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QC/T 491-2018: Automobile shock absorber technique requirements and test methods
QC/T 491-2018
AUTOMOBILE INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 43.040.60
T 20
Replacing QC/T 491-1999, QC/T 545-1999
Automobile shock absorber technique requirements and test
methods
ISSUED ON: JULY 04, 2018
IMPLEMENTED ON: JANUARY 01, 2019
Issued by: Ministry of Industry and Information Technology of PRC
Table of Contents
Foreword ... 5 
1 Scope ... 7 
2 Normative references ... 7 
3 Terms and definitions... 7 
4 Basic dimensions and parameters ... 9 
5 Performance requirements ... 12 
6 Test methods ... 15 
Automobile shock absorber technique requirements and test
methods
1 Scope
1.1 This standard specifies the performance requirements and bench test methods for
automobile shock absorbers.
1.2 This standard is applicable to the shock absorbers, which are used for the suspension
of categories M, N, O automobiles. The shock absorbers for cab suspension and other
shock absorber components can be implemented with reference to it.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 3730.1 Motor vehicles and trailers - Types - Terms and definitions
GB/T 15089 Classification of power-driven vehicles and trailers
QC/T 484 Automobile - Paint coating
QC/T 572 Directives for motor vehicle cleanliness - Measuring method
3 Terms and definitions
The following terms and definitions apply to this standard.
3.1
Telescopic shock absorber
The shock absorber, which is composed of the working cylinder and the outer
cylinder for oil storage, is a telescopic shock absorber. In this standard, unless
otherwise specified, the telescopic shock absorber is referred to as shock absorber
for short.
3.2
Suspension struts
The telescopic shock absorber, which is installed on the suspension to play a guiding
role, bears a certain lateral force, usually is composed of the accessories such as
spring discs and brackets, is called a suspension struts-type shock absorber. Unless
otherwise specified in this standard, the suspension struts-type telescopic shock
absorber is referred to as the suspension struts.
3.3
Stroke
The maximum moving distance, that the piston can reach, during the use of the
shock absorber. It is the difference, between the maximum length and the minimum
length of the shock absorber product.
3.4
Force-displacement characteristic
Under a certain test stroke and frequency, when the two ends of the shock absorber
perform relatively simple harmonic motion, the relationship between the damping
force (F) and the test stroke (S) is the force-displacement characteristic. The curve
(F-S) formed is called the force-displacement diagram.
3.5
Ratio of vacant path
The ratio -- of the fluctuation length (idle stroke) in the force-displacement diagram
TO the test stroke, which is measured at any speed, -- is called the ratio of vacant
path (δ).
3.6
Force-velocity characteristic
When the two ends of the shock absorber perform relatively simple harmonic motion,
the relationship between the damping force (F) and the piston speed (V) is the force-
velocity characteristic. The curve (F-v), which is formed at various speeds, is called
the force-velocity characteristic diagram.
3.7
Force-temperature characteristic
Under the same speed conditions of the shock absorber, the relationship between the
damping force (F), which is measured at different temperatures, and the temperature
(t), is the force-temperature characteristic. The curve (F-t), which is formed by it, is
called the force-temperature characteristic diagram.
3.8
Friction-force of damper (Ff)
When the shock absorber moves, at a speed not exceeding 5.0 x 10-3 m/s, the
resistance it experiences at this time is defined as friction.
3.9
Air-force of damper (Fair)
For gas-filled shock absorbers, when the piston is in the middle position of the
working stroke, the force of the gas, which acts on the piston rod, is the air-force of
damper.
Note: For the gas-force of damper, which is measured at the middle position of the non-
working stroke, it shall indicate the test position in the results.
3.10
Anti-foam characteristic
The ability of a force-displacement characteristic to resist the effects of foam is
called anti-form characteristic.
4 Basic dimensions and parameters
4.1 Working cylinder diameter and piston rod diameter of shock absorber
The diameter of the working cylinder and piston rod of shock absorber is as
recommended in Table l.
parameters shall be automatically recorded, saved, output; the sampling frequency shall
not be lower than 200 Hz.
6.1.3 The accuracy of sensors, such as displacement, load, speed, shall not be lower
than ±0.5% of the full range of each sensor; the indication error of the temperature
sensor shall not be greater than ±0.1 °C; the indication error of the weighing instrument,
which is used in the test process, shall not be greater than ±1 g.
6.1.4 The test device, which is used for the durability test, can be single-action or
double-action. The single-action test bench shall be able to conduct the test, according
to the composite waveform, which is formed by the superposition of low-frequency
waves and high-frequency waves.
6.2 Requirements for test method
6.2.1 Test preparation
6.2.1.1 Before the test, it shall ensure that the shock absorber samples are stored in a
vertical state, at room temperature for at least 2 hours.
6.2.1.2 Unless otherwise specified, install the shock absorber in the vertical direction
on the test bench for testing; ensure that there is no additional load, as caused by the
installation.
