Crown Gear Research Articles

Factor Analysis of Cracks Generated in 22CrMoH Steel Gear

Cracks is frequently generated in crown gear of main reducer of big modulus used in heavy duty truck after carbonizing and quenching. The heat treatment process and the pre-heat treatment before carbonizing, the carbonization process parameter and the quench treatment, all of which influence the component, structure and stress of the gear. In this paper, metallographic examination of the gear was taken after heat treatment with different process parameter, and the reasons that caused cracks in the 22CrMoH steel crown gear used in heavy duty truck after heat treatment was discussed. And strategies and methods are proposed as well.

Analytical Determination of Basic Machine-Tool Settings for Generation of Spiral Bevel Gears From Blank Data

An approach for analytical determination of basic machine-tool settings for generation of spiral bevel gears from blank data is proposed. Generation by face-milling is considered. The analytical procedure is based on the similitudes between the conditions of generation between the gear member and its head-cutter and the conditions of imaginary meshing between the gear member and its crown gear. The blank data considered are the number of teeth of the pinion and the gear, the module, the spiral and pressure angles, the face width, the shaft angle, the depth factor, the clearance factor, and the mean addendum factor. These starting data can be established following the directions of the Standard ANSI/AGMA 2005-D03. Once the gear machine-tool settings are determined, an existing approach of local synthesis is applied to determine the pinion machine-tool settings that provide the desired conditions of meshing and contact of the gear drive. The developed theory is illustrated with a numerical example.

2P1-C26 低バックラッシなクラウン減速機の小径化

We are developing a low backlash reducer using precessing crown gears. We call it crown reducer. The features of this reducer are low backlash, high reduction ratio, and advantage in miniaturizing. These features greatly contribute to design various small mechanisms such as a finger joint of a robot hand. In this paper, we describe some modifications of mechanical design for miniaturizing the crown reducer. Two prototype reducers, which diameter are φ6 and φ012 (gears' diameter are φ5 and φ10, respectively), are shown in this paper. Some evaluation results for φ6 type are also presented.

Magnetic planetary gear drive

In this study, a magnetic planetary gear drive is proposed and its operating principle is introduced. The equations of the geometrics and kinematics for the drive are given. The equations of the magnetic induction intensity for the magnetic gear teeth are deduced. The equations of the torques between the planetary gears and sun gear or crown gear are developed. The available parameters of the magnetic planetary drive are presented and the magnetic flux density distributions of the magnetic gear teeth are investigated. The torques between the planetary gears and sun gear or crown gear are analysed. When the relative rotating angle between the gears is increased, the magnetic torque grows, gets to a maximum value, and then drops. The maximum torque represents extreme load-carrying ability of the drive system. The pole pair number, the tooth thickness and the tooth width of the magnetic gears, and the speed ratio of the drive have obvious influence on the output torques. To obtain a large magnetic torque, a large tooth width of the gear, a proper pole pair number, a proper radial thickness of the tooth, a large planetary gear number, and a large speed ratio should be chosen.

2P1-B05 変形クラウンギヤを用いた低バックラッシュ減速機構の提案

2P1-B05 変形クラウンギヤを用いた低バックラッシュ減速機構の提案

Accuracy Measurement and Evaluation of Straight Bevel Gear Manufactured by End Mill Using CNC Milling Machine

Straight bevel gears are usually manufactured with various machines and systems, and the tooth profiles are produced by grinding or machining by means of a tool with many cutting edges. In recent years, the straight bevel gear has been manufactured by an end mill using a computer numerical control (CNC) milling machine because the use of the auxiliary apparatus, special cutters, and special machine tools is not needed. Using this method, the gear manufacturing with high accuracy is an important problem. In this paper, the coordinate measurement of the straight bevel gear manufactured in this method is performed and the gear accuracy is evaluated. The tooth profiles of the straight bevel gear generated by a quasi-complementary crown gear instead of a conventional complementary crown gear are introduced. For this study, the tooth profiles of the straight bevel gear were modeled using a 3D computer-aided design system and the gear was manufactured by an end mill using a CNC milling machine based on a computer-aided manufacturing process. Afterward, the coordinates of many points on the gear tooth surfaces were measured at random using a coordinate measuring machine. This coordinate measurement provides the information about the factors related to the gear accuracy such as pressure angle, tooth angle error, workpiece setting angle, apex to back, and so on. Therefore, the values of the above factors were estimated and were compared with the theoretical ones, respectively.

