Totally synchronized manual transmission unit for use in a vehicle

A gear-shift mechanism for a manual transmission unit for use in a motor vehicle, comprising:

• a housing assembly;
• an input shaft for connection to an engine;
• an output shaft supported in a parallel relationship to the input shaft within the housing assembly;
• a forward input gear integrally attached to the input shaft;
• a forward output gear mounted on the output shaft and constantly meshing with the forward input gear;
• synchronizing means which are slidably mounted on one of the input and output shafts and rotatable therewith;
• first actuating means for shifting the synchronizing means toward or away from one of the forward input or output gears;
• a reverse input gear integral with the input shaft;
• an idler shaft supported in a parallel relationship with the input and output shafts within the housing assembly;
• a reverse sliding gear mounted on the idler shaft;
• a reverse output gear mounted on the output shaft;
• second actuating means for shifting the reverse sliding gear into meshing engagement with the reverse input and output gears;
• a manual shift lever for changing gearing ratios between the input shaft and the output shaft;
• a shift-and-select shaft supported in a parallel relationship with the input and output shafts within the housing assembly and operatively connected to the manual shift lever;
• a fork shaft slidably supported in a parallel relationship with the idler shaft within the housing assembly and operatively connected to the manual shift lever for being selectively shifted by the operation between its neutral, forward and reverse positions;
• a detent mechanism mounted in the housing assembly to retain selectively the fork shaft in its neutral or shifted positions when subjected to a resilient load acting thereon, the detent mechanism comprising a first holder member and a second holder member, the first holder member being slidable on the shift-and-select shaft and rotatable relative to the housing assembly, rotation of the first holder member resulting in the movement of said synchronizing means, the first holder member having a first projection, a slot for permitting the rotation of the first holder member when shifting into reverse speed and a pawl which prevents a double shift in association with the first actuating means, the pawl including a means for retaining one of the synchronizing means associated with the reverse gear in its neutral position when the manual shift lever is shifted to a reverse speed, the second holder member having an engagement member which selectively engages with the first holder member, corresponding to the retained neutral position of one of the synchronizing means;
• and
• rotating means rotated by the manual shift lever, having a second projection engaged with the first projection of the first holder member when the first holder member slides upon shifting into reverse speed, rotation of the manual shift lever resulting in the rotation of the rotating means because of the engagement between the first projection and the second projection, this resulting in the effect of the synchronizing means for a forward speed, whereby when the manual shift lever is shifted to a reverse speed, the synchronizing means for a forward speed are effected to stop the rotation of the input shaft by inertia and the synchronizing means associated with the reverse gear is maintained to its neutral position by the engagement member of the second holder member.