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Quiet revolution: Audi’s mild hybrid that actually moves the car
Audi quietly introduced something that changes how we should think about mild hybrids. The 2025 A5 TDI and the Europe-only S5/S5 Avant lineup received a new 48-volt architecture Audi calls MHEV Plus — and it’s not just another torque-assist gadget. Unlike conventional mild-hybrid systems that only help the engine, this one can actually propel the vehicle at low speeds, producing an EV-like crawling ability and near-silent maneuvers in traffic or while parking.
Mild hybrids have traditionally been boring tech: a little boost, smoother start-stop, marginal fuel savings. That’s why the industry and many buyers have largely ignored them in the age of full electrification. With MHEV Plus, Audi rethinks the basic layout of a mild-hybrid system and extracts a capability most people didn’t think possible from a 48-volt setup.
What’s different about MHEV Plus?
At the center of Audi’s upgrade is the PTG — the powertrain generator. This compact electric motor is mounted on the transmission output shaft and can feed up to 18 kW (24 hp) directly to the wheels. The crucial mechanical detail: the PTG sits downstream of the clutch and gearbox, meaning it remains connected to the drivetrain even when the internal combustion engine (ICE) is disconnected or switched off.
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Most mild-hybrid systems place the electric assist upstream, on the crankshaft or via a belt-driven starter-generator. When the clutch is open or the engine is off, those systems are mechanically decoupled from the wheels and cannot drive the car. In practice that means other 48V systems provide torque assistance and regenerative braking but can’t move the car on electric power alone.
Audi’s approach is different: it connects the electric motor mechanically to the wheels instead of to the crank. The result is a rare and useful behavior for a mild hybrid — the ability to 'crawl' and perform low-speed maneuvers purely on stored electric energy.
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Real-world benefits: what you feel behind the wheel
During low-speed driving, such as stop-and-go city traffic or tight parking maneuvers, MHEV Plus can take over. The car can inch forward and slow down with the engine decoupled, avoiding restart noise, vibration, or clutch engagement. Regenerative braking recovers up to 24 kW when decelerating, helping recharge the small hybrid battery and keep the PTG ready for the next maneuver.
I experienced this in the 2025 A5 Avant with the 2.0-liter TDI. At a near-stop, the engine would shut down — and when it was time to creep forward, there was an odd, EV-like silence. Not the clunky, on-off shudder of typical start-stop systems: just a smooth, nearly inaudible motion provided by the powertrain generator. That silence changes the experience a lot more than the name 'mild hybrid' would imply.
Key numbers
- Electric contribution: up to 18 kW (24 hp)
- Recuperation (regen): up to 24 kW during deceleration
- Voltage architecture: 48-volt MHEV Plus
- Available models (initially): 2025 A5 TDI, Euro-spec S5 and S5 Avant, select Q5 variants
These figures make it clear this is not a substitute for a plug-in hybrid or an EV. The PTG is designed for seconds of electric driving at low speed — enough to crawl through traffic or maneuver without engine noise, not to deliver longer-range pure-electric travel.
Why Audi is understated about this
Audi’s press materials mention the PTG and even use the phrase 'partially electric driving,' but you’d be forgiven for missing the significance. The tone of the release is almost apologetic: the company is careful not to overpromise. That’s a deliberate strategy.
If Audi loudly marketed a mild hybrid as an 'electric driving' feature, the inevitable next question would be: how far, how fast? Answers like 'a few seconds' or 'a handful of meters' don’t make eye-catching headlines. By calling it a supporting technology rather than an electric mode, Audi protects expectations while giving buyers a genuinely useful functionality.
There’s also product-line clarity to consider. Audi already sells full EVs under the e-tron name and plug-in hybrids as TFSI e or e-hybrid quattro. Adding a third category that sits awkwardly between mild hybrid and PHEV could confuse customers, especially those trying to compare emissions, range, and incentives.
How this stacks up against Mercedes and BMW
Competitors also use 48-volt systems: Mercedes with EQ Boost and BMW with its own 48V architecture in some 5 Series engines. These systems deliver torque fill, improved start-stop behavior, and modest efficiency gains. Crucially, they cannot independently move the car with the combustion engine off — because their electric machines are upstream of the clutch.
