Hybrid Vehicle Power Source Discharge Limit Management

Solution Overview

Problem

Conventional battery discharge limits in hybrid electric vehicles (HEVs) are set without considering short-term, transient motor outputs, leading to unnecessary engine usage and reduced fuel economy, as they are based on continuous usage scenarios rather than brief, high-demand situations.

Innovation Solution

A system and method that sets two discharge limits for the power source in HEVs, with a higher Engine On/Off Discharge Limit and a lower Vehicle Usage Discharge Limit, using a temperature sensor and control system to manage engine operation based on the higher limit, allowing for reduced engine usage while protecting the battery from overheating and over-discharge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional discharge limit is set based on continuous motor use for two or more seconds, then the battery is protected from overheating and over-discharge, but the engine is started sooner than necessary, increasing fuel consumption

Engineering Contradiction:

Improvebattery protectionVSAvoidfuel consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent segments the discharge limit into two distinct values: a first discharge limit for continuous motor use and a second, higher discharge limit for transient engine starting. This segmentation allows the system to apply appropriate limits based on the specific operational context, protecting the battery during sustained high-demand scenarios while permitting higher discharge levels for brief, necessary events like engine starting, thereby reducing unnecessary engine starts and fuel consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic adjustment of discharge limits based on motor use duration. The control system monitors how long the motor has been operating and selectively applies the first discharge limit for continuous use scenarios and the second discharge limit for transient scenarios. This dynamic approach allows the system to adapt to changing operational conditions, enabling the engine to remain off longer when safe to do so, thus improving fuel economy while maintaining battery protection.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the engine is started sooner to stay within conventional discharge limits, then the battery is protected from damage, but fuel economy is reduced due to increased engine usage

Engineering Contradiction:

Improvebattery safetyVSAvoidfuel economy

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent segments the discharge limit into two distinct values: a first discharge limit for continuous motor use and a second, higher discharge limit for transient engine starting. This segmentation allows the system to apply appropriate limits based on the specific operational context, protecting the battery during sustained high-demand scenarios while permitting higher discharge levels for brief, necessary events like engine starting, thereby reducing unnecessary engine starts and fuel consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs feedback mechanisms where the control system continuously monitors battery conditions, motor use duration, and discharge levels. Based on this feedback, the system dynamically determines whether to apply the first or second discharge limit. This feedback loop ensures the battery remains protected while maximizing opportunities to keep the engine off, thereby improving fuel economy without compromising battery safety.

Inventive Principle:

Principle #23Feedback

3Device complexity

If a single discharge limit is used for all operating conditions, then the control system is simple to implement, but it cannot account for transient motor outputs, leading to unnecessary engine starts

Engineering Contradiction:

Improvecontrol system complexityVSAvoidfuel economy

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent segments the discharge limit into two distinct values: a first discharge limit for continuous motor use and a second, higher discharge limit for transient engine starting. This segmentation allows the system to apply appropriate limits based on the specific operational context, protecting the battery during sustained high-demand scenarios while permitting higher discharge levels for brief, necessary events like engine starting, thereby reducing unnecessary engine starts and fuel consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic adjustment of discharge limits based on motor use duration. The control system monitors how long the motor has been operating and selectively applies the first discharge limit for continuous use scenarios and the second discharge limit for transient scenarios. This dynamic approach allows the system to adapt to changing operational conditions, enabling the engine to remain off longer when safe to do so, thus improving fuel economy while maintaining battery protection.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS7797089B2System and method for managing a power source in a vehicle

Publication Date: 2010.09.14 FORD GLOBAL TECH LLC

AI summary

A system and method for managing a power source in a vehicle having an engine and an electric machine includes setting first and second discharge limits for the power source, where the second discharge limit is higher than the first discharge limit. A buffer value is determined as a function of at least the second discharge limit and an engine-on power requirement. A driver demand for power is determined, and the engine is started when the engine is off and the driver demand for power exceeds the buffer value.