n1.DOC.
Technical values \u200b\u200bdetermined by the expert
In addition to the source data, the expert uses a number of technical quantities (parameters), which is determined in accordance with the established source data. These include: Driver's reaction time, the time of delaying the brake drive, the time of deceleration, with emergency braking, tire clutch coefficient with an expensive, the resistance coefficient by moving when rolling wheels or body slip over the surface, etc. The adopted values \u200b\u200bof all values \u200b\u200bmust be justified in detail in research part of the expert opinion.Since these values \u200b\u200bare defined, as a rule, in accordance with the established source data about the circumstances of the incident, they cannot be attributed to the original (i.e. adopted without a substantiation or research), no matter how the expert determines them (according to tables, settlement by or as a result of experimental studies). These values \u200b\u200bcan be accepted for the initial data only if they are determined by investigative actions, as a rule, with the participation of a specialist and are listed in the investigator's decision.
1. Slow down in case of emergency braking of vehicles
Slow J. - one of the main values \u200b\u200brequired when carrying out calculations to establish the mechanism of the incident and solving the issue of technical opportunity Prevent incident by braking.The value of the maximum slowdown in emergency braking depends on many factors. With the greatest precision, it can be established as a result of an experiment at the scene. If this is not possible, this value is determined with some approach to tables or settlement path.
When braking negloyoye vehicle With good brakes on the dry horizontal surface of the asphalt coating, the minimum allowable deceleration values \u200b\u200bin emergency braking are determined in accordance with the rules of movement (Article 124), and when braking a loaded vehicle according to the following formula:
| Where: |  | - | The minimum allowable value of the slowing down of the tight vehicle, m / s, |
 | - | The coefficient of braking efficiency of a tight vehicle; |
|
 | - | The coefficient of braking efficiency of the loaded vehicle. |
The deceleration values \u200b\u200bduring emergency braking by all wheels are generally determined by the formula:
| Where | ? | - | clutch coefficient on the braking section; |
 | - | coefficient of vehicle braking efficiency; |
|
| | - | The angle of slope on the braking area (if ? 6-8 °, COS can be taken equal to 1). |
The sign (+) in the formula is accepted when the vehicle is moved to the rise, the sign (-) - when moving on the descent.
2. Tire clutch coefficient with expensive
Clutch coefficient ? represents the ratio of the maximum possible on this section of the road the values \u200b\u200bof the clutch between the vehicle tires and the road surface R sch By weight of this vehicle G. a. :
The need to determine the clutch coefficient arises when calculating a slowdown in emergency braking of the vehicle, solving a number of issues related to maneuver and movement in areas with large inclination angles. It depends mainly on the type and state of the road coating, therefore the approximate value of the coefficient for a particular case can be defined according to Table 1 3.
Table 1
| View of the road surface | Condition of coating | Clutch coefficient ( ? ) |
| Asphalt, concrete | dry | 0,7 - 0,8 |
| wet | 0,5 - 0,6 |
|
| dirty | 0,25 - 0,45 |
|
| Cobblestone, blocking | Dry | 0,6 - 0,7 |
| wet | 0,4 - 0,5 |
|
| Dirt road | Dry | 0,5 - 0,6 |
| Wet | 0,2 - 0,4 |
|
| dirty | 0,15 - 0,3 |
|
| Sand | wet | 0,4 - 0,5 |
| dry | 0,2 - 0,3 |
|
| Asphalt, concrete | icy | 0,09 - 0,10 |
| Snow Snow | Obladen | 0,12 - 0,15 |
| Snow Snow | without ice crust | 0,22 - 0,25 |
| Snow Snow | iced, after the place of the sand | 0,17 - 0,26 |
| Snow Snow | without ice crust, after planetic sand | 0,30 - 0,38 |
A significant impact on the magnitude of the clutch coefficient is the speed of vehicle movement, the state of tire protector, tire pressure and a number of other factors that are not included in the factors. Therefore, that the findings of the expert remain fair and with other possible in this case Its values, when conducting expertise, it is not necessary to accept the average, but the maximum possible values \u200b\u200bof the coefficient ? .
If it is necessary to accurately determine the value of the coefficient ? , Experiment should be carried out at the scene.
The values \u200b\u200bof the clutch coefficient, the most close to the actual, i.e. to the former at the time of the incident, can be established by towing the inhibited vehicle involved in the incident (with the appropriate technical condition of this vehicle), measuring with a dynamometer with a clutch force.
The definition of the clutch coefficient using dynamometric carts is inappropriate, since the actual value of the clutch coefficient of a particular vehicle can differ significantly from the value of the clutch coefficient of the dynamometer trolley.
When solving issues related to braking efficiency, experimentally determine the coefficient? It is inappropriate, since it is much easier to establish a slowdown in the vehicle, which is most fully characterized by braking efficiency.
Need to B. experimental definition coefficient ? It may arise in the study of issues related to maneuver, overcoming steep lifts and descents, withholding vehicles in the inverted state.
