Planetary drive system

A planetary drive system that has an input and a gear housing that is connected to a speed control system. A cross connecting shaft is drivingly engaged by the speed control system and rotatably connects to a forward and reverse gear set that is drivingly connected to a reduction gear set to provide an output. The speed control system, forward and reverse gear set, and reduction gear set are actuated by band clutch elements that frictionally engage the exterior of ring gears and carriers within the system to control the operation of the planetary drive system.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/478,712 filed Apr. 25, 2011.

BACKGROUND OF THE INVENTION

This invention relates to a planetary drive system for a vehicle. Specifically, this invention relates to a transmission used to power vehicles that steer by changing the speed of the wheels on one side of the vehicle relative to the wheels on the other side of the vehicle.

Typically, in lawnmowers, skid loaders and the like have vehicle steering that allows the changing of wheel speed on one side of the vehicle relative to the other and in some instances one side can actually be reversed while the other side travels forward such that the vehicle can execute a zero turn. This is commonly accomplished by using three different differentials. They are often times powered by hydraulic motors or pumps. Specifically, lawnmowers use a pair of hydraulic motors wherein one motor is attached to one side wheel and the other is attached to another side wheel. The motors can be reversed and speed adjusted to control the vehicle.

These systems are complicated and expensive. The most cost effective method of powering a lawnmower is by use of a transaxle. A transaxle is a box containing the gears to drive the machine at the required speed. The transaxle has a single input that is usually a pulley driven by the engine and a pair of axles that attach directly to the wheels of the machine. Thus, no chains or external gear boxes are required.

A disadvantage of using hydraulic drives and other methods is the attempt to synchronize the two drives when it required that the vehicle travel in a straight line. Lack of mechanical connection causes drift and constant adjustment to the travel direction is required by the operator. Other disadvantages of the hydraulic drives are the waste of power due to losses required to circulate the oil. In addition, internal leakage leads to loss of efficiency. Further, the hydraulic drives have a tendency to sustain damage when started in very cold temperatures and additionally the motor can sustain damage when the vehicle is moved with the engine turned off.

Additional disadvantages of current systems include that the available torque from the motors is too low to directly drive the transaxle to the wheel and a secondary speed reduction system must be used between the hydraulic motor and the axle. If this is not done, a large motor must be used. Unfortunately, the savings offered by the small motor is often offset by the requirement of employing a gear reduction to increase the torque. Thus, a need in the art exists for alternative methods to using such hydraulic motors that are presently within the art.

Thus, a principle object of the present invention is to provide a gear drive system for providing a zero turn transmission.

Yet another object of the present invention is to provide an inexpensive method of manufacturing the gear drive system.

Another object of the present invention is to provide a gear drive system that is both inexpensive and easy to manufacture.

BRIEF SUMMARY OF THE INVENTION

A planetary drive system having an input that is disposed within a gear housing and is connected to a speed control system. A cross connecting shaft is drivingly engaged by the speed control system and is rotatably connected to a forward and reverse gear set. A reduction gear set is drivingly connected to the forward and reverse gear set and rotatably connected to an output.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures show components of a gear drive system10utilized to drive the wheels of a vehicle such as a lawnmower, skid loader, and the like. The system10includes an engine or electric motor (not shown) that provides an input12into a transaxle14. The input12is not specific. It can be a pulley, a chain, a gear or a continuously variable drive system. Fixed connections to shafts can be splines or keys or tapers, which ever type suits the application. Snap rings and set screws may also be used. For clarity, these devices are not shown.

The input12drives and is mounted to the tubular cross shaft16that surrounds cross shaft18and which drives a speed control gear set20. The gear set20has a first section22having a sun gear24that meshingly and drivingly engages a planet gear26that meshingly engages a ring gear28. A first clutch element30is disposed around the ring gear28and is connected to a first actuator32such that when the first actuator32is rotated in a first direction the first clutch element frictionally engages the ring gear28to prevent rotational movement of the ring gear28.

