A brake ( Abbreviation: Br) on the railroad tracks and has similar modes of action such as the commonly known types of brakes, but is systematically structured differently. The requirements for today's operation lead to other technical systems.
- 2.2.1 Electric brake
- 2.2.2 Hydraulic brake
- 2.2.3 eddy current brake
- 3.1 sprains and strains
- 3.2 Sliding locomotives
- 3.3 Safety brake
- 3.4 vehicles with braking computer
In the very first early period consisted of the railroad from brakes levers, which worked on wooden chocks. Was slowed only in the car and on the Tender of the locomotive. Later, as braked road vehicles with crank mechanisms and brake pads. Already at that time was not only on the locomotive, but also at several or even all the cars of a train braked by a brakeman by hand beat signals of the locomotive. The car with brake then usually had a high set brakeman's cab at one end of the car.
To give the traveler an opportunity to move the locomotive crews of stopping the train, a plane extending through the entire train bell rope was installed with the communication line that operated a bell upon actuation of the locomotive.
A first really promising attempt to form a continuous brake, the Heberleinbremse dar. The rotation of the axes is used to press the brake pads. To release the brakes, the engineer must span across a winch, a rope which is passed over the roofs of the whole train. Tear down this rope, so the train is automatically braked. Thus the Heberleinbremse fulfilled even today the fundamental requirement of a train brake.
One in the mode of action for Heberleinbremse similar but highly variable in design details design of a mechanical brake cable brake is the brake Görlitz weight. These weights over lever with the brake pads are connected. By raising or lowering the weights over the passing cable, the braking force can be regulated. Another, the Heberlein brake similar type is the continuous Schraubenradbremse system Schmid.
From the mid- 1870s they developed the suction air or vacuum brake. She came to almost all types of tracks ( mountain railways, standard gauge and narrow gauge railways and tramways ) were used. In this, the spring-biased brake is achieved by means of a negative pressure in a continuous suction. By reducing the negative pressure in the brake cylinder, the braking power has been adjusted. In a train separation, the brakes automatically talked to in both tensile members. The biggest drawback that prevented further use, were the big suction cylinder in the car and the high steam consumption of the Injektorvakuumpumpe. In particular, narrow-gauge mountain railways and the vacuum brake used for many decades, because they are because of their general Mehrlösigkeit for long descents better suited than the first only einlösigen air brakes. The Rhaetian Railway and the Matterhorn -Gotthard Railway in Switzerland, for example they use to this day.
To overcome the disadvantage of large brake cylinder at Saugluftbremsen, steam locomotives and their tenders were often equipped with a vapor barrier, in which a steam cylinder acted directly on the brake rod. Disadvantage of the vapor barrier is its decreasing braking effect by cooling and condensation.
In the days of the steam engine, the downhill otherwise empty follower piston steam engine was used with threaded in the opposite direction control and throttle valve as a brake in particular for mountain railways. One type is the counter-pressure brake by Niklaus Riggenbach.
Usually come in railway vehicles following braking systems for:
As friction brake shoe or disk brakes are used mainly. More in special cases also drum brakes which can be configured as a strip or block brake.
The force generated by the brake shoe force on wheel tire friction generated friction force (braking force) tangentially engages the wheel circumference and is opposite to the direction of rotation of the wheel. An equal force ( adhesive force, friction force) is generated between wheel and rail, which inhibits the running of the vehicle.
The force from the brake pad to the wheel friction force must never be greater than the transmitted from the wheel to the rail static friction force, otherwise the wheels come to slide and there are flat spots. Because of the lower compared to road vehicles stiction caused significantly longer braking distances. Adhesion coefficient between wheel and rail is in clean, dry or completely wet rails greatest. When it starts raining, fog, frost, level crossings for road salt, but especially at leaf fall or contamination with oil, the rails can be slippery and the static friction value will be very small. Non-skid devices to prevent sliding, possibly also helps sands.
The block brake is the simplest and oldest type of friction brake. It belongs to the friction value- brakes. The braking force produced by brake shoes which are pressed against the tread surface of the wheels. In general, the brake shoes are designed as air brakes.
Brake shoes are cheap and easy, since only a few components are needed. By the braking, the tread of the wheels is cleaned, whereby the friction between the wheel and the rail is improved. Disadvantages are the large thermal load on the wheelset and the fretting wear of the wheel surface.
Another type of friction value is the brake disc brake. Also, it is usually implemented as a pneumatic brake. The brake lining press here on a specially provided a friction surface mounted on the wheel or on the axle plate. For often driven axles mounted on the wheel disc disc brakes are used as space for the drive units is then sufficient in the wheelset available. Non-driven wheel sets usually have two to four times with forced ventilation shaft brake discs.
Disc brakes have a constant over the entire speed range, coefficient of friction. For better cooling, a higher braking power is possible, the wheel treads are not worn by the brake and disc brakes generate less noise than shoe brakes. The disadvantage is the higher construction cost than with block brake.
