Brake testing South Africa

ECE90 Brake Testing (Pty) Ltd is a company that was established with the objective of providing a test and certification service for replacement brake lining assemblies. This being primarily to the requirements of the Economic Commission for Europe ECE Regulation 90 but also other national, international and industry specifications used in the brake friction industry.

Tuesday, October 24, 2006

What cause brake squeal?

It is no secret that a rushed brake job can leave some things undone that may contribute to noise and comebacks. So let’s start with the brake discs being the number one cause of squealing brakes.

Brake discs
Discs must be smooth, clean and flat to provide optimum braking. If the brake disc is rough, warped, scored or glazed the pads are going to vibrate or chatter every time you apply the brakes. If the brake discs are to thin the brake system will operate at a higher temperature resulting in glazed pads. For every 1mm taken of a disc it adds between 80-100 degrees to the operating temperature of the brake system.

Brake pad vibration
Another form of brake squeal is caused by the Brake Pad vibrating when brake pressure is applied. Heavy braking usually stops the squeal because the extra pressure dampens the vibration. If heavy braking does not stop the squealing it is a sign of a significant problem. Squealing that appears under light braking is not a safety concern; it is just very annoying.

When this type of squealing occurs it is usually the leading edge of the Brake Pad that is in contact with the rotor causing a twisting force on the pad making the trailing edge want to lift away from the disc.

Vibration dampers
One option to help reduce the Brake Pad squeal is to fit Brake Pad vibration damper pads. The vibration dampers are a self-stick fibre material shim that sticks to the back of the brake pad. Some Brake Pads have a spring at the back of the backing plate located in the middle of the pad. The spring fits tightly into the piston with the fibre shim sticking to the back of the brake pad. The theory is that the fibre shim will help cushioning the vibration of the brake pad.

Anti-squeal compounds
A second option is to coat the back of the Brake Pad with a quality anti-squeal compound. This is applied to the back of the brake pad. It is said that a combination of vibration dampers and a coating of anti-squeal compound usually reduces low speed squeal.

posted by ece 90 brake testing at 9:59 AM 4 comments links to this post

Friday, October 13, 2006

Dynamometer test results

Dynamometer Test Results and interpretation:
W.S. Scholtz
dynamometer testing results

The Test Results reported comply with both the ECE 90 and VC8053 regulations. By looking at the call-outs 1 to 4 in Fig. 2a above the reader is referred to a point by point explanation of the various results that is presented.

In the centre column a value of 1016 Nm was inserted. This is a very important value and is used as a base point for the % Difference calculation that appears in the 3rd column. This value is obtained by fitting a set of Original Equipment (OE) brake pads in the dynamometer and then to test it to the relevant amount of stop applications to the various pressures and speeds as is stipulated in ECE 90 and VC8053 regulations. This is a test that only needs to be done once to obtain this value. By selecting the pad reference to be tested this value is drawn from a database of OE tested pads and is inserted into the test program. It follows that this value is different from reference to reference.

These values, as is recorded in column 1, are the average of stops as is done during the Speed Sensitivity Test. See Fig. 2b. The value of importance is marked by the grey dots and is the average torque taken over 3 stops for the relevant speeds as shown. The Type-O (40 km/h) average is shown but does not form part of the % Diff. calculations. Although it is a meaningful and interesting value it is not required by both Regulations. Of interest to the reader at this point is to observe that all these values are not far from the recommended OE value as discussed in 1 above. By observing this the reader should get a sense of the fact that the pad that was tested compares well with an OE supplied brake pad. See the Speed Sensitivity discussion below for a better understanding of these values and how they were measured. The core idea is to understand that they are the average torque’s taken over 3 stops for the relevant speeds as shown. (These stops refer to points 4 to 7 in the Test Sequence as presented above.)

The value in the centre column is the same as the value in 1 above, the OE requirement. The value, 650 in this case, is the Residual Performance Test result. (See point 12 of the Test Sequence.) The 64% reported is the percent calculation between the residual (hot performance) and cold performance Value. Regulations ECE 90 & VC8053 require that the hot performance of the samples on test not be less than 60% of the performance obtained when the pads were cold. The pad in this instance also passes the test. An interesting fact is that an OE pad does not have to pass this specific requirement!

This residual value after the 2nd Fade is for observation purposes only and not a requirement. It can be noted that both these residual values does not differ much which is also a good sign.

Fig. 2b

Refer to points 5 to 8 of the Test Sequence as described above. Also see point 2 of Fig. 2a where the results of these stops are reported.

