Drivetrain Layout with CVT and Peak Torque Limiting
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Solution Overview
Problem
Vehicles operating in off-road conditions face challenges with transient torque events, leading to slip conditions in CVTs due to inadequate clamp load, and hydraulic clamping issues at high engine velocities, which can damage drivetrain components.
Innovation Solution
A drivetrain layout incorporating a primary gear reduction, steel belt CVT, and a peak torque limiting (PTL) device, which reduces primary pulley speed, manages torque transients, and protects the drivetrain from hydraulic clamping through a mechanical limiting mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a CVT is used to manage torque in off-road vehicles, then continuous variable transmission is achieved, but slip conditions occur between belt and pulleys under transient torque events
Solution Approach 1:
The launch clutch engages before the CVT operates, providing preliminary torque management and preventing transient torque from reaching the CVT belt-pulley interface. This preliminary action protects the CVT from shock loads during vehicle launch and transient conditions.
Solution Approach 2:
The launch clutch acts as an intermediary component between the engine and CVT, absorbing and managing transient torque events. This mediator prevents direct transmission of shock loads to the belt-pulley interface, ensuring reliable grip while maintaining CVT functionality.
2Extent of automation
If control strategies are used to manage transient torque, then active control is implemented, but reaction time is too slow to prevent damage
Solution Approach 1:
The mechanical launch clutch replaces electronic control strategies for transient torque management. The mechanical engagement and slip characteristics provide instantaneous response to torque events, eliminating the time delay inherent in sensor-based electronic control systems.
Solution Approach 2:
The launch clutch automatically engages and slips in response to transient torque events without requiring external control signals. The system self-regulates torque transmission based on mechanical conditions, providing immediate protection without waiting for control system detection and actuation.
3Power
If the primary pulley operates at high engine velocities, then high power transmission is achieved, but hydraulic clamping becomes excessive and ineffective
Solution Approach 1:
The primary gear reduction performs speed reduction before power enters the CVT, preventing high engine velocities from reaching the pulleys. This preliminary speed management ensures hydraulic clamping remains effective across the entire operating range while still allowing high engine speeds for power generation.
Solution Approach 2:
The gear reduction changes the rotational speed parameter entering the CVT, transforming high-speed low-torque engine output into lower-speed high-torque input suitable for the CVT. This parameter transformation keeps pulley speeds within the effective hydraulic clamping range.
4Speed
If a gear reduction is added before the CVT, then primary pulley speed is reduced, but drivetrain complexity increases
Solution Approach 1:
The launch clutch serves multiple functions: it manages transient torque events, protects the CVT from shock loads, and enables the primary gear reduction to effectively control pulley speeds. This multi-functional component adds complexity efficiently by consolidating several protective and control functions into one element.
Solution Approach 2:
The drivetrain merges the launch clutch, primary gear reduction, and CVT into an integrated power management system. These components work together as a unified system where the gear reduction and launch clutch collectively manage speed and torque, creating a coordinated solution rather than separate isolated components.
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 solution effectively manages transient torques and hydraulic clamping, reducing driveline inertia, improving acceleration, fuel efficiency, and preventing damage to CVT components, while allowing for higher engine speeds and extended vehicle range.
Implementation Method 1
The primary gear reduction reduces a rotational speed of the output of the motor that is coupled to the primary pulley of the steel belt CVT
Implementation Method 2
Vehicles that use continuously variable transmissions (CVTs) that are subject to transient torque events may result in a slip condition between a belt and pulleys of the CVT if a clamp load is not high enough to manage the transient torque
Implementation Method 3
pulleys of CVTs operated at high engine velocities, as is common in side-by-side vehicle operations, may experience hydraulic clamping due to velocity induced pressure gradients in the clamping piston
Data Source
AI summary
A drivetrain layout that includes a primary gear reduction, a continuously variable transmission (CVT), a peak torque limiting (PTL) device and a range box is provided. The primary gear reduction is operationally engaged to an output of a motor. The CVT includes a primary pulley and a secondary pulley. The primary pulley of the CVT is operationally engaged to the primary gear reduction. The primary gear reduction reduces a rotational speed of the output of the motor that is coupled to the primary pulley of the CVT. The range box is operationally engaged with the secondary pulley of the CVT. The range box is configured to coupled torque between the CVT and wheels of a vehicle. The PTL device in operational engagement between the secondary pulley of the CVT and the range box, the PTL device configured to protect the drivetrain layout from torque transients.