WO1997038234A1

WO1997038234A1 - Hydrostatic coupling comprising a planetary gear pump

Info

Publication number: WO1997038234A1
Application number: PCT/US1997/005148
Authority: WO
Inventors: Fred L. Baldwin
Original assignee: Baldwin Fred L
Priority date: 1996-04-04
Filing date: 1997-04-04
Publication date: 1997-10-16
Also published as: CA2250476A1; JP2001508156A; AU2596097A; EP0890036A1

Abstract

A hydrostatic coupling comprises a housing (10) adapted for rotation about a central axis (14). The interior of the housing (10) includes a reservoir (22) for retaining hydraulic fluid, an enclosure (32) retaining a planetary gear pump (26, 36) and ports (38, 40) connecting the reservoir (22) to the pump enclosure (32). A valve assembly (42) is adapted to restrict the flow through output port (40). Torque transmission between sun gear (36) and housing (10) is a function of the flow restriction generated by valve assembly (42).

Description

HYDROSTATIC COUPLING COMPRISING A PLANETARY GEAR PUMP

Field of the Invention

This invention relates to hydrostatic drives for power transmission systems and more particularly to such transmission systems employing an epicyclic gear set.

Background of the Invention

Hydrostatic transmissions are well known for power drive systems in the automotive industry and the like. In such system the output torque and revolutions are, conventionally, directly proportional to the flow rate of the pressurized hydraulic fluid used. Thus, as the speed ratios increase from low gear to high gear the fluid flow increases.

Planetary gear sets are also well known. Such known gear sets employ planetary gears, a sun gear and a ring gear.

The present invention represents a novel combination of a planetary gear set and a hydrostatic gear pump which provides continuously variable gear ratios through a fixed gear set. In this implementation a hydraulic fluid, such as oil, serves as a reaction medium replacing either the ring gear or the sun gear in the typical three element planetary gear set. This results in an efficient and versatile system which is extremely compact.

In most constantly variable transmission drive trains, i.e. friction cones systems, viscous drives, belt and variable diameter pulley, the torque is transmitted by friction. This has inherent force limitations, low efficiency, high wear and necessitates a clutch. The present invention overcomes these drawbacks.

Prior Art

A planetary drive set utilizing an inside oil pocket has been disclosed in prior German Patent DE 3918063 granted December 5, 1992 to Rhos. The German patent describes such a system used as a shock absorber for the ring gear of a clutch assembly and not as a continuously variable drive system as contemplated by the present invention.

Summary of the Invention

It is an object of the present invention to provide a continuously variable transmission employing a hydro- mechanical planetary gear set.

It is a further object of the invention to provide a continuously variable transmission wherein the speed ratio settings vary inversely with the flow of the hydraulic fluid. Therefore, in accordance with a first aspect of the present invention there is provided a transmission system comprising an epicyclic gear set within a rotatabie, sealed housing wherein the epicyclic gear set has at least two planetary gears, each journalled in its own planetary gear enclosure within the sealed housing. The gear set further has a complementary gear member connected to a power transfer means, the complementary gear being in meshing engagement with the planetary gears. A hydraulic fluid, such as oil, is contained within the enclosures. Inlet and outlet ports are provided within the planetary gear enclosure to permit flow of the hydraulic fluid into the enclosure. Valve means are provided in at least one of the output ports to controllably restrict flow of the hydraulic fluid.

The complementary gear member is a sun gear in one embodiment and a ring gear in a second embodiment.

In one implementation input power to the transmission system is applied to the rotatabie housing and the output torque is taken from the power transfer means. In an alternate implementation the input rotational power is applied to the power transfer means and the output torque is delivered to the rotatabie housing.

In accordance with a further aspect of the present invention there is provided a transmission system comprising a rotatabie, sealed housing having therein a epicyclic gear set, the epicyclic gear set having a pair of coaxial, longitudinally spaced first and second planetary gears each journalled for independent rotation in its own planetary gear casing. The gear set also has first and second longitudinally spaced sun gears operating on a common central shaft. The first and second planetary gears are in meshing engagement with the first and second sun gears respectively. Hydraulic fluid, such as oil, is retained within the sealed housing. Each of the planetary gear casings is provided with input and output ports for fluid communication therebetween. There is also valve means in at least one of the output ports for controllably restricting fluid flow therethrough.

