With more than 40 facilities in 30 countries, GKN Driveline commands approximately 40% of the automotive driveshaft market. The company’s latest technology involves development of the hybrid system that will feature on upcoming Peugeot models.
Peugeot is set to launch production of its hybrid model range under the name HYbrid4. While most hybrid vehicles position the electric motor within the engine compartment, Peugeot has elected to take a different route, making its hybrid system an integral part of the rear axle. The key component in this setup is GKN Driveline’s Electric Drive Axle (EDA), designed specifically for use with split-axle systems.
The solution developed for Peugeot is similar to the e-AWD system supplied to Nissan by GKN; since 2002, the company has delivered over 200,000 units for production of Japanese-built models including the March, Cube and Wingroad. Yet while the concept is similar, John McLuskie, Product and Business Development Director at GKN Driveline, says the Peugeot hybrid system offers additional flexibility. “The Nissan model produces 5kW (of power). The PSA version offers 27kW, the extra power delivered through new, stronger components. The original system would only engage if activated by the driver, generally if the vehicle was stuck, whereas this new version can deliver sufficient power to drive the vehicle using only electric power for short distances.”
Olivier Emily, GKN Driveline’s Global Programme Manager for Electric/Hybrid Engineering, continues by outlining how the new system offers drivers a choice of operating modes. “The system features four settings. ‘Auto’ is when the entire system is automatically controlled – this includes the HDI engine and electric motor. ‘ZEV’ is the all-electric option, with activation of the HDI engine limited to periods of sustained acceleration. ‘Sport’ mode favours quicker gear changes at higher engine speeds, while ‘4WD’ instructs both powertrains to operate in unison, the HDI engine driving the front wheels and the electric motor driving the rear wheels.”
Electric-only range is limited to approximately 2km, but while this is no extended-range EV, the advantage of the free-standing unit is that it can be adapted for use with other models with only a light redesign. With this in mind, it’s not surprising that McLuskie confirms that other OEMs have expressed an interest in the technology.
System design
The Electric Drive Axle consists of a gearbox, together with a 27kW electric motor supplied by Bosch. Within the gearbox is the differential, a two-stage reduction gear and a disconnect device, the components assembled in a die-cast aluminium housing. The housing and steel gear components are supplied by a third-party part provider. The differential and electromagnetically-controlled disconnect system were developed by GKN Driveline. “(The disconnect system) has a dog-type rather than a plate clutch. It is a dry, rather than a wet clutch” says McLuskie. “The system is engaged at up to 120km/h, at which point a spring-loaded pin in the dog clutch disengages the locking differential.” He adds that this eliminates any drag from the gearbox at motorway cruising speeds, improving overall system efficiency.
The system was developed to meet size specifications delivered by Peugeot. Olivier Emily: “There’s not a lot of space in the rear axle of the (Peugeot) 3008, the first vehicle to use the system. Although it is a very compact unit, the E-machine still weighs 35kg. The vehicle supervisor software sends control signals to connect and disconnect. There are no bearings in the unit; the input pinion of the gearbox is directly connected to the output shaft of the motor, it’s the differential and electromagnetic operation that separate this unit from the competing technology.”
Another feature which allowed GKN Driveline to develop this smaller system was the choice of joining technology. “In a typical arrangement, the ring gear is bolted to the differential housing,” says Emily. “In the EDA, we have used laser welding to join these two parts; removing the bolts has allowed us to make the unit considerably smaller.” The hybrid system also incorporates regenerative technology, with an 8kW motor at the front of the vehicle collecting the generated charge before passing it to the battery pack at the rear. Asked why the motor is not located at the rear of the vehicle, McLuskie says that like other hybrids, the front wheels must be used to collect this additional charge, as to do this through the rear wheels could make the vehicle unstable.
Unit production and installation
GKN Driveline assembles the Electric Drive Axle at its plant in Bruneck, Italy. In building the combined unit, the first procedure is to attach the electric motor to the first pinion of the gearbox. After that, it is a matter of installing the individual parts in the gearbox housing, including the differential, which is delivered to the assembly line as a prebuilt sub-assembly. In all, there are just two line operators that carry out all assembly steps, with automation limited to an ABB robotic lifter used to position the electric motor. Fully 100% of all completed units are subjected to on-bench testing, which includes clutch operation and drag torque data. Units should return less than 1Nm of drag torque, with any higher returns signalling a problem within the gearbox. The units are filled with oil for testing, drained and then filled again before shipping. Although the gearbox itself is designed to be maintenance-free during its operating lifetime, outer seals could need replacing, which Emily states is a relatively simple operation.
The gearboxes are also tested for noise and vibration characteristics, the collected data compared to a typical acceptable signal. “The motor is not a problem,” says McLuskie, “but one of the most difficult things to do is make a noiseless transmission.”
In Sochaux, France, where the first of the HYbrid4 models will be produced, sub-assembled axles are attached to the Electric Drive Axle. Acting as the joining point between the two separate axle assemblies, the EDA has cast-iron holding elements within the gearbox unit to provide the required support. Rails machined into the inserts facilitate lubrication. According to Emily, Peugeot has invested approximately €450m in the development of the EDA. “GKN has also invested a considerable sum,” he says. “We have had an average of 10 engineers working on this project at any one time since 2007.” With a start-of-production date scheduled for October, both parties will be looking forward to seeing the unit start to make some returns on this investment. Emily: “We will be making about 40 units per week. By 2012 or 2013, we are expecting production to reach about 30,000 units per year.”