Variable displacement swash-plate type compressor

Abstract: A variable displacement swash-plate type com­ pressor suitable for use as a refrigerant compressor of an automotive air conditioner has a cylinder block (5, 6) having a plurality of cylinder bores (64) each slidably receiving a double-headed piston (7), a shaft (1) driven by an automotive engine, a swash plate (10) tiltably mounted on the shaft (1) for rotation therewith to reciprocatorily move the pistons (7), and a spool (30) for moving the swash plate (10) axially of the shaft (1) and changing the angle of tilt of the swash plate (10). The swash plate (10) and the shaft (1) are connected in such a manner that, when the swash plate (10) is axially moved while changing its tilting angle, the position of stroke end of each piston (7) is changed only in a working chamber on one end of the piston (7), whereas no change in the posi­ tion of the stroke end occurs in the other working chamber on the other end of the piston (7).

Description: The invention relates to a variable displacement swash-plate type compressor according to the preamble of claim 1. Such a compressor is suitable for use as a refrigerant compressor in automotive air conditioners. US-A-4,236,875 discloses such a type of compressor comprising single-headed pistons. For adjusting the angle of tilt of the swash-plate a sleeve is provided coaxially on the shaft of the compressor, which sleeve is shiftable by a piston. In this way essentially constant top-dead-center positions for each of the pistons can be provided. The swash-plate is connected with the sleeve via a lug-portion which is secured in a transverse bore in the drive shaft and which extends radially from the drive shaft, so that it is not possible to provide double-headed pistons. A variable displacement swash-plate type compressor has been known in which the angle of tilt of a swash plate is linearly changed so as to effect a linear control of displacement between 0% and 100% as shown, for example, in Japanese Unexamined Patent Publication No. 58-162780. This known swash-plate type compressor, however, suffers from the following problem: Namely, a decrease in the angle of tilt of the swash plate in this compressor causes not only a reduction in the piston stroke but also an increase in the dead volume on each rear side of each piston of the compressor. The increase in the dead volume in turn causes a problem that, due to expansion of the gas in the dead volume, the displacement of the compressor is significantly changed even with a slight change in the tilting angle of the swash plate. In order to obviate this problem, Japanese Unexamined Patent Publication No. 60-175783 discloses a swash-plate type compressor which does not employ double-headed pistons but utilizes a swash plate arranged such that the angle and the position of the swash plate are changed by the control of a pressure acting on the rear side of each piston so that the dead volumes are not changed when the tilting angle is decreased. Thus, in this swash-plate type compressor, pistons are provided only on one side of the swash plate, so that the pressure of the gas discharged from the compressor greatly pulsates and the torque required for driving the compressor fluctuates undesirably. In addition, the capacity or displacement per size of the compressor is limited. In order to obviate this problem, it is preferred that the compressor employs a double-headed piston type mechanism, i.e., pistons arranged on both sides of a swash plate. In this double-headed piston type, however, it is impossible to make use of back pressure acting on the rear sides of the pistons for the purpose of controlling the angle and position of the swash plate because working chambers are provided on both sides of the swash plate. Accordingly, an object of the present invention is to provide a swash-plate type compressor in which double-headed pistons are provided and in which the displacement of the compressor is linearly changed while avoiding simultaneous increase in the dead volumes on both rear sides of each piston. This object is achieved by the features in the characterizing part of claim 1. There is provided a variable capacity swash-plate type compressor in which a swash plate, which is adapted to be rotationally driven by a shaft, decreases the angle of tilt thereof as a spool is moved along the shaft, thus changing the stroke of pistons. The swash plate is supported at its center by a spherical bearing which is also adapted to move in synchronization with the movement of the spool. In this compressor, no substantial increase in the dead volume occurs in working chambers on one side of the swash plate, although dead volumes increase in the working chambers on the other side of the swash plate. In consequence, it becomes possible to progressively decrease the displacement of the compressor and, hence, to linearly control the displacement of the compressor in response to the movement of the spool. