A FORCE MEASURING DEVICE

Technical Field

The present invention relates to a force measuring device for measuring forces at disc braking of a rail vehicle by means of a brake pad attached to a brake pad holder and brakingly engaging a rotating brake disc. Background of the Invention

For different reasons, it may be desirable to measure the forces occurring at such disc braking. Conventionally, it has been customary to measure such forces somewhere in the brake rigging connecting the brake pad holder to a brake actuator.

The main problem is that such measurement, which for example may be performed by means of one or several strain gauges, will not be especially exact, as it is not performed where the forces actually occur. Another problem is that the measurement shall not introduce undue disturbances in the normal braking sequence and shall not be cumbersome and expensive to carry out. The Invention These and other problems are according to the invention solved in that an insert, which contains force measuring means, is to be arranged between the brake pad holder and the brake pad and has similar attachment means as the brake pad holder and the brake pad.

The attachment is preferably accomplished in that the insert is provided on its upper side with a dovetail groove for cooperation with a corresponding longitudinal ridge arrangement on the lower side of the brake pad and on its lower side with a longitudinal ridge arrangement for cooperation with a dovetail groove on the upper side of the brake pad holder.

The brake pad may be kept in proper position in the insert in that the latter is provided with end closures.

The force measuring means preferably comprise elastically yieldable tongues machined out of the insert and strain gauges attached to the tongues.

Brief Description of the Drawings

The invention will be described in further detail below under reference to the accompanying drawings, in which Fig 1 is an isometric view of a conventional brake pad holder with an insert according to the invention and with a conventional brake pad,

Fig 2 is an isometric view corresponding to Fig 1 but without the brake pad, Fig 3 is an isometric view of only the insert according to the invention seen from above as in Fig 2, and

Fig 4 is a corresponding view of the insert seen from below.

Detailed Description of an Embodiment In a disc brake arrangement for a rail vehicle, a brake disc rotating with an axle is to be brakingly engaged by a brake pad, normally at each axial side of the disc. The replaceable brake pad is attached to a brake pad holder, which is suspended from a member of the vehicle undercarriage or bogie and is normally a part of a disc brake caliper, comprising a brake actuator for supplying a brake force to the brake pad holder substantially transverse to the brake disc.

The present invention relates to a force measuring device in connection with the brake pad holder for supplying measurement data regarding forces occurring at brake application of the brake pads against the brake disc.

Depicted in Fig 1 is a conventional brake pad holder 1. The brake pad holder has a planar upper surface, against which a planar portion of the lower surface of a brake pad

2 is to bear. For the releasable attachment of the brake pad 2, this planar upper surface has a longitudinal dovetail groove for cooperation with a corresponding longitudinal ridge arrangement on the lower surface of the brake pad 2. The cooperating groove and ridge arrangement may be defined as attachment means.

The dovetail groove of the brake pad holder 1 is open at the short end to the right in the drawing or the lower end in mounted condition. The brake pad holder 1 is here provided with fastening means 3 for a closure device (not shown) for the dovetail groove, so that the brake pad 2 is held in position after mounting.

The brake pad holder 1 is also provided with a suspension bore 4 for pivotal suspension of the brake pad holder, as is well known to any person skilled in the art. The bore 4 shall be parallel with the brake disc.

When it is desired to measure forces occurring at brake application, an insert 5 is mounted between the brake pad holder 1 and the brake pad 2. For this purpose, the insert 5 is provided on its upper side with a dovetail groove 6 corresponding to the dovetail groove in the brake pad holder 1 and on its lower side with a longitudinal ridge arrangement (Fig 4) corresponding to the ridge arrangement of the brake pad 2 and comprising two longitudinal ridges 7 and an intermediate, somewhat lower portion. In this way the insert 5 may be mounted between the brake pad holder 1 and the brake pad 2, as is shown in Fig 1. The latter may be held in position in the insert 5 by removable end closures 8 attached to the ends of the insert 5, preferably by screws. (The left end closure 8 in Fig 2 is removed for clearly showing the dovetail shape of the groove 6. )

Tongues 9 are machined out of the insert 5 at the dovetail groove 6 and over the ridges 7 at its lower side, for example to shapes shown in the Figures. These tongues 9

may for example be four at each side of a center line of the insert and may be symmetrically arranged. The tongues 9 may elastically yield to a certain extent under forces acting thereon. The central portion of each tongue 9 has a substantially square cross-section and can accordingly yield in two directions: in the longitudinal direction of the insert 5 and perpendicular thereto, i e normal to the insert. These two directions correspond to yield under friction forces and application forces, respectively, at brake application by means of the brake pad attached to the insert 5 on the brake pad holder 1.

The yield and thus the forces may be measured by strain gauges 10 attached to the central portion of each tongue 9, preferably at all four sides of the square. The tongues 9 and the strain gauges 10 may together be defined as force measuring means .

In the shown example there are 16 strain gauges in a bridge for measuring friction force and application force or brake force, respectively. The dovetail groove 6 may be provided with a central longitudinal channel 11 for connecting wires from the strain gauges 10. Wires may leave the insert 5 through bores 12 leading to the channel 11. A cover 13 may be arranged over each pair of tongues 9. Thermo elements 14 may be arranged at the side of the insert 5 for assessing the temperature attained at braking.

The force measuring means have been shown and described as strain gauges, but other technical solutions are feasible for the person skilled in the art. With the use of strain gauges or similar means the thickness of the insert 5 can be so small that an ordinary brake pad 2 can be used. If not, a brake pad with reduced thickness may be used for the measurement.