A second section34of the speed control gear set20similarly has a sun gear36that meshingly and drivingly engages a planet gear38that meshingly engages a ring gear40. A second clutch element42is disposed around the ring gear40and is connected to the first actuator32such that when the first actuator32is rotated in a second direction opposite the first direction, the second clutch element42frictionally engages the ring gear40to prevent rotational movement of the ring gear40. In a preferred embodiment the sun gear24of the first section22has a diameter twice the length of the diameter of the sun gear36of the second section34. In this manner the speed control gear set20provides different speeds depending upon which clutch30or42is actuated.

A first carrier44is mounted to and drives cross shaft18and has pin elements46and48that connect to the first and second sections22and34. Therefore, the planet gears26and38are mounted to separate sets of pins46and48mounted to carrier12and rotate within ring gears28and40respectfully, that are each engaged by clutch elements30and42respectfully. The carrier44is thus referred to as a common carrier because two separate sets of planets26and38are mounted to the carrier44.

A forward and reverse gear set46is rotatably and drivingly connected to the cross shaft18that is driven by first carrier44. The forward and reverse gear set46includes a second carrier48that has a third clutch element50disposed around its perimeter. The third clutch element50is connect to and actuated by a second actuator52that when actuated rotates in a first direction to cause the third clutch element to frictionally engage the second carrier48to prevent rotation of the second carrier48. The second carrier48is also connected to a third section54by a pin element56. The third section54includes a sun gear58that rotates a planet gear60that is meshingly engaged by and revolves in double ring gear62. The third section54via the pin element56is connected to a fourth section64that similarly has a sun gear66and a planet gear68. The planet gear68also meshingly engages and revolves in the double ring gear62.

A fourth clutch element70is disposed around the double ring gear62and is connected to the second actuator52. Thus, when the second actuator52is rotated in a second direction opposite the first direction, the fourth clutch element70frictionally engages the double ring gear62to prevent rotational movement of the double ring gear62.

A third carrier72is connected to the third and fourth sections54and64via pin elements74. Thus the planet gears68are mounted to the double ring gear62side of the third carrier72on pin elements74for bearings in planet gears68. A fifth clutch element76is disposed around the third carrier72and is attached to a third actuator78that surrounds the second actuator52. When the third actuator78rotates the fifth clutch element76frictionally engages the third carrier preventing rotational movement of the third carrier and thus brakes the system10.

A reduction gear set80is connected to the third carrier72via pin elements82. The reduction gear set80includes a sun gear84the meshingly rotates primary planet gears86that receive the pin elements82. The primary planet gears86via the pin elements82are connected to secondary planet gears88that rotate about a stationary sun gear90that is secured to the gear box housing92to prevent movement of the stationary sun gear90. In this manner gear reduction is realized such that an output94driving and rotatably connected to the sun gear84rotates the wheel of a vehicle at a desired rate. Thus third carrier72is equipped with pin elements82for bearings for gears86and88that are connected together and revolve as one. In addition, stationary sun gear90is mounted to the wall of the gear box housing92and secondary gears88orbit the stationary sun gear90to drive gear sun gear84that is fixed to and drives output shaft94. The system as indicated has a plurality of clutch elements30,42,50,70and76that are controlled by a plurality of actuators32,52and78. In one embodiment the clutch elements are clutch bands that comprise a conventional flat structure. In a preferred embodiment the clutch elements are round rods with threaded ends for adjustment. The rods have a circular cross section and rest within exterior grooves of the ring gears28,40and62and carriers48and72. Therefore actuator32activates clutch band30in one direction and clutch band42in the other direction. This selects the speed the system rotates. Actuator52meanwhile controls clutch bands50and70such that when actuator52activates clutch band50, reverse is supplied. In opposite, when actuator52activates clutch band70, forward is supplied. Actuator78controls brake band76such that when brake band76is activated, output shaft94is braked. Actuator78in one embodiment is made tubular and rotates about actuator52.

Actuator shafts32,52, and78extend through the walls of the case housing92of the gear boxes and are connected to suitable levers to control the machine. Spring action of all bands is used to return the control levers to the neutral position when released.

The right and left side gear boxes are identical mirrors of each other with the exception of the speed control gear sets20. Each side will have different ratios to provide four separate speeds to the input.

In operation, the transmission10begins with an input drive12connected to an engine or electric motor. The power flows first to a speed control section20. There are four speeds forward and reverse provided by planetary reduction sets of different reduction ratios selected to meet the desired operating requirements.

