Introduction
Functional properties determine the ability of the car to effectively perform their main function - transportation of people, cargo, equipment, i.e. characterize the car as a vehicle. This group of properties, in particular, belong: traction and high-speed properties - the ability to move with high average speed, intensively accelerate, overcome lifts; Controlness and stability - the ability of the car (handling) or maintain permanent (stability) motion parameters (speed, acceleration, slowing down, direction of movement) in accordance with the driver's actions; Fuel efficiency - travel fuel consumption under specified operating conditions; maneuverability - the ability to move on limited areas (for example, on narrow streets, in the courtyards, parkings); Patency - the possibility of movement in heavy road conditions (snow, dissolve, overcoming water obstacles, etc.) and off-road; The smoothness of the move is the ability to move on uneven roads with a permissible level of vibration and the driver, passengers and the car itself; Reliability - trouble-free operation, long service life, adaptability for maintenance and repair of the car. The traction-high-speed properties of the car determine the dynamism of the movement, i.e. the ability to transport goods (passengers) with the greatest average. They depend on the traction, brake properties of the car and its passability - the abilities of the car to overcome off-road and complex areas of roads.
High-speed car properties
The possibilities of the car in achieving the high speed of the message are characterized by high-speed properties. An indicator of high-speed properties is the maximum speed. In accordance with the equation of the maximum speed on the horizontal portion of the road corresponds to the equality of the traction force of the amount of the forces of the resistance for the round river and the resistance of the air P in. To determine the maximum velocity of the car, it is necessary to solve the power balance equation. The graphic method for its solution is shown in Fig. 1. On the chart in the coordinates, the velocity V A - the thrust force of the p t is caused by four curves for different transmissions of the four-stage transmission and the curve of the amount of resistance forces roc and air P in.
The intersection point of the curve of changes in the traction force p t at the 4th transmission with the total curve of the resistance of the P K + P B determines the maximum vehicle V Max on the horizontal site.
When moving on the rise, the resistance force is added to the rise p n, so the curve p K + P in is shifted upward by the amount of resistance force to the rise of P GHG. In our case, the maximum speed on the lift V in our case is determined by the point of intersection of the curve of changes in the traction force of the PT on the 3rd transmission with the total curve of the resistance of the P K + P B + P n.
The reserve of the traction force RES P T can be used to overcome the inertia strength P and when overclocking: RESR T \u003d P and \u003d R T - P K - R B.
Fig. one.
The magnitude of the acceleration J x, m / s 2 is proportional to the Resp T and inversely proportional to the mass of the car M A multiplied by the coefficient K j of accounting of rotating masses:
j x \u003d res p t / m a, k j
Changing the velocity of the car during acceleration is shown in Fig. 2. Duration of overclocking characterizes the inertia of the car, which is proportional to the time constant of overclocking T p. The value of T p is associated with the maximum speed V Max. During the time T \u003d T p, the car accelerates to the speed V T equal to 0.63 V Max.
It turned out that the average velocity of vehicles in free conditions coincides or close to V t. This can be explained as follows. The difference between the maximum speed V Mach and the current velocity V A is a speed reserve that the driver can use when performing overtaking. When the vehicle speed exceeds 0.63 V MAX, the driver begins to feel that if necessary, it cannot increase the speed with the desired intensity. Therefore, the reserve of the rate of RES V without \u003d V Max - V T T is the smallest safe reserve, A V T - the greatest safe speed in free conditions.
Fig. 2.
The maximum speed V Mach, the safe speed V T and the constant time of acceleration T p are indicators of the speed properties of the car. Safe speed V T can serve as a reference when choosing a vehicle in free movement. Values \u200b\u200bV MAX, V T and T R for different car models are given in Table. 1. The constant time of acceleration T p varies in proportion to the change in the mass of the car. Therefore, the intensity of overclocking the truck and the bus without load is much higher than with the load.
Table 1.
Indicators of high-speed properties of vehicles (TCs) of various categories with full mass
|
Model TC |
Middle T p for TC one category |
||||
|
Educational 1. |
|||||
|
Training 2. |
|||||
|
"C 3" + "E" |
Training 3. |
||||
|
"C 3" + "E" |
Training 4. |
||||
|
"C 3" + "E" |
|||||
|
"C 3" + "E" |
|||||
|
"C 3" + "E" |
|||||
|
"C 3" + "E" |
* Permitted maximum weight 3.5 ... 12 tons.
* * Allowed maximum mass of more than 12 tons.
The separation of the car occurs when the gear shift lever is translated into a neutral position. Such a movement is called rolling. In this case, the power of inertia p and is a driving force The equation takes the form:
P and \u003d m and j x \u003d - p to ± r p - p
By dividing the left and right parts of the equation on the MA, we obtain an expression to determine the value of a slowdown when the JN is rolled:
J n \u003d (- p to ± r p - p c) / m a
From the expression it is clear that the larger the mass of the car Ma, the less slowdown and the more time the time moves roll to the stop. The dependence of the velocity V A on time t can be shown in Fig. 3.
Fig.3.
As can be seen from the chart, the inertia of the vehicle at the same time is characterized by a constant time of rolling t n. The constant time of acceleration T p and rolls are interconnected, as they depend on the mass of the car Ma. The time constant is rolled out of approximately 1.5 - 2 times the constant time of acceleration T p. The larger, the most part of the path can be passed by rolling, which is of great importance to reduce fuel consumption.
The traction-high-speed properties of the car substantially depend on the structural factors. The engine type of engine, the efficiency of transmission, transmission ratios, mass and streamlining of the car have the greatest impact on the traction and high-speed properties.
Engine's type.The gasoline engine provides the best traction-high-speed properties of the car than diesel, under similar conditions and modes of movement. This is due to the form of the external high-speed characteristics of the indicated engines.
