Infiniti Q50 Hybrid and Lexus GS 450h: Technology Feature

More vehicle manufacturers than ever now offer hybrids, and it seems each has its own take on the technology. More often than not the set-up sees a petrol engine combined with an electric motor (or a series thereof) to extract an increase in range or performance from a familiar mechanical and architectural arrangement.

But not all hybrids are created equal, and as we discovered with the two prestige sedans tested, the technology differences are as interesting as they are complex.

To make things clear, this is not a comparison. The vehicles on test compete in different VFACTS categories with pricing that reflects the same. The Infiniti Q50 3.5 S Hybrid AWD fits into the Medium >$60K segment, one size beneath the Lexus GS 450h F Sport which plays in the Large >$70K arena.

Accordingly, there is $38,200 difference between the pair with the Q50 priced from $73,900 (plus on-road costs) and the GS 450h from $112,100 (plus ORCs). The difference is enough to pay for a Toyota Prius... but we digress.

Of course hybrid variety is not limited to large, luxury cars. There are equivalent examples of differences in hybrid technology at the lower end of the vehicle market (take the Toyota Prius and Honda Civic Hybrid, for example). It is, however, their size, and the greater fuel savings achieved as a result, that makes these flagship models particularly interesting.

Both the Infiniti and the Lexus use what is known as a parallel hybrid system, meaning two power sources (in this case petrol and electric) combine at a single ‘axis’ to provide motive drive, which is then focussed through a transmission of the conventional kind (be it manual, automatic or continuously variable) before being delivered to the wheels.

Thus it’s the way in which the Q50 and the GS 450h switch and select between petrol and electric power that differs most – and that’s most noticeable as you drive along.

The Infiniti is powered by the combination of a 3.5-litre V6 petrol engine developing 220kW and 345Nm and a synchronous electric motor developing 50kW and 270Nm.

The outputs of the electric motor and petrol engine are channelled, via two separate clutches, to an electronically-controlled seven-speed automatic transmission. Combined, the internal combustion engine and electric motor offer an output of 268kW and 546Nm.

Infiniti says the figures are enough to shuttle the Q50 from standstill to 100km/h in just 5.4 seconds (or 5.1sec for rear-wheel drive variants).

Our test vehicle featured what Infiniti calls Intelligent All-Wheel Drive with ATTESA ET-S (Advanced Total Traction Engineering System for all Electronic Torque-Split). It’s a bit of a mouthful, but essentially the system allows available torque to be distributed as required from front-to-rear, and left-to-right. It’s one of an array of electronically-controlled elements of the Infiniti Q50, not least of which is the steer-by-wire tiller. But that’s another story (see break-out).

The hybrid part of the Q50 equation uses the electric motor on demand to bolster the efforts of the petrol engine, regenerate power to charge the battery pack, or on its lonesome to operate in electric vehicle (EV) mode for short periods.

Electricity is supplied via a high-voltage storage capacitor fed by a lithium-ion (Li-ion) battery pack which, as well as supplying power to the electric motor, is also used (indirectly via an inverter) to charge the 12-volt lead-acid battery used to power the Q50’s regular electric needs.

The main battery pack is located over the rear axle in the cargo area and supplies up to 346 volts through a DC/AC inverter to the traction motor (see diagram), and also a separate electric motor which serves as the Q50’s air-conditioning compressor.

The battery pack itself is actually a series of much smaller cells. In the case of the Q50, the pack consists of 12 modules (comprising 96 cells each) that provide 28.8 volts apiece. The whole arrangement weighs about 50kg.

Infiniti says the combination of petrol and electric power is adequate to gift the Q50 with a combined cycle fuel consumption figure of 7.2L/100km and CO2 emissions of 169g/km.

ET, TU LEXUS?
Interestingly, the Lexus GS 450h also uses a 3.5-litre V6 petrol engine, though it’s slightly less powerful with 215kW and 352Nm. It is supported by twin permanent-magnet electric motors making a total of 147kW and 275Nm. Lexus says the system’s maximum power rating is 254kW, but does not provide a combined torque value.

