Brake checking system

#1. Field of the Invention

#The present invention relates to a brake checking system which compares the maximum distances of successive movements of the brake pedal of a vehicle to detect the inclusion of air into the brake system or the existence of an abnormal clearance or gap between the brake shoes and the brake drums.

#2. Description of the Prior Art

#FIG. 1 is a sectional view showing the construction of a brake sensor used with a system of this invention, with a part thereof broken away.

#FIG. 2 is a wiring diagram of the electric circuit section incorporated in the brake sensor shown in FIG. 1.

#FIG. 3 illustrates wiring diagrams useful in explaining the basic operation of the brake sensor shown in FIG. 1.

#The present invention will now be described in greater detail with reference to the illustrated embodiment.

#A brake sensor 1 which senses the distance of a stroke of the brake pedal and converts it into an electric signal, will now be described with reference to FIGS. 1 to 5. In FIG. 1, numerals 11 and 12 designate housings, and the housing 12 which is made from a non-magnetic material has a threaded portion 12a for mounting it in place. Numeral 13 designates a contact unit incorporating contacts which are opened or closed in response to the movement of a switch 115, 111 a shaft of a non-magnetic material movable in response to the movement of the brake pedal and inserted into the housing 12, L.sub.2 a spring coil serving to return the shaft 111 to a predetermined position and also serving the purpose of producing oscillations. Numeral 114 designates an electric circuit section comprising an oscillator circuit and a waveform shaping circuit, 120 an electric wire connecting the spring coil L.sub.2, coil L.sub.1 and electric circuit section 114 with one another, 121 and 122 output lines connected to the switch 115 for delivering its output signal, 123 a supply line, 124 an output line for delivering the output signal of the electric circuit section 114. The coil L.sub.1 is fixedly held in place in the housing 12 and the spring coil L.sub.2 is disposed to axially extend and retract in the central hollow portion of the coil L.sub.1.

#In FIG. 2 showing the construction of the electric circuit section 114 mounted in the housing 11, symbol B designates a power source, an oscillator circuit 211 is comprised of a transistor T.sub.r1, and resistor R.sub.1, capacitors C.sub.1 and C.sub.2, the spring coil L.sub.2, the coil L.sub.1 and a diode D.sub.1, and a waveform shaping circuit 212 is comprised of a transistor T.sub.r2 and resistors R.sub.2 and R.sub.3. Numeral 201 designates a supply terminal connected to the supply line 123 shown in FIG. 1, 202 an output terminal connected to the output line 124 shown in FIG. 1. With this construction, the brake sensor 1 operates as follows. When the shaft 111 is pressed in the direction of an arrow A.sub.1 in FIG. 1, the shaft 111 is moved within the housing 12 against the force of the spring coil L.sub.2 so that when the shaft 111 is moved from its predetermined initial position or point B.sub.1 to a point B.sub.2, the switch 115 is urged by the shaft 111 and the contacts in the contact unit 13 are opened thus disconnecting the output lines 121 and 122, whereas when the force urging the shaft 111 in the direction of the arrow A.sub.1 is removed, the shaft 111 is returned to the initial point B.sub.1 and the contacts in the contact unit 13 are closed. This operation is the same with that of the known types of brake sensor.