DESIGN AND MANUFACTURE OF STRAIGHT BEVEL GEAR FOR PRECISION FORGING DIE BY DIRECT MILLING

In the manufacture of straight bevel gears, a precision forging method has been mainly used in recent years and the precision forging die has been usually manufactured using electric discharge machining. However, it is difficult to content the high productivity and low manufacturing cost using electric discharge machining because the gears are produced through a process of several steps. In this article, a design and manufacture of a straight bevel gear for a precision forging die by direct milling is developed in order to improve the productivity and manufacturing cost for the gear production. The tooth profile of a straight bevel gear generated by a quasi-complementary crown gear instead of a usual complementary crown gear is introduced. For this study, first the numerical coordinates on the tooth surface of the straight bevel gear were calculated and the tooth profiles were modeled using a 3D-CAD system. Afterward, the direct milling of the precision forging die of the straight bevel gear in the hardened state was carried out using a CNC milling machine based on a CAM process through the calculated numerical coordinates.

Manufacturing process for a cylindrical crown gear drive with a controllable fourth order polynomial function of transmission error

A manufacturing process for fabricating a cylindrical crown gear drive that is provided with a controllable fourth order polynomial function of transmission error is proposed in this paper, and the procedures for creating the mathematical models of the tooth surfaces are described. In order to reduce the level of gear running noise, a pre-designed fourth order polynomial function of transmission error is assigned to the gear drive. To avoid edge contact, the tooth face of the output gear is longitudinally crowned by employing a form grinding wheel that is driven by a parabolic motion. Based on the theory of gearing, mathematical models of tooth contact analysis (TCA) are created, and mathematical models of principal curvatures and directions and contact ellipses are developed. A numerical simulation of meshing is performed, and the proposed gear drive is proved numerically to be able to reproduce the pre-designed fourth order polynomial function of transmission error. The influence of varying the parameter of parabolic motion of the grinding wheel on the dimensions of contact ellipses is also analyzed.

Analysis of the meshing of crown gear coupling

This paper presents an analysis result of three-dimensional meshing of crown gear coupling (CGC). Mathematic models of the surfaces of crown gear and internal gear are established. The equation of internal gear surface is given. The equation of conjugate surface of crown gear is solved according to the principle of gearing, and that of non-conjugate crown gear is derived with crown curve of a circular arc. The meshing state of conjugate and non-conjugate surfaces is analyzed through computation of contact lines and points. It is concluded that the meshing of conjugate CGC is line-contact, there are several pairs of teeth engage simultaneously, and non-conju gate CGC has point-contact condition of meshing and only 2 pairs of teeth engage in theory.

Modelling, Implementation, and Manufacturing of Spiral Bevel Gears with Crown

The operational performance of gears in terms of smoothness, quietness, wear and life span is largely affected by how gear and pinion teeth make contact. To enhance the operational performance, a crown is often applied to a standard (nominal) gear tooth surface. Regardless of the presence of a crown, all the gears are machined by special types of machine tools, such as gear hobbers and shapers. This paper develops a tooth surface for a spiral bevel gear with a crown so that it can be machined by numerically controlled machine tools. Specifically, we derived: 1. A bi-parametric tooth surface model for a standard spiral bevel gear. 2. A crown model along the spiral curve direction. 3. A crown model along the involute curve direction. The developed algorithm was tested and implemented in a prototype software system called GearCAM. With the GearCAM system, a set of spiral bevel gear and pinion was machined using a 4-axis CNC milling machine to check the validity and effectiveness of the crowning method. Through various verifications, it is shown that the models developed for the standard and crown gears can be used as a means for design and verification of spiral bevel gears.

