Vehicle tire pressure supervisory system

#Cross reference to related application: DENAMPS et al, Ser. No. 730,634, filed Oct. 7, 1976 assigned to the assignee of the present application.

#The present invention relates to a system to supervise vehicle tire pressure, and more particularly to such a system in which each wheel has associated therewith an energy absorbing circuit, typically a tank circuit, coupled with a fixed coupling transducer coil, the tank circuit being opened or closed in dependence on tire pressure.

#The lifetime of vehicle tires is greatly influenced by tire pressure, besides loading and vehicle speed. Loading and vehicle speed are under control of the operator; the tire pressure cannot be checked continuously, however, during operation of the vehicle. Design tire pressure should be accurately maintained. If the tire pressure is too low, the structure of the tire is damaged by excessive kneading; further, the tire will heat unduly, thus further decreasing the strength of the tire structure and also leading to rapid deterioration thereof.

#The invention will be described by way of example with reference to the accompanying drawings, wherein:

#FIG. 1 is a schematic block circuit diagram of the system in accordance with the present invention;

#FIG. 2 is a schematic illustration of the transducer arrangement with twin or tandem tires;

#Each wheel or, rather, each tire, has a transducer system associated therewith which includes a tank circuit formed by capacitor 12, inductance coil 13 and pressure switch 11. The system 10R for the right wheel is shown in FIG. 1 in detail; the pressure switch 11 is normally closed. It opens when the pressure drops below a predetermined level. Coil 13 is so located on the wheel of the vehicle that it can be coupled with a coil 14 of the tank circuit of a blocking oscillator 15 which is fixed on the frame of the vehicle. Blocking oscillator 15 has its output connected to a junction 16 which connects to two terminals; the right reset RR terminal 17 of an integrator 18 and to the SET input of a monostable multivibrator (MMV) or mono-flop 19. The output of the MNV 19 is connected to the setting connection 21 of integrator 22 which has its reset input RL coupled to a blocking oscillator 23 similaar to blocking oscillator 15. Blocking oscillator 23 is coupled to a tank circuit 10L associated with the left wheel. The output of oscillator 23 is connected to an MMV 27 similar to MMV 19, which MMV 27 is in turn connected to the left set SL terminal of integrator 18. A starting circuit 35, having a starting pulse applied at its input has two output terminals T, T' which are connected, respectively, to additional setting inputs of the MMV's 19, 27. The outputs 25, 26 of the integrators 18, 22 are connected to an OR-gate 30 to which also other inputs from other similar integrators associated with tire pressure sensing systems of other axles can be connected, as shown schematically. The OR-gate is connected to an amplifier and threshold circuit 32 which may include separately, or as part thereof, a memory portion 31, the output of which is connected to an indicator 33. The memory can be short-time, for example a monostable flip-flop or a self-holding circuit with an interrupt override. Thus, memory 31 may be no more but a self-holding circuit or switch. Besides the oscillators 15 and 23, each one of the systems associated with each wheel includes an amplitude demodulator and a pulse or wave-shaping circuit which provides output pulses only if oscillators 15, 23, respectively, are damped, so that the oscillating amplitude decreases or blocks. These circuits are inherent in the oscillators 15, 23 which may be blocking oscillators having an output tank circuit for oscillation and, upon presence (and closed circuiting) of the wheel tank circuit 10 block and provide an output signal.

#The memory 31 is used particularly if the system is associated with tandem or multiple tires. When used with tandem tires, the warning signal will appear only periodically at the output. To provide for a constant warning signal, however, the missing time is bridged by the memory 31, preferably an MMV. The timing of the MMV is so dimensioned that a warning lamp provides constant output, for example, to a speed of down to 8 km/h (about 5 mph); when the vehicle moves still slower, it will flash. If the lamp is fully illuminated at a stopped vehicle or not depends on the relative position of the respective wheels and the transducers. The effect thereof will be discussed below.

#Self-checking of the circuit is provided; to cause indicator lamp 33 to light before starting the vehicle, threshold and amplifier circuit 32 must have responded, which requires a predetermined value in at least one of the integrating stages 18, 22, or others from other axles. The integrating stages are charged from starting circuit 35, terminals T, T', to provide a malfunction signal, for example only during starter operation, indicating that the circuit is operating properly. The starting circuit 35 is connected to the MMV's 19, 27. It may, in a simple form, be a differentiating circuit which provides a pulse upon operation of the starter switch, for example when the starter switch is turned on. If the MMV's 19, 27 have a sufficiently long unstable time, and no reset pulse is derived from the other blocking oscillators 15, 23, indicator lamp 33 will light, thus indicating to the operator that the system is operating properly to supervise tire pressure.