Xiang Liu

Design of an Ackermann type steering mechanism

This article focuses on the synthesis of a steering mechanism that exactly meets the requirements of Ackermann steering geometry. It starts from reviewing of the four-bar linkage, then discusses the number of points that a common four-bar linkage could precisely trace at most. After pointing out the limits of a four-bar steering mechanism, this article investigates the turning geometry for steering wheels and proposes a steering mechanism with incomplete noncircular gears for vehicle by transforming the Ackermann criteria into the mechanism synthesis. The pitch curves, addendum curves, dedendum curves, tooth profiles and transition curves of the noncircular gears are formulated and designed. Kinematic simulations are executed to demonstrate the target of design.

Elastokinematics and compliance of a rectilinear rear independent suspension

A rectilinear rear independent suspension has a distinct difference from the traditional ones in that its wheel alignment parameters remain invariable in theoretical kinematics. However, they change within a narrow interval during jounce and rebound when the elasticity of parts, especially the rubber bushings, is taken into account. With the aim of investigating the compliance of the rectilinear rear independent suspension, an elastokinematic model is established in accordance with static equilibrium equations and compatibility conditions. The elastokinematic model has 28 unknowns corresponding to the 5 static equilibrium equations and 23 compatibility equations. Different configurations of rubber bushing and the sensitivity of the suspension stiffness to that of the rubber bushing are analysed. The analytical results indicate that the rubber bushings are best mounted close to the knuckle, and the suspension stiffness is sensitive to the compressive stiffness and the torsional stiffness about the z-axis of the rubber bushing. In addition, the results from kinematic and compliance tests not only verified the elastokinematic model but also revealed the excellent wheel alignment capacity of the rectilinear rear independent suspension compared with that of the MacPherson suspension. This work provided the foundations for the engineering design of a rectilinear rear independent suspension.

Instantaneous motion and constraint analysis of Bennett linkage

Bennett linkage is a well-known spatial four-bar linkage with one degree-of-freedom (DOF). Although mobility analysis of Bennett linkage has been carried out by many researchers, the type, direction and location of the instantaneous motion are seldom discussed. This paper focuses on investigating the full mobility information of Bennett linkage by using analytical method for mobility, and then addresses its extending application to a Bennett-based six-bar linkage. The result demonstrates that the instantaneous motion of Bennett linkage is always a helical motion. However, the location, direction and pitch of the helical motion are changing related to different configurations. An interesting phenomenon is that the direction of helical motion will reverse suddenly when passing through the configuration that the axes of these four links keep collinear. As an extending application, a Bennett-based six-bar linkage is discussed and its peculiar mobility is an instantaneous rotation without considering the bifurcation.

Compliant dynamics of a rectilinear rear-independent system

The rectilinear rear-independent suspension investigated in this paper could remain the wheel alignment parameters invariable in theory. However, its dynamics is much more complex than that of the existing suspensions because of its redundant constraints in structure. Considering the elasticity of the rectilinear rear-independent suspension, a rigid-flexible half-car dynamic model is established for the first time based on the discrete time transfer matrix method. At the same time, a rigid half-car dynamic model is established as a comparison. The natural frequency characteristics and dynamic response of the rectilinear rear-independent suspension under random road excitations are analyzed and compared with those of rigid half-car dynamic model. The results reveal that the suspension system has apparent influence to the dynamics of vehicle. The wheel alignment parameters will fluctuate within a narrow range which is mainly determined by the rolling vibration of vehicle. And the suspension system could reduce and filter the road excitations with high frequency and small amplitude. This provides a good effect on the ride comfort of vehicle. Dynamics analysis of the rectilinear rear independent suspension reveals that the proposed modeling approach could deal with the dynamics of rigid-flexible multibody systems with redundant constraints effectively.

Instantaneous Motion of a 2-RCR Mechanism with Variable Mobility

Mobility is a very important parameter for mechanisms, and many methods for calculating the mobility of mechanisms have been proposed till now since it came to be drawn attention in the middle of 19th century. The CKG formula is widely used in the textbook, manuals and applications. However, it has been proved repeatedly to fail to deal with many classical linkages and modern spatial mechanisms as well. On the other hand, although many modifications or extensions of CKG formulas have been proposed, all of them aim at calculating the number of mobility but ignoring other mobility information, such as type, direction and location of motion. Compared with the existing CKG formulas, the analytical method is regarded as a more general and reliable method which could obtain the full information of mobility. By using this method, this paper investigated the instantaneous motion of a 2-RCR mechanism that the number of its mobility is invariable but the type is variable corresponding to different configurations.

Synthesis of a rectilinear independent rear suspension and experiment research

This paper synthesises a rectilinear independent rear suspension in order to minimise the variation range of the alignment parameters during jounce and rebound. Simulation through the software of ADAMS verifies the rectilinear motion characteristics of the suspension. Based on the structure design and prototype test of the suspension system, the comparing experiments of rectilinear suspension and MacPherson suspension are carried out with kinematic and compliance (K&C) test rig. The experiments indicate that the alignment parameters of the rectilinear suspension are almost invariable compared with the MacPherson suspension.

Optimum design of a rack-and-pinion steering linkage matching a rectilinear suspension system

This paper proposes a spatial kinematic model of rack-and-pinion steering linkage matching a rectilinear suspension system. Minimising the steering error and avoiding the interference between the steering linkage and suspension system are used to optimise the steering linkage based on the requirements of transmission efficiency and understeering criterion. Numerical calculation and result comparison show the advanced performance of the steering linkage and verify the optimisation method. This work lays a foundation for the design of steering system and rectilinear suspension system.

Architecture innovation for the lower limbs of a humanoid robot

This paper analyzes and compares different architecture schemes for the lower limbs of a humanoid robot. According to the biology kinematic characteristics of the lower limbs of human being, we first establish a rough architecture model for the lower limb of a humanoid robot, and then investigate the twists of the chain. With reciprocal screw theory, we obtain the maximum linearly independent screw set and the different architecture schemes for the lower limbs of the humanoid robot via combining the maximum linearly independent screws. Considering the real requirements of engineering such as the compactness and manufacturing, we exploit and compare the different schemes for the lower limbs of humanoid robots. The methodology proposed in this paper can also be utilized to optimally synthesize and create the limbs of other bionic robots.