Patent Publication Number: US-4548124-A

Title: Radial piston hydraulic motor with variable eccentricity

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a radial piston hydraulic motor with variable eccentricity. 
     Hydraulic motors having a number of cylinder-piston units arranged radially about a cam or eccentric which is attached to the motor rotating shaft are known in the art. 
     Propulsive power is transmitted to the cam by means of a working fluid being pressurized by a specially provided pump and cyclically distributed to the various cylinder-piston units by a distributor. 
     In order to change the motor power output, the pump operation is controlled to variously set the working fluid flow rate and pressure. However, this requires the availability of a pump which can be adapted to different operating conditions of the motor, and accordingly, a large size one. 
     It has also been proposed to vary the motor eccentricity so as to change its swept volume and, hence, the torque transmitted to the rotating shaft and the rotational speed, while keeping the pump delivery rate constant. 
     SUMMARY OF THE INVENTION 
     Thus, it is a primary object of this invention to provide a variable displacement radial piston hydraulic motor of simple design, reliable operation, and limited weight and bulk. 
     That object is achieved by a hydraulic motor of the type comprising a plurality of cylinder-piston units arranged radially about an eccentric cam coupled for rotation with a rotating shaft, characterized in that said eccentric and said shaft have cooperating guide means allowing relative movement between said shaft and said eccentric in a direction transverse to the axis of rotation of said shaft and maintaining said eccentric and said shaft in common rotatory relationship, said guide means having cooperating cylinder-piston formations defining opposite cylinder-chambers and duct means for selectively supplying or exhausting pressure fluid in said cylinder chambers to thereby shift along said guide means said eccentric transverse with respect to said shaft in a selected relative position thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention features will be more clearly understood from the following detailed description of a preferred embodiment thereof, as illustrated by way of example in the accompanying drawing, where: 
     FIG. 1 is a longitudinal section view of a hydraulic motor according to this invention; and 
     FIG. 2 is a partly sectional view of that same motor as taken in a longitudinal plane perpendicular to that of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The motor shown in the drawing comprises a plurality of oscillating cylinder-piston units 1 which are arranged to bear with one end on an eccentric cam 2 having a spherical surface and with the other end, on respective spherical caps 3 rigid with the motor case 4. 
     The cylinder-piston units 1, which will be called hereinafter simply &#34;pistons&#34; are arranged radially about the cam 2 and each include, in a manner known per se, a pair of cylinders 1a, 1b, which are guided sealingly one within the other and biased against the cam and cap by a spring 1c. 
     The pistons are in communication with a respective working fluid delivery conduit 5 which is formed in the case 4 and extends through the cap 3. 
     The working fluid, which is pressurized by a specially provided pump, flows through the pistons 1 and acts on the cam 2. A conventional distributor member 6 distributes the working fluid cyclically to the various pistons. 
     The eccentric cam 2 is coupled for rotation with a rotating shaft 7 which is supported inside the case 4 on rolling bearings 8. For connection to the cam 2, the shaft 7 is provided with a drum-like formation 9a, a similar drum-like formation 9b being coupled for rotation on the opposite side of the cam 2 and is carried in a bearing 8a. 
     Formed inside each drum formation 9a, 9b, is a guiding seat of prismatic shape 10 having its longitudinal axis extending parallel to a diameter of the cam 2 and in which is slidably engaged and guided a related projection or shoe 11a, 11b. The shoes are formed frontally on opposite sides of the cam 2 and in the shown embodiment are advantageously offset at least in one direction with respect to the symmetry axis A of the cam. Thus, the cam can slide transversely to the rotating shaft 7, thereby its eccentricity can be changed from a zero value, whereat its axis A would coincide with the axis B of the shaft 7, up to a value &#34;e&#34; of maximum eccentricity. A cylindrical cavity 12 is formed inside the shoes 11a, 11b which in the embodiment shown has its axis perpendicular to that of the cam 2 and parallel to the longitudinal axis of the seat 10. Guided within each cavity 12 is a small piston 13 which divides said cavity in two chambers, 12a and 12b. 
     Each small piston is attached at a middle position to a respective rod 14a, 14b which extends longitudinally through a respective cylindrical cavity 12 and extends sealingly out of the shoes 11a and 11b. The rods 14a, 14b rest with their opposite ends against the confronting walls of the drum-like formations 9a, 9b and are arranged stationary therein. 
     The two chambers 12a, 12b of the cavities 12 are connected to a pressurized fluid supply. To this aim, on the case 4 there are provided a pair of holes 15a, 15b in communication with a rotary coupling 16, of conventional design, which surrounds the rotating shaft 7. That coupling 16 also communicates the holes 15a, 15b to respective conduits 17a, 17b extending inside the shaft 7 and drum formation 9b at diametrically opposite positions, so as to open respectively into bores 18a, 18b formed axially through the rod 14b. 
     The bores 18a, 18b each open, in the proximities of the small piston 13, into one of the chambers 12a, 12b respectively, defined in the cavity 12 of the shoe 11b. Such chambers, in turn, are in permanent communication with the corresponding two chambers 12a, 12b of the cavity 12 of the shoe 11a via channels 19a, 19b formed through the cam 2. Thus, the delivery of pressurized fluid through one of the two holes 15a or 15b into one of the conduits 17a or 17b enables two corresponding chambers 12a or 12b of both cavities 12 to be pressurized. The other two chambers 12b or 12a are, of course, selectively connected to the fluid exhaust. The alternative connection of the holes 15a, 15b with the pressure fluid or exhaust respectively occurs by valve and circuit means of conventional design, not shown, such as a slide valve or the like. 
     Since the small pistons 13 are stationary relatively to their respective drum formations 9a or 9b, respectively the pressurized fluid will move the shoes 11a, 11b within the seats 10 of the drum formations 9a, 9b. Accordingly, the cam 2 will move radially with respect to the axis of the rotating shaft 7, thus changing by a desired amount the eccentricity and hence the motor operating characteristics. It should be noted that the cam 2, being required to accommodate no devices on its interior, is a massive one and accordingly highly indeformable under the powerful hydraulic stresses, thus ensuring optimum volumetric efficiency. Further, it may have greatly reduced radial dimensions, thus affording enormous advantage from the standpoint of the motor overall radial space requirements. With this solution, therefore, it becomes possible to adopt the same cam diameter as used in fixed displacement motors, which results in the utilization of the same pistons and in related economic advantages. 
     It should be further noted that the cam 2 is effectively guided between the drums formations 9a, 9b in its radial movement with respect to the rotating shaft 7, thereby the motor reliability can be guaranteed. 
     In practicing the invention, the shapes and dimensions may be any ones meeting individual application requirements.