3. Brake efficiency coefficient
The coefficient of braking efficiency is the ratio of the estimated deceleration (determined, taking into account the magnitude of the clutch coefficient in this area) to the actual slowdown when the inhibited vehicle is driving on this site:
Consequently, the coefficient TO e. Considers the degree of use of coupling quality tires with the surface of the road.
In production autotechnical expertise Know the braking efficiency coefficient is necessary to calculate the slowdown in emergency braking of vehicles.
The magnitude of the braking efficiency is primarily depends on the nature of the braking, when braking a good vehicle with a blocking of wheels (when traces of the track remain on the road part) theoretically TO e. = 1.
However, with an uneasy blocking, the braking efficiency coefficient may exceed one. In expert practices, in this case, the following maximum values \u200b\u200bof the braking efficiency coefficient are recommended:
| To e \u003d 1.2 | at? ? 0.7. |
| To e \u003d 1.1 | at? \u003d 0.5-0.6 |
| To e \u003d 1.0 | at? ? 0.4. |
If the vehicle braking was carried out without blocking the wheels, it is impossible to determine the efficiency of braking vehicle without experimental studies, since it is possible that the braking force was limited to the design and technical condition of the brakes.
| Table 2 4. |
||||
| Type of vehicle | To e in the case of braking of neglemed and fully loaded vehicles at the following clutch coefficients |
|||
| 0,7 | 0,6 | 0,5 | 0,4 |
|
| Passenger cars and others on their base |  |  |  |  |
| Truck - with a lifting capacity of up to 4.5 tons and buses up to 7.5 m long |  |  | | |
| Cargo - loading capacity over 4.5 t and buses more than 7.5 m |  |  |  |  |
| Motorcycles and mopeds without stroller |  |  | | |
| Motorcycles and mopeds with a stroller | | |  |  |
| Motorcycles and mopeds with engine working volume 49.8 cm 3 | 1.6 | 1.4 | 1.1 | 1.0 |
In this case, for a good vehicle, it is possible to determine only the minimum permissible braking efficiency (the maximum value of the efficiency coefficient; braking).
The maximum permissible values \u200b\u200bof the inhibition efficiency coefficient of a good vehicle are mainly dependent on the type of vehicle, its load and the clutch coefficient on the braking section. With these information, you can define the braking efficiency coefficient (see Table 2).
The values \u200b\u200bof the efficiency of motorcycle braking efficiency in the table are valid with simultaneous braking with foot and manual brakes.
If the vehicle is not completely loaded, the braking efficiency coefficient can be determined by interpolation.
4. Resistance Coefficient Movement
In the general case, the coefficient of resistance to the movement of the body along the reference surface is the relationship of forces that prevent this movement to the weight of the body. Consequently, the coefficient of resistance to the movement allows you to take into account the loss of energy when moving the body in this area.Depending on the nature of the current forces in expert practice, they use various concepts of resistance coefficient of movement.
Coefficient of rolling resistance - ѓ Call the ratio of the resistance force by movement with the free rolling of the vehicle in the horizontal plane to its weight.
By the magnitude of the coefficient ѓ , in addition to the type and state of the road surface, has an impact of a number of other factors (for example, tire pressure, tread pattern, suspension design, speed, etc.), therefore, a more accurate value of the coefficient ѓ It can be determined in each case experimentally.
Energy loss when moving along the surface of the road of various objects, discarded during a collision (bypass) is determined by the resistance coefficient ѓ g. . Knowing the magnitude of this coefficient and the distance to which the body moved along the surface of the road can be installed its initial speed, after which in many cases.
The value of the coefficient ѓ You can approximately define on Table 3 5.
Table 3.
| Road covering | Coefficient, ѓ |
| Cement and asphalt concrete in good condition | 0,014-0,018 |
| Cement and asphalt concrete condition | 0,018-0,022 |
| Crushed stone, gravel with knitting materials processing, in good condition | 0,020-0,025 |
| Crushed stone, gravel without processing, with small potholes | 0,030-0,040 |
| Bruster | 0,020-0,025 |
| Cobblestone | 0,035-0,045 |
| Soil dense, smooth, dry | 0,030-0,060 |
| Soil uneven and dirty | 0,050-0,100 |
| Wet sand | 0,080-0,100 |
| Sand Sukhoi | 0,150-0,300 |
| Ice | 0,018-0,020 |
| Snow road | 0,025-0,030 |
As a rule, when moving the objects dropped during a collision (bypass), the movement is braked by irregularities of the road, the sharp edges are cut into the surface of the coating, etc. The influence of all these factors on the amount of resistance force to the movement of a particular object is not possible, therefore the value of the resistance coefficient of movement ѓ g. It can only be found experimentally.
It should be remembered that when the body falls from a height at the moment of strike, a part of the kinetic energy of the translational motion is quenched by pressing the body to the surface of the vertical component of the inertia. Since the lost kinetic energy is not able to consider, it is impossible to determine the actual value of the body velocity at the time of the fall, you can only determine its lower limit.
