【正文】 張建 Semiactive hydrogas suspension system for a tracked vehicle U. Solomon, Chandramouli Padmanabhan Machine Design Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India Received 18 June 2022。 received in revised form 12 November 2022。 Skyhook damper。 developed a 2DOF model of a vehicle incorporating a semiactive suspension with adaptive capability. In addition to a variable damper, a spring in which the stiffness can be discretely varied among the three different levels was proposed by them. They concluded that the adaptive system showed significant improvement in controlling vehicle vibration when pared to a semiactive suspension with a modulated damper and fixed stiffness. The literature reviewed in the previous paragraphs primarily deal with control strategies for semiactive suspensions in wheeled vehicles. Use of active dampers in offroad wheeled/tracked vehicles has also been investigated by several authors. Nell and Steyn developed and experimentally evaluated a twostate semiactive translational damper on a high mobility offroad vehicle. They modified the passive damper by adding a bypass assembly and a controllable valve and demonstrated significant improvement in both handling and ride fort. Giliomee and Els described the development and characterization of a semiactive hydro pneumatic suspension with a twostate pneumatic spring and a twostate hydraulic damper. Tests were conducted on a single DOF test rig and the semiactive damper control strategies were evaluated. It was shown that the acceleration levels were much lower with the semiactive mode. Els and Holman developed a twostate discrete adjustable semiactive rotary damper for heavy offroad wheeled vehicles. They carried out a full vehicle simulation using DADS mercial software and demonstrated that the semiactive rotary damper performance was better than both the passive rotary damper and traditional damper. Use of electrorheological (ER) fluids in dampers have also been attempted. Choi et al. have proposed ER dampers for ride fort improvement in tracked vehicles. Initially the damping characteristics are established with respect to the electric field using a Bingham plastic model and this is incorporated in a linearized statespace model of the vehicle dynamics. An optimal controller with a Kalman filter has been used to demonstrate the reduction in vertical acceleration of the vehicle. Most of the semiactive dampers reported in the literature for tracked vehicles are twostate dampers (on–off type) which require plex control strategies. In this paper, the skyhook damper strategy (on–off type) is used in a quartercar model to arrive at an optimal damping coefficient. Based on this a continuously variable damper, with a standard PID controller, is proposed for damping control. Using an analytical model of the suspension, validated with experiments on a suspension test rig, an inplane simulation model is prepared. Comparisons with the passive suspension clearly demonstrates the superior performance of the semiactive damper. 2. Passive hydrogas suspension Tracked vehicles fitted with torsion bar suspensions are limited in their ability to achieve high mobility due to their linear characteristics. Hydrogas suspensions due to their inherent nonlinear behavior can provide higher mobility and better ride fort performance. The hydrogas suspension model has usually been developed from experimental force–displacement characteristics, which requires availability of suspension hardware. A typical hydrogas suspension system, shown in Fig. 1a, consists of a stationary accumulator and accumulator cylinder, damper, crank pin, road wheel and axle arm. The crank, connecting rod and piston form a four link slider – crank mechanism as shown in Fig. 1b to convert the rotary movement of the axle arm to linear piston displacement for pressing the gas medium. A damper is animportant subsystem of a suspension located between and linking the actuator and accumulator cylinders. Applying loop closure along the X0 and Y0 axes for the slidercrank mechanism as shown Fig. 1 b yields for rebound position: velocity of the piston, with x being the angular velocity of the axle arm (crank), is given by To obtain the stiffness of the suspension, it is assumed that the gas pressure under pression/expansion is given by a polytropic law, pVn = constant, where n is the polytropic coefficient. The volume of the gas V is calculated from the slider position (Eq. (3)) and the force on the cylinder block is puted by multiplying the pressure p with the piston cross section area. The force–deflection relationship yields the gas spring characteristics corresponding to the permissible travel limits of the piston. To validate the stiffness calculations using the polytropic law, an experimental setup, as shown in Fig. 2, is used. Note that the same setup is used for both passive and semiactive suspension experiments. The suspension test setup has a capability to test a single station suspension with a maximum stroke of 600 mm. The displacement is sensed by a LVDT and the load is measured using a load cell with a rating of 250 kN. The test rig is capable of carrying out both static and dynamic tests at various conditions. The wheel is on a platform connected to an actuator. For varying the spring characteristics, the platform is moved from 0 to 500 mm in steps of 50 mm. the force at the fixed end of the suspension is measured for each position. The force–deflection curve obtained from experiment is pared with the analytical model. As seen from Fig. 3 the agreement is excellent indicating the validity of the theoretical model.