6.2.1.3 Carry out the test, at the middle position of the working stroke of the shock
absorber. During the test, the deviation, between the midpoint position of the piston’s
reciprocating motion and the middle position of the working stroke, shall not exceed
±5% of the working stroke.
6.2.1.4 The shock absorber is first subject to 3 cycles of gas exhaust. The exhaust
process is carried out, at a maximum speed of 0.52 m/s, which is obtained by adjusting
the test stroke s = 100 mm and frequency f = 1.67 Hz. For shock absorbers, which have
a working stroke of less than 100 mm, it may select 75 mm, 50 mm or 25 mm as the
test stroke, according to the product, OR according to the agreement between the
supplier and the buyer. The movement speed v of the piston of shock absorber is
calculated, according to formula (4):
6.2.2 Force-displacement characteristic test
6.2.2.1 Prepare the sample before the test, according to 6.2.1.
6.2.2.2 After the exhaust process is completed, conduct the test, in the form of a sine
wave, according to the test stroke used in 6.2.2.1. Adjust the frequency, to make the test
speed be 0.13 m/s, 0.26 m/s, 0.52 m/s, 1.04 m/s. Record the displacement and load data
requirements of 5.5. Both the supplier and the buyer may refer to the provisions of
6.2.6.1 ~ 6.2.6.5, to conduct the test, to obtain the rate of change of the damping force
and the force-temperature characteristic diagram of other speeds and temperatures;
evaluate the results, according to the technical requirements of the supplier and the
buyer.
6.2.7 Anti-foaming test
6.2.7.1 Prepare the sample before the testing, according to 6.2.1.
6.2.7.2 Under the condition that the shock absorber is allowed to be air-cooled and
dissipated, use the test stroke, which is selected in 6.2.7.1, to make 100 consecutive
movements, in the form of sine waves at a speed of 1.04 m/s. Record the last 3
movements continuously, namely the force-displacement diagrams of the 98th, 99th,
100th cycles.
6.2.7.3 The anti-foaming properties of the shock absorber shall meet the requirements
of 5.6.
6.2.8 Durability test
6.2.8.1 The relevant functional parts and accessories, that affect heat dissipation, such
as dust cover, shall be removed as far as possible from the test piece, to improve the
cooling effect.
6.2.8.2 Weigh the test piece. Record the mass of the test piece, m0, before durability test.
6.2.8.3 Install the sample on the durability test bench. The temperature measurement
unit shall be installed on the outer wall of the outer diameter guide of the shock
absorber’s liquid cylinder, at a position more than 20 mm downward from the upper
end of the liquid cylinder; it shall be thermally insulated from outside. During the test,
forced cooling is allowed, to dissipate heat from the shock absorber.
6.2.8.4 Carry out the test, under one of the following two conditions. During the test,
the temperature of the shock absorber shall be controlled within the range of (70 ±
10) °C:
1) The test condition of the low-frequency end (upper end) is f1 = 1.67 Hz; the test
stroke s1 = 100 mm. The test condition of the high-frequency end (lower end) is
f2 = 10 Hz; the test stroke s2 = 16 mm;
2) The test condition of the low-frequency end (upper end) is f1 = 1 Hz; the test
stroke s1 = 80 mm. The test condition of the high-frequency end (lower end) is f2
= 12 Hz; the test stroke s1 = 20 mm.
During the test, when the temperature exceeds the requirements of temperature range,
the test equipment is allowed to drive the piston of shock absorber, to reciprocate at a
low speed, to speed up the cooling of the sample under the forced cooling environment;
however, the number of cooling cycles shall not be included in the number of cycles of
the durability test.
6.2.8.5 The number of test cycles shall be accumulated, according to the high frequency
end, which shall not be less than 3.0 x 106 cycles.
6.2.8.6 For shock absorbers, whose working stroke is less than 100 mm, it may select
75 mm, 50 mm or 25 mm as the test stroke, for the low frequency end, according to the
product, OR according to the agreement between the supplier and the buyer. The
movement speed v of the piston of shock absorber is calculated, according to formula
(4), to meet the speed requirements of low frequency and high frequency.
6.2.8.7 During the durability test, lateral force is allowed to be applied within the range
of more than 20 mm, downward from the upper end of the liquid cylinder. The
magnitude and direction of the lateral force can be determined, through negotiation
between the supplier and the buyer.
6.2.8.8 After completing the number of tests required in 6.2.8.5, perform the force-
displacement characteristic test on the test piece, according to 6.2.2. Weigh the test
piece, according to the same conditions as 6.2.8.2. Record the mass of the test piece,
m1, after the durability test.
6.2.8.9 Calculate the change rate of the damping force of shock absorber, before and
after durability test, according to formula (9) and formula (10):
Where:
Fnr – The recovery resistance after durability test;
Fnc - The compression resistance after durability test.
6.2.8.10 Calculate the damping oil atomization rate of shock absorber, λ, according to
formula (11):
6.2.8.11 The durability test of the shock absorber shall meet the requirements of 5.7.
After the coordination between the supplier and the buyer, the durability index
assessment can also be carried out, at other speeds according to 6.2.8.1 ~ 6.2.8.10; the