Title:
Displacement detection device for variable displacement compressor
Kind Code:
A1


Abstract:
A displacement detection device for a variable displacement compressor in which a swash plate which is connected to a piston through shoes in a housing slides relative to the shoes and rotates synchronously with a drive shaft with a wobbling motion in an axial direction of the drive shaft as the drive shaft is rotated, and an inclination angle of the swash plate is controlled thereby changing a stroke of the piston, includes a detection object provided in a first portion of an outer periphery of the swash plate where an imaginary plane passing through a point of intersection between a line connecting top and bottom dead center positions of the swash plate and an axial line of the drive shaft in perpendicular relation to the line intersects with the outer periphery of the swash plate and a detector provided in the housing so as to face the detection object.



Inventors:
Ota, Masaki (Kariya-shi, JP)
Sonobe, Masanori (Kariya-shi, JP)
Suzuki, Atsuhiro (Kariya-shi, JP)
Umemura, Satoshi (Kariya-shi, JP)
Tarutani, Tomoji (Kariya-shi, JP)
Application Number:
11/644699
Publication Date:
08/02/2007
Filing Date:
12/22/2006
Primary Class:
International Classes:
F04B1/26
View Patent Images:
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Primary Examiner:
STIMPERT, PHILIP EARL
Attorney, Agent or Firm:
MORGAN & FINNEGAN, L.L.P. (New York, NY, US)
Claims:
What is claimed is:

1. A displacement detection device for a variable displacement compressor in which a swash plate is connected to a piston through shoes in a housing, the swash plate slides relative to the shoes and rotates synchronously with a drive shaft with a wobbling motion in an axial direction of the drive shaft as the drive shaft is rotated, and an inclination angle of the swash plate is controlled thereby to change a stroke of the piston, comprising: a detection object provided in a first portion of an outer periphery of the swash plate where an imaginary plane passing through a point of intersection between a line connecting a top dead center position and a bottom dead center position of the swash plate and an axial line of the drive shaft in perpendicular relation to the line intersects with the outer periphery of the swash plate; and a detector provided in the housing so as to face the detection object.

2. The displacement detection device according to claim 1, wherein the detector is located in a range between a minimum inclination angle position of the swash plate and a maximum inclination angle position of the swash plate.

3. The displacement detection device according to claim 1, wherein the detection object is a magnet or a magnetic material.

4. The displacement detection device according to claim 3, wherein the detector is a plurality of the magnetic sensors which are provided in a peripheral wall of the housing and aligned parallel to the axial line of the drive shaft.

5. The displacement detection device according to claim 3, wherein the detector is a magnetic sensor.

6. The displacement detection device according to claim 5, wherein the magnetic sensor is a Hall element, a magneto-inductive sensor, a magneto-resistive sensor or a magneto-impedance sensor.

7. The displacement detection device according to claim 1, wherein the detection object and the detector are of ultrasound type or optical type.

8. The displacement detection device according to claim 1, further comprising another detection object provided in a second portion of the outer periphery of the swash plate opposite to the first portion.

9. The displacement detection device according to claim 1, wherein the housing includes a plurality of housing members which are joined to each other by a bolt, the detector being connected to the bolt.

10. The displacement detection device according to claim 1, further including a fitting member which is provided to the housing, the detector being fixed to the fitting member.

Description:

BACKGROUND OF THE INVENTION

The present invention relates to a displacement detection device in a variable displacement compressor for use in a vehicle air-conditioner.

There is generally known a variable displacement compressor (hereinafter referred to merely as “compressor”) which is adapted for use in a vehicle air-conditioner and operable to control its displacement. Such a compressor has a swash plate which is accommodated in a crank chamber and inclinable relative to a drive shaft of the compressor. As the pressure in the crank chamber is raised, the swash plate is inclined toward its vertical position with respect to the axis of the drive shaft (or the inclination angle of the swash plate is decreased). As the pressure in the crank chamber is lowered, on the other hand, the swash plate is inclined approaching the axis of the drive shaft or moving away from its vertical position (or the inclination angle of the swash plate is increased). The compressor has a piston whose stroke length is changed according to the inclination of the swash plate. When the pressure in the crank chamber is high and the inclination angle of the swash plate is small, the piston reciprocates for a short distance of stroke thereby to provide a small displacement of the compressor. On the other hand, when the pressure in the crank chamber is low and the inclination angle of the swash plate is large, the piston reciprocates for a long distance of stroke thereby to provide a large displacement of the compressor.

