Hydromechanical Transmission Hill-Hold Without Parking Brake Wear
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Solution Overview
Problem
Existing hydromechanical transmissions, such as those employing Dix's hill-hold strategy, face inefficiencies and poor performance due to reliance on parking brakes, which can lead to unwanted vehicle movement on slopes and degradation issues, and may fail to prevent vehicle slide when restarting on hills.
Innovation Solution
A hydromechanical transmission system that selectively transitions between torque and speed control modes using a hydrostatic assembly with a hydraulic pump and motor, employing clutch blocking and pre-load pressure management to maintain vehicle standstill on slopes without mechanical brakes, reducing the chance of backsliding and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the parking brake is used to hold the vehicle stationary on a slope, then the vehicle can be held in place, but the parking brake degrades and may fail to prevent unwanted vehicle movement
Solution Approach 1:
The patent extracts the hill-hold function from the parking brake system and implements it through the hydrostatic assembly. The controller commands the hydrostatic assembly to provide holding force on slopes, separating this function from the parking brake which is then only used for mechanical parking. This resolves the contradiction by eliminating the degradation issue while maintaining hill-hold capability.
Solution Approach 2:
The patent replaces the mechanical parking brake system with a hydrostatic system for hill-hold operations. The hydrostatic assembly uses fluid pressure rather than mechanical friction to provide holding force, eliminating wear and degradation while maintaining reliable hill-hold performance across extended duration.
2Reliability
If the hydrostatic assembly is pressurized during hill-hold operation, then the vehicle is held stationary, but transmission efficiency decreases due to energy consumption
Solution Approach 1:
The patent implements dynamic control of the hydrostatic assembly by transitioning between speed control mode and torque control mode. During hill-hold, the system uses speed control mode to maintain standstill with minimal pressurization, then switches to torque control mode when clutches engage and blocking is achieved, allowing pressure reduction while maintaining holding capability through mechanical blocking.
Solution Approach 2:
The patent applies preliminary action by engaging the forward and reverse drive clutches to achieve mechanical blocking before reducing hydrostatic pressure. This pre-establishes the mechanical hold path so that the hydrostatic assembly can be depressurized without compromising vehicle hold capability, thereby improving transmission efficiency.
3Productivity
If the vehicle is restarted from standstill on a hill, then movement is resumed, but the vehicle may slide in unwanted direction due to pressure reduction
Solution Approach 1:
The patent implements feedback control through the controller that monitors vehicle conditions and adjusts hydrostatic assembly operation accordingly. During restart from standstill, the controller commands the hydrostatic assembly to re-pressurize based on stored differential pressure values, providing feedback-based pressure adjustment that prevents unwanted vehicle movement while enabling smooth restart.
Solution Approach 2:
The patent stores differential pressure values during hill-hold operation for use during restart. This preliminary storage of pressure information enables the controller to quickly re-pressurize the hydrostatic assembly in the correct amount during restart, preventing vehicle slide while maintaining productivity.
4Use of energy by moving object
If clutch blocking is used to hold transmission output stationary, then transmission efficiency improves, but the system complexity increases
Solution Approach 1:
The patent makes the hydrostatic assembly multi-functional by using it for both hill-hold operation and for providing the pressure storage function needed during restart. This universal use of the same component for multiple purposes reduces overall system complexity despite the added clutch blocking mechanism, as no additional dedicated components are required.
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
The system effectively holds the vehicle stationary on slopes, reduces fuel consumption by allowing lower engine speeds during restarts, and enhances transmission efficiency by minimizing pressurization during hill-hold operations, while preventing unwanted movement when transitioning from standstill to drive.
Implementation Method 1
a hydrostatic assembly with a hydraulic pump and motor in fluidic communication with one another
Data Source
AI summary
Methods and systems for a hydromechanical transmission in a vehicle are provided herein. In one example, the transmission system includes a hydrostatic assembly with a hydraulic pump in fluidic communication with a hydraulic motor. The transmission system further includes a controller configured to selectively transition between a torque control mode and a speed control mode of the hydrostatic assembly while the vehicle is on a slope.