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an axial sectional view of an embodiment of a swash-plate type compressor in accordance with the present invention; Fig. 2 is a sectional view of this compressor in a different state of operation; Fig. 3 is an exploded perspective view of an essential portion of the compressor shown in Fig. 1; Figs. 4 and 5 are sectional views of a compressor incorporating the shaft and the swash plate shown in Fig. 6; Fig. 6 is a perspective view of a shaft and a swash plate incorporated in a further embodiment of the swash-plate type compressor of the present invention; Fig. 7 is a diagrammatic illustration provided for the description of the shape of an engagement slot; and Fig. 8 is a diagrammatic illustration of loci of a pin engaged in the engagement slot. Preferred embodiments of the swash-plate type compressor in accordance with the present invention will be described in detail hereinunder with reference to the accompanying drawings. Fig. 1 is a longitudinal sectional view of a variable displacement swash-plate type compressor in accordance with the present invention. The compressor has an outer shell which is composed of the following parts assembled together by through bolts not shown: a front housing 4 made of an aluminum alloy; a front side plate 8; a suction valve 9; a front cylinder block 5; a rear cylinder block 6; a suction valve 12; a rear side plate 11 and a rear housing 13. Each of the cylinder blocks 5 and 6 is provided with five cylinder bores 64 formed therein in parallel with one another. The compressor further has a shaft 1 which is rotatably supported on the front housing 4 and the front cylinder block 5 through bearings 2 and 3 and which is adapted to be driven by the power of an automotive engine which is not shown. During operaton of the compressor, a thrust force is generated to act on the shaft 1 so as to urge the shaft to the left as viewed in Fig. 1. This thrust force is born by the front cylinder block 5 through a thrust bearing 15. A rear shaft 40 is rotatably mounted in a spool 30 through a bearing 14. A thrust force which acts on the rear shaft 40 rightwards as viewed in Fig. 1 is born by the spool 30 through a thrust bearing 116. The spool 30 is axially slidably received in a cylindrical portion 65 of the rear cylinder block 6 and a cylindrical portion 135 of the rear housing 13. A swash plate 10 is provided on the center thereof with a spherical surface portion 107 which receives a spherical portion 405 of the rear shaft 40 so that the swash plate 10 is rockably supported by the swash plate 10. The shaft 1, the swash plate 10 and the rear shaft 40 are shown in an exploded perspective view in Fig. 3. As will be seen from Fig. 3, the swash plate 10 is provided on its side adjacent to the shaft 1 with opposing walls defining a slit 105 which is adapted to receive a flat web portion 165 formed on the end of the shaft 1 adjacent to the swash plate 10. The flat web portion 165 makes a face-to-face contact with the opposing wall surfaces of the slit 105 so that a torque applied to the shaft 1 is transmitted to the swash plate 10. Shoes 18 and 19 are slidably disposed on both sides of the swash plate 10. The cylinder bores 64 in the front cylinder block 5 and the rear cylinder block 5 slidably receive pistons 7. The shoes 18 and 19, which slidably engage with the swash plate 10 as stated above, rotatably engage with inner surfaces of the pistons 7. In consequence, an oscillatory rotational movement of the swash plate 10 is converted into reciprocatory motions of the pistons 7 through the shoes 18 and 19. The shoes 18 and 19 are so designed and sized that their outer surfaces constitute parts of a common sphere when they are assembled in the compressor. The aforementioned flat web portion 165 of the shaft 1 is provided with an elongated slot 166, while the swash plate 10 is provided with pin-receiving holes formed in the opposing walls which define the slit 105. After the flat web portion 165 is placed in the slit 105, a pin 80 is inserted into the holes 106 and 108 through the elongated slot 166 so as to pivotally and movably connect the swash plate 10 to the shaft 1. A stopper ring 81 is provided on one end of the pin 80 to prevent the pin 80 from coming off these holes. The angle of tilt of the swash plate varies depending on a variable position of the pin 80 along the length of the elongated slot 166. A change of the position of the pin 80 also causes a change in the position of the center (portion supported by the spherical portion 405 of the rear shaft 40) of the swash plate. Namely, the elongated slot 166 is so designed that, even when the stroke of the piston 7 is changed due to a change of the angle of tilt of the swash plate 10, the top dead center of the piston 7 in a working chamber 60 on the right side of each piston as viewed in Fig. 1 is not changed substantially, thus eliminating substantial increase in the dead volume in this working chamber 60. In contrast, in a working chamber 50 which is disposed on the left side of each piston 7 as viewed in Fig. 1, the top dead center of the piston is changed as a result of a change of the angle of tilt of the swash plate, thus causing a change in the dead volume. The elongated slot 166 is so shaped, sized and positioned such that the position of the top dead center of the piston 7 in the working chamber 60 is not changed substantially even when the angle of tilt of the swash plate is changed. To meet this requirement, the elongated slot 166 must have an arcuate form in a strict sense. Particularly, however, such an arcuate form can be well approximated by a substantially linear elongated slot. In the described embodiment, the elongated slot 166 is disposed on the axis of the shaft 1 so as to prevent the shape and size of the flat web portion 165 from becoming excessively large-sized due to provision of the elongated slot 166. The reduction in the size of the flat web portion 165, which is realized by positioning the elongated slot 166 on the axis of the shaft 1, is advantageous particularly in the swash-plate compressor of the type in which the flat web portion 165 is disposed inwardly of pistons. A detail description will be made