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Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox

Hans · Aug 25, 2020 03:40 PM

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 01

Very soon, Honda Malaysia will be hosting the world debut of the first ever Honda City RS with the latest two-motor i-MMD full hybrid engine. The specs sheet, which will be released in due time, will say that the City drives its front wheels via an E-CVT gearbox.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 02

In truth, the Honda City RS doesn’t have a gearbox, at least not a conventional one. However as you can imagine, it’s difficult to explain to customers that the car doesn’t have a gearbox, hence the E-CVT name.

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There’s still the usual Park, Reverse, Neutral, and Drive modes on the shift-by-wire 'gear' selector, but none operates the usual drive belts of a conventional CVT, or multiple ratios of a conventional torque converter automatic transmission. There’s little need for torque multiplication because the electric motor (there’s two, but only one drives the wheels directly) is powerful enough to drive the car.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 01

All Honda hybrid models now wear the e:HEV badge

Honda says its i-MMD’s fixed ratio direct drive approach creates a direct connection between moving components, resulting in a smoother transfer of torque, and is more refined than planetary e-CVT typically found in other hybrid vehicles.

The e-CVT reference by Honda is aimed at Toyota, the only company to use planetary gear set e-CVTs, which like Honda's E-CVT name, doesn’t work like a conventional CVT at all, but that’s another story.

What’s so special about i-MMD hybrid?

Compared to the previous one-motor i-DCD, the two-motor i-MMD packs more power, and is also more fuel efficient. It was originally meant for upper segment cars like the Accord and CR-V.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 02

As the technology matures, Honda is now able to package it tight enough to fit into a smaller cars like the Honda City.

What is a two-motor hybrid and why is it better?

Most hybrids, be it mild or full hybrid ones, use only one motor. This is the simplest, most cost effective setup. The engine can be shared with a standard combustion engine variant and the transmission only needs some modification to accommodate a motor, nestled between the engine’s crankshaft and the transmission.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 03

Series-parallel hybrid is an obvious, indirect reference to Toyota, the only mainstream company that uses series-parallel hybrid 

One-motor hybrids work well enough but it’s not as efficient or as powerful (all else being equal) as a two-motor hybrid. With only one motor, the system can either drive the car, or recharge the batteries, but not at the same time. With two motors, it can.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 04

Why i-MMD doesn’t need a gearbox?

The reason why conventional cars need a gearbox is because:

1. Combustion engines have a narrow operating range where peak torque is achieved, but since a car will need to travel at different speeds, going uphill and downhill, it’s impossible to have an engine driving the car at this fixed engine speed (rpm) range all the time, hence why gears are needed.

2. Torque multiplication. All engines have a quoted peak torque but the actual torque that’s delivered to wheels can be a lot higher if you pair it with different gear ratio combinations. This is how small engines are able to haul heavy loads.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 05

Unlike engines, electric motors generate its peak torque immediately after 0 rpm. There’s no need to build up speed before peak torque is reached.

The Honda City RS makes 253 Nm and since it’s coming from an electric motor, peak torque is achieved from 0 rpm (OK technically it’s 0.1 rpm) until 13,300 rpm.

Where the motor tapers off, the 1.5-litre DOHC i-VTEC naturally aspirated combustion engine fills the torque gap, peaking at 127 Nm from 4,500 – 5,000 rpm.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 06

E-CVT, not really a gearbox, at least not a conventional one

Combining both drive sources, the car has enough torque to go uphill without needing lower gear ratios for torque multiplication, hence no need for a conventional gearbox.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 07

Honda Insight shown, different model but uses a similar i-MMD setup

i-MMD’s coupling clutch also allows the engine to be disconnected from the wheels and run at its most efficient operating range (most of the time).

How does it work its magic?

Below is a cross section of the i-MMD’s E-CVT, you will notice that it’s extremely compact.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 08

There are two motors. The traction motor is the one that does the actual driving. It also doubles as a generator, reversing the flow of current when the car is coasting or braking, to charge the lithium-ion traction battery at the rear.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 09

Located behind the traction motor is the generator, and this is where the added benefit of a two-motor setup comes in.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 10

As it implies, the generator doesn’t drive the wheels. It’s spun by the engine, to generate electricity. Note that the generator doesn’t charge the traction battery, but only to provide additional power to the traction motor.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 11

The 2-motor setup allows the engine to power the car without being directly connected to the wheels, thus allowing it to run at its optimal, most efficient rpm range. This is referred to as the Hybrid Drive mode, which is essentially a series-hybrid mode, but unlike Nissan e-Power, Honda’s i-MMD can also work in other modes as well.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 12

At higher speeds, where it’s more efficient to use the engine, a clutch engages and the power flow is diverted away from the hybrid system, using the engine to drive the wheels directly (Engine Drive mode). When there is surplus power, the traction motor also works as a generator to charge the traction battery.

As a full-hybrid, the City RS will accelerate from stationary using electric power alone (EV Drive mode), thus doing away with unnecessary jerks commonly associated with mild hybrids or cars with engine idle start-stop systems.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 13

Automatic transmission fluid is used to cool the motors, so it's important to observe the service interval

The two motors are cooled by automatic transmission fluid, so there is still some maintenance required (no different from a regular automatic transmission fluid change).

The clutch itself is maintenance-free and is designed to last the lifetime of the vehicle, so you don’t need to worry about replacement cost. Although Honda didn’t say what does it mean by ‘lifetime of vehicle’ (service life is dependent on driving habits too), but to car manufacturers, a vehicle’s designed lifespan is typically around 15 years/300,000 km.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 14

Road presence is good. It looks more like a C-segment sedan than a cheaper B-segment one.

The all-new 2020 GN series Honda City won’t be launched until another month or two, and interior photos of the Malaysian specs model have yet to be released.

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 15

For now, the car is put on a truck, touring across Peninsular Malaysia, with stopovers at the locations below:

Here’s why the all-new 2020 Honda City RS with i-MMD doesn’t need a gearbox 16

Hans

Head of Content

Over 15 years of experience in automotive, from product planning, to market research, to print and digital media. Garages a 6-cylinder manual RWD but buses to work.

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