Japanese Patent Application Publication No. 62-218670 discloses a wobble plate type compressor (cf. Pages 2-5 and FIG. 1 of the publication). This compressor has a drive shaft rotatably supported in a crank chamber, a rotation support member mounted on the drive shaft and a wobble plate fitting member coupled to the rotation support member. The wobble plate fitting member is mounted on the drive shaft through a hinge ball. As the drive shaft is rotated, the wobble plate fitting member is rotated while making a wobbling motion in the axial direction of the drive shaft. A wobble plate is supported by the wobble plate fitting member through a bearing so that the wobble plate is rotatable relative to the wobble plate fitting member. Pistons in cylinders which are formed around the drive shaft in a cylinder block are connected to the wobble plate through piston rods for reciprocating movement in the respective cylinders. Thus, the rotation of the drive shaft is converted through the wobble plate fitting member into the reciprocating and wobbling motion of the wobble plate in the axial direction, thereby causing the piston to reciprocate in the cylinder for the compressor to perform suction and compression of refrigerant gas.

A pin or a magnet as an object to be detected projects from the outer periphery of the wobble plate at a predetermined location. An electromagnetic induction type detector is disposed on the outer peripheral surface of the housing. The detector is located at a position where the pin moves past the detector as the wobble plate wobbles and at the center position of the wobbling motion path of the pin when the wobble plate is at its minimum inclination angle so that the detecting portion of the detector is located in facing relation to the pin. The detector is operable to detect the change of magnetic flux each time the pin passes the detecting portion and to also generate pulse signal, accordingly. The pulse signal is transmitted to a control unit which is connected to the detector. According to the inputted pulse signal, the control unit determines the periods of time during which the pin is located on the left and right sides of the detecting portion of the detector, respectively. It has been known that the ratio of each determined period of time to the sum of both detected periods of time on the left and right sides, namely to one complete cycle of the wobbling motion, depends on the displacement of the compressor. By using this, the control unit calculates the inclination of the wobble plate and hence the displacement of the compressor.

In a swash plate type compressor in which the piston is connected through shoes to the swash plate which has a sliding portion slidable relative to the shoes and rotatable synchronously with a drive shaft, however, a pulse signal is generated per one rotation of the drive shaft. Thus, the structure disclosed in Japanese Patent Application Publication No. 62-218670 cannot be used in such a swash plate type compressor. In order to detect the displacement of the swash plate type compressor, an object to be detected may be provided at an appropriate position on the outer periphery of the swash plate and one or more of detectors may be provided in the compressor housing. The position of the swash plate is sensed by detecting the magnitude of magnetic flux which varies according to the distance between the detector and the detection object.

If the detection object is located at the top or bottom dead center position of the swash plate, the distance between the detection object and the detector varies not only in the axial direction but also in the radial direction from the axis of the drive shaft as the inclination angle of the swash plate is changed. Thus, for permitting the detection in a wide range from the minimum inclination angle position of the swash plate to its maximum position, the detection output from the detector or the magnetic force of the detection object need be increased. In addition, the above-described prior art compressor has a problem in that there is a need to correct the distance of the detection output according to the inclination angle of the swash plate.

The present invention which has been made in view of the above-described problems is directed to a variable displacement compressor which is capable of accurately detecting the angle of a swash plate.

