Gear-shift mechanism for manual transmission

Claim 1

A gear-shift mechanism for a manual transmission comprising a housing for said transmission; a movable shaft mounted in place within said housing for both axial and rotary movements and being operatively connected to a manual shift lever to be axially shifted from its neutral position to a forward or reverse position in selecting operation of said manual shift lever and to be rotated at its shifted position in shifting operation of said manual shift lever; a shift-and-select lever fixed to an intermediate portion of said movable shaft; an interlock member rotatably mounted in place on said movable shaft and having a pair of interlock arms located at the opposite sides of said shift-and-select lever; means for restricting rotary movement of said interlock member and permitting axial movement of the name; a pair of resilient means for centering said movable shaft to retain said shift-and-select lever and said interlock member in their neutral positions; and first, second and third shift heads arranged in sequence within said housing, said first and second shift heads each being operatively connected to first and second synchronizers respectively for establishing first and second speed gear trains and for establishing third and fourth speed gear trains, said third shift head being operatively connected to a shift fork for establishing a reverse gear train, and each of said shift heads being integrally formed with a pair of projections to be brought into engagement with said shift-and-select lever; and in which said shift-and-select lever is engaged in its neutral position with the projections of said second shift head such that said interlock arms are respectively in engagement with the projections of said first and third shift heads to retain them in their neutral positions; said gear-shift mechanism being characterised in that a cam member is fixed to said movable shaft at one side of said interlock member; and a spring loaded cam follower element is assembled within said first shift head and positioned to engage a cam face of said cam member when said movable shaft is shifted to the reverse position against one of said resilient means to effect engagement of said shift-and-select lever with the projections of said third shift head, said cam follower element being arranged to disengage from the cam face of said cam member after said movable shaft is rotated at its reverse position to effect shift movement of said third shift head for establishment of said reverse gear train; and that one of said interlock arms is formed at one side thereof with a recess which is positioned to permit slight shift movement of said first shift head caused by engagment of said cam follower element with the cam face of said cam member during the shift movement of said third shift head, whereby said first synchronizer is temporarily operated in response to the slight shift movement of said first shift head to effect synchronous rotation of input and output shafts of said transmission prior to establishment of said reverse gear train.