The electric motors in the GS 450h serve different purposes, though in reality one does most of the work. The smaller of the pair is used to start the internal combustion engine, provide some charge for the battery pack and, in part, control the continuously variable transmission (CVT).

The second, larger electric motor sends drive to the wheels through a planetary gear set, and serves to retard the vehicle under deceleration, while at the same time using the recovered energy to charge the battery pack.

The distribution of motive drive from the petrol engine and the smaller electric motor, and the second larger electric motor, is essentially split by an epicyclical gear set best thought of as a differential.

Finally, the clever but complicated array of gear sets, reduction gears, electric motors and the internal combustion engine concentrate in axis through an eight-step continuously variable transmission which delivers motive power to the rear wheels.

Much like the Infiniti, power to the Lexus’ electric motors is supplied from a voltage inverter/converter which supplies not only the drive motors, but also AC and DC power for use in the car’s regular systems (again through a 12-volt lead-acid battery) and the electric-driven air-conditioning compressor.

Energy is stored in a boot-mounted nickel-metal hydride (NiMH) battery pack. This is comprised of 40 low voltage modules (7.2 volts each) connected in series to deliver 288 volts. The pack weighs 63kg.

Lexus says the GS 450h can achieve a combined cycle fuel economy figure of 6.3L/100km with CO2 emissions of 147g/km. The big Lexus will accelerate from 0-100km/h in 5.9 seconds (claimed).

The course took us through a mix of congested city and fast-paced freeway driving, before winding through some undulating rural roads.

Concentrating first on the Infiniti, it was the steer-by-wire that was most noticeable, and for those wanting an experience different from a ‘standard’ vehicle, the Direct Adaptive Steering system is certainly that: noticeable.

The Q50 S offers three distinct settings for both steering effort and response which can either be personalised by the driver, or accessed through four pre-programmed modes.

While technically interesting, the steering was the Infiniti’s biggest weakness, ranging from lightly detached to over-immediate in its more sporting modes.

Along with the steering, the intelligent all-wheel drive system and seven-speed automatic transmission meant the Infiniti felt less ‘organic’ than a more conventional mid-size sedan. Throw the hybrid system into the mix and you have a complex vehicle that, in many ways, feels it.

Perhaps the biggest hybrid system bugbear was the lack of a simple button to engage pure EV mode in an otherwise well-equipped interior. Instead, you have to search through the multi-function touch-screen display.

Despite this glitch, the Q50 is no more difficult to drive than a conventional vehicle. There was a (generally) smooth transition between electric and petrol motive power, and when the throttle was pressed with gusto it unleashed a fierce shove in the back as both power sources worked in unison.

The Q50’s petrol V6 sounds keen and is willing to rev through to its 7000rpm redline. Who said hybrids couldn’t perform?

Returning to the Q50’s complexity, it was apparent that when the driver was shifting quickly between throttle, brake and throttle in traffic, the systems would struggle to keep up and a brief shudder could be felt. Additionally the traditional automatic transmission would jolt on upshifts, a problem exacerbated though the use of the sporty manual mode.

The Infiniti’s small green ‘EV’ dash light was illuminated regularly through slow-speed city traffic, as one might expect, but the real surprise was how regularly it operated when coasting on the highway. Back on part throttle (say, to accelerate from 80 to 90km/h) EV mode would take the strain for a good portion of the throttle pedal’s travel.

Throughout the day, the Infiniti’s fuel consumption ranged from 7.5L/100km on a morning highway commute through to 8.0 through hilly, windy countryside roads. This is not too far off the combined claim and remarkable for the acceleration and performance on offer.

Inside, it impressed with its space and equipment levels, though the mouse-style device used to connect with the multi-function display was frustrating to operate. At least the GS 450h’s EV mode was easily engaged via a console mounted button.

In the realities of everyday traffic, the pure EV mode offered little benefit as it was unable to accelerate the large Lexus at a rate to keep up with normal flow. In short, it was better to let the car sort out when EV power was required.

Overall, the Lexus felt more natural to drive, though body roll was quite apparent, even in this ‘sportier’ F Sport variant.

