US3827338A

US3827338A - Fluid device

Info

Publication number: US3827338A
Application number: US00174097A
Authority: US
Inventors: H Oguni; M Nakagawa
Original assignee: Kawasaki Heavy Industries Ltd
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 1970-08-25
Filing date: 1971-08-23
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: SE379830B; GB1347332A; DE2142323C3; NO138225B; DE2142323B2; FR2106028A5; DE2142323A1; NO138225C

Abstract

This invention relates to fluid devices of the radial piston type providing eccentric rollers, eccentric pinions or cams of elliptic or any shape as desired which are mounted on the piston pins for increasing the number of piston strokes and producing a high output power with small capacity.

Description

United States Patent 1191 1111 3,827,338 Uguni et a1. Aug. 6, 1974 [5 1 FLUID DEVICE 1,004,504 9/1911 Van Nette 417/273 2,010,378 8/1935 Sassen 91/477 [75] Inventors: Hlmsh Ogum, Akashl; Masaya 2,303,685 12/1942 Eden et al .1 91 492 Nakagawa, Osaka, both of Japan 2,416,940 3 1947 Morton 91/492 [73] Assignee: Kawasaki Jukogyo Kabushiki gsfi Kyogo'km Japan 3:331:326 7/1967 Casey 91/496 22] Fil d; A 23 1971 3,656,405 4/1972 Klinkhammer.... 91/197 3,661,057 5/1972 Rogov 91/492 1 {21] Appl. N0.: 174,097

FOREIGN PATENTS OR APPLICATIONS [30] Foreign Application Priority Data 230,318 1/1959 Australia 91/183 Aug. 25, 1970 Japan 45 732150 Primary Emminer wmiam L- Frcch Assistant Examiner-G. P. LaPointe liil 17.11111131111 111 1132 Agent, or and 9 [58] Field of Search 91/472, 476-477,

91/481, 482, 483, 491, 492, 493, 495, 496, [57] ABSTRACT 183488; 123/44 This invention relates to fluid devices of the radial piston type providing eccentric rollers, eccentric pinions [56] References Cited or cams of elliptic or any shape as desired which are mounted on the piston pins for increasing the number UNITED STATES PATENTS of piston strokes and producing a high output power 593,470 11/1897 Heaton 123/44 B with mall capacity,

668,855 2/1901 Koetter 797,571 8/1905 Goddard 123/44 A 9 Claims, 15 Drawing Figures PAIEmmws emu INVENTORS "mas/n 0 s um mzuranw emu SHEH 3 BF 9 9 NM MW 0 H mm Euk w W w A am /M PAIENTED M 61974 3.827. 338 saw u or 9 Fig.5

ENTOR If! 6 All/*- BY W) IV M06011 FLUID DEVICE This invention relates to fluid devices, and more particularly it is concerned with a fluid pump or fluid motor of the radial piston type.

In conventional fluid pumps or motors of the radial piston type, it has hitherto been customary to provide means for increasing the pressure of an operation fluid and/or increasing the working volume of the fluid for each revolution of the shaft in order to produce a high output power with a small capacity. Attempts have therefore been made to increase the diameter of the pistons or to increase the total piston strokes for each revolution of the shaft in order to increase the working volume of the fluid for one revolution of the shaft. In such cases, the total piston strokes represent the total number of piston strokes of the pump or motor which can generally be obtained by multiplying the piston strokes by the number of pistons.

An increase in the diameter of pistons for increasing the working volume of the fluid generally results in a pump or motor (in the interest of brevity, reference will hereinafter be had to a pump) becoming greater in size. Therefore, it has been customary to provide means for increasing the number of piston strokes. Thus, attempts have been made to increase the length of piston strokes or to increase the number of pistons by arranging the pistons radially of the pump.

In order to increase the number of piston strokes, means has been provided for causing the piston heads to roll on an irregularly curved surface through ball bearings or the like. The use of such means has, however, a disadvantage in that the fabrication of an outer peripheral surface which is irregularly curved is troublesome and time consuming. Besides, such irregularly curved surface is subjected to forcesexerted by the pistons due to the fact that the pistons are brought into contact with the piston heads on such irregularly curved surface, so that such curved surface is under a markedly high pressure, thereby making it impossible to obtain a high pressure pump.

