Hydrostatic Transmission Hill-Holding via Pump Displacement Control
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Solution Overview
Problem
Existing work vehicles with hydrostatic transmissions face challenges in safely controlling movement on sloped terrains, particularly preventing downhill movements on inclines.
Innovation Solution
A hydrostatic transmission system with an electronically-controlled variable displacement hydraulic pump and motor, monitored by sensors for accelerator pedal position, vehicle speed, and hydraulic line pressures, activates a hill-holding function in the electronic control unit to prevent unwanted downhill movements by adjusting pump and motor displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hill-holder function is implemented using existing solutions (rotation angle detection, retarder valve, or hydrostatic braking), then the vehicle can be kept stationary on sloped terrains, but the system complexity increases due to additional sensors, valves, or control mechanisms
Solution Approach 1:
The electronic control unit is programmed to perform multiple functions: normal hydrostatic transmission control, hill-detection, and hill-holding control. The same hydraulic pump and motor serve both propulsion and hill-holding functions, eliminating the need for separate dedicated components for each function.
Solution Approach 2:
The system uses its own existing sensors (accelerator pedal position sensor, speed sensor, pressure sensors) and actuators (variable displacement pump and motor) to perform hill-holding, rather than requiring external dedicated components. The control unit processes signals from existing sensors and actuates existing components to achieve hill-holding.
2Reliability
If traditional hill-holder solutions are used (retarder valve or separate braking system), then downhill movement can be prevented, but the ease of operation deteriorates as the operator cannot easily disengage the function
Solution Approach 1:
The system continuously monitors the accelerator pedal position sensor signal and speed sensor feedback to determine when hill-holding is needed. The control unit adjusts the hydraulic pump and motor based on this feedback, and the operator can disengage the function by simply pressing the accelerator pedal, which the system detects and responds to automatically.
3Adaptability or versatility
If an electronically-controlled variable displacement hydraulic pump and motor are used, then the hill-holding function can be integrated into the existing transmission system, but the device complexity increases due to electronic control components
Solution Approach 1:
The hill-holding control functions are merged with the existing electronic control of the variable displacement hydraulic pump and motor. The same electronic control unit that controls transmission operation is also programmed to perform hill-detection and hill-holding control, combining multiple functions into a single integrated control system.
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
Effectively keeps the vehicle stationary on sloped terrains by controlling the hydrostatic transmission to counteract downhill movements, ensuring safe operation without operator intervention when the accelerator is released.
Implementation Method 1
a hydrostatic transmission comprising a hydraulic pump driven by the engine and a hydraulic motor for driving the wheels, the hydraulic pump and the hydraulic motor of the hydrostatic transmission being hydraulically connected to each other by means of a forward line and a backward line of a hydraulic circuit
Implementation Method 2
the electronic control unit is programmed to generate a hill-holding control signal depending on the accelerator pedal position sensor signal, a speed sensor signal, a first pressure sensor signal on the forward line and a second pressure sensor signal on the backward line
Data Source
Figure 1
Figure 2
AI summary
The hydrostatic transmission (100) for a work vehicle (10) comprises: a hydraulic pump (30) and a hydraulic motor (32) hydraulically connected in a closed hydraulic circuit (1), the hydraulic pump (30) being mechanically coupled to a combustion engine (28) of the vehicle (10), and the hydraulic motor (32) being mechanically connected to driving wheels (16) of the vehicle (10); and an electronic control unit (ECU) configured to adjust the displacement of the hydraulic pump (30) and of the hydraulic motor (32) based on information relating to: the position of an accelerator pedal (A) of the vehicle (10), the speed (vv) of the vehicle (10), the pressure on a forward line (101) and on a backward line (102) of the hydrostatic transmission (100) provided by sensors (111, 112, 113); wherein the electronic control unit (ECU) is programmed with a hill-holding function such that when the electronic control unit (ECU) establishes that the accelerator pedal (A) is released, but the vehicle (10) is nevertheless moving downhill, the electronic control unit (ECU) controls the hydraulic pump (30) and the hydraulic motor (32) so that the downhill movement is prevented.