Patent Application
20130005524
1. Field of the Invention
The present invention relates generally to transmissions and more particularly to a continuously variable transmission.
2. Background
A transmission provides both torque multiplication and output speed control of a power source. Vehicle transmissions allow an engine to run while a vehicle is at rest, accelerate the vehicle in a timely manner and provide a suitable output speeds congruent with modern roadways. It has been challenging to provide transmissions that meet these functions while maintaining a relatively constant engine output rpm.
Benefit would be realized by providing a transmission that achieves these functions while the engine remains in an optimally efficient rpm range. Because all engines have a specific peak efficiency range, a device which allows an engine to run within this range for a higher proportional amount of its operating time raising overall efficiency.
Continuously variable transmissions (or CVTs) has been proven to increase fuel mileage and vehicle efficiency, however most “shiftless” transmissions have been problematic, including such as low power handling capability, complexity, and high cost of manufacture.
Specific problems with CVT's as well as other modern transmission designs include slippage when it pertains to a belt or clutch system, blocking ring (synchronizer) wear, and heat damage due to torque converters. If the typical wear items are eliminated, the new design should prove superior as it will not require frequent overhauls, throughout the standard life of a vehicle.
One object of the present invention is to provide a continuously variable transmission wherein belt slippage and clutch system slippage are eliminated. Another object of the present invention is to provide a continuously variable transmission wherein blocking ring (synchronizer) wear, and heat damage due to torque converters are eliminated. An additional object of the present invention is to simplify transmission design eliminating pumps, stators and turbines associated with the torque converters for a common automatic transmission.
The present invention is directed to a continuously variable transmission that includes multiple gear sets and a hydraulic system with a control valve for use in a motor vehicle, vessel or for connection to any mechanized device, which serves to vary output speed and torque. Two of the gear sets work as the speed variation device in conjunction with a hydraulic pump as a braking device, while the third gear set multiplies torque. A sub-transmission serves as the range device, providing reverse, neutral and drive.
In a preferred embodiment, a continuously variable transmission includes the following rotational elements, each having a substantially identical primary axis of rotation: an input shaft, three planetary gear assemblies, a hydraulic vane type pump, a hydraulic vane type motor, a one-way clutch and an output shaft. A control valve is operatively connected between the pump and motor to direct flow to the motor or an attached reservoir.
Different from most designs, the gears, which are meshed at all times, contribute to the torque production throughout the entire speed range to overdrive, while the hydraulic system acts as a transfer and braking system only, allowing the gear sets to do the majority of the work.
In one embodiment, a sub-transmission is used to select operation mode. A sliding collar with cogs may alternately engage a final drive shaft directly or a reverse cog plate and idler associated with a reverse gear mechanism. Alternately the selector may be positioned between the two for neutral, without the use of clutches.
Simplicity of design in regards to the components lends to lower manufacturing costs. With use of a vane style pump and motor as well as planetary gear assemblies, the design allows all components to be inline. The advantage is use of a lighter weight transmission case as the components withstand strain within themselves as opposed to the use of countershaft, parallel shaft or beveled gears, which cause deflection of components and undue stress on the entire system.
The hydraulic pump and motor may be of the non-variable displacement type. This provides a less complex hydraulic system and depends on the gears to multiply torque in a smooth, stepless fashion.
Continuously variable transmission 10 also includes three planetary gear assemblies, first planetary gear assembly 47, second planetary gear assembly 48 and third planetary gear assembly 49. Continuously variable transmission 10 also includes primary hydraulic system 30. First planetary gear assembly 47 and second planetary gear assembly 48 operating in conjunction with primary hydraulic system 30, function in combination as a speed variation mechanism and as a braking device. Third planetary gear assembly 49 multiplies torque applied to output shaft 26.
Input shaft 11 is shown including primary axis of rotation A. First sun gear 12 is attached to input shaft 11 for coaxial rotation with input shaft 11. First planet gear set 13 mechanically engage first sun gear 12, imparting a rotational force against first ring gear 14, which is fixed to hydraulic pump 15, of a preferably positive displacement vane type. Planet gear carrier 20 is attached to and rotatable with the first planet gear set 13. Second planet gear set 23 is attached to and rotatable with planet gear carrier 20 such that rotation of the second planet gear set 23 corresponds to rotation of first planet gear set 13. Second sun gear 21 mechanically engages and is rotatable with second planet gear set 23. Second ring gear 32 mechanically engages second planet gear set 23 and is fixed against rotation. As such, all torque transmitted by second planet gear set 23 from first planet gear set 13 is ultimately transmitted to output shaft 26 attached to second sun gear 21.
