Vacuum motor

An improved vacuum motor for actuating heat, ventilating and air conditioning control systems (HVAC), which uses a conical spiral spring and a bonded connection between the housing and cap to reduce weight, size, cost and noise. The motor includes a bellows which forms an airtight compartment inside the motor housing with the cap and a plunger connected to the bellows. The conical spring biases the bellows to a fully expanded position. A negative pressure or vacuum in the air line connected to the housing causes the bellows to collapse and compress the spring. As the bellows collapses, the attached plunger is pulled axially into the motor housing. The movement of the plunger actuates the connected HVAC device.

FIELD OF THE INVENTION 
This invention relates to a vacuum motor and will have application to an 
improved vacuum motor which can be used to actuate heating, ventilating, 
and air conditioning controls. 
BACKGROUND OF THE INVENTION 
Vacuum motors are used for actuating valves or vents in heating, 
ventilating and air conditioning (HVAC) control systems in motor vehicles, 
and various other applications. Vacuum motors, such as the one described 
in U.S. Pat. No. 3,613,513 to Johnson, transfer vacuum pressure into 
linear motion. Typically, a vacuum motor includes a housing and a 
reciprocal plunger, which is connected generally by a linkage mechanism to 
a vent or other HVAC device for actuation. A collapsible bladder or 
bellows is connected to the plunger within the motor housing. The bellows 
forms an airtight compartment in the housing. A helical or cylindrical 
spiral spring is used to bias the bellows to a fully expanded position. 
The motor is connected to the air line of the HVAC control system. A 
negative pressure or vacuum in the air line causes the bellows to collapse 
and compress the spring. As the bellows collapses, the attached plunger is 
pulled axially into the motor housing. The movement of the plunger shifts 
the connected vent or otherwise actuates the connected HVAC device. When 
the pressure within the bellows is equalized through the air line, the 
spring tension expands the bellows to extend the plunger. The extension of 
the plunger returns the connected vent to its original position or further 
actuates the HVAC device. 
Improvements in vacuum motors have centered around attempts to reduce the 
size of the motor housings without decreasing the operational stroke of 
the plungers. Conventional vacuum motors are usually constructed of metal, 
which is costly, relatively heavy, and difficult to fabricate and 
assemble. Reducing the size of the housings can reduce the production 
costs of the motors. The dimensions of conventional housings are limited 
in part by the dimension of the cylindrical spiral springs used to bias 
the bellows. In a cylindrical spiral spring, each turn or coil of the 
spring overlies another. When the spring is fully compressed, its coils 
abut against each other. Consequently, the minimum collapsed height of a 
spring is limited to the band width of each coil multiplied by the number 
of coils in the spring. This minimum collapsed height of the spring adds 
additional size to the motor housing without any increase to the 
operational stroke of the plunger. Typically, the solution to this 
dimension problem was to use cylindrical springs with high spring 
coefficient (K) values and fewer coils. Decreasing the number of coils 
decreases the life of the motor and increases various other operational 
problems. For example, springs with fewer coils tend to bow outwardly 
during compression. Such bowing of the springs force the bellows' side 
walls into contact with the side walls of the housing. This contact 
increases the operational noise of the motors and may damage the bellows. 
SUMMARY OF THE INVENTION 
The vacuum motor of this invention uses a conical spiral spring to reduce 
the length of the housing without affecting the available stroke length of 
the plunger. A conical spiral collapses into itself and has generally a 
minimum collapsed height of a single band width of one coil. Consequently, 
the size of the housing can be significantly reduced, thereby reducing the 
cost of the vacuum motor. In addition, the vacuum motor uses a non-metal 
design which reduces the number of motor components and fabrication costs. 
The motor incorporates a snap fit plunger construction. The non-metal 
construction and conical spring use also reduce the noise created by the 
operation of the motor. 
Accordingly, an object of this invention is to provide for a novel and 
unique vacuum motor. 
Another object is to provide for an improved vacuum motor that uses a 
conical spring to reduce the size of the motor housing. 
Another object is to provide for an improved vacuum motor which 
incorporates non-metal components with an integral snap fit construction 
for easy assembly and reduction in the motor's expense, weight and 
operational noise. 
Other objects will become apparent upon a reading of the following 
description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment herein described is not intended to be exhaustive 
or to limit the invention to the precise form disclosed. It is chosen and 
described to explain the principles of the invention and its application 
and practical use to enable others skilled in the art to utilize its 
teachings. 
FIGS. 1-4 illustrate vacuum motor 2. Motor 2 includes four basic 
components: housing 5 having a body 10 and cap 20; a bladder or bellows 
30; a conical spiral spring 40; and a plunger 50. 
