Locally emission-free, efficient and fit for daily driving: Audi’s formula for plug-in hybrids

A conventional internal combustion engine or a fully electric powertrain? There is a third answer to this fundamental question of modern mobility: PHEV – a plug-in hybrid electric vehicle or in short: a plug-in hybrid. The combination of a conventional internal combustion engine (IC engine) and an electric motor supplied with energy from a lithium-ion battery at the rear of the vehicle enables locally emission-free driving and low overall consumption. An overview of the current Audi technologies and models.

What does the term hybrid powertrain mean and what exactly is a plug-in hybrid?

Traditionally, a powertrain is referred to as a hybrid system whenever two propulsion technologies – in other words, an IC engine and a motor and the respective energy storage system – are combined. A typical characteristic of hybrids combining an IC engine and an electric motor is that the electric motor can either be used as the sole, locally emission-free traction motor or assist the IC engine with additional boost capacity. The electric traction motor also serves as a generator for recuperation, converting kinetic energy into electrical energy and storing it in a lithium-ion battery. Today, the plug-in hybrid electric vehicle (PHEV) has become established as the most commonly used form of hybrid electric vehicle (HEV): The battery, in this case, can be charged externally, at a charging station or power outlet. The energy capacities of the batteries of plug-in hybrid electric vehicles have increased accordingly, which benefits customers by extending the car’s electrical range.

Plug-in hybrids are a complex balancing act between two powertrain worlds. What is Audi’s formula for the best total technology package?

The focus is placed on three objectives: a confident electric driving experience, easy charging management and high suitability for everyday driving. These three factors form the target triangle of PHEV development at Audi.

For one, the electric driving experience is defined by a powerful electric motor delivering up to 105 kW, depending on the model. This ensures fully electric operation across a large speed range in diverse driving situations. The sophisticated powertrain management of Audi’s plug-in hybrids provides the basis for frequent and sustained electric driving. The smart powertrain management system controls the interaction of the electric motor and the IC engine. It decides when the car will operate in fully electric mode, when energy is recuperated or when the car coasts while the IC engine is inactivated and when the IC engine is additionally activated. The utilization of diverse vehicle sensors, route data and route information for propulsion control is essential to smart powertrain management, large segments of electric driving – especially in real-life operation – and high energy efficiency. Measured according to the WLTP cycle, Audi’s PHEV models achieve an electric range of up to 59 kilometers.

Charging management is the second pillar of Audi’s PHEV model development. Audi’s PHEV models in the mid-size and full-size class have a charging capacity of up to 7.4 kW, which recharges the hybrid models in approximately 2.5 hours. This charging period is ideal for the typical user pattern of PHEV customers: It makes easy and fast charging of the car possible, once or twice a day, either at home or additionally at work. But Audi has also provided for easy charging on the road: Audi’s proprietary e-tron Charging Service gives PHEV models card-based access to some 137,000 charging points in 25 European countries. In addition to the “Compact” charging system with a cable for household and industrial power outlets, the standard equipment of all PHEV models includes a Mode-3 cable with a Type-2 plug for public charging stations.

High suitability for everyday driving marks the third corner in the target triangle. Obviously, this is initially derived from the first two objectives: frequent operation in electric mode and easy charging management. Ample space, high variability and usability of Audi’s plug-in hybrids are other important criteria for everyday suitability. Audi’s engineers have invested a major effort in the space-saving and compact integration of the batteries in the trunk of Audi’s PHEV models. Due to the batteries being located underneath it, the trunk floor is slightly elevated compared to the conventional models, but does not include a step. This makes for a flat, effectively usable floor without impairing the customer’s ability to load the trunk. Good usability also includes the availability of a trailer hitch, except for the A8 TFSI e, and towing capacity identical to the conventional models (exception Audi Q5: conventional 2,500 kg, PHEV 1,750 kg).