Those skilled in the art know that vehicles have a brake system (VBS), which, typically, has a brake reservoir for providing proper pressure levels of fluid (such as, air or a hydraulic fluid) within the brake system. It is further known that some vehicles (for example, trucks and tractors that pull trailers) have a tire management system (TMS), which uses pressurized air from a VBS reservoir to maintain pneumatic pressure in the vehicle tires. Often, the TMS is associated with a trailer attached to the vehicle.
Unfortunately, current vehicle air brake systems, with “spring brake priority,” allow a vehicle operator to move the trailer, regardless of the pressure level in the VBS reservoir. Consequently, it is possible to operate the trailer without adequate VBS reservoir pressure to stop the trailer. Low VBS reservoir pressure may be caused by a number of factors, for example, a faulty spring brake valve or a significant, though not gross, leak in the reservoir itself. In other circumstances (such as in a multiple trailer application), VBS reservoir pressure may be too low to hold off the spring brakes, resulting in overheated brakes.
Examples of relevant art involving a brake air pressure supply or VBS reservoir pressure are as follows. U.S. Pat. No. 4,593,954 to Campanini describes an air brake valve system. The air brake valve system has a valve cluster on the trailer responsible for filling and protecting the pressure in the air reservoir tank. The valve cluster has a low pressure warning means in the tractor to warn the operator of low air reservoir tank pressure. The valve cluster comprises a mechanical system that determines when the air reservoir tank pressure is too low.
U.S. Pat. No. 4,763,959 to Vandermotter provides for an electronic control for a vehicle braking system. The system includes a supply reservoir connected to the compressor of the vehicle. A pressure sensor is directly connected to the supply reservoir, which is connected to a front and a rear service reservoir. The front and rear service reservoir each have individual pressure sensors. These pressure sensors are connected to an electronic control unit, which monitors these pressure sensors.
U.S. Pat. No. 4,877,294 to Kuhn et al. teaches a tractor-trailer braking system having an electric pressure transducer disposed to sense the pressure of compressed air in the pneumatic power supply. The pressure transducer is mounted on the supply tank to sense the pressure inside of the tank. Kuhn also indicates that the transducer acts via electronics to operate an alarm in the operator's compartment, should the sensed pressure increase above, or decrease below, a predetermined amount.
U.S. Pat. No. 5,172,958 to Sell discloses a similar air brake valve system to that in Campanini, discussed above, however, the disclosure in Sell indicates three valve clusters can be used. A first valve cluster controls the passage of compressed air from the emergency gladhand supply line to the spring air brakes. A second valve cluster controls the filling and protection of the air reservoir tank. The third valve cluster eliminates compounding of the braking forces by the service brakes when the spring brakes have been applied.
U.S. Pat. No. 5,533,866 to Malecha teaches a pressurized air brake system for a vehicle comprising a first reservoir and a second reservoir connected to an air compressor. The first and second reservoirs are connected to a control system. The control system is also connected to the compressor for actuating and disengaging the compressor in response to air pressure levels in the first and second reservoirs. Malecha indicates that the reservoirs are connected to service brakes of the tandem and trailer, parking brakes, and wipers, however, other components can also be connected to the reservoirs. Each reservoir has a switch containing a pressure diaphragm. The diaphragms toggle between activated positions and deactivated positions in response to air pressure changes in the reservoirs. Malecha also states that microprocessors and air pressure sensors can be used to monitor reservoir air pressure and control the compression of air by the air compressor.
U.S. Pat. No. 5,592,754 to Krieder et al. provides for a pressure transducer connected to a reservoir to sense the pressure in the reservoir. The transducer provides an electrical signal indicative of the pressure in the reservoir to an electronic controller. The controller uses the signal to control three different outputs: a low pressure warning lamp, a compressor control solenoid and a purge control solenoid. Krieder teaches that the controller is designed to control these items in lieu of three separate mechanical units.
U.S. Pat. No. 6,079,436 to Delfs et al. discloses a pressure sensor connected to an air supply line between a check valve and the compressed air container. The sensor communicates the sensed pressure to control electronics. The control electronics signal one of two pressure regulating valves. The valve is connected to an outlet valve that allows air from a compressor to at least one compressed air consumer.
U.S. Pat. No. 6,682,459 to Knight teaches a vehicle brake compressed air supply system having an electronic air charge controller (EAC) and a first and a second pressure sensor. The first pressure sensor measures the pressure within a line connected to a supply reservoir. The pressure in the line is indicative of the pressure in the reservoir. The sensed pressure is sent to the EAC so that it can determine if the pressure in the reservoir is below a pre-determined amount. If the pressure is below the pre-determined amount, a signal is sent to the engine to increase RPM.
It would, however, be safer and economically advantageous for a vehicle to utilize a vehicle brake systems in conjunction with an existing tire management system, to detect and warn the vehicle operator of low brake pressure conditions.