Body 10 and cap 20 are constructed from a suitable light weight material, 
preferably a thermoplastic. Body 10 includes a cylindrical side wall 12 
and a bottom wall 14 which define a cylindrical housing cavity 13. Body 
side wall 12 has at its open end an outturned annular shoulder 15 which 
terminates in a projecting annular lip 16 paralleling the side wall. End 
wall 14 has a plurality of peripherally located holes 17 for venting the 
housing cavity 13 to ambient pressure and a central plunger opening 19. 
End wall 14 also includes a raised lip 18 around plunger opening 19. 
Cap 20 includes an outer annular rim 22 and a central port 24 defining an 
air passage 25, as best shown in FIGS. 3 and 4. When motor 2 is in 
operation, port 24 is connected to a conventional vacuum line or tube (not 
shown). The inner face of cap 20 has an annular inner groove 26 and has at 
rim 22 a generally concentric outer groove 27. Between grooves 26, 27 is 
an annular concave land 28. The diameter of cap groove 27 approximates the 
diameter of body flange 16, such that body flange 16 can be fitted within 
groove 27 when cap 20 is applied over and secured to the body 10. 
Bellows 30 has a flexible generally cylindrical side wall part 32, 
preferably constructed of a synthetic rubber, such as ethylene-propylene 
terpolymer (EPDM), and a rigid disc-shaped end part 36, preferably 
constructed of a thermoplastic. Bellows side wall part 32 terminates at 
one end in a circumferential flange 34. Side wall part 32 fits in a 
constructive air tight manner at its opposite end around end part 36 to 
form an inner wall for bellows 20. End part 36 includes a raised annular 
ring 37 which protrudes into the interior of bellows 20 and a split male 
connection part 38 which protrudes outwardly of the bellows. 
Conical spiral spring 40 is located in the sealed compartment 33 formed by 
body 10 and cap 20. Spring 40 can be constructed of any suitable material, 
preferably spring metal and may have any number of turns or coils with any 
desired spring constant value. Spring 40 is oriented in an inverted 
orientation with the base coil 42 of spring 40 seated within cap inner 
annular groove 26 and its vertex coil 44 seated about annular ring 37 of 
bellows end part 36. The length of spring 40 is at least equal to the 
length of bellows side wall part 32. 
Plunger 50 is also preferably constructed of a thermoplastic and has an 
elongated shank 52 adapted for connection to a vent or other HVAC control 
device to be actuated (not shown). As shown, plunger 50 includes a collar 
or female connection part 54 at one end of shank 52. Female connection 
part 54 is snap fitted over male connection part 38 to secure plunger 50 
to bellows end part 36. With bellows 30 retained in housing cavity 13, 
plunger shank 52 extends through plunger opening 19. The opposite end of 
plunger shank 52 includes a conventional connection part 53 for connection 
to any of a variety of HVAC control devices. 
Motor 2 is assembled using an interlocking component connection or snap fit 
construction for quick assembly. The assembly of the motor is as follows: 
Plunger 50 is inserted in interlocking engagement over male connection 
part 38 of bellows 30. Bellows 30 and plunger 50 are then inserted through 
the open end of body 10 with plunger 50 extending through plunger opening 
19 and bellows flange 34 abutting against body shoulder 15. Spring 40 is 
inserted in bellows 30 and seated about annular ring 37. Cap 20 is fitted 
in an interlocking engagement over body 10 with body lip 16 fitted into 
cap groove 27 and spring 40 seated in annular groove 26 of cap 20. Cap rim 
22 is sonically welded to body flange 16 to seal the connection between 
body 10 and cap 20. When cap 20 is fitted over body 10, bellows flange 34 
is compressed between cap land 28 and body shoulder 15 to form the 
hermetic sealed bellows compartment 33 inside of the bellows within 
housing cavity 13. 
FIG. 3 shows motor 2 with its bellows 30 expanded and its plunger 50 in its 
fully expended position. Spring 40 urges bellows end part 36 into contact 
with body lip 18 to limited one direction of travel of plunger 50. FIG. 4 
shows motor 2 with its bellows 30 collapsed and its plunger 50 in its 
fully retracted position within housing cavity 13. A negative pressure or 
vacuum drawn within bellows compartment 33 through cap port 24 collapses 
bellows 30 and compresses spring 40. As bellows 30 collapses, end part 36 
of bellows 30 is drawn towards cap 20, folding side wall 32 around the end 
part. This movement of end part 36 pulls plunger 50 linearly into housing 
cavity 13. When the vacuum is eliminated and the pressure inside 
compartment 33 begins to equalize with the ambient pressure, spring 40 
expands and urges end part 36 towards body bottom wall 12. In this manner, 
plunger 50 is thus extended. The movement or throw of the plunger can be 
varied between the fully extended position shown in FIG. 3 and the fully 
retracted position shown in FIG. 4 by regulating the pressure within the 
bellows compartment 33. 
It is understood that the above description does not limit the invention to 
the details given, but may be modified within the scope of the following 
claims.