In a preferred form of this aspect one of the first or second planetary gears/sun gears in the planetary gear set is wider than the other. This provides a preset torque multiplication which is constant over the entire range of continuously variable ratios. In a particular exemplary embodiment the width ratio of the first planetary gear to the second planetary gear is 1:3.

The valve means, which is preferably in the output port operates to restrict flow of the hydraulic fluid from the planetary gear casing. With zero flow restriction the planetary gears free-wheel about the sun gear as the housing is rotated. A restriction in flow from the output port creates a pressure within the casing and this pressure acts on the sun gear imparting rotational forces thereto. With maximum flow restriction, maximum rotational forces are applied to the sun gear resulting in a lock-up and a 1:1 gear ratio.

In a basic embodiment the valve means is operated by centrifugal force created as the housing is rotated. It is also contemplated that the valve means may be activated mechanically or electronically as will be apparent to one skilled in the art.

Brief Description of the Drawings

The invention will now be described in greater detail with reference to the attached drawings wherein: Figure 1 is a sectional view of the first embodiment of the present invention taken along line A-A of Figure 2; Figure 2 illustrates the system of Figure 1 viewed along line B-B of Figure 1;

Figure 3 is a sectional view of the embodiment shown in Figure 1 without the gear set; Figure 4 is a sectional view of the embodiment of Figure 1 taken along lines D-D of Figure 3 but including the gear set;

Figure 5 is a sectional view of an alternate embodiment of the invention.

Figure 6 is a sectional view of the embodiment of Fig. 5 taken along line X-X. Figure 7 is a sectional view of an alternate embodiment of the present invention taken along line E-E of Figure 8; Figure 8 is a sectional view of the embodiment of Figure 7 taken along the line F-F;

Figure 9 is similar to the sectional view of Figure 7 without the gear set;

Figure 10 is a sectional view of Figure 9 taken at lines H- H;

Figure 11 is a sectional view of the embodiment of Figure 5 viewed from the opposite face;

Figure 12 is a sectional view taken along line K-K of Figure

11;

Figure 13 is similar to Figure 11 without the gear set; and Figure 14 is a sectional view of Figure 13 taken along line M-M thereof.

Detailed Description of the Invention

The invention relates to two different drive systems: type A which is a clutch or coupling driver with a small amount of torque multiplication and a short gear-ratio range; and type B which is a true, continuously variable transmission (CVT) drive system with large torque multiplication and a wider gear-ratio range.

Figures 1 to 4 show a first embodiment of type A transmission system having a cylindrical, rotatabie housing 10. The housing has end or cover plates 12 sealed to the cylindrical body by fastening means and O-ring seals 13 as well known in the art. The housing is adapted for rotation about central axis 14 and for the sake of the following description only it will be assumed that the body rotates in the direction indicated by arrow 16.

The housing 10 has a shaft opening 18 for receiving a central shaft (not shown) . The interior of the housing includes vanes 20 and reservoir 22 for retaining a hydraulic fluid, such as oil, therein. Holes 24 extend through the internal vanes to permit securement of the end faces to the housing by known means such as bolts (not shown) .

Planetary gears 26, each having a gear shaft 28 and teeth 30 are retained within tightly-fitting, circular planetary gear casings or enclosures 32. The planetary gear sets are pressure balanced by bearing housings 34 on either side. The planetary gears 26 mesh with and orbit around sun gear 36.

Sun gear 36 is secured to the central gear shaft by well-know means such as a spline and is supported within the housing by a bearing-pressure balance assembly. The planetary gear enclosures and the cavity around the sun gear are isolated from the reservoir 22 except for input ports 38 and output ports 40. Valve assembly 42 is retained within the output port 40.