The ratio of the strength of resistance to movement by weight of the vehicle when it is free to ride it on a land plot of a road called the coefficient of total road resistance ? . The value of it can be determined by the formula:
The sign (+) is taken when the vehicle is moved to the rise, the sign (-) - when moving on the descent.
When moving along the inclined section of the road dried vehicle, the coefficient of total resistance to the movement is expressed by a similar formula:
5. Driver's reaction time
Under time, the driver's reaction in psychological practice is understood as the time interval from the moment of entering the driver's danger signal before starting the driver's exposure to the vehicle management bodies (brake pedal, steering wheel).In expert practice, under this term, it is customary to understand the time interval. t. 1 , sufficient to ensure that any driver (whose psychophysical capabilities meet professional requirements) after an objective opportunity arises to detect danger, managed to influence the vehicle management bodies.
Obviously between these two concepts there is a significant difference.
First, the danger signal does not always coincide with the moment when an objective possibility arises to detect an obstacle. At the time of the appearance of the obstacle, the driver can perform other functions distracting it for a while from observation in the direction of the obstacle that has arisen (for example, monitoring the testimony of control devices, the behavior of passengers, objects located aside from the direction of movement, etc.) .
Consequently, the reaction time (in the sense, which invested in this term in expert practice) includes the time that has passed since when the driver had an objective opportunity to detect an obstacle, until he was actually discovered, and the reaction time is actually Arrivals to the driver of the danger signal.
Secondly, the driver's response time t. 1 , which is accepted in the calculations of experts, for this road situation, the value is constant, the same for all drivers. It can significantly exceed the actual driver's response time in a particular case of a traffic accident, but the actual time of the driver's reaction should not be greater than this value, since then its actions should be assessed as late. The actual time of the driver's response during a short period of time may vary widely depending on the range of random circumstances.
Consequently, the driver's response time t. 1 which is adopted in expert calculations is essentially a normative, as if establishing the necessary degree of driver's care.
If the driver responds to the signal slower than other drivers, therefore, it should be more attentive when driving the vehicle to meet this standard.
It would be more correct, in our opinion, to name the amount t. 1 Not the time reaction of the driver, and the regulatory time of the driver's actions of the driver, such a name more accurately reflects the essence of this magnitude. However, since the term "driver's response time" is firmly rooted in expert and investigative practice, we keep it in this work.
Since the desired degree of driver's care and the ability to detect the obstacles in various road conditions of unequal, the standard reaction time is appropriate to differentiate. To do this, complex experiments are needed in order to identify the dependence of the time reaction of drivers from various circumstances.
In expert practice, it is currently recommended to accept the regulatory time of the driver's reaction. t. 1 equal to 0.8 seconds. The exception is the following cases.
If the driver is warned about the possibility of danger and about the place of the alleged appearance of the obstacle (for example, when the bus is a bus, from which passengers come out, or when driving with a small interval past a pedestrian), it does not need an extra time for discovering obstacles and decision, it should be Prepared for immediate braking at the time of the beginning of dangerous actions of a pedestrian. In such cases, the regulatory response time t. 1 It is recommended to take 0.4-0.6 sec (greater importance - under limited visibility).
When the driver detects a malfunction of the controls only at the time of the dangerous situation, the reaction time is naturally increasing, since it takes additional time to accept the driver of a new decision, t. 1 In this case, equals 2 sec.
The Rules of Move the driver is prohibited to control the vehicle even in the state of the easiest alcohol intoxication, as well as with such a degree of fatigue, which may affect the safety of motion. Therefore, the effect of alcohol intoxication on t. 1 Not taken into account, and when evaluating the degree of fatigibility of the driver and its influence on the safety of the movement, the investigator (Court) takes into account the circumstances that have forced the driver to control the vehicle in a similar condition.
We believe that the expert in the notice to the conclusion may indicate ascending t. 1 As a result of overwork (after 16 hour work driving about 0.4 s).
6. During the retardation of the triggering of the brake drive
Brake drive triggering time ( t. 2 ) Depends on the type and design of the brake system, their technical condition and, to a certain extent, on the nature of the driver's press on the brake pedal. In case of emergency braking good vehicle time t. 2 relatively small: 0.1 sec for hydraulic and mechanical drives and 0.3 sec -for pneumatic.If the hydraulic drive brakes are triggered from the second press on the pedal, time ( t. 2 ) does not exceed 0.6 secwhen triggered from the third click on the pedal t. 2 \u003d 1.0 seconds (according to the experimental studies conducted in TsNISE).
Experimental determination of the actual values \u200b\u200bof the retardation time of the triggering of the brake drive of vehicles with good brakes in most cases is unnecessary, since possible deviations from average values \u200b\u200bcannot significantly affect the results of the calculations and the findings of the expert.
After each road accident, the vehicle speed is defined before and at the moment of impact or departure. This value has such great importance for several reasons:
- The most frequently broken point of rules road It is excess of the maximum permissible speed of movement that is, and thus it becomes possible to determine the probable perpetrator of an accident.
- Also, the speed affects the braking path, and therefore the opportunity to avoid a collision or the departure.