Accordingly, this invention obviates the aforementioned disadvantages of conventional fluid pumps or motors. The invention has as its object the provision of a fluid pump or motor which is simple in construction, easy to make and adapted for operation under high pressure and/or at high speed.

The aforementioned object of this invention is accomplished by providing eccentric rollers, eccentric pinions or cams of elliptic or any other shape as desired which are mounted on the piston pins.

This invention will now be described with reference to preferred embodiments thereof shown in the accompanying drawings in which a number of eccentric pinions are each mounted on the piston pin.

FIG. 1 is a sectional side view of the device according to this invention;

FIG. 2 is a fragmentary sectional front view of the device of FIG. 1;

FIG. 3 is a fragmentary enlarged view of FIG. 1;

FIG. 4 is a fragmentary enlarged view of FIG. 2;

FIG. 5 is a fragmentary sectional side view of another embodiment of this invention;

FIG. 6 to FIG. 8 are views in explanation of variations in the torque produced by the pistons;

FIG. 9 is a diagrammatic representation of variations in a piston stroke in a conventional device;

FIG. 10 is a diagrammatic representation of one example of the piston stroke according to this invention;

FIG. 11 is an enlarged elevational view of one embodiment of the cam and ring rest;

FIG. 12 is an elevational view of another embodiment of the cam and the ring rest;

FIG. 13 is a cross sectional view similar to FIG. 3 illustrating another embodiment of the invention;

FIG. 14 is a cross sectional view of a further embodiment of the present invention; and

FIG. 15 is a side view of the embodiment illustrated in FIG. 14.

In FIG. 1, a main shaft 1 is connected to a cylinder body 2 and held against rotation relative to the cylinder body by means of a spline 25. A number of pistons 3 are fitted in the cylinder body 2 and arranged radially thereof. A pair of pistons 3 disposed in 'side-by-side relation are connected to a piston pin 8 formed integrally with a pinion shaft 4. The pinion shaft 4 has an axis 4 which is eccentric with respect to the axis 8 of the piston pin 8 (See FIG. 4). A pinion 5 is mounted on each pinion shaft 4. The pinions 5 are maintained in meshing engagement with an internally toothed gear 9 which is secured to a case.

A plurality of cams 6 (which are in the form of rings in this embodiment) are each disposed on opposite sides of the pinion 5 (See FIG. 3) and each mounted on the outer peripheral surface of each pinion shaft 4. The cams 6 are adapted to move in rolling motion on the inner peripheral surfaces of ring rests 7 mounted on opposite sides of the teeth of the internally toothed gear 9.

A rear cover 10 and a front cover 11 are clamped to opposite side portions of the internally toothed gear 9. The main shaft 1 is journalled by

bearings

26 and 12 mounted on the rear cover 10 and front cover 11 respectively. A portion of the front cover 11 through which the main shaft I extends is sealed by an oil seal 13.

The rear cover 10 is formed with working fluid outlet and

inlet ports

23 and 24. Whether these ports serve as outlet ports or inlet ports may vary depending on whether the device is used as a pump or a motor. The rear cover 10 is further formed with

annular fluid passageways

21 and 22 maintained in communication with the outlet and

inlet ports

23 and 24 respectively, and fluid passageways 21' and 22' branching off from such

annular fluid passageways

21 and 22 respectively.

A number of cylinder fluid chambers 18 each containing a quantity of fluid acting on the pistons 3 are formed in the cylinder body 2. A number of fluid passageways l7 and 17' extending from the cylinder chambers 18 along the axis of the main shaft 1 to open in opposite side portions of the cylinder body 2 and a number of fluid passageways 19 each connecting a pair of cylinder chambers 18 disposed in side-byside relationship are also formed in the cylinder body 2.

Interposed between the cylinder body 2 and rear cover 10 is a valve plate 14 which is formed with

ducts

15 and 16, the ducts 15 being maintained in communication with the fluid passageways 21' formed in the rear cover 10 and the fluid passageways 17 formed in the cylinder body 2 and the ducts 16 being maintained in communication with the fluid passagway 22' formed in the rear cover 10 and the fluid passageways 17 formed in the cylinder body 2. Formed in the front cover 11 is an oil pocket 20 which is maintained in communication with the fluid passageways 17 formed in the cylinder body 2.