The 1st Speed Sensitivity section of the test is a requirement in both regulations. These Type-O stops are plotted as in the graph above to supply a graphical indication of the test. For instance, at 40 Km/h, the average of the 3 stops, a Friction Co-efficient (Mu) of about 0.36 was achieved. At 80 Km/h the Mu was almost 0.4! (Mu, the Friction Co-efficient is simply put the value obtained by dividing the clamping force of the calliper by the driving force of the disk. Mu is therefor simply a ratio and has no “magic” attached. – The writer will soon publish a full article explaining Friction Co-efficient (Mu) in more detail.

This is an repeat of the stops done in 5 above but after the fade tests have been done as per point 11 of the Test Interpretation described above.

During the Cold Performance Equivalence Test 6 stops are made from 80km/h allowing the stop to zero. The stops are made at increments of pressure specified in bar, whilst the torque, reported in Nm is recorded. These stops are then plotted as per the blue line in the graph above.

The lines in red indicate the upper and lower limits as is specified by Regulation ECE90. It is required that the torque curve obtained be within the limits in the upper two thirds of the graph. It is clear from this graph that this test passes the requirement. It follows that if the brake pads being tested do not comply the graph will be plotted well below the bottom limit and typically curving downwards.

Fig.2c

Fade Test Section

This indicates the pressure (information only) at which the fade test was conducted as per calculations done by the test software. (See 10. of the Test Interpretation above) The lower this pressure is the better the test pad performs. In this instance, with a test pressure of 31 bar the test pad performs well and it is close to the test pressures reported for OE pads of the same reference.

During the fade test 15 brake applications are done at very short intervals from fairly high speed. The temperature versus the friction co-efficient is plotted together. During these stops pressure is applied which allows the pad to be tested to become very hot and as a result one can observe the behaviour of the test pad during high temperature applications. An inferior test pad will fade drastically, especially during the 1st 7 stops after which it will recover somewhat. This is also referred to as Green Fade (Please see the previous article “Burnishing of Brake Linings” for a full explanation of Green Fade)

After completion of the total Dynamometer test the Wear and Mass loss is calculated and reported in this position. Although this is not a wear test per say it does give one an idea of durability, especially when compared to other tests. There are specifically designed wear tests but is not within the scope of this article. Mass loss is of interest to the manufacturer of the brake pad and is specific to the friction material being tested. It is not an indication of pad performance as such and is of academic value only to the layman.

This graph shows a second fade test and is not required by Regulation ECE90 requirement of Safeline as a further indication of pad performance. Temperature and Mu is plotted for a further 5 brake applications.

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posted by ece 90 brake testing at 9:20 AM 0 comments links to this post

Thursday, September 07, 2006

ECE regulation 90 and brake testing

“January 2004 – Bad brakes make trucks death traps”
Seventy percent of trucks inspected by road traffic police during a blitz operation on KwaZulu-Natal roads last week were found to have defective brakes….
http://www.rra.co.za/media.cgi?id=4054&action=det

“November 2004 - 'Death-trap taxis have no place on our roads' (2004)”
The traffic officers thought it was a can of cooldrink on the minibus taxi's dashboard - but they were about to be stunned. They found there was a pipe attached to the can that led to the brake fluid reservoir in the engine compartment. The driver was continuously pouring brake fluid into the can while driving. This was just one of the horrifying defects found by Johannesburg Metro Police Department (JMPD) officers conducting raids on taxis as part of their 500-day Operation Token Days, which includes the blitzing of taxis at ranks… (Ref. IOL.co.za, 5 November 2004)

Radebe blames brake failure in bus accidents (2006)
Brake failure was a major factor in a recent spate of bus accidents, Transport Minister Jeff Radebe said on Thursday. "Buses involved in these accidents are clearly old and not roadworthy," he told a SA Bus Operators Association (Saboa) conference in Pretoria. In some instances, buses were fitted with new parts to pass roadworthy tests, after which they were removed. Operators whose buses crashed because of negligence, recklessness and unroadworthiness would be held responsible, he warned. Radebe said all bus operators receiving state subsidies will have to renew their fleets and undergo regular testing at authorised facilities…
http://www.rra.co.za/media.cgi?id=10399&action=det

The above headlines extracted from articles and news sites, are just a couple of examples where brake failure have been identified as the major cause of accidents and potential deaths on South African roads. Taxis and buses are however not the only culprits. Every vehicle owner that service their own vehicle, using counterfeit brake pads in order to save a couple of Rand, risk not only their own lives but also those of their families and other drivers on the road. In this article we will take a look at the importance and reasons for using tested, standards compliant brakes.

When should I replace my brakes?
Symptoms of brake failure:

Noises
Your brake system may be crying for help if you're hearing strange noises when you depress the brake. Two of the most common are squeaks and grinding.

Squeaks
Friction from the brake lining causes heat. Under extreme conditions this can damage the pads and/or lining, brake drums and rotors.

