Precession modulated transmission

Abstract

This invention pertains to a continuously variable differential transmission utilizing an axial array of dampers to induce and control the gyration frequency of a precessing plate.

Description

TECHNICAL FIELD

[0001] This invention relates to a Continuously Variable Transmission that utilizes an innovative process for controlling the reduction ratio, termed by the Inventor, “Precession Modulation”. The Precession Modulated Transmission (PMT) is able to produce a wide range of Reduction Ratios in a highly controllable, increment-less fashion. Variations in the Reduction Ratio are produced by converting the rotary motion of the Input, into the rotating and oscillating motion characteristic of a Precessing Body. As only the oscillating component is transferred to the Output, controlling the frequency of this component, which can be readily varied independent of input speed, varies the reduction ratio. This process produces the effect of an inclined plain, with a slope that can be varied from Zero to 90 degrees, with the attendant power transmission characteristics.

BACKGROUND OF INVENTION

[0002] To date, proposals for a variety of Continuously Variable Transmissions (CVT) that have been published or patented: Few of which have demonstrated commercial viability despite the compelling performance potential offered by such a device. For mechanical power transmission applications requiring a broad range of operating ratios, A CVT is in theory, the ideal solution: offering the potential for optimal efficiency and maximized productivity. The efficacy of these systems, however, has produced mixed results due to the many trade-offs resulting from one or more serious limitations.

[0003] The most prevalent form of Continuously Variable Transmissions on the market today is the Hydrostatic Transmission (HST). HST's fill a wide range of applications and power levels, however their efficiency tends to be comparatively poor. This inefficiency manifests itself in the large heat exchangers that are typically necessary to dispose of waste energy created by their operation. As well as the high noise and vibration levels inherent to their dependency on the high volume flow of a pressurized hydraulic medium. They also tend to be quit expensive and therefore are reserved primarily for high end, industrial or capital equipment applications.

[0004] The hydrostatic type can be divided into subgroups: The hydrodynamic type, and the positive displacement type. Positive Displacement HST's are characterized by a pump driven by a prime mover, which serves to pressurize a hydraulic fluid. This charged fluid is than delivered to a hydraulic motor that converts this energy back into a mechanical form able to perform work on the assigned load.

[0005] In many industrial applications, the ability to remotely mount the prime mover and pump from the motor and load is a significant advantage. This is particularly true in the case of Industrial, Off-road, Construction and Agricultural machinery where a limited speed range and/or the distribution of power to ancillary systems separate from the propulsion systems are significant considerations. In addition to the benefit of continuous variability, the EST is also able to handle high power levels with a relative immunity to shock and overload conditions. This constitutes the primary reason that it is the transmission of choice in applications of this type. However, because of their comparatively poor efficiency, objectionable noise and the substantial space required by supporting systems for cooling, conditioning and filtration of the hydraulic fluid, it has had little impact on other markets.

[0006] To date a number of developments have been introduced to address the various shortcomings in conventional HST's. Much research has been centered upon development of the Integrated Hydrostatic Transmission (IHST). The thrust of this development effort has been toward the integration of the pump/motor into a single casing or composite assembly and sharing as many components as possible. The intent being to minimize size and production cost by reduce the number of components required in the device, while improving operating efficiency by minimizing losses from hydraulic friction. The resulting IHST's are compact, highly controllable CVT's that have found acceptance in a range of products. While they are the most efficient of displacement type HMT's, there maximum efficiency is still only in the mid 80% range. Also, due to the fact that fluid pressure and volume is at or near maximum, at operating speed, they tend to produce a significant amount of noise and vibration. While, as a byproduct of there inefficiency, consume excessive amounts of fuel and generate a considerable amounts of heat. The ensuing stress on the hydraulic fluid necessitates a rigorous maintenance schedule and the over sizing of systems to deal with the filtration of the fluid, as well as the removal of entrained gasses and excess heat as compensation for this environment.

SUMMARY OF THE INVENTION

[0007] The Preferred Embodiment of the PMT is intended for use with hydraulic fluid that is put into circulation by the dampers when the transmission is provided with a positive power input from the prime mover. This fluid enters and exits the transmissions Housing Group 45 for control and conditioning purposes via Ports 46,47 in the Head 6. The Core Group 43 depicted in this design is in fact, a slightly modified rotary group obtained from a hydraulic motor (see FIG. 10.) As such, being a mature technology in the public domain, this aspect of the PMT will be covered in a cursory fashion.