SUMMARY OF THE INVENTION

An aspect in accordance with the present invention provides a displacement detection device for a variable displacement compressor in which a swash plate is connected to a piston through shoes in a housing, the swash plate slides relative to the shoes and rotates synchronously with a drive shaft with a wobbling motion in an axial direction of the drive shaft as the drive shaft is rotated, and an inclination angle of the swash plate is controlled thereby to change a stroke of the piston. The displacement detection device includes a detection object which is provided in a first portion of an outer periphery of the swash plate where an imaginary plane passing through a point of intersection between a line connecting a top dead center position and a bottom dead center position of the swash plate and an axial line of the drive shaft in perpendicular relation to the line intersects with the outer periphery of the swash plate and a detector which is provided in the housing so as to face the detection object.

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 variable displacement compressor according to a first preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of taken along the line I-I in FIG. 1;

FIG. 3 is a schematic view explaining the detection of the inclination angle of a swash plate according to the first preferred embodiment;

FIG. 4 is a schematic view as seen in the direction of the arrow B in FIG. 3;

FIG. 5 is a schematic view explaining the detection of the inclination angle of a swash plate according to a second preferred embodiment;

FIG. 6 is a schematic view as seen in the direction of the arrow C in FIG. 5;

FIG. 7 is a cross-sectional view of a variable displacement compressor according to an alternative embodiment of the present invention;

FIG. 8 is a cross-sectional view of a variable displacement compressor according to an alternative embodiment of the present invention; and

FIG. 9 is a cross-sectional view of a variable displacement compressor according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a variable displacement compressor (hereinafter referred to merely as “compressor”) according to a first preferred embodiment of the present invention with reference to FIGS. 1 through 4. Referring to FIG. 1, the compressor 10 has a housing 11 as an outer shell which includes a cylinder block 12 defining therein a plurality of cylinder bores 12a, a front housing 13 and a rear housing 14. The front housing 13 is joined to the front end of the cylinder block 12 and the rear housing 14 is joined to the rear end of the cylinder block 12. The front housing 13, the cylinder block 12 and the rear housing 14 are integrally fastened to each other by a plurality of bolts 15 (only one being shown in FIG. 1) inserted through the front housing 13, the cylinder block 12 and the rear housing 14.

The front housing 13 and the cylinder block 12 cooperate to define a crank chamber 16 through which a drive shaft 17 extends. The drive shaft 17 is rotatably supported by a radial bearing 18 provided at the front of the front housing 13 and a radial bearing 19 provided at the center of the cylinder block 12. A shaft seal mechanism 20 is provided on the drive shaft 17 at a position forward of the radial bearing 18 in slide contact with the outer circumferential surface of the drive shaft 17. The drive shaft 17 is connected at its front end to an external drive source (not shown) through a power transmission mechanism (not shown).

A lug plate 21 is secured to the drive shaft 17 in the crank chamber 16 for rotation therewith. A swash plate 22 as a part of the displacement-changing mechanism of the compressor is provided behind the lug plate 21 and supported by the drive shaft 17 so as to be slidable in the axial direction of the drive shaft 17 and also inclinable relative to the axis of the drive shaft 17. A hinge mechanism 23 is interposed between the swash plate 22 and the lug plate 21 so that the swash plate 22 and the lug plate 21 are connected therethrough. The hinge mechanism 23 allows the swash plate 22 to rotate synchronously with and be inclined relative to the drive shaft 17 and the lug plate 21.

A coil spring 24 is disposed on the drive shaft 17 between the lug plate 21 and the swash plate 22. A tubular body 25 is slidably disposed on the drive shaft 17 and urged rearward by the coil spring 24. The tubular body 25 urges the swash plate 22 rearward or in the direction which causes the inclination angle of the swash plate 22 to be decreased. It is noted that the inclination angle of the swash plate 22 refers to an angle made between an imaginary plane perpendicular to the axis of the drive shaft 17 and a flat surface of the swash plate 22.

