The modern excavator's house sits atop an undercarriage withtracks orwheels, being an evolution of thesteam shovel (which itself evolved into thepower shovel when steam was replaced by diesel and electric power). All excavation-related movement and functions of a hydraulic excavator are accomplished through the use ofhydraulic fluid, withhydraulic cylinders andhydraulic motors,[2] which replaced winches, chains, andsteel ropes.[3] Another principle change was the direction of the digging action, with modern excavators pulling their buckets toward them like a dragline rather than pushing them away to fill them the way the first powered shovels did.
Excavators are also called diggers, scoopers, mechanical shovels, or 360-degree excavators (sometimes abbreviated simply to "360"). Tracked excavators are sometimes called "trackhoes" by analogy to thebackhoe.[4] In theUK, wheeled excavators are sometimes known as "rubber ducks".[5]
The principle of a hydraulic excavatorHydraulic excavator controls illustration, color of the control matches the moving part
Modern hydraulic excavators come in a wide variety of sizes. The smaller ones are called mini orcompact excavators.[7] For example,Caterpillar's smallest mini-excavator weighs 2,060 pounds (930 kg) and has 13hp;[8] their largest model is the largest excavator available (developed and produced by the Orenstein & Koppel, Germany, until the takeover 2011 by Caterpillar, named »RH400«), the CAT 6090, which weighs in excess of 2,160,510 pounds (979,990 kg), has 4500 hp, and a bucket as large as 52.0 m3.
Hydraulic excavators usually couple engine power to (commonly) threehydraulic pumps rather than to mechanicaldrivetrains. The two main pumps supply oil at high pressure (up to 5000psi, 345 bar) for thearms, swing motor, track motors and accessories while the third is a lower pressure (≈700psi, 48 bar) pump for pilot control of thespool valves; this third circuit allows for reduced physical effort when operating the controls. Generally, the three pumps used in excavators consist of two variable displacement piston pumps and a gear pump. The arrangement of the pumps in the excavator unit changes with different manufacturers using different formats.
The three main sections of an excavator are theundercarriage, the house and the arm. The boom, the front part that is attached to the house itself and holds the arm, is also used. The undercarriage includes tracks, track frame, and final drives, which have ahydraulic motor and gearing providing the drive to the individual tracks. The undercarriage, especially frequently for a mini-excavator, can also haveblade similar to that of a bulldozer. The house includes the operator cab,counterweight, engine, fuel and hydraulic oil tanks. The house attaches to the undercarriage by way of a center pin. High-pressure oil is supplied to the tracks' hydraulic motors through a hydraulic swivel at the axis of the pin, allowing the machine to slew 360° unhindered and thus provides the left-and-right movement.[9] The arm provides the up-and-down and closer-and-further (or digging movement) movements. Arms typically consist of a boom, stick and bucket with three joints between them and the house.
The boom attaches to the house and provides the up-and-down movement. It can be one of several different configurations:
Most common are mono booms; these have no movement apart from straight up and down.
Another option is a hinge at the base of the boom allowing it to hydraulically pivot up to 180° independent to the house; however, this is generally available only tocompact excavators.
Variable angle booms have additional joint in the middle of the boom to change the curvature of the boom. These are also called triple-articulated booms (TAB) or 3 piece booms.
Attached to the end of the boom is the stick (or dipper arm). The stick provides the digging movement needed to pull the bucket through the ground. The stick length is optional depending whether reach (longer stick) or break-out power (shorter stick) is required. Most common is mono stick but there are also, for example, telescopic sticks. The largest form ever of an excavator, thedragline excavator, eliminated the dipper in favor of a line andwinch.
On the end of the stick is usually abucket. A wide, large capacity (mud) bucket with a straight cutting edge is used for cleanup and levelling or where the material to be dug is soft, and teeth are not required. A general purpose (GP) bucket is generally smaller, stronger, and has hardened side cutters and teeth used to break through hard ground and rocks. Buckets have numerous shapes and sizes for various applications. There are also many other attachments that are available to be attached to the excavator for boring, ripping, crushing, cutting, lifting, etc. Attachments can be attached with pins similar to other parts of the arm or with some variety ofquick coupler. Excavators in Scandinavia often feature atiltrotator which allows attachments rotate 360 degrees and tilt ±45 degrees, in order to increase the flexibility and precision of the excavator.
Before the 1990s, all excavators had a long or conventional counterweight that hung off the rear of the machine to provide more digging force and lifting capacity. This became a nuisance when working in confined areas. In 1993Yanmar launched the world's first Zero Tail Swing excavator,[10] which allows the counterweight to stay inside the width of the tracks as it slews, thus being safer and more user friendly when used in a confined space. This type of machine is now widely used throughout the world.
There are two main types of control configuration used in excavators to control the boom and bucket, each distributing the four primary digging functions across two x-y joysticks. This allows a skilled operator to control all four functions simultaneously. The most popular configuration in the US is theSAE controls configuration while in other parts of the world, the ISO control configuration is more common. Some manufacturers such as Takeuchi have switches that allow the operator to select which control configuration to use.
Hydraulic excavators now perform tasks well beyondbucket excavation. With the advent of hydraulic-powered attachments such as abreaker, a cutter, agrapple or anauger,a crusher and screening buckets[11] the excavator is frequently used in many applications other than excavation. Many excavators feature aquick coupler for simplified attachment mounting, increasing the machine's utilization on the jobsite. Excavators are usually employed together withloaders andbulldozers. Most wheeled,compact and some medium-sized (11 to 18-tonne) excavators have a backfill (or dozer) blade. This is a horizontalbulldozer-like blade attached to the undercarriage and is used for leveling and pushing removed material back into a hole.