[0008] While the core Group 43 finds antecedent in art Axial Piston HST's, the PMT employs this arrangement in a decidedly unconventional fashion; as an array of dampers. Nonetheless, the well-documented performance characteristics of this type of device provide a strong basis for projecting the performance characteristics and operating range in their new roll.

[0009] The design depicted here in, is in accordance with the preferred embodiment, and is intended for applications with a speed range of 400 to 4000 RPM's and torque to 100 lb/ft. It is anticipated that the transmission will produce reduction rations to 5:1 with acceptable efficiency. 2500 RPM's Input, probably represents the practical upper range over which the transmissions full range of reduction ratios cm be utilize Input speeds in excess of 3500 RPMs will probably be limited to Reduction Ratios of less that 2. At Reduction Ratios below three, it should exhibit levels of efficiency and torque transmission characteristics comparable to the sophisticated transmissions used in modern automotive applications. This design achieves maximum efficiency at ratios approaching direct drive, a point where the transmission would essentially function as a coupling producing a top efficiency in the mid 90% range. This level of efficiency will drop off progressively as the reduction ratio goes up, with the efficiency probable falling below 80% at ratios exceeding 4:1 (ref FIG. 8).

[0010] This departure from the conventional mode of operation exhibited by art axial piston HST's produces significant enhancements in performance as well as an entirely different mode of operation.

[0011] The PMT differs from art HST's in that it provides a direct mechanical input and output arrangement. As illustrated herein, the preferred embodiment consists of a collinear input and output shaft on apposite ends of a compact case. While similar to the Integrated Hydrostatic Transmission in this respect, the PMT is able to achieve a significantly smaller form factor due to the elimination of the Pump-Motor relationship typical of said art.

[0012] The PMT also makes a significant departure from art HST's in the method used to vary the transmissions displacement as well as the relationship of fluid flow to duty cycle. In the PMT, the flow rate of the hydraulic medium is inversely proportional to output speed. This results in an effective displacement that fall off rapidly as the transmission approaches direct drive. At which point the transmission would become, essentially, a direct mechanical coupling. However, losses from volumetric efficiency invariable being less than 100% will produce a certain degree of slippage in the absence of secondary systems to counter or compensate for such losses.

[0013] This inverse flow rate is a result of the PMT's employment of a unique differential transmission function: whereby the rotational components, while coaxially arrayed in the preferred embodiment, possess a common moment of rotation. While beneficial in preventing excessive RPM's by summation of shaft speeds, a more pertinent consideration is preventing the conflicting moments of torque that would result from the retrograde precession that would result from a comparable design utilizing the conventional approach of driving the transmission with a charged fluid provided by an external source.

[0014] This differential function is achieved by means of a Transfer Case 44. While the Core Group 43 is typically coupled directly to the Prime mover, and rotates at a speed dicta by this driver, the transmissions output is derived from the Transfer Case 44. When provided with positive power input, the output speed and hence rotational velocity of the Core Group 43 will range from zero rpm's to parity with the prime mover. The transfer of forces between these two major assemblies occurs across the juncture of the precession plate and abutment plate, and is regulated by an axial array of dampers.

[0015] The damping rate of this array is controlled by regulating the differential pressure between the Control 47 and Return 46 ports in the Housing Group 45. This circuit provides for the exchange of a hydraulic medium via Supply and Return ports through porting in the transfer case to the Dampers 27,30,31 in the Core Group 43. The preferred embodiment of this invention utilizes a damper system employing a Piston 27 in the fashion of an expansible chamber devices, however, any component able to produce a constant resistance throughout a range of linear motion, could serve in this capacity, provided it is also possible to vary the damping rate as a means to regulate the reduction ratio.

[0016] As Dampers, these pistons no longer serve as the driving elements typical of their function in a hydraulic motor, but instead, provide a reaction force to the speed differential between the Prime Mover and the Load More specifically: Their function is to modulate the gyration frequency of what is conventionally termed the swash plate.

[0017] The range of motions exhibited by this swash plate are unique to this invention and warrant the more descriptive term of, Precession Plate, favor by the Inventor. An appropriate term, give the fact that this plate, while rotating at a speed diced by the prime mover, precesses in the same direction at a reduced speed. It is the function of the modulators to regulate precession frequency, with precession frequency determining final drive ratio.