Valve assembly 42 includes end cap 44, plunger 46 and spring 48. In this version of the valve assembly, spring 48 urges plunger 46 inwardly of the output port to allow hydraulic fluid within the planetary gear enclosure 32 to freely flow from the enclosure via the output port 40 to the reservoir 22 and back into the enclosure by way of the input port 38. The value assembly is activated by centrifugal force such that as the housing 10 rotates the plunger is urged outwardly against the spring to a position which restricts flow of the hydraulic fluid through valve port 50. As the rotational speed of housing 10 increases the valve plunger is caused to further restrict the fluid flow and will eventually stop flow altogether.

Also shown in Figure 2 are power transfer means 52 which may be a further gear, pulley, etc. Power transfer means 52 are secured to the end plate for rotation-of the housing 10 therewith .

Operation of this embodiment will now be described with reference to Figures 1 to 4. In steady state condition the hydraulic fluid fills the reservoir and the cavities created by the planetary gear casings and the sun gear casing. As the housing is slowly rotated in the direction shown by arrow 16 the central shaft and sun gear attached thereto initially remain stationary. Planetary gear 26 free-wheels about sun gear 36 in the direction shown by arrow 54. This interaction leads to pumping action causing oil to be drawn through input port 38 and forced back toward the reservoir through output port 40. Since valve plunger 46 is fully extended inwardly there is no restriction of the fluid flow. As the rotational speed increases, however, the plunger is forced outwardly by centrifugal force to partially close off valve port 50 and an initial flow restriction is generated. The result of this is to cause a pressure differential at the output port relative to the input port resulting in the rotational rate of the planetary being reduced. This is translated to sun gear 36 and tends to induce drive forces and some rotation thereof. The torque applied to sun gear 36 increases continuously as the flow restriction increases. When the plunger completely closes off valve port 50 there is maximum pressure at the output port and the planetary gear and sun gear are in a locked-up condition. This results in maximum torque and a gear ratio of 1:1 between input torque and output torque.

As will be apparent, valve assembly 42 may be of an alternate type whereby control of the fluid flow restriction is accomplished mechanically or electronically.

Figures 1 through 4 illustrate two planetary gears 26 although it is contemplated by the present invention that additional planetary gears may be incorporated within the housing so as to mesh with and orbit around the sun gear.

As a further alternative the input torque can be provided to the sun gear via the central shaft in which case the output torque is taken from the rotating housing. A second example of the type A system is shown in Figures 5 and 6. In this example the epicyclic gear set includes planetary gears and a ring gear rather than the sun gear of Figures 1-4.

This transmission system includes circular body 60 having outer side plates 62 enclosing therebetween the epicyclic gear set. The interior of the body 60 includes inner side plates 64, planetary container housing 66 and input shaft 68. Planetary gears 70 are located within tight-fitting circular housing 72. Each gear 70 has a shaft 73 journalled for rotation within housing 72 and secured in place by planetary bearing/pressure balance assembly 74.

Ring gear 76 has teeth 78 in meshing engagement with the planetary gears. Ring gear output member 80 is secured to the ring gear and rotates therewith. Output is provided by a pulley or cogged belt around the circumference 82.

Reservoir 84 retains hydraulic fluid such as hydraulic oil. Each planetary gear housing 72 has an inlet port 86 and an outlet port 88. Horizontal valve means 90 operated remotely is used to regulate the oil flow from the outlet port 88 to the reservoir 84 and subsequently back to the input port 86.

In operation, input rotational torque is applied to body 60 by way of shaft 68. Without flow restriction planetary gears 70 free-wheel in ring gear 76 which remains at rest. This action causes oil to be pumped from the input port to the output port. Rotation of the input shaft in the direction of arrow 91 causes the planetary gears to rotate in the direction given by arrows 92. As in the previous embodiment, restriction of oil flow from the output port eventually leads to rotational forces being imparted to the ring gear in the direction shown by arrow 94. Maximum flow restriction results in maximum torque transfer and the output torque is delivered by ring gear output member 80. The type B drive system will now be described in greater detail with reference to Figures 7 to 14.