In fig. 5.1 shows a graph of the power balance of the same car with different engines: with gasoline (curve N " T) and diesel (curve N " T). Maximum power values N. Max and speed v N.at maximum power for both engines the same.
From fig. 5.1 It can be seen that the gasoline engine has a more convex outer speed characteristic than diesel. It provides him with a greater power supply. (N " Z\u003e N " Z. ) at the same speed, for example, at speed v. 1 . Consequently, a car with a gasoline engine can develop high accelerations, overcome sharp rise and tow trailers of greater mass than with diesel.
Traffic efficiency.This coefficient allows you to evaluate power loss in friction transmission. The decrease in the efficiency caused by the growth of power losses for friction due to deterioration of the technical condition of transmission mechanisms during operation leads to a decrease in the traction force on the drive wheels of the car. As a result, the maximum vehicle speed and the road resistance overcome by the car are reduced.
Fig. 5.1. Car Power Balance Schedule with Different Engines:
N " T - gasoline engine; N " T. - diesel; N " s N " Z. – Relevant power reserve values \u200b\u200bat vehicle speed v. 1 .
Transmission ratios.The maximum vehicle speed significantly depends on the transfer number of the main transmission. Such a gear ratio of the main transmission is considered optimal, in which the car develops the maximum speed, and the engine is maximum power. An increase or decrease in the gear ratio of the main transmission compared to the optimal leads to a decrease in the maximum velocity of the car.
The gear ratio I gear transmission affects how the maximum road resistance can overcome the car with uniform motion, as well as on the transfer numbers of intermediate transmissions.
An increase in the number of transmissions in the gearbox leads to a more complete use of engine power, an increase in the average velocity of the vehicle and increase the indicators of its traction and high-speed properties.
Additional gearboxes.Improving the traction-high-speed properties of the car can also be achieved by applying with the main transmission of additional gearboxes: divider (multiplier), demultiplier and dispensing box. Usually additional gearboxes are two-speed and allow you to increase the number of gears twice. In this case, the divider only expands the range of gear ratios, and the demultiplier and the dispensing box increase their values. However, with an overly large number of gears, the mass and complexity of the gearbox design is increasing, and the car is difficult.
Hydraulic.This transmission provides ease of control, smoothness of overclocking and high cargo vehicle. However, it worsens the traction-high-speed properties of the car, since its efficiency is lower than that of the mechanical step gearbox.
Mass of the car.An increase in the mass of the car leads to an increase in the forces of resistance to rolling, lifting and overclocking. As a result, the traction-high-speed properties of the car deteriorate.
Thinking car. Cropling has a significant impact on the traction and high-speed properties of the car. With its deterioration, the reserve of traction force decreases, which can be used to accelerate the car, overcoming the lifts and towing trailers, increase the power loss to air resistance and the maximum vehicle speed is reduced. For example, at a speed of 50 km / h, power losses in a passenger car associated with overcoming air resistance are almost equal to the loss of power to rolling the car when it moves along the road with a solid coating.
Good streaming of passenger cars is achieved by a minor inclination of the roof of the body back, the use of the sidewalls of the body without sharp transitions and a smooth bottom, installation of windshield and the beading of the radiator with the inclination and such placement of the protruding parts in which they do not go beyond the external body dimensions.
All this allows you to reduce aerodynamic losses, especially when driving at high speeds, as well as improve the traction-high-speed properties of passenger cars.
For trucks, air resistance reduces, applying special fairing and covering the body with a tarralet.
Brake properties.
Definitions.
Brake -creating artificial resistance in order to reduce speed or retention in a fixed state.
Brake properties -determine the maximum deceleration of the car and the limit values \u200b\u200bof the external forces that hold the car in place.
Brake mode -the mode in which the brake moments lead to the wheels.
Braking distances -the path passing by a car from distinguishing the driver to the complete stop of the car.
Brake properties -major defining traffic safety.
Modern brake properties are normalized by rule No. 13 of the Inland Transport Committee of the European Economic Commission for the UN (UNECE).
National standards of all countries participating in the UN are based on these rules.
The car must have several brake systems that perform various functions: working, parking, auxiliary and spare.
Working The brake system is the main brake system that ensures the braking process in normal conditions of the vehicle functioning. The brake mechanisms of the working brake system are wheeled brakes. Management of these mechanisms is carried out through pedals.
Parkingthe brake system is designed to hold the car in a stationary state. The brake mechanisms of this system have either on one of the transmission shafts or in wheels. In the latter case, the brake mechanisms of the working brake system are used, but with an additional drive control of the parking brake system. Manual parking brake system management. Parking brake system drive all only mechanical.
Sparethe brake system is used in the failure of the working brake system. Some cars feature a parking brake system or an additional circuit of the working system.
Distinguish the following types of braking : Emergency (emergency), service, braking on slopes.
Emergencybraking is carried out by means of a working brake system with maximum conditions for these conditions intensity. The number of emergency braking is 5 ... 10% of the total number of braking.
Servicebraking is used for a smooth reduction of vehicle velocity or stop in advance
Estimated indicators.
Existing standards GOST 22895-77, GOST 25478-91 are provided by the following brake properties car:
j set - established deceleration with a constant effort on the pedal;
S T - the path passing from the moment of clicking on the pedal to the stop (stopping path);
t cf is the response time - from pressing the pedal before reaching the J mouth. ;
Σ P TOR. - Total brake force.
- specific brake force;
- the coefficient of non-uniformity of the brake forces;
Installed speed on the descent V. T.Ust. when brake brake - retarder;
The maximum slope of H T MAX, on which the car is held by the parking brake;
The slowdown provided by the spare brake system.
