This paper deals with the synchromesh behaviour of the manual car gearbox. Firstly, the state of the art on Borg-Warner-type synchronizers is presented. Then, the gear-changing process is studied and eight main operating phases are defined. The phases are described using classical tribological, mechanics, and thermodynamics theories. Models are interconnected to describe synchronizer behaviour and they are included in a numerical simulation software. Measured data are compared with the results of simulation software. Then, stick-slip phenomenon during gear changing is studied. Stick-slip is supposed to be present in two contact zones: sleeve splines and the synchronizer cone. The effects in both zones are discussed. Finally, the double bump phenomenon is studied. Double bump is assumed to be the maximum axial operating force coming from short successive phases at the end of the gear-changing process. Due to the angular integer division of splines and to the non-definite angular position of mechanical parts, sliding sleeve displacement into the ring and gear claw clutch splines gives secondary angular rotation and large increases in the axial operating force. The model can explain large variations and random dispersion of the measured double bump force peaks.

This paper focuses on the engagement process of face-dog clutches on heavy duty automated mechanical transmissions (AMTs) considering special engagement conditions caused by the actuation of an electro-pneumatic transmission brake. A dynamic model of the transmission brake-single face-dog clutch system is developed and the engagement probability map characterizing the engagement capability of face-dog clutches under different engagement conditions is determined through numerical simulations for different gears of a given AMT. A region of engagement conditions is recognized where the engagement of the face-dog clutch is not ensured. Parameters influencing that region are highlighted. Optimal engagement conditions providing major gearshift comfort are given for the cases of stopped and moving vehicles. Simulation results are partly validated through statistical evaluation of measurement data obtained from a series of measurements performed on a gearbox test bench.

Face dog clutches regain popularity in heavy duty AMT's. Though the reduction of the speed difference between the dogs is the key to a smooth gear shift, the excellent engaging capability is experienced to degrade at low mismatch speed and the outcome of the engagement process becomes uncertain. Using a simple mechanical model, that uncertainty is described and the probability of the successful engagement is given as a function of the initial mismatch speed. Results are validated through statistical evaluation of measurement data.Keywords heavy duty AMT · face dog clutch · mismatch speed · statistical evaluation Acknowledgement This work is connected to the scientific program of the " Development of quality-oriented and harmonized R+D+I strategy and functional model at BME" project. This project is supported by the New Hungary Development Plan (Project ID: TÁMOP-4.2.1/B-09/1/KMR-2010-0002).

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