Abstract:
A piston of an axial piston cylinder group A of an expander is driven by a cam surface with a height that changes in a direction of an axis L of a rotor formed on a cam member fixed to a casing to surround the axis L. A roller rotatably provided at a tip end of the piston abuts against the cam surface. Therefore, timing and length of each intake stroke, expansion stroke and exhaust stroke are optionally set, and the piston is driven in an optional timing and at an optional speed, to enhance the efficiency of the expander. The roller rolls on the cam surface to minimize transmission, from the cam surface to the piston, of the reaction force which does not contribute to torque of the rotor, and to prevent the sliding surfaces of the piston and the cylinder sleeve from twisting to enhance durability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-416233, filed in Japan on Dec. 15, 2003, the entirety of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a rotating fluid machine including a casing, a rotor rotatably supported in the casing, and an axial piston cylinder group disposed at the rotor to surround an axis of the rotor.  
         [0004]     2. Description of the Related Art  
         [0005]     A rotating fluid machine is disclosed in Japanese Patent Application Laid-open No. 2002-256805. This rotating fluid machine includes a first axial piston cylinder group disposed in an inner side in the radial direction, and a second axial piston cylinder group disposed in an outer side in the radial direction. A tip end of a piston of the first axial piston cylinder group abuts to a dimple of a swash plate, and a piton of the second axial piston cylinder group is connected to the swash plate via a connecting rod.  
         [0006]     When the stroke of the piston of the axial piston cylinder group of the expander is controlled by the swash plate, the stroke of the piston with respect to the rotational angle of the rotor is disadvantageously restricted to a sinewave shape. Therefore, increasing the expansion ratio by enlarging the length of the expansion stroke to exceed 180° of the rotational angle of the rotor is impossible, because the maximum length of the expansion stroke is limited to 180° by the swash plate.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention has been achieved in view of the above circumstances, and has an object to optionally set the relationship of the stroke of a piston with respect to a rotational angle of a rotor of a rotating fluid machine.  
         [0008]     In order to attain the above-described object, according to a first feature of the present invention, there is provided a rotating fluid machine including a casing; a rotor which is rotatably supported in the casing. An axial piston cylinder group is disposed at the rotor to surround an axis of the rotor. An annular cam member is fixed to the casing to surround the axis, and is provided with a cam surface whose height changes in a direction of the axis. A cam follower is provided at a tip end of a piston of the axial piston cylinder group, and abuts to the cam surface of the cam member.  
         [0009]     According to a second feature of the present invention, in addition to the first feature, the cam follower is a roller having a rotary shaft extending in a radial direction with the axis as a center.  
         [0010]     According to a third feature of the present invention, in addition to the second feature, the rotating fluid machine further includes a rotation preventing device which prevents the piston from rotating with respect to the cylinder sleeve.  
         [0011]     A ball  56 , a roller  76  and a roller pin  77  in embodiments correspond to the rotation preventing device of the present invention. A roller  73  in the embodiments corresponds to the cam follower of the present invention.  
         [0012]     With the arrangement of the first feature, in order to guide the piston of the axial piston cylinder group of the rotating fluid machine, the cam surface whose height changes in the direction of the axis of the rotor is formed on the annular cam member fixed to the casing to surround the axis. In addition, the cam follower is provided at the tip end of the piston and is made to abut against the cam surface. Therefore, the timing and the length of each of the strokes such as an intake stroke, an expansion stroke and an exhaust stroke are optionally set, and the piston is operated in an optional timing and at an optional speed, to thereby enhance the efficiency of the expander.  
         [0013]     With the arrangement of the second feature, the cam follower is provided at the piston and abuts to the cam surface of the cam member and is constructed by the roller having the rotary shaft extending in the radial direction with the axis of the rotor as the center. Therefore, the reaction force acting from the cam surface on the piston is made to act only in the tangential direction of the rotor, so that twisting of the piston and an increase in the slide resistance can be minimized. In addition, the contact between the cam follower and the cam surface is not a sliding contact but a rolling contact, whereby the abrasion of the cam follower and the cam surface is suppressed to enhance durability.  
         [0014]     With the arrangement of the third feature, the piston is prevented from rotating with respect to the cylinder sleeve by the rotation preventing device. Therefore, the direction of the rotary shaft of the cam follower is always made to correspond to the radial direction with respect to the axis line, so that the reaction force acting from the cam surface on the piston can be made to act only in the tangential direction of the rotor.  
