RESEARCH OF THE WEAR MECHANISM OF BEARING SEATS OF AUTOMOTOR-TRACTOR TRANSMISSIONS

A significant number (up to 25%) of failures of automotive transmissions are associated with a loss of rigidity in the rolling bearings. One of the main reasons for the loss of stiffness in rolling bearings is a violation of the tightness of the bearing on the shaft and in the housing due to fretting corrosion. The paper presents the results of a study of the causes of fretting corrosion in bearing fits and the patterns of its development. The conditions promoting the occurrence of the fretting process are determined and the factors characterizing the nature and intensity of destruction of contacting surfaces during fretting corrosion are established. It was also found that the greatest influence on the occurrence and course of the fretting process is exerted by the specific load on the contact surface, the duration and frequency of its application, and the amplitude of the relative slip of the contacting surfaces. Analytical expressions for calculating the actual values of the listed factors of the fretting process in the coupling of the rolling bearing with the shaft are determined by the calculation method, and a mathematical model of its destruction is proposed. For the practical implementation of the described mechanism of destruction of the rolling bearing landing on the shaft as a result of fretting corrosion, an algorithm and a program have been developed to determine the limiting state of the bearing landings of automotive transmissions. Subsequent laboratory tests confirmed the adequacy of the proposed model. As an example, the results of modeling the limiting state of the rolling bearing of the intermediate shaft of the gearbox of the K-700A tractor and the ball bearing 313 are given. It is revealed that the main role in reducing the intensity of the fretting process, along with the hardness of the shaft, is played by the roughness of its seating surface. In particular, a decrease in the roughness parameters from Ra = 2.0 µm to Ra = 0.5 µm at the same hardness HRC48 and an interference fit in N = 24 µm leads to an increase in the joint resource by 1.5 times

Application of Goertzel Algorithm to Piezoresistive Pressure Sensing Fabric for Custom Fitting of Wheelchair Cushions

Pressure sores are a costly, painful problem for wheelchair users, caused by prolonged periods of mechanical loading. A common location of pressure sores in wheelchair users is the tissue between the ischial tuberosities and the seating surface. The pressure exerted on the tissue, or interface pressure, can be measured using piezoresistive fabric. This work demonstrates the use of the Goertzel algorithm for efficiently acquiring interface pressure data from a fabric assembly consisting of a layer of piezoresistive fabric between two layers of fabric with conducting and non-conducting stripes. The Goertzel algorithm was used to sample sums of sine waves from the conductive columns of the fabric assembly and calculate the amplitudes of each component sine wave corresponding to the local interface pressure. The Goertzel algorithm is more efficient for this application than a fast Fourier transform due to the limited number of calculated frequency bins needed for this application and more freedom in choice of sample size. The algorithm was successfully used to generate two-dimensional, 32 × 32 sensel interface pressure maps once per second. The Goertzel algorithm can be used in tandem with generated sine waves to measure interface pressure from piezoresistive fabric. Low-cost, accurate interface pressure measurements will help lessen the risk of pressure sores in wheelchair users.

Active Cloth Fabricated by a Flat String Machine and its Application to a Safe Wheelchair System

In this study, a pneumatically contracting active cloth has been developed; its application is proposed for a safe sitting-posture recovery system for wheelchair users to avoid fall-related accidents. The active cloth consists of thin artificial muscles knitted via a flat string machine. The safe wheelchair system is configured with an active cloth and seating pressure sensor. The seating pressure sensor, located on the seating surface of the wheelchair, estimates the inclination of the upper body of the user; when this reaches an angle that is dangerous for falling from the wheelchair, the active cloth contracts to correct the posture of the upper body. In this paper, we clarify the fabrication process and fundamental characteristics of the active cloth and indicate its potential as a mechanical element for welfare apparatuses by demonstrating a safe wheelchair system.

Effect of thermal loading on sealing behavior of single and twin-gasketed flange joints

Gasketed flange joints are usually subjected to internal pressure at high temperature. The most important requirement of flange joint is to provide leak-free joint under operating condition. In the present study, temperature-dependent nonlinear gasket properties of spiral-wound gasket at elevated temperatures are obtained experimentally and included in the analysis. The relaxation of gasket contact stress in both single and twin-gasketed joints at elevated temperatures is compared. It is observed that the ability to withstand internal pressure decreases with increase in temperature in both single and twin-gasketed flange joints. But, the twin-gasketed flange joint is found to withstand higher internal pressure than single-gasketed joint at a given bolt preload and temperature. The influence of gasket seating surface rotation on the distribution of gasket radial contact stress at elevated temperature is studied. The effect of elevated temperature on flange stresses of twin-gasketed joint is also examined.

