Project Group VDA Ad hoc AK Betriebsfestigkeit Radbremse · stresses of the service brake and...

VDA Operating Strength for Brake Calipers Requirements and Testing

311

The objectives for this (non-binding) VDA recommendation by the German Association of the Automotive Industry are as follows: To define the technical standards for the operational strength testing of passenger car brake calipers of vehicle categories M1, M1G and N1. To provide a summary of necessary operating strength tests for the development release of brake calipers.

Project Group VDA Ad hoc AK Betriebsfestigkeit Radbremse

Publisher: Verband der Automobilindustrie Behrenstrasse 35 10117 Berlin Telefon 030/897842-0 Telefax 030/897842-606 Internet: www.vda.de

Copyright: Reprinting and any other form of reproduction is permitted only with reference to the source.

VDA-Empfehlung 311 Version 1.2 - Feb. 2017 page 2

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Disclaimer

VDA recommendations are available to the public. They offer orientation for all interested companies, but do not take into consideration any general conditions for specific cases. They have to be interpreted by each party or company involved in the processes. At the time of release of each VDA recommendation, the document is considered to represent existing knowledge and state of the art. It is the ultimate responsibility of the users of this document to access that it is adequate for the design(s) involved. Liability by VDA and those who are involved in the VDA recommendations is excluded. Users are asked to bring to the attention of the VDA any errors found with the document and to become involved in the continuing standardization process. The official language of this document is German. The English translation is for information only. In case of dispute over translation the German text shall prevail.

VDA-Empfehlung 311 Version 1.2 - Feb. 2017 page 3

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Content

1 Basics ........................................................................................................................... 4

1.1 Scope .................................................................................................................... 4

1.2 Nomenclature ........................................................................................................ 4

1.3 Evaluation Concept ............................................................................................... 5

1.3.1 Service Load Test Caliper Assembly ................................................................ 6 1.3.2 Simplified testing in single-stage ....................................................................... 6 1.3.3 Parallel endurance test ..................................................................................... 6

2 Requirements / load assumptions ................................................................................ 7

2.1 Service brake ........................................................................................................ 7

2.1.1 Standard Collective ........................................................................................... 7 2.1.2 Traction Collective ............................................................................................ 7 2.1.3 Collective Data .................................................................................................. 8

2.2 Park Brake ............................................................................................................ 9

2.2.1 Brake torque from load case “parking on a slope” ............................................ 9 2.2.2 Clamp loads in manual operation ..................................................................... 9 2.2.3 Clamp loads in electric-mechanical operation (EPB) ........................................ 9

2.3 Thermal stress..................................................................................................... 11

3 Operational Strength Tests ......................................................................................... 13

3.1 SN test ................................................................................................................ 13

3.1.1 Test Conditions ............................................................................................... 13 3.1.2 Test Evaluation ............................................................................................... 13

3.1.3 Statistical safety factors .................................................................................. 14 3.1.4 Determination of minimum cycles requirement ............................................... 15

3.1.5 Fatigue life estimation ..................................................................................... 15

3.2 Single-stage test of caliper assembly .................................................................. 16

3.2.1 Test setup ....................................................................................................... 16

3.2.2 Test execution ................................................................................................ 17 3.2.3 Requirements ................................................................................................. 18

3.2.4 For brake calipers with integrated parking brake ............................................ 19

3.3 Service Load Test (SLT) ..................................................................................... 20

3.3.1 Test setup ....................................................................................................... 20 3.3.2 Test execution ................................................................................................ 20

3.3.3 Test requirements ........................................................................................... 21

3.4 Parking brake actuator endurance test ................................................................ 21

4 Overload tests ............................................................................................................ 22

4.1 Static strength tests ............................................................................................. 22

4.1.1 Test setup and execution ................................................................................ 22 4.1.2 Requirements ................................................................................................. 22

4.1.3 Additional requirements for brake calipers with integrated parking brake ....... 22

4.2 Burst pressure test .............................................................................................. 23

4.2.1 Test setup and execution ................................................................................ 23 4.2.2 Requirements ................................................................................................. 23

5 Hydraulic leakage test ................................................................................................ 23

5.1 Test setup and execution .................................................................................... 23

5.2 Requirements ...................................................................................................... 23

VDA-Empfehlung 311 Version 1.2 – Feb. 2016 page 4

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1 Basics

1.1 Scope

This recommendation covers all requirements with regard to operating strength, which must be met by a passenger car caliper on public roads, even under high loading. It does not apply to special operating conditions such as motorsport events. In these cases, special tests may be needed with more severe or different requirements. Alternative test methods may be used and have to be coordinated among development partners. The correlation must be demonstrated.