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Determination of the velocity of the car on the brake path
Under the braking, it usually understands the distance that this or that vehicle comes from the start of braking (or, if more accurate, from the moment of activating the brake system) and until a complete stop. General, non-discipled formula from which it is possible to withdraw the formula for calculating speed, looks like this:
Va \u003d 0.5 x T3 x j + √2Su x j \u003d 0.5 0.3 5 + √2 x 21 x 5 \u003d 0.75 +14.49 \u003d 15,24 m / s \u003d 54.9 km / h where: in the expression √2Su x j, where:
- VA. - the initial speed of the car, measured in meters per second;
- t3. - the increase in the growing car slowing down in seconds;
- j. - established slowing down of the car when braking, m / s2; Note that for a wet coating - 5m / s2 according to GOST 25478-91, and for dry coating J \u003d 6.8 m / s2, hence the initial velocity of the car under the "Yose" in 21 meters is 17.92m / s, or 64 , 5km / h.
- Syu. - The length of the brake trail (UNA), measured in the same place in meters.
In more detail the process of determining the speed in dTP time told in a wonderful article Accounting for potential deformation when determining the velocity of the car at the time of the accident. You can in the pdf form. Authors: A.I. Dega, O.V. Yaksanov.
Based on the equation specified above, it can be concluded that the vehicle speeds affect the braking path, which is not difficult to calculate with the remaining other values. The most difficult part of the calculations for this formula is the exact definition of the friction coefficient, since a number of factors affect its value:
- type of road surface;
- weather conditions (when the surface is wetted with water, the friction coefficient decreases);
- tire type;
- tire status.
For the exact result of calculations, it is also necessary to take into account the peculiarities of the brake system of a particular vehicle, for example:
- material, as well as the quality of manufacturing brake pads;
- the diameter of the brake discs;
- functioning or disorder electronic devicescontrolling the brake system.
Brake mark
After a sufficiently fast activation of the brake system on the road surface remains prints - brake trails. If the wheel during braking is blocked completely and does not rotate, continuous traces remain, (which is sometimes called the "Trail of Uza") which many authors urge to consider the result of the highest possible pressure on the brake pedal ("brake to floor"). In the case when the pedal is pressed not to the end (or there is any defect of the brake system) on the road surface, as it were, as it were, "lubricated" tread prints, which are formed due to incomplete blocking of wheels, which, with such a braking, retain the ability to rotate.
Stopping path
The stopping path is considered that the distance that a certain vehicle is running from the detection of the driver of the threat to the car stops. This is the main difference between the braking path and the stopping path - the latter includes the distance that the car overcomed during the operation of the brake system, and the distance that was overcome during the driver needed to awareness of the danger and reaction to it. At the time of the driver's reaction, factors affect:
- the position of the driver's body;
- psycho-emotional driver's condition;
- fatigue;
- some diseases;
- alcoholic or narcotic intoxication.
Determination of speed based on the law of conservation of the amount of movement
It is also possible to determine the velocity of the vehicle by the nature of its movement after the collision, as well as in the event of a collision with another vehicle, to move the second machine as a result of the transfer of kinetic energy from the first. Especially often this method is used in collisions with fixed vehicles, or if the collision happened at an angle close to direct.
Determining the velocity of the vehicle based on the deformations obtained
Only a very small number of experts determine the speed of the car in such a way. Although the dependence of the damage to the car from its speed is obvious, but a single efficient, accurate and reproducible method of determining the speed of the obtained deformations does not exist.
This is due to the huge number of factors affecting the formation of damage, as well as the fact that some factors simply cannot be taken into account. To influence the formation of deformations can:
- design of each particular car;
- features of cargo distribution;
- the service life of the car;
- the quantities and quality of body work passed by the vehicle;
- metal aging;
- modifications of the design of the car.
Determination of speed at the time of the arrival (collision)
Speed \u200b\u200bat the time of the departure is usually determined by the braking trail, but if it is not possible for a number of reasons, then approximate speed digits can be obtained by analyzing injuries obtained by pedestrian and damage formed after the vehicle.
For example, the velocity of the car can be judged by the features of the bumper fracture - Specific car injury, which is characterized by the presence of a cross-fragmentation fracture with a large bone fragment of the wrong diamond-shaped form on the side of the strike. Localization when hit by a bumper of a passenger car - an upper or middle third of the lower leg, for a truck - in the thigh area.
It is believed that if the vehicle speed at the time of the strike exceeded 60 km / h, then, as a rule, a referee or transverse fracture arises, if the speed was below 50 km / h, then the transverse and fragmentation fracture is most often formed. When colliding with a fixed car, the speed at the moment of the strike is determined on the basis of the law of preserving the amount of movement.
Analysis of the method of determining the velocity of the car during an accident
On the brake trail
Advantages:
- relative simplicity of the method;
- a large number of scientific work and compiled guidelines;
- fairly accurate result;
- the ability to quickly obtain the results of the examination.
