Proton X90 is P1's first hybrid but it's a mild one - what's the difference between MHEV, HEV and PHEV?

Hybrids are not new in Malaysia. Dual-power petrol-electric hybrid drivetrains were first introduced here by Honda Malaysia in 2007, with the mild-hybrid Honda Civic IMA (Integrated Motor Assist).

In 2009, UMW Toyota Motor launched the first full-hybrid car in Malaysia, the two-motor Hybrid Synergy Drive (HSD) Toyota Prius.

Plugged-in hybrids came into the market in the mid-2010s, mainly Volvo and BMW models.

The hierarchy of electrified vehicles

Any car that receives electric power assistance in its motion is referred as an electrified vehicle (or xEV), with x being the variable determining the vehicle’s position in the hierarchy.

Mild-hybrids (MHEV) rank at the bottom, while fully electric battery-powered vehicles (BEV) sit at the top. Every step up the xEV hierarchy, the vehicle relies less on the engine, more on battery power, culminating in zero-engine, battery-only BEVs.

MHEVs have the smallest battery (around 0.5 kWh) and provides the least electric power assistance. An MHEV cannot accelerate from standstill in electric power-alone. The small electric motor serves only to assist the car’s forward motion once it gets moving. 

When coasting the motor works in reverse, as a generator to recover energy that would've otherwise been lost as heat.

Mild hybrids are also known as MHEV, for mild-hybrid electric vehicle. They usually run on 48V electrical architecture (regular 12V battery still maintained), either with a belt-driven starter motor-generator (BSG) mounted outside the engine block to replace the alternator, or an integrated starter motor-generator (ISG) within the car's transmission housing.

An ISG setup is more advanced than BSG as the latter don't need a separate engine starter motor.

But because the battery and motor are the smallest, MHEV is also the cheapest xEV method to reduce fuel consumption.

Examples include early generation Honda IMA hybrids like the Insight and Jazz, as well as current generation W206 Mercedes-Benz C-Class and B-badged Volvo models like the Volvo XC60 B5.

Sitting one step above MHEV are full hybrids, which curiously are not called FHEV but just HEV, for hybrid electric vehicle.

The biggest difference between MHEV and HEV is that a full-hybrid HEV can accelerate away from traffic lights in electric power alone, meaning that the driving experience in urban stop-go traffic will be a lot smoother than an MHEV, whose engine will keep cutting in and out every time the vehicle stops or move.

In theory a HEV can drive in electric power alone but with a range of less than 2 km, it's silly to do so. The electric power-only drive is meant to accelerate a HEV car from standstill - the driving cycle period where engines are least efficient and fuel consumption is highest.

Examples of full-hybrids include the previous generation Honda models with Sport Hybrid i-DCD, current generation e:HEV Honda models like the City, HR-V and Civic, and of course, all Toyota and Lexus hybrids including the Corolla Cross Hybrid.

If you are wondering about the Nissan Serena S-Hybrid, that's not a hybrid at all, not even a mild-hybrid. There is no electric motor in the car's transmission. S-Hybrid is just an amped engine starter motor given a faux hybrid badge. The Serena e-Power (available in Singapore and Japan) however, is a proper series-type full-hybrid.

Above HEV, we enter the realm of plugged in hybrid electric vehicles or PHEVs. PHEVs bridge the gap between regular hybrids and fully electric battery EVs (BEVs).

A PHEV is a HEV with a far bigger battery capacity - 20x to 30x bigger than a regular HEV’s 1 kWh battery capacity. It can be driven like a regular HEV but for long-term battery health and to get the optimal performance, the car needs to be plugged in regularly to charge.

Examples include all BMW hybrids currently on sale and T-badged Volvo models like the XC90 T8.

All HEV and PHEVs are split into either:

• Series hybrids (Nissan e-Power, Honda IMA, Daihatsu / Perodua hybrids) - engine doesn't drive the car, serving only as a generator to charge the battery.
• Parallel hybrids (Honda Sport Hybrid i-DCD, all European PHEVs) - engine / electric motor drive the car or charge the battery, but not simultaneously.
• Series-parallel hybrids (Honda i-MMD, all Toyota hybrids) -  engine / electric motors can drive the car and charge the battery simultaneously. This possible because such hybrids use two electric motors - one smaller motor to start the engine or charge the high voltage battery, another bigger motor to drive the car or charge the high voltage battery.

A BEV runs purely on electricity and unlike a PHEV, it becomes a brick if you don’t charge it. With no engine, a BEV has a very big battery capacity of around 50 kWh or more.

Generally, PHEVs use the same AC charging socket as a BEV so they can use the same charging infrastructure. PHEVs don’t support high speed DC charging used by BEVs.

There’s also another category of xEV called fuel-cell electric vehicles (FCEVs). Like a BEV, an FCEV is also fully electric but unlike a BEV, an FCEV needs to be refueled with hydrogen.

While a BEV stores its energy in a big battery, an FCEV is generates its own electricity on-the-move by mixing hydrogen with oxygen. As such, FCEVs don’t need a big battery, only a HEV-like circa 1 kWh capacity battery to store energy recovered from braking and coasting.

Examples include the Hyundai Nexo, Toyota Mirai, BMW iX5 Hydrogen, and several heavy trucks by Volvo and Mercedes-Benz.

Generally, FCEVs cannot support plugged in charging although the Mercedes-Benz GLC F-Cell is an exemption.

Why is the Proton X90 only a mild-hybrid?

The simple answer is that the X90’s donor car, the Geely Haoyue, is not offered as a HEV or PHEV, only MHEV.

The other reason is cost. Every step up the xEV hierarchy increases cost.

Prices of the Proton X90 have yet to be announced but it is estimated to start from circa RM 130k ++, assuming that there will be no overlap with the Proton X70, which tops out at RM 128,800.

Proton has yet to reveal the claimed fuel consumption figures for the Proton X90, but the company says the MHEV setup improves fuel efficiency by 15 percent.

The Proton X90’s electrified 1.5-litre 3-cylinder turbocharged engine makes 190 PS / 300 Nm, delivered to the front wheels via a 7-speed dual-clutch automatic transmission.

The D-segment SUV will be available either as a 6- or 7-seater. A nationwide tour will begin in April. Market launch is to be expected sometime around mid-2023.

Also read: It's 2023 but the Proton X90 still has no Android Auto / Apple CarPlay - this is ACO Tech's reply