1.2 Nomenclature

Formula character

Definition

C Confidence interval

D Damage sum as defined by Palmgreen & Miner

f Test frequency

F1, FA, FB, Fi Load at load step 1, A, B, i

FD Load step of the deviation point of the SN curve to the theoretical fatigue limit

𝑭�� Average value at load level i

𝑭(𝒙;𝝀) Density function of the exponential distribution

Hi Cumulative frequency of the load collective up to the level i

H0 Cumulative frequency of the total load collective

JC, n Risk factor for a confidence level C at n single experiments

JL Life-related safety number for the extrapolation to a given probability of the lognormal distribution

k Slope exponent of the SN curve (straight line of finite life fatigue strength in a double logarithmic coordinate system)

L Component fatigue life

LKollektiv Vehicle life represented by the load collective

M Brake torque

MHA Brake torque rear axle

MST Brake torque for static strength testing

MVA Brake torque front axle

n Sample size

ni Single frequency of load step i

N Cycle count

N1, N2, Ni Bearable number of load cycles at load step 1, 2, i

N1k Damage-equivalent number of load cycles at the 1g-load level

N1Park Damage-equivalent number of load cycles of the parking brake at the 1g-load level


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𝐍𝐢,𝟓𝟎% Number of load cycles of the regression line at the individual load levels of the individual experiments

N1rev Test load cycles at the 1g-load level in reverse direction

N1spec Test load cycles at the 1g-load level in forward direction

N1WL Number of load cycles of the S/N-curve at the 1g-load level for 50% survival probability

ND Number of load cycles of the deviation point of the SN curve to the theoretical fatigue limit

Nsoll Required number of load cycles for the service load test

p Hydraulic brake pressure

pHA Hydraulic brake pressure at rear axle

pVA Hydraulic brake pressure at front axle

R survival probability

RT Ambient (room) temperature

S standard deviation

SF Statistical safety factor

Slog Logarithmic standard deviation

t time

TN Ratio between 10% and 90% survival probability

U Quantile of the standard normal distribution

Uc Quantile of the standard normal distribution for the confidence interval C

X Scaled load

x Gradient of the road inclination

λ Failure rate of the exponential distribution

1.3 Evaluation Concept

In principle, all brake calipers must endure with sufficient safety the stresses of service braking and based on its application, additional stresses from parking brake load cycles. This recommendation identifies methods to run time-consuming endurance test in parallel and to submit only the relevant components to the combination of loads in accelerated tests.


Copyright: VDA

Figure 1: Flowchart of different strength assessment methods

1.3.1 Service Load Test Caliper Assembly

Regardless of their design all calipers can be tested in service load tests. The stresses of the service brake and possibly existing integrated parking brake are thereby mixed randomly. For calipers manufactured from light metal materials, additional thermal and corrosive stresses must be considered.

1.3.2 Simplified testing in single-stage

In the case of a brake caliper made from cast iron materials, the simplified single-stage test can be used. Thermal and corrosive stress can be omitted here. In the case of an integrated parking brake, it is imperative to carry out the single-stage test of the service brake and the endurance test of the parking brake with the same components.

1.3.3 Parallel endurance test

The parallel endurance testing can be used for all materials. Components that are loaded by service brake and parking brake, must be subjected to the combination of these load collectives in a separate component test. Thermal and corrosive stresses must be considered for the relevant components from light metal materials. The single-stage test cannot be used for proof of strength for these components.


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2 Requirements / load assumptions

2.1 Service brake

The foundations for the operating strength analysis are the collectives described below. The Standard Collective (SK) and the Traction Collective (TK) cover also the respective vehicle manufacture specific design courses in addition to normal customer operation. The Traction Collective is applicable to vehicles with a driven rear axle, equipped with automatic traction control, and only on rear brake components that are loaded by brake pressure or clamp load. The Traction Collective covers the increased clamping force needed, in the case of the brake fade during intensive use of traction control. To all other applications the Standard Collective applies. Question: Answer

Vehicle equipped with traction control? Yes No

Caliper of a driven rear axle? Yes No

Loaded by brake pressure or clamp load? Yes No

Applicable load collective: TK SK

Table 1: Decision matrix for load collective selection

The respective collectives apply to a vehicle life span of 300,000 km with a probability of occurrence of the collective of 1%.

