USOO5369974A

United States Patent (19) 11 Patent Number: 5,369,974

Tsymberov 45 Date of Patent: Dec. 6, 1994
(54) SUSPENSION TESTER AND METHOD Assistant Examiner-James M. Olsen
(75) Inventor: Anatoly Tsymberov, Ballwin, Mo. Attorney, Agent, or Firm-Polster, Lieder, Woodruff &
Lucchesi
(73) Assignee: Hunter Engineering Company, 57 ABSTRACT
Bridgeton, Mo.
The apparatus and method of the present invention is
21 Appl. No.: 974,249 designed for testing dampers of a motor vehicle without
22 Fled: Nov. 10, 1992 removing the dampers from the vehicle. The apparatus
includes a movable support for contacting the bottom
(51) Int. Cl: ............................................ GO1M17/04 surface of a tire associated with a damper to be tested
(52) A - - - - 0 73/11.08; 73/670 and members for oscillating the movable support to
(58 Field of Search .................... 73/116, 11.07, 11.08, impose vertical oscillations on the tire. Transducers
73/865.3, 669, 670 sense the force applied by the tire to the support during
56) References Cited oscillation of the support while the oscillating members
are controlled to oscillate the support over a predeter
U.S. PATENT DOCUMENTS mined range of frequencies. Circuitry is provided re
3,855,84. 11/1974 Hunter ............................... 73/11.08 sponsive to the transducers for determining, as a func
3,902,352 9/1975 Buzzi ....... ... 63/11.08 tion of the frequency of oscillation, the adhesion of the
3,937,058 2/1976 Hilbrands ... ... 73/11.08 tire to the support and the phase angle of the response of
4,002,051 1/1977 Hilbrands.... ... 73/11.08 the tire to the oscillation. The circuitry further deter
4,589,273 5/1986 Tamasi et al........ ... 73/11.08 mines from the phase angle at a single frequency the
4,703,645 11/1987 Hudacsek et al. ... ... 73/1108 adequacy of the damping of the damper under test.
5,056,024 10/1991 Stuyts ................................. 73/1108
Primary Examiner-Hezron E. Williams 19 Claims, 4 Drawing Sheets

ra PRINTER-23

25

MOTOR
CONROL
U.S. Patent Dec. 6, 1994 Sheet 1 of 4 5,369,974

Rm 3 vs.
YE as in Wt

23

25

MOTOR
CONTROL
F. G. 2
U.S. Patent Dec. 6, 1994 Sheet 2 of 4 5,369,974

i-MEASURED LOAD

POSITION OF
TOP PLATE

PER CENT AOHESION

5 O S 2O
FREQUENCY (HZ)

5 O 15 20
FREQUENCY (HZ)
U.S. Patent Dec. 6, 1994 Sheet 3 of 4 5,369,974

S 2O
FREGUENCY (HZ)

O S 20
FREQUENCY (HZ)
PERCEN AOHESION

N-2

O 5 10 15 20
FREUENCY ( HZ ) F I G () 5 A

O 5 O LS 20
FREGUENCY (HZ)
U.S. Patent Dec. 6, 1994 Sheet 4 of 4 5,369,974

O
FREQUENCY (HZ )

far
fif
O 5 O S 2O
FREQUENCY (HZ)

SUMMARY
SUSPENSION MEASURED MARGINAL FAILEO UNITS
FRONT AXLE
- LEFT ADHESION
a RIGHT ADHESION
as EFTARGH BALANCE
- LEFT DAMPING FACTOR
- RIGHT OAMPING FACTOR
REAR AXLE
- LEFT ADHESION
- RIET ADHESION
:i g
a. M s

g
LEFT/RIGHT BALANCE
LEF DAMPING FACTOR
RIGHT DAMPING FACTOR 8:
t A
i
VEHICLE DATA TOTAL UNITS
FRONT AXLE WEIGHT 749 LBS
REAR AXLE WEIGHT 979 LBS
WHEELBASE (ESIMATED ) OO. 4 IN
C.G. HEIGHT (ESTMATED ) 2.6 IN

