Sisu K-44

Single axle semi-trailers were commonly used for log transportation in Finland in the 1960s. The maximum axle load of the existing 4×4 Sisu K-40 was often exceeded in logging work. The solution was a truck incorporating the addition of a non-driven third axle at the back, paired in a tandem axle with the rear driven axle. This drivetrain layout, called 4×4+2, is seldom seen outside Finland. However, Vanajan Autotehdas, SAT's main domestic competitor, had already introduced a similarly configured vehicle a year earlier. == Characteristics ==

The Sisu K-44 was expressly designed for good rough-terrain capability. The vehicle's ability to grip on many types of terrain and retain traction on steep slopes is further enhanced by a mechanism whereby the non-driven rear axle could be raised, thus maximising the proportion of vehicle weight available to push down on the driven axle at the front of the tandem axle. On a surface with friction coefficient of μ=0.65 its maximum gradeability is 86%. A corresponding 6×4-model has a 55% and a 6×2-model just a 29% gradeability. The powerful and reliable Leyland O.680 used in the stronger Jyry K-44 models had helped to make Sisu a market leader in Finnish heavy-duty road transportation. Problems began in 1963 when the Jyry's received the new O.680 "Power Plus" engine. Sisu was the first vehicle powered by the Power Plus unit, and suffered badly from the teething problems experienced by this engine. == Usage ==

Although the K-44 was originally designed for hauling a logging semi-trailer, the trucks were soon being used to tow conventional twin axle trailers, which permitted a significantly greater overall load capacity. == Technical data ==

Engine The K-44 was offered with one of five different engine types, the power units being supplied by Leyland Motors. The middle-weight "Kontio-class" K-44SU is powered by the Leyland O.375 engine. All the engines are six-cylinder inline direct injection diesels incorporating dry cylinder liners: the light alloy pistons are fitted with three pressure rings and two oil rings. The crankshaft is supported by seven main bearings. The injection pump and the 24-volt electrical system were supplied by CAV. A gear driven compressor is fitted as standard. while the heavy-duty Jyry's came with a six speed gearbox on which the sixth gear was an overdrive. There is no synchromesh, but the gear-cog tooth ends were bevelled in order to ease shifting. An additional power output shaft, used to power additional functions such as a dumping mechanism, was available as an option. The other key component in the transmission is a transfer case incorporating the torque-splitter, located between the main gear box and the tandem axle. This apportioned the torque from the gearbox between the front axle and the driven rear axle. The torque-splitter incorporates a two-step reduction gear Tandem axle The foremost axle on the tandem axle is powered. When fully loaded, the K-44 carries approximately 62% of the weight lying on the tandem axle. The rear, non-driven axle, is linked to the driven axle through a simple sub-assembly consisting of Both axles on the bogie are fitted with double wheels as standard other than on the K-44ST, which made do with single wheels on the non-driven rearmost axle. On the early K-44s the tandem's driven axles are identical on the middle-weight "Kontio" and the heavy-weight "Jyry" versions. The axle, designated "Type ATK" was designed by SAT and was based on the manufacturer's "Type ATD" axle originally introduced for earlier models n the early 1950s. The "Type ATK" proved durable in the Kontios, but was unable to cope with the greater power and load of the Jyry trucks, and in the early 1960s SAT developed a more robust driven axle, known as the axle "Type BTK", for the heavier variants. The axle housing is a welded construction made from formed steel. The total weight of Sisu K-44SP with a four wheel Sisu "FA-22"" or "FA-32" trailer was given in 1962 as , and the maximum payload was up to . == References ==