A new automotive electronic tire pressure detection program

The normal operation of tires is an important guarantee for safe driving. A considerable part of automobile safety accidents are caused by tire failures. This solution adopts the key components of Infineon's tire pressure detection scheme (SP37, TDA5235/TDA5240). The whole tire pressure detection system consists of three parts: tire pressure sensor, receiver and low frequency transmitter.

【An Introduction】

Hazard of abnormal tire pressure

• When the tire pressure is too low: Tire wear is intensified, life is reduced, fuel consumption of the car is increased, and puncture is likely to occur at high speeds, causing a serious traffic accident.

• When the tire pressure is too high: The tire grip is reduced, the brake performance is weakened, and the tire wears quickly while increasing the wear of the suspension system.

• When the tire is completely leaking: Continue driving the car will cause complete damage to the tire and cause unnecessary damage.

• When the tire pressure is not balanced: Easy to run when driving and braking

How the tire pressure monitoring system works

Each tire is equipped with a highly sensitive transmitter (sensor) that detects the pressure and temperature of the tire in real time, and the data is transmitted by radio signals to the display mounted on the bridge.

The display shows the air pressure and temperature values ​​of the tire. Any reason (such as foreign matter piercing the tire, tire scratches, etc.) caused the tire to leak, the tire pressure during driving is not normal, the system will automatically alarm, thus ensuring the safety of the car, extending the life of the tire, while reducing fuel Consumption.

Function of tire pressure detection system

• Real-time monitoring function: The tire's pressure and temperature status can be monitored regardless of whether the vehicle is running or at rest. The tire status is under control.

• High pressure/low pressure alarm function: The system issues an alarm when the tire pressure is above or below the set value.

• Air leak alarm function: The system will give an alarm if a foreign object penetrates into the tire to generate a leak.

• High temperature alarm function: When the tire temperature exceeds 80 °C, the system will give an alarm.

• Ultra-low power consumption: Extremely optimized operating mode, system battery life of up to 5 years.

Tire pressure sensor module working state Because the tire pressure detection module is powered by battery, the battery life problem becomes a problem that needs to be considered. Especially in software design, the low-power algorithm implementation should be carefully designed and can be roughly divided into The following states:

• Storage status: The system is in an unused state and should enter deep sleep mode

• Transportation status: The detection module has been loaded and is not actually used during transportation.

• Parking status: Activated and started working, but stopped at this time, the speed is 0

• Driving status: Through the acceleration sensor, the vehicle speed is detected, enters the running state, detects the tire pressure, tire temperature, speed, etc.

• Low voltage status: If the battery voltage is too low, continuing to work will cause the related functions to not work properly and issue a warning.

• Leakage condition: A tire is leaked through continuous inspection and a warning is issued.

[program features]

• Sensor communication fault alarm duration: ≤10min

• Battery model: CR2450HR (electricity: 550mAh)

• RF frequency: 433.92±0.1MHz

• No RF emission average operating current: ≤1μA

• Maximum operating current for RF emission: ≤15mA

• High frequency transmit power: 7~9dBm@50Ω

• High frequency modulation method: FSK (9.6Kbps)

• Low frequency receiving frequency: 125±5 KHz

• Low frequency receiving mode: ASK (3.9Kbps)

• Low frequency signal receiving sensitivity: 1~50mVp-p

• Pressure measurement range: 0~4.5Bar

• Pressure measurement resolution: 25mBar

• Temperature measurement resolution: 2 ° C

• Pressure measurement accuracy: ±75 mBar @ -20°C~+70°C, ±150 mBar @ -40°C~+120°C

• Temperature measurement accuracy: ±4°C@ -20°C~+70°C

• Resistance to rotation: ≥1500g

• Operating temperature range: -40°C to +105°C

• Storage temperature range: -40 ° C ~ +125 ° C.