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A typical environment rig for software integration testing. (GKN image)

GKN using modular control algorithms for added systems’ integration

At its Lohmar, Germany, R&D facility, GKN Driveline is creating modular control algorithms for new applications including integration of drivetrain software into a vehicle’s overall control system.

Control software for an AWD or electric driveline system demands more than a megabyte of code in multiple layers, while the sheer volume of software code per vehicle has increased dramatically. One 2019-model SUV using GKN technology will feature 10 times as much software code as its 2014 predecessor, according to Michael Schomisch, the Software and Electronics Manager at Lohmar.

He noted that with rapidly increasing technical complexity of vehicle systems comes "the increasingly challenging task of synchronizing the various systems to work together.” To do this, GKN's “unique” modular algorithm approach brings together multi-disciplinary teams from its Lohmar, Auburn Hills (USA) and Shanghai facilities.

The company’s specialist teams model the system’s physics and graphically create control algorithms to embed into a microprocessor. After simulation and rapid prototyping facilities provide early validation, GKN undertakes rig tests and vehicle integration activities on OEM development programs at its winter test sites. Software development and integration teams are fully incorporated into the vehicle engineering teams throughout this process.

This is crucial because for many programs GKN is "entirely responsible for the software development and integration," Schomisch said. "Each controller contains various layers of software. These include the basic operating system, connectivity applications, and the drivers for electronic actuators.”

A general-application software layer provides the interface between the driveline’s functions and other electric systems in the vehicle. These different layers of software interact but have "distinct areas of responsibility,” he said.

As always, safety software is paramount, enabling hardware to self-manage malfunctions or operations outside assigned parameters. Function applications software looks after specific control of the driveline systems and their performance.

Providing control on multiple levels

Driveline energy losses have been reduced by around 25% on recent programs, Schomisch said, and now account for only 10% of the total energy losses associated with transferring torque from the motor to the wheels. Much of this progress has been achieved through more precise control of the driveline subsystems.

For example, in GKN’s Twinster twin-clutch rear drive module that is fitted to the AWD Ford Focus RS and various GM vehicles, a vehicle dynamics controller manages the on-demand AWD, limited-slip and torque vectoring strategies (including the over-speed offset which, in the Focus RS, is exploited further with Drift mode), and the integration with the vehicle’s ABS and ESC systems.

The system is operated by an actuator controller and a vehicle dynamics controller. The actuator controller manages the twin-clutch actuation to achieve very fast response rates. It also monitors and adapts to clutch temperature, compensates for clutch wear, manages the wide clutch opening (to reduce drag torque) and delivers a self-diagnostic capability.

Five separate software packets manage the more advanced "hang-on" AWD system with axle disconnect used by Jaguar Land Rover, according to Schomisch. The disconnect system’s actuator controller manages the dog clutch, enabling the propshaft disconnect and brake function, which also incorporates connection feedback and self-diagnostics.

The next higher level controller controls the activation of the connect/disconnect sequence. The highest level controller manages the system’s strategy for activation of the connect/disconnect, based on data inputs from the vehicle’s sensors.

New controllers for electric drives

Even more complex software is used to control GKN's eDrive. A completely new range of controllers was developed to manage advanced electrified drivetrains, including the system in BMW’s i8 which has a 2-speed electronic transmission.

For this system, software within the driveline plays a vital role in managing the frequency levels emitted from the components; it would be unacceptable for vehicle occupants to be disturbed by a high-pitch whine resonating from the electric driveline through the vehicle structure.

Equally crucial is that the software developed to manage the driveline is able to communicate with other vehicle systems, so that data can be analyzed and acted on as part of the control strategies. It also has to securely accept over-the-air (OTA) updates.

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