Abstract:
A hydraulic machine of the gerotor type. The machine uses two gerotors which are preferably coplanar, and positioned nearly concentric to each other. This dual arrangement approximately doubles the displacement of hydraulic fluid per revolution, compared with a single gerotor, and thus doubles power transfer. Yet the housing containing the gerotors need only be large enough to contain the larger gerotor.

Description:
The invention concerns a dual-rotor gerotor machine. All rotors are placed in a single plane. This arrangement succeeds in placing the gerotors in a housing of small axial length, yet causing them to provide a large displacement of hydraulic fluid per revolution. This arrangement provides large horsepower in a small package. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 illustrates a hydraulic machine  2  of the gerotor type, found in the prior art. A shaft (not shown) engages splines  9 , and rotates rotor  6 . The machine  2  can operate either as a pump or motor, but since operation as a pump is perhaps easier to understand, the explanation will be framed in terms of a pump. Plates such as plate  18  in FIG. 7 seal the chambers  3  and  12  in FIG. 2, which are described below. 
     In FIG. 2, rotor  6  rotates about center CA, as indicated by the arrow pointing to that center. Rotor R rotates about center CB, as indicated by the arrow. The distance between centers CA and CB is defined as the “eccentricity” of the two rotors. 
     FIGS. 3-6 illustrate these two rotations. FIG. 3 illustrates the starting position. Dots D 1  and D 2  have been added for reference. In FIG. 4, rotor  6  has been rotated counter-clockwise by the shaft (not shown) through about 20 degrees. The other rotor R is carried along, but not through a full 20 degrees (because the tooth ratio between the rotors is 6/7). Chamber CH 1  has been reduced in volume, thereby causing fluid to become expelled through conduits which are not shown. 
     In FIG. 5, rotor  6  has been further rotated another 20 degrees counter-clockwise. Rotor R is again carried along, but not the full 20 degrees, and chamber CH 1  is further reduced in volume. 
     In FIG. 6, rotor  6  has been further rotated another 20 degrees, for a total of 60 degrees, compared with FIG.  3 . Rotor R is carried along, but, again, not by the full 20 degrees. Now a visible separation SEP between dots D 1  and D 2  begins to appear, indicating the lag of rotor R behind rotor  6 . Chamber CH 1  is almost compressed to zero volume. 
     When the machine operates as a motor, the opposite sequence occurs: pressurized fluid delivered to chambers such as CH 1  forces the chambers to expand, thereby inducing rotation of both rotors  6  and R about their respective centers CA and CB. 
     OBJECTS OF THE INVENTION 
     An object of the invention is to provide an improved hydraulic machine. 
     A further object of the invention is to provide a dual gerotor hydraulic machine in which all gerotors occupy a single plane. 
     SUMMARY OF THE INVENTION 
     In one form of the invention, a first gerotor set is coplanar with a second gerotor set, and the second set surrounds the first. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 illustrate a prior-art hydraulic machine  2 , of the internal gear, one-tooth difference type. 
     FIGS. 3-6 illustrate a sequence of events occurring during rotation of motor  2  of FIG.  1 . 
     FIG. 7 is a prior art figure illustrating a wall  18 , which is part of a housing (not shown) containing the motor  2 . 
     FIG. 8 illustrates one form of the invention. 
     FIG. 9 is a plan view of one form of the invention. 
     FIG. 10 illustrates centers C 1 , C 2 , and C 3 , about which respective rotors OR, RR, and IR rotate. 
     FIGS. 11-18 illustrate a sequence of events occurring during rotation of the invention. 
     FIG. 19 is a cross-sectional schematic view of the invention of FIG.  10 . 
     FIG. 20 illustrates one embodiment of the invention, wherein block  58  represents a radiator in a motor vehicle. 
