brake calipers

VDA-Empfehlung 311
February 2016
Operating Strength for Brake Calipers
Requirements and Testing
Seite 1
VDA
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.
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.
Publisher: Verband der Automobilindustrie; Behrenstrasse 35; 10117 Berlin; www.vda.de
© 2015 Verband der Automobilindustrie, Berlin
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February 2016
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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.
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February 2016
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Content
1
2
3
4
5
Basics ........................................................................................................................... 4
1.1 Scope .................................................................................................................... 4
1.2 Nomenclature ........................................................................................................ 4
1.3 Evaluation Concept ............................................................................................... 6
1.3.1 Service Load Test Caliper Assembly ................................................................ 6
1.3.2 Simplified testing in single-stage ....................................................................... 6
1.3.3 Parallel endurance test ..................................................................................... 7
Requirements / load assumptions ................................................................................ 7
2.1 Service brake ........................................................................................................ 7
2.1.1 Standard Collective ........................................................................................... 7
2.1.2 Traction Collective ............................................................................................ 8
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
Operational Strength Tests......................................................................................... 14
3.1 SN test ................................................................................................................ 14
3.1.1 Test Conditions: .............................................................................................. 14
3.1.2 Test Evaluation ............................................................................................... 14
3.1.3 Statistical safety factors .................................................................................. 15
3.1.4 Determination of minimum cycles requirement ............................................... 15
3.1.5 Fatigue life estimation ..................................................................................... 16
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 ............................................ 20
3.3 Service Load Test (SLT) ..................................................................................... 21
3.3.1 Test setup ....................................................................................................... 21
3.3.2 Test execution ................................................................................................ 21
3.3.3 Test requirements ........................................................................................... 21
3.4 Parking brake actuator endurance test................................................................ 22
Overload tests ............................................................................................................ 23
4.1 Static strength tests ............................................................................................. 23
4.1.1 Test setup and execution ................................................................................ 23
4.1.2 Requirements ................................................................................................. 23
4.1.3 Additional requirements for brake calipers with integrated parking brake ....... 23
4.2 Burst pressure test .............................................................................................. 25
4.2.1 Test setup and execution ................................................................................ 25
4.2.2 Requirements ................................................................................................. 25
Hydraulic leakage test ................................................................................................ 25
5.1 Test setup and execution .................................................................................... 25
5.2 Requirements ...................................................................................................... 25
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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 Palmgren & Miner
f
Test frequency
F1, FA, FB, Fi
Load at load step 1, A, B, i
Load step of the deviation point of the SN curve to the
theoretical fatigue limit
Average value at load level i
FD
ࡲഥଙ
ࡲ(࢞;ࣅ)
Hi
H0
JC, n
JL
k
Density function of the exponential distribution
Cumulative frequency of the load collective up to the
level i
Cumulative frequency of the total load collective
Risk factor for a confidence level C at n single
experiments
Life-related safety number for the extrapolation to a
given probability of the lognormal distribution
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
Damage-equivalent number of load cycles at the 1gload level
N1k
N1Park
Damage-equivalent number of load cycles of the
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September 2015
parking brake at the 1g-load level
‫ܑۼ‬,૞૙%
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
Nsoll
Number of load cycles of the S/N-curve at the 1g-load
level for 50% survival probability
Number of load cycles of the deviation point of the SN
curve to the theoretical fatigue limit
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
S
standard deviation
SF
Statistical safety factor
Slog
Logarithmic standard deviation
t
time
TN
Ratio between 10% and 90% survival probability
U
X
Quantile of the standard normal distribution
Quantile of the standard normal distribution for the
confidence interval C
Scaled load
x
Gradient of the road inclination
λ
Failure rate of the exponential distribution
N1WL
ND
Uc
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1.3
September 2015
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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.
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 singlestage 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.
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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.
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
Yes
No
•
Vehicle equipped with traction control?
•
Caliper of a driven rear axle?
Yes
•
Loaded by brake pressure or clamp load?