         [0015]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0017]      FIG. 1  is a longitudinal sectional view of an expander;  
         [0018]      FIG. 2  is a sectional view taken along the  2 - 2  line in  FIG. 1 ;  
         [0019]      FIG. 3  is a view seen along the line  3 - 3  in  FIG. 1 ;  
         [0020]      FIG. 4  is an enlarged view of the section  4  in  FIG. 1 ;  
         [0021]      FIG. 5  is an exploded perspective view of a rotor;  
         [0022]      FIG. 6  is a sectional view taken along the line  6 - 6  in  FIG. 4 ;  
         [0023]      FIG. 7  is a sectional view taken along the line  7 - 7  in  FIG. 4 ;  
         [0024]      FIG. 8  is a view seen along the line  8 - 8  in  FIG. 4 ;  
         [0025]      FIG. 9  is a perspective view showing the relationship between a cam member and a piston;  
         [0026]      FIG. 10  is a graph showing the relationship between the rotational angle of the rotor and the stroke of the piston;  
         [0027]      FIGS. 11A and 11B  are views showing the relationship between the rotational angle of the rotor and each stroke;  
         [0028]      FIG. 12  is a view corresponding to  FIG. 4 , according to a second embodiment of the present invention;  
         [0029]      FIG. 13  is a sectional view taken along the line  13 - 13  in  FIG. 12 ;  
         [0030]      FIG. 14  is a view seen along the line  14 - 14  in  FIG. 12 ;  
         [0031]      FIG. 15  is a view corresponding to  FIG. 4 , according to a third embodiment of the present invention;  
         [0032]      FIG. 16  is a sectional view taken along the line  16 - 16  in  FIG. 15 ; and  
         [0033]      FIG. 17  is a view taken along the line  17 - 17  in  FIG. 15 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]     An expander E of this embodiment is used in, for example, a Rankine cycle system. The expander E converts the thermal energy and the pressure energy of high-temperature high-pressure steam as a working medium into mechanical energy, and outputs it. A casing  11  of the expander E is formed from a casing body  12  with a front cover  15  joined via a seal  13  to a front opening of the casing body  12  by a plurality of bolts  14 . A rear cover  18  is joined via a seal  16  to a rear opening of the casing body  12  by a plurality of bolts  17 . An oil pan  21  is joined via a seal  19  to a lower opening of the casing body  12  by a plurality of bolts  20 .  
         [0035]     A rotor  22  is arranged rotatably around an axis L extending in the fore-and-aft direction through the center of the casing  11  and includes a front part supported by combined angular bearings  23  provided in the front cover  15  with a rear part thereof supported by a radial bearing  24  provided in the casing body  12 . A cylindrical cam member  25  is fixed to a rear surface of the front cover  15  to surround an axis L by a plurality of bolts  26 . An endless cam surface  25   a  with a height that changes in the direction of the axis L is formed on a rear end surface of the cam member  25 .  
         [0036]     The rotor  22  includes an output shaft  32  supported in the front cover  15  by the combined angular bearings  23 . Three sleeve support flanges  33 ,  34 , and  35  are formed integrally with a rear part of the output shaft  32  via notches  57  and  58  (see  FIG. 4 ) of predetermined widths from one another. A rotor head  38  is joined by a plurality of bolts  37  to the rear sleeve support flange  35  via a metal gasket  36  and is supported in the casing body  12  by the radial bearing  24 . A heat-insulating cover  40  is fitted over the three sleeve support flanges  33 ,  34 , and  35  from the front and is joined to the front sleeve support flange  33  by a plurality of bolts  39 .  
         [0037]     Sets of five sleeve support holes  33   a ,  34   a , and  35   a  are formed in the three sleeve support flanges  33 ,  34 , and  35 , respectively, at intervals of 72° around the axis L. Five cylinder sleeves  41  are fitted into the sleeve support holes  33   a ,  34   a , and  35   a  from the rear. A flange  41   a  is formed on the rear end of each of the cylinder sleeves  41 , and axial positioning is carried out by abutting the flange  41   a  against the metal gasket  36  while fitting the flange  41   a  into a step  35   b  formed in the sleeve support holes  35   a  of the rear sleeve support flange  35  (see  FIG. 4 ). A piston  42  is slidably fitted within each of the cylinder sleeves  41  with a steam expansion chamber  43  being defined between the rear end of the piston  42  and the rotor head  38 .  
         [0038]     A plate-shaped bearing holder  92  is overlaid on a front surface of the front cover  15  via a seal member  91  and is fixed by bolts  93 . A pump body  95  is overlaid on a front surface of the bearing holder  92  via a seal member  94  and is fixed by bolts  96 . The combined angular bearings  23  and  23  are sandwiched between the step portion of the front cover  15  and the bearing holder  92  and fixed in the direction of the axis L.  
