Reduction of Handball Impulse Forces Produced in Synchromesh Gear Boxes by Parametric Analysis of Synchronizer Pack Design

Reduction of Handball Impulse Forces produced in Synchromesh Gear Boxes by Parametric analysis of Synchronizer-Pack Design

Abhisek Chandra Dev V1 and Dr. Marimuthu P2

Abstract— Bulk of the heavy vehicles in use operate on manual transmissions with synchromesh type gear boxes. Here the lack of high speed performance necessities and frequent service requirements resulted in persistent usage of less complex Single and Dual cone synchronizers. However the greater Torque-capacity requirements and ever increasing focus on Ergonomic comfort for the driver have put the spotlight back onto synchronizer technologies. This document deals with the parametric value changes that can bring in more comfort while operating manual transmissions with synchronizers and also the possible use of Triple cone synchronizers for the first time in commercial Vehicles.

1. INTRODUCTION

Synchronizer technologies have long been in use, in man- ual transmissions, albeit with different companies having their own technique of synchronizing, to suit their own transmission systems. More robust and complex synchroniz- ers are used in cars/light vehicles, where compactness and efficiency at high speeds are crucial. However, in commercial vehicles, the synchronizers are limited to less complex single cone type synchronizers mostly and sparsely, double cone synchronizers for low speed gears.

In this paper we emphasize on parameters that have predominant impact on impulse forces generated. Impulse forces are a sum of 1) Product of Shift force applied and the Synchronization time and 2) Reaction forces offered by the gear box components during the gear shifts. The reaction forces change with the each gear box and the gear that is engaged. But they constitute only a fraction of the impulse forces generated. Hence we look at the primary cause that is the shift force applied. By reducing the shift force applied   at the handball, we can decrease the effort of the driver and also the impulses the driver would experience. But reducing the shift effort would decrease the friction torque necessary to achieve the synchronizing required. Hence, we look at the parameters involved in the friction torque production and explore the possibilities of achieving the required friction torque by altering these parameters with a reduced shift effort for a gear shift.

1. EXPERIMENTATION PROCEDURE

1. Equipment, Apparatus and Software requirements

A 6 Speed (+Reverse) 700-Nm torque capacity gear box of a medium commercial vehicle is considered and its synchro-

1Abhisek Chandra Dev V, M.Tech Automobile Engineer-  ing(Integrated), SASTRA University, Thanjavur, India , 613402 117107002@sastra.ac.in

2Dr.    Marimuthu    P,     is    with    the    Department    of    Mechanical

Engineering,        SASTRA        University,        Thanjavur,        India,        613402

marimuthu@mech.sastra.edu

pack design is taken for the parametrical analysis. The analysis is done in Ricardo Synchro Prediction Software.

1. Parameters involved

The friction torque is a function of number of friction cones in the  synchro-pack(n),  co-efficient  of  friction(µ)  of the friction lining used on  the  synchro  cones,  effec-  tive diameter(dm) of the friction cone used, shift force applied(Fa) and cone angle(α).

Number of cones in the synchro-pack is determined by the friction torque requirements, affordable pack length and the complexity allowed. Co-efficient of friction is a constant, for a given friction material, however its variance with temperature gradient has to be considered when analyzing the synchronizer performance. Effective diameter of the synchro cone is limited by the gear size and the centre distance between the main shaft and lay shaft. Cone angles are limited by the locking torque (premature locking of the synchro cones). Here, the friction material chosen is crucial because, each material has its own co-efficient of friction. Lower cone angles increase the friction production and greater the friction greater the chance of premature locking to occur. In the gear box chosen, the friction material is Molybdenum (Mo) and the cone angles are at 6.5◦ for single cones and 9◦ for double cones.

1. Approach

Friction material choice is persisted with molybdenum, because changing it would require changes in the transmis- sion fluid used, no. of grooves on the synchro ring and other factors that account for lubrication and cooling of synchro rings. For the Molybdenum synchro cones, the minimum cone angle should be 6.5◦ to avoid premature locking. The centre distance between the shafts available in this gear box is 145 mm. The mean effective diameter of the synchro cones is at 130 mm. Thus there is room for potentially increasing the diameter to 180mm after accounting the necessary room for the sleeve blocker ring teeth etc. The other option is       to increase the no. of cones. But this increases the no. of components, synchro-pack length and the complexity of the synchro pack with all the linking mechanisms to keep the synchro rings in place. They also increase the overall length and production cost of synchronizers.

1. MATH

The equation for friction torque calculation is considered and the torque produced with the available parametric values is calculated. The obtained value is taken as a bench mark

and is used to optimize the function parameters so as to reduce the shift effort without compromising the friction torque production.[pic 1]

1. Equations

Friction Torque,

T  = nµdmFa R        2 sin α

(1)

(n)        - Number of friction cones in the synchro-pack (µ)        - Co-efficient of friction

(dm)        - Effective diameter of the friction cone