Triumph Gear Position Sensor Design
Triumph motorcycles use an electronic gear position sensor to determine the position of the gear shifter. The description of the gear position sensor from the service manual is below.
The gear position sensor is situated in the lower crankcase below the final drive belt pulley. The gear position sensor provides the ECM with selected gear information. This is used to prevent the engine from starting if the transmission is in gear. The sensor also provides information to the neutral lamp in the instruments.
While the Triumph Thunderbird Storm, Thunderbird LT, Rocket, and Speed Triple all have different part numbers for the sensor, the differences between models are likely due to either physical size and mounting, or slightly different sensing system.
The similar gear position sensors are Triumph part numbers T1190814, T1292057 and T1290666 (Thunderbird Storm).
Triumph Gear Position Sensor For Newer Models
The gear position sensor for newer models has 7 electronic switches that are activated in sequence as the gear selector moves through the 1-N-2-3-4-5-6 positions. These switches connect increasing resistance values to electrical ground through a fixed resistor in the ECM module, and this creates a different output voltage for each gear. The computer inside the ECM module reads the voltage to determine which gear the bike is in.
The gear position sensor is designed this way to reduce the amount of wiring and the size of the connector and harness between the gear position sensor and the ECM. With this system, only 4 wires are required: one for the voltage, one for the neutral position (for compatibility with older designs), one for power, and one for ground. Connecting the switches directly to the ECM would require a minimum of 8 wires.
The sensor for older bikes has a three wire sensor in stead of four. These sensors are likely based on a variable resistor element instead of the switched resistances of the new models. It is possible that Triumph moved to the switched version because of improved longevity and reliability -- variable resistor elements are more prone to wear.
The ECM uses the gear position information to operate the ignition, adjust the timing or fuel mixture, and the neutral light. The ECM module in Triumph motorcycles also transmits the gear information onto the CANBUS network within the bike's wiring. The diagnostic connector connects to the CANBUS network with a proprietary communication protocol and not as OBDII. The Gearingo gear indicator has the internal circuity to listen to the CAN communication, and having deciphered the messages, can display the gear for the rider.
OBDII communication is available on the diagnostic connector, but as a K-LINE signal and not CANBUS
Cut-Apart View of Gear Position Sensor
We took apart a Triumph gear position sensor to see what is inside of it, see the picture in Figure 2 below. The sensor has the following basic components:
- Sensor housing with two mounting ears.
- Rotating disk with a small magnet that attaches to the bike's gear selector assembly with the camshaft housing.
- Printed circuit board that has 6 Hall Effect magnet sensors which pickup the location of the magnet.
- Cable and connector that connects the sensor to the main connector on the ECM module. This cable has a braided sheath on it to protect the wiring against heat and abrasion.
Gear Position Sensor Schematic
The simplified schematic in Figure 3 below depicts the gear position sensor's internal circuit. The transistors marked Q1-Q7 are actually hall effect switches that are positioned in a circular pattern around the center of the unit so that the small magnet rotates over and activates them in sequence.
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