Kinetic Energy Recovery System

Mack Murray, President of French technology company, Adgero, came up with the idea of a hybrid trailer, using KERS (Kinetic Energy Recovery System), adding extra impetus to the combination.

Kinetic Energy Recovery System

At its simplest the Adgero system sees the central axle in a triaxle being fitted with an electric motor/generator alongside an ultra capacitor. When decelerating the axle charges the batteries and then when acceleration is required, adds some impetus to the combination by driving the trailer axle.

The ultra capacitor can absorb power from the generator very quickly and release it again, very quickly. Batteries would be an option, but they would weigh more to get the same charge and discharge levels. The base module Edgero fit weighs in at 50 kg.

The system uses a drive axle with a short drive shaft to a motor, just in front of the leading axle. The  motor and ultra capacitor are mounted between the chassis rails, out of harm’s way. Wheel motors were considered, but this would considerably increase unsprung weight and potential damage.

“In terms of the regulatory environment for this there are two types of regenerative braking, A and B,” said Murray. “Our system acts as a retarder and starts regenerative braking on throttle-off, it’s category A. The reason we do this is because, in order to maximise the energy recovery, we don’t want to be competing with the friction brakes.

“This is managed by an accelerometer in the system. The system doesn’t need to know the mass of the combination, our how fast it is going. The same principles work at 7.5 tonnes or 160 tonnes. All we are paying attention to is the threshold of deceleration when it plateaus. This is configured by the operator. Once you go to a certain deceleration, you have to activate the brake lights on the vehicle.

“Category B is more complicated, when the driver pushes the brake pedal, the service brakes come on as well as the regeneration, in concert. The control of the Adgero system is handed over to the braking control system. This is possible but adds in complexity with Adgero having to collaborate with the brake supplier and the system is competing with five or six extra axles’ friction brakes.”

The system has been built and there is a few trailers, built by UK trailer builder SDC and running in the Eddie Stobart fleet in the UK. Legal status on the road is being questioned, although a regulatory framework is expected to be worked out for Europe by the end of 2017.

“The advantage of an ultra capacitor is, the internal resistance of the cell is very low, compared to a battery,” said Murray. “You generate less heat and reduce the amount of wear on the cell. We guarantee ours for one million charge/discharge cycles, which equates to about fifteen years of operation in regular service.

“Our system is compatible with any truck, because all we do is capture CANbus commands. Any vehicle using CANbus is compatible. We could fit it to a non-CANbus vehicle, but we would have to fit some form of sensor to generate commands for the system.”

Another advantage of the ultra capacitor is the fact it can be fully discharged before any fitting or maintenance. This means a trailer builder will be able to fit the unit themselves during production. Litium-ion batteries cannot be fully discharged as this will damage them. This means the battery is an electrical hazard when being fitted or maintained.

Edgero have also developed a hybrid module for rigid trucks. In this case, the motor is fitted where the truck normally has a centre bearing on the shafts. There are three different types of motor. One is extremely compact, the same size as the centre bearing, at 33 kg and putting out 295 hp (220 kW) of power.

The larger motors take up more room and are trickier to package. Murray reckons, if a retarder will fit on the truck, the Edgero system will also.

“The ultra capacitor is something built to our specification by Skeleton Technologies,” said Murray. “Skeleton make the cells inside it, they are used by the military and more expensive versions of the cells are used by the European Space Agency. They contain graphene, the problem with which has been, making it in large quantities.

“Skeleton has developed an industrial process which allows them to produce large quantities of graphene. The have built a new automated plant to build these things in Germany. So, we are going to be able to get large quantities of these cells, to be able to offer the system at a very competitive price.

“If I compare this module, which is 160 volts, with existing modules on the market, we have 50 per cent more energy stored, much less internal resistance and a much longer life for the module. If something goes wrong, it is fitted with 3G so we know and when you stop we undo four bolts and swap it out.”

Because there is a large energy store on the truck when the system is fitted, this means systems like trailer telematics will always have power. The system is also connected to the EBS system, so the load can be measured at anytime and any tampering with the load will be detected. A system which trickle charges a battery on the trailer is being developed in order provide independent power for items like electric fork lifts or refrigeration units, on the trailer, at all times.

If there is a common thread though these two case studies, it is the fact the new technologies just seem to make the possibilities for further development much wider for future trucks technology developers.

Author: Tim Giles

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