     FIG. 21A illustrates another form of the invention; 
     FIG. 21B is a view taken along the line  21 B— 21 B in FIG. 21A; 
     FIGS. 22-25 illustrate other forms of the invention; and 
     FIG. 26 illustrates another form of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 8 illustrates one form of the invention, comprising an inner rotor IR, a ring rotor RR, and an outer rotor OR. Two gear sets, or sections, are present. The outer gear  33  of inner rotor IR and the inner gear  36  of ring rotor RR cooperate to form a first gear set S 1 , or first gerotor pair. The outer gear  27  of ring rotor RR and the inner gear  30  of outer rotor OR cooperate to form a second gear set S 2 , or second gerotor pair. 
     Both gear sets are shown as one-tooth difference type, but that type is not considered essential. Each gear set operates as a separate, though linked, hydraulic motor, or pump, depending on the mode of operation chosen. 
     A plate  37  contains ports HP 1 , HP 2 , LP 1 , and LP 2 , which deliver fluid to the two gear sets. FIG. 9 illustrates the plate  37  in plan view. Two high-pressure ports, HP 1  and HP 2 , deliver fluid to respective gear sets S 1  and S 2 . Two low-pressure ports, LP 1  and LP 2 , exhaust fluid from the respective gear sets S 1  and S 2 . 
     In operation, outer rotor OR rotates about center C 1  in FIG. 10, as indicated by the arrow pointing to C 1 . Ring rotor RR rotates about center C 2 , and inner rotor IR rotates about center C 3 , both as indicated by arrows. 
     In actuality, the ring rotor RR would be sized so that point P 1  would contact point P 2 , and the contact would act as a seal. Similarly, point P 3  would contact point P 4 , for the same reason. However, for ease of generating drawings, in order to show the rotation which will now be discussed, these points P 1  and P 3  are shown separated from points P 2  and P 4 . 
     Operation as a motor will now be explained. FIG. 11 illustrates the starting position. Pressurized fluid is injected into chambers CH 2  and CH 3 , through the ports HP 1  and HP 2  in plate  37  in FIGS. 8 and 9. In FIG. 11, reference dots D 3 , D 4 , and D 5  are added. 
     The pressurized fluid causes all rotors to rotate about their respective centers shown in FIG. 10, as the sequence of FIGS. 11 through 18 indicates. The ratios of rotation are in proportion to the tooth ratios, and are 6/7 and 10/11. Thus, for every  7  revolutions of inner rotor IR, the ring rotor RR undergoes  6  revolutions with respect to the inner rotor IR. Similarly, for every  11  revolutions of ring rotor RR, the outer rotor RR undergoes 10 revolutions. Overall, a speed reduction occurs from inner rotor IR to outer rotor OR, in the ratio (6/7)×(10/11). 
     FIG. 19 is a schematic cross-sectional view of the apparatus of FIG.  8 . Wall  37  is not a flat plate, but contains fluid conduits, and other apparatus. The motor operates under two speed conditions, using a single pressure source (not shown), applied to line  50 . For high speed of shaft SH, displacement valve D is closed, thereby causing hydraulic fluid to be applied to port HP 1  exclusively. Both rotors IR and OR rotate as shown in FIGS. 11-18, and at a relatively high speed and high pressure drop across the motor  2 . This is called “single-displacement” mode. 
     A check valve CK is used during single-displacement mode. At this time, gear set S 2  in FIG. 9 is not used as a motor, so that set operates as a pump. The check valve CK allows oil being pumped by set S 2  to flow in a continuous loop from outlet LP 2  to inlet HP 2 , and at low pressure. 
     For relatively low speed of shaft SH, displacement valve D opens, based on a pressure differential sensed on lines L 1  and L 2  (or other measured parameter, such as engine speed, radiator fluid temperature, vehicle speed, and so on), and applies pressurized fluid to both ports HP 1  and HP 2 . The same rotation occurs as shown in FIGS. 11-18, but now at a lower speed and with the same flow rate. That is, the same relative rotation of the three rotors IR, RR, and OR occurs, at the same ratio as before, namely, (6/7) and (10/11), but now at a lower speed, and lower pressure drop across the motor  2 . This is called “dual-displacement” mode. Check valve CK is closed. 