The entire load collective results then from the assumption “4 brake applies per kilometer” to 1.2 x 106 brake applies. Data analysis from previous extensive vehicle testing has shown that the brake load collectives generally can be expressed using the normal distribution. The equation for the collective normal distribution (without additional loads above the 1g load level) is:

𝐻𝑖 = (𝐻0 − 2149) ∗ 𝑒− ln 𝐻0∗𝑋2+ 2149

2.1.1 Standard Collective

The Standard Collective includes additionally to the normally distributed load collective the specific load cases listed below:

20 brake applies at 1,3-times 1g tangential force (braking on extreme rough road sections, roadway thresholds etc.);

2130 brake applies at 1g load level, covering a severe driving fashion conceivable due to ABS (anti-lock brake system) operation.

2.1.2 Traction Collective

Specific load cases added to the normally distributed load collective are:

80 brake applies at 2-times 1g load level

220 brake applies at 1.6-times 1g load level

1850 brake applies at 1g load level


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2.1.3 Collective Data

Scaled load level X Standard Collective Traction Collective

[g] Single

frequency Sum

frequency Single

frequency Sum

frequency

2 0 0 80 80

1,6 0 0 220 300

1,3 20 20 0 300

1 2130 2150 1850 2150

0,95 3 2153 3 2153

0,9 10 2163 10 2163

0,85 35 2198 35 2198

0,8 105 2303 105 2303

0,75 302 2605 302 2605

0,7 802 3407 802 3407

0,65 1978 5385 1978 5385

0,6 4525 9910 4525 9910

0,55 9595 19 505 9595 19 505

0,5 18 836 38 341 18 836 38 341

0,45 34 175 72 516 34 175 72 516

0,4 57 199 129 715 57 199 129 715

0,35 88 061 217 776 88 061 217 776

0,3 124 215 341 991 124 215 341 991

0,25 159 564 501 555 159 564 501 555

0,2 184 877 686 432 184 877 686 432

0,15 189 938 876 370 189 938 876 370

0,1 167 163 1 043 533 167 163 1 043 533

0,05 115 274 1 158 807 115 274 1 158 807

0 41 193 1 200 000 41 193 1 200 000

Table 2: Service Brake Load Collectives

Figure 2: Service Brake Load Collectives


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2.2 Park Brake

If the brake caliper assembly is not only used as the service brake, but also functions as a parking brake caliper, additional test requirements must be completed by the same components. These include brake torque according to 2.2.1 and clamp loads, depending upon parking brake version after Fehler! Verweisquelle konnte nicht gefunden werden. or Fehler! Verweisquelle konnte nicht gefunden werden.. The brake design must be examined for whether the loads of Fehler! Verweisquelle konnte nicht gefunden werden. and 2.2.2 (or 2.2.3) have to be combined or can be tested separately. The following endurance tests, must be passed as a success runs without failures,

with a sample size n 4. The tests defined in Section 2.2 already include statistical safety factors.

2.2.1 Brake torque from load case “parking on a slope”

5000 cycles

Required brake torque and tangential forces calculated according to parking a fully loaded vehicle on a 20% grade, with an additional 1.5x margin on the calculated loads (component specifically most unfavorable load case)

2.2.2 Clamp loads in manual operation

20 000 cycles

Required clamping forces on the parking brake element of the brake caliper calculated according to parking a fully loaded vehicle on a 20% grade, with an additional 1.5x safety margin on the calculated loads.

2.2.3 Clamp loads in electric-mechanical operation (EPB)

100 000 cycles with the following input parameters:

With superposed temperature profile of the actuator (Fehler! Verweisquelle konnte nicht gefunden werden., Fehler! Verweisquelle konnte nicht gefunden werden. )

With clamp loads according to the system functionalities, i. e. clamp loads in accordance with the gradient distribution from Fehler! Verweisquelle konnte nicht gefunden werden., including voltage and temperature variations.