[0018] The PMT's control system works by effectively changing the angle of the precession plate, producing an effect similar to changing the slope of an inclined plane. The preferred embodiment is able to create the effect of an inclined plane that can be varied from the Physical slope (15 degrees in the embodiment depicted here) to 90 degrees even though the Physical slope remains constant. FIG. 6 is a two-dimensional force diagram representing the power transmission process and demonstrating how the modulators can influence the reduction ratio. These Modulators create a force “C” that varies the Effective Slope (SE). Bear in mind that the Modulators as well as the modulation plates are part of the Core Group 43, and as such rotate as an assembly at a speed determined by the prime mover. The As dampers, these pistons no longer serve as the driving elements typical of their function in a hydraulic motor, but instead, provide a reaction force to the speed differential between the Prime Mover and the Load. The gyrational component is a result of the dampening process introduced by the Modulators and its frequency can be varied from zero to parity with rotation. The former state is the result of the modulators operating with a minimal damper rate and produces no output. The latter state provides sufficient hydraulic pressure to prevent the dampers from cycling (the dampers would be essentially incompressible) and result in the transmission operating in direct drive. As the gyrational component alone is transmitted to the output shaft, the ratio of the rotary speed of input to that of the output determines the Reduction Ratio. These dampers also insure the Precession Plate 29 effectively engages the Abutment Plate 7, permitting the dynamic translation of forces across this junction. As depicted in FIG. 6, if the reaction force C, generated by the dampers equals RN the transmission will be in direct drive. If the damper rate is gradually reduced by increasing fluid flow trough the control circuit, a commensurate reduction in the Pressure Differential of the control circuit (ΔP) will result. This reduction in Pressure Differential will produce an increase in the reduction ratio. Conversely, if the load on the output shaft is increased, the reduction ratio will decrease accordingly.

[0019] Unique to this invention, is the manner in which the Precession Plate 29 exhibits a range of motions characteristic of a Precessing body, as it interacts with the Abutment Plate (item 7). Typical of such motion, the swash plate exhibits two axis of rotation (see FIGS. 2 & 3). The Primary axis Z is collinear with the transmission centerline, while the secondary axis theta, intersects at an acute angle 56 with the point of intersection coincident with the Precession Plate's 29 center of gyration 58 and at a right angle to the face of the Abutment Plate.

[0020] The Core Group's 43 rotation speed is dictated by the Prime Mover and provides a torsionally ridged assembly. However, the Dampers provide the degree of axial motion necessary to insure the Swash Plate (item 29) remains square to the Abutment Plate 7, thereby providing a positive pre-load pressure between the Damper Shoe Bushings (item 30) and the Abutment Plate 7. Consequently, an equal reaction load between the Valve Plate (item 36) and the Damper Block (item 31) on the opposite end of the assembly is produced. As both these interfaces provide a Hydrodynamic-bearing surface, a certain speed differential between the transfer case and core assembly is called for to maintain proper lubrication. This fact is depicted in FIG. 8. Which indicates a minimum input speed, and also, effectively prevents the PMT from operating in direct drive. However, with a pressure differential of at least 50 PSI and a minimum speed differential of 250 RPMs, this arrangement provides a very smooth, quite and responsive method of power transmission with minimal wear on internal components. Within this operating range the PMT will seek the appropriate reduction ratio when loads change on either the output, control circuit or power input, due to its positive, self-centering, stability.

[0021] In addition to speed constraints imposed by the need for hydrodynamic lubrication, which is characteristic of all axial piston HST's, the PMT also requires a certain speed differential to insure a sufficient pressure drop across the hydraulic control circuit. This is due to the fact that the PMT displaces no fluid in direct drive. Essentially its displacement has fallen to zero. As the design approaches direct drive, losses from internal leakage will impact the Dampers ability to retain sufficient pressure to maintain the Transmission in a locked state FIG. 8. These losses are a result of limitations in volumetric efficiency. Given the PMT's similarity to Axial Piston motors with respect to the Core Group, It would seem safe to expect a comparable level of volumetric efficiency (Ev) with the PMT. As a typical axial piston motor experiences a volumetric efficiency of around 95%, we can use this figure as a basis for projecting a minimum reduction ratio that can be achieved without auxiliary sys to compensate for such losses. As in a typical HST, the PMT's efficiency is largely the sum of EV and losses from heat/friction Eparasitic(EP) however; a Positive Displacement HST requires the overhead of both a pump and a motor; with both components producing comparable levels of efficiency. As such a conventional HST in the real world will see efficiencies in the mid to low 80% range. The control system in the PMT, however, should expend a maximum of 17% of power input at a reduction ratio of 5, with the remainder due to losses from Ev+EP.

