Title: Motor Stepped By Reciprocating Annular Cams
Inventor: Robert Carl Rice
Address: 3724 Amsterdam Terrace, Burtonsville MD. 20866-1927
Status: Provisional application filed 3/9/2009 accepted 4/14/2009
US 61/209,633 Small Entity
Description of the Invention:
An output rotor (5) has a rigid construction supporting an output device, e.g., shaft, pulley or gear, and three or more of evenly spaced "planetary" idler rollers (3). In some embodiments, the rollers (3) may encompass and bear on axles rods (2). In other embodiments the roller surfaces are directly provided by rods journalized at intervals to the output rotor by needle roller bearings (4). A center “sun” roller (1) is optional to relieve the planetary roller bearings (4) of radial load and enable higher torque embodiments.
The planetary rollers double as roller cam followers for annular cams (20..23) that encompass the rollers and react reciprocally with them to produce a motive output torque. In some embodiments the motive annular cams may provide sufficient centering force for the rotor but most embodiments will include fixed rings (110) to provide additional journalling.
Each annular cam (20..23) is roughly analogous to a phase winding within an electric motor. In electric motors, activation of different phase windings rotates the magnetic field produced by either the stator or the armature such that the armature needs to rotate to realign the magnetic fields. In the cam motor, each cam acts on the output rotor to step it to a different angular displacement. Many similarities exist and an embodiment of the present invention can be designed analogous to many types of electric motors. As with electric motors, the preferred embodiment may vary depending upon the application.
Other than for symmetry and balance, the direction of movement for each annular cam (20..23) is relatively unimportant. The internal cam reactive surface can be designed to step the rotor to the desired angular displacement given any movement direction of the cam linear or rotational. Therefore, each annular cam may have either linear bearings or it may be rotatable for a small angular displacement around a pivot point. The annular cams (20..23) are fabricated from plate material to enable relative motion in different directions. Lower power cams can be molded, cast or die cut. High power cams would likely be machined by router.
Embodiments having three or more phases may use single acting actuators or double acting actuators for more power and a smaller output step angle. The step angle for single acting actuators is calculated simply as 360° / (number of motive cams) / number of planetary rollers. The step angle for double acting actuators is calculated as 180° / (number of motive cams) / number of planetary rollers. Increasing the number of planetary rollers increases the number of steps but reduces the maximum displacement possible from each annular cam. However phases can be added both to reduce step angle and to increase the power available for a given motor diameter.
Description of Figures:
A preferred high torque hydrostatic motor embodiment is illustrated in figures 1 through 5. Figure 1 is a split profile view for a complete fluid motor or pump with distribution valve. Figures 2 through 4 are transverse views as indicated in Figure 1. Figure 5 is a composite showing the shape of motor plates separately.
The rotor (5) is machined from a square cross section with a recess at each corner to support needle roller bearings (4) further supporting roller shafts (3). A flanged pulley (7) drives the distribution valve through synchronous belt (212).
The motor body (101) is machined from a solid block, e.g., aluminum extrusion. Circular bed (102) supports steel bearing races (110) providing journaling for rotor (5) and reacts directly against compression force from the annular cam levers (20, 21, 22 and 23). Slots (103) are cut across the top to accept the cam levers (20..23). Holes (107) are bored from the side to accept cam lever hinge shafts (104) and retaining rings (108). Mounting holes (105) are drilled and tapped from the bottom.
The motor body (101) has a through bore (201) that accepts a rotary distribution valve retained by snap rings (202). A valve barrel (203) is machined from a cylinder with interchangeable source and drain chambers (204), cylinder ports (205) and axial bore (206) to accept valve rotor (207) retained with the barrel by plug (208). Threaded fittings (210) are machined to provide external connection to the source and drain chambers (204). Control ports (312) are drilled with a small diameter from each side to enable a restricted interchange of fluid between limit stop expansion chambers (305).
The valve rotor (207) is machined from bar stock with symmetrically opposed recesses (209) corresponding to each opposed pair of cylinders (301). In this four cylinder embodiment, each pair of opposed recesses (209) has an angular offset from the other pair of 45°. The valve rotor (207) is driven from the output rotor (5) by synchronous belt (212) and flanged pulley (211) at 1.5 times the output rotor speed.
Four cylinders (301) are machined from the bottom in three stepped diameters. The bottom diameter interferes with bore (201) to provide a connection with valve cylinder ports (205). An assembly is inserted into each cylinder comprised of a clevis (304), a shaft (310), pistons with seals (306, 307 and 309), compression spring (308) and retaining snap rings (311). The clevis (304) is secured to a corresponding cam lever (20..23) by pin (303).
Fixed piston (307) separates two expansion chambers (305 and 301). The lower chamber (301) is the working expansion chamber translating pressure to downward force on the cam levers (20..23) through the tensile linkage between working piston (309) and the cam lever. Compression spring (308) preloads this tension so that the chamber (301) will draw fluid at low pressure when the machine is operating as a pump rather than a motor.
The upper expansion chamber (305) raises limit stop piston (306) to interfere with clevis (304) and reduce the working piston stroke. The motor’s displacement is reduced as the contact between cam levers (20..23) and planetary rotors (3) becomes intermittent. The volume of fluid in expansion chamber (305) is varied through control port (312). The chambers are interconnected by small orifices to prevent rapid movement of limit stop pistons (306).
The preferred embodiment would likely be enclosed in an outer housing (not illustrated) to protect the machine from dirt and to contain a small volume of oil to keep all parts lubricated.
The four cylinder motor has a full step angle of 30° and the pistons reciprocate at three times the rotor speed. The embodiment is easily expanded in length to accommodate additional pairs of cam levers for additional torque and smoother torque response with angular displacement of the rotor.
a machine comprising:
a rotor having an output device and a plurality of evenly spaced planetary idler rollers;
a plurality of annular plates encompassing said idler rollers and journalling said rotor;
said annular plates having an internal cam surface reacting reciprocally to the rotation of said idler rollers;
a single or double acting linear actuator to reinforce said reciprocal motion of each said annular plate.