With hydraulic pressure overlay in accordance to Fehler! Verweisquelle konnte nicht gefunden werden..

2.2.3.1 Temperature profile:

step Temperature

[°C] cycles

1 23 5000

2 85 250

3 65 1500

4 45 13 250

5 23 1000

6 0 1750

7 -20 1750

8 -40 500

Table 3: Temperature profile EPB-Actuator

Figure 3: Temperature profile EPB-Actuator

The temperature profile has to be repeated 4-times for 100 000 cycles.

-40-30-20-10

0102030405060708090

100

0 10000 20000Act

uat

or

tem

per

atu

re

[°C

]

cycles


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The defined temperatures must be ensured for all efficiency-relevant components.

2.2.3.2 Electric-mechanical clamp load

For the evaluation of the operating strength in the component test (e.g. caliper) the average clamping force is assumed to apply. The average clamp force adjusts itself system-characteristically as function of the temperature. An exemplary illustration of how the average clamp force varies with temperature is shown in Fehler! Verweisquelle konnte nicht gefunden werden.. The endurance test of the EPB actuator should be controlled with a ECU and actual software. The clamp loads will adjust themselves accordingly over temperature ranges and cycle number.

Figure 4: EPB clamp load over temperature

2.2.3.3 Hydraulic pressure overlay

The hydraulic pressure overlay is based on an assumed exponential distribution of

road gradients, with 1% of operations at gradients ≥ 20%

𝐹(𝑥;𝜆) = 1 − 𝑒−𝜆𝑥 with

𝜆 = −𝑙𝑛1%

20%= 23

A discretized version of the gradient distribution results in Fehler! Verweisquelle konnte nicht gefunden werden.. According to these gradients, the required holding pressure for a specific vehicle design can be calculated.


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The required holding pressure is increased by 33% to account for over-pressurization by the driver:

gradient [%] 25 - >30 20 - 25 16 - 20 12 - 16 8 - 12 4 - 8 0 - 4

Percentage of operations

0,3% 0,7% 1,5% 3,8% 9,5% 24% 60,2%

Pressure level [g]

0,38 0,32 0,26 0,21 0,16 0,11 0,05

Table 4: Distribution of gradients and hydraulic pressure overlay

2.3 Thermal stress

The application of this recommendation on components made of light metal materials requires the consideration of thermal aging and corrosion. In addition to the mechanical load collectives, the changing thermal and corrosive stresses described below are applied. The temperature profile is based on measurement results from a vehicle test in a specific sequence braking program; the mechanical loads from that are covered by the brake load collective. The test sequence with 38 individual steps corresponds to the damage equivalent of 1 year or 30,000 km mileage. To obtain a similar mileage equivalent to the service brake collective of 300,000 kilometers, a total of 10 repeats of the 38 individual steps are necessary.


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Temperature and corrosion profile for light metal brake calipers:

Program step

Temperature sequence Duration

1 heating from ambient temp to 100°C

25 min

2 heating from 100°C to 170°C 15 min


4 holding 200°C 2 min

5 cooling from 200°C to 170°C 15 min








13 cooling from 100°C to Rt 15 min

14 heating from Rt auf 100°C 25 min























37 cooling from 100°C to Rt 15 min

38 holding Room temperature Salt Spray Test with NaCl 5% acc. EN ISO 9227

65 min

478 min

Table 5: Temperature profile for the aging of light metal alloys, including corrosion


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3 Operational Strength Tests

3.1 SN test

For each released caliper assembly, it is necessary to determine an SN curve. This is determined either with the complete caliper assembly or with its weakest component. The weakest component is the component which has the lowest life on the 1g-load level and therefore will fail first in the single-stage test.

3.1.1 Test Conditions

Sample size: a minimum of 12 (caliper assembly or component)

Either on 2 load levels (at least 6 parts per load level), in which the upper load level fatigue lives geometric mean is < 200 000 cycles and the lower load level geometric mean is > 450 000 cycles.

Or alternatively on multiple load levels (at least 4). Test loads shall be distributed uniformly in the range of fatigue strength to obtain fatigue live results between 50 000 cycles and 600 000 cycles. Repeated tests at load levels are acceptable.

The failure criterion is a technical crack initiation, which is detectable by the usual, operationally applicable inspection procedures on site. It must be ensured that at the end of the test, all test samples have similar crack lengths.

