Vehicle thermal Management Systems Conference and Exhibition (VTMS10)

IMechE

• Publisher: Woodhead Publishing
• Year: 2011
• Print ISBN:
  9780857091727
• eBook ISBN:
  9780857095053
• Topic: Physical Sciences
• Subtopic: Thermodynamics

This book contains the papers presented at the IMechE and SAE International, Vehicle Thermal Management Systems Conference (VTMS10), held at the Heritage Motor Centre, Gaydon, Warwickshire, 15-19th May 2011. VTMS10 is an international conference organised by the Automobile Division and the Combustion Engines and Fuels Group of the IMechE and SAE International. The event is aimed at anyone involved with vehicle heat transfer, members of the OEM, tier one suppliers, component and software suppliers, consultants, and academics interested in all areas of thermal energy management in vehicles. This vibrant conference, the tenth VTMS, addresses the latest analytical and development tools and techniques, with sessions on: alternative powertrain, emissions, engines, heat exchange/manufacture, heating, A/C, comfort, underhood, and external/internal component flows. It covers the latest in research and technological advances in the field of heat transfer, energy management, comfort and the efficient management of all thermal systems within the vehicle. - Aimed at anyone working in or involved with vehicle heat transfer - Covers research and technological advances in heat transfer, energy management, comfort and efficient management of thermal systems within the vehicle

Alternative Powertrain

Development of cooling system sign-off criteria for hybrid vehicles

B. Wicksteed, P. Burchill and A. Tarpey, Jaguar Land Rover Cars Ltd, UK

ABSTRACT

This paper reviews the experience at Jaguar Land Rover (JLR) of developing cooling system performance sign-off criteria for hybrid powertrain vehicles.The paper explores customer expectations for electric vehicle mode operation in extreme hot and cold environments and describes a process to assist in determining the upper and lower ambient temperature thresholds to ensure customer satisfaction.A method to assist in the development of new transient thermal sign-off drive cycles for hybrid power trains is proposed, together with examples of how this can be applied to typical hybrid driving scenarios. The role of CAE methods in this process and examples of the key considerations are also discussed.Example test results are reviewed which show the extent to which the new hybrid cooling sign-off criteria developed at JLR has achieved its objectives.

Keywords

Hybrid Powertrain

Cooling System Performance

Sign-Off Criteria

1 INTRODUCTION

Hybrid vehicles present a significant challenge for thermal system design; driven primarily by the low operating temperature requirements for the new electrical systems, but also by the complex nature of their interaction with the existing internal combustion engine and cabin cooling systems. The multiple control strategies required to ensure seamless hybrid powertrain operation mean that identifying driving conditions which deliver worst-case thermal loading is not a simple task.

Successful hybrid cooling system design hinges on two key factors:

1) A clear definition of the vehicle-level (customer) requirements for hybrid mode availability.

2) A translation of these vehicle-level requirements into clear and objective Engineering targets, defined by specific driving cycle(s), the range of ambient temperatures at which they must be delivered and the level of hybrid system functionality required for each.

Historically, vehicle cooling system performance has been validated against key steady-state operating points which represent the envelope of typical worst case usage ^[1]. More recently additional transient cases have been added to cover specific driving scenarios such as race track usage and sand driving for 4x4 product ^[2]. These drive cycles have been developed and refined over many years to cover the full spectrum of worst-case usage for vehicles using a conventional internal combustion engine (ICE).

However, these worst-case driving cycles do not necessarily translate into hybrid powertrain applications, since the traction and power generation systems are exercised hardest under transient driving scenarios which differ from the traditional cooling system sign-off conditions. Additionally, multiple cooling sub-systems are often required to achieve the diverse thermal requirements of the new electrical systems and each of these systems will have their own worst-case operating points and interactions with various other sub-systems. It is therefore clear that defining the operating conditions to validate the thermal performance of a hybrid powertrain requires a structured approach and the use of analytical tools to ensure that the full spectrum of worst-case usage is captured.

2 CUSTOMER EXPECTATIONS FOR HYBRID VEHICLE EV MODE AVAILABILITY (RISK ANALYSIS)

Jaguar and Land Rover (JLR) products are sold into virtually every major automotive market in the world. Each marketplace has its own specific usage requirements, and it is the role of the automotive manufacturer to understand these requirements and to ensure that their products achieve the market expectations. In common with most other automotive manufacturers JLR conducts detailed customer profiling in key markets using information from customer questionnaires, dealer feedback and contacts within the marketplace.

For hybrid electric vehicles (HEV’s) the existing customer usage data available at JLR was not adequate and needed enhancement. A study was undertaken to gather data and provide a better insight into HEV customer aspirations and usage. For the purposes of this paper only one element of the study will be discussed; namely the process used to define the ambient temperature range under which Electric Vehicle (EV) mode is required.

Previous studies have shown that hybrid electric vehicle fuel economy can vary dramatically (around 100% difference) with respect to ambient temperature in the range of −15 to +20°C ^[3]. Papers and Patents published by Toyota also indicate that significant research & development has been conducted to extend the ambient temperature range of EV mode availability for their second generation HEV’s ^[4]. It is therefore clear that in order to meet customer expectations the envelope of EV mode availability must be compatible with the market ambient temperature range in which the vehicle is sold.

The flow chart in Figure 1 outlines a method which can be used to build a more detailed picture of how customers in various markets will be affected by the availability or otherwise of EV mode at high and low ambient temperatures. This type of risk analysis can form an important input when defining the acceptable range of EV mode operation versus ambient temperature.

Figure 1 Risk analysis of population affected vs HEV ambient range

2.1 Definition of key markets & establishing major population centres

The JLR sales and marketing department use a 'voice of the market' process to determine specific market requirements and trends, which together with an understanding of future legislative requirements enables a sales forecast for each particular model line and powertrain type to be created. This data was used to determine the key markets for each vehicle employing a hybrid electric powertrain. Details of the precise process used are outside of the scope of this paper.

Sources of population data, such as the United Nations database ^[5] can be used to determine the cities with the greatest population in each key market region. The example in Figure 2 shows such data for Europe, highlighting the top ten most populous cities in this region.

Figure 2 European ma...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Co-Chairmen’s welcome message
• Heat and A/C
• Heat Exchange/Manufacture
• Engines
• Alternative Powertrain
• Engines/Emissions
• External and Internal Component Flows
• Underhood
• Heat and A/C Vehicle Comfort
• Author Index