Patent ID: 9127436
Filing Date: 2015-09-08
Classification: B60W,B60Y,E02F,F02D

Abstract:
1. An engine output control system for a work vehicle composed of an engine, a travel device and a power transmission unit, the power transmission unit including a torque converter and transmitting an output of the engine to the travel device via the torque converter, the engine output control system comprising: a fuel dial configured to be operated by an operator; a target engine speed setting portion configured to set a target value of an engine rotational speed of the engine according to an operating amount of the fuel dial; a speed ratio computation portion configured and arranged to compute a speed ratio of the torque converter; a determination portion configured and arranged to determine whether the computed speed ratio is equal to or less than a speed ratio threshold set in advance, the speed ratio threshold being smaller than a speed ratio at which a torque ratio of the torque converter corresponds to a maximum efficiency of the torque converter, the speed ratio threshold being a speed ratio equal to and below which the vehicle operates in a state selected from the group consisting of a nearly stalled state and a completely stalled state, the nearly stalled state being when the speed ratio is roughly zero and the completely stalled state being when rotation of an output side of the torque converter is stopped, and above which the vehicle does not operate in a state selected from the group consisting of the nearly stalled state and the completely stalled state; a storage unit configured and arranged to store data indicative of a relationship between the speed ratio of the torque converter and a plurality of torque lines defining an output torque of the engine with respect to the engine rotational speed, the data including at least a maximum torque line, a middle torque line, and a lowest torque line such that the output torque with respect to the engine rotational speed is largest with the maximum torque line, smaller with the middle torque line than with the maximum torque line, and smaller with the lowest torque line than with the medium torque line; and an engine output reduction control portion configured and arranged to perform a reduction control of the output torque of the engine when the computed speed ratio is equal to or less than the speed ratio threshold, the engine output reduction control portion being configured to execute the reduction control of the output torque by referring to the data stored in the storage unit and selecting one of the torque lines other than the maximum torque line in accordance with a difference between the computed speed ratio and the speed ratio threshold such that the output torque of the engine is reduced in comparison with the maximum torque line without changing the target value of the engine rotational speed, the selected torque line being shifted downward toward the lowest torque line as the difference between the computed speed ratio and the speed ratio threshold increases, the downward shifting of the selected torque line being executed in stages to discrete torque lines.