Drive technology

The efficient engines in the Audi A5 family cover a wide range, from the conventionally powered entry model to the comfortable long-distance tourer and the dynamic sports car. The engine packages, transmission, degree of electrification, and drivetrain layout are geared toward customer expectations.

The new MHEV plus system in the Audi A5 and S5

The mild hybrid system in the new Audi A5 and Audi S5 consists of three main components: a 48-volt battery, a belt alternator starter (BAS), and a new powertrain generator with integrated power electronics.

The new MHEV plus system in the Audi A5 model series offers significant advantages in terms of CO₂ emissions and fuel consumption compared to the previous MHEV system. In the 2.0 TDI (150 kW front/quattro) (combined fuel consumption in l/100 km: 5.7-4.8; combined CO₂ emissions in g/km: 149-125; CO₂ class: E-D), these are up to 10 g/km or 0.38 l/100 km and in a 3.0 TFSI with V6 engine (270 kW quattro) (combined fuel consumption in l/100 km: 8.0-7.4; combined CO₂ emissions in g/km: 182-169; CO₂ class: G-F) up to 17 g/km or 0.74 l/100 km (according to the WLTP standard test procedure).¹

The powertrain generator can contribute up to 18 kW (24 PS) of electric power to the drive. When decelerating, the powertrain generator recuperates energy back into the battery (regenerative braking) with up to 25 kW of power. On slight inclines and when maneuvering slowly, the car can be moved solely by the drive train generator. For example, partially electric driving can be used when driving slowly in the city, in slow-moving traffic, or outside city limits when coasting to the next village. The powertrain generator is mounted directly onto the transmission output shaft.

The lithium-ion battery is based on lithium iron phosphate (LFP) and has a storage capacity of 37 ampere-hours, corresponding to just under 1.7 kilowatt hours (gross). Its maximum discharge capacity is 24 kW. The battery is integrated into a low-temperature water cooling circuit, ensuring the temperature remains within optimum conditions between 25 and 60 degrees Celsius.

This is the first time that Audi has used an LFP battery for its mild hybrid systems. Compared to conventional lead-acid batteries, these offer advantages in terms of size, storage capacity, and weight and are also very cycle-resistant. This means they lose only an insignificant amount of capacity even after several thousand charging cycles. They can also be charged with high charging currents and are very resilient when delivering electrical power.

The belt alternator starter is responsible for starting the engine and supplying electrical energy to the battery. The belt drive has acoustic advantages and achieves a higher starting speed. This results in a fuel consumption advantage and greater starting comfort. In addition, the belt alternator starter can recover the engine's kinetic energy when switched off, placing the cylinders in the optimum position for restarting.

The powertrain generator is the most powerful electric drive module in the new MHEV plus system. It marks the biggest distinction from Audi’s earlier MHEV technology, which works exclusively with a belt alternator starter. The powertrain generator can contribute up to 18 kW (24 PS) of electrical power to the drive. It sits in a compact unit with integrated power electronics directly on the transmission's output shaft. The position directly behind the gearbox offers several advantages: The power supplied or recuperated by the powertrain generator does not have to go through the transmission. This arrangement means it can be used for both front-wheel drive and all-wheel drive models.

It also makes it possible to move the vehicle purely electrically, even without a combustion engine, when driving slowly – for example, in slow traffic. This is also possible when parking or maneuvering at low speeds. It additionally results in significantly improved vehicle acceleration, as the powertrain generator is the first drive component to deliver torque to the wheels. As a result, the new Audi A5 offers noticeably better responsiveness, and a clear gain in agility is evident, especially during the first few meters when pulling away.

The powertrain generator can support the combustion engine in the speed range between 0 and 140 km/h. This means that MHEV plus briefly provides additional electrical power, enabling the combustion engine to operate as efficiently as possible. Over the entire speed range, the powertrain generator can recoup energy through regenerative braking until the vehicle comes to a standstill. The recuperation power of the powertrain generator is up to 25 kW. The integrated blending-capable brake control system ensures frictionless braking and the best possible recuperation without using the friction brake.

This makes it possible to cover some distances electrically in city traffic with frequent recuperation phases and when moving along in traffic. Thanks to the electric air conditioning compressor, MHEV plus allows continuous operation of the air conditioning system even when the combustion engine is switched off, for example, during red light phases.