The transmission10is divided into two separate gear boxes that directly connect to the wheels of the vehicle. Two of the speed ratios are mounted in one side box and the other two speed ratios in the second gear box. The speed control sections22and34send power to the forward reverse sections54and64. The forward and reverse sections54and64of the transmission have forward and reverse planetary gear sets. The forward reverse sections54and64provide input to a final speed reduction planetary reverted four gear set80.

The reduction gear set80provides output94from the gear box directly to the wheel. The reduction gear set80is made with a stationary gear90mounted to the wall of the case housing92that is orbited by a planetary gear88that is connected to a primary planetary gear86that drives a gear84connected to the output shaft94. This particular gear train can be configured to provide high ratio reductions and allows the input rpm of the engine to be directly converted to the desired output rpm. There are some 20,000,000 ratios that can be selected using the various numbers of teeth in the gear train.

The forward and reverse gear set46uses a pair of sun gears58and66connected together and driven by the input18to the set46. In one embodiment the first sun gear58has twice the number of teeth as the second sun gear66. A pair of ring gears referred to as a double ring gear62, which connected together can be one gear, engages separate planetary gears60and68that couple the respective sun gears58and66to the ring gears62. It will be noted that both the sun gears58and66and the ring gears62of the forward reverse set46are connected together. The planet carriers48and72are separate. The double ring gear62is provided with a clutch band70that surrounds the outside of the ring gear62. The band70allows the ring gear62to rotate freely as the planets60and68turn or will stop the ring gear62rotation when the band70is applied.

A pair of carriers48and72are provided to control the planet gears60and68of the forward reverse set46. The first carrier48is mounted free to rotate about the input shaft18and the outer rim of the carrier disc is provided with a control clutch band50. The pins56of the carrier are provided with suitable bearings to control the planet gears60of the third section54. If the carrier48is allowed to rotate by releasing the clutch band50, the carrier48rotates but does not drive anything. If the band50is applied, the carrier48stops rotating and the double ring gear62is forced to rotate in the reverse direction.

Stopping the carrier48of the third section54, causes the fourth section64to drive the intermediate carrier72in reverse. The intermediate carrier72is a carrier designed with planet gears60,68,86and88on both sides of the disc. The carrier72provides coupling of the forward reverse gear set46to the reduction gear set80. The intermediate carrier72is also mounted free to rotate about the central shaft18. The central drive shaft18in one embodiment can be extended to provide the bearing for the intermediate carrier72or the output shaft94can be extended to provide the bearing.

If the ring gear62of the forward reverse set46is stopped, the intermediate carrier72is driven in the forward direction. If the two sun gears58and66of the forward reverse gear set46has a ratio of two to one, the forward speed is the same as the reverse speed.

The control actuator52activates one band50or70but not both with neutral in the middle position. The intermediate carrier72is provided with pins74and82for bearings for planet gears on both sides of the disc. The outer rim of the intermediate carrier disc is also provided with a band76that acts as the brake and stops the final output shaft94from rotating.

The pins74on the ring gear side of the intermediate carrier72engage the planetary gears60or68of the forward and reverse gear set46. The pins82on the output side of the intermediate carrier72control the planets86and88of the reduction gear set80that drives the final output shaft94. These planetary gears86and88are actually two separate gears connected together axially. A plurality of the gears may be used to increase the strength of the drive. A two to one ratio of teeth in the sun gears causes the reverse speed to be the same as the forward speed.

Planetary gear sets that use ring gears have a practical limit to the reduction ratio that can be obtained with a single set of about 6 to 1. The higher the ratio the smaller the sun gear must be. The smaller the sun gear the less power can be transferred through the set.

If the sun gear be enlarged the planets must be reduced. Therefore the optimum power capacity of gear sets using the same tooth pitch and ring gear size will have the sun gear nearly the same size as the planets. A ratio of 4 or 5 to one will have a lot more torque capacity because of the increased size of the sun gear.

The planetary reverted4gear train, or reduction gear set80with no ring gear enjoys an almost unlimited selection of gear ratios and can be used as the final reduction. The final drive gear to the wheel can be much larger than can be used in a ring gear planetary set.

