RPM sensors are normally installed near a phonic wheel, also called flywheel.
They detect the variations of the magnetic flow produced by the alternation between the presence and absence of the tooth or cam of the flywheel which generate an electrical signal. This signal is sent to the engine control unit whereby, depending on the phonic wheel where the sensors are installed, the detected signal indicates:
• The revolving speed of the drive shaft (Crankshaft Rotational-speed Sensors)
• The top dead center by detecting the position of the drive shaft (Crankshaft Position Sensors)
• The ignition sequence/timing by detecting the position of the camshaft (Camshaft Position Sensors)
RPM sensors and timing sensors are installed on any type of engines. One or more sensors with different functions can be installed on the same car. Structurally equivalent sensors must be installed in the specified position only.
Depending on the specific application, the connector of the RPM sensor may be integrated or connected to the body of the sensor with a cable.
Connectors may have 2 terminals (variable reluctance sensors) or 3 terminals (Hall effect sensors) or, if there is an interference suppression, 3 (variable reluctance sensors) or 4 terminals (Hall effect sensors).
The main reasons for failures in the product are:
• deformation and dents
• sensor overheating
• lack of signal, broken wire from chafing or excessive vibration, short circuit, internal breakage
• infiltrations of liquids or impurities through poor sealing.
The signs of malfunctions of the sensor are indicated by illumination of the engine warning lamp, difficulty in starting the vehicle, high fuel consumption, increased exhaust gas emissions.
RPM sensors are designed and assembled to withstand the critical installation conditions inside the engine compartment. In particular, the following requirements shall be met:
• Operating temperature: -40°C ÷ +150°C
• Degree of protection: IP67 (entrance of dust not allowed and protection against water immersion effects for 30 minutes).
The RPM sensors undergo qualification and endurance tests on these RPM sensors to determine if the product is suitable for construction and sale:
• Resistance to thermal shocks for a total of 60 hours
• Resistance response to current spikes
• Resistance to impacts
When these tests have been passed and after the approval to manufacture has been given, the product, in the assembly process, is strictly checked through a series of cycles which include 100% testing processes to verify the resistance and inductance of the sensor, the intensity and polarity of the signal, the resistance response to current spikes and the absence of interruptions or short-circuits.