И инновации современной

41 
where: 
0
TD
M
– friction torque in the engine at minimum 
angular speed;
TR
i
– transmission gear ratio;
D
r
– dynamic wheel radius;
a
V
– vehicle speed;
TR
– transmission efficiency factor;
K
r
– wheel rolling radius;
b
– coefficient of increase of mechanical losses from the 
engine angular speed. 
K
a
F
f m g
(5) 
where: f – is the coefficient of rolling friction of the wheels;
g – is the acceleration of free body fall. 
B
B
a
F
W V
(6) 
where: 
B
W
– is a flow factor. 
Then the deceleration of the car in fractions g: 
2
0
2
1
TD
TR
TR
a
a
B
a
a
D
TR
K
TR
M
i
b i
V
a
f m
g
W V
g m
r
r
(7) 
In Figure 5 shows the calculated dependencies of modern 
passenger car deceleration on the speed in the process of stopping the 
combustion engine on the horizontal road section in different gears 
[1]. 

42 
Figure 5 – Dependence of deceleration of a modern passenger car on 
speed during braking of an internal combustion engine on a 
horizontal section of the road in various gears. 
Analysis of Figure 5 shows that at the beginning of braking by 
the engine at the speed of IV gear the deceleration of the car 
decreases from 1.1 to 0.4 m/s2, which is due to the peculiarity of the 
power characteristic of the mechanical losses of combustion engines 
(Figure 4). At the same time, the car's speed can be reduced to 40 
km/h. For further speed reduction it is reasonable to switch to II gear. 
Then the deceleration will first increase to 1.5 m/s2, and at 20 km/h 
speed it will decrease to 0.9 m/s2. 
It is advisable to use the service braking system to complete 
the braking process. For more comfortable braking, you can use 
another technology: reduce the speed from 120 to 60 km/h; engage 
III gear and start braking with the same small initial deceleration – 
1.1 m/s2; complete braking with the service brake system. Figure 5 
can see that the lower the gear, the steeper the curves, i.e. the more 
intensive the deceleration decreases. It complicates estimation of 
braking efficiency, because GOST gives values for steady-state 
decelerations typical for working brake system (Figure 6). 
Analysis of Figure 5 shows that deceleration within the 
specified limits can only be achieved if the engine starts braking at 
25 km/h in first gear. However, this is inexpedient, because 
practically all kinetic energy of the car will be extinguished by the 
main braking system. The engine should be braked immediately if it 
is necessary to reduce the speed of the car. Analysis of Figure 5 also 

43 
shows that braking of a car within the speed range defined by GOST 
during tests of the auxiliary braking system (25-35 km/h) can be 
performed in the second gear, where the minimum deceleration (0.9 
m/s2) is higher than that defined by GOST for vehicle of the 
permitted maximum weight (0.8 m/s2). Therefore, it can be 
concluded that the efficiency of braking a modern car engine meets 
the requirements of the current GOST. However, such low 
deacceleration values do not provide effective service braking of the 
car by the engine. Much higher values are given in the literature. The 
textbook by V.N. Kravts [1] states that service braking of the car is 
performed with 0.8-1.7 m/s2 deceleration. It is noted in [12] that 
smooth service braking is usually used under operating conditions 
without causing unpleasant sensations and discomfort for passengers 
with a deceleration of 1.5-2.5 m/s2. Even higher deceleration values 
during service braking are given in [13] – 2.5-3.0 m/s2. 
As a result of the author's research on slowing down of the 
route taxi while operating on the city route, it was found to be in the 
range of 2.66-3.08 m/s2. With less deceleration, the driver practically 
did not slow down, because then the braking distance becomes 
unacceptably large. 

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