3.1.2 Test Evaluation

In principle, a regression line is calculated using the method of least error squares from the fracture load cycles and their associated load levels. In the range of fatigue strength, the SN curve can be described by the following equation:

𝐹𝐴𝑘 × 𝑁𝐴 = 𝐹𝐵

𝑘 × 𝑁𝐵 This results in a straight line in double-logarithmic scale, with the exponent k as a measure of the linear slope. The fatigue strength range of the SN curve is uniquely described using a point on the line (position), the slope and the scatter of test data. These parameters are calculated according to the following equations. Slope exponent k:

𝑘 = −∑(𝑙𝑔𝐹𝑖 − 𝑙𝑔𝐹𝑖

) ∙ (𝑙𝑔𝑁𝑖 − 𝑙𝑔𝑁𝑖 )

∑(𝑙𝑔𝐹𝑖 − 𝑙𝑔𝐹𝑖 )

2

Location of the regression line (load 𝐹𝐷 at 𝑁𝐷 cycles):

𝐹𝐷 = 10(𝑙𝑔𝑁𝐷−𝑙𝑔𝑁𝑖 −𝑘∙𝑙𝑔𝐹𝑖

−𝑘)


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Logarithmic standard deviation:

𝑆𝑙𝑜𝑔 = √1

𝑛 − 1∑(𝑙𝑔𝑁𝑖 − 𝑙𝑔𝑁𝑖,50%)

2𝑛

𝑖=1

Scatter span:

𝑇𝑁 = 10(𝑆𝑙𝑜𝑔∙2∙𝑈) With the 90% quantile of the standard normal distribution parameter U (=1,28155)

3.1.3 Statistical safety factors

Based on analysis of exemplary test results from brake and vehicle manufacturers, key statistical parameters for small samples and population variability have been computed:

𝐽𝐶,𝑛 = 𝑆𝑈𝐶

√𝑛 with:

S = 1.43 (from Slog = 0.155 according TN = 2.5)

n = 4

UC = 1.282 for a confidence level C = 90%

follows: JC,n = 1.26

Although the SN-test sample size is 12 parts, the value JC,4 = 1,26 is used instead of

JC,12 = 1.14, thus an additional safety is achieved for JC,n.

The probability-related safety factor for a required survival probability of 99.9% is computed using:

𝐽𝐿 = 𝑆𝑈 with: S = 1.43 (as above) U = 3.10 for R = 99.9% follows: JL = 3.03

Thus one receives a statistically justified safety factor:

𝑆𝐹 = 𝐽𝐶,𝑛 ∙ 𝐽𝐿 = 3.82

If the experimental scatter span 𝑇𝑁 > 2,5, this safety factor has to be calculated using the actual value of TN.


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3.1.4 Determination of minimum cycles requirement

Using the collectives specified under Section Fehler! Verweisquelle konnte nicht gefunden werden., and depending upon the slope of the S/N-curve (k-value), the damage equivalent cycle count is calculated with the following formula:

𝑁1𝑘 = ∑ (𝐹𝑖

𝐹1)

𝑘

∙ 𝑛𝑖

The assumed condition is that the Miner Number is 1 (D = 1). Depending upon material and constructional layout design of the caliper assembly, a different D-value may be more appropriate. The D-value shall be determined and specified by the brake manufacturer. Using the Miner Number and the statistical safety factor SF from Section Fehler! Verweisquelle konnte nicht gefunden werden. the cycle count for the success run of the caliper assembly in the forward direction is calculated using the following equation:

𝑁1𝑠𝑝𝑒𝑐 =𝑁1𝑘 ∙ 𝑆𝐹

𝐷

The number of reverse stops is calculated using the equation below:

𝑁1𝑟𝑒𝑣 = 0,1 ∙ 𝑁1𝑠𝑝𝑒𝑐

3.1.5 Fatigue life estimation

Using the linear damage accumulation defined by Palmgreen & Miner in their elementary form as a sufficiently conservative lifetime prediction, the component fatigue life can be calculated using the following equation:

𝐿 =𝑁1𝑊𝐿

𝑁1𝑠𝑝𝑒𝑐∙ 𝐿𝐾𝑜𝑙𝑙𝑒𝑘𝑡𝑖𝑣

If the designs will be subjected to additional load collectives, e. g. reverse braking and park brake applications, fatigue life can be calculated using the following equation:

𝐿 =𝑁1𝑊𝐿

𝑁1𝑠𝑝𝑒𝑐 + 𝑁1𝑟𝑒𝑣 + 𝑁1𝑃𝑎𝑟𝑘∙ 𝐿𝐾𝑜𝑙𝑙𝑒𝑘𝑡𝑖𝑣

For example, the damage portions from parking brake loading are calculated by the equation below:

𝑁1𝑃𝑎𝑟𝑘 = ∑ (𝐹𝑖

𝐹1)

𝑘

∙ 𝑛𝑖


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3.2 Single-stage test of caliper assembly

For parts constructed of cast iron, a single-stage test can be run as a simplified proceeding, instead of fulfilling the brake load collective in a service load test (0). This approach does not require testing against a fixed number of cycles with associated scattering; instead, the test continues until it achieves a component-specific minimum number of cycles, which is representing a specific lifetime in years or distance.

3.2.1 Test setup

The caliper can be tested using a positive-fitting test rig or a frictionally-engaged test rig. Positive fitting setup (oscillating disc or lever pulsator): Mounting of the brake caliper assembly on the original steering knuckle or wheel carrier on a pulsating disk, use of brake pads with as little friction as possible that are connected to the brake disk by a triple ball pin. The ball pin is covered with the effective frictional radius of the wheel brake (reff); greased DU* disks are inserted between the original brake pad and the original brake disk for minimizing any friction. *Translator's note: A trade designation; component structure of aluminum base element, bronze and PTFE coating. Frictionally engaged setup (rotating disc): Setup of the brake caliper assembly with the original steering knuckle or wheel carrier on a suitable test rig with a rotating disk (frictionally engagement), whereby the applied braking torque can be controlled per Section (Fehler! Verweisquelle konnte nicht gefunden werden.). Limiting conditions: The brake assembly should be mounted according to drawing specifications if possible (steering knuckle, rotor, hub/bearing, mounting bolts). If production-level components are not available, the caliper can be mounted on a simple but stiff plate. Before production release, the test has to be confirmed using production-level mounting components. Confirmation has been provided if the required minimum numbers of stress cycles of the constant amplitude test is achieved and the fracturing location is identical on a component in the original connection. As an alternative to this, transferability of the results of the test rig setup to the original setup can be corroborated by means of suitable testing and measuring procedures (e.g.: expansion analysis). Those brake components that have a limited service life due to wear-related issues, such as e.g. brake pads and their carrier plates and springs, are to be corroborated with testing in accordance with their required useful life.


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3.2.2 Test execution

To ensure reproducible and comparable results the following requirements must be complied with: The brake torques for front or rear brakes is: MVA = 1 g

MHA = 1 g

Calculated for a fully loaded vehicle, use the higher value of “ideal” and “installed-system” distribution of front and rear torque. Fasteners shall be tightened to drawing specifications. Otherwise with control of yield point and slightly oiled screws. Specified brake torque and hydraulic pressure are required to be within the tolerances below: MVA + 5 % or MHA + 5 %

pVA + 20 % or pHA + 20 %

Respecting these tolerances is mandatory; the braking torque in particular must not exceed the tolerance value during the test run (in particular: no overshoot of M and p out of the tolerance range when starting). The hydraulic pressure has to lead the brake torque while raising pressure. The hydraulic pressure has to lag or fall simultaneously with torque when the pressure is released. Refer to Figure 5 (does not apply to a test setup with a rotating disk, frictional engagement);

Rate of pressure buildup: 500 10 bar/sec.

Figure 5: schematic pressure and torque curves


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3.2.3 Requirements

Additionally to the minimum cycle numbers in forward direction (𝑵𝟏𝐬𝐩𝐞𝐜) also cycles in

reverse direction have to be run. The number of reverse cycles is computed in Section 3.1.4 (𝑵𝟏𝒓𝒆𝒗). The reverse brake torque value is the same as the forward torque value. Table 6 lists the required number of brake cycles for a service-brake-only design for

the rare case where 𝐷 = 1 and 𝑇𝑁 ≤ 2,5:

3.2.3.1 For service brake components -Standard Collective

k-value cycles

𝑁1𝑘

Test cycles forward 𝑁1𝑠𝑝𝑒𝑐

Test cycles backward

𝑁1𝑟𝑒𝑣

2,0 74 546 285 000 28 500

2,5 43 633 167 000 16 700

3,0 26 832 102 500 10 250

3,5 17 329 66 500 6 650

4,0 11 766 45 000 4 500

4,5 8 411 32 500 3 250

5,0 6 334 24 500 2 450

5,5 5 017 19 500 1 950

6,0 4 167 16 000 1 600

6,5 3 608 14 000 1 400

7,0 3 237 12 500 1 250

7,5 2 988 11 500 1 150

8,0 2 822 11 000 1 100

8,5 2 713 10 500 1 050

9,0 2 644 10 500 1 050

9,5 2 604 10 000 1 000

Table 6: test cycles according to the Standard Collective

Sample size n 4 Remark:

The cycle numbers `forward' are rounded up to 500

The load cycles for 'reverse drive' are performed at the beginning of the test (for example: for k = 6,5: first 1 400 LW backwards than 14 000 LW forward)


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3.2.3.2 For service brake components -Traction Collective

The procedure is carried out for rear brakes of vehicles with rear-wheel drive and traction control per Section Fehler! Verweisquelle konnte nicht gefunden werden.. In the special case of a fist-type caliper, this requirement is understood as a pressure test for the caliper housing only. The requirements according to Fehler! Verweisquelle konnte nicht gefunden werden. apply to the brake carrier (see Section Fehler! Verweisquelle konnte nicht gefunden werden.).

k-value cycles

𝑁1𝑘

Test cycles forward 𝑁1𝑠𝑝𝑒𝑐

2,0 75 116 288 000

2,5 44 480 170 000

3,0 28 049 107 500

3,5 19 044 73 000

4,0 14 151 54 500

4,5 11 700 45 000

5,0 10 846 41 500

5,5 11 191 43 000

6,0 12 601 48 500

6,5 15 127 58 000

7,0 18 977 72 500

7,5 24 516 94 000

8,0 32 308 123 500

8,5 43 162 165 000

9,0 58 230 222 500

9,5 79 132 302 500

Table 7: test cycles according to the Traction Collective

Sample size n 4

3.2.4 For brake calipers with integrated parking brake

For calipers incorporating an integrated parking brake mechanism, additional requirements as specified in Section (Fehler! Verweisquelle konnte nicht gefunden werden.) must also be conducted for the same components.


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3.3 Service Load Test (SLT)

This test procedure applies during the release phase of the brake design for all types of material.

3.3.1 Test setup

The representation of the necessary servo-hydraulic testing equipment, as well as the particularly required environmental conditions in a (isolated) temperature/corrosion chamber with correct sequence of time- and temperature-controlled loading (see 2.3) is up to the brake manufacturer. The transferability of the stress conditions at the component between the selected test principle and original building are to be guaranteed. With regard to the positioning of the temperature measurement on the caliper housing, the housing bridge is defined as measuring location.

3.3.2 Test execution

This test is a randomized sequence of relevant loads from the Standard Collective or the Traction Collective. Parking brake cycles from Section Fehler! Verweisquelle konnte nicht gefunden werden. are mixed in if the brake design also includes a parking brake feature. It should be noted, that in contrast to the service brake load collective, the load cycles in chapter 2.2 already include a statistical margin of safety. The total number of cycles required is calculated using the equation below: (Overall collective: Nsoll=(service brake collective x 1,1(for reversing)) x SF + park brake collective) It is acceptable to omit non-damaging lower-load cycles. Those are the load levels, which contribute in total less than 5% to the overall damage. To calculate the number of cycles to omit, eliminate all cycles on the low end of the collective and represent up-to-5% of the total damage (according to Palmgren / Miner). Use the applicable S/N curve to extract the appropriate number of cycles. For components made of light metal materials, a temperature and corrosion profile is combined with the mechanical loads from the load collectives. For this purpose, the test schedule includes the overall load collective (with consideration of the 5% omission level) separated into 30 blocks, and the temperature profile (Section Fehler! Verweisquelle konnte nicht gefunden werden.) separated into 38 program steps. The mixed load collective is divided in 30 equal sections. To temperature profile sections 1-37, 2 sections of the load collective are applied. To temperature profile section 38, one section of the load collective is applied. Each of the ten temperature profile repetitions will be superposed with new subsequent load collective sections.