FIG. shows another embodiment of this invention in which a number of pistons 29 are mounted in a cylinder body 28 and arranged radially thereof. Each of the pistons 29 is connected to a piston pin 30 which is formed integrally with a plurality of pinion shafts 31 disposed on opposite sides of the piston pin 30. Each piston pin 30 is eccentric with respect to the associated pinion shafts 31. A plurality of rings 33 are mounted on the pinion shafts 31 through bearings 33. The rings 33 are adapted to move in rolling motion along the inner surfaces of ring rests 34 attached to a cover 35. External gears 36 whose central axial line is aligned with the axis of the main shaft 1 are formed integrally with the cover 35 and disposed in the inwardly projecting portion thereof. The pinions 32 are maintained in meshing engagement with the external gears 36.

The manner of operation of the device according to this invention follows from the structures described hereinabove. The operation of the device will be explained with the device functioning as a fluid motor.

A working fluid is supplied through the inlet port 23 and passes through the annular fluid passageway 21 and fluid passageway 21 to reach one of the ducts in the valve plate 14, thence is passes through one of the fluid passageways 17 in the cylinder body 2 to flow into one of the cylinder fluid chambers 18 to actuates one of the pistons 3. At the same time, part of the fluid passes through one of the fluid passages 19 to the cylinder fluid chamber 18 disposed in side-by-side relation with the first-mentioned cylinder fluid chamber 18 so as to actuate the adjacent piston 3. Part of the fluid further passes through one of the fluid passageways 17 into the annular channel 20. Thedevice according to this invention is designed such that the pressure of a quantity of fluid introduced into the oil pockets and the pressure of a quantity of fluid in the ducts 15 balance so as to preclude axial movement of the cylinder body 2.

As the pressure of fluid is applied to each of a pair of pistons 3 disposed in side-by-side relationship, the pair of pistons 3 are pushed to move outwardly so that the piston pin 8 to which the pair of pistons 3 are connected is pushed to move radially of the center of the motor. Since the piston pin 8 is eccentric with respect to the pinion shaft 4, a force acting on the piston pin 8 acts as a rotational force for rotating the piston shaft 4 on its own axis 4. The pinion 5 rotates on its own axis as the pinion shaft 4 rotates, so that the pinion moves in rolling motion while being maintained in meshing engagement with the internally toothed gear 9.

Rolling movement or rotation of the pinion 5 on its own axis causes the associated pair of pistons 3 to move in reciprocating motion in the cylinder body 2 which in turn is caused to rotate relative to the internally toothed gear 9. A path of movement of the axis 8 of a given piston pin 8 can be expressed as a curve 27 shown in FIG. 2. If the internally toothed gear 9 is firmly fixed, rotation of the pinions 5 on their own axis will cause the cylinder body 2 to rotate about the main shaft 1, thereby causing the main shaft 1 to rotate through the spline 25. Thus, the main shaft 1 functions as an output shaft.

In considering the significant development afforded in the invention, attention is directed to FIG. 2 illustrating the relationship between adjacent pinion shafts 4 as the fluid device operates. As can be seen in FIG. 2, the pistons 3 effect a radially directed, relative to main shaft 1, reciprocating movement, however, the location of the pinion shaft 4 attached to each pair of pistons 3 is not always in direct radial alignment with the piston.

If we consider that FIG. 2 illustrates the arrangement of the pistons 3 in a somewhat clock-like arrangement, it can be assumed that the uppermost piston is the [2 oclock position and the lowermost piston is in the 6 oclock position with the four pistons between them being located in the 7 oclock, 8 oclock, 10 oclock, and 1] oclock positions. The pistons 3 in the 12 oclock and 6 oclock positions have the axis of the pinion shaft in alignment with the axis of the corresponding piston, however, the four other pistons between the 6 oclock and 12 oclock positions have the axis of the pinion shaft displaced on one side or the other of the radially extending axis of the piston. In other words, the spacing between the axes of the pinion shafts is a variable between the 12 oclock and 6 oclock positions. For instance, the maximum spacing appears to be between the pinion shafts in the 12 o clock-ll oclock and 6 oclock-7 oclock positions. It can be noted that the spacing between the l 1 oclock and 10 oclock positions and the 7 oclock and 8 oclock positions of the pinion shafts are considerably less due to the position of the piston pins 8.