Method of Predicting Differential Case Bolt Behavior

This paper proposes a CAE-based method to predict the maximum load at which bolts start to loosen. The qualitative validity of this method was confirmed using the fastening bolts between the differential case and ring gear. In general, the differential case and ring gear are fastened with bolts. Therefore, it is essential to estimate the maximum load of bolt loosening when designing these bolts. Moreover, prototypes found that tightening bolts are more likely to loosen as the thickness of the differential case or ring gear decreases and becomes easier to deform. This indicates that the deformation of the differential case and ring gear must be considered in bolt design. However, predicting the maximum load is relatively difficult because the behavior of both the screw and the contact surface between the differential case and ring gear is complicated. In contrast, recent transmissions require further weight reduction without sacrificing reliability. Consequently, a method of predicting the maximum load of bolt loosening is required. First, this paper describes a CAE model for estimating the pressure and friction generated at the contact surface between the differential case and ring gear, as well as at the screw surface and bolt seating surface. Furthermore, a method for determining bolt loosening is described that incorporates the pressure and friction on the bolt seating surface into friction circle theory. This method was used to derive the maximum load of bolt loosening. In addition, it was also confirmed that the results qualitatively agree with actual cases of bolt loosening. Second, this paper identifies the relative sliding of the screw surface and contact surface when the load increases. In this case, it was verified that the sliding on the contact surface between the differential case and ring gear induces relative sliding of the screw, followed by sliding of the bolt bearing surface and loosening of the bolt. Finally, this paper refers to design guidelines for reducing the weight of the differential case using an experimental design method. Certain ribs cause non-uniform bolt bearing surface pressure distribution, which likely affects bolt loosening. Through this research, the validity of the method was confirmed and the bolt behavior was clarified when a differential case and ring gear are loaded in one direction. Based on these results, it should be possible to apply this method to more complicated load cases in the future.

Improvement of Flange Tightening Method for Small Bore Low Rating Bolted Flanges

An appropriate flange tightening methods for small bore and low rating piping flange joints are clarified to improve the sealing performance of the bolted flange joints and the workability of flange tightening work. It is said that lubricant on the screw of the bolts and the nut-seating surface can minimize the variability of axial force acting on flange bolts, while this process might make it harder to tight the bolts uniformly especially for small bore low rating flanges. So, in this paper the appropriate condition to apply lubricant is clarified by a series of bolt tightening tests and sealing tests results. On the other hand, for the bolted flanges applying spiral wound gaskets, measuring the gasket compress dimensions help us to prevent uneven tightening balance and to perform the appropriate tightening work. Appropriate gasket compress dimensions are also clarified to ensure the sealing performance for the flanges based on the sealing tests results. Based on these test results, recommended flange-tightening methods have been summarized as an instruction and tightening work procedure to improve the sealing performance of the bolted flanges and the workability of flange tightening work.

Improvement of Flange Tightening Method for Small Bore Low Rating Bolted Flanges

An appropriate flange tightening methods for small bore and low rating piping flange joints are discussed to improve the sealing performance of the bolted flange joints and the workability of flange tightening work. The lubricant on the thread of the bolts and the nut-seating surface can minimize the variability of axial force acting on flange bolts, however this process might make it harder to tight the bolts uniformly especially for small bore low rating flanges. In this paper the appropriate condition to apply lubricant is clarified by a series of bolt tightening tests and sealing tests results. On the other hand, for the bolted flanges using spiral wound gaskets, measuring the gasket compressed dimensions help us to prevent uneven tightening balance and to perform the appropriate tightening work. Appropriate gasket compressed dimensions are also clarified to ensure the sealing performance for the flanges based on the sealing tests results. Based on these test results, recommended flange-tightening methods have been summarized as an instruction in tightening work procedure to improve the sealing performance of the bolted flanges and the workability of flange tightening work.