RU2525347C2 - Method of heating and cooling of brake drums of carrier drum-shoe brake for evaluation of their thermal balance - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: invention relates to ship building. Proposed method consists in that surfaces of the first brake drum are completely isolated from ambient medium. Surfaces of the second brake drum interact with the latter at internal heaters separately connected for equal time interval and surrounding drum working surfaces to external electric current source. Then, heaters are disconnected from said source, temperatures (t₁) and (t₂-t₁) of the first and second drum surfaces are measured to define portion of heat dissipated in ambient medium by convective and radiant heat exchange. Proposed method consists in cyclic braking of the carrier. Here, the brake friction pairs are heated to define from ratio of measured surface temperatures (t₁-t₀/(t₂-t₀) at different intensity of radiant and forced convective heat exchange from said surfaces the portion of heat derived to rear axle hub flange.

EFFECT: possibility of definition of heat losses for proper selection of friction lining materials.

4 cl, 5 dwg

Description

The invention relates to mechanical engineering and can be used in heavily loaded drum-shoe brakes, for example, vehicles.

Known methods for determining the amount of heat (the so-called calometry), consisting in the use of various types of calorimeters, namely:

- an ordinary variable temperature calorimeter with an isothermal shell;

- a massive variable temperature calorimeter with an isothermal shell;

- a variable temperature calorimeter with an adiabatic shell;

- differential calorimeter with variable temperature;

- constant temperature calorimeter [1, prototype].

However, the presented methods for determining the fraction of generated, accumulated and dissipated heat in the environment by the surfaces of the brake drum of a vehicle cannot be used for the following reasons:

- due to the complex configuration of the surfaces of the brake drum;

- it is impossible to accurately assess the heat loss from radiation heat transfer and separately taken natural and forced convective heat transfer of the surfaces of the brake drum; it is not possible to take into account the heat loss from the brake drum by conductive heat transfer.

Known methods for solving problems of thermal conductivity, which include: analytical, numerical, analog, graphic and experimental [2, analog]. Using the proposed methods, the temperature values in the studied objects are determined by calculation or experimentally. In the dependencies used, in order to calculate the amount of heat that is removed from the brake drum of the shoe brake device, it is necessary to know not only the temperature difference (t _H -t ₀ ), where t _H , t ₀ are the temperatures: heating the surface of the brake drum and the environment, but also process intensity factors, i.e. heat transfer during natural and forced convection, as well as during radiation heat transfer. As for the determination of heat loss from the brake drum by conductive heat transfer, it is almost never determined. This is because no one simply takes it into account. Knowing the surface temperatures of the friction pairs of the brake during its operation allows you to make the right choice of material for friction linings, as for the weakest link in the friction unit.

The disadvantage of calculation methods is that when determining heat losses in the studied object, it is necessary to know two parameters: surface temperatures and heat transfer coefficients by convection and radiation. The former are calculated, and the latter are accepted from the reference literature as some averaged values.

A known method of heating and cooling the brake pulleys of the tape-shoe brake of a drawworks when evaluating their heat balance [3, analogue].

The band brake contains hollow, sealed brake pulleys filled with fusible metal (potassium, sodium, lithium), in which heating devices are located around the perimeter of the cavity. Thermocouple thermoelectrodes are connected to the outer surfaces of the brake pulleys. The surfaces of the first brake pulley are completely insulated from the environment, and the surfaces of the second brake pulley interact with it when the heating devices are separately connected for the same period of time to an external electric current source, which ensures heating of the brake pulley body by means of molten low-melting metal. The heating devices are disconnected from an external source of electric current and the proportion of heat that is dissipated into the environment by radiation heat exchange is determined by the ratio of the measured surface temperatures of the first (t ₁ ) and second (t ₂ -t ₀ ) brake pulleys. According to the second variant, the tape-shoe brake contains friction pads, which are located on the arc of the brake band, through which thermocouple thermoelectrodes are passed. The protrusion of the first brake pulley is thermally insulated from the drum flange, and the protrusion of the second brake pulley is not thermally insulated. By cyclic braking, ensuring the interaction of friction brake assemblies, brake pulleys with low-melting metal are heated to its molten state, and by the ratio of measured surface temperatures (t ₁ -t ₀ / (t ₂ -t ₀ )) of the first and second brake pulleys at different intensities radiation and convective heat transfer from their surfaces judge the fraction of heat from its total amount, which is removed to the drum flange, i.e. conductive heat transfer. The technical result is the ability to determine heat loss in the brake pulley of the tape-shoe brake by the temperature method for determining the heat transfer coefficients for natural and forced convection and radiation, as well as conductive heat transfer for the correct choice of materials of friction linings and work in the surface temperature ranges below acceptable.