Sophisticated MHEV plus operating strategy

The charging strategy for a purely battery electric vehicle (BEV) is simple: the fuller the battery, the greater the available range and the more power it can deliver. The optimum state of charge for a BEV is around 80 percent. This target margin is set lower for a hybrid system. As a rule of thumb, a battery charged to 50 to 60 percent can work most efficiently because it can deliver high currents to the electric motor and store them during recuperation.

The focus of the hybrid system is not on the electric range but on emptying and filling the battery in fast cycles. This allows as much energy as possible to be recovered and used efficiently for propulsion again in a timely way.

The control software evaluates the vehicle's operating status for the interaction between the combustion engine vehicle, powertrain generator, and belt alternator starter. Characteristic maps are stored for the sensible use of the two electric motors and desired torque for drive or recuperation. The battery charge status is also taken into account. The aim is to achieve a stable driving state – the control system arrives at different results depending on the situation. This is because the operating strategy differs not only depending on which combustion engine is installed – the electric components in the drivetrain are always the same – but also on the transmission mode engaged or the style in which the accelerator pedal is pressed and how the Audi A5 is driven. The result for the Audi A5 is not a fast lap time but the lowest possible fuel consumption without compromising driving dynamics.

In driving mode D, the additional electric power from the powertrain generator only kicks in when the accelerator pedal is pressed more than 80 percent – in other words, when the car is deliberately accelerated hard in kickdown. If the characteristic value is below 80 percent, the belt alternator starter takes on the function of delivering additional electric power. If the dual-clutch transmission is set to the sportier S position, the powertrain generator engages considerably earlier.

During sporty driving, the system control also allows the battery to be discharged more deeply because it anticipates that braking will cause electricity to flow back into the battery. At the same time, the system raises the target charge level to over 65 percent so that a lot of energy is available at the exit of the bend to support the combustion engine electrically. The use of the powertrain generator also has advantages in terms of driving dynamics, as the additional torque makes the vehicle more agile when exiting corners.

The powertrain generator is decoupled from the drivetrain at speeds above 140 km/h and when driving in transmission mode D at a slower pace. This is the case at highway speeds going uphill, for example, when the powertrain generator cannot contribute any power. To avoid unwanted drag at the expense of efficiency, the system decouples the powertrain generator from the drivetrain.

The new Audi A5 can also be driven electrically, for example, when the vehicle rolls towards a town limit and then maintains speed with the help of the powertrain generator. Fixed limit values regulate the engagement of the combustion engine: If the battery is at a lower state of charge, the combustion engine switches back on when the power requirement exceeds 14 kW. For emission-free electric parking or maneuvering – not only on level roads but also on slightly sloping terrain – the threshold value for switching on the combustion-engine vehicle is 10 kW of powertrain generator power.

The efficiency improvements in the drivetrain combined with the increased tank capacity of up to 60 liters for diesel models (56 liters for petrol models) ensure a noticeably improved range. This contributes significantly to the long-distance capability and travel comfort of the Audi A5.

2.0 TFSI engines as entry-level version

The entry-level engine is a 2.0 TFSI with 110 kW (150 PS) (combined fuel consumption in l/100 km: 7.6-6.6; combined CO₂ emissions in g/km: 173-150; CO₂ class: F-E). Alternatively, the same engine is optionally available with an output of 150 kW (204 PS) (combined fuel consumption in l/100 km: 7.9-6.6; combined CO₂ emissions in g/km: 179-151; CO₂ class: G-E). The 110-kW variant is only available with front-wheel drive, and the 150-kW variant with front-wheel drive or quattro ultra all-wheel drive.

Many technical modifications raise the 2.0 TFSI to a new level of efficiency. These include the fact that the engines operate using the modified Miller cycle combustion process. It brings advantages, especially under partial load – i.e., in the engine’s most common operating range. In the Miller cycle, the intake valves are closed early, and the compression of the injected fuel-air mixture is high. The fuel-air mixture can be run in stoichiometric operation over the entire map. This allows the engine to operate in the optimum range. Fuel consumption and CO₂ emissions are reduced.

In the new A5, Audi is using an exhaust gas turbocharger with variable turbine geometry in a TFSI engine for the first time. This improves the responsiveness and efficiency of the direct injection engine. It enables a more harmonious and agile build-up of torque at low engine speeds. The turbine guide vanes are closed further if the driver accelerates in the lower speed range. This reduces the inlet cross-section into the turbine housing and directs the exhaust gas directly onto the blades. The turbine wheel rotates faster, the amount of fresh air moved increases, and the boost pressure builds up quickly. As the amount of exhaust gas increases or the boost pressure requirement is low, the guide vanes are opened again.