As each pair of pistons 3, note FIG. 3, reciprocate within the cylinder body 2, the pinion shafts are free to a certain extent, to move in the circumferential direction of the cylinder body. It is this variable displacement of the shafts relative to one another that affords the invention its particularly distinguishing characteristic. It should be noted that with this arrangement the space between the cylinder body 2 and the toothed gear 9 can be reduced.

The particular advantages gained from the arrangement shown in FIG. 2 are as follows:

a. Since each pinion 5 and cam 6 is swingably supported by the piston pin 8 mounted on each piston 3, bearings supporting the pinion shaft are unnecessary and the portion of the piston supporting the piston pin can be made compact. Accordingly, the space between the cylinder body and the case containing the gear 9 can be reduced with the pump being made more compact.

b. It is possible to provide an increased contact area for the piston so that the pump can be used as a high pressure pump.

In this operation, the number of revolutions of a given pinion 5 on its own axis for each one complete revolution of the main shaft 1 can be expressed by the formula where D is the diameter of the pitch circle of the internally toothed gear 9, and d is the diameter of the pitch circle of the pinion 5. That is, each piston 3 will move in reciprocating motion m times for each one complete revolution of the main shaft 1, so that the volume of operation fluid of the fluid motor for each revolution of the main shaft can be greatly increased. FIG. 2 shows a state in which m is 8.

The valve plate 14 is constructed and arranged such that the cylinder fluid chambers 18 associated with those pistons 3 which are in the state inwhich they are pushed and moved outwardly of the cylinder body 2 by the working fluid communicated through the ducts with the fluid passageway 21 on the higher pressure side, and that the cylinder fluid chambers 18 associated with those pistons 3 which are in the' state in which they are pushed and moved inwardly of the cylinder body 2 by the working fluid communicated through the ducts 16 with the fluid passageway 22 on the lower pressure side or discharge side.

If the cams 6 mounted on the pinion shafts 4 have an outer diameter which is equal to the diameter of the pitch circle of the pinions 5, then the pinions move in rolling motion while being maintained in meshing engagement with the internally toothed gear 9, add no slip occurs between the cams 6 and ring rests 7 when the cams 6 move in rolling motion along the inner peripheral surfaces of the ring rests 7, thereby permitting the cams 6 to be maintained in rolling contact with the ring rests 7. Accordingly, a component of the force exerted by the associated pistons 3 which is directed radially of the pinion shaft will be borne by the portion of the internally toothed gear 9 in which the associated pinion 5 meshes with the internally toothed gear 9 in addition to the points of contact of the cams 6 with the ring rests 7. Thus, the device according to this invention is adapted for operation with a high pressure working fluid. Besides, the device can withstand high speed operation because centrifugal forces exerted by the pinions 5 are borne by the associated ring rests 7.

In the first embodiment described, occurrence of slip between the cams 6 and associated ring rests 7 during operation is precluded by the meshing engagement of the pinions 5 with the internally toothed gear 9. It is to be understood that if surfaces of high frictional dragging which do not tend to cause occurrence of slip are used between the cams 6 and ring rests 7, the pinions 5 can be done without. In FIG. 13 such an arrangement is shown where a knurled peripheral surface is provided on the cam 6 and a similar knurled surface is provided on the inner surface of the ring rest 7.

While this invention has been shown and described with reference to embodiments in which the device according to this invention has application as a fluid motor, it will be appreciated that the device can also be used as a fluid pump if the operation set forth hereinabove is reversed in the same fashion as conventional fluid motors and fluid pumps. Therefore, further explanation of the operation of this device as a fluid pump will be omitted. When the device according to this invention is used as a fluid pump, the pistons 3 will move in reciprocating motion m times during one complete revolution of the main shaft for delivering fluid.

A spring may be provided in each piston for facilitating the actuation of pistons during the suction stroke of the pump.

In the second embodiment shown in FIG. 5, the pinions 32 are maintained in meshing engagement with the external gears 36 as contrasted to the pinions being maintained in meshing engagement with the internally toothed gear 9 in the first embodiment. Consequently, the cams or rolling rings 33 moves in rolling motion along the inner surfaces of the ring rests 34. Since the piston pin 30 is eccentric with respect to the pinion shafts 31, the piston 29 can be moved in reciprocating motion.