Method of Cutting Klingelnberg Spiral Bevel Gears by Using Pseudo-Complementary Crown Gear

A new method to cut the spiral bevel gears of Klingelnberg cyclopalloid system is proposed. The feature of the cutter used in this method is the straight cutting edge whose extension line does not pass through the cutter axis. The blade having a cutting edge can be made easily and its rake face can be reground to sharpen the cutting edge with an ordinary surface grinding machine. In the method, the pinion is generated with a complementary crown gear and the gear is generated with a newly introduced Pseudo-complementary crown gear. The pseudo-complementary crown gear is the generating gear whose pitch plane is not tangent to the pitch cone of work gear. The tooth (tool) surface of each crown gear is made up with the above mentioned cutter. The availability of the method is confirmed by trial gear manufacturing.

Development of Crown Motor.

Conventional fluid motors require high-pressure fluid (10 MPa∼) and the rotation speeds of these motors are extremely high (10, 000 rpm∼). Therefore, it is difficult to apply these motors to mobile robots. This paper describes a new fluid motor composed of new mechanisms. The motor consists of two crown gears and 3 or more cylinders. It is named 'Crown Motor' after the two crown gears, the precession gear and the output gear. The precession gear is driven by the cylinders meshing the output gear. In each cycle, the output gear rotates an angle equal to the difference of the numbers of teeth between precession and output gears divided by the number of teeth of the output gear. With this mechanism, compact size and high gear ratio can be obtained. Thus, a high-torque fluid motor with slow rotation speed is accomplished. The rotation speed of the motor can be continuously controlled from CW (max) to CCW (max) by changing the timing of valve opening, similar to the sequence of electric DC brushless motors. ln addition, the Crown Motor can be driven with low- pressure fluids, such as tap water (0.2 MPa∼). Two control systems of Crown Motors are proposed in this paper. One is with conventional electric valve system (stepping drive system) and the other is with new mechanical valve system without any electric device (self-excited drive system). With stepping drive system, Crown Motors can be used as a stepping motors with one-by-one cylinder operation. On the other hand, self-excited drive system is proper and reliable if water is used as driving fluid in practical applications. In general, high-torque motors with free or lock states available require large clutches or brakes. However, the prototype of Crown Motor achieves both states without any additional components. With these properties, Crown Motors can be used in not only mobile robotic applications but also other various applicatlons. The prototype accomplished a high torque of 16 Nm at 15 rpm under 0.5 MPa and with efficiency of 35%.

Near-net shape forging of a crown gear: some experimental results and an analysis

This paper presents a few salient results of an experimental investigation made into the quasi-static progressive incremental closed-die forging of crown gear forms starting initially from both solid and hollow circular cylindrical specimens made of tellurium lead as the model material. The detailed observations made on the die loads and the deformation modes, etc. at various incremental stages are given and these are compared with those based on an upper bound simulation of forging of the crown gear with rectangular and trapezoidal shaped teeth. The tooth profile patterns are also compared with the resultant CAD outputs based on the upper bound analysis. Reasonably good correlations between the experimental observations of die loads and tooth profile patterns with those estimated from theoretical simulations were obtained and these and other results given are commented upon.

Neutron diffraction measurements for the determination of heat treatment effectiveness in generating compressive residual stress in an automotive crown gear

Thermal austenitizing and tempering treatments are being developed in automotive industry to prevent crack initiation and propagation, especially in components where stress intensity factors influence the stress field and ultimately the fatigue life of the component. This is the case of crown gears, where the tooth root typically undergoes impulsive and very high loads which frequently cause cracking if tensile residual stresses are present at the surface. The sign reversal of these stresses is the aim of austenitizing and tempering treatments. In this work neutron diffraction measurements of residual stress (RS) on a UNI55Cr3 steel crown gear, carried out at HMI-BENSC 1 Experiments at HMI-BENSC have received financial support by the European Commission under the TMR/LSF Access Programme (contract no. ERBFMGE CT950060). 1 , are presented. The sample was submitted to a new multi-frequency induction technique whose effectiveness was checked. Comparisons with X-ray measurements are shown, and RS measured by X-rays on a similar shot-peened sample are also mentioned.

