Design of a Single Rail Internal Gear Shift System for a 5 Speed Manual Transmission 2013-01-1771

This paper presents the detailed design of a Single Rail Internal Gear Shift System for a 5-speed manual transmission of a load carrier vehicle. Gear shifting in manual transmissions is achieved by actuating a synchronizer sleeve and engaging it with the required gear. Actuation of synchronizer sleeves is effected by gear shift forks which are supported in the transmission by a rail/shaft. Conventional 5-speed transmissions use Multi Rail Gear shift systems, wherein each of the forks viz. Fork 1-2, Fork3-4 & Fork 5^th, for actuating the synchronizer sleeves, are supported by and fixed to individual rails. This paper presents the design of a Single Rail Gear shift system, wherein all the gear shift forks will be supported on a common rail/shaft, thus making the entire system compact and reducing the system weight. The Single Rail, in the proposed design, apart from supporting the three forks, also serves to actuate the Reverse Gear, which is of sliding mesh type in this case.

All the three forks used in the design are Aluminium die cast forks. The Forks 1-2 & 3-4 are of sliding type, and slide over the stationary rail, while actuating the respective synchronizer sleeves. These two forks have an integral rail end within them. The rail end is a sheet metal part, inserted within the fork during die casting process itself, thus integrating two parts and making the design simple. Further simplifying the design, rail ends inserted within the forks 1-2 & 3-4, have been made common, thus reducing the cost of component development also.

Fork 5^th, in this design, is fixed to the rail by a pin. The actuating rail end and reverse gear actuating finger are also pinned to the rail. Thus during both 5^th & Reverse gear actuations, the entire rail moves along with Fork 5^th, Rail end and Reverse finger. Care has been taken in the design to ensure that Reverse gear doesn't get actuated during 5^th gear engagement, as actuating members of both the gears are fixed to the rail and move together. Detailed CAE simulations have been performed to ensure the stiffness of the aluminium forks and strength of the entire system. Chamfers on the rail ends of forks have been designed in correlation with the chamfers of the H-Gate on Shift tower to ensure a smooth diagonal shifting between gears.

The design can also be used for a 4 speed transmission of load carriers with lesser payload capacity, by eliminating fork 5^th. An overall weight reduction of about 500 grams has been achieved in this design, in comparison to a Multi rail gear shift system.