Most locomotives and passenger and freight cars, most are equipped with a manually actuated mechanical friction brake. This mechanical brake or hand brake acts directly ( mechanically ) on the pads of the vehicle. It brings the braking force regardless of the pneumatic brake on, and is thus suitable to secure parked vehicles. A locking the inactive parked vehicle permit only mechanical brakes because the holding force of the air brakes is only guaranteed up to 30 minutes after stopping.
There are two types of construction. Provided by the vehicle or from the ground to use handbrake suitable for protection against elopement of parked cars. It can be designed as a hand wheel or operable as a spring -loaded brake. This brake weight is framed in red wagons.
The only from the vehicle operated hand brake is used on the one hand protecting vehicles against elopement and on the other hand, regulated the speed for certain shunting and stopping of trains in case of faulty automatic brake. It is mostly designed as a brake spindle and is operated by a brake platform. This brake weight is framed in white wagons ( white like the rest of braking Address, alternatively black on white or light background ). Hand brakes in tenders and tender locomotives are often designed as a throw lever brake.
Track brakes are typically constructed as a magnetic brake. Brake shoes are lowered under the carriage and pressed by means of magnetic force on the rail head. Because the friction force is independent of the wheel-rail friction, they are suitable for shortening the braking distance when initiating an emergency application, especially in trams.
One of the first applications of the electric magnetic brake, there were 1933 with diesel- electric powered high-speed railcars Flying Hamburger.
The centrifugal brake is not used to reduce the speed, but prevented by light braking the spinning of the drive wheels in low Adhäsionsverhältnissen. Thus this brake works properly, the rapid application of the brake pads and the immediate loosening must be ensured. This is achieved with an electro-pneumatic valve which is actuated by an automatic control unit or a push button switch.
The braking force can exceed the transmitted from the wheel to the rail static friction force in unfavorable cases. There is the danger that the axes from locking during braking. The results in longer stopping distances and also has the effect that the running surfaces of the wheels may be damaged by flats. Non-skid devices can prevent sliding of the wheel.
The anti-skid device compares the speed of the vehicle axles. As soon as the rotational speed difference reaches a certain value, the brake cylinder is depressurized, and the supply is interrupted. Once the axle has reached the normal speed, the venting of the brake cylinder is interrupted, and the normal brake starts again.
Electric and hydrodynamic brakes
Electric and hydrodynamic brakes are wear-free and support the air brake in their effect. The drive of the drive vehicles plays a constructive role. In electric drives, electric brakes can be installed while in internal combustion engines with hydraulic power transmission hydraulic brakes may be present. Recently found in railway vehicles also called retarder - a variant of the hydraulic brake for non-driving axles. Of historical interest are the Riggenbach counter-pressure brake for steam locomotives.
In the electric brake, the drive motors of the traction units act as generators. The thus generated electrical energy is fed back to the regenerative braking to overhead line network, converted at the dynamic brake resistors over into heat energy. The electric brake is used for regulating and reducing the speed in some cases, to a stop.
Electric brakes can be used on electric ( electric locomotive, electric multiple unit ) and on diesel- electric powered locomotives. In diesel-hydraulic locomotives powered missing for an electromotive brake the electric traction motor for generator operation.
Electric brakes are usually used as auxiliary brake. Usually, a compressed air brake, the brake master system because this allows a deceleration to a stop and not just to close to zero in contrast to the electric brake. In the Notbremsberechnung only brakes should be considered, which are independent of the catenary or power generation. This includes all of the contact wire line regeneration or excited by external power brakes.
Drive vehicles with hydraulic power transmission are suitable for the installation of a hydraulic brake. For this purpose, an additional hydraulic clutch is installed in the hydraulic transmission, the turbine wheel is fixed to the housing. The impeller is driven by the wheel sets ( clutch brake, retarder). The braking force can be controlled by the filling of the clutch with oil. The coupling is thus operated with 100% slip, thereby providing a high amount of heat must be dissipated via the cooling system of the locomotive. The efficiency of the cooling system therefore usually also limits the maximum power of the hydraulic brake.
Another possibility is the use of so-called turbo reversing transmissions that use their own hydraulic circuits for each direction of travel. Here the cycles of opposite direction can be used to brake. A disadvantage in comparison to the brake coupling is the increased fuel consumption, since the motor has to generate the braking force.