As previously described with relation to Figs. 1 to 4 housing 110 is, preferably, cylindrical with a central shaft opening 112. The housing 110 is adapted for rotation about central axis 114 as described in relation to the previous embodiment. Again, for descriptive purposes only it will be assumed that the housing rotates in the direction shown by arrow 116. It is to be understood, of course, that the housing may be rotated in the opposite direction. The housing has end faces 118 which are secured to the housing 110 by known means so as to retain hydraulic fluid within the housing. Either one of end faces 118 may have attached thereto means for imparting rotational movement to the housing such as power transfer means 52 in Figure 2.

The type B embodiment has twinned planetary gears as best seen in Figure 8. These are planetary gears 120 and 122. Each planetary gear is secured within its own planetary gear enclosure 124, 126 respectively. The planetary gear sets are pressure balanced by bearing housing 128. Planetary gear 120 has planetary gear shaft 130 and radial teeth 132 as best seen in Figure 7. Planetary gear 122 is free to rotate about shaft 130. As shown the two planetary gears are separated by a partition 134 integral with the housing 110. It will also be apparent from Figure 8 that one planetary gear, 120, is considerably narrower than the other, 122, thus providing a pump side (narrow gear set) and a motor side (wider gear set) . In the attached drawings Figures 7 and 9 are cross sectional views of the pump side (narrow) and Figures 11 and 13 are cross sectional views of the motor side (wide) .

As discussed in relation to the type A system the planetary gears mesh with teeth 136 of sun gear 138. It will also be apparent from Figure 8 that the sun gear is also twinned comprising sun gear 138 (narrow) and sun gear 140 (wide) . Sun gear 138 includes shaft 142 which is secured to a central shaft (not shown) . The wider sun gear 140 is separated from gear shaft 142 by a Sprague clutch ring 144 and roller bearing 146. This allows gear 140 to transmit output torque to gear 138 but allows gear 140 to free-wheel backwards.

The type B embodiment also includes reservoir 150 for containing hydraulic fluid such as oil. Each of the planetary enclosures or casings have inlet port 152 and outlet ports 154 and each outlet port has a valve assembly 160, 162 similar to those previously described.

In operation of this embodiment input torque to the housing 110 causes the pump planetaries 120 to free-wheel around the stationary sun gear 138 when oil flow is unrestricted. In this state the CVT is in neutral. As oil flow is restricted by valve 301 the pump side planetaries 120 build up pressure in outlet ports which are connected by orifice in the partition to the inlet ports of the motor planetaries 122. This pressurized oil from the pump side (narrow gears) drives the motor side, wider gears at a mechanical advantage proportional to the width ratio (pump side to motor side), which multiplies torque. For example, Figure 8 shows the motor side gear set to be three times the width of the pump side gear set thus providing 3:1 torque multiplication in all gear ratio settings until full lock-up (1:1) is reached.

The oil flow in low gear setting is as follows: oil pressure from the pump outlet is transferred directly through the partition orifice to the motor inlet port causing the motor gear set (planetary and sun gear) to be driven in opposite directions. The motor planetaries carry the oil to its outlet port where it will be recycled through the valve back to the reservoir to repeat the flow cycle.

The primary sun gear interfaces with the pump planetaries and the secondary sun gear interfaces with the motor planetaries. As the sun gears are separated by a Sprague clutch output torque may be transferred to sun gear 138.

The oil flow is controlled by valves 160 and 162 which respond to centrifugal force in the most basic of drive systems. As previously discussed, for more precise ratio control the valve means can be regulated manually or electronically to optimize the torque transmitted with the engine speed. In the basic embodiment utilizing centrifugal valves, the valve bodies are installed radially. When using manually or electronically controlled valves (through remote valve manifold) the valves in the housing are installed horizontally thus unaffected by centrifugal forces. Centrifugal valves are shown in Figures 7 to 14. Valve 160 controls the outlet pressure of the pump planetary. When valve 160 is open the gear sets (pump and motor) free-wheel about the sun gear 138 and CVT is in neutral, (vehicle is stationary) . When valve 160 is closing, pressure is built up in pocket 126 and will begin driving the motor gear set. Valve 162 controls the outlet port 164 of the motor planetaries 122. When the valve 162 is open the lowest gear ratio setting is achieved. As the valve 162 progressively closes the CVT approaches full lock-up or a 1:1 gear ration (high gear) . There are two valves 160 and 162 for each planetary gear on the motor side. It should be noted that drive input can be arranged to flow through the sun gear thus driving the housing (output) through the planetaries. This is the reverse of the general description given above. The operating principles remain the same.