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3.3.3 Test requirements

Sample size n 4 Based on taking over the scatter of the S/N-curve, the test can be accomplished as success run. The test is passed if the number of samples withstands Nsoll load cycles without failure. Alternatively, the test is passed, if the be tested load collective is met with a survival rate of R = 99.9%, based on a confidence interval of C = 90%. The statistical safety margin can be calculated with the results of the SLT according to Fehler! Verweisquelle konnte nicht gefunden werden..

Figure 6: exemplary representation of the SLT requirement

3.4 Parking brake actuator endurance test

A suitable endurance test for the actuator of the parking brake is to be agreed between vehicle manufacturer and brake manufacturer.


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4 Overload tests

4.1 Static strength tests

4.1.1 Test setup and execution

Test setup as described under Section 3.2.1. The brake torque MST for static strength testing is:

For front axle: MST = 1.75 x MVA For rear axle: MST = 1.75 x MHA

Calculated for a fully loaded vehicle, use the higher value of “ideal” and “installed-system” distribution of front and rear torque. Rise of pressure and torque synchronously. Remark: The components from the test as per subsection Fehler! Verweisquelle konnte nicht gefunden werden. may be used for this test.

4.1.2 Requirements

After applying the static load, the following conditions must be fulfilled:

No leakage of the hydraulic system (similar to Section Fehler! Verweisquelle konnte nicht gefunden werden.)

test pressure: p = 150 bar;

p/t 10 bar over a period of 2 minutes

Caliper body slide load: 10 - 150 N Piston threshold pressure: 0,2 - 3,0 bar

Piston retraction load: 50 - 700 N

Note: Before the measurements, move the piston two times ± 5 mm, then place the piston in the new pad position and subject the brake one time to a hydraulic pressure of 100 bar.

Sample size n 4

4.1.3 Additional requirements for brake calipers with integrated parking brake

For the following additional test, the caliper has to be mounted on a suitable test rig. The basic setting of the parking brake mechanism is based on the respective instructions of the vehicle manufacturer. Apply a one-time load according to Section Fehler! Verweisquelle konnte nicht gefunden werden. multiplied by 1.5, including the safety factor. This load is applied over a period of 5 minutes. Following this load, the parking brake function must not be impaired.

Sample size n 4 Remark:


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The components from the test as per subsection 5 may be used for this test.


Copyright: VDA

4.2 Burst pressure test

4.2.1 Test setup and execution

Test setup similar as described under Section 3.2.1. Burst pressure test by applying the corresponding hydraulic pressure.

4.2.2 Requirements

Burst pressure p 350 bar.

Sample size n 4 Remark: The components from the test as per subsection 4.1 may be used for this test.

5 Hydraulic leakage test

5.1 Test setup and execution

Setup as described under Section 3.2.1, but with original brake pads

Application of hydraulic pressure in accordance with following table (pressure build-up rate approx. 500 bar/s, piston travel results in the case of original pads to approx.0.3 mm) 135 000 cycles room temp. (RT) f=800 - 1200 [1/h] p = 70 bar

45 000 cycles - 40 2 °C f=600 - 800 [1/h] p = 70 bar

69 000 cycles + 150 2 °C f=800 - 1200 [1/h] p = 70 bar

1 000 cycles + 200 2 °C f=800 - 1200 [1/h] p = 100 bar Total: 250 000 cycles

5.2 Requirements

The following conditions must be met upon conclusion of the testing program:

No leakage of the hydraulic system; tested by means of Test pressure p = 150 bar;

p/t 5 bar / minute Test duration: 2 minutes

No function-impairing wear of piston and cylinder surface; checked over: Piston threshold pressure: 0,2 - 3,0 bar Piston retraction load: 50 - 700 N

Note: Before the measurements, move the piston two times by ± 5 mm, then place the piston in the new pad position and subject the brake one time to a hydraulic pressure of 100 bar.

Sample size n 4 Remark: This release examination as per subsection 5 is necessary only once per housing diameter, if the deflection of the calipers is in the same range of tolerance and also the geometric values (e.g. rollback groove) and the materials are identical.

Project Group VDA Ad hoc AK Betriebsfestigkeit Radbremse · stresses of the service brake and...

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