EP0119460A2

EP0119460A2 - Hydraulic energy-conversion device

Info

Publication number: EP0119460A2
Application number: EP84101477A
Authority: EP
Inventors: Arthur E. Rineer
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-17
Filing date: 1984-02-14
Publication date: 1984-09-26
Also published as: CA1233364A; JPS59158394A; ES8505768A1; ES529739A0; EP0119460A3

Abstract

A device capable of functioning as a fluid pump or motor has a shaft provided with an eccentric (48) rotating with the shaft in an axially short cylindrical chamber (47). A ring (57) is rotatable on the eccentric, the thickness of the ring being close enough to the minimum distance from the periphery of the eccentric to the wall of the cylindrical chamber to cause the ring to roll along the wall on rotation of the shaft. The presence of the bearing (56) interposed between the ring and the eccentric has the effect of adding to the thickness of the ring in this relationship. A high pressure (59) and a low pressure port (60) are closely spaced about the chamber periphery, and a moveable dam (64) is mounted between these ports. A second moveable dam (69) is mounted on the opposite side of the high-pressure port from the the first dam.

A valve and a related hydraulic circuit control the relationship of the case pressure to the pressure in the high-pressure port, and another system suppresses pressure pulsations otherwise arising from the sequential operation of one or more of the sections of the device. Mechanical provision is made for providing greater axial length of roller bearing engagement against the convex surface of the eccentric than is present on the concave inner surface of the ring. The shaft is balanced by recesses (53a, 53b) in the eccentric, and these are surrounded by a continuous sleeve (55) functioning as the inner bearing race.

Description

This invention relates generally to hydraulic energy-conversion devices, and more particularly, to a device capable of functioning as a fluid pump or motor foe converting rotary mechanical torque to fluid pressure and vice versa.
Hydraulic energy-conversion devices have been in wide use for decades. These are adapted to convert rotary mechanical torque to fluid pressure and vice-versa. One type of this general class of machine utilizes an eccentric, cam, or crank on the rotatable shaft to induce reciprocating movement of a piston, and another type has a rotor driven by the shaft in an eccentric chamber, with moveable vanes on the rotor controlling the fluid as the shaft rotates. Other types referred to as centrifugal and gear devices are also common, but these are of no interest in connection with the present invention. All of these types have been subject to such intense development that general design details from all manufacturers of each type are closely similar. Performance criteria,for comparing these devices include pressure and rotational speed capability, flow volume with respect to overall size, minimum alteration of performance from wear, and relative freedom from vibrations due to mechanical imbalance or pressure pulsations.
The present invention provides an hydraulic energy-conversion device, comprising: a housing having a chamber defined by a cylindrical peripheral surface and opposite end surfaces; a shaft rotatably mounted in said housing for rotation coaxailly with said cylindrical surface, said shaft having an eccentric portion disposed between said end surfaces; a ring surrounding said eccentric portion, and interposed between said eccentric and said peripheral surface in close relationship; means forming relatively high-pressure and low pressure ports in said housing communicating with said chamber; a first dam moveably mounted in said housing between said ports, and adapted to close off the cross-section of the portion of said chamber between said ring and said peripheral surface in all positions of said ring; and a second dam moveably mounted in said housing and adapted to close off the cross-section of said chamber between said ring and said peripheral surface in response to an excess of pressure in said high-pressure port over the pressure in the adjacent portion of said chamber, said second dam being disposed on the opposite side of said high-pressure port from said first dam.
In a preferred embodiment, a passageway communicates between the portion of the housing adjacent the principal shaft bearings and the low-pressure port, and this passage also communicates with the high-pressure port. A valve system is preferably incorporated in this passage which maintains a pre-determined relationship between the case pressure and the high pressure space to control the loading on the shaft bearings and the seals. Another passageway may also be provided in a further preferred embodiment for communicating with the high-pressure port and having an overflow conduit communicating with the low-pressure side of the device. A piston is mounted in this passageway influenced by a combination of the high-pressure and the action of a spring system, so that pulsations, and consequent vibrations, can be effectively suppressed.
The structure of the device is arranged so that the engagement of roller bearings with the eccentric sleeve takes place over a greater axial length than does the engagement of the same rollers with the inside concave surface of the ring. Since the wear conditions are much more severe on the shorter-radius convex surface of the sleeve, the wear conditions are thus equalized.
Further features and advantages of preferred embodiments of this invention will now be described below with reference to the accompanying drawings wherein:

