Scroll compressor with back pressure chamber cavity for assisting in start-up

1. A scroll compressor comprising:

a first scroll member having a base and a generally spiral wrap extending from its base, and a second scroll member having a base and a generally spiral wrap extending from its base;

an electric motor for driving a shaft to cause said second scroll member to orbit relative to said first scroll member;

a back pressure chamber defined behind a base of one of said first and second scroll members, said back pressure chamber receiving a tapped refrigerant from a compression chambers, said back pressure chamber biasing said first and second scroll members together, and a start-up cavity formed in said back pressure chamber to increase a volume of said back pressure chamber and reduce a starting load on said electric motor, said back pressure chamber is defined by at least one seal receiving within a seal cavity, wherein said seal cavity extends for a first depth away from said base of said one of said first and second scroll members, and said start-up cavity extends from said base for a second depth, with said second depth being greater than said first depth; and

said start-up cavity contains more than 50% of a volume of said back pressure chamber.

2. The scroll compressor as set forth in claim 1 , wherein said back pressure chamber is defined behind said base of said second scroll member and a crank case that supports said second scroll member.

3. The scroll compressor as set forth in claim 1 , wherein said start-up cavity extends as a continuous ring for 360° about an axis of rotation of said shaft.

4. The scroll compressor as set forth in claim 1 , wherein there are two of seals and seal cavities, said seals being radially spaced, and said start-up cavity being radially intermediate said seal cavities.

5. The scroll compressor as set forth in claim 1 , wherein said seal cavity extends for a first radial distance, and said start-up cavity extends for a second radial distance, said second radial distance being greater than said first radial distance.

6. A scroll compressor comprising:

a first scroll member having a base and a generally spiral wrap extending from its base, and a second scroll member having a base and a generally spiral wrap extending from its base;

an electric motor for driving a shaft to cause said second scroll member to orbit relative to said first scroll member;

a back pressure chamber defined behind a base of said second scroll member, said back pressure chamber receiving a tapped refrigerant from a compression chambers, said back pressure chamber biasing said first and second scroll members together, and a start-up cavity formed in said back pressure chamber to increase a volume of said back pressure chamber and reduce a starting load on said electric motor; and

said start-up cavity extends as a continuous ring for 360° about an axis of rotation of said shaft, said back pressure chamber is defined by an at least one seal received within a seal cavity, wherein said seal cavity extends for a first depth away from said base of said one of said first and second scroll members, and said start-up cavity extends from said base for a second depth, with said second depth being greater than said first depth.

7. The scroll compressor as set forth in claim 6 , wherein there are two of said seals and seal cavities, said seals being radially spaced, and said start-up cavity being radially intermediate said seal cavities.

8. The scroll compressor as set forth in claim 6 , wherein said seal cavity extends for a first radial distance, and said start-up cavity extends for a second radial distance, said second radial distance being greater than said first radial distance.

9. The scroll compressor as set forth in claim 6 , wherein said start-up cavity contains more than 50% of a volume of said back pressure chamber.