The standards for the brake properties of the PBX, prescribed by the standard, are shown in the table. Note Category Note:
M - Passenger: M 1 - passenger car and buses no more than 8 seats, m 2 - buses more than 8 places and a long weight up to 5 tons, m 3 - buses with a complete mass of more than 5 tons;
N - trucks and automobiles: N 1 - with a total weight of up to 3.5 tons, n 2 - over 3.5 tons, N 3 - more than 12 tons;
O - trailers and semi-trailers: O 1 - complete weight of up to 0.75 tons, 2 - complete weight of up to 3.5 tons, 3 - total weight of up to 10 tons, about 4 - full mass of more than 10 tons.
Regulatory (quantitative) values \u200b\u200bof estimated indicators for new (developed) cars are prescribed in accordance with categories.
Introduction
The methodical instructions provide a method for calculating and analyzing the traction and high-speed properties and fuel efficiency of carburetor vehicles with a stepped mechanical transmission. The paper contains the parameters and technical characteristics of domestic cars, which are necessary to perform the calculation of dynamism and fuel efficiency, the procedure for calculating, constructing and analyzing the main characteristics of the specified operational properties is given, recommendations are given on the selection of a number of technical parameters reflecting the design features of various cars, modes and conditions their movements.
The use of these guidelines makes it possible to determine the values \u200b\u200bof the main indicators of dynamism and fuel efficiency and identify their dependence on the main factors of the design of the car, its loading, road conditions and engine mode, i.e. Solve those tasks that are placed in front of the student in the course work.
Main tasks of calculation
When analyzing tractor-speed The properties of the car are calculated and the construction of the following characteristics of the car is calculated:
1) traction;
2) dynamic;
3) accelerations;
4) overclocking transmission;
5) rank.
They are based on the definition and evaluation of the main indicators of the car's traction and high-speed properties.
When analyzing fuel economy The car is calculated and the construction of a number of indicators and characteristics, including:
1) fuel consumption characteristics in the process of overclocking;
2) the fuel and speed characteristic of overclocking;
3) the fuel characteristic of the steady movement;
4) car fuel balance indicators;
5) Indicators of the operational consumption of fuel.
Chapter 1. Tractive vehicle properties
1.1. Calculation of forces of thrust and resistance to movement
Motion of motor vehicles is determined by the action of thrust and resistance to movement. The combination of all the forces acting on the car expresses the equations of the power balance:
P i \u003d p d + p o + p tr + p + p w + p j, (1.1)
where P i is the indicator force of thrust, H;
R D, P O, P TR, P, P W, P J - respectively, the power of the resistance of the engine, auxiliary equipment, transmission, roads, air and inertia, H.
The value of the indicator forces can be represented as the sum of the two forces:
P i \u003d p d + r, (1.2)
where P e is an effective traction force, H.
The value of the P E is calculated by the formula:
where M e is an effective torque of the engine, nm;
r - Radius of Wheel, M
i - gear number of transmission.
To determine the values \u200b\u200bof the effective torque of the carburetor motor with one or another fuel supply, its speed characteristics are used, i.e. The dependence of the effective moment on the rotation frequency of the crankshaft at different positions of the throttle. In its absence, the so-called uniform relative speed characteristic of carburetor engines can be used (Fig. 1.1).
Fig.1.1. Unified Relative Partial Speed \u200b\u200bCharacteristics Carburetor Automotors
This characteristic makes it possible to determine the approximate value of the effective motor torque at different values \u200b\u200bof the rotational speed of the crankshaft and the throttle positions. To do this, it is enough to know the values \u200b\u200bof the effective torque of the engine (M n) and frequency of rotation of its shaft at maximum efficient power (n n).
Torque value corresponding to maximum power (M n), can be calculated by the formula:
, (1.4)
where N E. Mach is the maximum efficient engine power, kW.
Taking a number of values \u200b\u200bof the rotational speed of the crankshaft (Table 1.1), calculate the corresponding number of relative frequencies (N E / N N). Using the last, in fig. 1.1 Determine the corresponding number of values \u200b\u200bof the relative values \u200b\u200bof the torque (θ \u003d m e / m n), after which they calculate the desired values \u200b\u200bby the formula: m e \u003d m n θ. ME values \u200b\u200bare booked in Table. 1.1.
Ministry of Agriculture and
Food of the Republic of Belarus
Establishment of education
"Belorussian Agovernmental
Agrarphota University
FacultyTeeherization of agriculture
Farm
Department of "Tractors and Cars"
Course project
By discipline: the foundations of the theory of the calculation of the tractor and car.
On the topic: travelery and fuel efficiency
car.
5th year student 45 groups
Snopkova A.A.
Head of CP
Minsk2002.
Introduction
1. Thought-high speed car.
The traction and speeds of the car are called a set of properties that determine the engine potentially possible engine or the adhesion of the leading wheels with expensive movement speeds and the limit intensities of overclocking and braking equipment during its operation on the traction mode of operation in various roads.
The indicator-high-speed properties of the car (maximum speed, acceleration of the example or slowing down when braking, the thrust force on the hook, efficient power, the lift, overcome in various road conditions, the dynamic factor, the speed characteristic) is determined by the designer traction. It implies the definition of constructive parameters that can be able to use optimal conditions of movement, as well as the establishment of limit road conditions for each type of car.
Traction and speeds and indicators are determined with the traction calculation of the car. As a settlement of calculation, the cargo car is low loading capacity.
1.1. Determining the power of the car engine.
The calculation is based on the nominal loading capacity of the machine /\u003e in kg (the mass of the installed load + the mass of the driver and passengers in the cockpit) or the road trip /\u003e, it is equal to the task -1000 kg.
Engine power /\u003e necessary for the motion of a loaded car with a speed of /\u003e award-rate road conditions characterizing the resistance of the road /\u003e is determined from the dependence:
/\u003e own car mass, 1000 kg;
/\u003e Air resistance (in H) - 1163.7 when driving with a smart velocity /\u003e \u003d 25 m / s;
/\u003e - CPD of transmission \u003d 0.93. Nominal load capacity /\u003e is specified in the task;
/\u003e \u003d 0.04, taking into account the work of the car in agriculture (the coefficient of road resistance).
