Special vehicles: controllability and stability.

Special vehicles: controllability and stability.

Special vehicles: controllability and stability

Russia, joining the World Community (World Trade Organization), signed the Agreement on Tariffs and Trade with the following mandatory conditions:

— a high level of product safety must be ensured;

— free movement of goods through customs barriers;

— minimal time and financial costs for any control when processing the relevant documents;

— mutual recognition of the results of compliance (assessment) for safety indicators;

— the manufacturer's responsibility for the compliance of the documentation with the requirements aimed at ensuring the safety of life and health of consumers, preventing damage to their property, the environment and other indicators adopted in the current Certification System, including special vehicles for the transportation of money and valuables; its basic principles can be formulated as follows:

• voluntary participation of participants in work under this System; non-discriminatory access; objectivity of assessments; reliability and reproducibility of assessment results; confidentiality of assessment results; broad information content; high qualification of specialists involved; speed and efficiency of conducting the necessary testing procedures for checks; creation and use of a database for objective assessment of test results;

• creation of the necessary regulatory and technical framework for certification purposes, both mandatory (according to the minimum approved list) and voluntary at the initiative of manufacturers, as well as for an independent objective assessment of the consumer properties of products for their compliance with national and international standards, including reliability indicators;

• creation of scientific potential that allows qualified development, if necessary, of measures to bring the design to compliance with the necessary requirements and to assess the technical level of the object under study;

• technical and economic aspects when putting the developed product into production.

All these requirements must be met by the amended version of the «System of certification of mechanical vehicles and trailers» approved and put into effect by the relevant decree of the State Standard of Russia dated October 9, 1996, No. 20. Special vehicles for the transportation of cash proceeds and valuable cargo (armored vehicles) were also included in the list of products subject to mandatory certification.

Although it should be noted that the above-mentioned rather structurally complex vehicles had previously undergone various levels of testing (preliminary, factory, acceptance) with the involvement of specialists from various departments within the framework of GOST 15.0001-88 «System for the development and launching of products into production. Products for industrial and technical purposes.»

So, for the normal functioning of the Specialized Vehicle Certification System, it was necessary to approve the Certification Authority (or, more precisely, to undergo a complex accreditation procedure), which was done in 1996: the Scientific and Research Center of the State Automobile Inspectorate of the Ministry of Internal Affairs of Russia was accredited by the State Standard of Russia as the Certification Authority for «Road Safety». And one of the leading Technical Services (Test Center) in this area was determined to be the Central Automotive Testing Range, operating in the International Certification System since 1985, under registration number B 22 (Geneva Agreement of 1958 on the Certification of Motor Vehicles). Its specialists made a significant scientific contribution and their practical experience in the development of OST 37.001.519-96 «Vehicles for the transportation of cash proceeds and valuable cargo. Technical requirements. Test methods», put into effect on September 1, 1996.

The standard is intended for developers of armored vehicle designs and establishes the main group of requirements (active and passive safety, visibility, environmental safety and special requirements for armored vehicles) with a term of their introduction from one to three years. This regulatory document can also be used by consumers (customers) of this equipment, as it contains a number of promising requirements.

It should also be noted that the domestic Certification System for Armored Vehicles, based on the already certified group of properties of the base vehicle chassis, is more advanced and promising. Such key developments have not yet been developed in the USA, Canada and Western European countries, whose products for transporting valuable cargo «furrow» the expanses of Russia. A similar standard appeared in 1996 only in Belarus, based on the developments of the Russian standard.

By the way, taking into account the difficult climatic and road conditions, the organization of traffic flow and pedestrians, the following Russian national requirements are applicable to armored vehicles of all categories in this Certification System: interior noise, content of harmful substances in the air of the passenger compartment (cabin); controllability and stability; ventilation and heating; visibility (with maximum harmonization with the EEC Directives), which should help ensure the required level of road safety, taking into account the specifics of operation in Russia.

The main shortcomings of braking systems revealed during testing. Braking properties are one of the most important aspects of active safety of cars. Therefore, testing of braking systems is the most labor-intensive and requires constant development of regulatory and technical documentation, as well as a large number of road structures, bench equipment and devices. And the developers of armored vehicles have a question: is it worthwhile to engage in this procedure if they have not made any significant changes to the chassis design.

The specific design of armored vehicles based on serial chassis usually consists of changes in mass indicators, axle weight distribution, and cooling conditions for brake mechanisms.

