Hydraulic CVT Control for Snowmobiles
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Solution Overview
Problem
Conventional snowmobile CVTs have drive ratios directly linked to engine speed, leading to high fuel consumption, noise, and vibrations at cruising speeds due to engine operation at unnecessary high speeds.
Innovation Solution
A method for controlling a hydraulic continuously variable transmission (CVT) that includes determining the speed of rotation of driving and driven shafts, calculating a base and corrective clamping force, and adjusting hydraulic pressure to control the belt tension, using a proportional-integral-derivative controller and calibration maps to optimize the drive ratio independently of engine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the drive ratio of the CVT is directly related to engine speed, then acceleration characteristics are improved, but fuel consumption increases and noise and vibrations are generated at cruising speeds
Solution Approach 1:
The patent applies dynamics by making the CVT system adjustable and adaptive rather than fixed. The control system dynamically modifies the relationship between engine speed and drive ratio based on operating conditions, allowing the system to optimize performance for both acceleration and cruising scenarios. This is achieved through electronic control that can independently manage clutch engagement and CVT ratio selection.
Solution Approach 2:
The patent changes the operational parameters of the CVT system by introducing multiple selectable ratio ranges and allowing decoupling of engine speed from drive ratio. The system can operate in different modes with different characteristic curves, changing the fundamental parameter relationship between engine speed and vehicle speed to optimize for different operating conditions.
2Speed
If the drive ratio of the CVT is directly related to engine speed, then acceleration characteristics are improved, but noise and vibrations are transmitted to riders at cruising speeds
Solution Approach 1:
The system dynamically adjusts the connection between engine and transmission based on operating conditions. During cruising, the control system can decouple the direct relationship, allowing the engine to operate at optimal speeds independent of vehicle speed, thereby reducing noise and vibrations transmitted to riders.
Solution Approach 2:
The patent introduces an electronic control system as an intermediary between the engine and CVT. This mediator can selectively engage/disengage the clutch and choose appropriate ratio ranges, acting as a buffer that prevents direct transmission of engine vibrations and noise to the drivetrain during cruising operations.
3Device complexity
If a centrifugal CVT is used, then the structure is simple and provides many advantages, but the drive ratio cannot be independently controlled from engine speed
Solution Approach 1:
The patent merges a traditional centrifugal CVT mechanism with an electronic control system. The mechanical simplicity of the centrifugal CVT is preserved while adding electronic sensors, processors, and actuators that enable independent drive ratio control. The combination maintains structural simplicity where possible while adding intelligence for adaptability.
Solution Approach 2:
The patent replaces purely mechanical centrifugal force-based control with an electronic control system that can independently determine optimal drive ratios. The electronic system substitutes for the mechanical centrifugal governor, allowing the drive ratio to be controlled based on multiple parameters rather than just engine speed, while maintaining the mechanical CVT structure for actual ratio adjustment.
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 approach reduces fuel consumption, noise, and vibrations by allowing the CVT to maintain efficient speed while reducing engine speed, improving the overall performance and comfort of the snowmobile.
Implementation Method 1
controlling a hydraulic pressure applied to the movable sheave to apply a sum of the base clamping force and the corrective clamping force onto the belt
Implementation Method 2
a spring biasing the movable sheave away from the fixed sheave
Implementation Method 3
a centrifugally actuated adjusting mechanism through which the drive ratio of the CVT is varied progressively as a function of the engine speed
Data Source
AI summary
A method of controlling a hydraulic CVT of a vehicle includes: determining a speed of rotation of a driving shaft; determining a speed of rotation of a driven shaft; determining a ratio of the speed of rotation of the driving shaft versus the speed of rotation of the driven shaft; determining an engine torque; determining a base clamping force to be applied by the driving pulley onto the belt based on the ratio and the engine torque; determining a desired speed of rotation of the driving shaft; determining a corrective clamping force by comparing the speed of rotation of the driving shaft to the desired speed of rotation of the driving shaft; and controlling a hydraulic pressure applied to a movable sheave to apply a sum of the base and corrective clamping forces onto the belt. A vehicle having a CVT controlled by the method is also disclosed.