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Council Directive of 26 July 1971 on the approximation of the laws of the Member States relating to the braking devices of certain categories of motor vehicles and of their trailers (71/320/EEC) (repealed)
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- Revised 01/11/20140.44 MB
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- Revised 01/05/20041.16 MB
- Revised 24/10/20021.16 MB
- Revised 07/04/19981.14 MB
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- Revised 30/03/19880.84 MB
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- Revised 24/04/19790.57 MB
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[F1Appendix 4 Determination of friction behaviour by machine testing
Textual Amendments
1. INTRODUCTION U.K.
1.1. Samples of a replacement brake lining assembly type shall be tested on a machine capable of generating the test conditions and applying the test procedures described in this Appendix. U.K.
1.2. Test results shall be evaluated to determine sample friction behaviour. U.K.
1.3. The friction behaviour of samples shall be compared to assess conformity with the standard registered for a replacement brake lining assembly type. U.K.
2. EQUIPMENT U.K.
2.1. The machine shall be designed to accept and operate a full size brake similar to those fitted to the vehicle axle used for approval testing to point 5 of this Annex. U.K.
2.2. The disc or drum rotational speed shall be 660 ± 10 min -1 without load and shall not fall below 600 min -1 on full load. U.K.
2.3. The test cycles and brake applications during the cycles shall be adjustable and automatic. U.K.
2.4. Output torque or brake pressure (constant torque method) and working surface temperature shall be recorded. U.K.
2.5. Provisions shall be made to direct cooling air across the brake at a rate of 600 ± 60 m 3 /h. U.K.
3. TEST PROCEDURE U.K.
3.1. Sample preparation U.K.
The manufacturer's bedding schedule shall ensure a minimum of 80 % surface contact area for pad assemblies without exceeding a surface temperature of 300 °C and 70 % surface contact area for the leading shoe assemblies without exceeding a surface temperature of 200 °C.
3.2. Test schedule U.K.
The test schedule comprises a number of consecutive braking cycles each containing χ braking intervals of 5 seconds brake applied followed by 10 seconds brake released.
The following two methods may be used alternatively:
3.2.1. Test schedule with constant pressure U.K.
3.2.1.1. Pad assemblies U.K.
The hydraulic pressure p under the piston(s) of the calliper shall be constant following the formula:
M d
=
150 Nm for A k ≤ 18,1 cm 2
M d
=
300 Nm for A k > 18,1 cm 2
A k
=
area of calliper piston(s)
r w
=
effective radius of disc
| No of cycle | Number of brake applications χ | Initial brake rotor temperature (°C) y | Maximum brake rotor temperature (°C) | Forced cooling |
|---|---|---|---|---|
| 1 | 1 × 10 | ≤ 60 | open | no |
| 2-6 | 5 × 10 | 100 | open (350) | no |
| 7 | 1 × 10 | 100 | open | yes |
3.2.1.2 Shoe assemblies U.K.
The mean contact pressure at the brake lining working surface shall be constant at 22 ± 6 N/cm 2 calculated for a static brake without self-energising.
| No of cycle | Number of brake applications χ | Initial brake rotor temperature (°C) | Maximum brake rotor temperatur (°C) | Forced cooling |
|---|---|---|---|---|
| 1 | 1 × 10 | ≤ 60 | 200 | yes |
| 2 | 1 × 10 | 100 | open | no |
| 3 | 1 × 10 | 100 | 200 | yes |
| 4 | 1 × 10 | 100 | open | no |
3.2.2. Test schedule with constant torque U.K.
This method applies only for pad assemblies. The brake torque shall be constant within a tolerance of ± 5 % and adjusted to guarantee the maximum brake rotor temperatures given in the table below.
| No of cycle | Number of brake applications χ | Initial brake rotor temperature (°C) y | Maximum brake rotor temperature (°C) | Forced cooling |
|---|---|---|---|---|
| 1 | 1 × 5 | ≤ 60 | 300-350 | no |
| 2-4 | 3 × 5 | 100 | 300-350 | no |
| 5 | 1 × 10 | 100 | 500-600 | no |
| 6-9 | 4 × 5 | 100 | 300-350 | no |
| 10 | 1 × 10 | 100 | 500-600 | no |
| 11-13 | 3 × 5 | 100 | 300-350 | no |
| 14 | 1 × 5 | ≤ 60 | 300-350 | no |
3.3. Evaluation of test results U.K.
Friction behaviour is determined from the brake torque noted at selected points in a test schedule. Where brake factor is constant, e.g. a disc brake, brake torque may be translated to coefficient of friction.
3.3.1. Pad assemblies U.K.
3.3.1.1. The operational coefficient of friction (μ op ) is the mean of the values recorded during cycles two to seven (constant pressure method) or during cycles 2-4, 6-9 and 11-13 (constant torque method); measurement being made one second after commencing the first brake application of each cycle. U.K.
3.3.1.2. The maximum coefficient of friction (μ max ) is the lowest value recorded during all cycles. U.K.
3.3.1.3. The minimum coefficient of friction (μ min ) is the lowest value recorded during all cycles. U.K.
3.3.2. Shoe assemblies U.K.
3.3.2.1. The mean torque (M mean ) is the average of the maximum and minimum values of brake torque recorded during the fifth brake application of cycles one and three. U.K.
3.3.2.2. The hot torque (M hot ) is the minimum brake torque developed during cycles two and four. If the temperature exceeds 300 °C during these cycles the value at 300 °C is to be taken as M hot . U.K.
3.4. Acceptance criteria U.K.
3.4.1. With each application for approval of a brake lining assembly type there shall be submitted: U.K.
3.4.1.1. for pad assemblies, values for (μ op ), (μ min ) en (μ max ) U.K.
3.4.1.2. for shoe assemblies, values for M mean and M hot . U.K.
3.4.2. During production of an approved brake lining assembly type, test samples must demonstrate compliance with the values registered under point 3.4.1. of this Appendix with the following tolerances: U.K.
3.4.2.1. for disc brake pads: U.K.
μ op ± 15 % of registered value
μ min ≥ registered value
μ max ≤ registered value
3.4.2.2. for simplex drum brake linings: U.K.
M mean ± 20 % of registered value
M hot ≥ registered value.]
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