An automotive heating, ventilating and air conditioning system is subject to control by electrical switching and often by vacuum valve operation. A control panel advantageously employs a single rotary knob for selection of the mode of operation. Such modes may be, for example, Off, Vent, Bi-level, Heater, Blend and Defrost. It is already known to use a combination vacuum valve and electric switch rotatably positioned by the single knob.
FIG. 1 illustrates such a prior art switch/valve assembly. A generally cup-shaped housing 10 has an aperture 12 surrounded by an inner hub 14 which rotatably supports a carrier shaft 16. Fixed switch conductors 18 are secured to the inner face of the housing and end in terminals 20. A cylindrical inner surface of a circumferential wall of the housing is provided with detent teeth 22.
A carrier 24 supported by the shaft 16 has a radially spring biased detent ball 26 for engaging the teeth 22, and a movable spring loaded contact assembly 28 for selectively engaging the switch conductors 18. An E-ring 30 is clipped onto the shaft 16 just outside the housing to hold the shaft against inward movement. The outer end of the shaft may be provided with a control knob. Thus, the switch may be operated to different positions by rotating the shaft to those positions determined by the detent mechanism.
The vacuum valve arrangement in FIG. 1 comprises a stator 32 assembled to the housing 10 as by snap-on spring fingers 34. The stator has a plurality of vacuum ports 36 with outwardly protruding coupling tubes 38. A molded plastic rotor 40 holds a rubber selector plate 42 against the inner side of the stator 32. Surface passageways on selector plate 42 selectively interconnect ports 36 at each position. A snap-in pivot pin 44 extends through central holes in the stator, the selector plate and the rotor.
A spring 46 compressed between a head of the pin 44 and the rotor holds the valve assembly together in sealing relationship. Drive pins 48 on the rotor 40 engage notches in the carrier 24 to rotate the rotor with the carrier. Barbed posts 50 on the stator 32 retain a sealing grommet, not shown, which aids in connection to the vacuum system.
Due to the location of the detent teeth 22 on the wall of the housing 10 and the large radius of the wall, the teeth cannot have sufficient slope to provide a crisp feel and at the same time to minimize the possibility of the switch being positioned between discrete modes. To obtain steeper slopes it is desirable to locate the teeth on a smaller radius. It is already known, in a valve having no electrical switch, to locate the teeth at the desired radius on the end wall of the housing 10 in lieu of the conductors 18. The presence of the switch, however, prohibits that structure.
Due to the mounting geometry of the shaft within the housing, undesired wobble of the shaft can occur. While the inner hub 14 helps stabilize the shaft, the hub can not be made deep enough to prevent the wobble. Also, to retain the shaft, an E-ring or other fastener is required.
As is common with injection molded components, the rotor has some warpage on the surface that mates with the selector plate, and has an adverse effect on sealing between the selector plate and the stator which leads to vacuum leakage. Such warpage is aggravated by the force exerted by the grommet on the barbed posts 50.