What is the driving principle of a small car?

if a car wants to move and run at a certain speed of bai, a driving force must be exerted by the outside along the direction of the car to overcome all kinds of resistance when the car is running.

1 the driving force Ft

the driving force is obtained by transmitting the torque of the engine to the driving wheels through the transmission system. The effective torque Te generated by the automobile engine is transmitted to the driving wheel through the automobile transmission system, and the torque Tt acts on the driving wheel, thus generating a circumferential force F on the ground, and at the same time, causing the ground to generate a tangential reaction force Ft consistent with the driving direction of the automobile, which is the driving force Ft of the automobile. As shown in the figure below.

2 Driving resistance of automobiles

When automobiles are driving on roads, there are generally four kinds of resistance: rolling resistance, air resistance, ramp resistance and acceleration resistance.

(1) Rolling resistance FF:

Rolling resistance is the general term for the energy loss caused by the interaction between wheels and corresponding deformation when they roll on the road. When a car runs on a hard road, the wheels roll, and all parts of the tire circumference are constantly compressed and deformed, and then the deformation is constantly restored. In this deformation process, rubber molecules rub with each other, which generates heat and emits it to the atmosphere. The work done to deform the tire can not be fully recovered, thus consuming the output power of the automobile. This part of power loss is called elastic hysteresis loss of tire. When the car is driving on soft road, its rolling resistance comes from the hysteresis loss of soft road deformation and tire elastic deformation.

(2) air resistance fw:

when a car is traveling in an air medium, the component of air force in the traveling direction is called air resistance. Air resistance is divided into friction resistance and pressure resistance. Friction resistance is the component of the resultant tangential force on the body surface due to the viscosity of air in the driving direction. Friction resistance is related to the surface quality and surface of car body, accounting for about 8% ~ 1% of air resistance. Pressure resistance is the component of the resultant force of normal pressure acting on the exterior surface of an automobile in the driving direction. Shape resistance is the main part of pressure resistance, so the shape of the body is the main factor affecting air resistance, and improving the streamlined body of the body is an effective way to reduce air resistance.

(3) Ramp resistance fi:

When a car runs uphill on a longitudinal ramp, the mass of the car produces a component parallel to the ground, and the direction of the component is opposite to that of the car, that is, the uphill resistance of the car is formed. The uphill resistance of a car is directly proportional to the slope value.

(4) Acceleration resistance FJ:

When a car accelerates, it needs to overcome the inertia force when its mass accelerates, which is acceleration resistance. The mass of a car is divided into two parts: translational mass and rotational mass. When accelerating, it is necessary to overcome not only the inertia force generated by the translational mass of the automobile during the acceleration process, but also the inertia couple moment generated by the rotating mass. PART

2 driving equation of automobile

When the automobile is running, the driving and attachment conditions must be met, that is, the driving force of the automobile should be balanced with the resistance, thus the driving equation of the automobile can be obtained: Ft= Ff+Fi+Fw+Fj

Among the above resistances, the rolling resistance and air resistance always act on the driving automobile, and the slope resistance and acceleration resistance only exist under the corresponding driving conditions. There is no slope resistance and acceleration resistance when driving at a constant speed on a horizontal road. When the car goes downhill, Fi is negative, and then the component of gravity along the road surface is not the driving resistance of the car, but the power. When the car slows down, the inertial force is the force that makes the car move forward, and Fj is also negative at this time. PART

3 conditions for driving a car

In order to ensure the normal driving of the car on the road, it is necessary to have enough driving force to overcome various driving resistances, which is the driving conditions of the car; The condition that makes the driving wheel of the automobile and the road surface not slip is called the adhesion condition of the automobile driving.

1 Driving conditions of the car

When the driving force of the car is greater than the sum of rolling resistance, air resistance and uphill resistance, the car accelerates; The driving force is equal to the sum of the above resistances, and the car runs at the same speed; Less than the above resistance, the car slows down until it stops.

the driving condition of the car can be written as: Ft≥Ff+Fw+Fi

2 the adhesion condition of the car

usually, the limit value of the maximum tangential reaction force between the ground and the wheel when the tire does not slip is called the adhesion f? . Make the adhesion greater than or equal to the maximum driving force, which is the adhesion condition of the car.

the attachment condition of a car can be written as: Ft≤F?

where: f? =Fz? ，? It is called the adhesion coefficient, which is determined by the road surface and tires; Fz is the normal reaction force of the driving wheel.