hereinunder as to the configuration of the elongated hole 166 with specific reference to Fig. 7. In the illustrated embodiment of the present invention, the compressor is structured such that the position of the top dead center of each piston 7 at the end denoted by 1081 is maintained substantially constant regardless of the change of the tilting angle of the swash plate 10. To this end, the compressor is designed such that the position of a point P shown in Fig. 7 is not changed, while the swash plate 10 is controllable between the maximum tilting position shown by solid line and the minimum tilting position shown by broken line. The point X represents the position of the center of the spherical support 405. When the tilting angle of the swash plate 10 is changed, the position X of the center of rotation is also changed. In the embodiment of the invention, the transmission of the torque from the shaft 1 to the swash plate 10 is not conducted at the position of center of rotation but is conducted at the power transmitting portion which is constituted by the flat web portion 165 and the slit 105 and which is offset from the center of rotation. As explained before, the transmission of the torque from the shaft 1 to the swash plate 10 relies upon the face-to-face contact between the flat web portion 165 and the surfaces of the walls defining the slit 105. In the described embodiment, in order to prevent the flat web portion 165 from coming off the slit 105, the flat web portion is connected to the walls defining the slit 105 by means of the pin 80 as explained before in connection with Fig. 3. In consequence, the locus of movement of the pin 80 is varied in accordance with a change in the tilting angle of the swash plate 10. The present inventors have made an intense study on the locus of movement of the pin 80 and obtained results which are shown in Fig. 8. As shown in this figure, it has been confirmed that the locus of movement of the pin can be approximated by a substantially linear line when the swash plate is tilted at a predetermined angle while the position P of top dead center of the piston is fixed, and particularly when the locus crosses the axis of the shaft 1. More specifically, when the tilting angle of the swash plate is around 20°, the locus of movement of the pin 80 is almost straight. This is the reason why the elongated slot 166 defining the path of movement of the pin 80 is disposed in the vicinity of the axis of the shaft 1 so as to cross this axis. The arrangement in which the elongated slot 166 is so disposed as to cross the axis of the shaft 1 also contributes to reduction in the size of the flat web portion 165. Namely, if the elongated slot 166 is disposed on a line a-a' or c-c' in Fig. 7, it is required that the flat web portion 165 be disposed at a position radially substantially offset from the axis of the shaft 1. This inevitably causes the size of the whole compressor to be increased. Thus, the elongated slot 166 is disposed at a position corresponding to the locus of movement of the pin 80. In the described embodiment, the length of the elongated slot 166 is so selected that the pin 80 does not contact the ends of the elongated slot 166. Thus, the pin 80 moves along the elongated slot 166 in accordance with movements of the swash plate 10 while the angle of tilt of the swash plate 10 is changed in accordance with movements of the spool 30. The axial movement of the spool 30 is limited by the stopper 305. That is, the tilting angle of the swash plate 10 and the displacement of the pin 80 are limited by the stopper 305. In other words, the movement of the pin 80 within the elongated slot 166 is stopped when the spool 30 is stopped by the stopper 305. In this state, the pin 80 is still spaced from an adjacent end of the elongated slot 166. For this reason, the described embodiment of the compressor does not require any strict control of the length of the elongated slot 166, provided that the length of the slot is greater than the length of locus of movement of the pin 80. The compressor also has a shaft seal device 21 which prevents internal fluids such as a refrigerant gas or a lubricating oil from leaking along the surface of the shaft 1. The compressor further has discharge ports 24 which open to the working chambers 50 and 60, respectively, and communicate with discharge chambers 90 and 93, respectively. The discharge ports 24 are adapted to be opened and closed by discharge valves 22 which are fixed together with valve retainers 23 to the front side plate 8 and the rear side plate 11, respectively, by means of bolts which are not shown. The compressor further has suction ports 25 which provide communication between the working chambers 50 and a suction chamber 72 and between the working chambers 60 and a suction chamber 74. These suction ports are opened and closed by suction valves 9 and 12. The suction chamber 72 on the front side leads to a suction chamber 70 in a central portion of the housing through a suction passage 71. Similarly, the suction chamber 74 on the rear side of the compressor is connected to the suction chamber 70 via a suction passage 73. The provision of a biasing spring 900 eliminates the reversed tendency of the travel of the spool 30 relative to the thrust load which is caused due to a dead volume in the working chamber 50. In the embodiment shown in Figs. 1 and 2, the biasing spring 900 is a coiled spring disposed between one end of the shaft 1 and a retainer plate 901 provided on one end of the rear shaft 40. The shaft 1 is prevented by the thrust bearing 15 from being moved axially. The