Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B61—RAILWAYS
  • B61G—COUPLINGS; DRAUGHT AND BUFFING APPLIANCES
  • B61G11/00—Buffers
  • B61G11/12—Buffers with fluid springs or shock-absorbers; Combinations thereof

Definitions

• railway vehicles in most countries show a similar basic design, which inter alia includes that both ends of the vehicles are provided with a coupling device in the middle, surrounded by two buffers.
• the main task of the coupling device is to transfer traction forces from one vehicle to another, whilst the buffers have to take care of compressive forces or impacts between the vehicles elastically in order to reduce impact loads on structure or cargo to a harmless level.
• buffers Due to practical reasons, it is not possible to design buffers with extremely long stroke, and a considerable energy absorption capacity thus implies a considerable resistance to closure. If buffers are are designed to take care of impacts between heavy wagons at quite high speeds, it is difficult to avoid that such buffers cause a brutal deceleration to a light wagon running into a heavy one at a moderate speed. The heavy wagon is in this case almost immovable, and the deceleration of the light one is equal to the buffer force divided by the mass of the wagon.
• the kind of buffer predominant in Sweden as well as many other countries is the ring spring buffer. It is here used in two basic models. Wagons with four axles, as well as new two axle wagons, are usually equipped with the heavier model, designed for a potential stored energy of 32 kJ, whilst a majority of two axle wagons are equipped with the weaker model having only about the half of this capacity. The ratio between resistance to closure and stroke length is almost the same in both cases, although the weaker one reaches its bottom after a shorter stroke, corresponding to a lower maximum resistance.
• Ring spring buffers are generally a poor compromise, being too weak to cope with heavy wagons bumping at speeds much higher than 2 m/s, although rigid enough to give light wagons a deceleration of up to 3 g ( ⁇ 30 m/s 2 ) already at a bumping speed of 1,5 m/s which is the maximum value allowed in Sweden.
• the Swedish State Railways have recently started testing a buffer with a hydraulic shock absorber, which gives a resistance approximately proportional to the square of the closure speed. The energy absorption thus adjusts itself to the demand, and the stroke will always be sufficient.
• the highest impact speed such a buffer can take care of is only limited by the hydraulic pressure which its cylinder unit can stand, and is at least twice as high as the maximum possible speed for ring spring buffers.
• the invention provides a buffer which takes advantage of a specially controlled hydraulic shock absorber. It is based on the experience that the maximum bumping speed allowed, in our typical case 1,5 m/s, is often exceeded so that impact speeds in the order of 2,5 m/s are not completely rare.
• the buffer is made in such a way that the entire possible stroke is utilized for speeds in this order, no matter whether the involved wagons be light or heavy. This will dramatically reduce the top value of the impact deceleration in most critical cases which else - with conventional buffers - cause the majority of cargo damages.
• the buffer is shaped as a hydraulic capsule which fits in a conventional buffer casing.
• the invented buffer is dimensioned on basis of the fact that the speed limit of 1,5 m/s in the reality is quite often exceeded.
• control valve is made as a flow-limiting valve possessing means to restrict the flow of hydraulic liquid in the mentioned way.
• the mentioned flow-restricting means are made to allow a pre-determined maximum flow, which defines the maximum impact speed allowed.
• means are arranged to, under considerable pressure drop, shunt the flow beside the flow-limiting valve if the velocity of the inward movement of the buffer exceeds the velocity defined by said valve.
• the flow restricting means are arranged to define an allowed velocity of the buffer movement, which, velocity regarded as a function of the buffer travel creates a horizontal parabola, through which the movement is uniformly decelerated.
• valve system comprising control valve and flow restricting means is arranged in order not to become initially activated at impact speeds below the allowed maximum, the buffer movement thus being initially retarded only by negligible hydraulic losses, although as soon as the movement reaches the allowed buffer velocity in relation to the travel, it is forced to follow this by the valve and flow restricting means defined relation.
• the arrangement is such that the flow control valve comprises a sleeve with an internal orifice plate, said sleeve being slidably mounted in the plunger unit and affected by a recoil spring, whereas the orifice plate has a communicating connection with an outlet aperture for the hydraulic liquid, the area of said outlet aperture being defined by the position of the sleeve, and that a metering pin is mounted coaxially with the orifice in such a way that said orifice combined with the cross sectional area of the pin determine the course of the movement.
• a reservoir chamber for the hydraulic liquid is surrounding the plunger/cylinder device, and a one-way valve is mounted between the outlet from the sleeve and the reservoir chamber.
• the above-mentioned means for shunting the flow of hydraulic liquid comprises a thinned cylinder wall which is expandable when exposed to high pressure.
• the pressure of the hydraulic liquid is prevented from increasing dramatically with the help of a leakage slot, the area of which depends on the pressure, by letting out the liquid flow which the flow-limiting valve refuses to release.
• the dependence of the slot area on the pressure is progressively reduced during the inward movement of the buffer.
• Fig. 1 shows a basic arrangement of a buffer according to the invention.
