EVALUATION OF RESULTS OF ROAD RESEARCH OF LANOS CAR, EQUIPPED WITH AN ADVANCED HYDRAULIC BRAKE DRIVE

The results of studies of road emergency braking of the car, the brake system equipped with an improved hydraulic brake actuator according to the patent number 76189 Ukraine are analyzed. This drive provides more efficient emergency braking of cars under operating conditions by of installing in each of the contours of the rear brakes one brake-power, each of which provides distribution of braking forces between the wheels of the corresponding side.


Introduction
The estimated figures of brake efficiency of operated motor cars is the value of steady maximum deceleration and the value of the minimum stopping distance, traveled by the car from the beginning of braking with the required speed up to its full stop.
Both evaluation indexes are linked. Therefore, in US only one of them is normalized -the minimum stopping distance.
It is considered that the steady deceleration is independent of the initial braking speed, which creates certain advantages when used; however, the braking distance characterizes the traffic safety.
There are established different standards for assessing the performance of brake systems of passenger cars, which are regulated by a number of both international and national standards [1][2][3].

Analysis of publication
Road tests of motor cars, carried out according to the known standards, are to determine their inhibitory properties, i.e. the value of the steady deceleration and braking distance under certain road conditions [1][2][3].
The requirements of different standards establish the value of implemented deceleration of the car in running order at least 7 m/c 2 and the limit braking distance at a certain initial braking speed on level ground with a dry asphalt surface.
Thus, at the initial braking speed of 40 km/h the braking distance of the car in the running order shall not exceed 17,4 m and at 80 km/h, the stopping distance should not exceed 43,2 m. These values are listed in the present Highway Code of Ukraine. In this case, the action of the aerodynamic resistance of the vehicle movement is neglected, stipulating the wind speed to be 0,3-0,5 m/s, at which the tests are conducted [1,3].
For the same reason in the classical literature [4,5] there are given the dependencies to determine the limiting deceleration values and the braking distance of the vehicle, ignoring the force of air resistance.
However, as shown by theoretical studies [6][7][8][9] the longitudinal component of the aerodynamic drag force acting on the vehicle during braking has an impact on the redistribution of normal axial reactions.
With that, in case of vehicle braking on level roads they are homogeneously distributed between the wheels of similar axes.
A completely different situation occurs during braking of vehicles in the event of total aerodynamic force components action not only on a flat road, but on a level road with a transverse slope, with a fixed radius of curvature and on the roads with a longitudinal slope, i.e. under operating conditions [10][11][12][13].
Such a law [14] of axial normal reactions distribution, and thus the braking forces between the axles must be satisfied by the vehicle braking drive action.
However, the modern methods of braking force distribution between the axles of passenger cars [15] and the design of brake actuators, providing it, fail to effectively implement the change of normal reactions in operating conditions not only between the axles, but also between the wheels of various vehicles.
One of the options for improving the braking drive of cars is the designed brake actuator [16], which implements the method [17] of brake force distribution between the wheels of its various sides.

Purpose and problem statement
The purpose of road tests lies in establishment of the minimum amount of change in the steady deceleration and braking way of the Lanos motor car standard configuration, equipped with an improved hydraulic brake actuator, on a level road.
The object of road tests is to estimate the effect of the aerodynamic factor on the inhibitory properties of the Lanos motor car.
Subject of research -the process of emergency braking of Lanos motor car.

The methodology of carrying out road tests
Lanos car tests of basic configuration were held in a state of partial (1220 kg) and full load (1595 kg). At this, there was allowed the presence of instrumentation and the load balancer, evenly placed in the passenger compartment and the trunk of the car in accordance with the requirements [1][2][3].
A series of emergency braking of the car in a different weight state was produced in calm weather on a road site with dry asphalt concrete pavement (without longitudinal and transverse slope) of Zaporozhe Auto Plant.
Initial braking speed varied from 40 to 150 km/h. The wind speed at the indication of the anemometer was 0,3-0,5 m/s. Before carrying out the road test the braking system of the Lanos motor car, equipped with an improved hydraulic brake actuator [16], one of the circuits of which is shown in Fig. 1, was tested for compliance with requirements [1][2][3].
To register the value of deceleration and the stopping distance of the Lanos motor car there was used the equipment of the design and operational department of Zaporozhe Automobile Building Plant ZAZ: a decelerometer with an integrated Maha VZM 300 printer, a cup anemometer MS-13 GOST 6376-74. Fig. 1. Equipment of the car with an advanced brake actuator [16]: 1 -master brake cylinder assembly; 2 -controlled brake force governor; 3 -pilot cylinder assembly; 4front axle brake actuator; 5 -rear axle brake actuator; 6 -articulation-linkage assembly In the process of testing, the motor car accelerated to the speed exceeding the initial braking speed of 3-5 km/h. Then the clutch was disengaged and, when the magnitude of the initial braking speed was reached, the brakes were engaged and the vehicle stopped.
After the braking process was over, there were registered the displayed measured values of both deceleration and the braking distance.
The average value of 2 measurements in the forward and backward direction was considered to be the result of measurements conducted.
As part of the above road research program five experiments were conducted.

