Front Motorbike Suspensions Research Articles

Analysis of the Stress State in Brake Caliper Mounts of Front Motorbike Suspensions

The aim of this work is to analyze the stress and the strain fields in the brake caliper mounts of front motorbike suspensions produced by the braking action. First of all, some formulae useful to evaluate the maximum braking force in function of the vehicle features (e.g., total mass, centre of gravity position, tyre dimension, and brake disk diameter) have been developed. A mathematical model useful to calculate the axial, the bending, and the torque stresses on the braking caliper mounts has been then defined. The model has been developed by comparing the theoretical results with those obtained by some numerical analyses, based on the finite element method. An ad hoc test equipment has been, finally, designed and manufactured in order to define and analyze experimentally the strength of different types of brake caliper mounts and, at the same time, to verify the proposed model.

Tightening Tests and Friction Coefficients Definition in the Steering Shaft of Front Motorbike Suspension

Abstract: The steering shaft of front motorbike suspensions is, usually, tightened up the fork by means of a nut and a locknut. The aim of this study is to evaluate the actual relation between the bolt torque and the preloading force of the steering shaft by performing some tightening tests. The bolt torque is given by a torque wrench whereas the preloading force has been evaluated by means of a strain gauge located on the steering shaft. The steering shaft has a hollow section with an external thread so that the strain gauge has been applied on its internal surface. In relating the bolt torque to the bolt tension, the friction coefficients have been accurately calculated: the friction coefficient values increase notably after the first set of tightening tests mainly because of the spoiling of the contact surfaces.

Failure analysis of bolted joints: Effect of friction coefficients in torque–preloading relationship

The aim of this study is to provide an experimental methodology useful to determine the friction coefficients in bolted joints and, therefore, to relate precisely the tightening torque to the preloading force. The components under investigation are clamped joints made of aluminium alloy and used in front motorbike suspensions to connect steering plates and legs, or legs and the wheel pin: static failures of clamps occurred during the tightening, because of the bending stress introduced by the preloading forces. Some specific specimens have been appropriately designed and realised with the same process of the actual components. The bolt torque is given by a torque wrench whereas the preloading force has been evaluated by means of a strain gauge. The overall friction coefficient and the torque coefficient (nut factor) have been calculated. Experimental tests have been carried out by applying the Design of Experiment method in order to obtain an accurate mathematical model that involves the significant friction variables and their interactions. Then, results of present study have been applied to actual components: the tightening torque has been precisely related to the preloading force by means of the friction coefficients definition and the tensile state of clamps have been evaluated both experimentally (strain gauges) and numerically (FEA) in order to shed light on the failures which occurred during the tightening.

Recent improvements and design formulae applied to front motorbike suspensions

The aim of this paper is to provide a methodology useful for the structural design and optimization of front motorbike suspensions. Two different types of shaft–hub couplings are used to assembly the whole suspension: interference fit couplings and bolted joints. Some mathematical models and engineering design formulae are proposed in order to calculate the tensile state and the fundamental design parameters of the main couplings, such as, for example, the fork–steering shaft and the leg–wheel pin couplings. Both experimental tests (based on the Design of Experiment approach) and numerical analyses (based on the Finite Elements Method) have been carried out to obtain the proposed results. All the research findings culminate in an innovative software (Front Suspension Design©) which is useful to design and to verify the whole front motorbike suspension, by applying correct and effective results, obtained for different geometries and materials combinations.

Experimental study of friction in aluminium bolted joints

This study aims at developing an experimental tool useful to define accurately the friction coefficients in bolted joints and, therefore, at relating precisely the tightening torque to the bolt preloading force in some special components used in front motorbike suspensions. The components under investigation are some clamped joints made of aluminium alloy. The preloading force is achieved by applying a torque wrench to the bolt head. Some specific specimens have been appropriately designed and realized in order to study the tribological aspects of the tightening phase. Experimental tests have been performed by applying the Design of Experiment (DOE) method in order to obtain a mathematical model for the friction coefficients. Three replicas of a full factorial DOE at two levels for each variable have been carried out. The levels include cast versus forged aluminium alloy, anodized versus spray-painted surface, lubricated versus unlubricated screw, and first tightening (fresh unspoiled surfaces) versus sixth tightening (spoiled surfaces). The study considers M8x1.25 8.8 galvanized screws.

Experimental and numerical analysis of clamped joints in front motorbike suspensions

Clamped joints are shaft-hub connections used, as an instance, in front motorbike suspensions to lock the steering plates with the legs and the legs with the wheel pin, by means of one or two bolts. The preloading force, produced during the tightening process, should be evaluated accurately, since it must lock safely the shaft, without overcoming the yielding point of the hub. Firstly, friction coefficients have been evaluated on “ad-hoc designed” specimens, by applying the Design of Experiment approach: the applied tightening torque has been precisely related to the imposed preloading force. Then, the tensile state of clamps have been evaluated both via FEM and by leveraging some design formulae proposed by the Authors as function of the preloading force and of the clamp geometry. Finally, the results have been compared to those given by some strain gauges applied on the tested clamps: the discrepancies between numerical analyses, the design formulae and the experimental results remains under a threshold of 10%.

Design improvement of clamped joints in front motorbike suspension based on FEM analysis

This paper aims at defining the tensile state in shaft–hub joints realized between the clamp (hub) located at the end of the suspension leg of the front motorbike suspensions and the wheel pin (shaft). The clamp under investigation has an asymmetric shape and a slot useful for the assembly operation: one or two bolts (depending on the vehicle performances) are tightened in order to generate the coupling pressure which is necessary to lock the pin. The fundamental objective of this work is to define a mathematical model to calculate the maximum stress generated on the clamp by the tightening forces. The mathematical model was defined by comparing the De Saint Venant theoretical bending stress (the maximum stress on the clamp) with several FEM results. Thus a sort of theoretical stress concentration factor was calculated in function of the dimension and of the location of the spot facings of the clamp. The new developed model is useful to optimize and to verify, in a very short time, this type of coupling without performing any complex numerical analysis. The validity of the model has been demonstrated by several FEM results and by some experimental tests carried out on a high performance vehicle.

The design and optimization of fork–pin compression coupling in front motorbike suspensions

The fundamental goal of this work is to determine a mathematical model useful to calculate the tensile state in the fork–pin compression-fit couplings of front motorbike suspensions. The second goal is to update an original software (Fork Design © ) which may be used in order to design and to verify this type of coupling. The mathematical formulas used by the program are based on the thick wall theory appropriately modified with the newly developed model. The new formulas were determined for the forks, which have an asymmetric tangential stiffness, by performing several finite element analyses with different geometrical and stiffness parameters. At this time, the mathematical model has been verified for all the Paioli Meccanica S.p.A. fork–pin couplings and thus it is useful to compute analytically their tensile state. Anyway, the authors think that the findings may be extended and applied to other fork–pin couplings. Finally, a specific software has been updated with the aim to perform accurately the design and verification of the coupling.