         [0039]     A shim  97  of a predetermined thickness is held between a flange  32   d  formed at the output shaft  32  which supports the combined angular bearings  23  and  23 , and an inner race of the combined angular bearings  23  and  23 . The inner race of the combined angular bearings  23  and  23  is fastened by a nut  98  screwed into an outer periphery of the output shaft  32 . As a result, the output shaft  32  is positioned in the direction of the axis L with respect to the combined angular bearings  23  and  23 , namely, the casing  11 .  
         [0040]     An oil passage  32   a  extending on the axis L is formed inside the output shaft  32  integral with the rotor  22 . A front end of the oil passage  32   a  branches in the radial direction and communicates with an annular groove  32   b  at an outer periphery of the output shaft  32 . At an inside position in the radial direction of the sleeve supporting flange  34  at the center of the rotor  22 , an oil passage blocking member  45  is screwed into an inner periphery of the oil passage  32   a  via a seal member  44 . A plurality of oil holes  32   c  extend in the radially outward direction from the oil passage  32   a  in the vicinity of the oil passage blocking member  45  and open to an outer peripheral surface of the output shaft  32 .  
         [0041]     A trochoid oil pump  49  is disposed between a recessed portion  95   a  formed in a front surface of a pump body  95  and a pump cover  48  fixed to the front surface of the pump body  95  via a seal member  46  by a plurality of bolts  47 . The trochoid oil pump  49  includes an outer rotor  50  rotatably fitted into the recessed portion  95   a , and an inner rotor  51  fixed to the outer periphery of the output shaft  32  and meshed with the outer rotor  50 . An internal space of the oil pan  21  communicates with an inlet port  53  of the oil pump  49  via an oil pipe  52  and an oil passage  95   b  of the pump body  95 . A discharge port  54  of the oil pump  49  communicates with an annular groove  32   b  of the output shaft  32  via an oil passage  95   c  of the pump body  95 .  
         [0042]     Next, the structure of the piston  42  will be described in detail with reference to  FIG. 4  to  FIG. 9 .  
         [0043]     The piston  42  is constructed by integrally connecting a tip end part  61  and a base end part  62  by welding. A large-volume and vacuum heat-insulating space  64  is defined inside the piston  42 . A top ring  65  and a second ring  66  are supported at an end portion of the base end part  62  on the side of an expansion chamber  43 . At a connecting portion of the tip end part  61  and the base end part  62 , an annular oil groove  63  is formed which is slightly smaller in diameter. A ball guide groove  61   a  is formed that extends from the oil groove  63  in the direction of the axis L along an outer periphery of the tip end part  61 . A semispherical ball supporting hole  41   d  is formed in an inner surface of the cylinder sleeve  41 . A ball  56  is placed astride the ball supporting hole  41   d  and the ball guide groove  61   a.    
         [0044]     A roller  73  in a ball bearing shape is rotatably supported via a rotary shaft  72  between a pair of brackets  61   b  and  61   b  projecting forward from the tip end part  61  of the piston  41 . The piston  41  is positioned in the rotational direction while being enabled to move in the direction of the axis L by the ball  56  engaged in the ball supporting hole  41   d  and the ball guide groove  61   a . In this positioned state, the rotary shaft  72  of the roller  73  extends in the radial direction with respect to the axis L. The roller  73  rollably abuts against a cam surface  25   a  of the cam member  25 . At this time, the roller  73  and the cam surface  25   a  are in linear contact with each other within a plane perpendicular to the axis L.  
         [0045]     An oil supply pipe  74  leading to an oil supply source (not shown) is inserted into the cam member  25  in order to lubricate the cam surface  25   a  on which the roller  73  rolls. An oil supply hole  25   b  extends from the oil supply pipe  74  and opens to a position near the cam surface  25   a.    
         [0046]     An annular groove  41   b  (see  FIG. 4  and  FIG. 5 ) is formed in an outer periphery of a middle portion of the cylinder sleeve  41 . A plurality of oil holes  41   c  are formed in the annular groove  41   b . The oil groove  63  formed in the piston  42  communicates with the oil holes  41   c  of the cylinder sleeve  41 .  
         [0047]     An annular lid member  69  is welded to a front side of a rotor head  38  connected to a rear surface of the sleeve supporting flange  33  at the front side of the rotor  22  by bolts  37 , or is welded to the side of the expansion chamber  43 . An annular heat insulating space  70  (see  FIG. 4 ) is defined on a back or rear surface of the lid member  69 . The rotor head  38  is positioned by a knock pin  55  in the rotational direction with respect to the sleeve supporting flange  35  at the rear.  
