1. Field of the Invention
This invention relates to self-regulating pressure systems and methods for vehicle tires, and more particularly to self-regulating systems and methods in which the tire is automatically replenished from a high pressure reservoir in response to a sensed low pressure condition in the tire.
2. Description of the Related Art
Low tire pressure is an important cause of excessive fuel consumption, tire wear and impaired steerability. A normal tire will typically leak on the order of 25 percent of its pressure per year due to its inherent permeability. It is thus good practice to check tire pressure on a regular basis. However, even checking tire pressure every few weeks may not prevent these adverse affects when a slow leak is present, and the leak may go undetected unless a careful record is maintained of how frequently the pressure in each tire has to be replenished. A fast leak or flat condition can rapidly cause damage to the tire and even render it unusable in a short period of time, but this condition may go unnoticed by an inexperienced driver until it is too late.
It is thus highly desirable to have some mechanism that automatically replenishes the tire pressure when it is too low, and that warns the driver of the low pressure condition. One such system is disclosed in U.S. Pat. No. 4,067,376 to Barabino. This patent incorporates a high pressure reservoir into the vehicle wheel, and uses a valve that automatically opens a passageway between the high pressure reservoir and the tire in response to the tire pressure falling below a selected threshold level. Operation of the valve also causes a sonic or ultrasonic signal to be generated which is detected by a sensor mounted in close proximity to the wheel, typically within the wheel well. When it senses a valve operation, the sensor initiates a visual and audio warning for the driver. To differentiate between the different tires, the valve on each tire may be tuned to generate a signal with a unique frequency, or the sensors for the different tires may be tuned to detect different components of a uniform valve signal.
Another system is disclosed in U.S. Pat. No. 4,742,857 to Gandhi. In this patent the tire valve includes a magnet that moves in response to a falling tire pressure. Movement of the magnet to a low pressure position is sensed by a solenoid mounted on the shock absorber adjacent the tire. The magnetic field from the moveable magnet intercepts the solenoid at each tire revolution, generating a voltage in the solenoid that varies with the magnet's position. When the magnet's sensed position indicates a low pressure condition, a warning is provided to the vehicle operator. If the operator wishes to replenish the tire pressure, he or she actuates a switch that supplies current to the solenoid for the appropriate tire. The solenoid produces a magnetic field that moves its associated magnet to a position at which a valve from a high pressure reservoir within the wheel is opened so that air can flow into the tire.
While the above systems can effectively replenish the air pressure within a tire, they are incapable of distinguishing between normal long term leakage from a tire, a slow leak condition that requires repair, and a fast leak or flat tire condition. The vehicle operator is thus uninformed as to whether a tire repair or replacement is called for. The operator is also not supplied with any information as to the condition of the high pressure reservoir, and whether it requires replenishment. Furthermore, the prior use of separate transmitters within each wheel and associated receivers on the vehicle requires a power source within each wheel and complex electronics, and is unduly expensive.
An after market sensor for low tire pressure has been marketed by Epic Technologies Inc. The sensor monitors tire pressure and causes a radio frequency (RF) signal to be transmitted in case the pressure falls below a predetermined set point; transmission of the RF signal actuates a warning for the vehicle driver. However, the system does not have any mechanism to automatically replenish the low tire pressure.