An analysis of the characteristics of the weight indicators of armored vehicles in comparison with serial equipment showed that a significant portion of such designs exceed the weight indicators for serial equipment within the following limits: 50% of the armored vehicles that passed the tests have up to 10% cases of excess chassis weight; 35% — up to 20% cases of excess chassis weight; and 15% of such vehicles have excess tare weight in 25% or more cases.

Analysis of the braking dynamics of armored vehicles shows that all of the above leads to a decrease in braking efficiency due to overload and stability during braking, since the symmetrical weight distribution is disrupted both along the axles and along the sides of the armored vehicle. This is especially true for those special vehicles whose main chassis brake mechanisms do not have sufficient design power reserve. Experience shows that these are outdated chassis designs in terms of their technical level and, accordingly, are cheaper on the automotive market.

Improving the braking properties of special vehicles under these conditions can only be achieved by optimizing the characteristics of the realized adhesion to the road, as well as the setting parameters of the brake force regulator, which is only possible for highly qualified specialists with the appropriate instrumentation on special road structures.

In many cases, according to the requirements of the customer of armored vehicles, it is necessary to cover the lower part of the chassis with armor plates, thereby reducing the access of the oncoming air flow going to cool the brake mechanisms. In this case, it is especially necessary to pay attention to special vehicles with a hydraulic drive of the brake system. As is known, the main disadvantage of such a drive, which uses brake fluid as a working fluid, is its reduced parametric reliability, depending on the following main factors: the transported mass, its distribution, driving intensity, deterioration of the cooling process of the brake mechanisms, changes in the physical and chemical properties of the brake fluids used, its hygroscopicity and some other indicators.

All of the above issues and many others can be resolved by using a modern regulatory framework, corresponding instrumentation and road structures for these purposes.

Which regulatory aspects are best to use for assessing braking properties? In current practice, two documents are recommended for use: GOST 22895-77 and Rules No. 13 of the UNECE.

Let us dwell on them in more detail and give an appropriate assessment. At present, GOST 22895-77 significantly lags behind international requirements in terms of technical level, and above all in such important areas as:

— requirements for compensation of brake lining wear;

— requirements for the protective properties of the drive;

— requirements for the mandatory use of asbestos-free brake linings;

— requirements for the mandatory use of ABS.

Therefore, for the purposes of certification of armoured vehicles, it is recommended to use UNECE Regulation No. 13. In October 1996, Revision 3 of UNECE Regulation No. 13 came into force, which took into account all previously effective amendments (from 04 to 08) and adopted new transitional provisions concerning the terms of introduction of ABS into the design of braking systems, etc. This document most fully meets the requirements for the creation of modern braking systems and is oriented towards the future. At the same time, manufacturers of armoured vehicles must take into account that since 2000, braking systems with pneumatic brake drive must comply with the requirements of Regulation No. 51.02 «Noise generated by compressed air». The noise generated when air is released from the braking systems is recorded during the engagement of the service and parking brakes.

The Central Auto Testing Ground, constantly developing and improving testing technology, including armored vehicles, is the only testing center in Russia with a laboratory base and a complex of road structures that allow for a full assessment of the braking properties of any vehicles. The efficiency of the service and spare brake systems is determined on a dynamometric road with asphalt concrete pavement. To determine the efficiency of the parking brake system, slopes of 12, 16, 18% are used, and to determine the efficiency of engine retarders, slopes of low steepness of 4, 6, 8, 10% are used. In accordance with the requirements of regulatory documents OST 37.001.519-96 and UNECE Regulations No. 13.08, armored vehicles of categories N2 and N3 manufactured after 01.06.98 must be equipped with a braking system with ABS.

In 1997, the only road complex in Russia for testing ABS was put into operation, which is a set of sections with different coefficients of adhesion (rough cement concrete, basalt tiles, smoothed cement concrete, asphalt concrete).

The use of these road surfaces in combination with water irrigation allows obtaining highly stable values ​​of adhesion coefficients from 0.15 to 0.8, which makes it possible to test ABS in full compliance with UNECE Regulation No. 13. To determine the adhesion coefficient of the road surface, NITsIAMT has developed and manufactured a tire tester, the use of which allows determining the values ​​of the adhesion coefficients of road surfaces depending on the wheel slip (s) — diagrams in accordance with the requirements of UNECE Regulation No. 13.07.