The swash plate 22 has a stop 22a projecting from the front thereof for determining the maximum inclination of the swash plate 22 by contact with the lug plate 21 as shown in FIG 1. A retaining ring 26 is fitted on the drive shaft 17 rearward of the swash plate 22 and a coil spring 27 is disposed on the drive shaft 17 between the retaining ring 26 and the swash plate 22. The minimum inclination of the swash plate 22 is determined by the contact thereof with the front of the coil spring 27. In FIG. 1, the swash plate 22 indicated by the solid line is positioned at its maximum inclination angle and the swash plate 22 indicated by the two-dotted line is inclined at its minimum inclination angle.

Referring to FIG. 2, a magnet 35 as a detection object is provided in the outer periphery of the swash plate 22 and a magnetic sensor 36 as a detector is provided in the peripheral wall 12b of the cylinder block 12 which faces the magnet 35. These elements will be described in detail later.

Referring back to FIG. 1, a single-headed piston 28 is reciprocatably disposed in each of the cylinder bores 12a of the cylinder block 12 (five cylinder bores in this preferred embodiment). The piston 28 is engaged at its neck with the outer periphery of the swash plate 22 through a pair of shoes 29 in a manner well known in the art. The swash plate 22 has a sliding portion which is slidable relative to the shoes 29 and rotatable synchronously with the drive shaft 17. As the drive shaft 17 is rotated, the swash plate 22 is rotated therewith while making a wobbling motion in the axial direction of the drive shaft 17, thereby causing the pistons 28 to reciprocate through the shoes 29 in the longitudinal direction of the compressor 10.

As shown in FIG. 1, a valve plate 31 is interposed between the rear housing 14 and the cylinder block 12. The rear housing 14 defines therein at the center a suction chamber 32 and at the radially outer region a discharge chamber 33, respectively. The suction chamber 32 and the discharge chamber 33 are in communication with a compression chamber 30 in each cylinder bore 12a through a suction port 31a and a discharge port 31b formed in the valve plate 31, respectively. Meanwhile, as the piston 28 moves from its top dead center toward its bottom dead center, refrigerant gas in the suction chamber 32 is drawn into the compression chamber 30 through the suction port 31a. As the piston 28 moves from its bottom dead center toward its top dead center, the refrigerant gas which has been drawn in the compression chamber 30 is then compressed to a predetermined pressure and discharged into the discharge chamber 33 through the discharge port 31b.

The compressor 10 has a displacement control valve 34 which is disposed in the rear housing 14 for changing the inclination angle of the swash plate 22 thereby to adjust the stroke of the pistons 28 or the displacement of the compressor 10. The displacement control valve 34 is arranged in a supply passage (not shown) which connects the discharge chamber 33 to the crank chamber 16. The pressure in the crank chamber 16 depends on the balance between the amount of high-pressure refrigerant gas introduced from the discharge chamber 33 into the crank chamber 16 through the supply passage and the amount of refrigerant gas flowing from the crank chamber 16 into the suction chamber 32 through a bleed passage (not shown) which connects the crank chamber 16 to the suction chamber 32, which balance is adjusted by changing the opening of the displacement control valve 34. Thus, the pressure difference between the pressure in the crank chamber 16 and the pressure in the compression chamber 30 through the piston 28 is varied thereby to change the inclination angle of the swash plate 22.

As shown in FIG. 2, the swash plate 22 has a round hole 22b which is formed at a portion R of the outer periphery thereof where an imaginary plane passing through the point of intersection O between the line connecting the top dead center position P and the bottom dead center position Q of the swash plate 22 and the axial line m of the drive shaft 17 in perpendicular relation to the line between P and Q intersects with the outer periphery of the swash plate 22. The round hole 22b is recessed from the outer peripheral surface 22c of the swash plate 22 toward the axial line m of the drive shaft 17. The magnet 35 or a permanent magnet is disposed in the round hole 22b. The cylinder block 12 has a plurality of through holes 12c which are formed in the peripheral wall 12b thereof between the piston 28 and the bolt 15 and arranged in parallel relation to the axial line m of the drive shaft 17 at position where the through holes 12 may face the magnet 35 in the swash plate 22. A plurality of magnetic sensors 36 (five magnetic sensors 36a, 36b, 36c, 36d and 36e in this preferred embodiment) are disposed in the through holes 12c, respectively. Hall elements are used as the magnetic sensors 36 for detecting the position of the swash plate 22.

