The Theoretical analysis of operational properties helps to find out limiting possibilities of the car and to realise in road conditions design features of concrete model of the car.
To the basic operational properties characterising &quo t;поведение" the car on road, concern:
Dynamism, fuel profitability, stability, controllability, passableness and smoothness of a course.
In the car theory its operational properties consider separately one from another. Actually all of them are closely interconnected. So, speed of the car on turns can be limited not by dynamism, and controllability and stability, and on rough roads smoothness of a course.
Dynamism - property of the car to move with the greatest possible average speed, characterised in the maximum speed of movement, intensity of dispersal till the set speed and intensity of braking.
Dynamism of the car depends first of all on its traction and brake properties.
The Car moves as a result of influence on it of various forces (fig. 1) which are divided into forces, driving the car, and the forces, showing resistance to its movement. The basic motive power is the force of draught enclosed to driving wheels. Force of draught results from interaction of driving wheels (loaded with a twisting moment transferred from the engine) with road. Overcoming of forces of resistance depends on size of traction effort on wheels to movement, speed of dispersal, or as speak, priemistost the car.
Force of draught basically is defined by the high-speed characteristic of the engine, and also the transfer relation and transmission EFFICIENCY. High-speed characteristics of the engine are characterised by change of capacity and a twisting moment, developed by the engine, depending on frequency of rotation of a cranked shaft.
In a mode of the maximum twisting moment the engine develops the greatest draught necessary for overcoming of the big resistance to movement and maintenance of high accelerations at dispersal, and in a mode of the maximum capacity before car movement.
a Fig. 1. The forces operating on the car at movement:
Ri - inertial, Rib - lateral inertial, Rbs - resistance to lateral sliding, Rrd - reactions of road to a support of a wheel, Rt - draughts on driving wheels, Rv - resistance of air, Rd - resistance kacheniju.
Operational frequency of rotation of a cranked shaft of the engine should be in a range between twisting moment and capacity maxima. In this case the minimum specific expense of fuel is provided at high dynamic indicators of the car.
The Big help to the driver for a choice of the optimal mode of movement in concrete road conditions render a tachometre which supervises power setting, and ekonometr, specifying depression size in the inlet pipeline.
To forces of resistance to car movement carry force of a friction in transmissions, force of resistance kacheniju Rd and force of resistance to air of Rv.
Losses in the transmissions spent for overcoming of a friction in gearings of cogwheels of a transmission and the main transfer, in kardannyh hinges, bearings and epiploons, characterise transmission EFFICIENCY. This size while in service the car with the account extra earnings of details changes and for cars makes 0,90... 0,97.
Hence, the capacity and twisting moment size brought to driving wheels, will be less sizes received directly from the engine, on size of losses in transmission, i.e.
NT=Ne - NTP,
Where the NT-traction capacity brought to driving wheels, Ne - effective power of the engine, NTP - the capacity necessary for overcoming of forces in transmission.
Force of draught of Rt as the basic force, driving the car, should be sufficient for troganija the car from a place, maintenance of necessary speed and giving of demanded acceleration. Force of draught is regulated by limiting value of factor of coupling of tyres with road which characterises a relative instant immovability of a point of contact of the tyre and road, i.e. The superfluous force of draught realised by a twisting moment of the engine, leads to slipping of wheels are rather expensive. Most often slipping is observed at sharp troganii the car from a place and at movement on slippery road.
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