HEV Coasting Engine Control via Regenerative Torque Management

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Solution Overview

Problem

Hybrid electric vehicles (HEVs) face challenges in maintaining fuel economy and preventing unnecessary engine activation when coasting downhill, as existing control systems fail to prevent pinion gear overspeed, leading to engine activation and reduced regenerative energy recoupment.

Innovation Solution

A method involving an electronic control unit (ECU) that determines regenerative torque based on vehicle and road conditions, applying it to maintain the engine off condition while managing battery charge limits, and engaging friction brakes to prevent pinion gear overspeed, thereby optimizing energy recoupment and reducing fuel consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the HEV engine is enabled to prevent pinion gear overspeed during coasting, then reliability is improved, but fuel economy deteriorates

Engineering Contradiction:

Improvepinion gear protectionVSAvoidfuel economy

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent converts the potentially harmful coasting condition (which causes pinion overspeed) into a beneficial regenerative braking opportunity. By applying regenerative torque during coasting, the system protects the pinion gear while simultaneously recovering energy to charge the battery, transforming a harmful scenario into a dual-benefit situation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The system dynamically changes the regenerative torque parameter based on real-time monitoring of pinion gear speed. When pinion speed approaches the overspeed threshold, regenerative torque is increased to reduce speed; when safe, torque is reduced or eliminated. This dynamic parameter adjustment allows the system to protect against overspeed while minimizing unnecessary energy consumption.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If regenerative torque is applied to maintain engine-off condition, then fuel economy is improved, but pinion gear overspeed risk increases

Engineering Contradiction:

Improvefuel economyVSAvoidpinion gear protection

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The system implements continuous feedback monitoring of pinion gear speed during coasting operations. The control unit receives real-time speed data and compares it against the overspeed threshold, dynamically adjusting regenerative torque application accordingly. This closed-loop feedback ensures pinion protection while maximizing fuel economy benefits.

Inventive Principle:

Principle #23Feedback

3Loss of energy

If the charge power limit of the battery is increased to accommodate regenerative energy, then regenerative energy recoupment is improved, but battery safety risk increases

Engineering Contradiction:

Improveregenerative energy recoupmentVSAvoidbattery safety

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The battery charge power limit is made dynamic rather than static. The system temporarily increases the charge power limit above the maximum level but below the absolute maximum level when regenerative braking is occurring, then returns to the normal maximum level when regenerative braking stops. This dynamic adjustment allows enhanced energy recoupment during coasting while maintaining safety margins.

Inventive Principle:

Principle #15Dynamics

4Loss of energy

If the state of charge limit of the battery is increased to accommodate regenerative energy, then regenerative energy recoupment is improved, but battery overcharge risk increases

Engineering Contradiction:

Improveregenerative energy recoupmentVSAvoidbattery overcharge

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The state of charge (SOC) limit is dynamically adjusted during regenerative braking events. The system temporarily raises the SOC threshold above the normal maximum level but maintains it below the absolute maximum level, allowing additional regenerative energy to be stored. When regenerative braking ceases, the SOC limit returns to its normal maximum, preventing overcharge conditions while maximizing energy recovery during coasting.

Inventive Principle:

Principle #15Dynamics

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 effectively maintains the engine off condition during coasting, reduces fuel consumption, and maximizes regenerative energy recoupment by dynamically managing regenerative torque and battery charge limits, enhancing the overall efficiency and fuel economy of HEVs.

Implementation Method 1

setting an initial amount of regenerative torque to be generated by a motor of the HEV... determining whether a pinion gear of the HEV is approaching a pinion gear overspeed limit... generating an additional amount of regenerative torque

Methodology Applied

Scientific EffectRegenerative braking: Electromagnetic Induction

Implementation Method 2

engaging friction bakes of the HEV

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS20200339100A1Limiting engine on condition while coasting

Publication Date: 2020.10.29 TOYOTA MOTOR ENG & MFG NORTH AMERICA INC

AI summary

Systems and methods are provided that prevent or override a hybrid electric vehicle (HEV) from operating in an engine-on mode or condition when the HEV is coasting, such as when the HEV is traveling on a downhill grade. Regenerative torque is generated by one or more electric motors of the HEV so that the pinion gear of a planetary gear set of a power distribution mechanism operates below an overspeed limit at which hardware failure may occur.