with the remainder of the actuator assembly results in opening or closing of the fuel injector valve. Cooling of the SMA element returns the element to its low temperature, easily deformed phase. The bias spring force results in mechanical motion in the actuator which closes or opens the fuel injector valve. A major challenge in the use of SMAs in automotive fuel injectors has been to reduce the response time of the alloy so that the opening or closing cycle of the actuator is reduced to one millisecond or less. This fast response time is required in order to provide the necessary minimum flow control necessary under light load engine conditions.
It is known in the art that the response time is affected by the rate of heat transfer (i.e., cooling) of the SMA element, and that the geometry of the alloy element has a direct affect on this heat transfer rate. SMA actuator geometries comprising small-diameter wires, ribbons, or thin films, for example, have been shown to maximize the heat transfer rate of the alloy, thereby achieving faster response times. Such geometries have been described in U.S. Pat. No. 4,806,815 to Homma; U.S. Pat. No. 4,973,024 to Homma; U.S. Pat. No. 5,061,914 to Busch, et al.; U.S. Pat. No. 5,211,371 to Coffee; and U.S. Pat. No. 5,325,880 to Johnson et al. The width-to-thickness ratios disclosed in the prior art are in the range from 50:1 to 4:1, and resulted in best minimum response times of about 10 milliseconds. However, none of these geometries yield the requisite degree of heat transfer effective to provide response times at the 1 millisecond level required for fuel injector applications.
It is further known in the art that the response time is affected by the energy input (e.g., resistance heating) into the SMA element. Ordinarily, a high energy input into the SMA element is desirable, in order to decrease the response time. This energy input has an inherent limitation, however, due to the nature of the materials suitable for shape memory alloys. An “over-temperature” condition results in strain recovery loss or destruction of the alloy. The response time of SMA actuators in the prior art have accordingly been limited in the amount of input power which may be applied to the SMA elements, and again, are limited to response times of no less than 10 milliseconds.
A further major challenge in the use of SMAs in automotive fuel injectors has been to reduce the response time of the alloy to submillisecond levels while at the same time reducing the cost of overall production.
There thus remains a need in the art for economical methods and apparatus for controlling the operating conditions of shape memory alloy actuators for fuel injectors so as to provide response times of less than 10 milliseconds, and preferably less than about 1 millisecond.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the method and apparatus of the present invention, wherein the response time of an SMA actuator assembly for a fuel injector is decreased to less than 10, and even to less than about 1 millisecond by forced, convective heat transfer from the SMA element or elements. The forced, convective heat transfer is provided by the circulation of fluid across the SMA element by a metering orifice plate and housing design, which direct a fluid flow across the SMA element so as to maximize the area of contact between the fuel and the SMA element regardless of whether the fuel injection valve is opened or closed. Use of forced, convective heat transfer in accordance with the present invention allows greater power input levels than previously possible without resulting in an over-temperature condition of the SMA alloy.
In another embodiment of the present invention, the response time of the actuator is adjusted or optimized by controlling at least one of the convective heat transfer coefficient, the fluid flow path across the actuator, the fluid flow rate across the actuator, the thickness of the thermal boundary layer adjacent to the SMA element, the maximum temperature reached by the SMA element, the ambient temperature of the fluid, the circulation rate of the fluid, and the temperature difference between the actuator and the ambient fluid.
In still another embodiment of the present invention, the minimum lift of the valve is adjusted so that any variation above this minimum has no significant effect on the flow rate of fluid through the valve, and the input power into the SMA element is controlled in order to maintain consistent maximum material temperature, thereby maintaining relatively consistent reverse transformation response times. Maintenance of consistent response times results in minimum flow rate shifts and thus enhanced fuel injector operation.
In another embodiment of the present invention, actuator production costs are reduced by 40%, whereby side frame rails of the actuator are eliminated, and the spacer and the orifice plate are incorporated into a second wafer, which is bonded to the first wafer, which includes SMA material and a valve seal island.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
REFERENCES:
patent: 4806815 (1989-02-01), Parker et al.
patent: 4973024 (1990-11-01), Homma
patent: 5061914 (1991-10-01), Busch et al.
patent: 5211371 (1993-05-01), Coffee
patent: 5325880 (1994-07-01), Johnson et al.
patent: 5671905 (1997-09-01), Hopkins, Jr.
patent: 5984258 (1999-11-01), Knebel et al.
patent: 6019113 (2000-02-01), Allston et al.
Knebel Albert Martin
Salemi Michael Raymond
Delphi Technologies Inc.
Evans Robin O.
Scherbel David A.
VanOphen John A.
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