Thermal throttle actuator

A thermal throttle actuator adapted to be mounted in an opening of a throttle body of an internal combustion engine wherein the fuel system is electronically controlled. The thermal throttle actuator comprises a housing in which a plunger is mounted for reciprocating movement and is adapted to contact a spring loaded throttle plate in the throttle body. The plunger is yieldingly urged toward the throttle plate by a bias spring. A shape memory alloy in the shape of a helical spring is provided to produce a force on the plunger in a direction opposite to that of the bias spring when the shape memory alloy is heated to a temperature above a predetermined temperature. When the temperature is below the predetermined temperature, the shape memory alloy spring is readily deformable, the bias spring functions to provide a force on the throttle plate which maintains the throttle plate in an open position to enhance performance during cold starting of the engine.

This invention relates to thermal actuators for the throttle plate of a 
throttle body utilized in connection with the internal combustion engines 
wherein the field system is controlled electronically. 
BACKGROUND AND SUMMARY OF THE INVENTION 
In internal combustion engines, the fuel systems have been replaced most 
recently by electronically controlled fuel injection systems. Accordingly 
the conventional carburetor with a choke to enhance performance during 
cold starting is eliminated. It has been found that in large engines, such 
as truck engines utilizing a throttle body fuel injection system, the 
engine requires long cranking start times at cold temperatures, and 
occasional restarts due to stalling. Accordingly, it was determined that 
this could be corrected by opening the throttle plates called cracking, 
approximately 0.1 inch. However, there is a need for a device that would 
function as the engine temperature increases to eliminate the opening of 
the throttle plates at idle and thereby avoid rough idling as well as 
minimize the undesired fuel emissions. 
In consideration of this problem, various solutions were considered. Among 
these were a direct actuation of the throttle plate by metal coil but this 
was rejected because of the large size required to develop the loads that 
were needed. Bi-metal snap-action discs were investigated but, they were 
found to be limited in force, had a limited stroke and required a stack of 
a plurality of discs which would result in a costly solution. Wax pellet 
actuators were considered but it was found that no wax was available that 
could provide a transition point at cold temperatures such as 32.degree. 
F. It was also judged that such a device would be complex and would have a 
large variation in the actuation temperature tolerance. Vacuum actuators 
were also considered which would function to extend when the engine is off 
and retract when engine starts. However this was found to be an expensive 
and bulky solution. 
Among the objectives of the present invention were to provide a thermal 
throttle actuator that would function to maintain the throttle plates open 
the desired amount while at cold temperature, which would function at 
proper temperature tolerances to eliminate the cracking of the throttle 
plates at warm idle; which had minimal hysterisis; which was compact; 
which could readily be adapted to a throttle body; and which was 
relatively low in cost. 
In accordance with the invention, the thermal throttle actuator is adapted 
to be mounted in the opening of a throttle body of an internal combustion 
engine wherein the fuel system is electronically controlled. The thermal 
throttle actuator comprises a housing in which a plunger is mounted for 
reciprocating movement and is adapted to contact a spring loaded throttle 
plate in the throttle body. The plunger is yieldingly urged toward the 
throttle plate by a bias spring. A shape memory alloy in the shape of a 
helical spring is provided to produce a force on the plunger in a 
direction opposite to that of the bias spring when the shape memory alloy 
is heated to a temperature above a predetermined temperature. When the 
temperature is below the predetermined temperature, the shape memory alloy 
spring is readily deformable and the bias spring functions to provide a 
force on the throttle plate which maintains the throttle plate in open 
position to enhance performance during cold starting of the engine.