/\u003e (0.04 * (1000 * 1352) * 9,8 + 1163.7) * 25/1000 * 0.93 \u003d 56,29kW.
Own MassAutomobile is associated with its nominal capacity dependence: /\u003e
/\u003e 1000 / 0.74 \u003d 1352 kg.
where: /\u003e - the coefficient load capacity of the car - 0.74.
The car has a special load capacity \u003d 0.7 ... 0.75.
The coefficient load capacity of the car significantly affects the dynamic and economic treatment of the car: the more, the better these indicators.
The resistance depends on the density of air, the coefficient /\u003e of the streaming content and the bottom (coefficient of sailing), the area of \u200b\u200bthe front surface F (in /\u003e) of the car and the speed of the movement. Determined by addiction: /\u003e,
/\u003e0.45*1.293.3.2625\u003d 1163.7 N.
where: /\u003e \u003d 1,293 kg //\u003e - air density of the peperature 15 ... 25 S.
The coefficient accuracy of the car /\u003e \u003d 0.45 ... 0.60. Rein \u003d 0.45.
The surface area can be calculated by the formula:
F \u003d 1.6 * 2 \u003d 3.2 /\u003e
Where: B - the rear wheel killet, accept it \u003d 1.6 m, the value of H \u003d 2m. The values \u200b\u200bof B and H are clarified with subsequent paintings when determining the size of the platform.
/\u003e \u003d Maximum speed across the road with a firm coating with a complete fuel supply, on the task it is 25 m / s.
Since the car is developing, as a direct transmission,
where: /\u003e 0.95 ... 0.97 - 0.95 kpddviller at idle; /\u003e \u003d 0.97 ... 0.98- 0.975.
KPD-headed transmission.
/>0,95*0,975=0,93.
1.2. Selecting the wheeled formula of the car of the gameometric parameters of the wheels.
The amount of wheel size (wheel diameter /\u003e and the mass transmitted to the wheel axis) are determined based on the car carrying capacity.
With a full-loaded car 65 ... 75% of the total mass of the car, you have to rear axle and25 ... 35% - on the front. Consequently, the load coefficient of the front and rear-winding wheels is respectively 0.25 ... 0.35 and -0.65 ... 0.75.
/\u003e /\u003e; /\u003e 0.65 * 1000 * (1 + 1 / 0.45) \u003d 1528.7 kg.
on the front: /\u003e. /\u003e 0.35 * 1000 * (1 + 1 / 0.45) \u003d 823.0kg.
Take the following: on the rear axle -1528.7 kg, on one wheel of the rear axle - 764.2 kg; Forest axis - 823.0 kg, on the wheel of the front axle - 411.5kg.
Based on the load /\u003e and tire pressure, the sizes of the tires are selected, in M \u200b\u200b(tire profile /\u003e width and the diameter of the plant rim /\u003e). Then the calculated radiowing wheels (in m);
Estimated data: Tire name -; Its dimensions is -215-380 (8.40-15); Rackingradius.
/\u003e (0.5 * 0.380) + 0.85 * 0.215 \u003d 0.37m.
1.3. Determination of the capacity of the gameometric parameters of the platform.
For carrying capacity /\u003e (in T), the installation of the platform /\u003e into the cube. m., outstanding:
/> />0,8*1=0,8 />/>
For the ongoing automotive /\u003e it is accepted \u003d 0.7 ... 0.8 m., I choose 0.8 m.
Having determined the volume of the internal dimensions of the platform of the car in M: width, height and length.
Truck platform width accept (1.15 ... 1.39) from the rut of the car, that is \u003d 1.68 m.
The height is body-determined size of a similar car - UAZ. It is equal to 0.5 m.
Length platform-receiving - 2.6 m.
By the internal length /\u003e I define the base of the LAutomotive (the distance between the front and rear wheel axes):
i accept the base machine \u003d 2540 m.
1.4. Brake properties of the car.
Brake-processing of creating and changing the artificial resistance to the movement of the car by an extension of its speed or retention with a fixed road.
1.4.1. Estimated slowdown in motion machine.
Slowing down /\u003e \u003d /\u003e,
Where G is an accelerated fall drop \u003d 9.8 m / s; /\u003e - the clutch coefficient of the wheels with the road, the values \u200b\u200bof which are taken from Table 3 for various road refers; /\u003e - Current accounting of rotating masses. Its values \u200b\u200bfor the projected car 1.05 ... 1.25, accept \u003d 1.12.
The better the road, the more there may be a slowdown in braking machine. On solid roads, slowing can reach 7 m / s. Bad road conditions reduce braking intensity.
1.4.2. Minimum brake path.
The length of the minimum path /\u003e /\u003e can be determined from the condition that the work perfect by the machine during the braking must be equal to kinetic energy that has lost it during the time. The braking path will be minimal when the most intense braking, that is, when it has the maximum value. If braking is carried out on a horizontal road with a permanent development, then the path to the stop is equal to:
I define the slowdown for various values \u200b\u200b/\u003e, three-wheeled speeds 14.22 and 25 m / s, and will bring them to the table:
Table № 1.
Support surface.
Slow down on the road. Brake power. Minimum brake path. Motion speed. 14 m / s 22 m / s
1.Asfalt 0.65 5.69 14978 17.2 42.5 54.9 2. Gravel. 0.6 5.25 13826 18.7 46.1 59.5 3. Cobblestone. 0.45 3.94 10369 24.9 61.4 79.3 4. Dry primer. 0.62 5,43 14287 18.1 44.6 57.6 5. Primer after the rain. 0.42 3.68 9678 26.7 65.8 85.0 6. Sand 0.7 6,13 16130 16.0 39.5 51.0 7. Snow road. 0.18 1.58 4148 62.2 153.6 198.3 8. Care of the road. 0.14 1.23 3226 80.0 197.5 255.0
1.5. Dynamic properties of the car.
The dynamicity of the car is largely determined by the correct election of the gear and the high-speed movement mode on each of the selected-name.