2P2-47-067 低速高トルク流体駆動ユニット Crown Motor の開発 : 第 2 報自立回転装置の導入と基本特性実験

Conventional fluid motors require high-pressure fluid (15∿20Mpa) and rotation speeds of thesemotors are extremely high (10,000∿20,000rpm or more). Therefore it is difficult to apply these motors to mobile robots. This paper describes a new fluid motor named "Crown Motor" using a new mechanism that consists of two crown gears. Torque of this motor is high with a high gear ratio of 77 : 11 while rotation speed is slow enough to allow for mobile robotic applications. The motor is able to control its torque and rotation speed independently when it is controlled by electric valve. Moreover, it can drive with a low-pressure fluid like tap water (2∿7MPa). To use water fluid practically, it is necessary to introduce mechanical valve system. Last section describes the fundamental mechanism of the system and how to build a test model.

A kinematics parametric method to generate new tooth profiles of gear sets with skew axes

The geometric characteristic of tooth profiles of gear sets with skew axes can be studied by using the parametric polar angular (pressure angle) function, the meshing equation, and the constraints of continuity conditions. In this paper, the general mathematical model of skew gear sets, their numerical solution methods and special analytic solutions are presented. These can be used to investigate the inherent characteristics of skew gears and architect special gears such as bevel gears when the small pinion offset above or below the center of the gear is made equal to zero, helical gears or spur gears if the shaft twisting angle is equal to zero. Two examples are presented to demonstrate the application of the mathematical model developed in this paper. The first example is proposed to synthesize new skew gear sets when the special twisting angle for crossed axes and rotation speed ratio are given. The second example is deduced to demonstrate the special case for the spherical crown gears with skew axes.

Three-Dimensional Measurement for Straight Bevel Gear.

A method for inspecting the machine settings for straight bevel gear cutting is proposed. The bevel gear is generated by a newly introduced "quasi-complementary crown gear" instead of a conventional complementary crown gear. A tooth bearing of a pair of generated gears is theoretically desirable. The coordinates of many points on a tooth surface are measured at random using a coordinate measuring machine. The measured data should be including various type of information derived from the machine settings. Taking this fact into consideration, each information on the machine settings is extracted from the data using the method of least squares. The extracted items can be corrected, and they are: tool pressure angle, tooth angle, root cone angle, apex to back and tooth thickness. Using the proposed method, it is possible to produce interchangeable bevel gears.

Method for Cutting Straight Bevel Gears Using Quasi-Complementary Crown Gears.

Method for Cutting Straight Bevel Gears Using Quasi-Complementary Crown Gears.

Duplex Spread-Blade Method for Cutting Spiral Bevel Gears Using a Quasi-Complementary Crown Gear.

In this study, an ordinary complementary crown gear generates both an actual spiral bevel gear and an imaginary spiral bevel gear whose pitch cone angle is 80o∼87o. The tooth surface of the imaginary bevel gear is replaced by a simple conical surface. The imaginary gear with the conical tooth surface is designated as a quasi-complementary crown gear and is used as a tool gear to generate the pinion. The quasi-complementary crown gear produces a tooth surface modification. As a result, the engagement of the gears is a point contact with a negligibly small non-conjugate. The complementary crown gear and the quasi-complementary crown gear each generate both sides of a tooth space of the work gear simultaneously because the cutter blades forming a tooth of each crown gear are widely spread by an adequate amount. The conditions which satisfy this duplex spread-blade method relating to both the complementary and quasi-complementary crown gears are shown in this PaPer.

A Method of Cutting Spiral Bevel Gears Using a Quasi-Complementary Crown Gear.

In the manufacture of spiral bevel gears with depthwise tooth taper, there is usually a need for some "cut and try" process by which a good tooth bearing is obtained. In this paper, a method of cutting spiral bevel gears in which "cut and try" is not necessary is newly proposed. The gear is generated by a complementary crown gear, as usual, but the pinion is generated by a newly introduced "quasi-complementary crown gear". The quasi-complementary crown gear produces both crowning and profile modification to the pinion tooth surfaces. As a result, the engagement of the gears is a point-contact with a neglibibly small non conjugate. The gears made on an experimental basis showed a good tooth bearing, as might have been expected.