Referring to FIGS. 3 and 4, the maximum and minimum inclination angle positions of the swash plate 22 are indicated by the solid line and the chain double-dashed line, respectively. The swash plate 22 is inclinable between the minimum and the maximum inclination angles. As the inclination angle of the swash plate 22 is changed between the minimum and the maximum inclination angles, the outer peripheral portion R of the swash plate 22, in which the magnet 35 is disposed, is displaced parallel to the axial line m of the drive shaft 17. For the sake of the description, positions on the outer peripheral portion R of the swash plate 22 at its minimum and maximum inclination angles are defined as spot R0 and spot R1, respectively. A distance Δg of displacement of the outer peripheral portion R of the swash plate 22 from the spot R0 is directly proportional to the inclination angle of the swash plate 22.

As shown in FIG. 4, the distances between the spots R0 and R1 and the peripheral wall 12b in the radial direction from the axial line m of the drive shaft 17 toward the peripheral wall 12b, more specifically, the spaced distances between the spots R0 and R1 and the points of intersection between lines passing through the spots R0 and R1 in perpendicular relation to the axial line m of the drive shaft 17 and the peripheral wall 12b of the cylinder block 12 are referred to as distances h and i, respectively. These distances h and i are substantially the same. In other words, the spaced distance between the outer peripheral portion R of the swash plate 22 and the peripheral wall 12b in the radial direction remains substantially constant when the inclination angle of the swash plate 22 is changed. Incidentally, the spaced distance between any other point on the periphery of the swash plate 22, e.g. the top dead center position P, and the peripheral wall 12b of the cylinder block 12 in the radial direction varies with the inclination of the swash plate 22 between the minimum and maximum inclination angles as indicated by symbols k and j in FIG. 3, wherein the distance j is smaller than the distance k. Therefore, the distance between the magnet 35 provided in the outer peripheral portion R of the swash plate 22 and the peripheral wall 12b in the radial direction remains substantially constant when the swash plate 22 is rotated while changing its inclination angle. The magnet 35 is rotated while being displaced for the displacement distance Δg in the axial direction from the spot R0 of the outer peripheral portion R of the swash plate 22 at its minimum inclination angle.

For detecting the position of the magnet 35, the magnetic sensors 36 are provided in the peripheral wall 12b of the cylinder block 12. As shown in FIG. 4, the five magnetic sensors 36a through 36e having the same specifications are provided in a line in the range between the minimum and maximum inclination angle positions of the swash plate 22. The magnetic sensor 36a is located at a position where it faces the magnet 35 when the swash plate 22 is inclined at the minimum inclination angle. The magnetic sensor 36e is located at a position where it faces the magnet 35 when the swash plate 22 is inclined at the maximum inclination angle. The other magnetic sensors 36b through 36d are located at positions corresponding to the positions of the magnet 35 at intermediate inclination angles of the swash plate 22.

The magnetic sensors 36a through 36e are operable to sense magnetic flux density and send an electrical signal indicative of the sensed flux density to a control unit (not shown) which is connected to the magnetic sensor 36. The control unit determines the position of the magnet 35 and hence the current position of the swash plate 22 according to the magnitude of the magnetic flux density sensed by each magnetic sensor 36. The control unit stores therein data about the displacement distance Δg of the swash plate 22 corresponding to each of the magnetic sensors 36a through 36e and also data of the relation between the displacement distance Δg and the inclination angle of the swash plate 22. The control unit is operable to perform arithmetic processing based on a certain program to calculate the inclination angle of the swash plate 22, thereby determining the displacement of the compressor 10.