The cams 6 of the embodiments which are adapted to be maintained in engagement with the ring rests 7 have been explained with reference to an example in which the cams 6 are in the form of eccentric rings. It is to be understood, however, that any shape as desired may be selected for the cams 6, note FIGS. 14 and 15 where the cam 6 and the pinion 5 are egg-shaped, so long as the shape satisfies the characteristics required of a fluid device.

FIG. 6 A shows the relation between the angle of rotation 0 of the main shaft 1 and the torques produced by the pistons (which are required torques in the case of a fluid pump, hereinafter to be referred to as produced torques) when the cams 6 are eccentric rings or eccentric cams. The angles of rotation of the main shaft are set forth along the axis of abscissa and the produced torques along the axis of ordinates. It will be seen that a piston (which may be called a first piston) produces a torque which can be represented by a sine curve formed by connecting points 40,. 43 and 41, together and that a second piston (which is a piston operating next to the first piston in chronological sequence and which need not necessarily be a position disposed adjacent the first piston) produces a torque which can be represented by a sine curve formed by connecting

points

42, 44 and 45 together. If a No. 3 piston and the following pistons are successively actuated, the fluid motor provided with these pistons will produce torque which can be represented by a composite curve which can be formed by connecting

point

46, 47, 48 and 49 together as shown in FIG. 6 B which is obtained by combining the sine curves representing the torques produced by all the pistons. It will be seen that this composite curve has highly elevated portions and highly depressed portions, indicating that the produced torques exhibit great changes in value.

It has been found that if the cams 6 are made in suit able shape, such as egg-shape and if the pinions are of the same shape, note FIGS. 12, 1.4 and 15, and not as the eccentric rings as aforementioned, the pistons will produce torques which can be represented by trapezoidal curves as shown in FIG. 6 C, and that torques produced by all the pistons can be represented by a straight line when the trapezoidal curves representing the torques produced by all the pistons are combined into a composite curve, indicating that there is no change in the values of torques produced by all the pistons. As shown in FIG. 6 C, a first piston will produce a torque which can be represented by a curve formed by connecting

points

50, 52 53 and 51 together, and a second piston will produce a torque which can be represented by a curve formed by connecting

points

54, 56, 57 and together. It will be seen that a portion of the torque produced by the first piston between the

points

52 and 53 and a portion of the torque produced by the second piston between the

points

56 and 57 are equal to each other, and that the time intervals during which the torques are produced by the first piston and second piston between the

points

53 and 51 and the

points

54 and 56 respectively overlap each other.

If the decrease initiation point 53 of the torque produced by the first piston and the production initiation point 54 of the torque produced by the second piston are caused to occur at the same point in time and if the decay point 51 of the torque produced by the first piston and the increase termination point 56 of the torque produced by the second pistons are caused to occur at the same point in time so that the sum of the torque produced by the first piston and the torque produced by the second piston at one point in time may be constant at all times, and the sum of the torque produced by the first piston and the torque produced by the second piston at another point in time is constant at all times, a curve representing the composite torque obtained by combining the torque produced by the first piston and the torque produced by the second piston will be represented by a straight line as shown in FIG. 6 D, indicating that there is no change in the values of torques produced by the pistons.

To render the sum of the torque produced by the first piston and the torque produced by the second piston at one point in time equal to the sum of the torque produced by the first piston and the torque produced by the second piston at another point in time at all times as aforementioned is to render the sum of the

torque

83, 81 produced by the first piston and the

torque

83, 82 produced by the second piston shown in FIG. 6 C constant al all times. In this specification, a plurality of pistons related to each other in the torques produced by then as aforementioned will be referred to as being in corrected relationship.

FIG. 6 E shows an example in which the torques produced by the pistons undergo changes that can be expressed linearly. In this case too, changes in the torques produced by the pistons are defined such that the composite curve of the produced torques can be expressed as a straight line in the same manner as the case shown in FIG. C.

If the time interval 60, 64 (corresponding to the distance between the points 60 and 64) during which the second piston lags behind the first piston in being actuated is one-half the time interval 60, 61 (corresponding to the distance between the points 60 and 61), it will be impossible to bring the first and second pistons into corrected relationship unless the torques produced by the first and second pistons are made to undergo changes which are triangular in shape as shown in FIG. 7

While theembodiment shown and described hereinabove concerns a case in which two pistons are brought into corrected relationship regarding the torques produced by them, it is to be understood that it is also possible to bring more than two pistons into corrected relationship with one piston with regard to changes in the torques produced by them. This embodiment is shown in FIG. 8 A and FIG. 8 B.

