ATTENUATION OF MOTORCYCLE HANDLE VIBRATION USING DYNAMIC VIBRATION ABSORBER

Motorcycle riders are exposed to hand-transmitted vibration of the hand-arm system due to the vibration of the handle and extended exposure can result in numbness and trembling. One feasible solution to attenuate the handle vibration is by using a dynamic vibration absorber (DVA). In this work a DVA is designed and mounted on the motorcycle handle in order to reduce the vibration at the handle by transferring the vibration from the primary system handle to the secondary mass. Removal of elastomeric material at the DVA mounting locations, symmetry of secondary mass and the direction of DVA attachment influence the vibration absorption. A series of tests conducted show that the vibration on the handle is mainly induced by the engine and there is additional source of vibration from the road surface roughness. Installation of DVA at different locations on the handle resulted in various attenuation levels at different speed in the x and z directions. The attenuation level is between 59-68 % in the biodynamic x-directions for speed at 30-50 kmh.


INTRODUCTION
Motorcycles are one of the major transportation vehicle used in the world because they are cheap with low fuel consumption and easy to handle [1].The engine vibration and road conditions can result in excessive vibration which will reduce the user comfort [2] [3].The excessive exposure of vibration to the user can cause vascular disorder, muscle disorder, neurological disorder and bone and joint disorder which can be called hand arm vibration (HAVs) [4].Studies showed that more than 50 % of respondents suffer from discomfort at the hands and the arm and more than 50 % of non-occupational motorcyclist experienced discomfort at their low back, neck, shoulders, elbows, and upper back.Meanwhile occupational motorcyclists experienced greater discomfort [2][5].4.2 % of motorcyclist police officer suffered from finger blanching [6].Standard human vibration exposure limit set by the European Directive (European Directive/2002/44/EC) can be used to achieve the acceptable level to reduce the prevalence of hand arm vibration syndrome.The daily exposure action value (EAV) required users to reduce the any vibration exposure above than 2.5  −2 while the exposure limit value (ELV) is 5.0  −2 .From previous research, the frequency of interest of a motorcycle vibration is in the range of 50 Hz to 300 Hz while the vibration magnitude on the motorcycle handlebar is between 2.2  −2 to 9.77  −2 [2][6][7] [8].The high variance of the exposed vibration magnitude of different respondents are related to several uncontrolled parameters [2].Some of the uncontrolled parameters are the user handlebar griping force [9][10] and the area of contact between the hand to the vibrating components [11].Numerous studies have been done to overcome the hand arm vibrations.One technique is with the use of vibration absorber [12] [13].It is a tunable secondary mass with spring and damping properties with natural frequency similar to the excitation force frequency.Examples of application are in electrical grass trimmer [14], a motorcycle handle [7], machine [15] and hand blender [16].Most studies in the past were mainly done by measuring handle vibration with the motorcycle stationary on the dynamometer [7] or at relatively low speed of up to 10 ℎ −1 [2] or at a mean velocity of 40 ℎ −1 [8].This paper covers the development of dynamic vibration absorber for use on motorcycle handlebar which include on the road test of speed range at 30-50 ℎ −1 .

METHODOLOGY Modal analysis of motorcycle handlebar
Figure 1 shows the measurement nodes located on the motorcycle handlebar labelled with stickers.Modal analysis was carried out with the motorcycle handlebar suspended using rubber chords to represent the free-free condition.A small light weight accelerometer (Dytran 3055B2T) was used to measure the vibration response in the x-axis while an impact hammer (Krisler 9724A5000) was used to excite the motorcycle handlebar.Both are connected to the 8-channel LMS SCADAS mobile.The accelerometer is calibrated and placed on the measured nodes using the roving accelerometer techniques.

Modal Analysis of Motorcycle Handlebar
The handlebar dimension of the motorcycles was measured and this is then used in the drawing of the "node" & "line" functions of the LMS Test Lab to visualize and analyze the vibration for modal analysis.

Motorcycle handlebar Response Spectrum on the Road Test
The RMS acceleration for a series of road tests are listed in Table 1 based on the acceleration of the handlebar at node 1.The accelerations are highly affected by the speed.The dominant direction is in the x-axis and the z-axis acceleration is always lower and does not follow the trend of the acceleration in x-axis.The response spectra for the RMS accelerations in the x-axis and z-axis are plotted in figure 4. Both axes exhibited frequencies clustering around a fixed frequency at 160 Hz.The relatively constant peak frequency in this case is basically speed independent, which indicated the possibility of resonance within this speed range.

Figure 1 .
Figure1shows the measurement nodes located on the motorcycle handlebar labelled with stickers.Modal analysis was carried out with the motorcycle handlebar suspended using rubber chords to represent the free-free condition.A small light weight accelerometer (Dytran 3055B2T) was used to measure the vibration response in the x-axis while an impact hammer (Krisler 9724A5000) was used to excite the motorcycle handlebar.Both are connected to the 8-channel LMS SCADAS mobile.The accelerometer is calibrated and placed on the measured nodes using the roving accelerometer techniques.The signals from the test were recorded to derive the FRF (Frequency Response Function) for each measurement nodes, post processed and displayed on LMS Impact Testing Rev. 8B Software.

Figure 2 .
Figure 2. Schematic diagram for the vibration analysis on road test.a) Handlebar accelerometer b) Hand Accelerometer c) Front Fork Accelerometer and d) LMS SCADAS & LMS Test Lab

Figure 3 Figure 3 .
Figure 3. FRF Spectrum of the handlebar (a) x-axis and (b) z-axis

Figure 5 Figure 5 .Figure 6 .Figure 7 .
Figure 5 below shows the comparison of vibration level on the motorcycle handlebar during road test evaluation before and after the installation of the added mass.The higest vibration peak of the x-axis and z-axis at 207.5 Hz shifted to 200.0 Hz, with the peak vibration attenuation is 59 % and 50 % from 3.32  −2 to 1.35  −2 and 3.29  −2 to 1.65  −2 respectively.