     In one embodiment, the motor  2  in FIG. 20 is used to drive a fan  55  to cool a radiator  58 , used in an automotive vehicle  62 . Pressure is applied by an engine-driven pump (not shown), and the pressure reaching the motor  2  is controlled by a regulator (also not shown). The regulator provides the desired pressure to the motor. Such pumps and regulators are known in the art. 
     At low engine speeds, as in slow traffic, large cooling from fan  55  is required, so single-displacement mode is used, to provide high-speed operation of motor  2 , at relatively high fluid pressure. At high engine speeds, as in highway driving, incoming ram air is sufficient to cool the radiator  58 , so that low-speed operation of motor  2  is desired. Dual-displacement mode is used, to provide low-speed operation of motor  2 , at relatively low fluid pressure. 
     Other modes of operation are contemplated. For example, at engine idling speeds, the motor  2  can operate in either single or dual-displacement mode, depending on the cooling requirements. As another example, when the vehicle tows a trailer, a high fan speed and pressure during dual displacement may be required, such as 3500 rpm at 1400 psi. 
     The selection between low- and high-speed operation is, as explained above, determined by displacement valve D in FIG.  19 . That valve can be controlled by a signal on an input line IN. Alternately, the fluid supplied on line  50  can be provided by a hydraulic pump which is driven by the engine (not shown) of the vehicle  62 . The flow on line  50  will be closely proportional to the speed of the engine. 
     Thus, at low engine speeds, the valve D is designed to remain closed, thereby providing high speed of motor  2 . As engine speed increases, the pressure in line L 1  will increase. When the differential reaches a threshold, the valve D opens, thereby providing low speed of motor  2 . 
     It should be understood that the preceding discussion illustrates a specific embodiment of the invention, and that other modes of operation can be implemented. 
     Two examples of the two modes of operation are the following. The motor  2  is designed such that, in dual-displacement mode, it displaces 0.6 cubic inch per revolution, written as 0.6 cu. in./rev. In single-displacement mode, it displaces 0.25 cu. in./rev. 
     One gallon of fluid occupies 231 cubic inches. Thus, two gallons occupy 462 cubic inches. For the motor  2  to consume two gallons per minute in single-displacement mode, 1848 revolutions per minute (rpm) are required: 462/0.25=1848. For the motor  2  to consume the same two gallons in dual-displacement mode, 770 rpm are required: 462/0.60=770. 
     Thus, for a given flow rate, two speeds are possible, by selecting between single- and dual-displacement modes. Further, in each mode, modulation is possible, by modulating the pressure applied to the motor. 
     The ratio of these two speeds is roughly two: 1848/770 or 2.4 to 1. If a fixed, single-displacement pump, of the prior art type, were used, then, to accomplish this change in speed, a corresponding change in displacement would be required. That is, if rotation at 770 rpm required two gallons per minute, then rotation at 1848 would require 2.4×2 gallons per minute. The invention eliminates this requirement. 
     It is a fact that, in motor  2 , torque produced equals displacement*pressure/constant, where the constant is 75.4. Adding units: 
     torque (lb. ft.)=displacement (cu. in./rev) * pressure (psi). 
     For a pressure of 1,000 psi, the torques produced by single- and dual-displacement modes are the following: 
     dual: 0.6 * 1,000/75.4=7.95 lb. ft. 
     single: 0.25 * 1,000/75.4=3.31 lb. ft. 
     Alternate Embodiments 
     The two gear sets S 1  and S 2  may be constructed of four distinct gears, as shown in FIGS. 21A and 21B. The gears  27  and  36  are not carried by a single ring rotor RR as in FIG. 8, but take the form of separate gears RR 2  and RR 1  in FIGS. 21A and 21B, bottom. The axial thicknesses T 1  and T 2  of the two pairs are shown, and need not be the same. 
     For example, in FIG. 22, the gear RR 2  is physically separate from gear RR 1 , and rests upon RR 1  as indicated by the dashed lines in FIG.  22 . Alternately, gear RR 2  may occupy two axial regions, as shown in FIG.  23 . When inserted into gear RR 1 , gear RR 2  may occupy the axial thickness T 1 , and also extend beyond T 1  by the difference (T 2 −T 1 ), as shown in FIG.  25 . 