Figure 1 is an exterior side elevation of the two-stage fluid pump illustrated in the remainder of the views;
Figure 2 is a left end view of the device, with respect to Figure 1;
Figure 3 is a sectional elevation on a plane perpendicular to the axis of the device, taken through one of the pressure-generating chambers. Figure 3 is on an enlarged scale;
Figure 4 is an axial section through the fluid motor;
Figure 5 is a plan view (perpendicular to the axis of the device) of one of the plates defining a pressure-generating chamber. Figures 5-22 are on an enlarged scale over Figures 1, 2 and 4;
Figure 6 is a plan view of the right end- plate, with respect to Figure 1, showing the end shaft bearing in position;
Figure 7 is a section on the plane 7-7 through the intermediate manifold plate that forms an end barrier to each of the pressure-generating chambers;
Figure 8 is a side view of the shaft of the device;
Figure 9 is an end view with repsect to Figure 8;
Figure 10 is a plan view of the ring surrounding the shaft eccentric;
Figure 11 is a section on the plane 11-11 of Figure 10;
Figure 12 is a view of the system for controlling the relationship between the case pressure and the high-pressure side of the device, shown as a section through the central plate appearing in Figure 7;
Figure 13 is a side elevation of the piston appearing in Figure 12;
Figure 14 is an end view with respect to Figure 13;
Figure 15 is a side elevation of the closure plug shown in Figure 12;
Figure 16 is an end view with respect to Figure 15;
Figure 17 is an end view of the moveable sealing dam;
Figure 18 is a side view with respect to Figure 17;
Figure 19 is a side view of the tubular dam member forming the momentary seal blocking back flow from the pressure port;
Figure 20 is an end view with respect to Figure 19;
Figure 21 is a view of one of the conical spring washers;
Figure 22 is an axial section through the washer shown in Figure 21 and
Figures 23 through 26 are schematic views illustrating successive positions taken by the components of the machine during a single rotation of the shaft.

