Hybrid EV Brake Control for High-SOC Engine Braking
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Solution Overview
Problem
Hybrid electric vehicles face challenges in rapidly generating braking force when the battery state of charge is high, as existing systems struggle to balance engine brake engagement with regenerative braking, leading to potential battery overcharge and inefficient braking performance.
Innovation Solution
A control device that sets a lower fuel-cutoff-permission rotation speed when starting the engine, allowing for easier fuel cutoff and rapid engine brake engagement, thereby enabling quicker generation of braking force based on the engine brake when the battery state of charge exceeds a threshold, while preventing excessive battery charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel-cutoff-permission rotation speed is set to a high value to prevent starting failures, then starting reliability is improved, but fuel cutoff cannot be performed easily and rapid braking force generation is delayed
Solution Approach 1:
The patent applies dynamics by making the fuel-cutoff-permission rotation speed variable rather than fixed. The control device dynamically adjusts this parameter based on the operating condition: setting it to a first high value during normal starting to prevent starting failures, and to a second low value during battery protecting processes to enable rapid fuel cutoff and braking force generation. This dynamic parameter adjustment resolves the contradiction between starting reliability and braking response speed.
2Reliability
If the engine is started to engage the clutch for battery protection, then regenerative brake effectiveness is improved, but clutch engagement shock occurs and braking force generation is delayed
Solution Approach 1:
The patent applies preliminary action by performing torque control of the engine before and during clutch engagement. The control device sets the engine torque to a specific value prior to clutch engagement and maintains it during the engagement process, which prevents shock while enabling the engine to start and engage the clutch in time for battery protection. This preliminary torque preparation resolves the contradiction between regenerative brake effectiveness and clutch engagement smoothness.
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 control device effectively curbs engine rotation speed fluctuations, prevents starting failures, and rapidly transitions to motor-driven travel with stable braking force, ensuring efficient energy management and reduced battery overcharge.
Implementation Method 1
the hybrid electric vehicle can perform braking using a regenerative brake that generates a braking force by generating electric power using the motor generator at the time of deceleration. By using such a regenerative brake, kinetic energy can be converted to electric power and the electric power can be stored in a battery.
Implementation Method 2
a clutch between an engine and a motor generator. This hybrid electric vehicle may perform motor-driven traveling in which the hybrid electric vehicle travels using a driving force of the motor generator without using a driving force of the engine in a state in which the clutch is disengaged such that transmission of a driving force between the engine and the motor generator is cut off.
Data Source
AI summary
A control device performs braking using a regenerative brake based on power generation in a motor generator in motor-driven traveling and performs a battery protecting process of starting an engine to set up transmission of a driving force between the motor generator and the engine using a clutch and performing braking based on an engine brake when a state of charge of a battery is equal to or greater than a threshold value in the motor-driven traveling. The control device sets a fuel-cutoff-permission rotation speed to a second rotation speed lower than a first rotation speed when the engine is started through the battery protecting process.