KatE

The electrical systems subteam is responsible for all the components in the car which relate to power and voltage. To this end, they integrate all circuit boards, the low and high voltage cable harnesses, the programming, the sensors, and the safety circuit in the car. Alongside that they also work on the whole tractive system, which is composed of the accumulator, AC converter and motors. The electrical components also helped to build on the experience from the previous car, Murph-E. During the transfer to the new car, KatE, the focus was placed strongly on the components which exhibited potential for improvement in Murph-E. Components which already functioned well were further developed for better efficiency and reliability.

Electrical specifications of KatE:

Propulsion:

• 2 brushless synchronous motors Siemens 1FE1064
  • max. power: 50 kW
  • max. torque: 105 Nm
  • max. revolutions: 8000 rpm (electronically limited)

• 2 Siemens inverters SINAMICS S120
  • max. output current: 141 A (RMS)
  • max. output voltage: 480 VAC (RMS)

Accumulator:

• max. voltage: 600 V DC
• total energy: 5,3 kWh
• 288 lithium-polymer pouch cells with 144s2p interconnection
  • nominal voltage: 3,7 V
  • capacity: 5 Ah
  • max. continuous current: 275 A
• complex, self developed battery management system
• DC/DC converter to power the 24 V electrical system

Sensors:

• wheel speed sensors
• steering angle sensors
• 6-axis-sensors
• travel sensors
• coolant temperatur sensors
• brake discs temperature sensor
• tyre temperature sensor
• SmartSensor-approach for direct conversion of the sensor data to the CAN-bus

Other electronics:

• Single Board RIO from National Instruments
• Vehicle software implemented with LabView
• Recuperation, electronic differential, traction control, torque vectoring
• CAN-buses to the on-board communication
• WLAN for real-time telemetry logging

Aside from that, the module is responsible for electrical safety. The development and supervision of safety measures ensures all team members are able to work with the electric car and its high voltage components in a hazard-free environment.

Becoming an integral part of Elbflorace in the last years, the selfsupporting chassis (monocoque) in its fifth version is manufactured out of pre-coated carbon-fiber mats using the autoclave-process.
Our priority this season was the improvement of the layer-construction and the level of lightweight-construction. Again we where able to save approx. 2 kg. Using a new joining method for the adhesive joint was one of our major interests.
Alongside the monocoque our module has focussed on the following essential subject areas:

Implementation of aerodynamic aspects

• intensive use of universities know how
• Use of underfloor
• Aerodynamically optimised design of the nose and side pods
• Design of the steering rack cover to level out with the monocoque layers

Weight reduction

• Distinguish between structural and non-structural parts
• Optimisation of the crash element
• New method for the firewall plate (also to simplify the manufacture cost)
• Use of a shoulder harness bar

Ergonomic improvements

• Adjustable pedals including heel guidance and a lateral support for the driver
• More space for the driver’s legs
• Upright sitting position with higher stiffness in the sides of the seat for stability in the corners
• Use of a cushion for short drivers
• Adjustable head-restraint

Maintainability

• Rail-System for the battery case
• use of a pedal mount
• Clear arrangement and accessibility of all pedal box parts
• Re-use of the cover concept for the motor

Safety improvements

• LEO-system for the firewall und battery case for fire protection
• local strength improvement of the laminate-structure for the harness attachment-point

Putting the potential (electrical energy) in kinetic form on the road is the responsibility of the powertrain module.
Comprising the divisions gearbox, drive shaft and cooling, they are the link between electrical subsystems and suspension.

Gearbox
The gearbox was based on the existing concept from Murph-E, since the general set up of the motors was the same. During the transfer particular attention was paid to failures of the last season, and above all to the maintainability, so that the assembly in the car could be simplified and sped up. The transmission wheel was connected directly to the engine gear wheel in order to obtain the best possible sensor signal and improved access to the motor shaft-gear connection. The gear ratio was also changed from 4.6 to 5.8 to improve the acceleration. This was also done so a better motor efficiency could be achieved because the increased stress was spread across a wider field. During the design of the gearbox housing the main focus lay on simplifying the manufacturing process, to enable the shortest possible build time and stick to the tight schedule.

Drive shaft
The concept of the last season could also be reused, but choosing a new high strenght steel reduces weight and the number of parts drastically.

Cooling
We have chosen a complete diffrent way in terms of cooling: two cooling circuits instead of one, smaller hose diameter, stronger and yet smaller water pumps, lower volumetric flow rate, and a modular design. The coolers are mounted in front of the main roll hoop,in order to enable improved airflow and thus cooling efficiency along with the aerodynamically designed side pods. Due to the modular nature of it, the cooling circuits can always be changed, so we can test out different cooling circuit layouts.

KatE’s suspension was largely similar to Murph-E, which amongst other things was due to the use of the same monocoque. We corrected many of the failures and problems from the previous season’s design, but parts which had worked well were just worked on with weight optimisation and manufacture in mind. The hub kinematics were completely redesigned. For example the vertical dampers on the front axle are triggered by pull-rods and on the rear axle by push-rods. The design allowed us an effectively lossless wheel deflection and so a good performance on track. Some technical information:

Tyres and rims:

• Continental 205/510 R13
• Braid 6,5×13 central lock

Spring / damper / anti-roll bar

• ZF dampers connected to H&R racing springs
• Sword-type anti-roll bar

Brake system

• ISR calipers – 4 pistons at the front, 2 pistons at the back
• Self-developed steel discs
• Adjustable brake balance

Steering

• progressive steering gear box from PSS
• adjustable steering column holder

Wishbones

• Carbon fibre tubes with aluminium inserts
• Injection adhesive technology for high reliability

Uprights

• High strength aluminium
• Manufactured on a 5-axis mill, topology optimised
• Geared camber setting