However, the presented method for determining the fraction of generated, accumulated and dissipated heat into the environment by the brake pulleys of the band brake cannot be used for the following reasons: due to the large weight of the brake pulley; due to the presence of fusible metals in the pulley cavities, which affects the accuracy of determining the amount of heat spent on heating the brake pulley.

The purpose of the invention is the determination of heat loss in the brake drum of a drum-shoe brake of a vehicle by the temperature method for determining heat transfer coefficients during natural and forced convection and radiation, as well as conductive heat transfer for the correct choice of materials of friction linings and work in the surface temperature ranges below acceptable.

This goal is achieved by the fact that at the first stage, the surfaces of the first brake drum are completely insulated from the environment, and the surfaces of the second brake drum interact with it when the internal heating devices covering the working surface of the drum rims are separately connected to an external electric current source, then disconnect the heating device from the drums and the ratio of the measured surface temperatures of the first (t ₁ ) and second (t ₂ -t ₁ ) brake drums determine the fraction of heat that is dissipated into the environment by convective and radiative heat transfer. At the second stage, the time interval of natural convective and radiation cooling of the surfaces of the second brake drum from the obtained thermal state as a result of electric heating to ambient temperature is recorded and the intensity of convective and radiation heat transfer of the surfaces of the second brake drum in predetermined temperature ranges is determined. At the third stage of operational tests, cyclic braking of the vehicle is performed, heating the brake friction pairs, and according to the ratio of measured surface temperatures (t ₁ -t ₀ (t ₂ -t ₀ )) of the first and second drums at different intensities of radiation and forced convective heat transfer from their surfaces judge the fraction of heat from its total amount, which is removed to the rear axle hub flange, i.e. conductive heat transfer.

At the fourth stage of operational tests at various constant speeds of the vehicle, and therefore, at different constant speeds of rotation of the brake drums for the same periods of time, the temperatures are fixed with thermocouples installed on the outer surface of their rims, and then the intensity of radiation and forced convective heat transfer of the drum surfaces is determined in given intervals of its surface temperatures.

A comparative analysis of methods for assessing heat loss in drums of drum-drum brakes, based on the prototype and analogues, showed the following advantages of the proposed temperature method:

- the possibility of a phased determination of the heat loss of the brake drum in laboratory and operating conditions;

- the heat introduced into the brake drum is achieved by heating with the help of electric current continuous and separate ring devices mounted on the working surface of the rims of the brake drums;

- determination of heat loss caused by natural convective and radiative heat transfer is carried out for the same time by comparing the heated non-heat-insulated and heat-insulated brake drum in the laboratory;

- determination of the intensity of heat exchange of natural convection and radiation of the brake drum is performed when it is cooled from a given thermal state to ambient temperatures in laboratory conditions;

- the determination of heat loss caused by conductive heat transfer is performed for the same time by comparing the heated brake drum and brake drum from a portion of a thermally insulated flange under operating conditions;

- determination of the intensity of heat transfer by forced convection and radiation of a heated brake drum is made for the same time at different constant frequencies of its rotation under operating conditions.