Primary hydraulic system 30 includes hydraulic pump 15 having pump vane 46 attached to first ring gear 14, such that rotation pump vane 46 corresponds to rotation of first ring gear 14. Primary hydraulic system 30 also includes hydraulic motor 25 including motor vane 50 is hydraulically connected to and drivable by hydraulic pump 15. Hydraulic pump 15 and hydraulic motor 25 are both preferably of a positive displacement vane type. Third sun gear 35 is attached to hydraulic motor 25 such that rotation of third sun gear 35 corresponds to rotation of hydraulic motor 25. Third planet gear set 33 mechanically engages third sun gear 35, such that rotation of the third planet gear set 33 corresponds to rotation of third sun gear 35 on operation of hydraulic motor 25. Third ring gear 36 mechanically engages third planet gear set 33. Third ring gear 36 is fixed against rotation. One-way clutch 34 is operatively disposed between and connected to clutch carrier 37 and output shaft 26. Because third ring gear 36 is fixed against rotation all torque transmitted by hydraulic motor 25 to third sun gear 35 and consequently third planet gear set 33 is ultimately transmitted through one-way clutch 34 to output shaft 26.
Hydraulic system 30 also includes valve 19 hydraulically connected between hydraulic pump 15 and hydraulic motor 25. Valve 19 is configured to selectively regulate a fluid flow from hydraulic pump 15 to hydraulic motor 25, such that as fluid flow increases through hydraulic motor 25 a corresponding rotational force is applied to output shaft 26. Valve 19 is also configured to selectively diminish and cease the fluid flow from hydraulic pump 15 to hydraulic motor 25 in a manner that a progressively increasing hydrostatic lock condition develops between valve 19 and hydraulic pump 15 creating a progressively increasing resistance to rotation of first ring gear 14, causing increased rotational movement of first planet gear set 13 and thereby rotational movement of planet gear carrier 20 causing rotation of output shaft 26.
Valve 19, which may consist of any of a variety of control devices including electric, mechanical, electro-mechanical and electronic, alternately regulates the fluid flow through transfer line 27 to hydraulic motor 25 based on user input or a selected or programmed set of criteria, or through dump line 18 to reservoir. Controller 28 is connected to valve 19, and is configured to analyze data representative of performance of a connected engine, (not shown), to control operation of valve 19. In a preferred embodiment, valve 19 is a three-way variable flow valve controlled by an electronic control unit for a vehicle as is well known to those skilled in the art.
Referring to
The relatively high torque of the rotational force imparted by hydraulic motor 25 to output shaft 26 is more than adequate to initiate motion of a vehicle, watercraft or other mechanized device connected to continuously variable transmission 10. An initial gear ratio varies on the combination of input shaft 11 to first ring gear 14 and third sun gear 35 to third planet gear set 33. For example, if first ring gear 14 rotates at half speed of input shaft 11, a 2:1 ratio exists combined with a of 3:1 ratio at third planetary gear assembly 49, a 6:1 output gear ratio results, multiplying engine crankshaft torque by six. These ratios may be altered according to manufacturer desire and application. With applicable gear ratios, an overdrive condition may be achieved. Selection of pump size/volume will affect torque as well as relative ratios in the planetary gear assemblies.
Resistance to maintaining a given speed is considerably less that a force required to overcome a state of inertia. As speed of output shat 26 increases, valve 19 is adjusted so as to diminish fluid flow FF to hydraulic motor 25. As fluid flow FF decreases a progressively increasing hydrostatic lock condition L, as shown in
Continuously variable transmission 10 provides torque multiplication at low output rpm, where needed and a variation in output rpm through a range of zero rpm to an rpm greater than that of an engine, (not shown), connected to input shaft 11. Operation of the continuously variable transmission throughout its range is relatively seamless and step-less, allowing smooth operation.
In the embodiment shown in
While this invention has been described with reference to the described embodiments, this is not meant to be construed in a limiting sense. Various modifications to the described embodiments, as well as additional embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
