Caterpillar D9 - Engineering and Technical Description

Engineering and Technical Description

The D9 is a series of heavy tracked-type tractors, propelled by Caterpillar tracks and usually used as bulldozers. The series began in 1954 with a prototype tractor called the D9X. Ten D9X prototype models were built in 1954. In 1955, the 286 hp (213 kW) D9 was introduced to compete against the more powerful Euclid TC-12. The D9 came equipped with a 1,473 cid D353 which powered the D9 right up until the 1980 introduction of the D9L. In 1956 the D9 had its engine power raised to 320 hp (240 kW). The new 335 hp (250 kW) D9E replaced that model in 1959. Two years later, in 1961, the legendary 385 hp (287 kW) D9G was introduced, that remained in production for 13 years. Over its 13-year life the D9G became the main crawler on many job sites, testifying to its sturdiness and design.

In 1965, west coast businessman Buster Peterson hooked up a pair of D9Gs to pushload the largest wheel tractor scrapers built. In 1986 Caterpillar bought the rights to this concept and thus the 770 hp (570 kW) DD9G was created (D stands for Dual D9G). Peterson also built the first SxS D9G which has two D9Gs side-by-side, pushing a 24-foot (7.3 m) wide bulldozer blade.

In 1969, Caterpillar introduced this new SxS D9G. In 1974, the improved 410 hp (310 kW) D9H was introduced to replace the D9G. The D9H is still the more powerful conventional track-type tractor in company history. The DD9H and the SxsD9H would soon follow.

The D9 is the real star of the 1974 ABC cult classic movie "Killdozer".

In 1980, the 460 hp (340 kW) D9L was introduced. The unit featured the same new type of elevated sprocket undercarraige as was used in the larger D10. The D9L was the first variation of the D9 to employ elevated drive sprocket design in which the drive sprocket is elevated above the track, and not on the ground. The new undercarriage design reduced strain and shock loads on the final drives and gave the "belly pan" more ground clearance. The elevated drive sprocket undercarriage is a modular design. To repair the machines one breaks down the tracks and pulls the drive sprockets out. As a result, one can pull the powershift transmission out the rear. The 370 hp (280 kW) D9N replaced the D8L in 1987.

In 1988, Caterpillar produced their 25,000th elevated drive sprocket track-type tractor, a D9N. The 405 hp (302 kW) D9R replaced the D9N in 1996. The 410 hp (310 kW) D9T replaced the D9R in 2004. The D9T has a low emissions ACERT diesel engine. The current model is the D9T, however older models such as the D9R, D9N, and D9L are still commonly used. The L, N, R and T models of the D9 are visually very similar, differing primarily in the design of their internal systems.

The D9L was replaced by the 520 hp (390 kW) D10N in 1987. The 370 hp (280 kW) D9N replaced D8L in 1987. The main difference between the D9T and the D9R is the installment of the new Cat C18 ACERT engine. The D9L is the most powerful D9 in history, with a flywheel power of 460 hp. The D9L is also the heaviest D9 in history at 130,000 lbs.

The D9's primary working tools are the blade, affixed to the front and controlled by six hydraulic arms, and an optional ripper, which can be attached to the back. The blade is mainly intended for earthmoving and bulk material handling: pushing up sand, dirt, and rubble. It also can be used to push other heavy equipment such as earthmoving scraper pans, and in military applications, main battle tanks. The dozer blade usually comes in three variants:

1. A Straight Blade ("S-Blade") which is short and has no lateral curve, no side wings, and can be used for fine grading.
2. A Universal Blade ("U-Blade") which is tall and very curved, and has large side wings to carry more material.
3. A "S-U" combination blade which is shorter, has less curvature, and smaller side wings. This blade is typically used for pushing piles of large rocks, such as at a quarry.

Like many other bulldozers, the D9 can be fitted with other devices such as mineplows.

The rear ripper is intended for use in loosening rocky ground and ripping out larger stones. It can also break frozen ground and excavate small ditches. The ripper can be replaced with a multi-shank ripper, allowing the bulldozer to comb the ground.

The size, power and weight of the larger track-type tractors dictate that they are used primarily for major projects. The D9 is most commonly found in use in construction, forestry, mining, waste, and quarry operations.