HST Relief Pressure Control for Stable Work Vehicle Torque
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Solution Overview
Problem
The pressure in the HST circuit of a continuously variable transmission in work vehicles can increase rapidly due to load fluctuations during operations like excavation and braking, leading to excessive output torque and reduced riding comfort.
Innovation Solution
A control device for a work vehicle that includes a relief pressure setting unit to adjust the relief pressure of the relief valve in the hydrostatic continuously variable transmission based on a target output value, preventing rapid changes in output torque by managing the pressure differential between hydraulic paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the relief pressure of the HST circuit is increased to handle load fluctuations, then the output torque increases more than necessary, but riding comfort deteriorates
Solution Approach 1:
The relief pressure is made dynamically adjustable based on operating conditions. The control device varies the relief pressure according to the operation amount of the accelerator pedal, making the system adaptive rather than static. This allows the relief pressure to be high when needed (during acceleration) and low when not needed (during cruising), resolving the contradiction between handling load fluctuations and maintaining riding comfort.
Solution Approach 2:
The relief pressure parameter is changed based on accelerator pedal operation. When the accelerator pedal operation amount exceeds a threshold, the relief pressure is increased to a higher value; otherwise, it is maintained at a lower value. This parameter change strategy allows the system to optimize performance under different operating conditions, preventing excessive torque during normal operation while providing sufficient torque during acceleration.
2Speed
If the relief pressure is set high to prevent torque drop during acceleration, then acceleration performance improves, but torque increases excessively during cruising
Solution Approach 1:
The relief pressure is dynamically adjusted based on accelerator pedal operation. During acceleration (when pedal operation exceeds threshold), high relief pressure prevents torque drop and maintains acceleration performance. During cruising (when pedal operation is below threshold), low relief pressure prevents excessive torque, resolving the contradiction between acceleration performance and cruising power efficiency.
Solution Approach 2:
The relief pressure parameter changes based on operating conditions detected via accelerator pedal position. The control device switches between two relief pressure values (higher and lower) depending on whether the accelerator pedal operation amount exceeds a predetermined threshold, optimizing both acceleration and cruising performance.
3Device complexity
If a fixed relief pressure is used, then the system structure is simple, but the system cannot adapt to varying operating conditions
Solution Approach 1:
The relief pressure control system transitions from a fixed static design to a dynamic adaptive design. The control device monitors accelerator pedal operation and automatically adjusts relief pressure accordingly, providing adaptability to varying operating conditions while maintaining relatively simple implementation through electronic control.
Solution Approach 2:
The relief pressure parameter is made variable based on accelerator pedal operation. The control device changes the relief pressure between two predetermined values depending on whether the accelerator pedal operation amount exceeds a threshold, enabling the system to adapt to different operating conditions without requiring complex control mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively stabilizes the output torque, enhancing riding comfort by maintaining the HST circuit pressure within a target range, even during load fluctuations, thereby preventing sudden changes in engine rotation speed and vehicle jerking.
Implementation Method 1
a hydrostatic continuously variable transmission having a relief valve capable of setting a relief pressure
Implementation Method 2
a power transmission device that includes a hydrostatic continuously variable transmission and is configured to transmit power of the power source to the travel device
Data Source
AI summary
A work vehicle includes a power source, a travel device, a power transmission device, and a control device. The power transmission device includes a hydrostatic continuously variable transmission having a relief valve capable of setting a relief pressure, and is configured to transmit power of the power source to the travel device. The control device includes a relief pressure setting unit configured to set the relief pressure of the relief valve in accordance with a target output value of the travel device.