Volkswagen Touareg and Porsche Cayenne Parallel full hybrid technology from Bosch goes into series production · Launch of first full hybrid vehicles with parallel technology · Intelligent drive control system provides key to extraordinary comfort · Bosch-made power electronics, electric motor, and adaptive clutch The hybrid variants of the Volkswagen Touareg and Porsche Cayenne S, which recently went into production, feature hybrid technology supplied by Bosch. This is the first time that either of these models has been available as a parallel full hybrid. As well as key components such as the power electronics and electric motor, Bosch is also providing the “brain” of the vehicles in the form of the Motronic control unit for hybrid vehicles, which governs when the electric motor, internal-combustion engine, or a combination of the two kick into action. Volkswagen and Porsche both chose to equip their hybrid vehicles with a 3.0-liter V6 supercharged direct-injection engine and an eight-speed automatic transmission. The six-cylinder V-engine delivers 245 kilowatts (333 horsepower) and a maximum torque of 440 Newton meters starting from 3,000 rpm. The vehicle also features an Integrated Motor Generator (IMG) developed by Bosch. The water-cooled electric motor includes a separate clutch.
The hybrid module is positioned between the internal-combustion engine and the transmission, taking up impressively little space thanks to a diameter of 30 centimeters and a length of just 145 millimeters. The IMG delivers 34 kilowatts and a maximum torque of 300 Newton meters. That means the Volkswagen and the Porsche can cruise at a maximum of 50 to 60 kilometers per hour running on electric power alone, as long as the nickel metal hydride (NiMH) battery has enough charge. The battery has an energy capacity of 1.7 kilowatt-hours with a peak of 288 volts. During braking, the electric motor – now operating as a generator – recovers kinetic energy, which is then stored in the high-voltage battery. Lifting off the throttle at any speed up to around 160 kilometers per hour activates what the engineers refer to as ‘sailing’ mode: the combustion engine automatically shuts down and the vehicle coasts along without consuming fuel – obviously without sacrificing any of the functionality of the systems required for a safe and comfortable drive. Braking is also a fully automatic process, with the hybrid control unit monitoring the pressure on the brake pedal to determine what brake torque should be electrically set by the IMG. This does not affect safety systems such as ABS and ESP®, which take precedence whatever the situation. ‘Power boost’ from the electric motor For drivers in a hurry, the electric motor and the combustion engine can also work in tandem, allowing the Volkswagen and the Porsche to sprint from 0 to 100 kilometers per hour in 6.5 seconds. This ‘power boost’ function increases the vehicle’s performance to 279 kilowatts (380 horsepower), offering the driver a maximum torque of 580 Newton meters. Compared to the first-generation V8 vehicles, these hybrid vehicles cut fuel consumption by up to 40 percent. EU cycle fuel consumption falls to 8.2 liters per 100 kilometers, equivalent to CO2 emissions of 193 grams per kilometer. Both vehicles also comply with the Euro 5 standard and the U.S. emissions standard ULEV 2.
Intelligent control system provides key to extraordinary comfort The fact that the internal combustion engine and the electric motor work together so seamlessly stems from the perfectly tuned interaction between modern management and control technology and optimized hybrid components. Bosch can draw on many years of experience in this field thanks to its work on developing gasoline injection systems. “The hybrid control unit injects a healthy dose of innovation into the best field-proven technology. We based the system on the Motronic, which has already proved its worth in so many direct injection gasoline vehicles. We then integrated the additional functions you need for hybrid operation, which we developed in collaboration with our customers,” says Matthias Küsell, who heads up development and customer projects for hybrid and electric vehicles at Bosch. One of the biggest challenges was ensuring a smooth transition between electric-powered, hybrid, and combustion engine-powered driving. It was essential to ensure that driving comfort would not be impaired by the switch between drive and generator operation. This is achieved by giving the control unit continuous access to sensor data from the combustion engine, electric motor, battery, clutch, and other components. It uses this data to analyze and control how the two powertrains interact in real time, using an adaptive clutch to make seamless transitions.
The control unit ensures that the electric motor and engine are turning at exactly the same speed when transferring the torque. Küsell sees this as the core element of the parallel hybrid technology. Hybrid and direct injection engines – the perfect combination The supercharged V6 engine is a key part of the overall concept. The Motronic control unit manages the combustion engine with tremendous precision, right down to the rate of individual injections. It employs an additional CAN bus interface to exchange all relevant data with the hybrid components, power electronics, and battery, and the efficient direct injection system also reduces exhaust emissions. The combustion engine and electric motor complement each other perfectly, enabling parallel hybrids to offer a whole series of new features to improve driving comfort. Active Damp Control is the name Bosch chose for the concept that provides the six-cylinder engine with the sedan-like feel of a much larger engine. In the future, this concept is set to iron out some typical disadvantages of smaller turbocharged engines such as poor low-end torque, paving the way for highly economical downsizing concepts to enter the mass market. Optimized components offer inroads into mass market Parallel full hybrid technology can be implemented as a more cost-effective solution in comparison to other hybrid concepts. For example, it requires just one electric motor, which operates as both a motor and a generator. To enable broader application of this environmentally friendly technology in different classes of vehicle, Bosch is engaged in a continuous process of developing the system on a component level, tackling issues such as reducing the volume of space taken up by the power electronics. Despite having to maintain a tricky balance between robust design, maximum efficiency, and minimal space requirements, the developers have now succeeded in reducing the volume of the power electronics by one third to ten liters – without compromising performance. “Our aim is to get the next-generation version down to five liters,” Küsell says. The power electronics are a core component, providing an interface between the high-voltage electric drive and the vehicle’s 12-volt electrical system, and featuring an inverter that converts the direct current from the battery into three-phase alternating current for the electric motor, and vice versa.