Background of the Invention In the railway car field, there is increasing use of a car control unit (CCU) at each car in a train of cars for controlling the braking of cars. The CCU is electrically connected to a Head End Unit (HEU) in the locomotive for control and indicating purposes. See, for example, U. S. Patents Nos. 5,335,974 and 5,503,467.

Normally, the brakes are applied by an air operated piston and cylinder assembly which is connected to the brakes by a series of levers and beams. Brake rigging ratios to increase braking force, along with the 5/8"allowable wear of eight shoes, will produce major rigging component displacement problems and excessive piston stroke. It is, therefore, necessary to include a brake slack adjuster in the mechanism or"rigging"which interconnects the piston and cylinder assembly with the brake shoes. See, for example, U. S.

Patents Nos. 3,850,269; 4,312,428 and 3,283,861. Normally, the pressure of the air in the piston and cylinder assembly is an indication of whether the brakes are applied or released.

However, such air pressure, e. g. when it is relatively low or zero, does not necessarily indicate that the brake shoes have become disengaged from the car wheels because there may be a fault in the brake shoe driving mechanism which, even though the air pressure in the piston and cylinder assembly is low or zero, will not permit the brake shoes to move away from the wheels. In the event of such a fault, the brake shoes and the wheels which they engage will overheat when the car is put in motion. Accordingly, an indication at the Head End Unit (HEU) that the bar brakes have been released, which is based on the air pressure in the piston and cylinder assembly, is not always reliable.

When the brake rigging includes a brake slack adjuster, it is disposed intermediate the brake force generator, i. e. the piston and cylinder assembly, and the brake beams which support and move the brake shoes. The trigger or actuator return spring of a brake slack adjuster usually has a size and strength sufficient to return the levers, etc., of the brake rigging to the full release position provided that there are no extraneous forces which prevent full release. In other words, the position of the actuator or trigger is a direct, rather than an indirect, indication of brake shoe disengagement from the car wheels.

Summary of the Invention In accordance with the preferred embodiment of the invention, an electrical switch is mounted so that it is operated by the slack adjuster actuator or trigger, and therefore, the electrical condition of the switch indicates whether or not the brake shoes have become disengaged from the associated wheels. The switch is connected to the CCU and hence, the HEU, in the conventional manner, e. g. the same manner as other electrical devices on a car for indicating conditions at the car, such as the piston and cylinder air pressure indicator, so that an indicator at the HEU, e. g. a light source, or other electronic indicator, will indicate the condition of the brake shoes on the car.

In the preferred embodiment, the electrical switch is a normally open switch so that in the event of a failure of the brake shoes to assume their brake release positions, a failure of the switch or a failure of the medium, e. g. wires which interconnects the switch with the CCU, the indicator at the HEU will not indicate that the brake shoes are in their released positions.

Preferably, the slack adjuster interconnects a pair of the brake shoe beams, each of which caries a pair of brake shoes with each shoe being engageable with different car wheels so that if any one of the brake shoes has not fully released, the electrical switch will not be operated.

Brief Description of the Drawings Fig. 1 is a fragmentary, partly schematic elevation view of a brake slack adjuster in combination with the apparatus of the invention; and Fig. 2 is an enlarged, partly schematic, plan view of a portion of the apparatus shown in Fig. 1.

Detailed Description of Preferred Embodiments The invention will be described in connection with a brake slack adjuster of the type described in detail in U. S. Patent No. 3,850,269, the disclosure of which is incorporated herein by reference, and connected to the brake rigging as illustrated in U. S. Patent No.

4,312,428, the disclosure of which is incorporated herein by reference. However, it will be apparent to those skilled in the art that the principles and apparatus of the invention can be used with other types of slack adjusters and with other connections of a slack adjuster the brake rigging.