Further optimizations in the 2.0 TFSI include using a friction-optimized timing chain drive and the integration of charge air cooling into the intake manifold. There is also improved oil supply to the crankshaft thanks to a change in the bore concept and a vane cell oil pump with increased delivery volume. An increase in injection pressure to 500 bar brings benefits in terms of emissions; this is achieved by relocating the high-pressure pump to be driven by the intake-side balance shaft.

2.0 TDI engine with MHEV plus

The 2.0 TDI with 150 kW (204 PS) (combined fuel consumption in l/100 km: 5.7-4.8; combined CO₂ emissions in g/km: 149-125; CO₂ class: E-D) sets new standards in the A5 with its MHEV plus technology. This two-liter powerplant of the EA288 Evo generation inherits from its predecessor the optimized combustion engine with cylinder pressure sensor, Twin Dosing for exhaust emission control, and two balance shafts for smooth engine operation. It develops a maximum torque of 400 Nm between 1,750 and 3,250 rpm. The 2.0 TDI is available with a dual-clutch transmission and front-wheel drive or quattro ultra all-wheel drive.

To increase efficiency and comfort, the engine is partially electrified using the new MHEV plus system with a 48-volt on-board electrical system. Partially electric driving reduces CO₂ emissions thanks to the high recuperation performance. The comfort of the TDI is further enhanced by the 48-volt belt starter generator, which ensures a smooth engine start.

When starting, the car’s reaction time is reduced and it is noticeably more agile. Other technical refinements of the 2.0 TDI include separate cooling water circuits for highly flexible thermal management, a cylinder pressure sensor for optimum combustion and minimized internal friction for high efficiency.

3.0-liter V6 TFSI engine with MHEV plus

Athletic, evocative, and real eye-catchers: the new Audi S5 models are the most powerful in the range at launch and set the benchmark for the sporty mid-size segment. The 3.0-liter V6 turbo engine delivers 270 kW (367 PS) (combined fuel consumption in l/100 km: 8.0-7.4; combined CO₂ emissions in g/km: 182-169; CO₂ class: G-F) and generates a maximum torque of 550 Nm. The top speed of the S5 models is 250 km/h. The V6 TFSI is supported by the MHEV plus system, which provides additional electric power and enables partially electric driving.

Partial electrification using the new MHEV plus system with a 48-volt onboard electrical system reduces CO₂ emissions thanks to partially electric driving and high recuperation performance. Compared to an S4 Sedan TDI (predecessor model), the S5 Sedan TFSI reduces CO₂ emissions by up to 14 g/km.

The revised S tronic dual-clutch transmission in the Audi S5, designed for more torque, also reduces weight on the front axle and makes the vehicle more agile. The standard use of quattro with sports differential with torque vectoring in combination with an adjustable all-wheel drive clutch is tuned for lateral dynamics at the highest level.

The new 3.0-liter V6 TFSI (EA839evo generation) is the logical further development of the unit that has been in series production since 2015. The following changes have been made to the engine: redesigned turbocharger with variable turbine geometry (VTG), indirect charge air cooling, optimization of load changes, use of Miller cycle combustion, and modifications to the injection system. In conjunction with the MHEV plus system, very positive characteristics are achieved in terms of driving dynamics, comfort, and CO₂ emissions.

In the V6 TFSI in the Audi S5 models, an exhaust gas turbocharger with variable turbine geometry ensures boost pressure builds up even at low engine speeds. Revised intake ports in the cylinder head, optimized timing, and a compression ratio increased from 11.2:1 to 12:1 achieve an efficient combustion process with more complete combustion of the air-fuel mixture. Two indirect water-to-air intercoolers integrated with the engine replace the previous system with a direct air-to-air intercooler. The water side is integrated into the low-temperature circuit. In addition to more efficient cooling, particularly at low speeds and high loads (hill climbing, towing), the complexity of the application and the integration in the front end of various vehicle variants is significantly reduced. The very short intake paths also improve engine response.

¹ The advantages described regarding CO₂ emissions and fuel consumption include the influence of the additional weight of the MHEV plus system compared to the MHEV system. Further CO₂ -effective effects at vehicle level, which may result from deviations in the drivetrain, weight or driving resistance of the vehicle under consideration with the MHEV plus system compared to a reference vehicle with MHEV technology (e.g., further development of the combustion engine or basic transmission, changes in rolling resistance, aerodynamics or weight) are not taken into account.

The equipment, data and prices specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.