The number of job shifts - 5. Direct transmission is choosing -4, fifth - economical.
Thus, one of the most important tasks when performing coursework on cars is the combustion of the number of gears.
1.5.1. Selection of car gear.
Gear ratio /\u003e \u003d /\u003e,
Where: /\u003e - gear-cutting gear transmission; /\u003e - Gotate the main transmission.
Transferred numerous transmission to be in equation:
where: /\u003e - Estimated Radio Wheels, M; accepted from previous calculations; /\u003e - the speed of the rotation at the rated frequency of rotation.
Gotate Number Transmission on the first gear:
where /\u003e is the maximum peramic factor, permissible under the clutch conditions of the car's leading wheels. There is an in the range of it - 0.36 ... 0.65, it should not be exceeded:
/>=0.7*0.7=0.49
where: /\u003e is the clutching coefficient with an expensive, depending on the road conditions \u003d 0.5 ... 0.75; /\u003e - the coefficient of the car's loading wheels; Recommended values \u200b\u200b\u003d 0.65 ... 0.8; Maximum loading moment of the engine, in H * M, is taken from the speed characteristic of the supercarboratory engines; G - full weight of the car, n; - The efficiency of transmission automotive on the first transmission is calculated by the formula:
0.96 - Kpdvigator at idle scrolling of the crankshaft; /\u003e\u003d0.98 - CPD Cylindrical Container Gears; /\u003e\u003d0.975 -cpdconic pair of gears; - Accordingly, the number of cylindrical of the conical couples involved in engaging on the first gear. They are quantified, focusing on the transmissions schemes.
In the first proclaimation, under preliminary calculations, the transfer numbers of thermaceous vessels are selected according to the principle of geometric progression, the formation, where Q is the denominator of the progression; It is counted for mills:
where: Z is the nominations specified in the task.
The gear ratio of the nominated car's main gear is taken, converted by the prototype \u003d.
According to the transmission transfer, the maximum velocities of the vehicle of the car on-site transmissions are calculated. The obtained data is reduced to the table.
Table number 1.
Transfer gear ratio speed, m / s. 1 30 6.1 2 19 9.5 3 10.5 17, 4 7.2 25 5 5.8 31
1.5.2. Construction of theoretical (outer) high-speed accuracy of the carburetor engine.
Theoretical external characteristic /\u003e \u003d F (n) is built with a sheet of millimeter paper. Calculation and construction of external characteristics are produced in such a sequence. On the abscissa axis, we depose in the adopted value of the speed of rotation of the crankshaft: nominal, maximum fiber, with a maximum torque, minimal corresponding to the engine.
Nominal frequency is set in task, frequency /\u003e,
Frequency /\u003e. The rotational frequency is made based on the reference data of the prototype -4800 rpm engine.
Intermediate points of the power of the carburetor motor are found from an expression, setting /\u003e (at least 6 points).
The values \u200b\u200bof the torque /\u003e are calculated depending on:
Current values \u200b\u200b/\u003e and /\u003e Berutis graphics /\u003e. The specific efficiency of the carburetor engine fuel is calculated by dependence:
/\u003e, g / (kW, h),
where: /\u003e Specific efficiency of fuel at rated power specified in the task \u003d 320 g / kW * h.
The clock consumption is determined by the formula:
Values \u200b\u200b/\u003e and /\u003e take from the constructions, according to the results of the calculation of the theoretical external characteristics of the table.
Data for software characteristics. Table № 2.
№1 800 13,78 164,5 4,55 330,24 2 1150 20,57 170,86 6,44 313,16 3 1500 27,49 175,5 8,25 300 4 1850 34,30 177,06 9,97 290,76 5 2200 40,75 176,91 11,63 285,44 6 2650 48,15 173,52 13,69 284,36 7 3100 54,06 166,54 15,66 289,76 8 3550 57,98 155,97 17,49 301,64 9 4000 59,40 141,81 19,01 320 10 4266 58,85 131,75 19,65 333,90 11 4532 57,16 120,44 20,01 350,06 12 4800 54,17 107,78 19,97 368,64 /> /> /> /> /> /> /> /> /> />
1.5.4. Universal Dynamic Characteristics of the car.
Dynamic accuracy of the car illustrates its traction-high-speed properties with an equaline movement with different speeds on different transmissions and in various vehicles.
From the equational balance of the car when moving without a trailer on the horizontal reference surface, it follows that the difference between the forces /\u003e (touching the thrust and resistance of the air when the car moves) in this equation it is the force of thrust consumed to overcome all external resistance of the movement, with the exception of air resistance. Therefore, the ratio /\u003e characterizes the supply of power to the vehicle per unit weight of the car. This meter of dynamic, accomplice, traction-high-speed, car properties is called the dynamic factors of the car.
Thus, the dynamic factor of the car.
Dynamic factor is determined on each transmission in the process of operation of the engine with a full load when the fuel is complete.
Between the dynamic factor and parameters characterizing the road resistance (coefficient /\u003e) and inertial loads, there are the following dependences:
/\u003e /\u003e - with unspecified motion;
/\u003e With the steady movement.
Dynamic factors dependent on the vehicle speed mode - the engine speed (its grinding) and the transmission turned on (transmission transmission). Graphic image and called dynamic characteristics. Its value depends on the site's weight of the car. Therefore, the characteristic is built first for the extensive vehicle without cargo in the body, and then by additional constructions to form it into a universal, allowing the dynamic factor for the lobes of the car.
Additional packages to obtain a universal dynamic characteristic.
We apply a mine characteristic from above the second axis of the abscissa, on the coefficient-release value of the car load coefficient.
