Abstract
An electric compressor generates a mechanical vibration that is transmitted from the engine to the vehicle body and then the vibration of the vehicle body creates a vehicle interior noise. The noise can be calculated by a transfer force from the electric compressor to the engine and transfer characteristics from the electric compressor to the vehicle cabin. The transfer force can be measured with a force sensor installed between the electric compressor and the engine. However， the force sensor interferes with other components and changes the vibration mode of the electric compressor. Therefore， the conventional force sensor cannot measure the transfer force of the actual phenomenon. In this paper， a new low-profile 3-axis force sensor was developed by use of piezoelectric quartz crystals， which achieved measuring the transfer force in as close to the actual phenomenon as possible.
In recent years， the market demands of the vehicle quietness are increased， therefore the reduction of the vibration and noise from an electric compressor is require
Then， the influence on vibration mode of the electric compressor is present in this paper by installing a 3-axis force sensor. Test pieces of different thickness are installed between an engine and the electric compressor， and a resonance frequency variation of the electric compressor is measured by shaking it up and down. The experimental system configuration is shown in
Fig.1 Experimental system configuration with 3-axis load sensor
Fig.2 Resonance frequency between test pieces of different thickness
Fig.3 Resonance frequency variation
The low-profile 3-axis force sensor developed in this paper is shown in
Fig. 4 3-axis force sensor
The internal structure of the 3-axis force sensor is shown in
Fig. 5 Internal structure of 3-axis force sensor
The principle of the piezoelectric quartz crystal to measure the force in the shearing direction is shown in
a The electrical charge output is amplified twice
b The electrical charge is canceled out
Fig.6 Principle to measure shearing load
a The electrical charge is canceled out
b The electrical charge output is amplified twice
Fig.7 Principle to measure compression load
The electrical axes of two crystals are aligned with the shearing direction， one crystal is placed in the opposite direction to another one， and machine axes of the crystals are aligned in the same direction as shown in
The electrical axes of two crystals are aligned with the compression direction， one crystal is placed in the opposite direction to another one， and machine axes of the crystals are aligned in the same direction as shown in
The 16 kN load in the axis direction generates in the 3-axis force sensor at screwing bolt. In case that the piezoelectric quartz crystal incurs all load， it will be destroyed. The 3-axis force sensor developed divides the load into the crystal and the housing， whose safety factor ensures 2.3. The load distribution image is shown in
Fig.8 Load distribution image
The calibration method of the 3-axis force sensor in the shearing direction is shown in
Fig. 9 Calibration for shearing direction
Fig.10 Calibration for compression direction
The calibration method for compression direction as shown in
The calibration results are shown in
Fig.11 Calibration Results of 3-axis Force Sensor
The electric compressor is mounted on three places of stay that simulates the engine， and the load generates on the fastening places is measured when the electric compressor is operating. The 3-axis force sensor is installed between the electric compressor and stay and screwed together. The system configuration is shown in
Fig.12 System configuration of load measurement
Fig.13 Picture of 3-axis force sensor
The measurement load in the axis direction when the electric compressor is operating is shown in the
Fig.14 Load Test Result of electric compressor
A low-profile 3-axis force sensor was developed. The machine axes of the two piezoelectric quartz crystals were installed in parallel and the electrical axes were installed in opposite. Thus， the electrical charge output was amplified twice on the load of the measuring axis and canceled on the other axes. The load was divided with the piezoelectric quartz crystals and housing， then the safety rate of the crystals was ensured. The first-order load component of the electric compressor was measured not to be buried in the electromagnetic noise. An experiment was conducted to confirm that the developed sensor could measure the load transferred from the electric compressor to the engine in a state close to the actual phenomenon.
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