Grinding
Metallic grinding sounds indicate your brake pads are worn through. Metal-to-metal contact will damage drums or rotors.

Low or Fading Brake Pedal
Do your brakes require pumping to stop the car? Does the pedal sink to the floorboard when you're stopped at a light? There may be a leak in the brake system, air in the brake lines, or the need for a brake adjustment.

Pulling to one side or brake drag
Worn or uneven brake linings or a damaged brake line can cause your vehicle to pull to one side. Brakes that are out of adjustment or have contaminated fluid can cause brakes to drag.

Brake testing and the importance of brake pad certification – ECE R 90 and VC8053

ECE R90 is a European standard for brake components that requires brake manufacturers to conform and guarantee to the original equipment standards as far as performance and quality is concerned. Products complying to these standard carry an “E” mark on products and packaging. In Europe brake pads cannot be used or sold unless they carry this mark proving that they performance and quality standards compliant.

Most countries around the world are following suit by setting standards to which brake pads have to comply.

Regulation VC8053 is minimum specification published in the Government gazette No. 22014 of 2 February 2001, to which brake lining assemblies in South Africa has to comply and this specification is regulated by the SABS.

The tests for both these regulations consist of laboratory and road tests – we will not go into detail about it but rather summarize the requirements:

Brake pad road tests:

A series of 0-type standardisation tests – braking suddenly under different conditions of vehicle speed and load with the aim to test the correct response in emergencies, parking and different braking situations.

Loss of efficiency when warmed up – In the first test the brake is used 15 times in succession to test its performance under different conditions. In the process, the brake warms up. In the last instance its performance is measured and checked for correct operation after which the results are compared to brake performance when the brakes are cold.

Speed-sensitivity test – The pressure is identified in the previous test to obtain a deceleration of 5m/s2. The same kind of test is repeated at 65 km/h, 90km/h and 135km/h in order to check that the brake’s deceleration is maintained irrespective of the speed at which the vehicle is traveling.

Brake pad laboratory tests:
Once the road tests are completed, mechanical laboratory tests are done:

Compressibility test – the compressibility of the brake pad should not exceed 5% of its thickness at 400 deg. C.

Resistance to brake seizure – this test simply determines the adherence of the friction material to the metal support.

Once the tests are completed an approval number is issued and it is compulsory that the brake pads and packaging contain the specific number – example: E1 XXXXX. Packaging should be tamper proof and contain instructions in the local language where the product will be sold.

Standards compliant brake pads will not only ensure roadworthy vehicles but also ensure safety for both the driver and their passengers when it is needed most. So all vehicle owners are urged to ensure that the replacement brake pads they purchase complies to industry requirements and standards.

Please visit ECE90 brake testing for details of our services.

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posted by ece 90 brake testing at 11:42 AM 0 comments links to this post

Thursday, August 17, 2006

Dynamometer test design

by W.S. Scholtz
It is logical to conclude that dynamometer tests will be designed using the ECE90 and VC8053 specifications as a guide. These specifications are specific about the required testing and go as far as to supply the pressures, speeds, temperatures and torque’s required to do the testing.

A test report should supply the required results in a format that would be recognised by engineers world-wide. Such a report is supplied by ECE-90 Brake Testing (Pty) Ltd and is discussed in some detail below.
dynamometer test design

Fig. 2 Dynamometer Results Data Sheet

Test Interpretation

Dynamometer Test Overview

A short overview of the Test Sequence will be presented below, followed by a more detailed explanation of each stage supported by presenting actual portions of the complete test sheet that is shown above. This will assist the reader to have a better understanding when interpreting a test.

Brake pad bedding-in procedure.
In order to do a test the friction surface of the pad need to be bedded-in first of all. This is to ensure a proper contact surface between disk and pad. (For the same reason one should drive careful for the 1st 100 km’s when a vehicle was fitted with new pads. Also see article on Burnishing) There are proposed bedding-in procedures in existence but this portion of the test is not regulated as such. It is therefore up to the manufacturer to specify a specific and suitable procedure. For this reason it is common that a full dynamometer test is used for bedding-in.

Test Preparation.
After the bedding-in cycle the pads are removed from the calliper, weighed and measure for thickness. The pads are then replaced when the weight and thickness measurements as well as the other relevant information have been entered into the control program. (See Fig. 2 above, the General Information call-out.)

3 stops at 30 km/h are then done to heat up the brake pad samples but are not reported on the Test Sheet.