Eddy current brake
The linear eddy current brake is the ICE 3 in the DB used. The advantages with this braking system are that the eddy current brakes are independent of wheel - rail adhesion and thus independent of the weather (so-called adhesion value independent brake) and that they contact and controlled very accurately derive their braking force to the rail head, what a wear-free operation allows. Associated with this there is also the possibility to control the train on long slopes safe because - there is no risk overheating the brakes - in contrast to block, disc or magnetic track brakes. However, can not be entirely dispensed with these brake systems because the braking force of the eddy current brake is dependent on the speed and the vehicle alone can not be completed in time to stand with her. Other problems bring the strong induction currents which heat the rails, forcing the operators to monitor the temperature of the rails to prevent a shift in the track position by excessive heating, and the resulting strong magnetic fields that can interfere with the signals at the edge of the track.
Wherein the rotating eddy-current brake, the rail is used as an electromagnet and current in the wheels of the train induced their magnetic interaction with the electromagnet, and which respond to brake the vehicle. This brake is currently used only in test vehicles.
With gear webs safe stopping is not possible only with friction or magnetic track brakes. The vehicles of these orbits are therefore equipped with gear brakes. It is braked by gears which engage with the rack. As gear brakes mechanical brakes are used. For tractive rolling the wheel brake is often implemented as a resistor or regenerative braking.
Rail tractors without indirectly acting air brakes are fitted in Switzerland with a Nachbremse (N). They can thus be slowed down when towing. At an operating or full braking the Nachbremse does not operate. The Nachbremse causes the air brake of a main air pipe connected to the tractor is to the response, when the pressure in the main air line is reduced to about 2.5 bar. With the increase in brake pipe pressure on the value of a full brake the Nachbremse triggers.
Because the indirectly acting pneumatic brake when towing is not effective for the Re 460 SBB, the locomotives were equipped with a Nachbremse how previously seen in tractors.
For driving on rack trolley routes can be mixed Zahnrad-/Adhäsionsbahnen with an adhesive and a delayed-action gear brake equipped. At a moderate lowering of the vacuum ( 25 cm Hg ) and the air pressure in the main air line is responsive to only the Adhäsionsbremse. This is sufficient for maintaining the speed when going downhill. A greater reduction of the vacuum ( from 24 cm Hg) and the pressure in the main air line causes additionally responsive the brake gear.
Today's operating requirements
With the introduction of railway construction and operation order was prescribed in 1967 that all vehicles - except for small locomotives and cable cars - must be equipped with continuous automatic brake.
Today Trains must be equipped with a top speed of more than 50 km / h with a continuous and automatic brake. Continuous means that the brakes of all vehicles of a train can be operated centrally from one location. When automatically applies a brake when brake at a separation of the brake line the train or both sets of detached automatically to a standstill. Other operating requirements are:
- Compatibility with the brake systems of other railways,
- Distribution of braking force on the entire train,
- Braking force regulation by train weight,
- High and continuous braking power.
Sprains and strains
A special feature of trains is that at the end of a train an adequate braking force must be present in order to avoid upsetting or tugging of the train and to ensure a train has stopped at a train separation.
Is compressed a train when the rear brakes pull part is pushed against the front, pulling part already braked and so compresses the train. This occurs because of the breakdown time, especially in long trains with air brakes, the brake is controlled centrally from a driver's cab. The triggered by cab air pressure difference travels at a finite speed back through the train, so that vehicles at the Zugspitze at slowing earlier than vehicles of the train.
A sprain in the train is produced when the rear brakes pull part earlier than the unbraked front pulling part or even slows down, while the front brakes pull part no more. In this case, the forces acting in the longitudinal direction of the train can be greater than the train and can absorb shock devices. The result is a train separation, which is a risk for subsequent trains.
On routes with steep inclines, it may be necessary for particularly heavy trains (such as coal or ore trains ) must be pushed with additional locomotives. This is accomplished with the help of so-called sliding locomotives, although they bring additional driving power, but not necessarily contribute to the braking effect. An additional braking effect of the compressed air brake depends on whether the helper locomotive is coupled to the main air line. On the descent in mountain railways, the electric brake, the helper locomotive is used. She wears no wear on the braking performance of the train and the train remains inserted.
The emergency brake is independent of the friction between wheel and rail. As a safety brakes, among other rail and gear brakes apply. Safety brakes are in Switzerland required for driving on routes with more than 60 ‰ slope and trams if the speed is not reduced appropriately.
Vehicles with braking computer
In modern locomotives and driving coaches the control of braking systems is integrated into the control system. The controls in the cab control via the data bus and the vehicle control a computer and the pneumatic brakes. A rapid braking can be executed with a emergency valve or emergency brake valve, bypassing the computer in any case directly by opening the main air line.
Time work on brakes
As a safety-relevant components brakes on rail cars must be checked regularly and maintain. This work must be carried out by specially qualified personnel ( " brake locksmith "). The provisions of the VDV apply to the field of non- federally owned railways in Germany 885 (Maintenance Guide brakes and air tank at the NE railways - IBD -NE) as recognized rules of technology. Exist for the division of Deutsche Bahn AG rules with similar content.
The IBD -NE currently provide for four types of brake revisions before ( condensed version):