Hybrid Powertrain Engine Braking Control Strategy
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Solution Overview
Problem
In hybrid vehicles, the integrated starter/generator (ISG) may not be able to provide sufficient driveline braking when the state of charge of the electric energy storage device is high, leading to inefficient engine braking, increased emissions, and reduced brake life due to unnecessary engine rotation during low driver demand power conditions.
Innovation Solution
A powertrain operating method that inhibits engine rotation when engine braking is desired unless a human/machine interface input is received, allowing the engine to rotate and initiate engine braking only when explicitly requested, thereby reducing unnecessary engine operation and emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the engine rotates to provide engine braking when the ISG lacks capacity, then driveline braking power is improved, but fuel consumption increases and emissions increase due to unnecessary engine rotation during short low driver demand power periods
Solution Approach 1:
The system dynamically adjusts engine rotation strategy based on real-time assessment of driver demand power duration and vehicle operating conditions. The controller monitors whether low driver demand power conditions are transient or sustained, and only activates engine rotation when the duration justifies the fuel consumption, thereby optimizing the balance between driveline braking power and fuel efficiency
Solution Approach 2:
The system changes the operational parameters of the engine based on vehicle speed, driver demand power duration, and ISG capacity. When the assessment indicates that low driver demand power will persist long enough to benefit from engine braking, the controller transitions the engine from a stopped state to a rotating state, adjusting engine speed and load parameters to provide optimal braking while minimizing fuel consumption
2Power
If the engine rotates to provide engine braking, then driveline braking power is improved, but engine emissions increase due to unnecessary engine operation during short low driver demand power periods
Solution Approach 1:
The system dynamically evaluates the duration and magnitude of low driver demand power conditions to determine whether engine rotation will provide net benefit. By continuously monitoring operating conditions and predicting the persistence of braking opportunities, the controller avoids unnecessary engine cycles that would generate emissions without providing meaningful braking assistance
Solution Approach 2:
The system uses the ISG to provide the primary braking function during transient low driver demand power conditions, making the engine rotation unnecessary. The ISG's ability to convert kinetic energy to electrical energy allows the system to maintain driveline braking power without engaging the engine, thereby eliminating emission sources while preserving braking capability
3Loss of energy
If the ISG provides driveline braking power, then energy conversion efficiency is improved, but braking capacity is limited when state of charge is high due to electric energy storage device power limits
Solution Approach 1:
The system merges the braking capabilities of the ISG and the engine into a unified driveline braking system. When the ISG operates near its power limits due to high state of charge, the controller can selectively engage the engine to supplement braking capacity, creating a combined braking system that leverages both the high efficiency of the ISG and the unlimited capacity of the engine
Solution Approach 2:
The driveline braking system is designed with multi-functionality, allowing it to operate in different modes depending on energy storage device state of charge. The system can switch between ISG-only braking, combined ISG-engine braking, and engine-only braking modes, ensuring that full braking capacity is available across all operating conditions while maintaining optimal energy conversion efficiency when the ISG is capable
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 engine emissions, increases brake life, improves occupant perception, and decreases fuel consumption and driveline noise, while ensuring effective engine braking is provided when needed.
Implementation Method 1
the ISG may convert the vehicle's kinetic energy into electric energy
Data Source
AI summary
Systems and methods for operating a hybrid powertrain or driveline that includes an engine and an integrated starter/generator are described. In one example, rotation of an automatically stopped engine may be inhibited when engine braking is requested so that the engine may not be rotated without providing a desired outcome.