GB2032028A - Rail-mounted hydraulic retarder - Google Patents

Abstract

The specification describes embodiments of a hydraulic retarder mounted on a rail 1 with a plunger 7 being depressed by a passing wheel. A piston 6 of the plunger 7 forces hydraulic fluid through restricted orifice ducts, the cross-sectional area of which are proportioned at each point of the stroke of the piston 6 to ensure uniform hydraulic pressure in the cylinder, resulting in uniform loading of the plunger throughout its downstroke, a surge chamber 2c being provided. The retarder may be mounted on either side of the rail 1. Figure 16 shows a retarder mounted vertically with a treadle bar 17 acting on plunger 7. <IMAGE>

Description

SPECIFICATION Auto-regulable retarder A typical modern railway marshalling yard comprises a receiving yard with a short grade to a hump, followed by gravity flow of wagons from the hump to the sorting yard.

As each wagon, or cut of wagons, tops the hump it rolls down a short steep grade which ensures adequate separation of cuts. At the bottom of the short steep grade the first speed check point is located near the entrance to the primary retarders.

Between the hump and the primary retarders means are provided to ascertain the axleloads of passing wagons. This is done by installing a weighbridge or by measuring the rail deflexion produced by a passing wheel load.

Between the primary retarders and the sorting yard secondary retarders are installed, each bank of secondary retarders controlling the entry speed to four sorting lines. Near the entrance to each secondary retarder there is an approach speed check point.

The general practice has been to install clasp type retarders, with the jaws operated by compressed air or hydraulically operated cylinders.

The cut of wagons is weighed as it passes from the hump and entry speed to the retarders is measured by Doppler radar. The data for weight and speed of cut are fed into a computer, when an electro-servo mechanism controls the air or hydraulic pressure to the retarder cylinders, so as to exert the required degree of clamping force for the jaws pressing against the sides of the tyres of passing wheels.

With clasp type retarders the controlled exit speeds from the retarders are generally between 5 to 3 m/s from the primary retarders and from 2 to 1.5 mIs from secondary retarders.

Track speed is restricted in a marshalling yard, and generally does not exceed 7.5 m/s at entrance to the first bank of retarders nearest to the hump.

Within the last decade two types of railmounted hydraulic retarders have been introduced, which it is claimed are speed sensitive and eliminate the need for costly weighment, speed measurement and electronic control equipment to be provided. A hydraulic retarder exerts a resistance to motion which is primarily related to velocity.

One type has a horizontal drum with a helical radially projecting lip on its cylindrical surface. A passing wheel flange engages the helical lip causing the drum to rotate through 360 degrees, the retarding force being exerted by the hydraulic circuit within the drum. This type of retarder permits wagon movement in one direction only, and if movement in either direction is required the drum is withdrawn from the gauge side of the rail by a power operated thrustor, which means the thrustor must be connected by piping to a compressed air supply.

The other type has a plunger which is depressed by the flange of a passing wheel. The plunger forces hydraulic fluid through a restricted orifice, the orifice openings being controlled by coil springs. A pocket of gas above the hydraulic fluid is compressed on the downward stroke of the plunger and exerts sufficient force to return the plunger to the top of its stroke once the wheel has passed clear. As the orifice openings are controlled by the compression of coil springs the design is essentially one for linear deceleration, but the deceleration of a plunger depressed by a passing wheel is not linear. Consequently the hydraulic pressure at the commencement of the down-stroke can be three to four times the mean pressure during the stroke.This type of retarder permits of wagon movement in either direction, and is completely self-contained requiring no external power connexions.

Two features in the design of rail-mounted hydraulic retarders with plungers depressed by passing wheels, need to be appreciated. One is that when a wheel rolling along a rail at a steady speed depresses a plunger, the downstroke velocity of the plunger is not uniform. It is a maximum at the commencement of the downstroke and decreases as the square of the diminishing distance between the vertical plane of the plunger and the vertical centre line of the approaching wheel. The initial velocity of the plunger is generally four times the mean velocity of the down-stroke. It follows that the sectional area of the orifice controlling the flow of the hydraulic fluid from the cylinder should be designed to match the downstroke velocity of the plunger at each point of its stroke, if fluctuations in hydraulic pressure are to be avoided.