Analysis of road test results
Comparative evaluation of the results of road tests of the Lanos motor car was performed, using the results of theoretical research and the results of road tests of the Lanos motor car equipped with a modern brake actuator (according to the manufacturer's testing protocol №058.BSI 2010).
Since at the initial deceleration speed of less than 80 km/h the values of fixed parameters of Lanos vehicles, equipped with an existing and advanced brake actuator, revealed the least difference (up to 6 %), then the latter in Table 1 and Table 2 are conditionally not shown.  Analysis of outcomes of road (Table. 1) and theoretical (Table. 2) investigations show that with the growth of the initial braking speed for Lanos cars equipped with an advanced hydraulic brake actuator [16] there are implemented large deceleration and the corresponding lower values of braking distances for both weighting states.
The results of road tests were determined according to [18].
Thus, the value of the average steady deceleration for Lanos passenger cars, braking on dry asphalt concrete at the initial speed that varies from 80 km/h to 150 km/h constitutes (Table 1) As a result of theoretical studies ( Table 2) there were determined the values of deceleration and braking distances obtained for the Lanos car: -by classical dependencies [4,5] (with an existing brake actuator) where  -coefficient of adhesion; T1 T2 , P Pthe braking force applied to the front and rear axle, respectively; a m -weight of the vehicle; 0  -the initial vehicle deceleration speed; -According to the obtained dependencies [19] (with an improved brake actuator) where z -drag coefficient; 0 K = 0,35 kg/m 3streamlining factor of the Lanos car body; w Ffrontal drag area of the vehicle; z  =0,1 -share of the lifting component in the drag force; i Jmoment of inertia of rotating masses; k r -rolling radius of the wheel.
As the analysis of calculated values of braking parameters of the Lanos vehicle equipped with an improved hydraulic brake actuator shows (Table. 2) when the initial braking velocity changes within 80-150 km/hour, the theoretical value of steady deceleration is: -curb weight 8,19-9,02 m/s 2 ; -complete load 8,06-9,13 m/s 2 . At the same time the estimated value of the braking distance of the Lanos car is: -curb weight 30,91-97,5 m; -complete load 36,14-99,5 m.
Relatively lesser values of deceleration magnitudes at emergency braking of the Lanos car, obtained during experimental studies, take place in connection with a decrease in the coefficient of wheels friction with the road surface [10], which is caused by an increase in the initial braking speed and the normal load on the wheels of the rear axle. However, this issue requires further research.
Comparative analysis of theoretical braking parameters (Table. 2) of the Lanos car, equipped with an improved and existing hydraulic brake actuator, shows that under emergency braking on a dry asphalt road covered with an increase of the initial braking speed of 80-150 km/h: -at curb weight the steady deceleration is increased by 15 %, while the braking distance is reduced by 12 %; -at the complete weight the steady deceleration increases by 24 %, thus the limiting stopping distance is reduced by 16 %.
Consequently, despite the change in the coefficient of friction during emergency braking, consideration of the effect of aerodynamic resistance of the vehicle leads to improved braking characteristics.
Based on the results of road tests of Lanos cars equipped with an existing hydraulic brake actuator (Table. 3), it can be stated that vehicles with a basic configuration (without ABS) at partial loading on a dry asphalt road surface at the initial speed of 100 km/h, according to the factory test data, have a braking distance of 48,2 m with a steady deceleration of 6,2 m/s 2 At the same time according to the road test conducted (Table 3) for the same vehicle, equipped with an improved hydraulic brake actuator, the maximum braking distance is 42,9 meters, which is 11% less than for Lanos cars with a basic configuration at steady deceleration of 7,35 m/s 2 . Note. In the top line there is indicated deceleration in m/s 2 , in the bottom line -the braking distance, m.
As a result, the above-said theoretically and practically confirms the opportunity to improve the efficiency of potential passenger cars with any degree of loading and under any operating conditions equipped with an improved hydraulic brake actuator [16], which allows implementing the specific vehicle braking force more fully.

Conclusions
Based on comparative analysis of road studies and theoretical data, it was revealed that at initial braking speed up to 80 km/h the values of limit braking distance of Lanos cars differ insignificantly (up 6 %). This is due to the fact that in case of emergency braking of passenger cars with the streamlining car body factor of K o = 0,35 kg/m 3 , at braking speed below 80 km/h the strength of the aerodynamic air flow resistance does not have a noticeable effect.
Comparative analysis of theoretical parameters of emergency braking shows that the considered passenger vehicles equipped with an advanced hydraulic brake actuator, when performing emergency braking on dry asphalt concrete with an initial speed varying from 80 to 150 km/h: а) at partial loading steady deceleration increases by 15 %, thus the limiting stopping distance is reduced by 12 %; b) at complete load steady deceleration increases to 24 % and the limiting stopping distance is reduced by 16 %.
According to the road research the limiting stopping distance for the Lanos car, equipped with an improved hydraulic brake actuator, with partial load at the initial braking speed of 100 km/h is 42,9 m, which is 11% less than for the Lanos car of basic version.
At the same time the implemented minimum deceleration speed is 7,35 m/s 2 , which meets the requirements of the national standard regulating the value of implemented deceleration no less than 7 m/s 2 .
The results of theoretical and experimental studies confirm the potential opportunity for increasing the efficiency of cars with any degree of loading by advanced hydraulic brake actuator equipment [16], which allows implementing the specific vehicle braking force in all operating conditions more fully.