Front brake shoes is one of the most popular products among automotive consumables. In this market segment dozens of manufacturers are represented, much of which today are represented by Chinese firms. The latter, yielding in production quality and characteristics of their shoes to European brands, are actively advancing on the automotive market, even despite the fact that individual modifications of the “Chinese” do not meet safety requirements.
In this sense, the results of recent comparative testing of brake shows, organized by a major European manufacturer of automotive components, have become very revealing. The basis for testing was the official request of a well-known Russian retailer supplying automotive components. For this test, comparable brake shoe sets were purchased, represented by three fairly well-known trademarks. Two participants (let's call them Brand-1 and Brand-2) are Chinese brands, the third participant - shows of the popular German brand BLITZ.
During testing, international experts decided to find out to what extent the above shows are able to guarantee the required level of passive safety. For this purpose, special attention was paid to two main points that helped to correctly position the studied samples and to make their rating based on the results obtained. In this case it is a matter of strength (pull-out force) and friction (friction coefficient) indicators, the requirements for which are necessarily standardized by technical regulations.
Let's talk about strength
The main "design-power" indicator of modern brake shoes is the strength of the friction facing connection with a metal sole or, as it is sometimes called, the show base. In practice, the real values of this parameter are determined in the course of experimental studies on a special bench. During such tests, the control sample is intentionally destroyed. This is done using a special hydraulic jack, the plunger of which presses on the sidewall of the friction facing with increasing force. The force at which it is detached from the sole is fixed by a dynamometer. Note that according to the regulatory requirements of Carberry GmbH, the manufacturer of the BLITZ brand brake shows, the strength of the friction facings for tearing off the sole should not less than 392 N/cm2. This value ensures that even with frequent intensive braking (including under the influence of large cyclic loads on the shoe and disc), the pads will not fall apart and will be able to provide the required braking performance. What did this stage of testing demonstrate?
The result of the force experiment impressed the experts! The “destructive” studies of the brake elements taken for the test turned out to be not only very curious, but also to some extent alarming. In particular, the pads of one of the Chinese brands (Brand-1) collapsed much earlier than stipulated by the standard. The friction facing of this brand has crumbled under force of just 314 N/cm2. As a result, this sample was immediately rejected and removed from further testing. The shoes of the second “Chinese”, which had the designation Brand-2, passed the strength test, but clearly at the limit of their capabilities. Their tearing force made 398 N/cm2, which is only one and a half percent higher than the required 392 N/cm2. Sparsely!
And the third participant, the German BLITZ shoes, demonstrated a more than substantial tearing force strength margin. It is more than on 40% higher than the standard value and amounted to 551 N/cm2. This means that in terms of passive safety, the BLITZ brand samples deserve the highest praise! Such a large strength margin, according to experts, is due to the fact that German manufacturers use well-developed and proven technology for the preparation of both friction mixtures and adhesive compounds. We will discuss this further below, but for now let us return to other types of tests, in particular, the evaluation of the frictional properties that the shoes of the remaining BLITZ and Brand-2 brands underwent in the test.
Pressure, speed and temperature
Recall that the main indicators, clearly demonstrating the ability of the shoes to provide effective braking under various operating conditions, are their friction properties. It is important to note that today experts apply several different approaches to the evaluation of the shoes friction characteristics, and all of them have the right to exist. In our case, the experts, at comparing the tests results, focused on the recommendations of automakers. The starting points for the study were the provisions of the international standard ECE R 90 and UNECE Regulation No. 90. According to these documents, the minimum value of the friction coefficient for shoes, supplied to the secondary market, should not be reduced by more than 15% from the lower limit of the established standard. For example, if for cars of B- and C-classes the average value of the front shoes friction coefficient varies between 0.35-0.40, then the permissible lower limit of this indicator, measured in the shoes been studied, should not fall below the value of 0.3.
Taking into account, that the braking efficiency is influenced by a lot of factors, during the tests, performed on a special computer bench, experts evaluated the shoes friction properties on such important parameters as the pressure in the brake cylinder, the speed at which the braking began, and the temperature of the brake facings. What is the nature of the studied dependencies?
Let's begin results analysis with an assessment of the dependence of the friction coefficient on the pressure in the drive, which changes when you press the brake pedal. For clarity of comparison, it was decided to use two options for the initial braking speed - from 80 to 40 km/h (typical braking mode in the city) and from 120 to 80 km/h (typical braking mode when driving on a country road).
As follows from the data obtained, when braking in urban conditions, the BLITZ shoes, in comparison with the Chinese counterparts Brand-2, show a better stability of the frictional properties, depending on the pressure in the drive. If we compare similar dependencies when braking on the highway, here the Chinese shoes simply do not stand up to criticism, since, starting with a pressure of 20 Bar, the friction coefficient of them decreases to a critical value of 0.3, and when the pressure in the drive exceeds 50 Bar, there is no braking reliability at all.
Comparison of the results of a comparative assessment of the friction properties depending on the pressure in the drive, taking into account the heating temperature of the shoes, is a separate issue. In particular, the dependence of the friction coefficient was considered when braking at a speed of 80 to 30 km/h at a temperature of 550℃. Such braking mode with strong heating of shoes is typical, for example, when driving on a mountain serpentine. Here, the picture is approximately the same as that observed when evaluating the friction properties of the shoes of both brands on the track. In other words, despite the pressure changes in the drive, the friction coefficient of the BLITZ shoes does not go beyond the limits of the standard even with strong heating, while for Chinese shoes, when the pressure in the drive exceeds 50 Bar, the friction coefficient of the hot pads drops below the critical value 0.3, so it is not safe to drive on them.
Thus, based on the results of bench tests, it can be stated that the differences in the parameters, that were determined during the test, may become an important additional, and in some cases, the determining factor in choosing the right brake shoe option. If we talk specifically about the shoes of the German brand BLITZ, then their high efficiency, as already noted above, is largely predetermined by the use of original technologies for the preparation of friction mixes and adhesive compounds. Recall that BLITZ friction facings are manufactured using modern mixes of the Premium Low Metallic category. Due to this, BLITZ shoes are distinguished by reliable and comfortable braking, stability of friction properties, high wear resistance and long operating life.
The "World Automotive Components" Award is one of the most important events on the Russian automotive component manufacturers market. Every year more and more interest is growing to the contest, gaining momentum both among reputable experts in the industry and among ordinary car enthusiasts.
In 2018, over 25,000 people voted for the award nominees, among which there were 230 brands from 25 countries. Numerous Internet users, representatives of auto dealerships and service stations, distributors of automotive components - all participated in a large-scale voting, which resulted in the selection of winners in a wide variety of nominations.
In an exciting festive atmosphere, leading automotive component manufacturers received their coveted deserved statues. Carberry GmbH won the "Dynamic Brand Development in Russia" nomination.
The company's general director, Eduard Digel, noted that this victory is the best evidence of recognition of the results of the hard and fruitful work of a team of professionals, engaged in the development of such brands as BLITZ, FIXAR, FREE-Z, GREEN FILTER, TORR, HAFT.
Carberry GmbH is not going to stop there: the main vector of our work is continuous improvement and enhancement. We are very pleased to receive the MAK award in Russia, which reflects an independent expert opinion on the automotive component manufacturing market. Customers have already loved our brands, they trust our quality products - and we, in turn, will try to continue to delight them and find professional solutions for the industry as a whole.