The other feature concerns the loci of points on the wheel tread and wheel flange as they depress a plunger. Plunger height above rail level is generally from 40 to 60 mm and wheel flange depth below rail level 30 mm. As a wheel rolls along a rail the loci for a point on the wheel tread is a common cycloid and that for a point on the wheel flange a prolate cycloid. In either case the angle at the cusp is acute and at points so near the rail the loci do not depart greatly from the vertical plane of the plunger; but for the prolate cycloid all points on the wheel flange when below rail level are moving backwards relative to the rail as the wheel rolls forward. This backward movement of the wheel flange results in severe scuffing of a depressed plunger. If mounted on the outer side instead of the gauge side of a rail the plunger would not be subjected to this scuffing action.

To facilitate movement through crossings, railway tyres are intentionally made wide and generally overhang the outer face of the rail head by 30 to 35 mm, making it feasible for plunger type retarders to be mounted on the outer side of a track rail.

When rail-mounted plunger-type hydraulic retarders are installed they are mounted on both rails of a track to form a continuous series, commencing from the bottom of the short grade from the hump right through to the sorting lines.

The number installed depends upon average wagon ioads and the magnitude of the retarding energy to be exerted.

The design of retarder according to this invention, and the method by which it is to be performed, is particularly described in and by the following statements: The invention relates to a rail-mounted plungeroperated hydraulic unit, the plunger being depressed by a passing wheel. The piston of the plunger forces hydraulic fluid through a restricted orifice, the cross-sectional area of the orifice ducts being correctly proportioned at each point of the stroke of the piston to give uniform flow discharge and uniform hydraulic pressure in the cylinder, resulting in uniform loading of the piston throughout the downstroke of the plunger. This is an important feature as it inhibits any tendency for a pressure surge to lift, and possibly derail, a lightly loaded passing wheel.At the upper end of the cylinder block a surge chamber is provided to receive the fluid forced out of the cylinder through the orifice ducts. The pressure in the surge chamber is negligible. Once the piston reaches the bottom of its stroke the hydraulic pressure has been dissipated completely and there is no hydraulic rebound force. To return the plunger to the top of its stroke a recoil spring is provided, but the thrust of this spring is negligible compared with the hydraulic load on the piston during its downstroke. In some cases where bogie wagons with a short wheelbase and where speed is relatively high, such as at the bottom of the short separation grade following the hump, it is necessary to ensure that the plunger is returned to the top of its stroke promptly.

To facilitate this holes are drilled through the piston and a reflux valve provided on the underside of the piston to enable the cylinder to be replenished readily with hydraulic fluid. At points further from the hump where speed falls below about 5 m/s, this refinement is unnecessary and the piston may be solid without a reflux valve and holes to permit fluid flow. Each retarder is fastened to the rail by one assembly stud enabling retarders to be removed readily to permit tamping of the track ballast, or to change the cylinder liner for one having a smaller or greater sectional area of orifice ducts to suit the retarding energy required at any particular location.

The invention will be elucidated more fully with reference to the accompanying drawings, wherein: Fig. 1 is a sectional side view of a retarder assembly mounted on the outer side of a track rail.

Fig. 2 is a side view of a retarder assembly mounted on the inner side of a track rail. The assembly is the same as for Fig. 1, the only difference being the mounting boss of the cylinder block.

Fig. 3 is a side view, partly in section, of the cylinder block.

Fig. 3a is an elevation of the mounting boss for a retarder mounted on the outer side of a track rail.

Fig. 4 is a sectional view of the retarder cylinder cover.

Fig. 4a is an inverted plan view of the cylinder cover.

