This invention relates to scroll-type vacuum pumps and, more particularly, to scroll-type vacuum pumps which have a two-stage design.
Scroll devices are well known in the field of vacuum pumps and compressors. In a scroll device, a movable spiral blade orbits with respect to a fixed spiral blade within a housing. The movable spiral blade is connected to an eccentric drive mechanism. The configuration of the scroll blades and their relative motion traps one or more volumes or xe2x80x9cpocketsxe2x80x9d of a fluid between the blades and moves the fluid through the device. Most applications apply rotary power to pump a fluid through the device. Oil-lubricated scroll devices are widely used as refrigerant compressors. Other applications include expanders, which operate in reverse from a compressor, and vacuum pumps. Scroll pumps have not been widely adopted for use as vacuum pumps, mainly because the cost of manufacturing a scroll pump is significantly higher than a comparably-sized, oil-lubricated vane pump. Dry scroll pumps have been used in applications where oil contamination is unacceptable.
A scroll pump includes stationary and orbiting scroll elements, and a drive mechanism. The stationary and orbiting scroll elements each include a scroll plate and a spiral scroll blade extending from the scroll plate. The scroll blades are intermeshed together to define interblade pockets. The drive mechanism produces orbiting motion of the orbiting scroll element relative to the stationary scroll element so as to cause the interblade pockets to move toward the pump outlet.
Various scroll pump designs have been proposed in the prior art to increase performance and to reduce pump size. A two stage scroll pump is disclosed in U.S. Pat. No. 5,616,015, issued Apr. 1, 1997 to Liepert. U.S. Pat. No. 4,650,405, issued Mar. 17, 1987 to Iwanami et al., discloses a scroll pump with axially-spaced pumping chambers in series. A double-sided first stage feeds a single-sided second stage. A scroll compressor having two stages on opposite sides of an orbiting plate is disclosed in U.S. Pat. No. 5,304,047, issued Apr. 19, 1994 to Shibamoto. A single-sided scroll compressor having scroll blades with portions of different axial heights is disclosed in U.S. Pat. No. 4,477,238, issued Oct. 16, 1984 to Terauchi. A multi-stage, single-sided scroll compressor is disclosed in U.S. Pat. No. 6,050,792, issued Apr. 18, 2000 to Shaffer. Scroll compressors having a relief valve in a passage which couples a moving volume between scroll blades to a discharge port are disclosed in U.S. Pat. No. 4,389,171 issued Jun. 21, 1983 to Eber et al. and U.S. Pat. No. 4,497,615 issued Feb. 5, 1985 to Griffith.
The prior art scroll pump designs have not been entirely satisfactory with respect to both performance and physical size. Accordingly, there is a need for improved scroll-type vacuum pumping apparatus.
According to a first aspect of the invention, vacuum pumping apparatus is provided. The vacuum pumping apparatus comprises a scroll set having an inlet and an outlet. The scroll set comprises a first stationary scroll blade and a second stationary scroll blade extending from a stationary plate and separated by a gap, and an orbiting scroll blade extending from an orbiting plate, wherein the first and second stationary scroll blades are intermeshed with the orbiting scroll blade to define one or more interblade pockets. The vacuum pumping apparatus further comprises a relief port in the gap between the first and second stationary scroll blades and coupled through a relief passage to an exhaust, a relief valve in the relief passage, and a drive mechanism operatively coupled to the orbiting plate for producing orbiting motion of the orbiting scroll blade relative to the first and second stationary scroll blades so as to cause the one or more interblade pockets to move toward the outlet.
The drive mechanism may include a motor having an axis of rotation. The first stationary scroll blade may have a first axial depth, and the second stationary scroll blade may have a second axial depth. The first axial depth may be greater than the second axial depth.
The first stationary scroll blade may define a first pumping stage and the second stationary scroll blade may define a second pumping stage. The first and second pumping stages may be coupled in series between the inlet and the outlet.
According to a second aspect of the invention, a scroll vacuum pump is provided. The scroll vacuum pump comprises a scroll set having an inlet, an outlet and first and second pumping stages coupled in series between the inlet and the outlet. The scroll set comprises a first stationary scroll blade and a second stationary scroll blade extending from a stationary plate, and a first orbiting scroll blade and a second orbiting scroll blade extending from an orbiting plate. The first stationary and orbiting scroll blades define the first pumping stage, the second stationary and orbiting scroll blades define the second pumping stage, and a gap is provided between the first and second stationary scroll blades. The scroll vacuum pump further comprises a relief port in the gap between the first and second stationary scroll blades and coupled through a relief passage to the outlet; a relief valve in the relief passage; and a drive mechanism operatively coupled to the orbiting plate for producing orbiting motion of the first and second orbiting scroll blades relative to the first and second stationary scroll blades.