CVT Belt Slip Control During Engine Stop
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Solution Overview
Problem
In vehicles equipped with belt-type continuously variable transmissions, the start-stop control system causes excessive belt slip relative to pulleys due to the reduction in hydraulic pressure when the engine is stopped during travel, exacerbated by the application of reverse torque from the brake system, leading to premature belt wear.
Innovation Solution
The implementation of an electronic control unit that adjusts the braking force using an actuator to maintain hydraulic pressure and control slip within predetermined limits, mitigating engine stop shocks and belt slip by correlating vehicle speed, slip ratio, and deceleration data to optimize braking force distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If start-stop control is performed to stop the engine during travel, then fuel consumption is reduced, but hydraulic pressure decreases causing excessive belt slip
Solution Approach 1:
The braking force adjusting device applies a counteracting force to the wheel in the opposite direction of the reverse torque generated during engine stop. This preliminary anti-action compensates for the harmful effect of reverse torque that causes excessive belt slip, allowing the engine to be stopped during travel without compromising belt reliability.
Solution Approach 2:
The system dynamically adjusts the braking force parameter based on the engine stop state. When the engine is stopped, the braking force is modified to counteract the reverse torque, thereby changing the operational parameters to maintain belt slip within acceptable limits while enabling fuel-efficient engine stopping.
2Object-generated harmful factors
If the engine is stopped during travel, then emissions are reduced, but belt life is shortened due to increased slip
Solution Approach 1:
By applying a counteracting braking force to the wheel, the system prevents the reverse torque from causing excessive belt slip. This protective measure allows the engine to be stopped for emission reduction while simultaneously protecting the belt from premature wear, thus extending belt life.
3Speed
If brake system applies reverse torque to stop wheel rotation, then vehicle deceleration is achieved, but belt slip increases due to hydraulic pressure reduction
Solution Approach 1:
The braking force is dynamically adjusted based on the engine operation state. When the engine is stopped, the braking force parameter is modified to counteract the reverse torque, thereby maintaining the reliability of belt clamping while still achieving the required vehicle deceleration.
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 configuration effectively prevents excessive belt slip and associated wear, ensuring the belt operates within a safe range during start-stop cycles, thereby extending its lifespan and maintaining transmission efficiency.
Implementation Method 1
slip of the belt relative to the pulley
Implementation Method 2
hydraulic pressure for clamping the belt is not supplied to a primary pulley or a secondary pulley
Implementation Method 3
an oil pump that is driven using power of the engine is also stopped accordingly. Thus, hydraulic pressure for clamping the belt of the continuously variable transmission decreases
Implementation Method 4
a force (reverse torque) in a direction to stop the rotation of the continuously variable transmission is transmitted to the continuously variable transmission from the wheel side through a power transmission path
Data Source
AI summary
A vehicle includes an engine, a continuously variable transmission, an engine stop system, and a brake system. The brake system is configured to control a braking force of the wheel based on an operation state of a brake operating portion that is operated by a driver. The brake system includes a braking force adjusting device. The braking force adjusting device includes an actuator and an electronic control unit. The actuator is configured to adjust a braking force of the wheel. The electronic control unit is configured to, when the engine stop system stops the driving of the engine, control the actuator such that slip of a belt of the belt-type continuously variable transmission relative to the pulley becomes less than or equal to a predetermined allowable limit.