In the swash-plate type compressor, a swash-plate is rigidly secured obliquely to a rotary shaft or is secured obliquely to a rotary shaft in such a manner that its slanting angle is variable. The compression and expansion are carried out by means of rotating the swash-plate which increases or decreases the volume of a partition space within a compressor, depending upon the rotation of the rotary shaft. Such swash plate is caused to slide on a sliding member referred to as a shoe, and reciprocates a piston via the shoe. The cooling medium can therefore be compressed and expanded in the stated space.
A salient point in the sliding conditions of a swash-plate is that, during the initial operational period of a compressor, the cooling medium reaches the sliding part prior to the lubricating oil reaching the sliding part; thus the cooling medium has a rinsing effect on the lubricating oil which remains on the sliding part, with the result that the sliding condition is in a dry condition free of lubricating oil. The requirements for the sliding condition of the swash plate are therefore very severe.
The sliding properties, which are required for a swash-plate used under the condition described above, are seizure resistance, wear resistance, and the like. Proposals have thus been made to add hard matters into the aluminum material for enhancing the wear resistance, to improve the material of the swash plate, and to subject an iron-based swash-plate to heat treatment or surface treatment for enhancing the hardness and hence wear-resistance.
One of the present applicants proposed in Japanese Unexamined Patent Publication No. Sho 51-36611 to bond sintered Cu material on the shoe in the case of an iron-based swash plate. That is, an iron-based swash plate was heretofore subjected to hardening treatment. However, when the material of the opposed member, i.e., the shoe, is an iron-based material, the sliding takes place between identical kinds of materials thereby incurring a problem that a seizure is liable to occur. Sintered copper alloy is used for the opposing material (shoe) opposed to an iron-base swash plate, so as to avoid the above mentioned problem.
In addition, it was also proposed to apply tin plating on the iron-based swash-plate so as to avoid the sliding between identical kinds of materials and hence to enhance the seizure resistance.
In the ordinary swash-plate type compressor, the cooling medium is sucked into and compressed in the cylinder bores at both sides of a piston. In a recently produced single-side compression type swash-plate compressor, the compression and suction are carried out usually only in the rear (R) side. This swash plate compressor is described with reference to an example of the variable volume type compressor disclosed in Japanese Unexamined Patent Publication No. 6-288,347 filed by one of the applicants.
As shown in FIG. 13, the front housing 2 is secured to one side of the cylinder block 1, while the rear housing 3 is secured to the other side via the valve sheet 4. The driving shaft 6 is included in the crank space 5 formed by the cylinder block 1 and the front housing 2 and is rotatably supported by the bearings 7a and 7b. A plurality of the cylinder bores 9 are formed in the cylinder block 1 at a location where they surround the driving shaft 6. A piston 10 is inserted in each cylinder bore 9.
A rotor 16 is synchronous rotatably supported by the driving shaft 6 in the crank space. In addition, a sleeve 12 having a spherical surface is slidably supported by the driving shaft 6. A compression spring 13 is provided between the rotor 16 and the sleeve 12 having a spherical surface and forces the sleeve having a spherical surface in the direction toward the rear housing 3. A rotary swash plate 14 is rotatably supported on the outer peripheral surface of the sleeve 12 having a spherical surface. In the condition of the compression spring 13, which is at the maximum shrinkage condition as shown in FIG. 13, the contact surface 14, which is formed aslant on the lower back surface of the rotary swash plate 14, abuts on the rotor 16. Therefore, a further inclination of the rotary swash plate 14 to increase its inclination angle is restrained. Although not shown in the drawing, a further inclination to decrease the inclination angle of the swash plate may be restrained.
Semi-spherical shoes 15a, 15b abut on the outer peripheral parts of the rotary swash plate 14. The outer peripheral surface of these shoes 15a, 15b are engaged with the ball-bearing surfaces of the piston 10. Therefore, a plurality of the pistons 10 are coupled with the rotary swash-plate 14 via the shoes 15a, 15b and are capable of reciprocating in each cylinder bore 9, in which the pistons are mounted.
The rear housing 3 is divided into the suction space 20 and the exhaustion space 21. The suction port 22 and the exhaustion port 23 are formed through the valve sheet 4 and these ports are opened through the respective cylinder bores 9. The compression space formed between the bearing plate 4 and the piston 10 is communicated with the suction space 20 and the exhaustion space 21 via the suction port 22 and the exhaustion port 23, respectively. That is, the compression is carried out only in the single side of the swash plate, i.e., the rear (R) side.
A suction valve is provided in each suction port 22 and opens or shuts the suction port 22 in accordance with the reciprocating movement of the pistons 10. An exhaust valve is provided in each exhaustion port 22 and opens or shuts the exhaustion port 22 in accordance with the reciprocating movement of the pistons 10, while the exhaust valve is restrained by the retainer 24. A control valve (not shown) is provided in the rear housing 3 to adjust the pressure in the crank space 5.
In the compressor as constructed hereinabove, when the rotary swash-plate 14 is rotated along with the driving of the driving shaft 6, each piston 10 is reciprocated via the shoes 15a, 15b in the cylinder bore 9, thereby sucking the cooling-medium gas through the suction port 20 into the compression space, compressing the cooling-medium gas and then exhausting it into the exhaustion space 21. Here, the amount of the cooling-medium gas, which is exhausted into the exhaustion space 21, is controlled by means of adjusting the pressure in the crank space 5.
In addition, the compressor is provided with the mechanisms K, 17 through 19 which enable the exhaustion amount to be adjusted.
With reference to FIG. 14, which shows the essential parts of the above described, single-side compression type swash-plate compressor, the problems of wear in the single-side compression type swash plate compressor are explained.
In the compressing process, the compression reaction-force in the cylinder bore is transmitted via the single-head piston 10 and the shoes 15 to the rotary swash plate 14. The shoe 15a at the side of the compression space is subjected to the compression reaction force, with the result that great sliding resistance is generated between the shoe 15a and the rotary 14. Since such sliding resistance results not only in the power loss but also in the wear of the swash plate, countermeasures against such results become necessary.
Meanwhile, since the shoe 15b at the opposite side of the compression space is also brought into contact with the rotary swash plate 14, sliding resistance generates due to the relative displacement between them. However, the rotary swash plate 14 is not subjected via the shoe 15b to the compressing reaction-force, and the sliding contact between the shoe 15b and the rotary swash-plate 14 occurs only during the suction process, where the single-head piston 10 moves from the top dead center to the bottom dead center. In the suction process, the piston 10 is accompanied by the rotary swash-plate 10 via the shoe 15b, and, the force necessary for accompanying the swash-plate 10 is less than the force required in the compression process. The sliding resistance between the shoe 15b and the rotary swash-plate 14 is accordingly slight.
Since the tin plating applied on an iron-based swash-plate of the single-side compression type swash-plate compressor is soft, a problem that arises is insufficient wear-resistance. Furthermore, although a hard element added to an aluminum alloy enhances wear resistance, a problem that arises is insufficient seizure resistance of the swash plate at the compression-space side.