Mechanism Synthesis And Analysis Of Variable Dof Compliant Mechanism For Vehicle Side Door Latch With Power Release Feature

To meet the developing demands of intelligent,multi-functional vehicle side door latches in the age of 5G,the power release feature of a type of traditional vehicle side door latch is realized in this paper,based on the combination of the actuating branches topology and the design of multi-mode motion compliant mechanism.Under the constraints of the confined space inside the latch and the motion compatibility among the interior actuating branches,the newly-added power release branch mechanism is adopted.A new type of compliant joint with torsion spring is proposed;A novel variable degree of freedom(DOF)compliant five-bar mechanism is constructed and implanted into the vehicle side door latch worked as the power release branch.Meanwhile,the influence of the introduction of compliant factors on the shaking force and motion stability of the compliant mechanism is taken into consideration,the specific research contents are as follows:(1)Considering the constraints of confined space and demands of multifunctional and lightweight design of vehicle side door latch,the concept of"multi-pair component"mechanism space sharing design is proposed.A single motor is used to drive latch lock/unlock branch and power release branch in time series.Based on the theory and application of mechanism topology,the power release branch of“gear-linkage”is synthesized and newly added.The different contact states between the power release branch and the lock/unlock branch of the latch are described by incidence matrix.(2)To solve the motion compatibility problem of multi-chain introduced by“multi-pair component”,a novel compliant joint with torsion spring force constraint is proposed,a variable DOF compliant five-bar mechanism is constructed as a portion of power release branch,which ensures that the latch can realize the timing sequence motion with a single actuator.The latch actuating mechanism with multi-mode motion possesses the characteristics of elastic energy storage,over-singular recovering motion without bifurcation,etc.The designed power release branch based on the variable DOF compliant five-bar mechanism meets the multi-mode actuated conditions of the door latch and the characteristic requirements of“active rigidity”and“passive compliant”.(3)The drifting amount d_m which is the torsion spring center sliding in the groove is used as the compliant index for measuring the force-adaptive characteristic of the compliant mechanism.The dynamic response of motion trajectories,position recovering time,accuracy and d_m to the spring stiffness k _T is revealed under the different working conditions of power release,electric lock and manual release.The shaking force and dynamic balance of the five-bar compliant mechanism at the fixed joint on the frame is analyzed.It is found that the introduction of compliant joint can reduce the peak actuating load of motor and weaken the shaking forces.Due to the difficulty of obtaining the analytical dynamic model for a complex nonlinear mechanical system,this paper uses Lyapunov exponents in numerical method to quantitatively analyze the stability of compliant mechanism in under-actuated conditions.Motion trajectories and velocity-displacement diagrams of characteristic points are shown under different stiffness of position recovering torsion spring.This paper aims to form a systematic design and analysis method for the space-confined multi-branch vehicle door latch.