Yes
No
TK
SK
Applicable load collective:
No
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:
૛
ࡴ࢏ = (ࡴ૙ − ૛૚૝ૢ) ∗ ࢋି ‫ࡴ ܖܔ‬૙∗ࢄ + ૛૚૝ૢ
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.
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2.1.2 Traction Collective
Specific load cases added to the normally distributed load collective are:
•
•
•
80
220
1850
brake applies at 2-times 1g load level
brake applies at 1.6-times 1g load level
brake applies at 1g load level
2.1.3 Collective Data
Scaled load level X
[g]
2
1,6
1,3
1
0,95
0,9
0,85
0,8
0,75
0,7
0,65
0,6
0,55
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
0
Standard Collective
Single
Sum
frequency frequency
0
0
0
0
20
20
2130
2150
3
2153
10
2163
35
2198
105
2303
302
2605
802
3407
1978
5385
4525
9910
9595
19 505
18 836
38 341
34 175
72 516
57 199
129 715
88 061
217 776
124 215
341 991
159 564
501 555
184 877
686 432
189 938
876 370
167 163
1 043 533
115 274
1 158 807
41 193
1 200 000
Table 2: Service Brake Load Collectives
Traction Collective
Single
Sum
frequency frequency
80
80
220
300
0
300
1850
2150
3
2153
10
2163
35
2198
105
2303
302
2605
802
3407
1978
5385
4525
9910
9595
19 505
18 836
38 341
34 175
72 516
57 199
129 715
88 061
217 776
124 215
341 991
159 564
501 555
184 877
686 432
189 938
876 370
167 163
1 043 533
115 274
1 158 807
41 193
1 200 000
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Figure 2: Service Brake Load Collectives
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
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 with the following input parameters:
•
With superposed temperature profile of the actuator (Fehler! Verweisquelle konnte
nicht gefunden werden., Fehler! Verweisquelle konnte nicht gefunden werden. )
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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
step
1
2
3
4
5
6
7
8
Temperature profile:
Temperature
[°C]
23
85
65
45
23
0
-20
-40
cycles
Actuator temperature
[°C]
•
5000
250
1500
13 250
1000
1750
1750
500
Table 3: Temperature profile EPB-Actuator
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
0
10000 20000
cycles
Figure 3: Temperature profile EPB-Actuator
The temperature profile has to be repeated 4-times for 100 000 cycles.
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.
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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%
#$;%
1 ' %$
with
)*1%
(
23
20%
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.
The required holding pressure is increased by 33% to account for over-pressurization
by the driver.
gradient [%]
Percentage
of operations
Pressure
level [g]
25 - >30
20 - 25
16 - 20
12 - 16
8 - 12
4-8
0-4
0,3%
0,7%
1,5%
3,8%
9,5%
24%
60,2%
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
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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
Temperature sequence
Duration
step
1
heating
from ambient temp to
25 min
100°C
2
heating
from 100°C to 170°C
15 min
3
heating
from 170°C to 200°C
10 min
4
holding
200°C
2 min
5
cooling
from 200°C to 170°C
15 min
6
heating
from 170°C to 200°C
10 min
7
holding
200°C
2 min
8
cooling
from 200°C to 170°C
15 min
9
heating
from 170°C to 200°C
10 min
10
holding
200°C
2 min
11
cooling
from 200°C to 170°C
15 min
12
cooling
from 170°C to 100°C
15 min
13
cooling
from 100°C to Rt
15 min
14
heating
from Rt auf 100°C
25 min
15
heating
from 100°C to 170°C
15 min
16
heating
from 170°C to 200°C
10 min
17
holding
200°C
2 min
18
cooling
from 200°C to 170°C
15 min
19
heating
from 170°C to 200°C
10 min
20
holding
200°C
2 min
21
cooling
from 200°C to 170°C
15 min
22
heating
from 170°C to 200°C
10 min
23
holding
200°C
2 min
24
cooling
from 200°C to 170°C
15 min
25
cooling
from 170°C to 100°C
15 min
26
heating
from 100°C to 170°C
15 min
27
heating
from 170°C to 200°C
10 min
28
holding
200°C
2 min
29
cooling
from 200°C to 170°C
15 min
30
heating
from 170°C to 200°C
10 min
31
holding
200°C
2 min
32
cooling
from 200°C to 170°C
15 min
33
heating
from 170°C to 200°C
10 min
34
holding
200°C
2 min
35
cooling
from 200°C to 170°C
15 min
36
cooling
from 170°C to 100°C
15 min
37
cooling
from 100°C to Rt
15 min
38
holding
Room temperature
65 min
Salt Spray Test with NaCl
5% acc. EN ISO 9227
Σ 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:
#,- × /, #0- × /0
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:
7777776 8
777776 8 ∙ 3)4/5 )4/
∑3)4#5 )4#
1
777776 8:
∑3)4#5 )4#
Location of the regression line (load #; at /; cycles):
#; 10
777777@ A-∙<=B
777777@
<=>? <=>
-
Logarithmic standard deviation:
1
:
C)D4 E
F3)4/5 )4/5,GH% 8