3 stops at 40 km/h are done at the predetermined pressure. The average torque is inserted under Test Results Type-O (40 km/h). (VC8053 & ECE90 requirement) – See plot in Speed Sensitivity area

3 stops at 80 km/h are done at the predetermined pressure. The average torque is inserted under Test Results Type-O (80 km/h) (VC8053 & ECE90 requirement) – See plot in Speed Sensitivity area

3 stops at 120 km/h are done at the predetermined pressure. The average torque is inserted under Test Results Type-O (120 km/h) (VC8053 & ECE90 requirement) – See plot in Speed Sensitivity area

3 stops at 160 km/h are done at the predetermined pressure. The average torque is inserted under Test Results Type-O (160 km/h) (VC8053 & ECE90 requirement) – See plot in Speed Sensitivity area

3 stops then done to calculate maximum pressure values for the Cold Performance Equivalence Test as well as the pressures for the residual performance test. These are not reported.

6 stops are then done at 80Km/h but at increasing pressures for the Cold Performance Equivalence Test. – An ECE90 requirement only.

A further 3 stops are done to determine the pressure to be used for both Fade Tests.

1st Fade Test – 15 repeated stops at regular intervals (eg. 45 sec. intervals from 120km/h to 60km/h.)

1-off residual performance stop to determine the hot performance of the brake pads.

2nd Fade Test – 5 more applications done at similar intervals as 1st fade (A Safeline only requirement.)

2nd residual performance stop (a Safeline requirement)

Steps 4 to 7 then repeated – This is done to see the change in performance after the pads were exposed to a high heat cycle (This is done for information purposes only and is not a requirement)

TEST COMPLETED AND PRINTED

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posted by ece 90 brake testing at 10:34 AM 0 comments links to this post

Thursday, July 20, 2006

Dynamometer testing

As part of our ongoing explanation about Brake testing, we take a look this week at the reasons behind the testing of brake lining assemblies.

Overview
It is mandatory that all replacement brake lining assemblies in South Africa complies with a minimum specification as is published in the Government Gazette No. 22014 of 2 February 2001. This specification is also known as VC8053.

The above specification is regulated by the South African Bureau of Standards (SABS).

In addition to this, a new and more stringent specification will soon be adopted and is referred to as ECE Regulation 90. This regulation is already in place in Europe. Any South African manufacturer that wishes to export to Europe and who complies with this regulation will obviously be favoured.

In principal ECE Regulation 90 tests uses some portions of the VC8053 specification but, in addition, specifies road tests. ECE Regulation 90 is also vehicle or reference specific. It does not, however, provide the manufacturer with generic compliance, as is the case with VC8053.

Next time we will take a look at the test design.

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posted by ece 90 brake testing at 11:26 AM 0 comments links to this post

Friday, July 14, 2006

ECE90 Brake Testing level 4 BEE certification

ECE90 Brake Testing laboratory announced this week that they received level 4 Contributor certification with low fronting risk certification in terms of the broad based black economic empowerment (BEE) Act 53 of South Africa 2003.

This implies that ECE90 Brake Testing qualifies for the following:
1. Preferential procurement by local and central Government
2. Issuing of licenses and concessions by Government agencies
3. Preferential procurement by private sector to improve BEE score.

For more details, please read the ECE90 Brake Testing BEE press release.

posted by ece 90 brake testing at 8:27 AM 0 comments links to this post

Thursday, June 15, 2006

Modern brake dynamometer

by W.S. Scholtz

A modern brake test Dynamometer uses an absorption unit, in this case a brake disk and calliper assembly, to dissipate or convert the power or kinetic energy into heat or thermal energy. The power used to do this is calculated as follows:

Horsepower = Torque x RPM / 5252
Remember that RPM is Revolutions per Minute and the unit for Torque in this instance is measured in foot/pounds. 5252 is a constant and is also derived from Watt’s observation.

The above imperial system for units of measure is used to provide the Horsepower formula as it describes the origins of the measure of power best. The SI system or metric system uses, amongst other units, kilowatts (Kw) in place of horsepower and Newton-meter (Nm) for torque.

With a modern dynamometer, such as is used by ECE-90 Brake Testing (Pty) Ltd, the Dynamometer Test Report uses Newton Meter (Nm) and the Friction-coefficient (Mu) as a unit and ratio of measure respectively.

Basic construction:
dynamometer construction

A Dynamometer consists of the following main elements. (See Fig.1 above)

The drive-train (revolving assembly) consists of the following elements: Motor (1), Interchangeable flywheels (2) and Brake Disk (3). The flywheels and brake disk is matched to the part number to be tested.

The test bed (mounted in bearings aligned with the drive-train but held in position with the load arm. It has therefor the potential to rotate but is retained by the load arm) The test bed consist of the following elements: Calliper & Adapter (4), Power transfer axle (5), Load Bearing Arm (6) and Loadcell.

Please visit Passenger vehicle dynamometer brake testing for more details and services on offer.