Shifting to lower gears2016/04/08
Peak season for timber truck drivers in northern Sweden begins when the ground freezes. The cold can be severe, often below minus 30°C, but the frozen surface makes it easier for the drivers to manoeuvre on forest roads. Spring and autumn present more of a challenge. Rain and melting water make surfaces difficult to manoeuvre with a 24 metre timber truck.
“Weather conditions are our greatest challenge. We often drive on narrow roads and in hard-to-manoeuvre areas when there is a lot of water in the forest,” says driver Jonas Lundmark who has just finished loading his timber truck.
A fully laden truck weighs 64 tonnes and it’s easy to see that starting with such a heavy load in the middle of the deep Swedish forests could pose a problem. Jonas climbs into the cab and shifts into the lowest gear in Volvo Trucks’ new I-Shift with crawler gears. A light touch on the accelerator pedal and the truck starts to slowly move forward.
“The new I-Shift gives me two crawler gears, which is incredibly valuable when I need to start with a heavy load in tough conditions,” says Jonas.
The new I-Shift gives me two crawler gears, which is incredibly valuable when I need to start with a heavy load in tough conditions.
timber truck driver
He is one of the field test drivers who have been testing the new transmission for the past 18 months.
“We’ve driven 250,000 kilometres with this gearbox and it’s worked perfectly.”
The gear shifting ratio in the lowest of the two crawler gears is 32:1 and that is twice as slow as a standard I-Shift. Jonas’s gearbox also has two reverse gears with a 37:1 gear shifting ratio in the lowest reverse gear.
In some situations, when the road conditions are poor or in certain terrain, I find the reverse gears to be as valuable. They allow me to reverse with a heavy load in a way that was previously not possible,” says Jonas.
It’s not uncommon for Jonas to have to load the timber while parked on a poor forest road in the middle of an incline. Previously, when Jonas drove a truck with a standard I-Shift, he had to use the transmission’s jerk start function in order to take off.
“On a steep incline or uneven surface, the power launch is the only alternative for starting the vehicle. This means I rev the engine to a relatively high RPM and release the clutch manually. Usually this works, but it causes wear on the driveline and it’s easy to get stuck with spinning wheels. With the new transmission, all I have to do is to select the correct starting gear and take off gently, which keeps wear on the driveline down to a minimum,” explains Jonas.
More than 40 field test vehicles from all over the world have been used to test the new transmission – from the deep forests of Sweden to the high Andes of South America. Niklas Öberg is the engineer in charge of the tests and he is thankful for the collaboration with the field test drivers.
“Reality presents much more difficult challenges than we can simulate in our test lab and feedback from drivers like Jonas is incredibly important.They work in these environments every day and know what type of features are important to make their work more effective.
Reality presents much more difficult challenges than we can simulate in our test lab and feedback from drivers like Jonas is incredibly important.
test engineer, Volvo Trucks
Niklas Öberg is one of some 100 people involved in developing the new transmission. He describes the principle behind the technology used in the new transmission as relatively basic. Putting a gear reduction set between the clutch and the base housing in a standard I-Shift makes it possible to add one or two extra crawler gears and two extra reverse gears.
“We’ve also improved the counter shaft brake that brakes the counter shaft when shifting gears, making it easier to manoeuvre heavy loads on steep inclines,” explains Niklas Öberg.
In the new transmission, several components, including cog wheels, clutch sleeves and split synchronisation, have been reinforced to cope with severe working conditions. Trucks that drive with extremely high gross combination weight (GCW) will also be equipped with reinforced prop shafts for a greater torque.
“We have to increase the prop shaft’s torque to maintain the same startability when the GCW increases together with faster total driveline ratio,” says Niklas Öberg. “Consequently, trucks with a total GCW of 65 tonnes will have a reinforced prop shaft to enable a torque of 33,000 Nm compared with the standard 28,000 Nm.”
Shifting in the lowest crawler gear is so powerful that the truck can start from standstill on a level road with loads of up to 325 GCW tonnes, which is absolutely unique for an automated transmission in heavy-duty trucks.
“The heavier the load and the worse the road or terrain, the more the driver gains from driving a truck equipped with I-Shift with crawler gears. The driver can take a heavy load without having to worry about getting into situations that, in a worst case scenario, can lead to costly standstills,” according to Peter Hardin, product manager for FM & FMX Range at Volvo Trucks.
The heavier the load and the worse the road or terrain, the more the driver gains from driving a truck equipped with I-Shift with crawler gears.
product manager, Volvo Trucks
The new transmission is available in direct-drive and overdrive models for Volvo Trucks’ 13 and 16 litre engines for the Volvo FM, FMX, FH and FH16 models. This means the transmission can be used for many different types of transport segments.
The transmission is perfect for a variety of precision jobs, including construction and maintenance work, because the crawler gears also make it possible to drive extremely slowly.
“A truck can drive at a speed of 0.5 to 2 km/h with this transmission. The ability to drive so slowly means a lot to those performing this type of work, since they can drive with much greater precision for a better final result. I-Shift with crawler gears also makes it possible to reverse extremely slowly, which is a huge advantage for reverse operations that demand incredible precision,” says Peter Hardin.
For small trucking companies that carry out assignments on demanding routes, I-Shift with crawler gears offers maximum flexibility and the opportunity for improved transport economics.
“While crawler gears make it possible to start with a heavy GCW in extreme situations it is now possible to use a rear axle ratio that lowers the engine RPM at normal road speeds resulting in lower fuel consumption. This is very significant for trucking companies dealing with this type of work,” adds Peter Hardin.
In the cab, Jonas Lundmark sits safely behind the steering wheel. He’s left the narrow forest road behind him and will soon reach the rural road that leads to the sawmill where he will unload. Jonas runs the trucking company along with his father and, together with a third driver, drives some 4,000 kilometres a week.
“We timber truck drivers often find ourselves in driving situations that demand a great deal of us. As a result, we are grateful for all solutions that can make our job easier. The new transmission gives a better sense of safety and control since you know you can start easily.
How it works: I-Shift with crawler gears
The large gear ratio in the I-Shift with crawler gears is made possible by a new gear reduction set that has been added to a standard I-Shift.
Extra gear reduction set
The extra gear reduction set is located directly behind the gearbox clutch housing and consists of two extra gearwheels – one on the input shaft and one on the counter shaft. The extra gear reduction set enables the gearbox to provide a ratio that is almost twice as large as a standard I-Shift.
To make room for the extra gear reduction set, the gearbox has been made 12 cm longer than a standard I-Shift. Many of the new components, such as gearwheels, engaging sleeves and split synchronisers are made of high-strength materials.
Gear ratio is the difference in speed between the input and output shafts in a gearbox. With the highest gear engaged, the gear ratio is 1:1 on a direct drive gearbox, which means that the shafts spin at the same speed. At the lowest gear in the I-Shift with crawler gears, the output shaft spins 32 times more slowly than the engine speed – at a gear ratio of 32:1.