On the extreme tolere of the upper axis of the abscissity coefficient r \u003d 1, which corresponds to the yield of the car; At the extreme point of the right, we postpone the maximum value indicated in the task, the value of which depends on the maximum weight of the loaded car. Then we apply on the upper axis of the abscissa a number of intermediate values \u200b\u200bof the load and carry out the vertical from them to the intersection with the lower abscissa.
Vertical, passing through the point Γ \u003d 2, I take the order for the second axis. Characteristics. All the dynamic factor at r \u003d 2 is twice as smaller than that of the empty car, the scale of the dynamic factor on the second axis of the ordinate should be two times than on the first axis, passing through the point r \u003d 1. Connect unambiguously on both orders by inclined lines. The intersection points of these straight verticals form on each vertical scale scale for the corresponding banning the car load coefficient.
The results of calculators are recorded in the table.
Table number 3.
Transmission v, m / s.
Torque, nm.
D \u003d 1 g \u003d 2.5 1,22 800 164,50 12125 2.07 0,858 0.394 2.29 1500 175.05 12903 7.29 0.912 0.420 3.35,22,21,921 13040 15,69 0,921 0,424 4,72 3100 166.54 12275 31,15 0,866 0.398 6,10 4000 141.81 10453 51,86 0.736 0.338 6,91 4532 120.44 8877 66,27 0,623 0,286 7.3 4800 107.78 7944 66.03 0.557 0.255 2 1,90 800 164.50 7766 5.06 0.549 0.291 3,57,500 175.05 8264 17,78 0.583 0.309 5.23 2200 176.91 8352 38.24 0.588 0.312 7.38 3100 166,54 7862 75,93 0,551 0,292 9.52 4000 141,81 6695 126,41 0,464 0.246 10.78 4532 120.44 5686 162.27 0.390 107.78 5088 182.03 0.346 0.184 3 3,44 800 164,50 4292 16,56 0,302 0,160 6.46 1500 175.05 4567 58.26 0.317 0.168 9.47,25,21,26,91,615,25,21,12,19,66,54,4345 248,61,289,245,222,4000 141, 81 3700 413.92 0,231 0,123 19,51 4532 120.44 3142 531.34 0.183 0.098 20.64 4800 107.78 2812 596.04 0,155 0.083
5,02 800 164,50 2943 35,21 0,206 0,094 9,42 1500 175,05 3131 123,79 0,212 0,096 13,81 2200 176,91 3165 266,29 0,204 0,090 19,46 3100 166,54 2979 528,73 0,172 0,071 25,11 4000 141,81 2537 880,30 0,144 0,04 28,45 4532 120,44 2154 1130,03 0,069 0,015 30,12 4800 107,78 1928 1267,63 0,043 0,001 5 6,23 800 164,50 2370 54,26 0,164 0,087 11,69 1500 175,05 2522 190,77 0,164 0,088 17,15 2200 176,91 2549 410,36 0,150 0,080 24,16 3100 166,54 2400 814,78 0,110 0,060 31,17 4000 141,81 2043 1356,56 0,044 0,026 35,32 4532 120,44 1735 1741,40 0,001 37,42 4800 107,78 1553 1953,53 /> /> /> /> /> /> /> /> /> />
1.5.5. A brief analysis of the data received.
1. Wow, on which gears will operate in a given roadway, characterized by a given coefficient /\u003e of roadmaps (at least 2 ... 3 values) and which maximum speeds can ondevelop with uniform movement with different values \u200b\u200b(at least 2-x) load coefficients Car, necessarily, at the same time, Max.
Definished values \u200b\u200bof the road resistances: 0.04, 0.07, 0.1 (asphalt, primedorog, primer after rain). With the coefficient \u003d 1 car can be moving /\u003e \u003d 0.04 at a rate of 31.17m / s per 5 transmission; /\u003e \u003d 0.07 - 28 m / s, 5 execution; /\u003e \u003d 0.1 - 24 m / s, 5 transmission. With the coefficient \u003d 2.5 (maximum load), the car can move at /\u003e \u003d 0.04 - the speed of 25 m / s, 4 execution; /\u003e \u003d 0.07 - speed of 19 m / s, 4 execution; /\u003e \u003d 0.1 - Speed \u200b\u200b17 m / s, 3 Transmission.
2. The largest road resistivity on the dynamic characteristic, which can overcome the car, moving on each transmission with uniformity (at the inflection points of the dynamic factor curves).
The resulting policy is in terms of the possibility of their implementation under the clutch conditions by road coating. For a car with rear driving wheels:
where: /\u003e - the coefficient of loading wheels.
Table № 4.
Transmission No. Overcome road resistance The clutch force with the road surface (asphalt). R \u003d 1 g \u003d 2.5 g \u003d 1 g \u003d 2.5 1 transmission 0.921 0,424 0.52 0,52 2 transmission 0,588 0,312 0,51 0,515 3 Transmission 0.319 0,169 0,51 0,51 4 Transmission 0.204 0.09 0.5 0,505 5 Transmission 0.150 0.08 0.49 0.5
According to the table, it is estimated that on 1 transmission the car can overcome the sand; on the 2nd Snowjunogue; on the 3rd icing road; on the 4th dry dump road; on the 5th asphalt
3. To determine the angular lines that the car is able to overcome in various road conditions (at least 2 ... 3 values) on various transmissions, and the speeds of it will develop.
Table number 5.
