1. Field of the Invention
The present invention relates to variable displacement compressors in automotive air conditioning systems, and more particularly, to slant plant-type variable displacement compressors with capacity control mechanisms.
2. Description of Related Art
Slant plate-type variable displacement compressors having capacity control mechanisms are known in the art. For example, Japanese Second Patent Publication (Examined) No. 5-83751 describes a slant plate-type compressor, more particularly, a wobble plate-type compressor having a variable displacement control mechanism in an automotive air conditioning system. In such automotive air conditioning systems, the compressor is driven by an engine of a vehicle.
This wobble plate-type compressor includes a valve member and a first passage, which communicates between a crank chamber and a suction side of a cylinder bore via a fixed orifice so as to allow pressure to release. The valve member is disposed in a second passage, which communicates between a discharge side of the cylinder bore and the crank chamber so as to provide a discharge pressure. The valve member is controlled by a suction pressure of the cylinder bore.
In operation, if the suction pressure within the cylinder bore is less than a predetermined value when the load on a fluid circuit, for example, a cooling circuit, of the air conditioning system is low, the valve member opens the second passage. Refrigerant gas from the discharge side of the cylinder bore is provided to the crank chamber, and pressure in the crank chamber increases. As a result, the difference between a first moment increasing a tilt angle between a wobble plate and a drive shaft and a second moment decreasing a tilt angle between the wobble plate and the drive shaft may be decreased. The first moment is results from a reaction force of a compression, which affects pistons. The second moment is results from the pressure in the crank chamber. Consequently, the tilt angle between the wobble plate and the drive shaft decrease, and the discharge capacity of this compressor may decrease. Alternatively, if the suction pressure of the cylinder bore is greater than a predetermined value when the load on the fluid circuit of the air conditioning system is high, the valve member closes the second passage, and refrigerant gas in the discharge side of the cylinder bore is not provided to the crank chamber. Refrigerant gas in the crank chamber flows to the suction side of the cylinder bore through the first passage because of the difference between the pressure in crank chamber and the suction pressure of the cylinder bore. As a result, the difference between the first moment and the second moment may be increased. Consequently, the tilt angle between the wobble plate and the drive shaft may increase, and the discharge capacity of this compressor may increase.
In this compressor, the orifice is disposed in the first passage, which communicates between the crank chamber and the suction side of the cylinder bore so as to allow pressure to release. The orifice reduces or eliminates the excessive flow of refrigerant gas from the crank chamber to the suction side of the cylinder bore, and a rapid decrease of the pressure in the crank chamber may be suppressed. As a result, a rapid increase of the discharge capacity may also be suppressed when the discharge capacity is increased in response to an increase of the load on the fluid circuit, and a rapid decrease of blowoff temperature of the air conditioning system may be suppressed.
In this compressor, just after the compressor operation begins, the valve member disposed in the first passage closes the first passage, and the discharge capacity is at a minimum discharge capacity. By starting the compressor operation, refrigerant gas flows from the suction side to the discharge side of the cylinder bore, and the suction pressure of the cylinder bore decreases. The difference between the pressure in the crank chamber and the suction pressure of the cylinder bore may occur, and refrigerant gas in the crank chamber may flow to the suction side of the cylinder bore. The pressure in the crank chamber may decrease because refrigerant gas flows to the suction side of the cylinder bore. Therefore, the difference between the first moment and the second moment increases, and the tilt angle between the wobble plate and the drive shaft may increase. As a result, the discharge capacity of this compressor may be increased, and the requisite amount of refrigerant gas may be provided to the fluid circuit.
In this compressor, however, just after the compressor operation begins, the discharge capacity is at a minimum discharge capacity, and the discharge pressure of cylinder bore is low. The moment, which increases the tilt angle between the wobble plate and the drive shaft and which arises from the reaction force of compression affecting pistons, is small. Therefore, the difference between the first moment and the second moment is small. Moreover, just after the compressor operation begins, the degree of suction preserve in the cylinder bore is reduced because the discharge capacity reaches a minimum capacity, and the difference between the pressure in the crank chamber and the suction pressure of the cylinder bore is reduced. Therefore, if the orifice is disposed in the first passage so as to allow the pressure to release, the flow of refrigerant gas from the crank chamber to the suction side of the cylinder bore may become slightly smaller because of a flow resistance created by the orifice, and the rate of pressure release in the crank chamber may become slightly smaller. Accordingly, a reduced rate of change of the moment, which decreases the tilt angle between the wobble plate and the drive shaft and which arises from the pressure in the crank chamber, may become slightly smaller. The difference between the first moment and the second moment, in other words, an increased rate of change of the difference between the first moment and the second moment may become slightly smaller, and this slightly smaller difference may be maintained. As a result, the requisite amount of refrigerant gas may not be provided to the fluid circuit because a rapid increase of the discharge capacity is hindered.
A need has arisen to reduce or eliminate the above-mentioned problems, which may be encountered in known slant plate-type variable displacement compressors with capacity control mechanisms.
In an embodiment of this invention, a slant plate-type variable displacement compressor comprises a housing enclosing a crank chamber, a suction chamber, and a discharge chamber. The housing comprises a cylinder block, and a plurality of cylinder bores are formed in the cylinder block. A drive shaft is rotatably supported in the cylinder block. A plurality of pistons are slidably disposed within the cylinder bores. A slant plate has an angle of tilt and is tiltably connected to the drive shaft. A plurality of bearings couple the slant plate to each of the pistons, so that the pistons reciprocate within the cylinder bores upon rotation of the slant plate. A valve member is disposed in a first passage. The first passage communicates between a discharge side of the cylinder bore and the crank chamber. The valve member is controlled by a suction pressure produced within the cylinder bore. A second passage communicates between the crank chamber and a suction side of the cylinder bore through an orifice. The second passage allows pressure to release. A cross-sectional area of the orifice is variably controlled, such that the cross-sectional area of the orifice when a compressor operation begins is greater than during a capacity control operation.
Objects, features, and advantages of embodiments of this invention will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.