Disadvantages:
- in the absence of traces of tires (if the car, for example, did not slow down in front of the collision, or the features of the road surface do not allow sufficient accuracy to measure the trace of the s) to carry out this method it is impossible;
- the impact of one vehicle during the collision to another may be taken into account.
According to the law of saving the amount of movement
Benefits:
- the ability to determine vehicle speed even in the absence of traces of braking;
- with careful accounting of all factors, the method has a high reliability of the result;
- ease of use of the method in cross collisions and collisions with fixed cars.
Disadvantages:
- the lack of data on the mode of movement of the vehicle leads to an inaccurate result;
- compared to the previous method, more complex and bulky calculations;
- the method does not take into account the energy spent on the formation of deformations.
Based on the demommatics received
Benefits:
- takes into account energy costs on the formation of deformations;
- does not require traces of braking.
Disadvantages:
- dubious accuracy of the results obtained;
- a huge number of factors taken into account;
- often the impossibility of determining many factors;
- lack of standardized reproducible determination techniques.
In practice, two methods are most often used - determining the speed along the traction trail and based on the law of preserving the amount of movement. When using two these methods, the maximum accurate result is simultaneously ensured, since the techniques complement each other.
The remaining methods for determining the vehicle speed of considerable distribution did not receive due to the inaccuracy of the results obtained and / or the need for bulky and complex computations. Also, when evaluating the velocity of the car, the testimony of witnesses of the incident is taken into account, although in this case you need to remember the subjectivity of the perception of speed by different people.
To some extent, help deal with the circumstances of the incident and eventually obtain a more accurate result can help analyzing video surveillance cameras and video recorders.
Brake power.When braking, elementary friction forces, distributed over the surface of friction linings, create a resulting torque moment, i.e. Brake moment M. Thor directed opposite to the rotation of the wheel. Breaking power arises between the wheel and expensive R TOR .
Maximum brake force R The MAX torus is equal to the tire clutch strength. Modern cars have brake mechanisms on all wheels. At a two-axis car (Fig. 2.16) Maximum brake force, n,
Projecting all the forces acting on the car when braking, on the plane of the road, we get in general Car motion equation when braking on a lift:
R Tor1 +. R Tor2 +. R K1 +. R K2 +. R P + R in + R.d. . + R g - R And \u003d R Thor +. R D + R in + R.d. . + R g - R n \u003d 0,
where R TOR \u003d. R Tor1 +. R Tor2; R d \u003d R K1 +. R K2 +. R P - the power of the resistance of the road; R etc. - friction force in the engine, shown to the leading wheels.
Consider the case of car braking only the brake system when the power R etc. = 0.
Considering that the speed of the car during braking decreases, we can assume that the force R in ≈ 0. Due to the fact that R Mala compared to power R The torus can also be neglected, especially with emergency braking. The adopted assumptions allow you to write the car equation for braking in the following form:
R Thor +. R d - R n \u003d 0.
From this expression, after the transformation, we obtain the equation of the movement of the car during braking on the projector of the road:
φ x + ψ - Δ n a. s / g. = 0,
where φ x is the coefficient of the longitudinal clutch of tires with the road, ψ is the road resistance coefficient; δ n is the coefficient of accounting of rotating masses on the projector of the road (with a rope); a. W is the acceleration of braking (deceleration).
A slowdown is used as the vehicle braking dynamics of the vehicle but s in braking and brake path S. TOR , m. Time t. Thor, C, use as an auxiliary meter when determining the stopping path S. about.
Slow down when braking the car.Delay in braking is determined by the formula
but Z. \u003d (P Tor + R D + R in +. R d) / (Δ BP m.).
If brake forces on all wheels have reached the validity of the clutch forces, then neglecting forces R in and R G.
a. s \u003d [(φ x + ψ) / ψ BP] g. .
The coefficient φ x is usually much larger than the coefficient ψ, therefore, in the case of a complete braking of the vehicle, the value of the expression can be neglected. Then
a. s \u003d φ x g. / Δ BP ≈ φ x g. .
If during braking the coefficient φ x does not change, then slowing but It does not depend on the velocity of the car.
Brake time.Stopping time (total braking time) is the time from the moment the driver's danger is discovered until the car stops. The total braking time includes several segments:
1) driver response time t. R - Time during which the driver decides on braking and transfers the foot from the fuel supply pedal to the pedal of the working brake system (depending on its individual characteristics and qualifications is 0.4 ... 1.5 s);
2) Brake Drive Time t. PR - time from the beginning of clicking on the brake pedal before the start of the deceleration, i.e. Time to move all moving parts of the brake drive (depending on the type of brake drive and its technical condition is 0.2 ... 0.4 C for hydraulic drive, 0.6 ... 0.8 C for pneumatic acting and 1 ... 2 C for a manifold with pneumatic drive brakes);
3) Time t. y, during which the slowdown increases from zero (the beginning of the brake mechanism) to the maximum value (depends on the intensity of braking, the load on the car, type and state of the road surface and the braking mechanism);
4) braking time with maximum intensity t. torus. Determine the formula t. Tor \u003d υ / a. s Max - 0.5 t. y
For a time t. P + t. Prom car moves evenly at the speed υ , during t. y - slowly, and over time t. TOR – slowly until the complete stop.
