In addition to the standard accelerator, brake, and clutch pedals, semi tractors have several extra pedals that are used to control various functions of the truck and trailer. These pedals are typically located on the floorboard of the cab, to the left of the driver's seat.
Here is a list of the extra pedals that are commonly found in semi tractors:
1. Jake Brake Pedal:** The Jake brake, or engine brake, is a device that uses the engine to slow down the truck. When the Jake brake is engaged, it closes the exhaust valves on the engine, trapping the hot exhaust gases in the cylinders. This creates backpressure, which slows down the engine and the truck. The Jake brake is typically used when the truck is going downhill or when the driver needs to slow down quickly.
2. Trailer Brake Pedal:** The trailer brake pedal controls the brakes on the trailer. When the trailer brake pedal is depressed, it applies air pressure to the brake chambers on the trailer, causing the brake pads to clamp against the brake drums. This slows down or stops the trailer.
3. PTO Pedal:** The PTO pedal, or power take-off pedal, controls the power take-off unit on the truck. The PTO unit is used to power auxiliary equipment, such as a hydraulic pump or air compressor. When the PTO pedal is depressed, it engages the PTO unit and allows it to draw power from the truck's engine.
4. Lift Axle Pedal:** The lift axle pedal controls the lift axle on the trailer. The lift axle is a non-driving axle that is used to support the weight of the trailer when it is not loaded. When the lift axle pedal is depressed, it raises the lift axle off the ground. This reduces the rolling resistance of the trailer and improves fuel economy.
5. Intarder Pedal:** The intarder, or hydraulic retarder, is a device that uses hydraulic fluid to slow down the truck. When the intarder pedal is depressed, it diverts hydraulic fluid from the transmission to the intarder, where it is used to generate heat. This heat is then dissipated through a heat exchanger, which helps to slow down the truck.
6. Exhaust Brake Pedal:** The exhaust brake is a device that uses the exhaust gases from the engine to slow down the truck. When the exhaust brake pedal is depressed, it opens a valve in the exhaust system, allowing the hot exhaust gases to escape. This creates backpressure, which slows down the engine and the truck.
7. Cruise Control Pedal:** The cruise control pedal is used to set and maintain a desired speed for the truck. When the cruise control pedal is depressed, the truck's engine speed and transmission are adjusted automatically to maintain the set speed.
These are just some of the most common extra pedals that are found in semi tractors. The exact configuration of pedals can vary depending on the make and model of the truck.
