Suction structure in double-headed piston type compressor

The present invention relates to a suction structure for allowing refrigerant from a suction pressure region into compression chambers in a double-headed piston type compressor. More specifically, the compressor has rotary valves rotated integrally with a rotary shaft and having introduction passages for introducing refrigerant from the suction pressure region into the compression chambers defined in cylinder bores by the double-headed pistons.

In double-headed piston type compressors, there are two types of suction valves. One is a rotary valve as disclosed in Unexamined Japanese Patent Publication No. 2007-032445. The other is a reed type suction valve as disclosed in Unexamined Japanese Patent Publication No. 2000-145629. The piston type compressor including the rotary valves has lower suction resistance in introducing refrigerant into cylinder bores, and has superior energy efficiency, compared to the piston type compressor including the reed type suction valves.

In the compressor disclosed in the above reference No. 2007-032445, pairs of a front cylinder bore and a rear cylinder bore accommodate double-headed pistons therein, and the pistons are reciprocated in accordance with the rotation of a rotary shaft. Each double-headed piston defines a front compression chamber in the front cylinder bore and a rear compression chamber in the rear cylinder bore. The rotary shaft has a front rotary valve and a rear rotary valve which are formed integrally therewith. A supply passage is formed in the rotary shaft, and outlets of the supply passage are formed in the front and the rear rotary valves. Communication passages are formed in cylinder blocks so as to communicate with the compression chambers. The outlets of the supply passage intermittently communicate with the communication passages in accordance with the rotation of the rotary shaft, or, the rotation of the rotary valves. When the outlets of the supply passage communicate with the communication passages, the refrigerant in the supply passage is introduced into the compression chambers.

Generally, the communication passages have elongated cross-sections, as disclosed in Unexamined Japanese Patent Publication No. 6-129350. The elongated holes are formed such that the dimensions of elongated holes in the axial direction of the rotary shaft are larger than the dimensions thereof in the circumferential direction. The elongated holes are applied in order to collect the residual gas in the compression chambers thereby improving the volume efficiency.

The supply passage communicates with the suction chamber formed in the rear housing so as to supply refrigerant in the suction chamber to the front and rear compression chambers therethrough. The refrigerant in the front compression chamber is discharged to the front discharge chamber formed in the front housing, by pushing open the respective discharge valve. The refrigerant in the rear compression chamber is discharged to the rear discharge chamber formed in the rear housing, by pushing open the respective discharge valve.

The pressure in the front discharge chamber is equal to the pressure in the rear discharge chamber. The refrigerant in the compression chambers is compressed up to the pressure level in the discharge chambers. Therefore, as the amount of the refrigerant introduced into the compression chambers is decreased, the compression rate is increased. When the compression rate is increased, the temperature of the compressed refrigerant rises, accordingly.

The distance to the front compression chamber from the suction chamber through the supply passage is greater than the distance to the rear compression chamber from the suction chamber through the supply passage. Therefore, the refrigerant amount into the front compression chamber is smaller than that into the rear compression chamber during the time when the communication passages communicate with the outlets of the rotary valves, respectively. The temperature of the refrigerant compressed in the front compression chamber becomes higher than the temperature of the refrigerant compressed in the rear compression chamber, accordingly.

When the temperature of the refrigerant compressed in the front compression chamber becomes excessively high, the temperature of the front housing rises. The sealing function may be deteriorated in seal members interposed between the front housing and the cylinder block, accordingly.

The present invention is directed to suppress increase in temperature of refrigerant compressed in compression chambers in a double-headed piston type compressor.

In accordance with the present invention, a suction structure is provided for allowing refrigerant from a suction pressure region in a double-headed piston type compressor. The compressor has a cylinder block, a rotary shaft, a double-headed piston, first and second cylinder bores, and first and second compression chambers. The rotary shaft is supported by the cylinder block. The double-headed piston reciprocates with rotation of the rotary shaft. The first and the second cylinder bores are formed in the cylinder block in a paired manner so as to accommodate the double-headed piston. The first and the second compression chambers are defined by the double-headed piston in the first and the second cylinder bores, respectively. The suction structure in the compressor includes first and second rotary valves, and first and second communication passages. The first rotary valve introduces refrigerant from a suction pressure region into the first compression chamber through a first introduction passage. The second rotary valve introduces refrigerant from the suction pressure region into the second compression chamber through a second introduction passage. Each part of the first and the second introduction passages is formed in the rotary shaft. The first communication passage has a circular cross-section and is formed in the cylinder block so as to connect the first compression chamber to the first introduction passage. The second communication passage has a circular cross-section and is formed in the cylinder block so as to connect the second compression chamber to the second introduction passage. The distance to the first communication passage from the suction pressure region through the first introduction passage is greater than the distance to the second communication passage from the suction pressure region through the second introduction passage. The diameter of the first communication passage is greater than the diameter of the second communication passage.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of a compressor according to a preferred embodiment of the present invention;

FIG. 2A is a partially enlarged cross-sectional view of the compressor according to the preferred embodiment;

FIG. 2B is a cross-sectional view which is taken along the line III-III in FIG. 2A;

FIG. 2C is a cross-sectional view which is taken along the line IV-IV in FIG. 2A;

FIG. 2D is a graph showing relation between temperature in front discharge chamber and cross-section ratio with regard to area of first communication passage to that of second communication passage according to the preferred embodiment;

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