Road resistance. № transmission angle of lift Speed \u200b\u200br \u003d 1 g \u003d 2.5 0.04 1 Transmission 47 38 3,35 2 Transmission 47 27 5.23 3 Transmission 27 12 9,47 4 Transmission 16 5 13,8 5 Transmission 11 4 17, 15 0.07 1 Transmission 45 35 3,35 2 Transmission 45 24 5,23 3 Transmission 24 9 9,47 4 Transmission 13 2 13,8 5 Transmission 8 17,15 0.1 1 Transmission 42 32 3.35 2 Transmission 42 21 5,23 3 Transmission 22 7 9,47 4 Transmission 10 13.8 5 Transmission 5 17,15
4. Consider:
The maximum speed with a steady movement in the most typical road conditions (asphalt coating). The values \u200b\u200bf by the preparation for various road conditions are accepted from the ratio:
At specified finding conditions, i.e. The asphalt highway resistance takes the value to 0.026 and the speed is 26.09 m / s;
The dynamic factor in direct transmission with the most commonly used for this type of automotive velocity of the movement (usually the rate equal to half themeximal) is 12 m / s;
n Maximum meaningful factor in direct transmission and speed value - 0.204 and 11.96 m / s;
n Maximum meaningful factor at lowest gear - 0.921;
n Maximum meaningful factor on intermediate transmissions; 2 transmission - 0.588; 3 execution - 0.317; 5 Transmission - 0.150;
5. Compared data from reference to a car having close to prototypes. The data obtained in the calculation is practically similar to the UAZ data.
2. Fuel economy of the car.
One of the fundamental economy as the operational property is considered to consider the fuel consumed at 100 km of the path with a uniform movement of a collaposed speed in the specified road conditions. On the characteristic, the curves appreciated, each of which meets certain road conditions; The performance of the work is considered three coefficients of road resistance: 0.04, 0.07, 010.
Fuel consumption, l / 100 km:
where: /\u003e - Instant fuel consumption of the car, l;
where /\u003e - the passage of 100 kmputi, \u003d /\u003e.
Hence the examination of the engine power spent on overcoming the resistance of expensive air we get:
Characteristic is built for visual standards on economy. The axis is ordinatened fuel consumption, on the abscissa axis of the speed of movement.
Order constructing. For different speed modes of the car movement
determine the value of the frequency of the crankshaft of the engine.
Knowing the engine frequency from the corresponding speed characteristics of the definition g.
According to the formula 17, the engine power (expression in square brackets), the required vehicle shift with different speeds on one of the specified roads, characterized by the corresponding resistance value: 0.04, 0.07, 0.10.
Calculations are conducted until speed at which the engine is loaded to the maximum power. The variable system is only the speed of movement and resistance of the air, all other indicators are taken from previous calculations.
Substitutional for different speeds count the desired fuel consumption values.
Table number 6.
/\u003e l / 100 km
5,01 800 940,54 46,73 5,36 330,24 5,5 13,1 9,39 1500 940,54 164,2 11,26 300 3,0 13,31 11,59 1850 940,54 250,11 14,97 290,76 2,4 13,91 13,78 2200 940,54 253,39 19,33 285,44 2,0 14,84 19,41 3100 940,54 701,68 34,58 289,76 1,4 19,12 22,23 3550 940,54 920,11 44,86 301,64 1,2 22,55 25 4000 940,54 1168 59,35 320,00 1,0 28,08
Dry sad
5,01 800 1654,8 46,73 9,20 330,24 5,5 22,46 7,20 1150 1654,8 96,55 13,61 313,16 3,9 21,92 9,39 1500 1654,8 164,28 18,44 300 3,0 21,82 11,59 1850 1654,8 249,90 23,83 290,76 2,4 22,15 13,78 2200 1654,8 353,39 29,88 285,44 2,0 22,93 16,59 2650 1654,8 512,75 38,84 284,36 1,7 24,66 19,41 3100 1654,8 701,68 49,43 289,76 1,4 27,33 0,1 5,01 800 2351,4 46,73 13,03 330,24 5,5 31,81 7,20 1150 2351,4 96,55 19,12 313,16 3,9 30,79 9,39 1500 2351,4 164,28 25,62 300 3,0 30,32 11,59 1850 2351,4 249,90 32,70 290,76 2,4 30,39 13,78 2200 2351,4 353,39 40,43 285,44 2,0 31,02 4000 4532 4800 /> /> /> /> /> /> /> /> /> /> /> /> /> /> />
For the analysis of the economic characteristics, two summarizing curves are carried out on it: the envelope curve of aa and the maximum speeds of movement on different roads, the overflow of the installed engine power and the C-Snap Curve the most economical speeds.
2.1. Analysis of economic characteristics.
1. To determine the most economical speed of movement on each roadfloor office (soil background). Specify the izsence and fuel consumption values. The most economical speed, as it should be expected on solid coating, at a speed of equal to half the maximum fuel trading is 14.5 l / 100 km.
2. Explain the nature of the changes to Economicity when deviating from economic speed to the right and left. The switch to the right increases the specific fuel consumption per kW, with deviations, it increases very sharply air resistance.
3. Determine the flow of fuel consumption. 14.5 l / 100 km.
4. Compared fuel control fuel console rate with a similar prototype indicator. The prototype control flow is equal to the resulting.
5. Based on the poles of the car (daily) traveled along the road with a submissive coating, to determine the approximate capacity /\u003e fuel bobcas (in L) on dependence:
On the prototype of tanks - 80 liters, I take such a container (it is convenient to refill the iskanaster).
The aftermaving calculation results are reduced to the table.
Table number 7.
Indicators 1.Type. Small cargo car. 2. Car load coefficient (on task). 2.5 3. Load capacity, kg. 1000 4. Maximum speed, m / s. 25 5. Mass of a curb car, kg. 1360 6. Number of wheels. four
7. Distribution of the curb mass along the axes of the car, kg
Through the rear axle;
Through the front axle.
8. Full weight of a loaded car, kg. 2350.
9. Distribution of full mass along the axes of the car, kg,
Through the rear axle;
Through the front axle.
10. Sizes of wheels, mm.
Diameter (radius),
Tire profile width;
Internal air pressure in tires, MPa.
