CVT Engine Braking via Throttle Vacuum Control
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Solution Overview
Problem
Vehicles with continuously variable transmissions (CVTs) and centrifugally actuated driving pulleys may not experience engine braking under certain conditions, such as when starting down a hill from rest, due to the pulley sheaves being too far apart to clamp the belt, leading to increased wear on brakes and added complexity with the use of mechanisms like overrunning clutches.
Innovation Solution
A method for controlling the internal combustion engine of a vehicle with a CVT, involving determining an idle speed set point based on driven pulley speed, and adjusting engine operation to implement engine braking by controlling the throttle valve position to create a vacuum resisting the torque, thereby enabling engine braking without additional mechanical devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a centrifugally actuated driving pulley is used in a CVT, then the pulley structure is simplified and cost is reduced, but engine braking is lost at low driving pulley speeds because the sheaves are too far apart to clamp the belt
Solution Approach 1:
The control system determines the idle speed set point in advance based on the driven pulley speed before engine braking is needed. By calculating the appropriate idle speed set point that corresponds to a throttle valve position creating sufficient vacuum, the system prepares the engine conditions beforehand to ensure engine braking effectiveness when the driver releases the throttle, even at low driving pulley speeds where the belt might otherwise turn freely.
Solution Approach 2:
The system dynamically adjusts the idle speed set point parameter based on the driven pulley speed. When the driven pulley speed is below a predetermined threshold, the control system modifies the idle speed set point to correspond to a throttle valve position that creates enough vacuum for engine braking. This parameter change ensures that the engine maintains braking capability across the full operating range of the centrifugally actuated pulley.
2Reliability
If an overrunning clutch is added to the driving pulley to enable engine braking at low speeds, then engine braking reliability is improved, but device complexity, cost and weight increase
Solution Approach 1:
The invention replaces the mechanical overrunning clutch system with an electronic control system that manages engine braking through throttle valve positioning. Instead of using mechanical components like clutches or additional friction elements, the system uses the existing throttle actuator to position the throttle valve at a specific opening angle that creates sufficient vacuum for engine braking. This substitution eliminates the need for additional mechanical devices while achieving the same functional result.
Solution Approach 2:
The existing throttle valve and electronic control system are made to serve a dual function: normal acceleration control and engine braking control. By programming the control system to determine and enforce an appropriate idle speed set point based on driven pulley speed, the same throttle mechanism that controls acceleration also provides engine braking capability across the entire operating range of the CVT, including low speeds where centrifugal clutches would be ineffective.
3Speed
If the throttle valve is positioned to create vacuum for engine braking, then vehicle speed reduction is achieved, but engine operation may become unstable at low driven pulley speeds
Solution Approach 1:
The control system dynamically adjusts the idle speed set point parameter based on the driven pulley speed to maintain stable engine operation during engine braking. When the driven pulley speed is low, the system calculates an idle speed set point that corresponds to a throttle position providing sufficient vacuum for braking while maintaining enough engine speed stability. As driven pulley speed increases, the idle speed set point is adjusted accordingly, allowing the system to optimize both braking effectiveness and engine stability across different operating conditions.
Solution Approach 2:
The control system continuously monitors the driven pulley speed and uses this feedback to adjust the idle speed set point. By comparing the actual driven pulley speed against predetermined thresholds and continuously updating the target idle speed, the system maintains stable engine operation during the engine braking process. This closed-loop control ensures that the throttle valve position is constantly optimized to balance braking effectiveness with engine stability.
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 method allows for engine braking in vehicles with CVTs and centrifugally actuated driving pulleys without the need for additional components like clutches, reducing wear on brakes and maintaining vehicle control while simplifying the system.
Implementation Method 1
because of the position of the throttle valve, a vacuum is created in the engine, and the torque applied on the crankshaft by the wheels needs to work against this vacuum
Implementation Method 2
Centrifugally actuated driving pulleys have a pair of sheaves that move closer together as the speed of the driving pulley increases
Data Source
AI summary
A method for controlling an internal combustion engine of a vehicle having a continuously variable transmission is disclosed. When a driven pulley speed is less than a predetermined driven pulley speed and an actual engine speed is less than an engine speed causing a driving pulley speed to be a driving pulley engagement speed: controlling the engine to increase the actual engine speed to increase the driving pulley speed to be at least the driving pulley engagement speed. When the driven pulley speed is above the predetermined driven pulley speed, the actual engine speed is greater than the engine speed causing the driving pulley speed to be the driving pulley engagement speed, and the desired engine speed is less than the engine speed causing the driving pulley speed to be the driving pulley engagement speed: controlling the engine to operate under conditions corresponding to an engine braking speed.