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In the previous paper(1), the authors reported the calculation method they developed for predicting the idling rattle in manual transmissions. This method provides data that represent noise levels to which human ear is not sensitive by numerical values. In the study described in this paper, the authors attempted to produce audible noise through a speaker by the following process: create time-series data of fluctuation in the angular acceleration obtained by the calculation (which is considered to correspond to rattle noise); create next-stage data by applying convolution of a transmission case's vibration transfer characteristics filter obtained by the experiment to the above-mentioned time-series data; convert the filtered data into a wave file; and then input the file to a personal computer to obtain audible sound as output. The audible noise thus produced provides a means of evaluating the level and nature of noise in the way humans naturally experience it.

It is generally known that the idling rattle in manual transmissions is caused by gear tooth portions that make repeated impact-generating vibrations in the backlashes. These vibrations result from rotational fluctuations of the flywheel induced by combustion in the engine. In the study reported here, the authors constructed an experimental setup using rotary encoders and a transient torsional angle converter that allowed the long-awaited direct measurement of impact-generating vibrations in the backlashes. Using this experimental result, the following ideas that the authors must pay attention for the numerical simulation are obtained. That is, transmission drag torque is to be input and treated as the offset value in the torque value of the torsional characteristics in the clutch disc, and coefficients of attenuation have great influence upon the calculation result.

To reduce the idling rattle of manual transmissions, the computer simulation has been utilized. However, the conventional simulation model could not express properly the relationship between the transmission oil temperature and the rattle noise level, especially in case of transmission with backlash eliminator in constant mesh gears. In this study, the authors carried out detail experiments investigating the motion of each part in the transmission. Based on the experimental results, an additional mass representing all constant mesh speed gears supported on plain or rolling element bearings was introduced to the simulation model. Using the improved model, it was confirmed that the calculated RMS value of the fluctuation in countershaft angular acceleration corresponds to the experimental rattle noise level.

We reported, in our first report1), the study of shapes of air deflectors that have strong yawing angle characteristics for the air resistance encountered when vehicles are running at high speed, taking into account the ambient wind. However, it is rarely the case that the optimum shape of air deflector, which was obtained and reported in our first report, is directly adopted for practical use. This paper reports the results of measurement tests on how the air resistance increases (worsens) when an air deflector is mounted on the cab of a vehicle: in the case when the air deflector was slightly changed on the same vehicle; or when the parameters of the vehicle (the height of the rear body) were changed for the same air deflector. We obtained the following results: Considerations and adjustments are required not to allow flows passing over upper and side surfaces of the air deflector to hit the front surface of the rear body.

The van-type truck is frequently equipped with an air deflector to reduce fuel consumption. When studying the shape of the air deflector, it is necessary to choose a shape that is less sensitive to yaw characteristics. Side wind induced yaw conditions are more typical of on-road usage. In this study, the basic characteristics for a shape with strong yaw sensitivity were first examined. Subsequently, an angle change test was carried out by replacing the space over the cab with a rectangular parallelopiped and letting the upper and side edges, just in front of the rear body be the reference lines. The yaw angle was varied between 0°, 5°, and 10°. From this result, the existence of the optimum upper and side incident angles was confirmed. Furthermore, the reduction in fuel consumption using the optimum shape as compared with the conventional shape was estimated by simulation.

Mud adhesion to the rear surfaces of trucks, vans and buses causes troublesome results such as aesthetic degradation, hindered rear view and laborious washing. To raise the product value of trucks and buses, it is important to develop effective measures for suppressing such mud adhesion. In this research the authors first clarified the mechanism of mud adhesion through flow visualization tests. Then, wind tunnel tests were performed to predict the effects of various countermeasures, and prospective ones were put under actual driving tests to verify their effects. The following measures were found effective in suppressing mud adhesion. (1) Aerodynamic improvement by attaching corner vanes to the upper and side edges of the rear surface. (2) Blocking road splash with a slanted plate under the truck and close to the base.

As a part of our efforts to conform to particulate emission regulation in the U.S., a particulate trap system has been developed that collects particulates using a filter and burns them by heat of the exhaust gas. In order to more easily burn the particulates, the system combines a platinum catalyst to lower the ignition temperature of particulates and a mechanism which causes the exhaust gas to bypass the filter during non-injection periods, thereby preventing a temperature drop of the filter. In the various driving tests conducted, including urban areas, almost no particulate deposits were found on the filter. This simplified particulate trap system is outlined in this paper.

Vehicle road tests, although time consuming, do not usually give accurate fuel consumption data due to the effect of many factors. In this paper, the authors describe a new method for calculating energy consumption during vehicle operation. By using this method, actual vehicle fuel consumption can well be correlated with the calculated energy consumption data. In calculating vehicle energy consumption, the vehicle was driven on a chassis dynamometer according to fixed driving cycles representing urban and suburban operations; as for highway operation, a computer simulation was used to obtain the vehicle energy consumption data. Analyzing this energy consumption data makes it possible to estimate the effects of various parameters, such as rolling resistance, accelerating resistance and so on. In this calculation, consideration of engine mechanical loss is an important factor for accurate and less scattered energy consumption vs. fuel consumption correlation data.

In SAE paper SAE850979, 1985, the authors reported on a design technique for a clutch disc with nonlinear torsional characteristics for reducing transmission idling rattle. However, when design conditions do not allow sufficiently large first stage torsional angle or the transmission is loaded with large drag torque (such as when transmission oil is cold or the transmission has a power take-off unit), clutch discs designed using the previously reported technique do not necessarily give satisfactory result. In this paper, the mechanisms generating idling rattle and their characteristics are further examined and a technique to reduce transmission idling rattle through elucidation of nonlinear torsional resonance is discussed.

Generation mechanism and characteristics of idling rattle are systematized analytically by experiments on vehicle and digital simulation of nonlinear torsional vibration system for an inline four-cylinder four-cycle compact diesel engine. Jumping and hysteresis of the noise level are caused by both decreasing engine torque fluctuations while engine rotating velocity increases, and clutch-disc torsional characteristics of two-staged hardening spring. An improved clutch disc with a decreased noise level of 5 dB (A) was developed clarifying the optimum combination of disc characteristics, and permitting engine rotating velocity, where jumping occurs, below idling rotating velocity.