Additionally, heavier throttle openings would lead to that awkward acoustic of a CVT shuffling as it accelerated the vehicle. The V6 petrol is disappointing is terms of its engine note. Generally, the engine felt lazier and less inspired to rev than the Infiniti’s -- even ‘manual’ shift mode was selected.

Under braking, the GS 450h offered an inconsistent feel, often varying retardation in spite of constant pedal pressure.

From freeway speeds, it took a series of ‘bites’ before linear stopping power arrived. This inconsistency is most likely due to the way the hybrid system recovers energy, but was perhaps the largest adjustment required to drive the Lexus.

Another aspect of the Lexus which proved confusing was the randomness of EV transition. When coasting on the highway, for example, the dash light would illuminate quickly, but at other points would not engage until a speed of less than 33km/h (indicated) was achieved.

Although the transitions between EV, petrol and combined drive were smoother than the Infiniti’s, it appeared that the electric side of the equation wasn’t as extensively used. Once settled, however, the GS 450h was a paragon of quietness, with a smooth ride and excellent NVH attenuation.

The larger Lexus almost matched the complex, but smaller, Infiniti where fuel economy was concerned managing 7.6L/100km during the morning commute, and 8.1L/100km across the more demanding country loop.

In essence, this test provided us with the opportunity to demonstrate that hybrid driving, despite the underlying complexity of the technology, is really no harder than driving a traditionally-powered vehicle.

Rather than their powertrains, our test revealed that it’s the lexus and Infiniti’s other systems (the steering in the case of the Infiniti and the human-machine interface in case of the Lexus) that added complexity to the ownership experience.

Pricing as tested:

Lexus GS 450h: $112,500
Metallic Paint: $1500 (White Nova)
Enhancement Pack: $6000 (Colour display screen, Premium 17-speaker audio, Lane-Departure Warning, LED headlights)
As Tested: $120,000 (plus on-road costs)

Infiniti Q50 S Premium Hybrid AWD: $73,900
Metallic Paint: $1500 (Hagane Blue)
As Tested: $75,400 (plus on-road costs)

Almost since we first started driving cars, the steering wheel and the front wheels have been connected by a shaft, and a means of turning the rotating action of the shaft to a lateral movement... Which in turn
directs the steering arm and tie rods, and ultimately, the angle of the front wheels.

Now, as is the case in aircraft and other vehicles, electronic control has caught up with the humble steering system. In addition to the now-common electric assistance, the Infiniti Q50’s
steering system is ‘by wire’. Instead of a mechanical connection, the direction of the front wheels is determined by electric motors.

A fail-safe remains (incorporating a clutched mechanical link) but in day-to-day operation, the electric system manages steering operations through a four-mode adaptive system Infiniti calls Direct Adaptive Steering.

A decade in the making, Direct Adaptive Steering uses a computer linked to a steering angle-actuator to apportion command to a trio of electronic control units, two of which act as a back-up should the primary ECU fail. These then direct a pair of electric motors which act to change the direction of the front wheels.

It’s a complex, somewhat heavy and (no doubt) quite expensive system, but is said by its makers to isolate the driver from undesirable inputs that could affect the car’s intended course.

It can also act in tandem with the car’s stability control system to correct skids, as well as reducing the
car’s tendency to deviate when pointed straight ahead.

To date, the Infiniti Q50 is the only car available with a steer-by-wire system.

WHERE IN THE WORLD?

motoring.com.au chose the enchanting Red Hill Epicurean as the venue for its cover image. This ‘hybrid’ building at one timed served as a cool store for produce originating from the Mornington Peninsula, but has now been repurposed as a chic but soft industrial space that accommodates an exciting 200-seat ‘cucina’ style restaurant.

With an innovative food and wine menu, and a spectacular open space beneath the atrium to enjoy (or take photos of cars in), diners are offered locally-sourced gourmet foods, delights from the artisan bakery, regional wine tasting and education, brilliant in-house roasted coffee, culinary master classes and authentic Italian wood-fired pizza.

For more information, visit www.redhillepicurean.com.au