Audi’s MHEV Plus is therefore a technical differentiator. It doesn’t leapfrog plug-in hybrids or EVs on capability, but it does offer a tangible improvement in everyday refinement and efficiency for internal-combustion models. For drivers who do a lot of city crawling, the small fuel and emissions savings — plus the absence of idle noise and vibration — add up to a better ownership experience.
Not a threat to EVs, but a smarter ICE option
MHEV Plus won’t slow EV adoption or replace plug-in hybrids. Its electric-only functionality exists for low-speed scenarios measured in seconds, not kilometers. But when EV incentives, charging infrastructure, and total cost of ownership remain uneven globally, increasing the appeal and efficiency of ICE vehicles is smart business. Audi gains a competitive edge without the full cost or complexity of PHEV components.
The transatlantic problem: why the U.S. might miss out
Here’s a surprising twist: while European models like the A5 TDI and S5 get MHEV Plus, U.S. spec S5 models do not. In the United States, Audi’s S5 retains the V6 TFSI without any 48-volt mild hybrid tech, not even the older-generation system found on some European A5 TFSI models.
That means U.S. buyers miss an efficiency and refinement feature that’s part of Audi’s current European lineup. It’s ironic that one of Audi’s most interesting mild-hybrid innovations could be almost invisible in the company’s second-largest market. The omission is likely down to packaging, certification, or emission-standards differences — but it’s a missed opportunity for buyers who would appreciate quieter low-speed operation.
Ownership and market positioning
From a buyer’s perspective, MHEV Plus changes the calculus in small but meaningful ways:
- Lower fuel use in stop-and-go traffic and parking situations
- Smoother start-stop without the immediate engine kickback during low-speed acceleration
- Slightly better local emissions performance during urban driving
- No need to pay for PHEV complexity if most electric needs are short maneuvers
For fleet buyers or drivers who spend a lot of time in urban congestion, those benefits translate to lower running costs and a more pleasant drive. Audi positions MHEV Plus not as an EV alternative but as a refinement and efficiency measure for internal-combustion models — and that’s an honest, practical stance.
What it feels like to drive
If you’ve driven a conventional mild hybrid, expect a different experience. With MHEV Plus you get moments when the car behaves like a very small electric vehicle: inching forward with no engine vibration, coasting without the engine dragging, and quick, quiet restarts when you demand more acceleration.
On rural roads or light-load cruising, the gearbox can be decoupled and the ICE shut off altogether while the PTG preserves momentum. That kind of behavior reduces fuel use and makes for a more civilized driving experience in everyday conditions.
One journalist’s note
When I first sampled the A5 Avant TDI with MHEV Plus, Audi’s own press material hadn’t primed me for the experience. I remember being puzzled by the silence when creeping away from a junction. The engine would restart, but not with the immediate hiccup you hear in other cars — instead there was a moment of benign silence and motion. It’s subtle, but moments like that add up.
Limitations and practical reality
It’s important to be realistic. MHEV Plus is not a PHEV or an EV: it doesn’t provide sustained electric range, high-speed electric acceleration, or charging-from-mains capability. The electric-only operation is intended for short, low-speed scenarios. Audi’s wording — 'partially electric driving' — is accurate, even if understated.
Still, the system’s ability to move the car and recuperate energy in everyday driving means noticeable fuel and emissions benefits without the weight, battery mass, or price tag of plug-in solutions. In markets where PHEVs are taxed differently or infrastructure lags, that balance may matter more than raw electric range.
Bottom line: a small change with outsized impact
Audi’s MHEV Plus is an elegant rethinking of mild-hybrid architecture. By relocating the electric motor to the transmission output shaft and keeping it mechanically linked to the wheels, Audi unlocked a practical behavior — crawling and silent low-speed driving — that most mild hybrids can’t match.
This is not a headline-grabbing EV breakthrough, nor is it a replacement for plug-in electrification. It is, however, a smart optimization for combustion-engine cars: better refinement, marginally lower fuel use, and a more convincing illusion of electrified driving where it matters most — in traffic and parking.
For buyers and enthusiasts focused on real-world usability and efficiency, MHEV Plus is an innovation worth noting. And for markets where Audi has chosen not to include it, the absence will likely be felt by drivers who simply want a quieter, cleaner experience without stepping up to a PHEV or EV.
"It’s a quiet triumph," I wrote after my first drive — and that description still feels right. Audi hasn’t shouted this feature from the rooftops, but the change is tangible: a mild hybrid that actually behaves a bit like an electric car when you need it most.
Source: autoevolution
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