Referring to the drawings, the device shown in Figure 1 includes the end members 30 and 31, the compression chamber members 32 and 33, the central partition and manifold member 34, and the shaft 35. This assembly is held together by a series of bolts indicated generally at 36 extending through these components parallel to the axis of the shaft 35. The screws shown at 37-39 in Figure 1 hold the bearing cap 40 in position. Referring to Figure 2, the flange 41 of the end member 30 is interrupted as shown at 42 and 43 to receive mounting bolts (not shown) associating the fluid pump with the equipment on which it may be mounted. The conduits 44 and 45 are the high pressure and low pressure lines, respectively, extending from the pump to the equipment which it serves (not shown). The locating shoulder 46 is customarily provided for assuring proper relative alignment.
Figure 3 illustrates the principal components responsible for generating the fluid pressure. The plates 32 and 33 are the same, and each define the cylindrical wall 47 of a pressure chamber coaxial with the shaft 35. The shaft 35 (refer to Figures 8 and 9) has a pair of eccentrics indicated at 48 and 49 machined as an intregal part with the axial end sections 50 and 51. The central portion 52 forms a journal for the central bearing support of the shaft, and is of suf_- ficient diameter so that a standard bearing can be slipped axially along the shaft into position. The eccentrics 48 and 49 have recesses shown at 53 and 54 machined into them for the removal of sufficient material to balance the eccentrics both statically dynamically with respect to each other, possibly also including the effects of the masses carried by the eccentrics.
A hardened sleeve 55 is pressed into position over the eccentrics to form the inner bearing race for the roller bearings 56 interposed between the sleeve 55 and the ring 57. This ring is shown in detail in Figures 10 and 11. The ring is continually pressed by the shaft and the bearing system against the peripheral wall 47 of the pressure-generating chamber. As the shaft rotates, the ring will roll along the surface 47 to induce a relative rotation of the ring 57 with respect to the plate 32 opposite to the direction of rotation of the shaft 35. The thickness of the ring 57 is approximately equal to the minimum distance from the eccentric (including the bearing system) and the peripheral wall 47 of the pressure-generating chamber, so that the ring 57 rolls on this peripheral wall 47 as the shaft 35 rotates. The discontinuity of the peripheral wall 47 indicated at 58 forms an auxiliary chamber communicating with the pressure port 59. Since the auxiliary chamber 58 extends axially for the thickness of the plate 32, it can be utilized in the assembly of the ring 57 into the chamber, which would otherwise be difficult because of the compression of the ring between the bearings and the peripheral wall 47. The ring can be displaced to a very slight degree into the discontinuity 58 so that the ring 57 does not have to be forced into its assembled position.
As the shaft rotates in a clockwise direction as shown in Figure 3, liquid enters through the low-pressure port 60 into the space indicated at 61. The clockwise movement of the point of contact 62 compresses the liquid in the space shown at 63, from which it is forced out through the auxiliary chamber 58 into the high-pressure port 59. The moveable sealing dam 64 separates the high and low pressure spaces so that this action can take place. This dam is in the configuration of a flap pivoted on the pin 65 suspended between the end plate 30 and the central partition member 34. For convenience, the member 30-34 shown in Figure 1 may be referred to as the "housing", functioning as a frame supporting the moving components. The sealing dam 64 is shown in detail in Figures 17 and 18, and it should be noted that the semi-cylindrical surface 66 mates with the similar surface 67 of the plate 32 for the effective support of the sealing dam independently of the pin 65 against the tremendous pressures involved, which will frequently exceed five thousand pounds per square inch. The placement of the pin 65, and the degree of clearance between it and the bore 68 of the sealing dam assures that the principal loading will be born by the cylindrical surfaces. It should be noted that the clockwise rotation of the shaft appearing in Figure 3 induces the counterclockwise rotation of the ring 57, resulting in preventing any tendency for friction to jam the sealing dam 64 against the ring. The freedom of rotation of the sealing dam 64 about the axis of the pin 65 (and also against the cylindrical support surface) is sufficient to maintain the sealing dam in contact with the periphery of the ring 57 at all times.
A second moveable dam is formed by the tubular member 69 shown in detail in Figures 19 and 20. This member is loosely mounted on the pin 70, which is also suspended between the end plate and the central partition member. As the point of contact shown in 62 proceeds around to the chamber discontinuity 58, the tubular member 69 will be riding on the periphery of the ring 57,_: and will prevent any tendency for high-pressure in the port to flow back into the space shown at 63. This condition persists until the rolling seal provided by the ring 57 clears the inlet port. The thickness of the chamber plates 32 and 33, the axial length of the rings 57, and of the moveable dams 64 and 69 can be controlled to great accuracy with standard grinding procedures, with the net result that the fits between these surfaces are controlled with sufficient accuracy to control leakage. To assure equal pressure on the inside and outside of the tubular dam 69 to avoid collapse, a groove shown at 7la is machined in the central partition plate to communicate between the interior of the tubular member 69 and its exterior. A similar groove 71b is formed in the end plates.
The bearing system transferring the pressure forces to the shaft, and supporting the shaft in the housing, should be noted in some further detail. The end members 30 and 31 provide recesses accommodating the roller bearing systems 72 and 73, respectively, and a thrust bearing assembly 74 is provided under the cap 40. This is retained in position by the snap ring 75 received in the groove 76 of the shaft 35. The conventional bearing indicated at 77 supports the central portion of the shaft. Referring to Figure 4, it should be noted that the sleeves 55 surrounding the eccentrics extend for substantially the full axial length of the eccentrics, which is a distance considerably greater than the thickness of the pressure-generating rings 57. This results in a transfer of bearing forces to the sleeves over a surface of considerably greater extent than the area provided for the engagement of the rollers with the inside of the rings. This relationship tends to equalize the vulnerability of the components to wear over extended periods, as the most vulnerable surface is the outside of the eleeve, which is of relatively greater curvature, and is convex. The amount of local deflection under load tends to produce greater deformity of the material as the roller passes than is the case where the rollers engage the concave surface of the inside of the ring in a configuration of less curvature. The end members 30 and 31, and the central partition member 34, have counterbored recesses as shown at 78 and 79, respectively, providing a chamber in which the rollers overhang the ends of the rings to give this effect of stress equalization.
