The serviceability of an automobile refers to its ability to adapt to various conditions of use and exert its maximum working efficiency. There are mainly the following items.
(A) the power of the car
This is the primary performance of a car. A car must have enough average speed to run normally. Cars must have enough traction, overcome all kinds of driving resistance and run normally. It all depends on power. Automobile dynamic performance can be evaluated from the following three indicators.
1, the maximum speed of the car
Refers to the highest speed that a car can reach when it is fully loaded on a good level road.
2, the acceleration ability of the car
Refers to the ability of a car to quickly increase its speed under various conditions of use. The shorter the acceleration time, the greater the acceleration, the shorter the acceleration distance and the better the acceleration performance.
3. The uphill ability of the car
The uphill capacity is expressed by the maximum slope that can be overcome when the car is fully loaded and driving at the lowest gear on a hard road at a constant speed, which is called the maximum climbing degree. It represents the maximum traction of the car. Different types of cars have different requirements for the above three indicators. Cars and buses emphasize the maximum speed and acceleration, while trucks and off-road vehicles have strict requirements on the maximum climbing degree. But no matter what kind of car, if you want to drive normally on the expressway, you must have a certain average speed and acceleration ability.
(b) Fuel economy of automobiles
In order to reduce the transportation cost of cars, cars are required to complete as much transportation as possible with the least fuel consumption. The ability of a car to complete the unit transportation workload with the least fuel consumption is called fuel economy, and the evaluation index is the fuel consumption per 100 km (liter).
(3) the braking performance of the car
Good braking is the guarantee of safe driving and the premise of giving full play to automobile power. Automobile braking has the following three aspects.
1, braking efficiency
The ability of a car to slow down quickly until it stops. Braking time, braking deceleration and braking distance are commonly used to evaluate the braking process. The braking efficiency of an automobile is not only related to the technical condition of the automobile, but also related to the braking speed, tires and road conditions of the automobile.
2. Stability of braking efficiency
After a short period of continuous braking, the braking efficiency decreases due to the increase of brake temperature, which is called brake thermal recession. The stability of braking efficiency after continuous braking is the constancy of braking efficiency.
3. Stability of direction during braking.
It means that the car will not run off, sideslip and lose its steering ability during braking. When the left and right braking forces are different, it is easy to run off; When the wheel is locked, it is easy to slip or lose steering ability. In order to prevent the above phenomenon, modern cars do not have electronic anti-lock devices to prevent the danger of wheel locking during emergency braking.
(d) the mobility and stability of automobiles.
The maneuverability of a car refers to its ability to respond to the driver's steering instructions, which directly affects the driving safety. The air pressure and elasticity of the tire, the stiffness of the suspension device and the position of the center of gravity of the car all have important influences on this performance.
The stability of a car is its ability to recover its original state of motion after being disturbed by the outside world, and it is its ability to resist overturning and sideslip. For automobiles, lateral stability is particularly important. When the car is driving on a transverse ramp. When turning, it is easy to slip or roll over due to other lateral forces. The lower the height of the center of gravity, the better the stability. Proper front wheel positioning angle enables the car to automatically position and keep straight running, which improves the stability of straight running. If the load is too high, overloaded, the speed is too fast when turning, the angle of the lateral ramp is too large and the load is unbalanced, it is easy to cause the car to slip and roll over.
(5) the flat roof of the car.
Due to the influence of uneven road surface, the car will vibrate, which will make passengers feel tired and uncomfortable and damage the goods. In order to prevent the above phenomenon, we have to slow down. At the same time, vibration will also affect the service life of the car. The degree of vibration reduction on uneven road surface during driving is called ride comfort.
The physical quantity evaluation index of automobile ride comfort, passenger cars and cars adopt the speed characteristic of "comfort reduction limit", when the speed exceeds this limit, it will reduce ride comfort and make people feel tired and uncomfortable. The higher the limit value, the better the ride comfort. The freight car adopts the speed characteristic of "fatigue-reducing the limit of working efficiency".
The natural frequency of automobile body can also be used as an evaluation index of ride comfort. From the point of view of comfort, the natural frequency of the car body is better in the range of 600Hz ~ 850Hz.
High-speed cars, especially cars, require excellent ride comfort. The elasticity of the tire, excellent suspension device, the shock absorption performance of the seat and the minimum non-suspension mass can all improve the ride comfort of the car.
(6) The passability of cars
Under a certain load, the ability of a car to pass through various bad roads and roadless areas at a high average speed and overcome various obstacles is called the passability of a car. The passing capacity of various cars is different. Cars and buses often run in cities. Poor passing ability. Off-road vehicles, military vehicles, dump trucks and trucks must have strong passing capacity.
Using wide-section tires and multiple tires can reduce rolling resistance; The deeper tread can increase the adhesion coefficient without slipping easily, and the all-wheel drive mode can give full play to the power of the car; Reasonable selection of structural parameters can make the car have excellent obstacle-crossing ability, such as larger minimum ground clearance, approach angle, departure angle, wheel radius, smaller turning radius, transverse and longitudinal passing radius, etc. All these can improve the passing capacity of cars.
(7) Other performances.
1, controlling portability
When driving, it needs to be evaluated according to the number of operations, the strength required for operation, the convenience of operation, vision, lighting, signals, etc. The car has good maneuverability, which can not only reduce the driver's labor intensity and tension, but also ensure safe driving. Using power steering, brake booster, automatic transmission and diaphragm clutch, the maneuverability is obviously improved.
2. Liquidity
Cars driving in urban areas often drive on narrow and tortuous roads, so mobility is particularly important. Maneuverability is mainly evaluated by the minimum turning radius. The smaller the turning radius, the better the maneuverability.
3, convenient loading and unloading
It is related to the height of the carriage, the number of overturned fences and the number and size of doors.
(8) Capacity
Passenger capacity refers to the number of goods or passengers that a car can transport at the same time. Freight cars are represented by carrying mass and carrying volume. Passenger cars are expressed by the number of passengers.
The weight utilization coefficient reflects the reasonable degree of automobile structure.
Weight utilization coefficient = rated loading mass/empty car mass