Figure 1 shows the construction of a thermally insulated brake drum with a continuous annular electric heating device; figure 2 shows the design of a non-insulated brake drum with separate annular electric heating devices, thereby simulating the real coefficient of mutual overlap of friction pairs in the drum-shoe brake; figure 3 shows a General view of the drum-shoe brake with a plot of insulated flange; figure 4 shows a view of figure 3 - installation of a thermocouple with electrodes in the details of the friction unit; figure 5 shows a General view of the drum-shoe brake with a plot of non-insulated flange. Legend: I and II - the first and second brake drums and, accordingly, the first and second brake mechanisms.

The method of heating and cooling the brake drums of a vehicle when assessing their heat balance is to determine the heat loss from the surfaces of the brake drum by radiation heat exchange, natural and forced convection, and also by transferring heat to the heat conduction (conductive heat transfer) from the portion of the brake drum flange interacting with the hub flange rear axle of a vehicle.

The method of heating and cooling the brake drums of the rear axle (as the most heavily loaded) of the vehicle is carried out in laboratory and operational conditions in four stages.

First step. In laboratory conditions, heat losses are determined by radiation and natural convective heat transfer from a heated brake drum (Figs. 1 and 2). To do this, take two serial brake drums 1 having a working surface 2 and a flange 3. Along the perimeter of the working surface of the 2 drums, ring electric heating devices 4 are installed and connected to the terminals 5 of the electric circuit. In the first brake drum 1, the annular electric heating devices 4 are closed on their outer side by a heat-insulating ring 5. In addition, the surface of the first of the brake drums 1 is completely covered by thermal insulation. Ring heaters 4 from the side of their outer surfaces are coated with the same insulation. The coefficient of mutual overlap of the annular electric heating devices 4 with respect to the working surface of the rim of the brake drum is equal to the coefficient of mutual overlap of the working surfaces of the friction linings of the brake pads of the drum rim. This allows you to take into account the heat loss from the inner surface of the rim of the brake drum by natural convective and radiation heat transfer. On the outer surface of each of the brake drums 1, thermocouples 8 are installed with thermoelectrodes 9 connected to recording equipment (not shown in FIGS. 1 and 2) for fixing the thermo-emf, which, according to the calibration schedule, is converted to temperature.

Before heating the brake drums 1, they are mounted on supports made of a material with low thermal conductivity, for example hard rubber or textolite.

Then, at the same time, the heating devices 4 in two drums 1 are connected via terminals 5 to the electric network. The heating devices 4 are turned on at the same time so that the temperature of the working surface of the second brake drum 1 reaches at least 350 ° C.

доля теплоты, которая рассеивается в окружающую среду радиационным и естественным конвективным теплообменом от поверхностей тормозного барабана, составляет 25,0%.Subsequently, the heating devices 4 are disconnected from the electrical network and after averaging the measured temperatures on the surfaces of the brake drums 1, their ratio is established. The latter characterize the ratio of the surface temperature of the first (t ₁ ) to the second (t ₂ -t ₀ ) brake drums, which determines the fraction of heat dissipated into the environment by radiation and natural convective heat transfer. So, for example, when the ratio of these temperatures $$\frac{350}{300-\mathrm{twenty}}=1.25$$

the proportion of heat that is dissipated into the environment by radiation and natural convective heat transfer from the surfaces of the brake drum is 25.0%.

Second phase. In laboratory conditions, heat losses are determined by radiation and natural convective heat transfer from the surfaces of the heated first brake drum.

As a result of the steady-state thermal state of the brake drum 1 obtained in the first stage, the time interval of radiation and natural convective cooling is fixed. Then determine the intensity of radiation and natural convective heat transfer, i.e. heat transfer coefficients from the surfaces of the brake drum 1 in predetermined temperature ranges.

