HV Battery SOC Management for Cold Weather Starting
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Solution Overview
Problem
Electrified vehicles face reduced power discharge capability from high-voltage traction batteries at extremely cold ambient temperatures, requiring increased battery power for engine cranking and starting, and the presence of a starter motor and low-voltage battery adds weight and complexity.
Innovation Solution
A vehicle system that includes an electric machine coupled to the engine and transmission, with a controller adjusting the state of charge (SOC) of the high-voltage traction battery based on forecasted temperatures to maintain sufficient power for cold weather starting, eliminating the need for a traditional starter motor and low-voltage battery by prompting the driver to activate a cold weather mode when temperatures are below a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the HV battery is used to power accessories and start the engine without a starter motor and low-voltage battery, then vehicle weight and complexity are reduced, but the power discharge capability of the HV battery is substantially reduced at extremely cold ambient temperatures
Solution Approach 1:
The system performs preliminary action by receiving forecasted temperature data in advance and adjusting the minimum SOC threshold before cold weather conditions occur. When the forecasted temperature is below a threshold, the controller proactively raises the minimum SOC requirement for the HV battery, ensuring sufficient power is available for engine cranking and accessory operation during the anticipated cold period. This preemptive adjustment resolves the contradiction by preparing the battery system ahead of time to maintain reliability without requiring additional hardware.
Solution Approach 2:
The system applies parameter changes by dynamically adjusting the minimum state of charge (SOC) threshold of the HV battery based on forecasted temperature conditions. The controller modifies the SOC parameter from a standard threshold to an increased threshold when cold weather is forecasted, thereby changing the operational parameters of the battery to ensure sufficient power discharge capability in cold conditions while maintaining the simplified vehicle architecture without starter motor or low-voltage battery.
2Reliability
If the SOC threshold is increased to provide robust cold weather starting, then cold weather power discharge capability is improved, but efficiency and performance during normal operation may be impacted
Solution Approach 1:
The system applies dynamics by making the minimum SOC threshold adjustable and condition-dependent rather than fixed. The controller dynamically modifies the SOC threshold based on real-time forecasted temperature data: raising the threshold when cold weather is forecasted to ensure reliable power discharge, and maintaining the normal lower threshold during favorable conditions to optimize efficiency and performance. This dynamic adjustment resolves the contradiction by adapting the SOC requirement to actual environmental conditions.
Solution Approach 2:
The system implements parameter changes by varying the minimum SOC threshold parameter according to forecasted temperature conditions. When the forecasted temperature is below the threshold, the controller increases the minimum SOC parameter to ensure sufficient power for cold weather starting. When temperatures are favorable, the controller maintains the normal SOC parameter, thereby optimizing efficiency and performance. This conditional parameter adjustment resolves the contradiction between cold weather reliability and normal operation efficiency.
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 ensures robust cold weather starting by maintaining a higher minimum SOC, providing additional battery power for engine starting without impacting efficiency or performance, allowing the elimination of a traditional starter motor and low-voltage battery, thus reducing vehicle weight and complexity.
Implementation Method 1
a battery, a step-ratio transmission, an electric machine configured to be selectively powered by the battery and to selectively charge the battery
Data Source
AI summary
A vehicle having an engine, a battery, and an electric machine configured to propel the vehicle and selectively coupled to the engine to start the engine includes a controller configured to prompt for input to activate a cold weather mode in response to an expected ambient temperature to be below a first temperature threshold for a time period during which a subsequent engine start is anticipated, and to operate the engine and electric machine to maintain a state of charge (SOC) of the battery above a first SOC threshold in response to activation of the cold weather mode, and a second SOC threshold lower than the first SOC threshold otherwise.