The zero turn application of the device uses two complete units described. One set drives the left side of the vehicle, the other drives the right. The band control device is configured to operate two bands at a time. Because of this it is desirable to have two separate gear boxes, one for the left side wheel and one for the right side wheel. Because of the need to have different operating speeds required by different operating conditions, a means to change the overall input speed to the drive is required in some cases.

This can be accomplished by adding two extra planetary reduction sets to the input to the forward reverse section of each side gear box. The two sets are controlled by the same design band actuator. The actuator selects one band or the other with neutral in the middle of the lever stroke.

The gear ratios on the left side gear box can be ratios 1 and 2. The gear ratios on the right side gear box can be 3 and 4. This will supply 4 speeds forward and 4 speeds reverse. The ideal handling is achieved if the steering speed increases in direct proportion to the travel speed. Because the steering is controlled by the speed of the wheels, all is proportional. When a higher gear is selected the steering speed increases in proportion to the ground speed.

The sun gears24and36of the speed selection gear set20are connected in common to a tubular cross shaft16that terminates inside each of the two gear boxes. Two ring gears28and40of the two planetary sections22and34in each gearbox are supplied with two separate control bands operated by the actuator32that activate one or the other but not both with a neutral middle position. This tubular cross shaft16rotates around the central cross shaft18that connects the sun gears58and66of the forward reverse gear set46.

The planets of the two planetary gear sets are mounted on common carriers. The speed control carriers48of the right side gearbox and the left side gear box are mounted to and drive the central cross shaft18that connects the sun gears58and66of the forward reverse gear set46. The sun gears58and66and the carriers48are connected in the speed control gear set46and the ring gears62are separate with separate clutch bands50and70for control.

The input12to the whole system in one embodiment is mounted to the tubular drive shaft14that drives the speed selecting planetary gear sets20. If a continuously variable drive system is used for the input12, the 4 speed selector gear set20can be eliminated and the drive would then be connected to the central cross connecting drive shaft18that powers the forward and reverse planetary gear sets.

The band control actuators32,52, and78are mounted concentric to each other and the shafts project out of the gear boxes and are connected to the control levers or servos. If servos are used they can be built into the gear boxes. A typical arrangement would have the brake actuator78be a tubular shaft surrounding the shaft to the forward reverse section actuator52extend out of the output side of the gear box. The speed selector actuator shaft32would extend out of the input side of the gear box. The speed selector lever mechanism may be provided with a detent device to “lock” it into gear so the operator does not have to hold the lever. Neutral is then supplied by the forward, reverse section.

Zero turn mowers of typical design mount the vertical shaft engine on the rear of the machine behind the drive wheels. The use of two separate gear boxes mounted near each wheel provides a space between the gear boxes for the V-belt that drives the mower deck to pass from the motor to the deck. If gear boxes were in the way, a more bulky design would be required. This feature allows an optimum front to back weight distribution. This is critical to how the mower handles on hills and slopes.

A small 90 degree gearbox drive mounted in the central space aligns the V-belt drive to the engine. The mower deck drive V-belt can be mounted just above or below the 90 degree gear box pulley and pass to the mower deck.

Because there is no requirement to stop the input to the transaxle for neutral it would be possible to equip the mower deck itself with an electric shutoff clutch and brake device. The V-belt drive could then power both the trans axle and the mower deck. The belt pulleys would turn with the engine all the time and the deck would be shut off and turned on with the deck mounted electric clutch. Thus provided would be a lawn mower that only uses one V-belt. Electric clutch brake assembles are available and are usually mounted on the engine. If the assembles are mounted on the blade deck, only one V-belt would be required.

This system is superior to belt tightening and releasing systems because the belt maintains proper tension and does not undergo slippage when the devices start and stop. They provide a faster safer blade brake. The electric control feature eliminates troublesome linkages. The transaxle has its own clutches internal. By combining the two drives, a lower profile machine can be built. This makes the machine safer on hills and slopes.

Thus presented is a system of gears and clutches designed to steer a zero turn lawn mower. The system is a transaxle style transmission that is reliable and low in cost. The combination of the ring gear forward reverse section with the 4 gear train final reduction set provides a compact durable speed reduction unit that can be configured to provide any desired reduction ratio between the engine and the wheels.