• Fig. 2 shows an arrangement where the shock absorber according to the invention is made as a complete capsule to be mounted in a conventional buffer casing
• Fig. 3 shows the forced flow-restricting action of the flow-control valve in terms of closing velocity of a buffer in relation to the stroke
• Fig. 4 shows the closing velocity as a function of the time for a flow characteristic according to Fig. 3.
• Fig. 1 is a longitudinal sectional view of a buffer according to the invention.
• the buffer casing 10 forms together with the slidable jacket 11 and the buffer head 12 a fluid-tight case, most of which is filled with hydraulic oil.
• a recoil spring 13 normally keeps the buffer in the extended initial position.
• the sleeve will thus partially close the outlet channel 17, thereby reducing the flow to a level which corresponds to balance between the spring force against the sleeve 16, and the pressure drop through the orifice 18.
• the tension of the spring is chosen so as to make this balance flow correspond to the allowed buffer closure velocity at the beginning of the stroke.
• the metering pin 19 will reduce the area of the orifice 18 as the stroke proceeds, thus reducing the flow required to achieve the pressure drop which balances the spring.
• the geometry is chosen so as to bring about the desired deceleration.
• the pin 19 has a cross-section corresponding to the orifice 18 which makes it almost completely choked.
• the recoil spring 13 returns the buffer, at which oil is sucked back to the cylinder 15 mainly through the bottom aperture of the outlet channel 17.
• the described arrangement should theoretically cause unreasonable oil pressures if two wagons should impact at a higher speed than permitted by the flow control valves of the buffers. Therefore, the cylinder 15 has to be provided with some kind of safety valve. In order to obtain a characteristic suitable for the buffer function, its pressure drop should depend on the degree of over-speed, and also on how long the stroke has proceeded.
• the cylinder 15 is made with a principally constant bore diameter, but somewhat varying outside diameter, thus making it thicker near the end wall.
• the plunger 14 has no sealing rings but forms a short sliding fit in the cylinder. An increased oil pressure will expand the cylinder and thus increase the leakage slot. Near the end of the stroke, the cylinder becomes more rigid, and here the leakage caused by a given pressure will be considerably lower.
• a wiper 21 is indicated on the buffer jacket 11. If the buffer function is correct, it scrapes a clean trace from the shown position to a point a couple of centimetres from the flange of the casing. If the trace becomes apparently shorter or longer, the buffer is out of order and requires service.
• a flow control valve comprising a spring-loaded sleeve 22 which initially accepts an oil flow corresponding to 1,2 m/s (i.e. half the bump speed 2,4 m/s). Should the velocity tend to grow higher, the pressure drop along the sleeve 22 will overcome the spring force. The sleeve will then move until its rear end 23 chokes the radial outlet, thus maintaining the correct flow to balance the pressure drop against the spring force.
• the radial outlet channel leads through boreholes 24, 25 to an annular chamber 27 inside the cylinder 26.
• the chamber 27 is communicating with a hydraulic reservoir chamber 29 through a hole provided with a one-way valve 30. An over-pressure is kept in the reservoir chamber 29, a part of which 31 being gas-filled.
• the metering pin 33 is shaped in such a way that the allowed velocity as a function of the stroke forms a horizontal parabola, as shown in Fig. 3.
• the deceleration pattern appears from Fig. 4.
• the flow control valve tries to close the outlet completely, but the end rim of the sleeve has such a shape that the valve in such case starts acting as a safety valve.
• the buffer then gets a characteristic similar to that of the earlier mentioned conventional hydraulic buffers, i.e. it absorbs the impact without exceeding the normal stroke, causing a deceleration rather equivalent to ring spring buffers.
• Fig. 2 thus shows the fundamental design of the complete hydraulic buffer capsule.
• the chamber 29 between the cylinder tube and the outer casing forms an oil reservoir , and ensures the proper function even if some decilitre of oil should leak out over the years.
• the reservoir 29 is half- filled with nitrogen to a pressure ⁇ f about 50 bar which gives the permanent recoil force the buffer must maintain.
• connection between the cylinder and the reservoir is situated at the bottom and is provided with a one-way choking valve 30.
• the purpose is to slow down the return movement to prevent the wagons from bouncing apart after the impact, and also to avoid that gas bubbles which might have been flushed out during the quick damping movement be sucked back. This makes the cylinder self-degassing.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Magnetically Actuated Valves (AREA)
• Fluid-Damping Devices (AREA)
• Fluid-Pressure Circuits (AREA)
• Train Traffic Observation, Control, And Security (AREA)
• Vehicle Body Suspensions (AREA)
• Vibration Dampers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20369590

Family Applications (1)

Country Status (6)

Cited By (4)

Families Citing this family (11)

Citations (2)

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• 1987
  • 1987-09-16 SE SE8703589A patent/SE460412B/sv not_active IP Right Cessation
• 1988
  • 1988-09-14 EP EP88907860A patent/EP0380516B1/en not_active Expired - Lifetime
  • 1988-09-14 WO PCT/SE1988/000476 patent/WO1989002385A1/en active IP Right Grant
  • 1988-09-14 AT AT88907860T patent/ATE89226T1/de not_active IP Right Cessation
  • 1988-09-14 DE DE88907860T patent/DE3881055T2/de not_active Expired - Fee Related
• 1990
  • 1990-12-28 US US07/635,940 patent/US5160123A/en not_active Expired - Fee Related

Patent Citations (2)

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