11. Dimensions of the freight platform:
Capacity, m / cube;
Length, mm;
Width, mm;
Height, mm.
12. Base of car, mm. 2540 13. Estimated slowdown in braking, m / s. 5,69.
14. Brake path, m when braking at speeds:
Maximum speed.
15. The maximum values \u200b\u200bof the dynamic factor on transmissions:
16. The smallest value of fuel consumption on soil backgrounds, l / 100 km:
17. The most economical movement speeds (m / s) on soil backgrounds:
18. Capacity of the fuel tank, l. 80 19. Car stroke, km. 550 20. Fuel control flow, l / 100 km (approximate). 14.5 Engine: Carburetor 21. Maximum power, kW. 59.40 22. The rotational speed of the crankshaft at maximum power, rpm. 4800 23. Maximum torque, nm. 176.91 24. The speed of rotation of the crankshaft at the maximum moment, rpm. 2200.
Bibliography.
1. Skotnikov V.A., Mashchensky A.A., Solonsky A.S. Basics of the theory and calculation of the tractor and car. M.: Agropromizdat, 1986. - 383c.
2. Methodological manuals on the execution of work work, old and new edition.
Wheel machines of any type are intended for transport work, i.e. For the transport of payload. The ability of the machine to commit useful transport work is estimated by its traction - high-speed properties.
True-high-speed properties refer to the set of properties that determine possible according to the characteristics of the engine or the adhesion of the drive wheels with expensive, the ranges of changes in the speed of rotation and the limit intensity of the car acceleration during its work on the traction mode in various road conditions.
A generalized indicator, according to which the high-speed properties of the wheel machine can most fully estimate; is the average speed ().
The average speed is the ratio of the time of the "pure" movement:
where - the path passed;
The time of the clean movement of the machine.
The average speed is determined by road (primer) conditions and modes of movement of the machine.
For wheel machines, the alternation of movement on the main highway with the movement along the dirt roads, or with the movement in off-road conditions is characterized.
High-speed modes can be divided into two types:
motion with steady speed;
movement with unsteady speed.
Strictly speaking, the mode of the first type practically does not exist, because Always on any roads there are at least small changes in resistance to movement (lifting, descent, irregularities of road coating, etc.), causing a change in the speed of the machine.
The mode of movement of the machine with the steady speed can be considered as conditional. Under this mode should be understood as such at which changes in the speed are small relative to the average speed of movement in this section of the path. On the lower gears, such modes are the more absent.
In general, high-speed modes of movement of the machine are folded from the following phases:
acceleration from space with shifting from a speed equal to zero to the ending speed of overclocking;
uniform movement with speeds that can be taken for the elapsed and equal to the ending speed of overclocking;
slowdowns from the speed equal to the finite speed of overclocking or the steady movement, to the initial braking rate;
braking from finite slowdown speed to speed equal to zero.
Currently, checking the speed properties of wheel machines is performed according to GOST 22576-90 "Motor vehicles, high-speed properties. Test methods. " The same standard defines the conditions and programs of control tests, as well as a complex of measured parameters.
Tests for estimating high-speed properties of cars and road trains are provided with a normal load on a straight line of a horizontal road with a cement-concrete coating. The slopes should not exceed 0.5% and have a length of more than 50 m. Tests are carried out at wind speed not more than 3 m / c and air temperature - 5 ... + 25 0 S.
The main estimated indicators of high-speed properties of cars and road trains are:
maximum speed;
overclocking time to a given speed;
speed \u200b\u200bcharacteristic "acceleration - elevated";
the speed characteristic "acceleration on the transmission that provides maximum speed."
Maximum car speed - This is the maximum speed, developing on a horizontal level road.
It is determined by measuring the time of travel by car of the measuring section of the road 1 km long. Before going to the measuring section, the car on the section of acceleration should achieve the highest possible stepted speed.
The speed characteristic of "acceleration - elevation" is the dependence of the speed from the path and time of the acceleration of the car from the place and the eleg to the stop.
Speed \u200b\u200bcharacter-style "acceleration - eating"
a) in time b) on the way; 2.3 - overclocking 1.4 - elevated
Characteristic "Acceleration - Nick" Resistance to the movement of the car is evaluated.
The speed characteristics of "overclocking on the transmission providing maximum speed" are the dependence of the velocity of the car from the path and time of acceleration when the car is moving on the highest and previous transmissions. Overclocking begins with minimally stable for this speed transmission by sharp pressing until the fuel supply pedal is stopped.
Speed \u200b\u200bcharacteristic "acceleration on the highest transmission".
a) in time b) on the way
The acceleration time on a given area (400m and 1000m), as well as the acceleration time to a given speed, is usually set according to the characteristic "acceleration".
For trucks, a given speed is 80 km / h, and for cars - 100 km / h.
The estimated indicator of traction properties is the maximum angle of lifting overcome by a car with a complete mass when driving on a dry solid flat coating at lowest gear in KP and RK.
In accordance with GOST in 25759-83 "Multipurpose cars. General technical requirements "- the maximum angle of lifting for all-wheel drive cars should be 30 0 S.
This indicator is at the same time one of the estimated indicators of the car's passability.
An indirect parameter, largely determining the level of car traction properties, is the specific power.
Specific power is the ratio of the maximum engine power to the total weight of the car or road trip:
where is the maximum engine power, kW;
Mass of a car and trailer, t.
Specific capacity as an indicator characterizes the energy-related vehicle or road trip. This indicator is especially important when comparing among themselves cars of various types, as parties in a single transport flow, in particular, car columns.
For passenger cars, the specific power fluctuates in the range of 40 - 60 kW / t, for cargo wheeled machines - 9.5 - 17.0 kW, for road trains - 7.5 - 8.0 kW / t.
The estimated characteristics of the traction - high-speed properties of cars are determined during testing or can be obtained during the execution of traction calculations.