*1
I
5JK
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L> 10MNOP∙:∙Q
With the 90% quantile of the standard normal distribution parameter U (=1,28155)
Scatter span:
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:
VS
RS,T U√T
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:
RX UV
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:
U RS,T ∙ RX Y. [
If the experimental scatter span L/ > 2,5, this safety factor has to be calculated
using the actual value of TN.
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:
_
^_ F ` a ∙ T
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.
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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:
^_ ∙ U
^bcd e
The number of reverse stops is calculated using the equation below:
^fg , ∙ ^bcd
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:
^hX
X
× Xijkk_lg
^bcd
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:
^hX
X
× Xijkk_lg
^bcd + ^fg + ^mnf_
For example, the damage portions from parking brake loading are calculated by the
equation below:
_
^mnf_ F ` a ∙ T
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 is based on the renouncement of testing against a fixed number of
cycles with associated scattering and their replacement by a test against a
component-specific minimum number of cycles, which is representing a specific
lifetime in years or mileage.
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):
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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.
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 “installedsystem” 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.
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Figure 5: schematic pressure and torque curves
Additionally to the minimum cycle numbers in forward direction ^opqr also cycles in
reverse direction have to be run. The number of reverse cycles is computed in
Section 3.1.4 ^fg ). The reverse brake torque value is the same as the forward
torque value.
3.2.3 Requirements
Table 6 lists the required number of brake cycles for a service-brake-only design for
the rare case where s 1 and L> t 2,5:
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3.2.3.1
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For service brake components -Standard Collective
cycles
^_
Test cycles forward
^bcd
74 546
285 000
Test cycles
backward
^fg
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
k-value
2,0
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
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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.).
Test cycles forward
^bcd
2,0
cycles
^_
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
k-value
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
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Service Load Test (SLT)
The test procedure in this section can be used to release any brake design regardless of the 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 temperaturecontrolled 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 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. These are the load levels
that contribute only a small proportion to the overall damage at a high number of
cycles. To calculate the number of cycles that can be omitted, eliminate all cycles of
lower loads that contribute up to 5% of the total damage (acc. Palmgreen / Miner).
This calculation of the damage portion is based on the slope value (k) of the SN
curve.
For components made of light metal materials, a temperature and corrosion profile is
superimposed in addition to the mechanical loads. For this purpose, the overall load
collective, with consideration of the omission level (see above) and the temperature
profile Section Fehler! Verweisquelle konnte nicht gefunden werden. is used. The
mixed load collective is divided in 30 equal sections and distributed to the
temperature cycle. In the temperature profile sections 1-37, 2 sections of the load
collective are applied. In the 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.
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%.
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The statistic safety is then 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 “installedsystem” 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.
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4.2
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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 buildup 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.