Downshift inhibitor

A downshift control for a manually shifted, multiple-speed vehicular transmission having a first (first/second), a second (third/fourth) and a third (fifth/sixth) manually selectable ratio, said first ratio intended for lower vehicle ground speed operation than said second ratio, and said second ratio intended for lower vehicle ground speed operation than said third ratio, said first ratio having a first predetermined maximum vehicle ground speed at which downshift engagement thereof is allowed and said second ratio having a second predetermined maximum vehicle ground speed, greater than said first predetermined maximum vehicle ground speed, at which downshift engagement thereof is allowed, said transmission including a shift mechanism having a shaft manually movable in a selection direction (Y--Y) to a first position for selection of engaging and disengaging said first ratio, to a distinct second position for selection of engaging and disengaging said second ratio, and to a distinct third position for selection of engaging and disengaging said third ratio, said second position located intermediate to said first and third positions in said selection direction, said shaft movable in an engagement/disengagement direction (X--X), distinct from said selection direction, to cause engagement and disengagement of a selected ratio, said control characterized by:

• control means for sensing a value (OS) indicative of current vehicle ground speed and for comparing said value indicative of current vehicle ground speed to a first reference value (REF.sub.1) corresponding to said first predetermined maximum vehicle ground speed and to a second reference value (REF.sub.2) corresponding to said second predetermined maximum vehicle ground speed,
• mechanical blocking means (216) responsive to control signals from said control means having (i) a non-blocking position (216A) when said value indicative of ground speed is less than said first reference value (OS<REF.sub.1 <REF.sub.2) wherein said shaft is not blocked from movement between said first, second and third positions thereof in the selection direction;
• (ii) an intermediate blocking position (216B) for blocking movement of said shaft to said first position in said selection direction, but allowing movement of said shaft to said second position in said selection direction, if said value indicative of vehicle ground speed is greater than said first reference value but less than said second reference value (REF.sub.2 >0S>REF.sub.1);
• and (iii) a fully blocking position (216C) for blocking movement of said shaft, both to said first and said second positions thereof, in said selection direction if said value indicative of vehicle ground speed is greater than said second reference value (OS>REF.sub.2 >REF.sub.1).