In Fig. 1, the slack adjuster 1 has a housing 2 which receives the mechanisms for adjusting the length of the slack adjuster 1, such as the mechanisms disclosed in said Patent No. 3,850,269. A non-circular rod 3 extends from one end of the housing 2 and is connected to the jaw 4. A tube 5 extends from the opposite end of the housing 2 and is connected to a jaw 6.

A trigger or actuator 7 is mounted on the housing 2 and is movable in the lengthwise direction of the housing 2. The trigger 7 is pivotably coupled to one end of a camming bar 8 which also is movable in the lengthwise direction of the housing 2. The opposite end of the camming bar 8 is secured to a rod guide 9 (Fig. 2) which slidably engages the guide rods 10 and 11.

The guide rods 10 and 11 are encircled by compression springs 12 and 13, respectively, and the rods 10 and 11 are secured at end to a member 14 in fixed relation to the housing 2. Thus, when the trigger 7 moves to the left, as viewed in Fig. 1, the bar 8 moves to the left causing the guide 9 to slide along the rods 10 and 11 and to the left and compressing the springs 12 and 13.

A pair of headless bolts 15 and 16 are threaded into the rod guide 9 and locked by nuts 17 and 18. The bolts 15 and 16 are encircled by compression springs 19 and 20. A plate 21 is slidably mounted on the bolts 15 and 16 and is held thereon by pins 22 and 23. A cover 24 having an end wall 25 has a switch 26 mounted thereon in any conventional manner, e. g. by screws 27 and 28. The switch 26 can be a normally open, single pole electrical switch having an operating member, such as a depressible actuating button 29.

Although the bolts 15 and 16, springs 19 and 20, plate 21, etc., can be omitted with the switch button directly engaging the rod guide 9 provided that the button has sufficient travel when depressed, the bolts 15 and 16, springs 19 and 20, plate 21, etc., act as overtravel means and are preferred to avoid damage to the switch 26 in the event of overtravel of the bar 8, and hence, the rod guide 9. Thus, the overtravel means permits the trigger 7 to move a greater distance than the button 29 without damage to the switch 26.

In a typical installation of a slack adjuster such as the slack adjuster 1, e. g. the installation illustrated in U. S. Patent No. 4,312,428, the jaw 4 is pivotally connected to a lever 30 which transmits braking force from a brake air cylinder to a brake beam (not shown) which carries brake shoes which are engageable with wheels of a railway car truck.

Similarly, the jaw 6 is pivotally connected to a lever 31 which transmits braking force to a brake beam which caries other brake shoes which are engageable with other wheels of the truck.

The trigger 7 is coupled to a control arm 32 comprising a threaded rod 33 secured to a yoke 34 which is pivotally connected to an actuating lever 35. A threaded adjusting nut 36 on the rod 32 engages the trigger 7 and is locked by a lock nut 37.

The operation of the braking apparatus and the slack adjuster 1 is described in detail in said Patents Nos. 3,850,269 and 4,312,428, both of which are incorporated herein by reference, and need not be repeated herein. However, it will be observed that the position of the actuating lever 35, and hence, the trigger 7, is dependent upon the positions of the brake beams carrying the brake shoes. Therefore, if, for some reason, brake shoes do not disengage from the truck wheels when the brake cylinder air pressure is released, the trigger 7 and the camming bar 8 will not return to the positions shown in Fig. 2 in which the plate 21 engages the switch button 29 and closes the switch 26.

If the brake shoes disengage properly from the truck wheels when the brake cylinder air pressure is released, the springs 12 and 13 return the camming bar 8 and the plate 21 to positions in which the button 29 is depressed and the switch 26 is closed. Closure of the switch 26, which is connected by wires 38 and 39 to the known car control unit (CCU) 40 causes the CCU to transmit a signal to the head end unit in a known manner, such as by way of wires 41 and 42, which provides an indication that the brake shoes of the truck on which the slack adjuster 1 is mounted have disengaged from the respective wheels. For example, the signal from the CCU can control the operation of a light, a visual image on a cathode ray