Design of Scotch yoke mechanisms with improved driving dynamics

Abstract

Input torque balancing through addition of an auxiliary mechanism is a well-known way to improve the dynamic behavior of mechanisms. One of the more efficient methods used to solve this problem is creating a cam-spring mechanism. However, the use of a cam mechanism is not always possible or desirable because of the wear effect due to the contact stresses and high friction between the roller and the cam. The Scotch yoke mechanism is most commonly used in control valve actuators in high-pressure oil and gas pipelines, as well as in various internal combustion engines, such as the Bourke engine, SyTech engine and many hot air engines and steam engines. This mechanism does not create lateral forces on the piston. Therefore, the main advantages of applications include reducing friction, vibration and piston wear, as well as smaller engine dimensions. However, the input torque of the Scotch yoke mechanism is variable and can be balanced. This paper proposes to balance the input torque of Scotch yoke mechanisms without any auxiliary linkage just by adding linear springs to the output slider. It is shown that after cancellation of inertial effects the input torque due to friction in joints becomes constant, which facilitates the control of the mechanism. An optimal control is considered to improve the operation of balanced Scotch yoke mechanisms. The efficiency of the suggested technique is illustrated via simulations carried out by using ADAMS software.