Graphic representation of the time of braking, changing the speed, slowing down and stop the car gives a diagram (Fig. 2.17, but).
To determine the stopping time t. about , necessary to stop the car from the moment of danger, you need to summarize all the time-called time segments:
t. Oh \u003d. t. P + t. Pr + T. in +. t. TOR \u003d. t. P + t. PR + 0.5 t. y + υ / a. Z Max \u003d. t. Sum + υ / a. z Max
where t. Sumy \u003d T. P + t. PR + 0.5 t. y
If the brake forces on all wheels of the car simultaneously reach the values \u200b\u200bof the clutch forces, then accepting the coefficient δ BP \u003d 1, get
t. Oh \u003d. t. sum + υ / (φ x g.).
Braking distances - This is the distance that the car passes during the braking t. torus with maximum efficiency. This parameter is determined using the curve. t. TOR \u003d. f (υ ) and considering that in each velocity interval the car moves equifiable. Sample view of the track dependence S. torus from speed R to , R in, r T and without taking into account these forces is shown in Fig. 2.18, but.
The distance required to stop the car from the moment of danger (the length of the so-called stopping path) can be determined if we assume that the slowdown is changed as shown in Fig. 2.17, but.
Stopping path can be divided into several segments corresponding to time segments t. R, t. etc, T. y, t. Tor:
S. Oh \u003d. S. P + S. Pr + S. in +. S. torus.
Car traveled during t. P + t. Progue with a constant speed υ, define as follows:
S. P + S. pr \u003d υ ( t. P + t. etc) .
Taking that when a speed reduction from υdo υ "car moves with a constant deceleration but cf \u003d 0.5 but Z M ah, we get the way passed by the car during this time:
Δs. y \u003d [ υ 2 – (υ") 2 ] / but s m ah.
Brake path with a reduction in speed from υ "to zero during emergency braking
S. Tor \u003d (υ ") 2 / (2 but s m ah).
If the brake forces on all the wheels of the car simultaneously reached the values \u200b\u200bof the clutch forces, then R etc. \u003d. R in \u003d. R r \u003d 0 brake car path
S. TOR \u003d υ 2 / (2φ x g.).
The braking path is directly proportional to the square of the velocity of the car at the time of the start of braking, so with an increase in the initial speed, the braking path increases especially quickly (see Fig. 2.18, but).
Thus, the stopping path can be defined as follows:
S. Oh \u003d. S. P + S. Pr + S. in +. S. tor \u003d υ ( t. P + t. PR) + [υ 2 - (υ ") 2] / but z M ah + (υ ") 2 / (2 but s m ah) \u003d
= υ T. Sum + υ 2 / (2 but s m ah) \u003d υ T. sum + υ 2 / (2φ x g.).
The stopping path, as well as stopping time, depends on a large number of factors, the main of which are:
vehicle speed at the time of the start of braking;
qualifications and physical condition of the driver;
type and technical condition of the working brake system of the car;
pavement state;
car load;
condition of car tires;
method of braking, etc.
Intensity intensity indicators.To test the effectiveness of the brake system, the largest allowable braking path is used as indicators and the smallest allowable slowdown in accordance with GOST R 41.13.96 (for new cars) and GOST R 51709-2001 (for auto-operating cars). The intensity of braking cars and buses under traffic safety conditions is checked without passengers.
The greatest permissible brake path S. Tor, M, when driving with an initial speed of 40 km / h on a horizontal section of the road with a smooth, dry, pure cement, or asphalt concrete coating, has the following values:
cars and their modifications for the carriage of goods ..........14,5
buses S. full mass:
up to 5 tons inclusive ............................................ 18.7
more than 5 tons ....................................... ... .................. 19.9
trucks With full mass
up to 3.5 tons inclusive ................ ...........................19
3.5 ... 12 T inclusive .................................... .. ... 18,4
more than 12 t ...................................................... .. ... 17.7
motor tractor with trucks with full weight:
up to 3.5 T inclusive ......................... .................. 22.7
3.5 ... 12 T inclusive ..................................... ... .22,1
more than 12 t .......................................................... 21.9
Distribution of brake force between car bridges.When braking the car inertia R and, (see Fig. 2.16), acting on the shoulder h. C causes the redistribution of normal loads between the front and rear bridges; The load on the front wheels is increased, and the rear is reduced. Therefore, normal reactions R. Z 1 I. R. z 2. , acting respectively on the front and rear axle bridges during braking, significantly different from loads G. 1 I. G. 2 , which perceive bridges in static condition. These changes are evaluated by the coefficients of changing normal reactions. M. P1, I. m. P2, which for the case of car braking on the horizontal road is determined by formulas
m. p1 \u003d 1 + φ H. H. C / l. 1 ; m. P2 \u003d 1 - φ H. H. C / l. 2 .