The basic pressure-generating system that has been described to this point is illustrated by the schemetic views appearing in Figures 23-26. In these views, the bearing systems have been eliminated, so that the ring 57 appears as a larger roller 79 rotatable about the eccentric 81. To illustrate the back-rotation of the ring (or the roller 79), a mark shown at 82 has been arbitrarily inscribed on the roller 79. As the shaft rotates in the direction of the arrow, the roller 79 proceeds to rotate in the direction of the outer arrow, which is in the opposite direction. This produces a movement of the mark 82 in a counterclockwise direction, and at a very slow rate resulting from the planetary relationship. Extremely high-velocity rotations of the shaft therefor translate into very low velocity rolling movement between the periphery of the roller 79 and the inside cylindrical wall 47. This obviously produces very favorable conditions for the reduction of wear, and the only reciprocating movements are the very minor ones associated with the dams 64 and 69.
Referring to Figures 7, 12 and 14-16, a system is incorporated in the device for controlling the relationship between the case pressure adjacent the shaft bearings and the high-pressure side of the hydraulic system. A control passage in the central partition member 34 has a section 83 of relatively small diameter, and a section 84 of relatively larger diameter. The section 83 communicates with the high-pressure port 59 and the opening 85 receiving the high-pressure line 44. The bore providing these two passage sections has a threaded outer section 86 accommodating the threaded portion 87 of the closure plug 88. The head of this plug is received in the counterbored area 89. The larger portion 84 of the control passage is associated with the low-pressure side of the system by the smaller conduits 90 and 91. Referring to Figures 12, 13, and 14, a piston 92 has a small end 93 in sliding engagement with the small-diameter portion 83 of the control passage. A groove 94 is provided for receiving a conventional "O" ring. The opposite end 95 of the piston slides within the larger-diameter portion 84 of the control passage, and is limited in its movement to the right in Figure 12 by the presence of the stop projection 96 on the closure plug 88. In this position, the portion 95 of the piston closes off the conduit 91. The function of the conduit 90 is to maintain the space in the large portion of the passage 84 to the left of the portion 95 of the piston at low pressure, in order to permit the leftward movement of the piston. A detector conduit 97 communicates with the large-diameter portion 84 of the control passage, and with the space adjacent the main shaft at the central bearing. The function of the stop 96 is to limit the movement of the piston to the right at a position where the end of the piston is at all times exposed to the pressure provided through the detector conduit 97.
As the pump begins its operation, the components are in the position illustrated in Figure 12. As the case pressure builds up, it is communicated through the detector passage 97 to the large end of the piston 92, and eventually builds up to the point where case pressure over the larger end area of the piston overpowers the action of the spring 98 and the high pressure over the smaller end of the piston, and induces a leftward movement of the piston sufficient to uncover the conduit 91. At this point, the case pressure is vented to the low pressure side of the system. The intensity of the force delivered by the spring 98 determines a threshold pressure differential between case and the high pressure of the system. The ratio between the diameters of the portions 83 and 84 of the control passage is the primary relationship determining the case pressure differential.
The pump is also provided with a system for suppressing pulsations in the fluid pressure which would otherwise induce objectionable vibrations. Referring to Figures 4 and 5, the plates 32 and 33 providing the compression chambers have cylindrical openings 99 parallel to the shaft axis, and the central partition member 34 has a hole 100 of smaller diameter and coaxial with these openings (refer to Figure 12). A lateral hole 101 communicates between the hole 100 and the high-pressure space 85. The pistons 102 are slideably received in the opposite ends of the hole 100, and are limited in their penetration into this hole by the shoulders 103. The opposite ends of the pistons 102, indicated at 104 in Figure 4, interengage with the central openings in the standard cone washers loosely received in the openings 99. These washers are arranged in pairs, with each pair consisting of oppositely facing washers that provide considerable axial resilience when stacked as shown in Figure 4. The result of this arrangement is to cause the pistons 102 to respond to surges of pressure in the high-pressure side of the system, and to move against the action of the stacked spring washers to reduce the intensity of the pressure surges. The openings 99 are drained by passages as shown at 99a in Figure 5 extending to the low-pressure side of the system.
It should be noted in passing that the bolts 36 responsible for resisting the mechanical and pressures forces are also responsible for the axial alignment of the components to very close tolerances. These bolts are preferably in the form of hardened steel dowel rods threaded at both ends. These special bolts are received in the holes 105-109 in the central partition member, in the holes 110_-114 in the pressure- chamber members 32 and 33, and in the holes 115-119 in the end members. The end members also are provided with the holes 120 for receiving one of the ends of the pins 70, and with the holes 121 for receiving one end of the pins 65. Similar holes aligned with these are provided in the central partition plate, but do not appear on the section planes illustrated in the drawings.
The requirement for maintenance of close running fits within the pump dictates that tolerances be kept to a practical minimum. One arrangement for reducing the degree of this problem centers in the washers 122-125 at the opposite ends of the bearings. These washers are to be selected for thickness on assembly to compensate for accumulations in tolerance in the various parts of the pump as manufactured. A very significant characteristic of this pump is its ability to maintain its original tolerances with continued severe usage at high pressure and speed of rotation. The gradual back-rotation of the ring 57 presents excellent wear conditions at the transverse plate surfaces due to the low linear velocities involved, and the continuing changes in relative surface positions. This tends to prevent the erosion of the parts to form leakage channels, and maintains a constant film of lubrication. The absence of heavy inertial forces from reciprocation facilitates the maintenance of the film and is largely responsible for the relatively low stresses on the components for a given pressure and flow volume.