Fig. 5 is a sectional elevation of the neck bush in the cylinder block.

Fig. 5a is a plan view of the neck bush.

Fig. 6 is an elevation of the filler plug.

Fig. 6a is a side view of the filler plug.

Fig. 7 is an elevation of the mounting stud.

Fig. 7a is a side view of the mounting stud.

Fig. 8 is an elevation of the mushroom head.

Fig. 8a is an inverted plan view of the mushroom head.

Fig. 9 is an elevation of the retarder plunger.

Fig. 9a is an inverted plan view of the retarder plunger.

Fig. 10 is a sectional elevation of the follower plate.

Fig. 1 Oa is an inverted plan view of the follower plate.

Fig. 11 is a sectional elevation of the reflux valve.

Fig. 11 a is an inverted plan view of the reflux valve.

Fig. 12 is an elevation of the spring guide pin.

Fig. 1 2a is a plan view of the spring guide pin.

Fig. 1 3 is a sectional elevation of the recoil spring.

Fig. 1 3a is a plan view of the recoil spring.

Fig. 14 is an elevation of the cylinder liner.

Fig. 1 4a is a plan view of the cylinder liner.

Fig. 1 4c is a development of the cylinder liner and orifice ducts.

Fig. 1 5 is an elevation of the rail plate.

Fig. 1 5a is a side view of the rail plate.

Fig. 1 6 is an elevation of a retarder assembly having a vertical plunger and mounted on the gauge side of a rail.

Referring to Fig. 1 in which 1 is the rail, 2 is the cylinder block and 2a the surge chamber for the hydraulic fluid. The mounting boss 2b with its strip footing 2c are cast integral as part of the cylinder block.

The cylinder cover 3 is screwed into the cylinder block but the cover could be designed for fastening to the cylinder block by studs if required.

The cylinder liner 4 and the neck bush 5 are inserted into the cylinder block during assembly.

The piston 6 forms part of plunger 7 which is provided with a wear resistant mushroom cap 8.

Formed as part of the piston is a reflux valve 9 retained in place by follower plate 1 0. The spring guide pin 11 is provided to prevent the recoil spring 12 from buckling, and 13 is the tyre of a passing wheel.

The rail plate 14 is formed by cutting a standard fishpiate into four equal lengths and 1 5 is the assembly mounting stud. The filler plug 1 6 is for filling the cylinder block with hydraulic fluid to the correct level.

In Fig. 1 6 the treadle bar 1 7 is fixed to the top of plunger 7 for retarders with vertical plungers and mounted on the gauge side of a track rail. To prevent the treadle bar from tending to rotate a tail piece 1 8 is provided which is guided between two lugs 20 forming part of the cylinder block. The contact surface 1 9 of the treadle bar is intentionally of narrow width parallel to the rail in order to inhibit wear due to scuffing; the surface is built up using electrodes for hard facing.

Provided a retarder is designed for a cylinder hydraulic pressure of 50 kN/mm at a wagon speed of 9 m/s, there is no need to incorporate a relief valve in the designs.

Claims (2)

1. A rail-mounted plunger-operated selfcontained hydraulic retarder in which the crosssectional area of the orifice is proportional to the downstroke velocity of the plunger at all points of its stroke.

The retarding effort exerted by the plunger is proportional to the track speed of the passing wheel, thereby making the retarder autoregulable.

A design incorporating a surge chamber in which the hydraulic pressure is dissipated.

2. A retarder suitable for mounting on the outer side of a track rail in order to avoid the excessive wear of the head of a plunger caused by the scuffing action of a wheel flange.

A design of mounting requiring only one assembly stud, thereby readily facilitating removal of the retarder when required.

A strip footing provided on the mounting boss to rest on the fishing surface of the rail foot, to ensure that the plunger is held in a vertical plane and that the assembly stud is not in shear.

Provision of a rail plate on the opposite side of the rail to avoid local flexural stress in the web of the rail.