[0022] The embodiment of the PMT depicted here in, employs an array of Modulators 27,30,31 to regulate the rotation rate of the Transfer Case Group 44 The rotational speed of the output can be varied from zero Rpm's, to parity with input speed. When the Modulators Damper rate is at a minimum and the Output Shaft has a sufficient load to prevent rotation of the Output Shaft, The PMT's displacement (In3) is at its maximum. Under these conditions, the Precession Plate 29 will rotate at a speed dictated by the driver; however, as the Abutment Plate 7 is stationary the Swash Plate will rotate only. The Oscillating components, which, in conjunction with the rotary motion typical of a Precessing body, at this point, do not exist: Consequently, each revolution of the input shaft produces a complete cycle of the Modulators. The amount of damper force generated by the modulators at this point, can be determined by the formula:

L O =ΔP*D

[0023] With respect to the PMT, this expression is valid only when there is no rotary output. At this point, the transmission is stalled and is producing maximum displacement. Flow volume is the product of Displacement and RPM's, while System pressure is a function of the load (LO) on the output shaft, and This may sound counter-intuitive, until you consider that LO is a reaction to Torque Input (LI), which is directly proportional to the Control Reaction (C) used in FIG. 3.

[0024] Interestingly enough: The PMT in this extreme mode of operation operates in the same fashion as a Swash Plate variant of an axial piston pump. This operating mode with respect to the PMT would typically represent a Neutral mode. Here the System Pressure (Ps) is very low and the Pressure Drop (ΔP) is approaching minimum allowable levels (less than 100 psi). This mode of operation may also be useful when driving auxiliary circuits: With the output shaft locked, all power output may be exported through the control circuit, while engine speed may be varied in accordance with flow volume and pressure requirements.

BRIEF DISCIPTION OF THE DRAWINGS

[0025] FIG. 1 provides a longitudinal Breakaway drawing of the preferred embodiment of the Precession Modulated CVT in accordance with the present invention.

[0026] FIGS. 2 & 3 are illustrations of the Precession Plates principle axis of rotation.

[0027] FIG. 4 shows a schematic of a hydraulic control circuit with provisions for the cooling and filtration of the hydraulic fluid, while providing power to auxiliary systems.

[0028] FIG. 5 is a cut away view of the transmission showing the internal porting arrangement

[0029] FIG. 6 is a force diagram demonstrating the basic principle behind precession modulation, and how it is able to compound torque through the reduction process.

[0030] FIG. 7 is a graph that demonstrates how fluid displacement varies in proportion to the reduction ratio.

[0031] FIG. 8 depicts a graph that plots the anticipated speed and reduction ratio operating range.

[0032] FIG. 9 provides an exploded view of the components of a Core Group in accordance with the present invention.

[0033] FIG. 10 provides an exploded view of the components of a Transfer Case Group in accordance with the present invention.

[0034] FIG. 11 provides an exploded view of the components of a Housing Group in accordance with the present invention.

DISCRIPTION OF THE PREFERED EMBODEMENTS

[0035] Unique to this invention is the inclusion of a Transfer Case Group 44 between the Core Group 43 and the Housing Group 45. Given the fact that the Dampers 27 provides a reaction force to the speed differential between the Transfer Case 44 and the Core Group 43, through the inclination of the Abutment Plate 7, this arrangement will induce the Transfer Case 44 to rotate with the Core Group. The translations of forces at this interface are outlined in FIG. 6 and induce a range of motion upon the Precession Plate 29 that is characteristic of a gyroscope precessing about its main axis.

[0036] The Hydraulic fluid that circulates via the alternately expanding and compressing Dampers 27 passes through a Valve Plate 36, the orientation of which is clocked with a specific orientation to the Abutment Plate 7 to provide a Damping and Return circuit. This particular embodiment is driven m a counter-clockwise direction as viewed from the output end of the transmission. As such the Damper Pistons 27 as they ramp up the Abutment Plate 7 and are progressively compressed, discharging the hydraulic fluid through the Valve Plate 36. This phase, where the Piston 27 is rising up the Abutment Plate 7 constitutes the Damping Phase. There is a corresponding set of ports in the Valve Plate 36, arrayed 180 degrees out of phase with first said ports. These ports are dedicated to the discharging of fluid during the return phase that ensues after the cylinder reaches the top of its stroke and commences to travel down the backside of the Abutment Plate 7. At which time, these ports providing a path for the return of fluid to the Dampers.

