Patent Application
20050274216
The present invention relates generally to gears reducers, and more particularly, to gears box having an enveloping or globoid worm in mesh with a mating gear. This type of speed reducer could be used in industrial applications, medical devices, and any mechanical power reduction systems.
Enveloping worm speed reducers, particular double enveloping worm gear drive are used in various applications as a high ratio, more than 5:1 of mechanical drive. In double enveloping speed reducer a pinion shaft and mating worm gear shafts are crossed. (U.S. Pat. No. 1,980,237 by Trbojevich, U.S. Pat. No. 5,836,076 by Duta and Prom, U.S. Pat. No. 5,018,403 by Umezono and Maki.). Due to high ratios, it has been considered impractical to use the worm gear as the driven member and the worm as the driving member to transfer power from the worm gear to the worm. Most efficient and practical use of enveloping worm in lower ratio applications is drive axle assemble with enveloping worm described in my U.S. Pat. No. 6,537,174 and power take-off unit described in my U.S. Pat. No. 6,523,430.
The distance between axis of enveloping worm rotation and axis of worm gear rotation can not allow the use of above described enveloping worm in mesh with enveloping type worm gear in existing speed reducers, by substituting spiral bevel or helical gears. Spiral bevel gears have zero offset and hypoid gear set compared to double enveloping worm drive also has a very small offset, and helical gear sets are gears with parallel shafts.
Accordingly, it is an object of the present invention to provide a speed reducer with wide range of ratios, even with ratio less than 5:1. It is a further object of the present invention to be able to substitute existing speed reducers using spiral bevel, hypoid or helical gears, where input and output shafts are intersected, crossed or parallel.
These and other objects of the present invention are obtained by providing a speed reducer with a unique enveloping worm face gearset. In particular, an enveloping-type worm mounted thereto is meshed with a face type worm gear, where face worm gear teeth having a tooth surface is generated by a profile of the enveloping worm.
Enveloping worm or globoid worm face gear transmissions have not been known. Thus, those skilled in the art did not consider enveloping type worm gears in mesh with a face type worm gear to be feasible for commercial applications. In contrast, the enveloping face worm gears of the present invention utilize a worm gear that is easily manufactured.
Rolling motion with small percentage of sliding motion significantly increases efficiency of an enveloping speed reducer. For the same size, this invention has almost twice the torque capacity of traditional spiral bevel or helical gearing. Suction tooth action makes excellent tooth lubrication that also reduces heat. It allows different casting designs from not very heat conductive materials, even from plastic or ceramic. As compared to prior spiral bevel or helical gear speed reducers, enveloping worm face speed reducer is more compact, quiet and efficient. Thus, the present invention can replace bevel, hypoid, or helical gears in many powertrain applications.
In the present invention, the enveloping worm can be with less than one revolution of threads, which can have only one supporting shaft. Further areas of applicability of the present invention will become apparent from the comprehensive description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this complete description.
The present invention will become more fully understood from the details described below:
As will be detailed, an enveloping speed reducer with a unique worm-type input gearset embodying the principles of the present invention will be described below with reference to
Usually, face gear has straight side worm engagement in mesh with a face (ring) gear. The reason for using an enveloping worm is more torque capacity. A computer model simulation can be utilized to generate the configuration of the enveloping worm and gear teeth of the face gear. Then gears could be machined using multi-tasking turning center or special machine, like machines that are widely used for spiral bevel, hypoid gear or helical gear production.
Referring now to the drawings:
According with gear train in
The shape and material of housing 41 may have many different variations. Bearing support 42 for every design can be calculated according with engineering practice.
New enveloping worm transmission is comprised of worm gear 2 and enveloping worm 1. Worm 1 has at least one screw thread that is engaged by at least one tooth of said worm gear 2 wherein worm gear 2 is a face gear. Enveloping worm pinion 1 is placed into face arrangement with worm gear 2. In this enveloping worm face transmission the enveloping worm could have any design, however, it is preferred that the enveloping worm pinion 1 be relocated to face arrangement with said worm gear 2 from its original position (where it is usually generated for well known double enveloping worm/worm gear transmission). The profile of enveloping worm thread could be produce from mathematical equations, computer simulation or machined by a special program, but it is the same enveloping worm that is used as a pinion for double enveloping gears, where the enveloping worm pinion is placed in the original position in meshing engagement on the top of the worm gear, not on the face of the worm gear. This is a non obvious usage of well known enveloping worm. By repositioning the enveloping worm thread from its original position into face engagement with a worm gear makes the profile of the worm gear very different from profile of the worm gear of double enveloping worm gears. In standard double enveloping gearing each convex surface on one side of the thread becomes the concave surface and each concave surface of another side of the thread becomes the convex surface. In speed reducer the use of shortened threads with only concave surface on the one side of the thread and convex surface on another side of the thread is preferred. The enveloping worm threads with only concave surface on one side and convex surface on another side have less than one revolution. They can have less than 180 degrees of revolutions or even less than 90 degrees of revolutions. Longer worm thread has better contact ratio, but for low kinematics ratios (for example, less than 1:8) it is more difficult to manufacture enveloping worm transmission and even to assemble an enveloping worm with a worm gear. From manufacturing position it is more convenient to have an asymmetric worm thread.
A computer model simulation can be utilized to generate the surface of the worm gear tooth by using enveloping worm pinion profile as a material remover during moving meshing engagement with face gear blank. The worm gear can also be formed using known techniques such as hobbing by using profile of the enveloping worm pinion as a master gear.
The enveloping worm thread has a rolling action contact relationship with the teeth of the face gear, which provides an increased efficiency. In standard double enveloping worm gearing the enveloping worm thread has partially a rolling but mostly sliding action contact relationship with the teeth of the worm gear. In the present application, it is a surface-to-surface contact between the enveloping worm gear teeth and the face gear that increases the torque capacity of the drive axle assemble. For back drive, where the face gear is a driven member and the enveloping worm is a driving member, this speed reducer also has high efficiency compared to a spiral bevel, hypoid or helical gear set.
The lower noise of the enveloping worm face speed reducer gear compared to hypoid, bevel or helical speed reducers makes using the present invention more beneficial in powertrain applications. For the same size, this invention can provide more than twice the capacity of hypoid or helical gearing. The possibility to reduce number of gear teeth of the present invention due to high contact ratio makes each tooth thicker and therefore stronger.
Transmit More Power with Smaller Gears.
Compact alternative for speed reducers with hypoid, spiral bevel or helical gears. Enveloping worm face gears have high torque capacity due to surface to surface contact mesh that reduces contact stresses. It saves up to 30% of space and significantly reduces weight.
Efficiency is Extremely High
Hypoid, spiral bevel or helical gears are have always been used in the speed reducers, but enveloping worm face speed reducer is more efficient. It has higher percentage of rolling/sliding motion and excellent dynamic lubrication. It has extended life even without lubrication.
Lower Noise
Each thread of the pinion is in mesh with two teeth most of the time. It reduces impact of engagement and disengagement, increases the contact ratio and makes quieter motion.
Manufacturability
Using existing spiral bevel, hypoid or helical gear cutting machines can make enveloping worm face speed reducer not more expensive than hypoid, spiral bevel or helical gears. For some configuration, forging technology or power metallurgy could be applied as well.
Several embodiments of the present invention have been disclosed. A worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. In the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded, as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