So, for example, Q = IUτ, kJ (the amount of heat spent on heating the first brake drum); I is the current strength, A; U is the voltage, V; τ is the time, s. On the other hand, this amount of heat (Q) is dissipated from the surfaces (F) of the brake drum 1 in time (τ) at a temperature difference (t _H -t ₀ ) (t _H , t ₀ is the initial surface temperature of the heated brake drum and the environment , ° C). In this case, the heat transfer coefficient will be equal to

. $$a=\frac{Q}{F\tau \left(t_H-t_0\right)}$$

.

The third stage. In operating conditions, heat losses are determined by conductive heat transfer from parts of the surfaces of the flanges of the brake drums during their interaction with the surfaces of the flanges of the hubs of the rear axle of the vehicle (FIGS. 3 and 5).

To implement the third stage, thermoelectrodes 9 of thermocouples 8 are disconnected from the brake drums 1, as well as the electric wires coming from the heating devices 4 to the terminals 5. In addition, heat insulation 7 is removed from the first brake drum 1, leaving it only in the area of the thermally insulated flange 21 of the drum 1. Then the brake drums 1 are installed in the brake mechanisms of the rear axle of the vehicle, attaching them to its flange of the hub 25 with fixing bolts 23 with washers 24.

доля теплоты, которая передается кондуктивным теплообменом во фланец ступицы 25 заднего моста транспортного средства, составляет 9,3%.To measure the surface temperature of the friction pairs of the drum-shoe brake of the rear axle of the vehicle, thermoelectrodes 17 of thermocouples 18 are placed in its friction linings 12 (Fig. 4). A two-channel ceramic tube 16 is installed in the hole 14 of the friction lining 12 and is brought out almost flush with its working surface 13. In the pipe 16 with a diameter of 4.0 mm thermoelectrodes 17 of the thermocouple 18 are made of 0.4 mm diameter chromel-kopel wire. The positive thermoelectrode 17 is the chromel wire, and the negative is the kopel wire. The thermocouple head 18 (in the form of a sphere), which interacts with the working surface 2 of the brake drum 1, is formed of high-temperature copper solder in the form of a junction with a diameter of 3.0 mm and is installed in the restrictive ring 19. The latter prevents the thermocouple head 18 from failing and contributes to it work until complete wear and tear. A two-channel ceramic tube 16 (a ceramic tube consists of two parts) is installed with insulating sleeves 20 and 21 in the hole 11 of the brake pad 15. The length of the thermoelectrodes 9 and 18 is chosen so that the cold junction does not have time to warm up during the experiments, and equals 200-350 mm Conclusions to the recording equipment were carried out with copper wires. Thermocouples 8 and 18 were calibrated together with connecting wires before installation. After that, the vehicle is accelerated to a predetermined speed and cyclic braking is performed by the drum-shoe brake by applying and removing force from the brake pedal (not shown in Figs. 3 and 5), pressing the friction pads 12 with the working surfaces 13 against the working surface using brake pads 15 surfaces of 2 brake drums 1. After cyclic braking is completed, the vehicle is unloaded from the brake pedal and using a retractable coil spring 28, the ends of which sit on the fingers 28 and retract the brake connector blocks 15 with plates 12 of the working surface of the brake drum 2 of the rim 1. In this case, the second heat drum 1 by its flange 22 is transferred to the hub flange 25 and thus the working temperature of the surface 2 of the first drum 1 is greater than the second. This circumstance will contribute to different intensities of radiation and forced convective heat transfer from the surfaces of the brake drums 1. Then, by the ratio of the measured surface temperatures (t ₁ -t ₀ / (t ₂ -t ₀ )) of the first and second brake drums 1 of the brake, the fraction of heat is judged of its total amount, which is transmitted to the flange of the hub 25 of the rear axle of the vehicle, i.e. conductive heat transfer. So, for example, when the ratio of these temperatures $$\frac{350-\mathrm{twenty}}{340-\mathrm{twenty}}=\mathrm{1,093}$$

the proportion of heat that is transferred by conductive heat exchange to the flange of the hub 25 of the rear axle of the vehicle is 9.3%.