Claims

1. An hydraulic energy-conversion device, characterized by a housing having a chamber (32, 33) defined by a cylindrical peripheral surface (47) and opposite end surfaces (30, 31); a shaft (35) rotatably mounted in said housing for rotation coaxially with said cylindrical surface (47), said shaft (35) having an eccentric portion (48, 49) disposed between said end surfaces (30, 31); a ring (57) surrounding said eccentric portion (48, 49), and interposed between said eccentric (48, 49) and said peripheral surface (47) in close relationship, preferably with zero clearance, means forming relatively high-pressure and low-pressure ports (59, 60) in said housing communicating with said chamber (32, 33); a first dam (64) moveably mounted in said housing between said ports (59, 60) and adapted to close off the cross-section of the portion of said chamber (32, 33) between said ring (57) and said peripheral surface (47) in all positions of said ring (57); and a second dam (69) moveably mounted in said housing and adapted to close off the cross-section of said chamber (32, 33) between said ring and said peripheral surface (47) in response to an excess of pressure in said high-pressure port (59) over the pressure in the adjacent portion of said chamber (32, 33), said second dam (69) being disposed on the opposite side of said high-pressure port (59) from said first dam (64).

2. The device of Claim 1, characterized by bearing means (56) interposed between said eccentric shaft portion (48, 49) and said ring (47), and engaging a relatively greater axial length of said shaft portion (35) than said bearing means (56) engages said ring (47) .

3. The device of Claim 1 or 2, characterized in that said housing includes opposite end members (30, 31) providing bearing support for said shaft (35), and also includes a central partition member (34) defining certain of said end surfaces, said central member (34) preferably providing additional bearing support for said shaft (35) said housing also including a pair of chamber members (32, 33) disposed on opposite sides of said central partition member (34), said central and chamber members being in the form of apertured flat plates, said housing also including a plurality of bolts (36) disposed parallel to said shaft (35) and traversing said end, central, and cham_- ber members.

4. The device of Claim 3, characterized in that said shaft (35) has an eccentric portion (48, 49) within each of said chamber members (32, 33), said eccentric portions having balancing recesses (53, 54) in the peripheral surfaces thereof, respectively, and continuous sleeves (55) closely surrounding said eccentric peripheral surfaces.

5. The device of any of the preceding Claims, characterized in that said first dam is a member (64) having one end pivotally mounted in said housing by being loosely received on a first pin (65) mounted in said housing on an axis parallel to said shaft (35), and the opposite end adapted to.drag on the outer surface of said ring (57), said dam member (64) having a length from said pivotal mounting greater than the maximum distance from said pivotal mounting to said ring outer surface,and said housing and first dam member have interengaging arcuate concave and convex surfaces, respectively, concentric with said pin (65) whereby said dam member (64) is supported against pressure forces at one end by bearing against said ring (57), and at the opposite end by the interengagement of said concave and convex surface.

6. The device of any of Claims 1 to 5, characterized in that said housing has a chamber portion (58) extending outward radially beyond said peripheral surface (47), that preferably communicates with said high-pressure port (59), and providing space for partially receiving said ring (57) on assembly of said ring (57) into operating position on said eccentric portion (48, 49).

7. The device of Claim 6, characterized in that both the first and second dam (64, 69) are preferably disposed within said chamber portion (58), said device housing a second pin (70) mounted in said chamber portion (58) parallel to the axis of said cylindrical peripheral surface, and said second dam is a cylindrical sleeve (69) loosely received over said second pin (70).

8. The device of Claim 3 or 4, characterized by a system for suppressing hydraulic shock including a passage (100) in said central member (34) substantially parallel to the axis of said shaft (35) and communicating with said high-pressure port (59); passages (99) in said chamber members (32, 33), respectively, coaxial with said central member passage (100); pistons (102) respectively received in said central member passage (100) and extending into said chamber member passage (99); biasing means urging said pistons (102) against pressure provided from said high-pressure port (59); and means forming drain conduits from said chamber member passages (99), respectively, to said low-pressure port (60).

