Patent ID: 6851328

Claim:
In a transmission including: first and second transmission lines disposed in parallel between an upstream transmission shaft for receiving power from an engine and a downstream transmission shaft for transmitting the power to a traveling unit; a hydraulic multiple disc transmission clutch disposed transmission-wise downstream of the first and second transmission lines, the power of the upstream transmission shaft being transmitted via one of the first and second transmission lines to the downstream transmission shaft; a first gear change-speed mechanism disposed between either the upstream transmission shaft or the downstream transmission shaft and the first transmission line, the first gear change-speed mechanism having a plurality of speed positions; a first actuator for operating the first gear change-speed mechanism; a first friction clutch incorporated in the first transmission line; a second gear change-speed mechanism disposed between either the upstream transmission shaft or the downstream transmission shaft and the second transmission line, the second gear change-speed mechanism having a plurality of speed positions; a second actuator for operating the second gear change-speed mechanism; a second friction clutch incorporated in the second transmission line; and a control apparatus for controlling the transmission, said control apparatus comprising: first controlling means and second controlling means; wherein (i) when the power is being transmitted via the first transmission line, in response to a shift of the second gear change-speed mechanism into a predetermined speed position by means of the second actuator, the first controlling means operates the transmission clutch from its transmitting state to its semi-transmitting state by reducing its working pressure to one set by said first control means while operating the first friction clutch from its transmitting state to its non-transmitting state and the second friction clutch from its non-transmitting state to its transmitting state; and (ii) when the power is being transmitted via the second transmission line, in response to a shift of the first gear change-speed mechanism into a predetermined speed position by means of the first actuator, the second controlling means operates the transmission clutch from its transmitting state to its semi-transmitting state by reducing its working pressure to one set by said second control means while operating the first friction clutch from its non-transmitting state to its transmitting state and the second friction clutch from its transmitting state to its non-transmitting state.