Consequently, normal road reactions
R. z 1 \u003d. m. P1 G. 1 ; R. z 2 \u003d. m. P2. G. 2 .
During the car inhibition, the largest values \u200b\u200bof the reaction change coefficients are within the following limits:
m. p1 \u003d 1.5 ... 2; m. P2 \u003d 0.5 ... 0.7.
The maximum intensity of braking can be provided with the complete use of the clutch by all the wheels of the car. However, the braking force between the bridges can be distributed unevenly. Such unevenness characterizes Brake power distribution coefficientbetween the front and rear bridges:
β O \u003d. R TOR1 / R TOR \u003d 1 - R Tor2 / R torus.
This coefficient depends on various factors from which the mains are: the distribution of the car weight between its axes; intensity of braking; reaction change coefficients; Types of wheeled brake mechanisms and their technical condition, etc.
With the optimal distribution of brake force front and rear wheels The car can be brought to blocking simultaneously. Ad hoc
β o \u003d ( l. 1 + φ about H. c) / L.
Most brake systems provide a constant ratio between the brake forces of the front and rear axle (R Tor1 I. R Tor2. ), therefore, total strength R The torus can reach the maximum value only on the road with the optimal coefficient φ about. On other roads full use Coupling weight without blocking at least one of the bridges (front or rear) is impossible. However recently appeared brake systems With the regulation of the distribution of brake forces.
The distribution of the total brake force between the bridges does not correspond to the normal reactions varying during braking, therefore the actual deceleration of the car is less, and the time of braking and the braking path is more theoretical values \u200b\u200bof these indicators.
To approximate the results of the calculation to experimental data in the formula, the coefficient of braking efficiency is introduced TO E. , which takes into account the degree of use of theoretically possible efficiency of the brake system. On average for passenger cars TO E. = 1,1 ... 1.2; For trucks and buses TO E. = 1.4 ... 1.6. In this case, the calculated formulas have the following form:
a. s \u003d φ x g / K. e;
t. Oh \u003d. t. Sum +. TO e υ / (φ x g.);
S. TOR \u003d. TO e υ 2 / (2φ x g.);
S. O \u003d υ. T. Sum +. TO e υ 2 / (2φ x g.).
Methods of car braking. Cooperating brake system and engine.This method of braking is used to avoid overheating brake mechanisms and accelerated tire wear. Brake moment on wheels is created at the same time brake mechanisms and engine. Since in this case, the brake pedal is preceded by the release of the fuel supply pedal, the angular velocity of the engine of the engine should decrease to the angular velocity idle move. However, in fact, the drive wheels through the transmission are forcibly rotated crankshaft. As a result, an additional force of r TD resistance to movement appears proportional to the friction force in the engine and the deceleration of the car.
The inertia of the flywheel counteracts the inhibitory action of the engine. Sometimes the opposition of the flywheel turns out to be more inhibited engine action, as a result of which the intensity of the braking is somewhat reduced.
Joint braking of the working brake system and the engine more efficiently than braking only the brake system if slowing down when braking a. Z. from More than a slowdown in braking with a disconnected engine a. s, i.e. a. Z. from > a. s.
On the roads with a small clutch coefficient, joint braking increases transverse stability Car under the conditions of drift. When braking in emergency situations, the clutch is useful to turn off.
Brake with periodic termination of the brake system.The inhibited non-slip wheel perceives a large brake force than when moving with partial slippage. In case of free rolling, the angular velocity of the wheel ω k, radius r. to and progressive speed υ to the movement of the wheel of the wheel are associated with addiction υ to = ω K. R. to . The wheel moving with partial slippage (υ * ≠ ω K. R. K), this equality is not respected. The difference of velocities υ K and υ * determines the speed of sliding υ , i.e. υ с = υ -ω K. R. to.
The degree of slippage wheeldefined as λ = υ SC. / υ K. . The slave wheel is loaded only by the forces of resistance to movement, so the tangent reaction is small. The application to the braking torque wheel causes an increase in the tangent reaction, as well as an increase in deformation and elastic tire slipping. The clutch coefficient of the tire with a road surface increases in proportion to slipping and reaches a maximum when slipping around 20 ... 25% (Fig. 2.19, but -point IN).
Workflow maintenance of maximum tire clutch with road coating illustrates a graph (Fig. 2.19, b.). With an increase in the braking torque (section OA)the angular velocity of the wheel decreases. In order not to give the wheel to stop (blocked), the braking moment is reduced (plot CD).The inertia of the pressure control mechanism in the brake drive leads to the fact that the pressure reduction process occurs with some delay (section Aq). Location on EF. Pressure is stabilized for a while. The growth of the angular velocity of the wheel requires a new increase in the braking torque (section GA)to the value corresponding to 20 ... 25% slip values.
At the beginning of the sliding, the slowdown of the wheel increases and the linear proportionality of the dependence is disturbed: Ω \u003d f (M. TOR ). Plots DEand FG. characterized in inertia executive mechanisms. The brake system in which the pulsating pressure control mode is implemented in working cylinders (cameras) is called anti-lock.The depth of the pressure modulation in the brake drive reaches 30 ... 37% (Fig. 2.19, in).