In FIG. 8 B, changes in the torque produced by the first piston are expressed by a curve formed by connecting

points

91, 93, 94 and 92 together, changes in the torque produced by the second piston by a curve formed by connecting

points

95, 96, 93 and 97 together, changes in the torque produced by the third piston by a curve formed by connecting

points

98, 99, 96 and 100 together, changes in the torque produced by the fourth piston by a curve formed by connecting

points

101, 102, 99 and 103, and changes in the torque produced by the fifth piston by a curve formed by connecting

points

104, 105, 102 and 106 together. In this case, the first piston in the former half of the produced torque curve is in corrected relationship with the third, fourth and fifth pistons. More specifically, the sums of

yalge

91, 93 and the

values

96, 100, 99, 103, and 102, 106 at each point in time or at the same rotational angle are constant as shown in FIG. 8 B. In the latter half of the produced torque curve of the first piston, the pistons showing changes represented by

lines

103, 107, 100, 108 and 97, 109 are in corrected relationship with the first piston represented by the

line

94, 92, so that the sums of the values at each point in time are constant as shown in FIG. 8 B.

From the foregoing, it will be appreciated that the pistons can be brought into corrected relationship with one another even if the former half and the latter half of the wave form of a curve representing the torques produced by the pistons are not symmetrical.

FIG. 9 shows the relation between the rotational angle 6 of the main shaft 1 and the stroke S of a piston in a case in which the ring cams 6 are eccentric rings. In the figure, the rotational angle 6 of the main shaft is plotted as the axis of abscissa against the piston stroke S as the axis of ordinates. A given piston (which may be a first piston) moves in a piston stroke represented by a sine curve formed by connecting

points

120, 121, 122 and 123. In this case, the

points

121 and 123 are upper dead points and the point 122 is the lower dead point of the piston stroke.

Points

124 and 125 and 126 are points at which fluid passageway 17 to the cylinder fluid chamber 18 is switched from communication with one of the ducts 15 to communication with one of the ducts 16 or vice versa.

More specifically, the piston moves in force-in operation from the upper dead point to the lower dead point between the

points

124 and 125 so that the operation fluid in the cylinder fluid chamber 18 is discharged through one of the ducts 16. The piston moves in forceout operation from the lower dead point to the upper dead point between the

points

125 and 126, so that the operation fluid is supplied to the cylinder fluid chamber 18 through one of the ducts 15.

In such case, piston operation cannot be performed in synchronism with proper switching of the cylinder fluid chamber between communication with one type of duct of the valve plate 14 and communication with the other type of duct thereof and the piston movement cannot serve any useful purpose unless the upper dead point 121, lower dead point 122 and upper dead point 123 are brought into complete index with the switch points 124, 125 and 126 respectively. Besides, if this indexing is not obtainable, the fluid to be released is trapped in the cylinder fluid chambers, thereby causing noises and pulsations to occur. For this reason, tolerances are very severe and precise machine finishes and accurate assembling of parts are required in order that the upper and lower dead points may be brought into complete index with the switch points.

This invention obviates the aforementioned problem by providing in the vicinity of the upper and lower dead points of piston operation sections in which the piston stroke is zero. In FIG. 10, piston operation follows a curve formed by connecting

points

127, 134, 128, 135, 136, 129, 137, 138, and 139. The

points

128 and 130 are the upper dead points and the point 129 is the lower dead point, and the

points

131, 132 and 133 are points at which switching between the ducts of valve plate is effected. The sections in which the piston stroke speed is zero are formed between the

points

134 and 135 with the lower dead point 129 being disposed at its center, between the

points

136 and 137 with the lower dead point 130 being disposed at its center, and between the

points

138 and 139 with the upper dead point 130 being disposed at its center.

Piston operation can be performed as planned to achieve desired results if the deviation of the upper and lower dead points from indexing with the switch points is within the range of each of such sections. Besides unnecessary piston movement can be prevented and occurrence of noises and vibrations can be precluded.

The provision of sections in the vicinity of the upper and lower dead points of piston operation in which the piston stroke is zero can be readily effected by suitably designing the shape of the cams 6 adapted to come into contact with the ring rests 7 in view of the well-known art in machining.