In 1998, it is planned to put into operation a system of stationary watering of these sections with floor-type nozzles. For testing armored vehicles equipped with ASR systems (anti-slip systems), a project has been developed and construction of acceleration sections on low-slope slopes has begun. Three sections measuring 3 x 15 m, paved with basalt tiles, will be built. Modern, high-performance devices from such companies as Wabko, Hofman, Peiseler, Siemens, Motometer, Term, Datron-Messtechnik and others are used to measure and record the results of laboratory and road tests.

The creation of a highly effective testing technology, including certification, required the Central Auto Testing Ground team to incur significant financial costs, which is logically linked to the current pricing procedure for such services, which are usually 15-20° below those in effect at similar technical centers in Western Europe. But it pays off, since the unique combination of a modern laboratory base of road structures and test roads, and highly qualified specialists allow for the quick and high-quality performance of not only certification tests, but also the fine-tuning of the armored vehicle braking system in practice, which is very important when competing in the armored vehicle market.

Controllability and stability are the most important properties of vehicles, including armored vehicles, characterizing the ability to prevent emergency situations.

Analysis of the test results shows that the installation of armor on the base chassis, depending on the layout solutions, affects the controllability and stability indicators to varying degrees and in almost all cases leads to their decrease relative to the base vehicles.

Statistical processing of the results of bench tests allows us to conclude that the height of the center of mass of armored vehicles of categories M1 and N2 is 3-12° higher than that of the base vehicles. For categories N2 and N3, this indicator is 5-17 higher, which reduces the stability of armored vehicles against rollover.

It should be noted that armored vehicles on foreign chassis of Ford, Chevrolet, Mercedes Benz and other models showed a decrease in lateral stability to a lesser extent (up to 8%) than on domestic ones.

The main problems in terms of controllability of armored vehicles are an increase in the moments of inertia around the vertical axis and increased loads on the front axle (and sometimes for categories M1, NI and overloads).

The manifestation of these factors leads to an increase in the effort on the steering wheel, to a decrease in stability and controllability, which in some cases necessitates the modification of armored vehicle designs (installation of anti-roll bars, increased suspension rigidity, use of other tire models, optimization of tire pressure, installation of power steering).

Recommendations were also prepared to limit the total mass of individual armored vehicle models, which made it possible not to reduce their maximum permissible speed on roads of various categories.

The specifics of driving armored vehicles, associated with the features of their design, impose increased requirements on the driver to predict changes in the complexity of road situations, select a safe speed, distance and trajectory of movement in normal and critical modes.

All these criteria are laid down in the relevant regulatory framework for this indicator during static and dynamic tests.

The testing and evaluation methodology provides for determining the indicators of lateral static stability of a vehicle against rollover, including the lateral stability angle at which the wheels of one side are torn off the supporting surface, and the roll angle of the sprung masses.

During road tests, typical situations are simulated involving avoiding an obstacle that unexpectedly appears on the traffic lane (tests “rearrangement Sn=20 m”), and exceeding the permissible speed when entering a small-radius turn (tests “turn Rn=35 m”).

Tests are also provided in standard modes on roads of various profiles, including a mountain road, climbs of varying steepness, special roads and imitation of the urban traffic cycle.

Comparison of test results with standard values ​​of assessment indicators, in the event of their compliance, ensures the required level of traffic safety.

If the requirements of regulatory documents are not met, the stability and controllability of the test object may be assessed as unsatisfactory or its maximum permissible speed when driving on public roads must be limited, which does not apply to vehicles transporting valuable cargo.

The tilting platform of the stand and the test object are equipped with angular and linear displacement sensors to record the angle of the platform and the roll angle of the vehicle's sprung masses when the wheels on one side are lifted off the supporting surface.

On horizontal platforms, the magnitude of the forces on the steering wheel of a stationary special vehicle and during movement is assessed, including the case of amplifier failure when entering a turn.

During tests in critical driving modes on marked trajectories when performing lane change maneuvers «rearrangement» and «turn», the maximum speeds of maneuvers are determined, the values ​​​​of which are standardized for vehicles of various categories.

In operational driving modes, controllability and stability are assessed by test experts using a point method for expressing indicators in accordance with GOST 15467-79. An important element of improving active safety is special training of drivers to acquire and improve the skills of driving armored vehicles in difficult conditions.

The central auto testing ground has specialists and a set of roads for classes to improve driving skills, including in extreme driving conditions. The existing training programs provide for the possibility of conducting practical theoretical classes.