May 2012

Introduction

 

The Lola Drayson B12/69 EV is Drayson Racing Technologies’ biggest green tech project to date and a collaboration between a number of our technical partners. The B10 Le Mans Prototype (LMP) car, which was originally powered by a 5.5 litre bio-fuelled Judd engine has been converted to pure electric drive. Our aim is to produce the fastest electric racing car in the world and one which show cases some of the best technology in the electric car industry.

Drayson Racing Technologies have designed a complete electric drivetrain which has been integrated into the existing chassis resulting in an extremely exciting package which produces zero emissions. Designed to the highest standards of quality and safety, this car is being used to develop drivetrain technologies and systems to be used in a wide variety of future projects from road to race and truly demonstrates the philosophy of using the racing track as a laboratory for the development of next generation electric car technologies.

 

Performance
Top speed		320kph (higher with ratio change)
Acceleration	0-60mph	3.0s
	0-100mph	5.1s
Power		640kW / 850Bhp
Aerodynamics
Active elements		Rear wing element Rear gurney Dive planes
Drag reduction from active system		30%
Drivetrain Components
Motor		YASA
Inverter		Rinehart
Battery		Lithium Ion Phosphate
Energy Capacity		30kWh
Transmission		Single ratio, split drive Ratio: Track dependent

Safety

 

Safety is the highest priority at DRT. This is an area where we are using the project to improve industry learning and understanding on both general design and use of electric vehicles but also the maintenance and repair of these vehicles in high pressure situations.

 

DRT engineers have applied existing EV experience to the B12 system but are also working with industry experts, the FIA safety and medical teams and military high voltage system experts to develop new technologies and techniques to improve EV safety.

 

The B12 meets all road and motorsport electric drivetrain requirements and has been designed using expertise and analysis techniques previously applied to designing ASILD ISO26262 systems. The result is a system with multiple levels of failure tolerance comprising hardware and software, passive and active safety systems.

 

DRT HV Control Unit

Design Process

The design of the drivetrain followed an industry standard ‘V’ format. This involved a structured approach to the entire process with detailed and controlled documentation for all the key phases of the design. Key aspects include:

 

• Detailed requirements capture at vehicle, system and sub-system levels.
• Simulation and analysis of vehicle, system and sub-systems to set targets, aid in requirements generation and facilitate testing.
• Detailed test and analysis during all phases to ensure compliance with requirements.
• Use of test rigs including SiL, HiL and dynomometers in the V&V process.
• Vehicle level test and analysis to ensure that both the total vehicle meets the requirements and that the requirements were appropriate.

 

DRT V Cycle Process Diagram

Simulation

Simulation was a key to getting the design right before any commitment was made to components or designs. Various tools were used to simulate different key components and systems of the cars and help identify the optimum specification and layout of the car.

 

Working with various partners, the DRT engineers simulated all aspects of the car from the aerodynamics and chassis performance down to the high voltage electrical circuitry and control software on the car. This fed both into the specification and layout of the car as well as being used to prove the behaviour of key components prior to building the car.

 

System Architecture

Modern drivetrain and control systems are complex systems and require a clearly defined and analysed architecture for the physical and electronic makeup and information transfer of the system.

 

DRT engineers approached the B12 project by defining the top level System Architecture to give the optimum balance of safety, minimum complexity and maximum performance and reliability. This part of the design was key to ensure that the required safety and functional aspects of the system would be achieved as well as to identify requirements requiring addressing throughout the remainder of the design phase.

 

DRT System Architecture

Systems Design

DRT designed low and high voltage systems form the backbone of the vehicle drivetrain. These systems are designed to be inherently safe and easy to use.

 

The high voltage systems manage both driving and charging and include numerous safety features and sensing systems. The low voltage systems incorporate multiple levels of redundancy as well as passive mechanisms which ensure the safety and integrity of the system before the software systems are even considered.

 

Electromagnetic interference and noise issues are regular stumbling blocks on internal combustion vehicles and can be significantly worse on EVs. Attention to detail of the design of the low and high voltage systems, sensor systems, chassis design and communication systems result in a system which is inherently robust to such interference.

 

DRT HV Control Unit Model

Packaging and Cooling

Packaging and cooling of the main components was one of the major challenges of the project due to the need to integrate the EV system into a car originally designed for an internal combustion engine.

 

Using CAD tools (Computer Aided Design) design techniques the best possible layout was achieved with the minimum of compromises in safety, strength and weight. With these tools, the DRT engineers also evaluated the feasibility, simplicity and safety of key service and maintenance tasks which would have to be carried out in use.

 

Being pushed way beyond their original limits, the motor, inverter and battery systems required a lot of detail attention to be paid to thermal management. Working with the suppliers, DRT engineers optimised the existing cooling systems and identified key improvements which enabled the systems to be pushed to these limits.

 

DRT CAD Model

Mechanical Structure and Design

This project was the first time that anyone had designed an electric drivetrain comprising stressed chassis members. The electric drivetrain needed to be capable of supporting the entire chassis loads endured driving flat out on the track including those expected during crashes.

 

This was no easy task but extensive use of CAD and FEA (Finite Element Analysis) allowed this to be done in parallel with the packaging and cooling system work to enable quick iteration through numerous options in very short periods of time.

 

DRT CAD Model

 

Packaging the battery, motor and inverters within the confines of a race car proved highly challenging as the best balance of packaging efficiency, structural integrity, safety and serviceability had to be maintained.

Control Systems

The control system is the intelligence at the heart of an electric vehicle. DRT engineers designed the control systems for the B12 from first principles. Detailed specifications were produced and, working with technical partner Cosworth,the code was implemented and tested according to these specifications.

 

The system performs all vehicle control functions including:

 

• Drivetrain integrity and failure monitoring.
• Torque management and distribution.
• Electronic differential.
• Torque vectoring.
• Launch and traction control.
• Brake energy regeneration.
• Battery system control and safety monitoring.
• Motor and inverter control and monitoring.
• Charging control.
• On and off board charger control.

 

This part of the system is where the key integration challenges were met to ensure that the subsystems which make up the drivetrain work together correctly and are controlled and managed appropriately.

 

COSWORTH HiL Rig Model

Testing

DRT and our technical partners have used a range test rigs to prove the performance of all parts of the system. Key facilities include:

 

• HiL rig testing: Cosworth implemented a new EV simulation rig to allow the complete control system to be fully tested before it got near the car.
• Dyno testing: The motors and inverters were tested to the peak of their torque, power and speed capabilities prior to fitting to the vehicle.

 

Cosworth HiL Rig

Calibration

DRT engineers, using their prior experience of Formula 1, WRT and OEM projects, used a combination of the leading automotive and motorsport tools to methodically test, analyse and setup the complex calibration of the system to achieve the target performance, efficiency and reliability. This involved the precise setup of over 10,000 calibration parameters.

 

DRT Test Rig Control Panel

Driver Controls

Designing an electric racing car requires looking at more than just the engineering of the car itself. DRT engineers focused on the functionality and layout of the controls to ensure a simple and intuitive interface for the driver; one which requires little knowledge of the system and minimum attention while on track. These controls incorporate safety mechanisms within their function and simple, logical feedback to allow a driver to quickly understand the health and operation of the car.

 

DRT Dash & Wheel Photo