Hydrostatic Transmission Brake Torque Control
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Solution Overview
Problem
Work vehicles equipped with hydrostatic transmissions experience strong deceleration when the accelerator pedal is turned off, leading to difficulties in gentle coasting and reduced fuel efficiency, especially during downhill travel.
Innovation Solution
A control method that reduces brake torque by adjusting the differential pressure between hydraulic circuits in the hydrostatic transmission based on the deviation between actual and target engine rotation speeds or accelerator operation, using a controller with a low-pass filter and relief valve to manage the displacement of the travel pump and motor, allowing for smoother coasting and improved fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the accelerator pedal is turned off in a work vehicle equipped with a hydrostatic transmission, then the engine brake and hydrostatic transmission brake act together, but the deceleration becomes too strong and gentle coasting cannot be achieved
Solution Approach 1:
The patent dynamically changes the differential pressure parameter in the hydrostatic transmission based on vehicle speed and accelerator operation. When coasting is detected (accelerator off and vehicle speed above threshold), the control device reduces the differential pressure between the first and second hydraulic circuits, which reduces the brake torque and enables gentle coasting. This parameter adjustment resolves the contradiction by making the deceleration rate controllable rather than fixed.
Solution Approach 2:
The patent introduces dynamic control of the hydrostatic transmission brake torque based on real-time detection of coasting conditions. The control device continuously monitors vehicle speed and accelerator operation, and dynamically adjusts the differential pressure accordingly. This transforms the static brake system into a dynamic one that can adapt to different driving conditions, enabling gentle coasting when needed while maintaining strong braking when required.
2Reliability
If the accelerator pedal is turned off during downhill travel in a work vehicle equipped with a hydrostatic transmission, then the hydrostatic transmission brake stops the vehicle, but fuel efficiency is reduced because the operator must actively depress the accelerator
Solution Approach 1:
The patent adjusts the differential pressure parameter based on vehicle speed and coasting detection. During downhill coasting, when the vehicle speed is above the threshold and the accelerator is off, the control device reduces the differential pressure to minimize brake torque. This allows the vehicle to maintain speed without active accelerator input, improving fuel efficiency while still providing reliable braking when needed.
Solution Approach 2:
The patent implements a feedback control system that monitors vehicle speed and accelerator operation to detect coasting conditions. Based on this feedback, the control device automatically adjusts the hydrostatic transmission brake torque by modifying the differential pressure. This closed-loop control ensures that the brake system responds appropriately to driving conditions, maintaining reliability while reducing fuel consumption during coasting.
3Ease of operation
If the differential pressure in the hydrostatic transmission is reduced during coasting, then gentle coasting travel is achieved, but the brake torque control precision must be improved
Solution Approach 1:
The patent employs dynamic adjustment of the differential pressure based on real-time detection of coasting conditions (vehicle speed and accelerator operation). The control device continuously modifies the brake torque during coasting to maintain smooth deceleration. This dynamic control approach balances the need for smooth coasting with adequate control precision by adapting the brake torque to the specific driving conditions rather than using a fixed control strategy.
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
Enables easy gentle coasting travel and enhances fuel efficiency by reducing hydrostatic transmission brake torque, allowing the vehicle to maintain speed with the accelerator pedal off, particularly during downhill travel.
Implementation Method 1
The controller may output a command signal indicative of the target displacement to the travel pump through the low-pass filter
Implementation Method 2
The controller may reduce the relief pressure according to the deviation between the actual rotation speed of the engine and the target rotation speed or in accordance with the operation amount of the accelerator operating member when the vehicle is in the coasting deceleration
Data Source
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AI summary
A controller determines a target rotation speed of an engine from an operation amount of an accelerator operating member. The controller determines whether a vehicle is in coasting deceleration. The controller decreases a differential pressure between a first circuit and a second circuit of a hydraulic circuit according to a deviation between an actual rotation speed of the engine and the target rotation speed, or the operation amount of the accelerator operating member when the vehicle is in the coasting deceleration.