Variable capacity compressor

1. Field of the Invention

The present invention relates to a variable capacity compressor for varying its discharging capacity of a piston by adjusting a tilted angle of a tilting plate (swash plate, wobble plate).

2. Description of Related Art

A conventional variable capacity compressor is disclosed in Japanese Patent Application Laid-Open Number 2006-233855.

As shown in FIG. 5, the variable capacity compressor 100 includes a housing 101. The housing 101 is assembled primarily of a cylinder block 101a, a front head 101b provided at one end of the cylinder block 101a and a rear head 101c provided at another end of the cylinder block 101a via a valve plate 102.

A drive shaft 103 is provided at the center of the housing 101. Both ends of the drive shaft are rotatably supported by the housing 101 via radial bearings 104 and 105.

Within the cylinder block 101a, cylinder bores 106 are formed on a circumference with the drive shaft 103 as the center. A piston 107 capable of reciprocating is provided in each of the cylinder bores 106. A crank chamber 108 is provided within the front head 101a, which communicates with the cylinder bores 106. Within the crank chamber 108, provided are a rotor 109 fixed on an outer circumferential surface of the drive shaft 103, a sleeve 110 provided slidably on the outer circumferential surface of the drive shaft 103, a journal 112 provided outside the sleeve 110 and linked with the rotor 109 via a link 111 and a tilting plate 113 fixed on an outer circumferential surface of the journal 112. The pistons 107 are coupled to an outer circumference of the tilting plate 113 via pairs of shoes 114. First and second springs S1 and S2 are provided at both sides of the sleeve 110. The tilting plate 113 will be returned to its initial position due to a balance between elastic forces of the first and second springs S1 and S2 after a shutdown.

On the drive shaft 103 rotating, the pistons 107 are reciprocated within the cylinder bores 106, respectively, due to the rotor 109, the tilting plate 113 and so on. A reciprocating stroke amount of the pistons 107 is varied due to a tilted angle of the tilting plate 113.

A suction chamber 120 and a discharge chamber 121 are provided within the rear head 101c.

The valve plate 102 is interposed between the cylinder head 101a and the rear head 101c. Therefore, the cylinder bores 106 and the chambers 120 and 121 are partitioned by the valve plate 102.

According to the above-mentioned configuration, the tilting plate 113 swings to reciprocate the pistons 107 on the drive shaft 103 being rotated. Refrigerant is supplied into the cylinder bore 106 from the suction chamber 120 during a suction stroke of the piston 107. The supplied refrigerant is compressed and discharged into the discharge chamber 121 during a compression stroke of the piston 107. The discharged refrigerant is circulated in a refrigerating cycle to be served for air-conditioning or the like and returned to the capacity variable compressor 100.

A pressure in the crank chamber 108 is made low when thermal load for the refrigerating cycle becomes large during the capacity variable compressor 100 driving. As a result, a balance will be disrupted between a counter-clockwise moment (to move the tilting plate 113 in FIG. 5) due to a crank chamber pressure (a back pressure of the pistons 107) and the elastic force of the first spring S1 and a clockwise moment due to a front pressure of the pistons 107 and the elastic force of the second spring S2. Thereby, the clockwise moment becomes large to increase the tilted angle of the tilting plate 113, so that the link 111 swings in an arrowed direction a in FIG. 5 until the both moments are balanced. (A second pivot 111b is moved in the arrowed direction a from a small capacity state [FIG. 7] to a large capacity state [FIG. 5].) Such swinging of the link 111 makes the tilted angle of the tilting plate 113 large. The reciprocating stroke amount of the pistons 107 turns to be large when the tilted angle of the tilting plate 113 is made large. Thereby, a discharge amount of the refrigerant is made large, so that a cooling performance or the like is enhanced.

