Evaluation of the efficiency of the friction tread brake of the diesel motor car

. The article considers and calculates the brake system of a two-axle service diesel motor car, consisting of two brake subsystems acting separately on two axles of the diesel motor car, provided that each axle is served by one brake cylinder 501Б. A calculation was made in order to evaluate the effectiveness of the friction tread brake of the service diesel motor car model AS-01uz.


The relevance of the task
In modern conditions, to ensure the safety of railway traffic, maintenance of the track, transportation of teams of specialists on lightly loaded non-electrified lines, it is advisable to use railcars. The advantage of this type of rolling stock is economy, versatility, reliability, ease of repair, and operation [1][2][3][4][5].
At present, JSC "Tashkent Plant for the Construction and Repair of Passenger Cars" has launched the production of railcars, namely the "Avtomotrisa" model AS-01uz (railcar).
Railcars with diesel engines are equipped with a direct-acting automatic brake and a direct-acting non-automatic brake, and railcars with carburetor engines -only a directacting non-automatic brake.
The brake system in the presence of a carburetor engine is powered from a compressor installed on this engine; a compressor is mounted on railcars with a diesel engine.
In order to evaluate the effectiveness of the shoe friction brake of the AS-01uz service railcar, a calculation was performed in accordance with the procedure [1]. The brake is one of the most important elements in the organization of safety and speed control for rolling stock.
For wagons with braking (the impact of one or more brake cylinders on each bogie), the calculation is carried out for one or each bogie, taking into account the tare and load per bogie [5][6][7].
The braking system of a two-axle service railcar operates in such a way that there is one brake cylinder per two axles of the railcar. In this case, brake cylinder 501B is used. The system is supplied with air from a compressor and a reserve tank with a capacity of 78 liters [1][2][3][4][5][6][7][8].
The calculation of the brake is carried out in the following steps to confirm the provision: -the required braking efficiency of the railcar as part of the train; -skid less braking of the railcar (no skidding of the wheels during braking) [1][2][3][4][5][6][7][8] -the design diagram of the braking equipment is shown in Figure 1; -allowable power per block during braking; To carry out the calculation of braking equipment, the initial data given in Table 1 are required. The criterion for ensuring the required braking efficiency is the fulfillment of the condition for the calculated coefficient of the pressing force of the pads [3][4][5]: (1) where is the: р δ -calculated coefficient of the pressing force of the pads; р К -the calculated force of pressing the brake shoe, tf; n -the number of brake pads on the motorcar; Q -maximum gravity force of railcar, tf; [р] -0,873 -the minimum allowable value of the calculated coefficient of pressing force of cast-iron pads according to the availability of brake pressing [1][2][3][4][5].
The estimated load is Q accepted in accordance with the terms of reference.
Complies with the requirements for blocks used on railcars. The actual pressing force on one pad is determined by the formula: where is the m -number of brake pads of the railcar, which are subjected to the force from one brake cylinder;  For other values of limiting pressures in the brake cylinders, the minimum and maximum pressures in them are respectively taken [11][12][13][14][15][16][17]; ц η -КPD -Efficiency of the brake cylinder; 1 F -compression force of the internal release spring of the brake cylinder, tf; n -gear ratio of the lever transmission; ц η -КPD -Lever transmission efficiency.
The obtained value K = 1.306 tf meets the requirements for brake linkages. The force of the inner spring of the brake cylinder is determined by the formula: where is the ц P pre-compression force of the inner spring of the brake cylinder [12][13][14][15][16][17][18][19][20]; ц С --stiffness of the corresponding springs, tf/m; шт l --estimated output of the brake cylinder rod; According to the results of calculations, the force of the inner spring of the brake cylinder was F1=0.167 tf, thus the condition is met under which the output of the brake cylinder rod is calculated.
Calculations for the absence of skidding of wheel sets of railcars during braking are performed: -for the minimum load on the axle of the railcar from the mass; -at the maximum design pressure in the brake cylinders -for railcar speeds of 20, 40, 60, and 80 km/h.

Estimated friction coefficient of brake pads
where is the V -speed of movement, km/h.
The braking distance of the railcar during emergency braking on the site [1][2][3][4] was determined by the formula: where П S -preparatory (before braking) path, m; Д S -actual stopping distance, m.
The preparatory stopping distance was determined by the formula: where is the П t -time for preparing the brakes for action, (for electro-pneumatic -2 s, for pneumatic -4 s); o V -initial speed of railcar braking, km/h [10][11] The resulting value П S = 88.89 m meets the requirements.
The actual stopping distance was determined by the formula: where is the where is the V -average speed in the interval, km/h.
The value of the specific braking force was determined by the formula [19].
b T = 1000φ tr • δ r The specific driving resistance is calculated from the maximum axle load. The numerical value is r δ taken from the calculation of the possibility of using the user.
Comparison of the dependence of braking equipment and path (cast iron pads, pneumatic brakes) in Table 3. Based on the diagram, we can determine the length of the braking distance depending on the friction coefficient of the railcar.

Power per block during braking
The number of brake pads when calculating the brake system is determined based on the average power per pad during emergency braking from the maximum allowable speed [10][11][12][13][14][15][16][17]:

Conclusions
1. Obtained as a result of calculating the braking efficiency, the calculated coefficients of the force of pressing the brake pads p=0.873 are greater than the minimum allowable [δ ]=0,6; hence the condition is met. The calculated pressing force on the brake shoe is 1.714 tf with the actual pressing force of 1.306 tf [1][2][3][4][5].
3. Implemented wheel-rail adhesion coefficients at 60 km/h -0.129, which is less than the calculated coefficients. Therefore, there is no user interface. Realized wheel-rail adhesion coefficients at 80 km/h are 0.121, which is less than the calculated coefficients. Therefore, there is no user interface.
4. Checking the skid at speeds of 20 km/h, 40 km/h, 60 km/h and 80 km/h, the developed brake system showed that there is no slip to skid. 5. Checking the maximum value of the operating power attributable to the brake castiron shoe during braking (at the maximum allowable speed for a railcar of 80 km/h), showed that the calculated power N= 21,535 kW does not exceed the maximum permissible standard value [N]= 70 kW.