Modern hybrid drive in a retro vehicle
Johannes Huebner Giessen supports university with traction machine to hybridize a VW Beetle
- Objective: Practical experience with electrically powered drive solutions for young students studying to be engineers at the University of Applied Sciences in Cologne, Germany
- Implementation: Develop and install an electric machine (10 kW) from Johannes Huebner Giessen to convert a VW Beetle to a hybrid vehicle
- Result: Maintenance-free solution, lower fuel consumption and more fun to drive thanks to more power when accelerating
Rising prices for raw materials and more stringent regulations governing CO2 emissions are inducing development engineers to seek new drive solutions. For years the trend has been moving away from petrol and diesel fuels towards electric drive solutions. And it is not just the big motor vehicle manufacturers and their suppliers who are making full use of their development potential. Universities and institutes are entering into cooperation projects to demonstrate to their young budding engineers the wide variety of electric and low CO2 emission drives and facilitate a practical, hands-on approach to the technology behind them. Against this background the Institute of Automation Technology at the Cologne University of Applied Sciences launched a project with the objective of converting an old VW Beetle to a hybrid vehicle. As a cooperating partner to the university Johannes Hübner Fabrik elektrischer Maschinen GmbH, the specialists for individual drive solutions based in Gießen, developed the traction machine for the project.
The Institute of Automation (IA) is part of the "Faculty for IT, Media and Electrical Engineering" at the University of Applied Sciences in Cologne, Germany. Students and professors at the university study hybrid and electric drives day in and day out. The primary objective is to offer the students practical insights during their time studying at the university. "So to enable the students to have an object to study and work with during their training we came up with the idea of hybridizing an old VW Beetle", explained Prof. Dr. Ing. Andreas Lohner who in addition to teaching automation engineering and electric drives at the IA also heads the associated laboratory. Converting a vehicle built in 1982 was at the heart of the project, and a number of theses have been written in connection with the topic. In the first phase – and topic for the first thesis – Johannes Huebner Giessen developed the electric traction machine in 2007 to install in the vehicle. The starting point was to replace the old commutator-type generator of the Beetle with a modern hybrid drive, which is able to fulfil the functions of the generator.
High performance on a small footprint
Decisive for a suitable drive solution was the amount of space available in the vehicle as well as the dimensions of the dc generator. The new hybrid drive needed to be adapted to fit precisely the amount of available space. To keep the changes to the mechanical components to a minimum and not make drastic changes to the drivetrain of the Beetle during the modernisation project participants from the university and Johannes Huebner Giessen decided in favour of a parallel hybrid drive solution with an eight-pole, permanently excited synchronous machine as an electric motor. This hybrid drive is known as a parallel hybrid system, which in contrast to the series construction of the electrical machine is driven by means of a toothed belt and runs parallel to the combustion engine as a consequence. When braking the parallel driven machine acts as a generator to recover and store the energy used to decelerate and brake the vehicle in the battery. In contrast to series hybrids the output performance and overall efficiency can in this case only be significantly increased with the aid of an additional machine. Identical interfaces were fitted to ensure it was possible to install the machine perfectly in the existing vehicle system. Using the old dc generator made available by IA, Huebner was able to precisely measure the shaft as well as the other mechanical interfaces. The new machine was designed and built according to these measurements. "The big difference is that the machined used today has an output of good 10.8 kW at 5772 rpm – which corresponds to about 100 km/h", emphasizes Prof. Ing. Ewald Ohl, head of the energy and drive systems department at Johannes Huebner Giessen.
Drive and brake with the aid of a motor
The power electronics in the students' test vehicle were designed so it would be possible to exhaust all of the possibilities offered by the electric and electronic components and functions. The permanently excited synchronous machine can work as a motor as well as a generator. In other words, it can support the vehicle drive and braking performances. The VW Beetle is fitted with a 48 V, 2 kWh capacity lithium battery as an electrical energy storage medium. Energy fed from this storage medium to an inverter via a DC/DC converter is used by the synchronous machine as a drive motor when pulling away, and the majority of the kinetic energy converted back to electric energy when braking. This is in turn stored in the lithium battery. The high dc voltage of 500 V generated by the DC/DC converter for the drive inverter is also a special feature of this project. "Under normal circumstances the voltage in a vehicle is 12 or 48 V", explains Prof. Andreas Lohner. "In this application we had to ensure that all insulation measures were put in place to make sure nobody is able to come into contact with the high voltage." Quite different to the mechanical connections, the electrical interfaces in the modernized drive system in the vehicle were adapted and redesigned. For instance the carburettor had to be moved. Unlike a drive powered by a combustion engine the electric motor / generator is driven via a toothed belt instead of a V-belt.
Maintenance-free drive solution for use in day-to-day traffic
An air cooling system is one of the measures implemented to ensure the reliability of the hybrid engine. The parallel configured electric drive system is also fitted with lubricated-for-life ball bearings. The Huebner drive has required absolutely no repairs over the last few years, Prof. Andreas Lohner emphasizes. In addition to not needing maintenance, low fuel consumption is a decisive advantage offered by the hybrid drive concept. Registered for use during the summer the Beetle consumes on average four to five litres of petrol over 100 kilometres (approx. 63 mpg) – alternating frequently between the petrol engine and electric motor. "The converted VW Beetle handles much the same as a modern vehicle, but has significantly more power when accelerating", says Prof. Andreas Lohner.
Electric motor and cooperation as planned
The Institute of Automation at the Cologne University and Johannes Huebner Giessen began to collaborate in 2007 following a discussion held at the SPC IPC Drives in Nuremberg. "Huebner was interested in and very open to our idea of using a VW Beetle for our students to convert to a hybrid vehicle in a hands-on project", Prof. Andreas Lohner remembers. The objective was to integrate as much performance and high levels of efficiency as possible in this machine. The student degree candidate was able to exchange ideas with development engineers at Huebner and achieve a very good result. All in all Johannes Huebner Giessen has to date developed and produced two traction machines as part of projects to hybridize the VW Beetle. The first was donated to the institute and installed directly into the vehicle registered to drive during the summer months. And a second was set up on a test stand in the automation laboratory at the institute about three years ago to allow students access to the motor and carry out tests at any time. Apart from minor modifications to the cabling the machines are both mechanically and electrically identical, says Prof. Andreas Lohner. Final development of the traction machine, which was essentially carried out at the facilities of Gießen based company, fulfilled all of the boundary conditions and specifications put forward by the IA. The result: a modern vehicle with 15 per cent less fuel consumption and a lot more fun to drive.