It is also possible to combine a number of the described gear sets together in series to achieve specific ratio requirements including overdrive and reverse.

While the above description and illustration show the simplest form of hydraulic valve control (centrifugal) many combinations of fluidic control circuitry can be applied to this drive system.

Claims

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A transmission system comprising an epicyclic gear set within a rotatabie housing, said epicyclic gear set having; at least two planetary gears each journalled within its own planetary gear enclosure within said housing and a complementary gear member having power transfer means attached thereto, said complementary gear member being in meshing engagement with said planetary gears; hydraulic fluid within said housing; inlet and outlet ports in said planetary gear enclosures to permit flow of said hydraulic fluid into said enclosures; and valve means in said output ports to controllably restrict flow of said hydraulic fluid therethrough.

2. A transmission system as defined in claim 1 wherein said complementary gear member is a sun gear.

3. A transmission system as defined in claim 1 wherein said complementary gear member is a ring gear.

4. A transmission system as defined in claim 2 wherein input torque is applied to said rotatabie housing and output torque is delivered by said power transfer means.

5. A transmission system as defined in claim 2 wherein input torque is applied to said power transfer means and output torque is delivered by said rotatabie housing.

6. A transmission system as defined in claim 3 wherein input torque is applied to said rotatabie housing and output torque is delivered by said power transfer means.

7. A transmission system as defined in claim 1 wherein said hydraulic fluid is retained in a fluid reservoir in fluid communication with said input and output ports of said enclosure.

8. A transmission system for controllably transferring torque from a driving member to a concentric driven member, said system comprising a rotatabie body having sealingly retained therein, an epicyclic gear set, said gear set having at least two planetary gears journalled for free rotation in its own planetary gear casing about an axis parallel to the central axis and a complementary gear member having a power transfer means for rotation about the central axis, the planetary gears being in meshing engagement with the complementary gear member, the planetary gear casings, each having an input and output port and a valve means in at least one of the output ports, the rotatabie body having therein an hydraulic fluid communicating with said input and output ports of each gear casing whereby said valve means controllably restricts flow of said fluid into said casing such that minimum torque is transferred from said driving member to said driver member with minimum flow restriction and maximum torque is transferred from said driving member to said driver member with maximum flow restriction.

9. A transmission system as defined in claim 8 wherein said rotatabie body is said driving member and said power transfer means is said driven member.

10. A transmission system comprising a rotatabie, sealed housing having therein an epicyclic gear set, said epicyclic gear set having a pair of co-axial, longitudinally spaced, first and second planetary gears, each journalled for independent rotation in its own planetary gear casing, first and second longitudinally spaced sun gears operating on a common central shaft, said first and second planetary gears being in meshing engagement with said first and second sun gears respectively, hydraulic fluid within said sealed housing, input and output ports in said planetary gear casings for fluid communication therebetween and valve means in at least one of the output ports for controllably restricting fluid flow therebetween.

11. A transmission system as defined in claim 10 wherein said pair of first planetary gears and said first sun gear has a narrower gear face than said pair of second planetary gears and said second central gear.

12. A transmission system as defined in claim 10 wherein input rotational torque is supplied to said sealed housing and continuously variable output torque is delivered by said central shaft.

13. A transmission system as defined in claim 10 wherein input rotational torque is supplied to said central shaft and output torque is delivered by said sealed housing.

14. A transmission system as defined in claim 12 wherein torque transfer is controlled by varying the fluid through the valve means.

15. A transmission system as defined in claim 14 wherein said valve means is controlled by the centrifugal force of the rotating housing.

16. A transmission system as defined in claim 14 wherein said valve means is controlled mechanically.

17. A transmission system as defined in claim 14 wherein said valve means is controlled electronically.