Volvo OptiShift transmission

By: Dan Gilkes, Photography by: Dan Gilkes

Date: 18.03.2011

Some of Volvo’s latest wheel loaders are equipped with the OptiShift transmission, which the company claims provides a potential 15 percent fuel saving.

Volvo claims its OptiShift transmission can result in up to 15 per cent fuel savings.

OptiShift eliminates losses in the torque converter
Makes for smooth gear changes
Offers greater performance for hill climbing
Simple to operate
Reduced wear and tear on machine and omponents

OptiShift is an optional driveline system initially available on the mid-size L150F, L180F and L220F loaders.

Deals on Wheels recently had the chance to try a Volvo L150F with OptiShift in Sweden. The L150F that we drove uses the same Volvo D12D engine as the non-OptiShift machine, providing 209hp at 1400-1700rpm. This gives the loader enough power for a breakout force of up to 184kN and a static tipping load of 15,280kg at full turn.

There are two main parts to the OptiShift system: a lock-up torque converter with a free-wheel stator, and what Volvo is calling Reverse By Braking (RBB).

In a conventional torque converter the fluid is thrown by the engine-driven pump rotor into the turbine rotor, which is connected to the output shaft to the transmissions. This flow of oil causes the turbine to rotate, powering the transmission. The stator, which sits between the two rotors within the torque converter housing, is stationary and serves to return the oil to the pump rotor.

The losses associated with a torque converter come in the slip of fluid between the pump rotor and the turbine. Also, the torque increasing benefits of the torque converter drop as the speed of the turbine matches that of the pump rotor.

What Volvo has done is add a multi-plate drive clutch to the converter housing, one set of plates attached to the pump rotor and one set to the turbine. This clutch mechanically locks the two halves of the torque converter together, to eliminate losses and provide a locked-up transmission of power in second, third and fourth forward gears.

At the same time the stator is allowed to free-wheel, so that it isn't trying to force oil back into the pump rotor.

OptiShift makes very smooth gear changes and really comes into its own on longer cycles or load and carry work, where the operator has the chance to make use of all of the gears and the lock-up facility provides maximum drive. Volvo says that it also offers greater performance for hill climbing and quicker response to gear changes.

The RBB system makes its presence felt in short cycle work. Traditionally when the operator switches from forward to reverse, or the other way around, the machine's transmission slows the loader before engaging the alternative gear, putting excess heat and energy into the transmission. With RBB, as the operator selects a change of direction, the machine's control system automatically applies the service brakes in the axles, slowing the loader before the gear is selected and the machine moves forward or back.

This provides smoother deceleration and directional changes, and reduces stress and possible wear on the torque converter. That in turn reduces fuel consumption.

The test

In the L150F's cab there is little to let you know that you are in an OptiShift-equipped machine, aside from an additional switch in the bank of control switches on the right-hand A-pillar. Our test machine was also equipped with the firm's optional Comfort Drive Control (CDC) system, which uses a thumb lever on the left-hand armrest to steer the machine and finger buttons to select and change gears.

As you would expect, the machine digs normally, easily loading its bucket with shot granite in the Kallerad Quarry. Flick into reverse and the loader moves smoothly back while you turn and then flick back into the forward gears. Without touching the brake pedal the loader slows smoothly, engages forward and moves away again.

With the auto power shift transmission lever set in the highest forward gear the machine then simply accelerates away. Gear changes are almost seamless and it felt as if there was hardly a pause in the flow of power to the wheels going up through the box.

Our machine was equipped with the firm's boom suspension system (BSS) providing a gentle bounce in the loader arms for maximum load retention. This and a relatively smooth quarry floor, made it easy to reach high carry speeds in fourth gear, with minimal effort for the operator.

At the end of the run you simply lift off the throttle and the speed drops away, with a dab on the service brake bringing the transmission down a couple of ratios for the turn to the loading area. As that speed comes down, so the RBB system comes back into play, providing smooth changes in direction when pulling away from the dump area.

Summary

The OptiShift and RBB systems worked seamlessly, without the operator having to do anything in particular other than turn them on. The benefits in machine wear and tear, component stress and reduced fuel consumption would take a customer longer to assess, but there were certainly benefits in reduced operator effort.

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