Shift Power Transmission Apparatus and Travel Power Transmission Device

A shift power transmission apparatus comprising:

• an input shaft receiving engine drive force;
• a hydraulic continuously variable transmission driven by the input shaft;
• a planetary power transmission section combining the drive force from the input shaft and an output from the hydraulic continuously variable transmission for outputting the combined drive force therefrom;
• and
• an output rotary member outputting power to a travel apparatus,
• wherein a forward/reverse switching mechanism is provided to be switchable between a forward power transmission state for converting the drive force from the input shaft into forward drive force to be transmitted to the planetary power transmission section, and a reverse power transmission state for converting the drive force from the input shaft into reverse drive force to be transmitted to the planetary power transmission section, and
• the forward/reverse switching mechanism is further switchable to a neutral state in which power transmission between the input shaft and the planetary power transmission section is cut off;
• and
• wherein a clutch mechanism is provided for switching interlock from the motor shaft of the hydraulic continuously variable transmission to the output rotary member between an on state and an off state.

A travel power transmission apparatus comprising:

• a shift power transmission device including a hydrostatic continuously variable shift section and a planetary power transmission section;
• the hydrostatic continuously variable shift section receiving drive force from an engine and outputting the drive force after changing speed of the drive force along an HST shift line by the continuously variable shift section;
• and the planetary power transmission section receiving and combining the drive force from the engine and the speed-changed drive force from the continuously variable shift section, and outputting the combined drive force after changing speed of the combined drive force along an HMT shift line by the continuously variable shift section;
• the shift power transmission device further including a clutch mechanism switchable between an HST setting state in which HST power transmission is set for outputting the speed-changed drive force from the continuously variable shift section to a travel apparatus, and an HMT setting state in which HMT power transmission is set for outputting the combined drive force from the planetary power transmission section is outputted to the travel apparatus;
• and
• a shift control module for performing shift control on a hydraulic pump of the continuously variable shift section and switch control on the clutch mechanism, based on a shift instruction from a shift operation device,
• wherein the travel power transmission apparatus further comprises:
• a swash plate angle sensor detecting a swash plate angle of the hydraulic pump;
• and
• a shift swash plate angle setting module for setting, as a set shift swash plate angle of the hydraulic pump, the swash plate angle between a no-load swash plate angle and a load swash plate angle, wherein the no-load swash plate angle is achieved by the hydraulic pump in a shift state for outputting speed-changed drive force at a speed corresponding to an in-unison rotation achievement speed at which the continuously variable shift section achieves in-unison rotation of a sun gear, a carrier and a ring gear of the planetary power transmission section during the HST power transmission and no-load driving, and wherein the load swash plate angle is achieved by the hydraulic pump in a shift state for outputting the speed-changed drive force at a speed corresponding to the in-unison rotation achievement speed of the continuously variable shift section during the HST power transmission and set load driving;
• and
• wherein the shift control module is configured to control the clutch mechanism to be switched from the HST setting state to the HMT setting state when the swash plate angle sensor detects the swash plate angle equal to the set shift swash plate angle.

A travel power transmission apparatus comprising:

• a shift power transmission device including a hydrostatic continuously variable shift section and a planetary power transmission section;
• the hydrostatic continuously variable shift section receiving drive force from an engine and outputting the drive force after changing speed of the drive force along an HST shift line by the continuously variable shift section;
• and the planetary power transmission section receiving and combining the drive force from the engine and the speed-changed drive force from the continuously variable shift section, and outputting the combined drive force after changing speed of the combined drive force along an HMT shift line by the continuously variable shift section;
• the shift power transmission device further including a clutch mechanism switchable between an HST setting state in which HST power transmission is set for outputting the speed-changed drive force from the continuously variable shift section to a travel apparatus, and an HMT setting state in which HMT power transmission is set for outputting the combined drive force from the planetary power transmission section is outputted to the travel apparatus;
• and
• a shift control module for performing shift control on a hydraulic pump of the continuously variable shift section and switch control on the clutch mechanism, based on a main shift instruction from a main shift operation device,
• wherein a hydraulic motor of the continuously variable shift section is provided in form of a variable displacement motor,
• the travel power transmission apparatus further comprises an auxiliary shift operation device which is manually operable to issue an auxiliary shift instruction, and an auxiliary shift actuator operable to change a swash plate angle of the hydraulic motor,
• the shift control module is configured to control the auxiliary shift actuator such that the hydraulic motor is shifted to a higher speed side based on the auxiliary shift instruction, and
• wherein the travel power transmission apparatus further comprises a restraint control module, the restraint control module being configured such that:
• when the shift power transmission device is set to the HMT power transmission, and when a power transmission state is achieved in which the combined drive force to be outputted to the travel apparatus is increased in response to a speed-increase shift operation in a reverse shift range of the continuously variable shift section, and in which the combined drive force to be outputted to the travel apparatus is decreased in response to a speed-decrease shift operation in the reverse shift range of the continuously variable shift section, the restraint control module cancels restraint to permit control on the auxiliary shift actuator by the shift control module;
• and
• when the shift power transmission device is set to the HMT power transmission, and when a power transmission state is achieved in which the combined drive force to be outputted to the travel apparatus is increased in response to a speed-decrease shift operation in the forward shift range of the continuously variable shift section, and in which the combined drive force to be outputted to the travel apparatus is decreased in response to a speed-increase shift operation in the forward shift range of the continuously variable shift section, the restraint control module performs restraint to stop control on the auxiliary shift actuator by the shift control module.