9. The device of Claim 8, characterized in that said biasing means is formed by groups of oppositely-facing resilient conical washers received in said chamber member passages (99); said pistons (102) preferably have shoulders engageable with said central member (34) limiting the movement of said pistons (102) in the direction of said biasing.

10. The device of Claim 3 or 4, characterized by a system for controlling the relationship between case and output pressures, including a control passage in said central member (34) having portions (84, 83) of relatively larger and smaller diameters, said portion (83) of relatively smaller diameter communicating with said high-pressure port (59); a valve piston (92) received in said control passage, and having portions (95, 93) in sealing engagement with said portions (84, 83) of larger and smaller diameters, respectively, a detector conduit (94) communicating between said large-diameter control passage portion (P4) and the space adjacent said shaft (35), said detector conduit (97) being disposed to communicate with the large-diameter end (95) of said piston (92) in all positions thereof; a low-pressure conduit (91) communicating between said low-pressure port (60) and said portion (95) of larger diameter of said piston (92), said valve piston (92) being adapted to move between a position in which said larger diameter piston portion (95) covers said low-pressure conduit (91), and a position toward the piston portion (93) of smaller diameter of said piston (₉₂) exposing said low-pressure conduit (91); an equalization passage (90) communicating between said low-pressure port (60) and said control passage portion (84) of larger diameter, on the side of said piston portion (95) of larger diameter toward said piston portion (93) of smaller diameter, in all positions of said valve piston (92) and, preferably including biasing means (98) urging said valve piston (92) toward the first-specified position thereof.

11. A rotary hydraulic device at least one rotor chamber member (32, 33), and a partition member (34) defining an axial extremity of said chamber member (32, 33), said partition member (34) having relatively high and low-pressure ports (59, 60) communicating with said rotor chamber, said device having a rotor and valve system in said chamber adapted to induce a pressure differential between said ports (59, 60), said dvice being characterized by a pulse-suppressor system including a partition member (34) having a first pulsation suppression passage (100) communicating with said high-pressure port (59), said chamber member (32, 33) also having a second pulsation suppression passage (99) constituting an extension of said partition member passage (100), and communicating with said low-pressure port (60), a piston (102) mounted in said partition member passage (100) and extending into said chamber member passage (99), biasing means urging said piston (102) against the effect of pressure from said high-pressure port (59) and said piston (102) preferably has a shoulder (103) limiting its movement under the action of said biasing means, and said biasing means preferably comprises a group of oppositely facing resilient conical washers received in said chamber member passage (99).

12. A rotary hydraulic device including a housing having a rotor chamber (32, 33) provided with relatively high and low-pressure ports (59, 60), and a rotor and valve system with said chamber (32, 33) adapted to induce a pressure differential between said ports (59, 60), said housing having bearings (56) supporting said rotor, said device being characterized by a case-pressure control system including a control passage in said housing and having portions (83, 84) of relatively larger and smaller diameters, said portion (83) of relatively smaller diameter communicating with said high-pressure port (59), a valve piston (92) having portions (93, 95) in sealing engagement with said larger and smaller diameter portions (83, 84), respectively, a low-pressure conduit (91) in said housing communicating between said low-pressure port (60) and said portion (95) of larger diameter of said piston (92), said valve piston (92) being adapted to move between position in which said larger diameter piston portion (95) covers said low-pressure conduit (91), and a position toward the portion (93) of smaller diameter of said piston (92) exposing said low-pressure conduit (91); an equalization passage (90) communicating between said low-pressure port (60) and said control passage portion (84) of larger diameter, on the side of said piston portion (95) of larger diameter toward said portion (93) of smaller diameter in all positions of said valve piston (92), and preferably including biasing means urging said valve piston (92) toward the first-specified position thereof.

13. A balanced crankshaft (35) having an eccentric portion (48, 49) provided with at least one recess (53, 54) tending to balance said crankshaft (35), said eccentric (48, 49) having a cylindrical sleeve (55) surrounding said eccentric portion (48, 49) including said recess (53, 54).

14. In combination with a shaft (35) having an eccentric crank portion (48, 49, 55) and a member (57) connected to said portion (48, 49, 55) a roller bearing system (56) interposed between said member (57) and said portion (48, 49, 55) and engaging a greater axial distance on said portion .(48, 49, 55) than the axial distance of engagement of said roller system (56) on said member (57).