The following will describe the operation of the compressor 10 of this preferred embodiment. As the drive shaft 17 is rotated, the swash plate 22 is rotated with a wobbling motion. Accordingly, the piston 28 reciprocates in the cylinder bore 12, thus the compressor 10 performing suction, compression and discharge of the refrigerant gas. The inclination angle of the swash plate 22 is adjusted by the displacement control valve 34 which controls the pressure difference between the pressure in the crank chamber 16 and the pressure in the compression chamber 30 through the piston 28. When the magnet 35 is located, for example, at spot R2 where the outer peripheral portion R of the swash plate 22 has been displaced for a displacement distance Δg2 from the spot R0 as shown in FIG. 4, the magnetic sensors 36a through 36e sense the magnetic flux density at each location thereof and send the detection signals to the control unit.

In this case, the magnet 35 is located closest to the magnetic sensor 36c in facing relation thereto. Thus, the magnetic flux density sensed by the magnetic sensor 36c is the greatest and, therefore, the control unit determines that the swash plate 22 is located at the spot R2 corresponding to the position of the magnetic sensor 36c. Furthermore, the control unit performs the arithmetic processing based on the program according to the detection signal thereby to calculate the inclination angle of the swash plate 22.

The following advantageous effects are obtained according to the first preferred embodiment.

(1) The magnet 35 is provided in the portion R of the outer periphery of the swash plate 22 where the imaginary plane passing through the point of intersection O between the line connecting the top dead center position P and the pottom dead center position Q of the swash plate 22 and the axial line m of the drive shaft 17 in perpendicular relation to the line between P and Q intersects with the outer periphery of the swash plate 22. By virtue of such arrangement, the magnet 35 is displaced only in axial direction by the change of inclination angle of the swash plate 22. In other words, the distance between the magnetic sensor 36 provided in the peripheral wall 12b and the magnet 35 is variable in the axial direction but remains constant in the radial direction. Therefore, the displacement of the magnet 35 in the axial direction is accurately detected by the magnetic sensor 36, with the result that the inclination angle of the swash plate 22, which is proportional to the displacement of the magnet 35, is accurately detected.

(2) The minimum inclination angle position of the swash plate 22 is set as the base point for detection of the magnet 35 which is provided in the swash plate 22 and displaceable in the axial direction from the base point. Thus, the displacement distance Δg of the magnet 35 from the base point corresponding to the inclination angle of the swash plate 22 is detected by the magnetic sensor 36, thereby accurately detecting the inclination angle of the swash plate 22.

(3) The five magnetic sensors 36a through 36e are aligned in the axial direction in the range between the minimum and maximum inclination angle positions of the swash plate 22 and located at positions each corresponding a predetermined displacement distance Δg as measured from the base point. When the magnet 35 is displaced in the axial direction while the inclination angle of the swash plate 22 is changed, any one of the magnetic sensors 36a through 36e which is then positioned closest to the magnet 35 detects the magnet 35. Thus, the inclination angle of the swash plate 22 is detected with an increased accuracy.

(4) The distance between the magnet 35 in the swash plate 22 and the respective magnetic sensors 36 in the radial direction is substantially constant. Therefore, there is no need to make distance correction of the magnetic sensors 36a through 36e due to change of the above distance in the radial direction in making the detection sensitivity adjustment of the magnetic sensors 36a through 36e. Thus, the setting-up adjustment of the magnetic sensors 36 is simplified.

(5) The magnet 35 and the magnetic sensor 36 are easy to handle and they are merely fixed in the swash plate 22 and the peripheral wall 12b, respectively, thus easy to assemble.

(6) The magnetic sensor 36 is provided in the peripheral wall 12b of the cylinder block 12 between the piston 28 and the bolt 15 and, therefore, there is no intermediate between the magnetic sensor 36 and the magnet 35. Thus, magnetic flux density of the magnet 35 provided in the swash plate 22 is accurately detected by the magnetic sensor 36.