     It may be desirable to make gear RR 1  thicker than RR 2 , as shown in FIG.  24 . 
     Inner gear RR 2  may be constructed in a single piece, reducing the number of gears from four to three. 
     Additional Considerations 
     1. The volume between the pair of gears  27  and  30  in FIG. 8, which is displaced per revolution of rotor RR (with respect to rotor OR), depends on the shapes of the gear teeth, and is controllable. Similarly, the volume between the pair of gears  33  and  36 , which is displaced per revolution of rotor IR (with respect to rotor RR), depends on the shapes of the gear teeth, and is also controllable. 
     In one embodiment, these volumes are designed to be identical. In another embodiment, the volumes are 0.3 cubic inch between gears  27  and  30 , and 0.2 cubic inch between gears  30  and  33 . 
     In another embodiment, the volume between the inner gears  36  and  33  is larger than that between gears  27  and  30 . The physically larger gerotor pair displaces a smaller volume. 
     2. The invention of FIG. 20 provides a significant savings in energy, compared with other approaches. For example, one set of calculations shows that, if motor  2  delivers about 7 horsepower, then about 14 horsepower in hydraulic fluid is required to be delivered to motor  2 . That is, the motor  2  consumes 14 horsepower, and delivers 7 horsepower, for an efficiency of 50 percent. The efficiency exceeds 40 percent. 
     In contrast, clutch fans driven by the engine (not shown) are in widespread use to perform the function of motor  2 . Many of them consume about 30 horsepower, in order to deliver the same engine cooling capability. The efficiency is less than 25 percent. 
     3. The pressure ratio HP 1 /LP 1  need not be the same as the ratio HP 2 /LP 2 ; the pressure ratios may be different. Further, the pressures at ports HP 1  and HP 2  may be different. 
     4. The invention can be used either as a motor or a pump. In motor operation, fluid pressure is converted into torque. In pump operation, torque is converted into fluid pressure. In both cases, a transfer between pressure and torque occurs. 
     In addition, in some instances, dual operation can occur. For example, gear set S 1  in FIG. 5 can act as a motor, and gear set S 2  can act as a pump. In this case, port HP 2  becomes a low-pressure port, and port LP 2  becomes a high-pressure port. 
     The invention should be distinguished from gear systems, such as planetary gear systems, which contain lubricants. Because of factors such as viscosity and other fluidic effects, the lubricant exerts some forces upon the gears, and the gears also exert forces upon the lubricant. It could be said that a transfer between pressure and torque occurs. 
     However, any transfer of this type is of minor significance. No significant conversion between torque and these pressures occurs. “Significant” refers to a conversion rate exceeding 25 percent, so that, for example, over 25 percent of the energy contained in a given volume of fluid is converted into torque. 
     5. In FIG. 8, the rotors IR, RR, and OR contain axial faces A, which face in the axial direction (as viewed in FIG.  8 ), that is in the direction axis  51  extends. Plate  37 , when assembled to the motor, has a face F which is parallel to, and adjacent, the axial faces A. 
     6. FIG. 10 shows two pairs of gears: pair  27  and  30 , which have  10  and  11  teeth, respectively, and pair  33  and  36 , which have  6  and  7  teeth respectively. The tooth difference in each pair is one. 
     7. The rotors in FIG. 8 are substantially coplanar, and rotate about centers which have eccentricity, with respect to each other. 
     8. Gerotors are commercially available. The following U.S. patents, assigned to Sumatomo Electric Company of Japan, describe approaches to designing gerotors, and are hereby incorporated by reference: U.S. Pat. Nos. 4,504,202, 4,673,342, 4,657,492, 4,518,332. In addition, Sumatomo Electric designs gerotor motors and pumps to meet specifications provided by a purchaser. 
     9. The invention provides a “dual-displacement” hydraulic machine. One definition of “dual-displacement” is that, for a given machine speed, two selectable flow rates of fluid through the machine are available. Other definitions are possible. 
     10. During both single and dual-displacement operation, the speed of motor  2  is infinitely variable between its minimum and maximum limits. 
     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.