DESCRIPTION 
In fuel injection systems which are electronically controlled and includes 
a throttle body with throttle plates controlling the flow of fuel, it has 
been found that at cold temperatures, it is desirable to have the throttle 
plates open slightly. It is also desirable at warmer temperatures to have 
the throttle plates return to normal operating position in order to avoid 
rough idling and excessive fuel emissions. 
Referring to FIGS. 1 and 2, which are schematic views of a throttle body 
embodying the invention, the throttle body 10 includes throttle plates 11 
mounted on a rotatable shaft 12. A spring 13 yielding, urges the throttle 
plates to a closed throttle position. In accordance with the invention a 
thermal throttle actuator 15 is threaded into the throttle body 10 and has 
a plunger 16 yielding urging a tab 17 on the shaft 12 in a direction 
opposing the action of helical spring 13. 
As shown in FIG. 3, the thermal throttle actuator 15 comprises a 
cylindrical housing 18 having a closed end 19 at one end and a bushing 20 
at the other end which is held in place by crimping a portion of the 
housing 18, as at 21. The stem 16 has an integral enlarged portion 22. A 
helical bias spring 23 is interposed between the end wall 19 and the 
enlarged portion 22. A shape memory alloy in the form of a helical spring 
24 is interposed between the enlarged portion 22 and the bushing 20. 
It has been found that by providing such an arrangement in the throttle 
body wherein the bias spring 23 functions in the direction opposite to 
that of the torsion spring 13 and the shape memory spring 24 has the 
characteristics, as presently described, to provide desired control of the 
throttle plates is achieved. 
The shape memory alloy is of the well known nickel-titanium type that 
functions upon the phenomenon that it is mechanically deformable when it 
is below a specific temperature but will return to a predetermined shape 
when the temperature is raised above the specific temperature. Such alloys 
have been heretofore used for various devices, such as fog lamp actuators 
for automobiles, air vent springs for air conditioners and coffee makers. 
The alloys of this type where a result of the work at the Naval Ordnance 
Laboratory as reported in the reference of W. J. Buehler, J. V. Gilfrich 
and R. C. Wiley, J. APPL. PHYS. Volume 34 1963, page 1475. One 
manufacturer of such alloys is Raychem Corporation of Menlo Park, Calif. 
It has been found that by proper selection of the materials not only is the 
desired action obtained but a minimal hysterisis is achieved as shown in 
FIG. 4 is found. 
The manner in which it the thermal throttle actuator functions to provide 
the desired control can be more readily understood by reference to FIGS. 
5-8. 
Utilizing a nickel-titanium memory material wound in a compression spring 
configuration and having a predetermined temperature below which is 
readily deformable, namely 32.degree. F., and combined with a bias spring 
having a predetermined spring rate, it was found that the desired minimum 
travel was obtained. 
Referring specifically to FIGS. 5 and 6, when such a device is at a cold 
temperature less than 32.degree. F. or 0.degree. C., the bias spring 23 
and the alloy spring 24 function such that the alloy spring 24 is merely 
mechanically deformed and has substantially less resistance. In this 
condition the bias spring 23 produces a force slightly greater than that 
of the force of the spring 13 of the throttle plates so that the throttle 
plates are moved or cracked the desired amount, namely, 0.10 inch. This 
facilitates the starting of the cold engine. As the engine heats up and 
the environment of the engine exceeds a temperature set point above 
32.degree. F. or 0.degree. C., the alloy spring 24 functions to return to 
its predetermined configuration as shown in FIGS. 7 and 8, such that the 
force of the throttle return spring 13 combines with that of the alloy 
spring 24 to overcome the force of the bias spring 23 and eliminate the 
cracking of the throttle plates. The actuator 15 further includes a stop 
25 extending axially from end 19 within bias spring 23 to limit the 
movement of plunger 16 under the action of the shape alloy spring 24 and 
the throttle return spring to control plunger return. This aids setting 
the curb idle position of the throttle throughout the life of the system. 
It can thus be seen that there has been provided a thermal throttle 
actuator that would function to maintain the throttle plates open in the 
desired amount at cold temperature, which would function at proper 
temperature tolerances to eliminate the cracking of the throttle plates at 
warm idle; which had minimal hysterisis; which was compact; which could 
readily be adapted to a throttle body; and which was relatively low in 
cost.