The wheels of the car due to the cyclic loading of the braking torque rolling with partial slippage, approximately equal to the optimal, and the clutch coefficient remains high during the braking period. The introduction of anti-lock devices reduces tire wear and allows you to increase the transverse stability of the car. Despite the complexity and high cost, anti-lock brake systems are already legalized by the standards of many foreign countries, they are installed on the passenger cars of secondary and higher classes, as well as buses and cargo cars for long-distance transport.
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The established slowdown, m / s 2, is calculated by the formula
.
(7.11)
\u003d 9.81 * 0.2 \u003d 1.962 m / s 2;
\u003d 9.81 * 0.4 \u003d 3.942 m / s 2;
\u003d 9.81 * 0.6 \u003d 5.886m / s 2;
\u003d 9.81 * 0.8 \u003d 7.848 m / s 2.
The results of the calculations according to formula (7.10) are reduced to Table 7.2
Table 7.2 - Dependence of the stopping path and steady deceleration from the initial braking rate and the clutch coefficient
|
|
|
|||||||
, km / hAccording to Table 7.2, we build the dependence of the stopping path and the slowdown deceleration from the initial deception rate and the clutch coefficient (Figure 7.2).
7.9 Building a brake diagram PBX
The brake diagram (Figure 7.3) is the dependence of the slowdown and the speed of the PBX movement on time.
7.9.1 Determination of speed and deceleration on the diagram site corresponding to the timing of the drive
For this stage 
=
\u003d const 
\u003d 0 m / s 2.
In operation initial braking speed 
\u003d 40 km / h for all categories PBX.
7.9.2 Determination of the speed of the PBX on the diagram site corresponding to the time of deceleration
Speed 
, m / s, corresponding to the end of the deceleration of the deceleration time, are determined by the formula
\u003d 11.11-0.5 * 9.81 * 0.7 * 0.1 \u003d 10.76 m / s.
Intermediate velocity values \u200b\u200bin this section are determined by formula (7.12), while 
= 0
; Coefficient of clutch for category M 1 
=
0,7.
7.9.3 Determination of speed and deceleration on the section of the diagram corresponding to the time setting
Time of steady slowdown 
, C, calculated by the formula
,
(7.13)
from.
Speed 
, m / s, on the section of the diagram corresponding to the time of the steady deceleration, are determined by the formula
,
(7.14)
for 
= 0
.
The value of the steady deceleration for the working brake system of the Category M 1 is taken 
\u003d 7.0 m / s 2.
8
Definition of managing parameters PBX
Controllability PBX is its property in a specific road situation a given direction of movement or change it according to the driver's effect on the steering.
8.1 Determination of maximum angles of rotation of controlled wheels
8.1.1 Determination of the maximum angle of rotation of the external controlled wheel
Maximum angle of rotation of the outdoor controlled wheel
,
(8.1)
where R n1 min is the turning radius of the outer wheel.
The rotation radius of the outer wheel is taken equal to the corresponding prototype parameter -R H1 min \u003d 6 m.
,
\u003d 25,65.
8.1.2 Determining the maximum angle of rotation of an internal controlled wheel
The maximum angle of rotation of the internal controlled wheel can be determined by taking a king of a squash equal to the wheel track. Previously, it is necessary to determine the distance from the instantaneous center of rotation to the outer rear wheel.
Distance from instant turn center to the outer rear wheel 
, m, calculated by the formula
,
(8.2)
.
Maximum angle of rotation of an internal controlled wheel 
, hail, can be determined from expression
,
(8.3)
,
\u003d 33,34.
8.1.3 Definition of the average maximum angle of rotation of controlled wheels
The average maximum rotation angle of controlled wheels 
, hail, can be determined by the formula
,
(8.4)
.
8.2 Definition of the minimum width of the carriageway
Minimum carriage part 
, m, calculated by the formula
\u003d 5.6- (5.05-1.365) \u003d 1.915m.
8.3 Definition of critical under the conditions of traffic speed
Critical under the conditions of the traffic speed 
, m / s, calculated by the formula
,
(8.6)
where 
,
- coefficients of resistance to wheels front and rear axis Accordingly, n / hail.
Single wheel resistance coefficient 
, N / is glad, are approximately determined by empirical dependence.
where 
- internal tire diameter, m; 
- width of the tire profile, m; 
- Air pressure in the tire, kPa.
To Δ1 \u003d (780 (0.33 + 2 * 0.175) 0.175 (0.17 + 98) * 2) /57.32\u003d317.94, n / ha
To δ1 \u003d (780 (0.33 + 2 * 0,175) 0.175 (0.2 + 98) * 2) / 57.32 \u003d 318.07, n / ha
.
Turning the designed car - excessive.
To ensure traffic safety, a condition must be performed
>
.
(***)
The condition (***) is not performed, since in determining the impedance coefficients, only tire parameters were taken into account. At the same time, when determining the critical velocity, it is necessary to take into account the distribution of car mass, suspension design and other factors.