On the other hand, the pressure in the crank chamber 108 is made high when the thermal load for the refrigerating cycle becomes small. As a result, the balance will be disrupted between the counter-clockwise moment due to the crank chamber pressure (the back pressure of the pistons 107) and the elastic force of the first spring S1 and the clockwise moment due to the front pressure of the pistons 107 and the elastic force of the second spring S2. Thereby, the counter-clockwise moment becomes large to decrease the tilted angle of the tilting plate 113, so that the link 111 swings in an arrowed direction b in FIG. 5 until the both moments are balanced. (The second pivot 111b is moved in the arrowed direction b from the large capacity state [FIG. 5] to the small capacity state [FIG. 7].) Such swinging of the link 111 makes the tilted angle of the tilting plate 113 small. The reciprocating stroke amount of the pistons 107 turns to be small when the tilted angle of the tilting plate 113 is made small. Thereby, the discharge amount of the refrigerant is made small, so that the cooling performance or the like is reduced. The capacity variable compressor 100 conserves energy according to the above-mentioned operation.

In addition, the rotor 109 and the journal 112 are connecting each other with the link 111 as shown in FIGS. 6A and 6B in the conventional capacity variable compressor 100. Such a linkage with the link 111 can serve lower frictions than a linkage with an elongate hole and a pin slidable within the elongate hole. Note that the link 111 is provided in a pair and a first pivot 111a is also provided in a pair as shown in FIGS. 6A and 6B. However, they are referred as the “link 111” and the “first pivot 111a” hereinafter.

However, with respect to the first pivot 111a (connecting the rotor 109 and the link 111) and the second pivot 111b (connecting the journal 112 and the link 111), the first pivot 111a is arranged near the rotor 109 (on the side of the rotor 109) and the second pivot 111b is arranged near the journal 112 (on the side of the journal 112) in the above-mentioned conventional capacity variable compressor 100. Therefore, with respect to head clearance, there is a tendency indicated by a characteristic line of a conventional example in FIG. 4 at a time when the tilted angle of the tilting plate 113 is small (within a small discharge amount range of the piston 107) as shown in FIG. 7. Then, the head clearance increases as the capacity decreases toward its minimum value. Since stroke becomes small as a matter of course, dead volume ratio to the discharge amount increases drastically. As a result, a discharge flow amount from the cylinder bores 106 is cut off abruptly as a certain tilted angle. Since the small discharge amount range is basically an unstable range due to a small discharge amount, the tilted angle of the tilting plate 113 cannot be sustained stably when the discharge flow amount changes rapidly as mentioned above.

An object of the present invention is to provide a capacity variable compressor that can restrain a sudden cut-off of the discharge flow amount within the small discharge amount range as much as possible and can sustain the tilted angle of the tilting plate stably.

An aspect of the present invention is to provide a capacity variable compressor that includes a housing within which a plurality of cylinder bores and a crank chamber communicating with the plurality of cylinder bores are provided; a drive shaft rotatably supported within the housing; a rotor fixed with the drive shaft; a link for linking the rotor and a journal; a tilting plate capable of changing a tilted angle thereof by a movement of the journal; and a plurality of pistons capable of reciprocating within the plurality of cylinder bores, respectively, due to a swinging rotation of the tilting plate. The tilted angle of the tilting plate is changed due to a rotation of the rotor by way of the link. Each reciprocating stroke of the plurality of pistons is adjusted according to the tilted angle of the tilting plate. The link is linked with the rotor via a first pivot and linked with the journal via a second pivot. An arrangement of the first and second pivot is set so that each head clearance of the plurality of pistons decreases as a discharge capacity decreases toward a minimum value thereof within a small discharge capacity range.

According to the above aspect of the present invention, since the head clearance reduces as the capacity decreases toward its minimum value within the small discharge capacity range, it can be prevented as much as possible that the discharge flaw amount is cut off abruptly and the tilted angle of the tilting plate can be sustained stably.

It is preferable that a ratio of a head clearance B at the top dead center of the piston to a stroke A of the piston shall be defined as a stroke ratio B/A, and the arrangement of the first and second pivot is set so that the stroke rate B/A is made constant or decreases as the discharge capacity decreases within the small discharge capacity range.

According to this, since the stroke rate is made constant or decreases as the capacity decreases within the small discharge capacity range of the pistons, it can be prevented firmly that the discharge flaw amount is cut off abruptly and the tilted angle of the tilting plate can be sustained stably.

It is also preferable that the link is configured so that the first pivot is arranged nearer to the journal than the second pivot and the second pivot is arranged nearer to the rotor than the first pivot.