The fourth stage. Under operating conditions, heat losses are determined by forced convective and radiation heat transfer from the surfaces of the heated brake drums of the rear axle of the vehicle.

At various constant speeds of the vehicle, and therefore, at various constant frequencies of rotation of the brake drums 1 for the same periods of time, thermocouples record the temperature of the outer surfaces of their rims. For this, thermocouples are installed on the outer surface of the rim of the brake drum 1 and are connected through a current collector to a recording apparatus (not shown in FIGS. 3 and 5). Then determine the intensity of radiation and stimulated (heat transfer coefficient) in the specified intervals of surface temperatures. In this case, it is necessary to withstand the conditions for heating the drums 1 brakes corresponding to the second stage of research. In this case, heat transfer coefficients are determined (by radiative heat transfer plus forced convection) from the surfaces of the brake drum 1 during its free rotation by the dependence of a similar dependence given for the second stage of research.

Thus, in the laboratory and operating conditions, the brake drums are heated and cooled, which made it possible to determine the heat loss with radiation, natural and forced convective heat transfer from their surfaces to the environment, as well as conductive heat transfer from the drum flanges to the flanges of the rear axle of the vehicle.

Information sources

1. Kirillin V.A., Sheindlin A.E. Fundamentals of experimental thermodynamics. M. - L .: State Energy Publishing House, 1950. - 310 s [prototype].

2. Volchenko A.I. Thermal calculation of brake devices. Lviv: Higher school, 1987. - 133 s [analogue].

3. Patent of Russia 227959 C2, cl. F16D 65/813 for 2006 [analog].

Claims (4)

1. A method of heating and cooling brake drums of a drum-shoe brake of a vehicle to assess their heat balance, comprising a thermally insulated brake drum — the first, and a non-insulated brake drum — the second, and thermocouple thermoelectrodes connected to the thermally loaded surfaces of their rims, characterized in that the surfaces of the first the brake drum is completely insulated from the environment, and the surfaces of the second brake drum interact with it when separately connected to a different time interval of the internal heating devices covering the working surface of the drum rims to an external source of electric current, after which the heating devices are disconnected from the drums and the proportion of the measured surface temperatures of the first (t ₁ ) and second (t ₂ -t ₁ ) brake drums determines the proportion heat, which is scattered into the environment by convective and radiative heat transfer. 2. The method of heating and cooling brake drums of a drum-shoe brake of a vehicle for assessing their heat balance according to claim 1, characterized in that the time interval of natural convective and radiation cooling of the surfaces of the second brake drum is recorded from the obtained thermal state as a result of electrical heating to temperature environment and determine the intensity of convective and radiative heat transfer of the surfaces of the second brake drum in predetermined intervals t temperature. 3. A method of heating and cooling brake drums of a drum-shoe brake of a vehicle to assess their heat balance, comprising brake mechanisms with drums, one of which has a portion of a thermally insulated flange, and thermocouple thermoelectrodes are passed through the base of the brake pads and the body of the friction linings, and brake mechanisms are installed on the rear axle of the vehicle, as well as a drive, characterized in that they perform cyclic braking of the vehicle, while heating a pair of friction brake, and the ratio of the measured surface temperature (t ₁ -t ₀ / (t ₂ -t ₀₎₎ of the first and second drums with different intensity of radiation and forced convection heat transfer from their surfaces judged heat proportion of the total amount thereof, which is is diverted to the rear axle hub flange, i.e. conductive heat transfer. 4. The method of heating and cooling the brake drums of the drum-shoe brake of a vehicle for assessing their heat balance, characterized in claim 3 in that at different constant speeds of the vehicle, and, therefore, at different constant speeds of rotation of the brake drums at equal intervals time, temperatures are fixed by thermocouples mounted on the outer surface of their rims, and then the intensity of radiation and forced convective heat transfer to the surface is determined drum at predetermined intervals of its surface temperature.

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