A rotary variable admittance device and its application in vehicle seat suspension vibration control
Introduction
Since the introduction of inerter [1], it has attracted many researchers working on it. The inerter is a two terminals mechanical device, contrasted with the mass element which always has one terminal connected to ground, with the property that the equal and opposite force applied at the terminals is proportional to the relative acceleration between them. The passive mechanical networks are investigated and applied in vehicle suspension by employing the inerter [2], [3], [4], [5]. The inerter has also been used in structure vibration suppression [6], [7], [8] and railway applications [9], [10]. The nonlinear properties of inerters and their impact on vehicle suspension have been discussed in [11]. The experimental testing and analysis of inerter devices have been done in [12], which verified that the friction and backlash play significant roles in its nonlinear manner. The inerter has been extensively studied for more than one decade, and most of the studies are related to the passive vibration control.
The semi-active system with the inerter is studied in recent years. The inerter in semi-active suspension has been investigated in [13], [14], which shows great improvement compared with the conventional semi-active suspension. A hydraulic inerter is realized by hydraulic means instead of rack-and-pinion and ball screw devices [15], which has expanded the application possibility and can also be used in a semi-active inerter design [16]. In [17], a novel semi-active inerter is proposed, which replaces the fixed-inertia flywheel with a controllable-inertia flywheel. A variable-inertia device with magnetic planetary gearbox is proposed in [18]. A control strategy known as a parallel layout inerter damper is investigated to study the feasibility of a semi-active inerter with magnetorheological fluid (MRF) in [19]. With an assumption that the inertance may be adjusted in real-time, the control of vehicle suspension using an adaptive inerter is studied in [20]. A force-tracking approach is proposed for a semi-active suspension with semi-active inerter and semi-active damper in [21].
Heavy duty vehicles always work in severe conditions for a long time, which has a significant influence on drivers. Nowadays, people have paid more and more attentions on the improvements of drivers ride comfort and health. Seat suspensions as the most direct way to attenuate the vibration magnitude to drivers are believed to be an effective and economic solution. Many types of seat suspensions have been proposed. The negative stiffness seat suspension is a kind of effective passive seat for low frequency vibration [22]. The semi-active seat suspensions are popularly studied with electrorheological fluid and MRF [23], [24], [25]. The electromagnetic variable damping (VD) seat suspensions are proposed in [26], [27], which are energy saving. Several active seat suspensions have been designed with different actuators, the electromagnetic linear actuator [28], the hydraulic absorber [29] and the pneumatic actuator [30]. The multiple-degree freedom seat suspension is proposed for controlling the whole body vibration in [31]. However, there is no study about the seat suspension with inerters; it may be partly caused by that the conventional passive inerter needs to work in a mechanical network, which is difficult to be integrated into the limited space of a seat suspension and will increase the cost.
In this paper, a novel variable admittance (VA) concept is proposed, and a rotary VA device is designed and manufactured. In this paper, the single flywheel of a conventional inerter is replaced by a variable inertia flywheel (VIF) which comprises two flywheels and an MRF damper, and the rotary movement of the VIF is directly applied to a gear reducer. Theoretically, the inertance of the rotary VA device can vary from the inertance generated by its basic flywheel to the inertance coming from the two flywheels. The rotary VA device is installed in a seat suspension which has a scissors structure to transform the linear movement of the seat suspension to the rotation of the VA device. An effective controller is proposed for the rotary VA device based seat suspension with two acceleration feedbacks. Experiments are then implemented to validate the effectiveness of the proposed seat suspension and controller; the seat suspension shows an excellent performance in the vibration control.
The rest of the paper is organised as following: Section 2 proposes the VA device design; Section 3 presents the rotary VA device based seat suspension and its test results; the VA seat suspension control is shown in Section 4; the experimental evaluations are presented in Section 5; Finally, Section 6 presents the conclusions of this research.
Section snippets
The variable admittance concept
In the inerter based suspension systems, the rack-and-pinion and the ball screw devices are generally used to transform the linear movement of a suspension to the rotary one of a flywheel [32]. An ideal inerter is defined as a two-terminal mechanical device, as shown in Fig. 1(a) where b is the inertance which is a constant of proportionality; zu and zb are the upper and bottom terminals, respectively. The applied force at the two-terminal is proportional to the relative acceleration between
Seat suspension prototype
A rotary VA device based seat suspension prototype is shown in Fig. 9 which employs a modified commercial passive seat suspension (GARPEN GSSC7) with its original damper removed; the gear reducer (ratio 20:1) of the rotary VA device is installed in the centre of its scissors structure. The linear motion of the suspension caused by the vertical vibration is transformed to the rotation of the rotary VA device by the scissors structure; thus, no additional transmission device is required.
Test system
The seat
Rotary VA device based seat suspension control
In this section, a hybrid controller is proposed for the rotary VA device based seat suspension prototype, which uses the top and bottom accelerations of the seat suspension as feedbacks.
Experimental setup
The proposed seat suspension and controller are validated with the experimental setup shown in Fig. 21. The rotary VA device based seat suspension is mounted on a 6 degree of freedom (6-DOF) vibration platform which is controlled by an NI controller (CompactRio 9076). The Computer 2 is used to send vibration profile to the controller. Two accelerometers (ADXL 203 EB) are applied to measure the top and bottom accelerations of seat suspension, respectively. Based on the measurements of sensors,
Conclusions
In this paper, a novel VA concept is proposed, and an MRF damper based rotary VA device is designed and manufactured. The VA concept is inspired by the conventional variable stiffness design; it comprises a gear reducer, a basic flywheel, an additional flywheel and a VD device. By using MRF damper to vary the damping, the connection of the two flywheels can be controlled, thus, the system admittance can be varied. The rotary VA device prototype is applied in a seat suspension's scissors
Acknowledgement
This research is supported under the Australian Research Council's Linkage Projects funding scheme (project number LP160100132).
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