# Idle Vibration Reduction of a Diesel Sport Utility Vehicle
## 2 Experimental Analysis
To obtain the ODSs of the components, we used triaxial accelerometers (PCB 356A15) capable of sensing vibration signals in three mutually perpendicular directions. The accelerometers are attached to the measurement points to obtain the ODSs, as shown in Figure 3, wherein the squared and circled markers represent the measurement points for the reference and roving vibration signals, respectively. The reference signal was measured at the top end of the engine, whereas the roving signals were measured at the designated points to identify the behavior of each component. To obtain the ODS of the powertrain, vibration signals were measured at a total of eight points (four points at the top and four points at the bottom of the powertrain). To acquire the ODSs of the radiator and intercooler, vibration signals were measured at eight points, each with four vertices. Finally, vibration signals were measured at two points on each side member, a total of four points, and six points on the car body floor to analyze the ODSs of the side members and body floor. The vibration signals measured by the accelerometers were analyzed by a sound and vibration analyzer (B&K 3560-D) with 60 channels to obtain the ODSs. The amplitudes and phases of auto-spectra and cross-spectra were obtained using the analyzer. Based on these measurements, the ODS frequency response functions of the roving signals with respect to the reference signal were extracted, and subsequently, the ODS of each component was derived. The ODSs were measured for an operating engine speed of 830 rpm in the idle engine state. Considering the four-cylinder diesel engine of the SUV, the excitation frequency emitted by the engine in the idle state was 27.7 Hz. The frequency spectra for vibration signals in the three mutually perpendicular directions at the position of the driver's seat on the body floor under idling engine conditions are depicted in Figure 4. As shown in this figure, the spectra exhibit large peaks at the idling frequency of 27.7 Hz. The ODSs of the powertrain, radiator, intercooler, and body floor of the SUV were analyzed at an engine excitation frequency of 27.7 Hz in the idle state (Figure 5). All motions appearing later are described based on the global coordinate system. Figure 3: Measurement points of vibration signals to obtain ODSs. First, as shown in Figure 5a, the ODS of the powertrain exhibits a rotational vibration about the \(y\)-axis, which is generally called the pitch motion. This rotational vibration occurred because the SUV used in this study was driven by a transverse-mounted engine that generated a driving torque about the \(y\)-axis. Moreover, the ODS of the radiator, as illustrated in Figure 5b, represents the vibration shape in which the rotational motion about the \(x\)-axis and the translational motion in the \(x\) direction are combined. Because the rubber hoses attached to the upper left and lower right sides of the radiator are connected to the engine, the engine excitation force is transmitted through these hoses; accordingly, the combined motion of rotation and translation is represented in the ODS result depicted in Figure 5b. Conversely, as shown in Figure 5c, the ODS of the intercooler vibrates in the vertical direction with a slight longitudinal vibration. In other words, the intercooler possesses a vibration shape resembling that of a bounce motion when the engine is in the idle state. Because the hoses between the intercooler and the engine are connected almost symmetrically to the top and bottom of the intercooler, this particular ODS was observed. Finally, the ODS of the vehicle body floor, as illustrated in Figure 5d, appears in the  
Figure 4: Frequency spectra of the vibration signals at the driver’s seat on the body floor. Figure 5: Operational deflection shapes of various components at the idling frequency of 27.7 Hz: (**a**) powertrain; (**b**) radiator; (**c**) intercooler; and (**d**) body floor. shape of a combination of bending and torsional deformations.