From the foregoing description, it will be appreciated that this invention makes it possible to obtain a fluid device, simple in construction and easy to manufacture because no close tolerances need be maintained, which can be adapted as a pump or a motor for handling a fluid of high pressure at high speed.

It will be evident that, though the first embodiment shown and described herein operates such that the main shaft can be connected to an input shaft or output shaft, and the internally toothed gear is firmly fixed, the main shaft can be firmly fixed and the internally toothed gear can be connected to as an input shaft or output shaft.

The use of the gear according to this invention makes it possible to provide a fluid device which is less complex in construction and easier to manufacture than conventional fluid devices in which pistons are made to move in sliding motion on a complicated cam surface.

We claim:

1. A fluid device for use as a radial piston pump or motor comprising a casing, a main shaft rotatably supported in said casing, a cylinder body mounted on said main shaft and held against rotation relative thereto, a plurality of pistons in said cylinder body arranged radially thereof and spaced apart in an annular arrangement about said main shaft for reciprocating motion, said pistons arranged to operate in pairs with said pistons in each said pair spaced apart in the axial direction of said main shaft, pinion means operatively associated with each said pair of pistons and said pinion means in cluding a pinion shaft extending in parallel relation with said main shaft, a piston pin eccentrically positioned in said pinion shaft and mounted at opposite ends to said pistons in one said pair of pistons, and a pinion gear concentrically mounted on said pinion shaft, a casing gear fixed to said casing, said pinion gear disposed in meshed engagement with said casing gear so that reciprocation of said pistons and rotary displacement of said eccentric pins effects relative rotary motion between said meshing casing gear and pinion gear, said pinion shafts being displaceable relative to one another in the circumferential direction of said cylinder body so that the spacing between the centers of adjacent said pinion shafts is variable, engaging means disposed on said casing, and cam means on said pinion means having a cam surface engaging said engaging means whereby said cam means are operable to control the stroke of said pistons in said cylinder body.

2. A fluid device according to claim 1 wherein said cam means is formed in the shape of a ring.

3. A fluid device according to claim 1 wherein said casing gear has integral teeth.

4. A fluid device according to claim 1 including hearing means rotatably supporting said cam means on said pinion means.

5. A fluid device according to claim 1 wherein said engaging means comprises a ring rest element fixed to said casing.

6. A fluid device according to claim 1 wherein said eccentric pins extend from each longitudinal end of said body portion of said pinion means, said pinion gear being located on said body portion of said pinion means.

7. A fluid device according to claim 1 wherein said body portion of said pinion means has two parts, one each disposed at the longitudinal ends of said eccentric pin, each of said body portion parts carrying a pinion gear.

8. A fluid device according to claim 1 wherein said cam means has a configuration operable to cause two or more pistons to effect coordinated operating strokes so that the sum of the torques produced by said pistons is maintained constant during operation of the fluid device.

9. A fluid device according to claim 1 wherein said cam means has a configuration operable to cause said piston to remain at top dead center and bottom dead center for predetermined angles of relative rotary displacement between said main shaft and said casing.

Claims

1. A fluid device for use as a radial piston pump or motor comprising a casing, a main shaft rotatably supported in said casing, a cylinder body mounted on said main shaft and held against rotation relative thereto, a plurality of pistons in said cylinder body arranged radially thereof and spaced apart in an annular arrangement about said main shaft for reciprocating motion, said pistons arranged to operate in pairs with said pistons in each said pair spaced apart in the axial direction of said main shaft, pinion means operatively associated with each said pair of pistons and said pinion means including a pinion shaft extending in parallel relation with said main shaft, a piston pin eccentrically positioned in said pinion shaft and mounted at opposite ends to said pistons in one said pair of pistons, and a pinion gear concentrically mounted on said pinion shaft, a casing gear fixed to said casing, said pinion gear disposed in meshed engagement with said casing gear so that reciprocation of said pistons and rotary displacement of said eccentric pins effects relative rotary motion between said meshing casing gear and pinion gear, said pinion shafts being displaceable relative to one another in the circumferential direction of said cylinder body so that the spacing between the centers of adjacent said pinion shafts is variable, engaging means disposed on said casing, and cam means on said pinion means having a cam surface engaging said engaging means whereby said cam means Are operable to control the stroke of said pistons in said cylinder body.

4. A fluid device according to claim 1 including bearing means rotatably supporting said cam means on said pinion means.