The following will describe a variable displacement compressor according to a second preferred embodiment of the present invention with reference to FIGS. 5 and 6. The second preferred embodiment differs from the first preferred embodiment in that only one magnetic sensor is provided in the compressor 10. The other structure of this compressor is substantially the same as that of the first preferred embodiment. For convenience of explanation, common or similar elements or parts are designated by the same reference numerals as those of the first preferred embodiment and, therefore, the description thereof is omitted and only the modifications will be described.

Referring to FIG. 6, a magnetic sensor 40 is provided in the peripheral wall 12b of the cylinder block 12 at a position where the magnetic sensor 40 faces to the magnet 35 when the swash plate 22 is inclined at the minimum inclination angle. The magnetic sensor 40 detects magnetic flux density of the magnet 35 and send an electrical signal representative of the sensed flux density to the control unit. The magnetic sensor 40 detects the position of the swash plate 22 (or the displacement distance Δg in the axial direction from the base point) according to magnitude of the sensed magnetic flux density. The control unit stores therein data of the relation between the detection output (or the magnitude of magnetic flux density) of the magnetic sensor 40 and the displacement distance Δg of the swash plate 22 and also data of the relation between the displacement distance Δg and the inclination angle of the swash plate 22. The control unit performs arithmetic processing based on a certain program to calculate the displacement distance Δg of the swash plate 22 and the inclination angle of the swash plate 22, thus obtaining information concerning the displacement of the compressor 10.

According to the compressor of the second preferred embodiment, the same advantageous effects as mentioned in the paragraphs (1), (2), (5) and (6) for the first preferred embodiment are obtained. The second embodiment offers additional advantages as follows.

The magnetic sensor 40 is provided so as to face the magnet 35 when the swash plate 22 is positioned at the minimum inclination angle. Thus, as the magnet 35 is displaced in the axial direction with the inclination of the swash plate 22, the magnetic flux density of the displaced magnet 35 is detected by one magnetic sensor 40 for calculation by the control unit of the displacement distance Δg from the base point of the swash plate 22 and the inclination angle of the swash plate 22. As a result, the number of parts is reduced and the device is made simpler in structure.

The present invention is not limited to the embodiments described above but may be modified into various alternative embodiments as exemplified below.

In the first and second preferred embodiments, the magnet 35 is provided in the outer peripheral portion R of the swash plate 22 where the imaginary plane passing through the point of intersection O between the line connecting the top dead center position P and the bottom dead center position Q of the swash plate 22 and the axial line m of the drive shaft 17 in perpendicular relation to the line between P and Q intersects with the outer periphery of the swash plate22. Alternatively, the magnet may be provided at a portion S of the outer periphery of the swash plate 22 that is opposite to the outer peripheral portion R, as shown in FIG. 2. The magnetic sensor may be provided in facing relation to the magnet. As a further alternative of the invention, in addition to the magnet 35 at the outer peripheral portion R of the swash plate 22, another magnet 37 may be provided at the outer peripheral portion S of the swash plate 22 as shown in FIG. 7. In this case, reliability of detection is enhanced.

The object to be detected and the detector are provided by the magnet and the magnetic sensor in the first and second preferred embodiments. Alternatively, any magnetic material may be used as the detection object instead of the magnet. Any other types of magnetic sensors such as magneto-inductive sensor, magneto-resistive (MR) sensor, magneto-impedance (MI) sensor and the like other than the Hall element may be used.

The detection object and the detector are not limited to the magnet and the magnetic sensor, respectively. Alternatively, they may be of various types such as ultrasound type, optical type and the like.

The magnetic sensor 36 is provided in the peripheral wall 12a of the cylinder block 12 in the first and second preferred embodiments. Alternatively, a magnetic sensor 41 may be connected to the bolt 15 which is provided adjacent to the peripheral wall 12a of the cylinder block 12 for joining the housing members (the front housing 13, the cylinder block 12 and the rear housing 14) as shown in FIG. 8. Or, any other fitting member may be provided and the magnetic sensor may be fixed thereto. Fox example, a fitting member 42 may be provided to the cylinder block 12 and a magnetic sensor 43 may be fixed to the fitting member 42 as shown in FIG. 9.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.