Experimental results

The sinusoidal excitations were applied to the seat suspensions with 75 Kg load. Figure 15 shows the seat acceleration comparison in both time and frequency domain with resonance frequency (1.6 Hz). When the MR damper is powered off (0 A), the seat has maximum peak acceleration. The hybrid control has the best performance. When the vibration frequency is higher than resonance frequency range, a soft seat suspension should perform better than a hard suspension. Figure 5-16 shows the seat acceleration with 2.4 Hz vibration when the soft seat suspension (0 A) can successfully isolate vibration. When the MR damper is loaded with 0.1 A current, the peak acceleration will greatly increase. The performance of semi-active control is between when the MR damper has 0 A and 0.1 A current. The hybrid control can greatly reduce the acceleration; its acceleration is even lower than the 0 A current case.

Chapter 5: Hybrid active and semi-active seat suspension

(a)

(b)

(a)

(b)

Figure 5-16. Seat acceleration at 2.4 Hz vibration. (a) Time domain; (b) Frequency domain.

The transmissibility of the seat suspension is shown in Figure 5-17. When the MR damper is powered with 0.7 A current, the vibration transmissibility is around 1.05 in the whole testing frequency range. On the contrary, when the MR damper is power off (0 A), the vibration transmissibility is highest ay 1.6 Hz, and then going down. In other words, the soft seat suspension has the resonance around 1.6 Hz, and starts to isolate vibration when the vibration

Chapter 5: Hybrid active and semi-active seat suspension

frequency is above resonance frequency. The semi-active control seat suspension can suppress the resonance vibration and even performs better than a hard (0.7 A) suspension in 1.6 Hz. The hybrid control has lowest transmissibility in 1.6 Hz, and performs better than the soft seat suspension (0 A) in higher frequency. The experiments result verified the seat suspension’s design idea and validated the proposed control algorithm. When the vibration is around resonance frequency, the semi-active control MR damper can dissipate much vibration energy, and then a small active force, which is insufficient to control vibration independently, can successfully further isolate the vibration to a low magnitude. In the higher frequency vibration, the required active force is relative small, so the applied active force can reduce the vibration transmissibility to values lower than a soft seat suspension (0 A). Generally, the semi-active control is hard to perform as good as a passive soft seat suspension with high frequency vibration in practical application.

Figure 5-17. Transmissibility.

The random vibration is often used to evaluate seat suspension performance in the time domain. Figure 5-18 shows the seat acceleration with random vibration. When the MR damper is power off (0 A), there is resonance around the 8 second. On the other hand, when the MR damper is power on (0.7 A), its acceleration is obviously larger than other cases

except in the resonance range. Table 5-3 shows the RMS acceleration comparison. The acceleration of hybrid control seat suspension has 47.7% and 33.1% reductions when compared with power on and power off seat suspension. Furthermore, there is 26.5% reduction of RMS acceleration when compared with semi-active control seat suspension. Figure 5-19 shows the PSD value of acceleration, which further indicates that the hybrid seat suspension with a small active force can improve the performance of a semi-active control seat suspension greatly.

Figure 5-18. Seat acceleration with random vibration.

Table 5-3. RMS acceleration of random vibration (m/s2)

Power off Power on Semi-active Hybrid

Chapter 5: Hybrid active and semi-active seat suspension

Figure 5-19. PSD of acceleration with random vibration.

5.6 Conclusions

In this chapter, an hybrid active and semi-active seat suspension for heavy duty vehicles has been proposed, built and tested. The proposed control algorithm for the seat suspension prototype applied measureable variables in practical, namely, relative displacement and seat acceleration. The hybrid seat suspension has an active motor and a semi-active MR damper; gearboxes are applied to amplify the actuators torque output. The field, amplitude, and frequency-dependent performance of the seat suspension have been tested with MTS system. The tests results show that the semi-active actuator of the hybrid seat suspension is controllable. The simulation and experiment were implemented and both validated the proposed hybrid seat suspension and controller. In the random vibration experiment, the RMS acceleration of hybrid control seat suspension has 47.7%, 33.1% and 26.5% reductions when compared with power on, power off and semi-active control seat suspension, respectively. The acceleration PSD value further indicates that the hybrid seat suspension has best performance with random vibration. With the proposed seat suspension, the MR damper can suppress resonance vibration with low power consumption, and then a small active force can

further reduce the vibration magnitude; when vibration frequencies are above the resonance frequency, the MR damper is difficult to further improve the ride comfort, then the small active force can work to control the vibration; thus, the proposed seat suspension has much better performance than the semi-active one. When compared with the active seat suspension, the hybrid seat suspension will consume less energy, and because the low power motor is applied, the seat system will be easy to be integrated into the vehicle system. However, the hybrid seat suspension has two sets of actuators; the system is more complicated than the active and semi-active seat suspension. This hybrid seat suspension has a practical value in engineering application.

Chapter 6: Single-DOF Electromagnetic Seat Suspension

6 S

INGLE

_-DOF

E

LECTROMAGNETIC

S

EAT

S

USPENSION

6.1 Introduction

This chapter presents a design of an EMD seat suspension with the capability of continuously varying damping; two implementation methods are proposed to control the damping of the EMD in real time; one applies a variable external resistor, and another one uses a MOSFET switch and a resistor. In the first method, a rotary rheostat is applied to vary the circuit external resistance directly. The external resistance-dependent, frequency-dependent and amplitude-dependent tests have been implemented, respectively; the integrated mathematical model including the seat suspension and the generator can match the result very well. A MOSFET switch module and an external resistor are applied in the second implementation method. A test system is designed to analyze the variable damping characteristic of the EMD. The test result indicates that the damping of the EMD can be controlled by exerting PWM signal with different value of duty cycle on the MOSFET switch. Based on the test result and the kinematic of the seat suspension, the damping variation range of the seat suspension is

derived, The performance of the EMD seat suspensions in terms of vibration control are validated with experiments.

The main contribution of this chapter is that a new kind of semi-active seat suspension is proposed; different from the traditional semi-active seat suspension with a MR damper, the new system requires very small amount of energy; it is easy to manufacture and control.