Brake Pressure Control for Engine Restart on Road Grades
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Solution Overview
Problem
Micro-hybrid vehicles experience vehicle roll-back and engine stall issues during engine restart on steep grades due to insufficient torque and unexpected acceleration, leading to uncomfortable driving experiences and potential engine stalling.
Innovation Solution
The method involves using brake pressure to engage wheel brakes and produce reactive friction torque, initiating engine restart with wheel torque equal to or greater than the road gradient torque, and releasing brake pressure to maintain vehicle stability and suppress powertrain torque disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine is shut down during vehicle stop to reduce fuel consumption, then fuel economy is improved, but vehicle roll-back and engine stall occur during restart on steep grades
Solution Approach 1:
The brake system is activated in advance before engine restart to prevent vehicle roll-back. The controller detects steep grade conditions and applies brake pressure to the wheels before the engine restarts, ensuring the vehicle remains stationary during the critical restart phase when engine torque is insufficient.
Solution Approach 2:
The brake system provides a counteracting force to prevent the harmful effect of gravity-induced roll-back. By applying brake pressure that counterbalances the gravitational force on steep grades, the system prevents vehicle movement in the opposite direction during engine restart.
2Stability of the object's composition
If brake pressure is applied to prevent vehicle roll-back, then vehicle stability is improved, but unexpected forward acceleration occurs during engine restart
Solution Approach 1:
The controller continuously monitors engine torque output, brake pressure, and vehicle status to dynamically adjust brake pressure. When engine torque becomes sufficient to counteract gravitational load, the controller reduces or releases brake pressure, preventing unexpected forward acceleration while maintaining stability during the transition phase.
Solution Approach 2:
The brake pressure is dynamically adjusted based on real-time engine performance. The system transitions from a static brake application to a dynamic control strategy where brake pressure decreases as engine torque increases, allowing smooth vehicle launch without sudden acceleration.
3Ease of operation
If the vehicle uses conventional automatic transmission with torque converter, then vehicle creeping is enabled on flat surfaces, but reverse torque transfer occurs on steep grades
Solution Approach 1:
The brake system acts as an intermediary between the engine and wheels during restart on steep grades. By applying brake pressure to the wheels, the system prevents reverse torque transfer through the transmission while the engine restarts, protecting the transmission from harmful reverse torque conditions.
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 solution prevents vehicle roll-back and engine stall during hill starts, reducing unexpected acceleration and ensuring smooth engine restarts by maintaining brake friction torque and balancing brake pressure with increasing driving torque.
Implementation Method 1
using brake pressure to engage wheel brakes and produce reactive friction wheel torque that holds the vehicle stationary
Implementation Method 2
operating the engine to produce wheel torque equal to or greater than the road gradient wheel torque
Data Source
AI summary
A method for restarting an engine of a vehicle stopped on a grade, comprising the steps of engaging a gear of a transmission through which the engine and wheels of the vehicle are drivably connected mutually, using brake pressure to engage wheel brakes and produce a road gradient wheel torque that holds the vehicle stationary on the grade, initiating an engine restart, operating the engine to produce wheel torque equal to or greater than the road gradient wheel torque, and releasing the brake pressure.