         [0048]     As shown in  FIG. 1 , a rotary valve  71  is provided between the rear cover  18  of the casing  11  and the cylinder head  38  of the rotor  22 . The rotary valve  71  sequentially supplies the high-temperature high-pressure steam from a steam supply pipe  67  to the five expansion chambers  43  following the rotation of the rotor  22 . The resultant low-temperature and low-pressure steam from the expansion chambers  43  is discharged into a steam discharge chamber  68  defined between the body casing  12  and the rear cover  18 .  
         [0049]     Five cylinder sleeves  41  and five pistons  42  constitute the axial piston cylinder group A of the present invention.  
         [0050]     Next, an operation of the expander E of this embodiment having the above-described construction will be described.  
         [0051]     When the high-temperature high-pressure steam generated by heating water with an evaporator is supplied from the steam supply pipe  67  via the rotary valve  71  into the expansion chamber  43  in the cylinder sleeve  41 , the piston  42  fitted in the cylinder sleeve  41  is pushed out forward from the top dead center toward the bottom dead center, so that the roller  73  provided at the tip end part  61  of the piston  42  presses the cam surface  25   a  of the cam member  25 . As a result, a rotational torque is given to the rotor  22  by the reaction force which the piston  42  receives from the cam surface  25   a . Each time the rotor  22  makes one-fifth of a rotation, the high-temperature high-pressure steam is supplied into a new adjacent expansion chamber  43 , to continuously drive the rotor  22  to rotate. While the piston  42 , which has reached the bottom dead center following the rotation of the rotor  22 , retreats toward the top dead center by being pressed by the cam surface  25   a , the low-temperature low-pressure steam forced out of the expansion chamber  43  is discharged into the steam discharge chamber  68  via the rotary valve  71 .  
         [0052]     The oil pump  49  provided at the output shaft  32  is operated following the rotation of the rotor  22 . Oil which is sucked from the oil pan  21  through the oil pipe  52 , the oil passage  95   b  of the pump body  95  and the inlet port  53 , is discharged from the discharge port  54 . Oil is then supplied to the oil groove  63  formed in the outer peripheral surface of the piston  42  through the oil passage  95   c  of the pump body  95 , the oil passage  32   a  of the output shaft  32 , the annular groove  32   b  of the output shaft  32 , the oil holes  32   c  of the output shaft  32 , the annular groove  41   b  of the cylinder sleeve  41  and the oil holes  41   c  of the cylinder sleeve  41 . The oil held in the oil groove  63  lubricates sliding surfaces of the piston  42  and the cylinder sleeve  41 , and is thereafter returned to the oil pan  21 .  
         [0053]     As shown by the broken line in  FIG. 10 , in the prior art in which the piston  42  of the axial piston cylinder group A is made to abut against the dimple of the swash plate, the stroke of the piston  42  with respect to the phase of the rotor  22  is determined to be a sinewave shape. However, this embodiment uses the cam member  25  in place of the swash plate, whereby the relationship of the stroke of the piston  42  with respect to the rotational angle of the rotor  22  can be optionally set as shown by the solid line in  FIG. 10 .  
         [0054]      FIGS. 11A and 11B  show the relationship of the rotational angle of the rotor  22 , and the intake stroke, the expansion stroke and the exhaust stroke. In the prior art using the swash plate shown in  FIG. 11A , the expansion stroke can be taken only up to the vicinity of the bottom dead center at the phase of 180°. However, in this embodiment using the cam member  25  as shown in  FIG. 11B , it is possible to take as long an expansion stroke as up to the vicinity of the bottom dead center of the phase of 240°. Therefore, the expansion ratio of the high-temperature high-pressure steam is increased to increase the output force of the expander E.  
         [0055]     In the prior art in which the tip end portion of the piston  42  is made to abut against the dimple of the swash plate, the abutting point between the piston  42  and the dimple of the swash plate moves following the rotation of the rotor  22 . Therefore, the reaction force which the piston  42  receives from the swash plate obtains components other than the component in the direction to causes the rotor  22  to generate effective torque (namely, the tangential direction of the rotor  22 ), causing a problem of twisting of the piston  42  and an increase in the slide resistance due to such unnecessary reaction force components.  
