Two for the Road

Sometimes referred to as ‘power shift’ transmissions, the use of a dual clutch format has been utilised across a diverse range of applications ranging from agricultural tractors to F1 racing cars.

There is a marked distinction between drivelines employing a twin plate clutch and those with a dual clutch driveline.

Twin plate clutches involve two friction discs sandwiched between the pressure plate surface and the engine’s flywheel, with a floater plate in the middle.

The intention is to spread the torque load over a larger surface area and such arrangements have been employed for decades in many vehicles from heavy trucks to performance cars.

A dual clutch set-up, however, is much more complicated and involves two independent clutch assemblies and a significant re-engineering of the transmission as well.

Volvo has been the first manufacturer to offer the dual clutch option across a range of trucks in Australia and New Zealand.

The dual clutch version of the Volvo I-Shift transmission uses two dry clutches which operate independently of each other and each clutch drives one of the concentric input shafts of the 12-speed transmission.

Unlike the familiar conventional I-Shift, the dual clutch version is essentially two parallel gearboxes in the one transmission case. One clutch connects to the odd numbered gears while the other is used when engaging the even numbered gears.

The fundamental benefit of this arrangement is the transmission pre-selects the next gear and has it ready to accept the drive force while still driving in the current gear.

As one clutch disengages the other engages the next gear and the process is repeated sequentially either up or down through the ratios.

The only exception is on the shift between sixth and seventh gears as this is the ‘range change’ and a conventional shift is required, albeit automatically without any driver input.

Gear changes take place in a fraction of a second and results in an almost seamless delivery of torque as the driveline between the engine and the rear wheels is in constant connection.

The latest dual clutch innovation brings a new dimension to the transmission’s ability to extract the maximum efficiency from the engine.

New drive modes have been developed to optimise the truck’s behaviour. That means it’s now easier for the driver to control the vehicle by toggling between the different Drive modes on the revised I-Shift control.

What were previously termed the ‘ECO’ and ‘POWER’ modes have been replaced with new modes focused on fuel efficiency being balanced with performance and utilising input from the I-See terrain predictions. The ‘Economy’ mode focuses on achieving the lowest possible fuel consumption and limits the level of power available.

There are two other transmission modes to select from: ‘Off Road’ in which agility is prioritised, and ‘Heavy Duty’ which optimises driveability at high loads above 85 tonnes GVM.

The inherent design of the dual clutch I-Shift with its concentric twin input shafts dictates that its maximum torque capability is 2,800Nm which results in it being limited to 13-litre applications.

The Volvo FH prime mover for this test is rated at 70 tonnes GCM and is powered by a 13-litre Euro V engine rated at 540hp between 1,450-1,900 rpm, with 2,600Nm of torque available from as low as 1,050rpm through to 1,450 rpm.

The dual clutch version of the Volvo I-Shift adds 100kgs to the truck’s weight and the overall transmission is 120mm longer than a standard version.

The Dual Clutch contributes to more effective engine compression braking due to faster down shifts to take advantage of the engine brake which has a maximum retardation of 375kW at 2,300rpm.

This transmission always starts in first gear and on the flat the difference in shift quality is immediately noticeable.

Reduced throttle application once rolling encourages the transmission to skip shift and maximise the advantage of the engine’s torque characteristics because the power is transferred continually to the wheels and therefore the risk of losing traction in slippery conditions is also greatly reduced.

The dual clutch is particularly suitable for applications which involve sensitive freight such as livestock and will be a definite advantage in carrying liquids by reducing the ‘slosh’ effect due to the almost imperceptible gear changes.

The additional stability will also be favoured by carriers moving loads with high centres of gravity and, if necessary, drivers can instigate manual shifts with confidence even midway through a bend without upsetting the stability of the vehicle.

Fuel consumption on flat terrain will essentially be similar to that obtained in the same circumstances if the truck has the traditional I-Shift.

It is on undulating roads where the Dual Clutch is able to assist in fuel efficiency. Volvo claims between three and five per cent improvement should be easily realised on travel on these roads.

The advantages of the dual clutch I-Shift are many. Driver comfort and load stability are obvious, as is improved fuel efficiency. Long term maintenance costs are also kept in check with transmission oil changes stipulated at intervals as far as 450,000km. As each clutch is only performing half of the shifts the service life of those components are extended significantly as well.

The combination of the Dual Clutch transmission and Volvo’s I-See terrain prediction program enhances fuel efficiency as well as safety and driveability and removes considerable pressure from the driver.

The first time the truck goes up a hill the information about ascending that hill is stored in the I-See memory. The next time the same hill is travelled this saved information is used to maximise fuel efficiency. The basic principle is to use the kinetic energy of the vehicle in an intelligent manner.

For example, when approaching a hill, the truck downloads data from a high-resolution commercial topography map and the information is then used to maximise the truck’s kinetic energy and reduce fuel consumption by up to five per cent, compared to a truck without I-See.

If the road isn’t featured on the map, or if the server connection should fail, the truck will fall back to a shared database solution.

I-See primarily uses shared data which is stored in the Cloud and if needed, the system uses locally stored data.

If a hill is ahead I-See knows it and has the truck build momentum by accelerating on the approach so the truck remains in a higher gear for longer as the hill is ascended and downshifts are minimised. Speed is curbed at the crest of the hill and when the downhill section is approaching I-See stops accelerating unnecessarily.

To save energy and minimise braking, I-See temporarily disengages the powertrain and engine brakes and lets the truck coast to build up speed for the next climb. I-See also controls downhill braking by knowing where one slope ends and where the next begins, and applies the brakes as needed.

Volvo is synonymous with safety and as an example this test Volvo FH Globetrotter XL has a passenger side ‘corner camera’ located in the foot of the kerbside mirror which is activated automatically via the turn indicator stalk and can also be activated manually by the driver at any time.

The wide vision on the side display screen is sharp even in the inclement weather which follows us for most of the trip along the Hume Highway.

Revealed in Europe in early 2020, the latest range of Volvo trucks incorporates an impressive array of innovations and improvements including the ability for the Volvo Dynamic Steering to be ‘customised’ to suit individual drivers’ preferences, all via the new touchscreen located on the left side of the dash.

Volvo’s adaptive cruise control continues to increase its level of sophistication without becoming too complicated to set and operate and automatic headlights and windscreen wipers make their own contributions to safety and convenience.