rear shaft 40 slidably fits on the shaft 1 and is connected to the spool 30 through the thrust bearing 116 so as to be able to move as a unit with the spool 30. Therefore, a leftward movement of the spool 30 as viewed in Fig. 2 is transmitted through the thrust bearing 116 to the rear shaft 40 and, hence, to the spherical portion 107. In consequence, the retainer plate 901 on the rear shaft 40 is also displaced and the end of the biasing spring adjacent to the shaft 1 is brought into contact with the shaft 1 when the travel of the spool 30 has reached 7 mm so that the biasing spring 900 begins to exert a pressing load on the spool 30. In the embodiment shown in Figs. 1 and 2, the shaft 1 extends through the swash plate 10 into the rear housing 6 and is supported at axially spaced points by the rear bearing 14 and the front bearing 3. Thus, the shaft 1 is stably supported for smooth rotation. It is also to be noted that the pin 80 is supported in the pin-receiving holes 106 and 108 in the walls defining the slit 105 through the intermediary of bearings 909. Therefore, the operation for changing the tilting angle of the swash plate 10 by an axial movement of the spool 30 encounters only a small friction resistance produced around the pin 80. In consequence, the movement of the spool 30 is smoothly converted into a change in the tilting angle of the swash plate 10 so that the compressor exhibits a highly continuous change in the displacement in accordance with the change in the tilting angle of the swash plate 10. Although the biasing spring 900 is disposed on the rear end of the shaft 1 in the embodiment shown in Figs. 1 and 2, this is not exclusive and the biasing spring 900 may be disposed at any other portion provided that it becomes effective only when the spool 30 has been moved beyond a predetermined stroke. In the embodiment shown in Fig. 3, the elongated slot 166 is formed in the flat web portion 165 on the shaft 1, while the pin-receiving holes 106 and 108 are formed in the members on the swash plate 10 defining the slit 105. This, however, is not exclusive and the relationship between the elongated slot 166 and the pin-receiving holes 106 and 108 may be inverted as shown in Fig. 6. Namely, as will be understood from Figs. 4 and 5, the same effect as that provided by the arrangement shown in Fig. 3 can be obtainable by arranging such that elongated slots 166 are formed in the walls defining the slit 105 adjacent to the swash plate 10 while a single pin-receiving hole for the pin 80 is formed in the flat web portion 165 of the shaft 1.

Claims: A variable displacement swash-plate type compressor, comprising: a cylinder block (5) having a plurality of cylinder bores (64) therein, a shaft (1) rotatably supported in said cylinder block (5), a swash plate (10) tiltably connected to said shaft and adapted to be rotated together with said shaft (1), double headed pistons (7) slidably received in said cylinder bores (64) and adapted to be reciprocally moved in said cylinder bores (64) in accordance with an oscillatory motion of said swash plate (10), working chambers (50,60) formed between the heads of each of said pistons (7) and adjacent surfaces of an associated cylinder bore (64), a support portion (40,405) disposed coaxially with said shaft (1) and supporting a central portion of said swash plate (10) rotatably and tiltably, and a spool (30) for driving said support portion axially of said shaft to move said central portion of said swash plate (10) axially of said shaft (1) to change the angle of tilt of said swash plate (10), whereby the central portion of the swash plate and the angle of tilt of the swash plate are related such that the pistons can strike to a predetermined position, characterized in that the shaft (1) is provided with a flat web portion (165) while the swash plate (10) has a slit (105) in which the flat web Portion (165) is received, that an elongated slot (166) is disposed on the axis of the shaft (1) on the portions defining the slit (105) of the swash plate (10) or on the flat web portion (165), and that a pin (80) extending through the elongated slot (166) is provided on the flat web portion (165) or on the portions defining the slit (105) of the swash plate (10). A compressor according to Claim 1, wherein said support portion (40) has a spherical support surface (405) which rotatably and slidably engages with a spherical surface portion (107) formed on said central portion of said swash plate (10). A compressor according to Claim 1, wherein said shaft (1) extends through said swash plate (10) and said spool (30) is slidably mounted on said shaft (1). A compressor according to Claim 1, wherein said shaft (1) is disposed only on one side of said swash plate (10). A compressor according to Claim 1, wherein said pin (80) is rotatably held in a pin-receiving hole (106,108) through the intermediary of a bearing (909). A compressor according to Claim 1, wherein, when the strokes of reciprocatory movements of said pistons (7) in said cylinder bores (64) are changed by a change in the angle of tilt of said swash plate (10), the top dead center of each piston is so positioned in the working chamber (50,60) on one side of the piston that no dead volume is formed in said working chamber regardless of the change in the angle of tilt of said swash plate.

Inventors: INAGAKI MITSUO, IWANAMI SHIGEKI, KOJIMA AKIKAZU, SASAYA HIDEAKI, TANAKA TARO, INAGAKI, MITSUO, IWANAMI, SHIGEKI, KOJIMA, AKIKAZU, SASAYA, HIDEAKI, TANAKA, TARO
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1987
Main classification: F04B1
IPC codes: F04B27