[0037] FIG. 10 shows the Transfer Case Group 44 containing the Abutment Plate 7 and Valve Plate 36. A Pin 16 is used to Align the Valve Plate 36 to the Spindle Shaft 5 Which is also fixed in radial alignment by two pins 15 to the Transfer Case Housing 4. The Abutment Plate 7 is similarly pinned in orientation, with all these components bolted into a rigged assembly that contains the Core Group 43.

[0038] This Core Group 43 is located via Bearings 8,33 to allow free rotation within the Transfer Case Group 44. The axial location of these components is maintained by a Spring 37 that provides a pre-load to the Precession Plate 29 via Pins 40 and a Hemispherical Bushing 32. This arrangement allows the Precession Plate 29 to capturing the Damper Slippers 30, forcing them into contact with the Abutment Plate 7, with Wear Washer 21 acting as an intermediary.

[0039] The Spindle Shaft 5 is ported in such a fashion as to discharge the fluid passing through the Valve Plate 36 via passages that terminate in annular passages within the Housing Head 6. From here, the hydraulic fluid exits the transmission though Ports that are threaded to accommodate Hydraulic fittings. FIG. 5

[0040] The annular Control Port 52 is flanked on both sides by Ring Seals 49,50 as pressure in this cavity may reach several kpsi. Any leakage past Ring 49 will pass into the output side and provide lubrication for the Output Shaft Bearing 39. This cavity is sealed by means of O-rings and Radial Lip Seals 23,19 held captive by End Cap 17 and Internal Retaining Ring 13, with excess fluid discharging via Passage 42 to the Housing; which is at atmospheric pressure. Any Fluid bypassing ring seal 50 will simply cross over to the Return Port and return to the dampers. From here, the hydraulic fluid exits the transmission though Ports that are threaded to accommodate Hydraulic fittings.

[0041] FIG. 4, Provides a schematic of an open loop circuit that features components fir cooling and filtration purposes. It also features a control circuit in series with a PTO system driven by a small hydraulic motor.

[0042] In many applications, not all the components shown in this schematic would be required. In addition, some of the if features could be incorporated into the transmission itself. This increased integration is more easily achieved than in the conventional Displacement HST, principally because of lower heat generation and much lower average fluid displacement in most operating regimes.

Claims

1. A continuously variable differential transmission comprising: A torsionally rigid input assembly consisting of an evenly spaced c array of dampers that are oriented so their respective damping actions is parallel to the rotational axis, while rigidly secured on one end to a carrier plate, with the other end engaging a swash plate with a means of retention, that insure the swash plates centroid of gyration remains coincident with, and axially located on, a specific position on the center axis of this more or less axis symmetric assembly, supported by ant-friction means, to be disposed to the rotational input introduced by the prime mover; a transfer case assembly that interfaces by anti friction means with the first units swash plate by an abutment plate, with said abutment plate providing a plane at a skewed angle that dictating said swash plates angle of repose, while first units damper array insuring a positive engagement between said interface and providing an output means collinear with first units input means; means to maintain the collinear relationship of the combined assemblies axis of rotation so as to insure a rotational input to the input assembly imparts a sequential compression and relaxation of the dampers in the damper array, thereby imparting a rotation of the swash plate, the orientation of which is dictated by a output assemblies abutment plate, or, alternately inducing the output assembly to rotate with the input assembly in a direct 1:1 ration, or a combination of both scenarios in which case the swash plate exhibits a motion characteristic of a precessing body with the gyrational frequency some fraction of rotation frequency; means to regulate the damper rate, of the damper array so to impart a common damping rate to the individual dampers in a concurrent fashion, as appropriate for a given operating mode;

2. A continuously variable differential transmission according to claim 1, where the damping process is accomplished by hydraulic means that includes an array of piston dampers, displacing hydraulic fluid by their cycling action, with said fluid passing through a valve plate ported in a manner to divide the fluid flow into control and return circuits; a valving means to regulate a pressure drop across these circuits; a housing assembly that contains and supports the core and transfer case assemblies, while providing an atmospheric pressure reservoir for hydraulic fluids emanating from said assemblies, and equipped with rotary seals at input and output as necessary to insure said housing is, practically leak free; means to regulate the internal damper pressure within said housing.

3. A continuously variable differential transmission according to claims 1 and 2; means to export the pressurized hydraulic fluid from control and return circuits by porting from the core assembly via a valve plate, through the transmission housing for control and/or conditioning and/or power to run auxiliary systems.