All internal parts and components of the engine are lubricated through a network of conduits and ducts, in which oil is pumped at high pressure through a pump. Passing through the ducts and due to centrifugal force, the oil reaches all parts that need to be lubricated: camshafts, valves, rocker arms, bearings, connecting rods, cylinders and pistons.
The lubricating oil is located inside the sump, from which it is drawn through the pump.
These switches, activated by the pressure of the lubricating oil used in engines, serve to indicate to the driver, by means of a LED on the control panel, when the pressure of the lubrication circuit is insufficient compared with the prescribed value.
Constituent elements and operating principles
Oil pressure switches comprise a metal body and a plastic casing.
The turned metal body allows mounting on the engine block, is equipped with a threaded end on which there is a hole to allow the lubricant to reach the interior of the device. The threaded part can be equipped with a metal gasket.
The metal body is rimmed with the plastic casing into which the terminal connection is moulded or chamfered. This part contains the internal elements of the device.
The internal elements of the device are protected from oil by a Mylar membrane. The pressure exerted by the oil on the membrane causes a ferrule to slide until, once the exchange pressure has been reached, applies/removes contact with the elements of the device by opening/closing the switch.
Benefits of the proper functioning of the oil pressure switch
- Engine lubrication ensures the longevity of all the internal components and moving parts.
- The lubrication system also contributes to the cooling of parts subject to strong thermal stress (pistons, connecting rods, cylinders, bearings, etc.)
Major causes of malfunctioning
- De-calibration, cracks and oil leaks
- Accelerated wear caused by cycles of pressure and high temperature
Effects of malfunctioning
- Lack of hermetic seal between the oil and the inner chamber of the device, with damage to the elements of the switch at high pressure
- Progressive degradation of the switch through wear
- In some cases, malfunctioning can also compromise the safety of the vehicle
Oil pressure switches can be of 2 types:
- N/O (normally open) circuit: normally open when the pressure in the oil is less than the pressure of exchange, they close when the pressure exceeds the pressure of exchange. The switch is closed by contact between the metal washer connected to the casing of the device and the movable metal capsule connected by the return spring to the terminal. Once the pressure of exchange has been exceeded, the tip (plastic) pushes the capsule, opening the circuit.
- N/C (normally closed) circuit: normally closed when the pressure in the oil is less than the pressure of exchange, they open when the pressure exceeds the pressure of exchange. The switch is closed by contact between the metal washer and the tip (metallic). The metal washer has a portion in moulded plastic so that the capsule does not close the switch. Once the pressure of exchange has been exceeded, the tip (metallic) pushes the capsule, coming into contact with the washer, closing the circuit.
Oil pressure switches can be of combined type (N/O – N/C): In a single device there are two switches.
These devices have 2 or 3 terminals.