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November 22, 2005
Advanced auto electronics help save fuel and emissions
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Electrical power management is an issue of ever growing importance in the automotive industry. As a specialist in this field, AFL Automotive in Frickenhausen have designed a system which breaks through the limits of existing vehicle electrical systems. A variable-voltage electrical system both enhances alternator efficiency and multiplies the available power. Helmut Ollhäuser, General Manager Sales and Engineering Electronic Division of AFL Automotive, explains the concept.
Mr Ollhäuser why have AFL Automotive designed a new vehicle electrical system?
As a designer of electrical and electronic automotive systems we have always been focusing on keeping power consumption low and avoiding unnecessary loads on the electrical system. With an ever growing number of electronic units used in cars, the demands on the vehicle electrical system have dramatically increased in recent years. However, power generation in an alternator and power storage in a vehicle battery are subject to physical limits and can, therefore, not be infinitely extended. Hence Alcoa have been conducting in-depth research in the field of power management. In 2000 we kicked off a joint project with a car manufacturer that dealt with power requirements, higher system voltages and effective power management.
What were the results?
We designed a vehicle electrical system without the existing 14 volt limit. A variable voltage has many benefits not only with reference to electronics. The system includes an alternator which is able to generate higher voltages when required. Maximum voltage lies within the protective low voltage range of 30 to 40 volt, with electrical outputs of 2 kW to 8 kW provided.
A fundamental departure from the traditional, inflexible 12 volt system?
There are two voltage domains which are separated by a linear controller, a conventional analogous control circuit with a capacity of up to 600 farad/cell. The existing 12 volt electrical system remains not only unchanged but benefits from the voltage stabilising effect provided by the controller. Furthermore the higher voltages generated by the alternator can be made directly available to the consumers that require them.
What kind of consumers do you mean?
For instance electrical rapid cabin heating systems which normally use PTC elements. With a variable voltage the output of such heater elements can be tripled. Voltage is also supplied to so-called transient heavy-duty consumers. These are applications with high short-term power requirements, such as the electric power steering during parking, the electric brake assistance system or an electric turbocharger. Such consumers require much more than 2 kW, but only for 2 or 3 seconds. Afterwards they remain idle for extended periods.
What kind of technical modifications are required?
The conventional claw-pole alternator has to be modified, since current-type alternators limit the voltage to 14 volt. Hence the controller has to be adapted to the modified control mode and fitted with a communications interface, such as LIN. The electric strength also requires a different type of rectifier diodes. Important aspect for weight and space: the alternator size remains unchanged from current-type units. Efficiency, on the other hand, increases significantly by up to 18% to 75% and more.
You mentioned other benefits of the system?
Yes. The power dissipation generated by the voltage difference within the linear controller is converted into heat which, when supplied to the coolant, allows faster heating-up of the circuit. Hence the cabin warms up faster, and the engine reaches its optimum operating temperature earlier.
Another benefit is recuperation. Imagine a long-distance trip at a constant speed of 100 or 130 kph. When neither heating nor power steering nor the turbocharger are required, the alternator is nevertheless able to generate a high voltage. The energy is then stored in a supercap, a twin-film capacitor with a capacity of up to 600 farad/cell, and can later be used as required.
The fleet consumption directive requires car manufacturers to achieve a significant reduction of CO2 emissions. What are the effects of the system on emissions and fuel consumption?
This is a very important aspect. Lower fuel consumption also means less emissions. We have proved that the system can increase fuel efficiency by up to 5%. The principle is simple: the capacitor is charged under braking or overrun conditions, whilst under acceleration the alternator is deactivated, so relieving the combustion engine of up to 9 Nm load – until the energy stored in the supercap is exhausted.
What are the benefits of the Alcoa system compared with other industry proposals?
Most other proposals are either unaffordable or unfeasible. With our system we have found an efficient compromise: it works, it is feasible and it is affordable.
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