         [0056]     In contrast, in this embodiment, the roller  73  provided at the tip end of the piston  42  is made to rollably abut against the cam surface  25   a  of the cam member  25 , and the piston  42  is prevented from rotating by the ball  56  to make the roller  73  and the cam surface  25   a  to be always in linear contact with each other on the radial line with the axis L as the center. Therefore, the reaction forces other than that in the tangential direction of the rotor  22  are prevented from acting on the piston  42 , so that the twisting of the piston  42  and the increase in the slide resistance are minimized, to thereby enhance output force and durability of the expander E.  
         [0057]     In the prior art, there is a limitation when the inclination angle of the swash plate is increased in order to secure a large expansion ratio of the expander E by increasing the stroke of the piston  42 . However, if the piston  42  is disposed on a large pitch circle to enlarge the stroke without increasing the inclination angle of the swash plate, there is also a problem that the dimensions of the expander E are increased. However, according to this embodiment, the cam member  25  is used in place of the swash plate. Thus, the stroke of the piston  42  can be easily enlarged, thereby securing a large expansion ratio to enhance the output force without enlarging the expander E.  
         [0058]     The ball  56  is engaged in the ball guide groove  61   a  formed in the outer peripheral surface of the piston and in the ball supporting hole  41   d  formed in the inner peripheral surface of the cylinder sleeve  41 . Therefore, the piston  42  can be reliably prevented from rotating with a simple structure involving small numbers of components and machining steps.  
         [0059]      FIG. 12  to  FIG. 14  show a second embodiment of rotation preventing structure for the piston  42 .  
         [0060]     In the second embodiment, the piston  42  includes a recessed portion  61   c  which opens to one side surface of the tip end part  61 . A roller  76  having a ball bearing shape is rotatably supported at a rotary shaft  75  which is inserted into a shaft hole  61   d  penetrating through the recessed portion  61   c . An outer peripheral surface of the roller  76  slightly protrudes in the radially outward direction from the outer peripheral surface of the piston  42 , and rollably abuts against a flat guide groove  41   e  which is formed on the inner peripheral surface of the cylinder sleeve  41  in the direction of the axis line L.  
         [0061]     As described above, the roller  76  and the guide groove  41   e  are in linear contact with each other in the tangential direction of the rotor  22 , and therefore the piston  42  can be prevented from rotating while the piston  42  is enabled to slide smoothly in the direction of the axis L. According to the second embodiment, the Hertzian surface pressure, which the guide groove  41   e  of the cylinder sleeve  41  receives from the roller  76 , can be made significantly small as compared with the Hertzian surface pressure which the ball guide groove  61   a  of the piston  42  of the first embodiment receives from the ball  56 .  
         [0062]      FIG. 15  to  FIG. 17  show a third embodiment of rotation preventing structure of the piston  42 .  
         [0063]     The third embodiment includes a roller pin  77  rotatably inserted into a pin hole  41   f  which penetrates through the cylinder sleeve  41 . A flat guide surface  61   e  that abuts against the roller pin  77  rollably is formed in the direction of the axis L on the outer peripheral surface of the tip end part  61  of the piston  42 .  
         [0064]     As described above, the roller pin  77  and the guide surface  61   e  are in linear contact with each other in the tangential direction of the rotor  22 . Therefore, the piston  42  can be prevented from rotating while the piton  42  is enabled to slide smoothly in the direction of the axis L. According to the third embodiment, although the third embodiment has a simple structure as in the first embodiment, the Hertzian surface pressure of the guide portion can be reduced as compared with the first embodiment.  
         [0065]     The embodiments of the present invention have been described, however various changes in design may be made without departing from the subject matter of the present invention.  
         [0066]     The profile of the cam surface  25   a  of the cam member  25  is not limited to the embodiments as described, and may be appropriately changed in accordance with its purpose so that, for example, the expansion stroke is performed at an early stage after the intake stroke to recover energy before thermal loss and mechanical loss become large. The exhaust may suddenly be performed when the tension of the top ring  65  and the second ring  66  become weak upon opening of the exhaust port to reduce the exhaust pumping loss and mechanical loss. The exhaust port may be closed after the piton reaches the top dead center by reducing the stroke in the vicinity of the top dead center of the piston  42  to compress the liquefied working medium and suppress the occurrence of minus torque.  
         [0067]     The cam follower is not limited to the roller  73  in the embodiments, and may be a ball rotatable in any direction. If such a ball is used, the prevention of rotation for the piston  42  is unnecessary. Also, it is possible to use a slider having abrasion resistance as a cam follower in place of a roller or ball. When the slider is used, the contact with the cam surface is not rolling contact, but sliding contact.  
         [0068]     The rotating fluid machine of the present invention is not limited to the expander E, and is applicable to a compressor.  
         [0069]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.