FIG . 6
 5,369,974
1. 2
lations of the vehicle. This method is less than satisfac
SUSPENSION TESTER AND METHOD tory, since its results are not quantitative. Another
method involves dropping the vehicle from a predeter
BACKGROUND OF THE INVENTION mined height to generate oscillation of the vehicle. This
This invention relates to testing of vehicles, and more second method is superior to the first, but still could be
particularly to testing dampers of automobiles and the improved since it reflects the response of the damper at
like. a single frequency of excitation. Neither method pro
An automotive suspension is meant to provide both vides testing over as wide a range of frequencies as
safety and comfort for the occupants. When a vehicle 10 might be desired, since both are basically low frequency
hits a bump in the pavement, the shock is taken up by tests.
various components of the vehicle. For example, the One measure of the roadworthiness of a vehicle can
tire deforms as the suspension displaces, while most of be given in terms of the minimum amount of traction
the energy is stored in the suspension springs. The that the wheels will provide on uneven pavement. This
springs release this energy as a damped oscillation. 15 number is called the "adhesion.' This minimum traction
Shock absorbers and struts (hereinafter referred to col allows the vehicle to maneuver despite bumps and other
lectively as dampers) in motor vehicles serve to damp irregularities in the pavement. A method of testing ad
oscillations of the vehicle chassis resulting from travel hesion has been proposed by the European Shock Ab
over uneven surfaces and to reduce the magnitude of sorber Manufacturers Association (EUSAMA). This
spring deflections in response to large bumps. method, set out in Recommendation TS-02-76 issued by
More specifically, a damper is a hydraulic mechanism 20 EUSAMA includes the following requirements: (1) the
positioned between sprung and unsprung masses to vertical static contact force between the tire and the
dissipate kinetic energy put into the system by bumps. support member on which the tire associated with the
Dampers provide desired ride characteristics, but also damper to be tested is disposed is measured; (2) the
play a key role in keeping good tire-to-road contact supporting member is given a sinusoidal excitation to
essential for handling and safety. The dampers are prob 25 bring the vehicle into vibration; (3) adhesion is defined
ably the most versatile members of the group of compo as the ratio of the minimum dynamic contact force
nents that affect ride and handling. The dampers con measured on the supporting member at the wheel reso
trol vibration and improve handling and load control. nance frequency to the static contact force, expressed as
Without dampers, a car would go out of control at just a percentage; and (4) the proposed minimum frequency
twenty miles per hour and braking distance would in 30 for exciting the supporting member is 24 Hz. Using the
crease. One faulty damper can cause unbalanced damp EUSAMA standards, when a test result of less than
ing in suspension. Weak dampers allow the vehicle to 20% adhesion is obtained, the damper is unsatisfactory;
continue to oscillate three or more times after the distur
bance, causing an undesirable condition known as from 20% to 40% the damper is fair; above 40% adhe
“float.’ 35 sion, it is good, and over 60%, it is excellent.
Some signs of a worn damper are (1) riders feeling The apparatus for performing the EUSAMA damper
carsick or tired, (2) excessive wear on the tires due to test includes a supporting member for the tire, and a
bumpy contact with the road, (3) vibration of steering, drive motor with eccentric and spring for driving the
suspension and body parts, (4) car roll on turns, (5) supporting member. The frequency of vibration with
nose-dive when braking, (6) veer in crosswinds, (7) this apparatus is increased into the range beyond the
headlights pitch up and down when driving over un resonance frequency of the chassis (vehicle suspension).
even surfaces, and (8) oil leakage from the dampers. Then, the excitation frequency is gradually reduced. As
Dampers can be divided in the compression stage and the frequency is reduced, the frequency of vibration
in the rebound stage to either “firm’ or “soft.” For ride passes through the natural resonance or "wheel-hop'
comfort, both compression and rebound stages should 45 frequency.
be 'soft,' but vertical body motion velocity could con In fact, there are a number of vibrational frequencies
siderably exceed desirable limits. The damper rebound associated with a vehicle. Any vehicle is made up of a
stage should be "firm' and compression should be number of different components (rigid body, suspen
'soft' to minimize vertical body motion velocity. But if sion, wheel, chassis, body panels, steering wheel, en
vertical body velocity is low, usually on a smooth road, SO gine, etc.) with different vibrational behaviors. Vibra
the damper compression stage should be "firm' and the tion of the rigid bodies occurs at low frequencies, such
rebound stage 'soft', which should maximize adhesion. as 0.5 to 5 hertz. Vibration of the suspension, on the
For ride safety, especially at wheel hop resonance, both other hand, occurs at frequencies of 5 hertz and above.
the compression and rebound stages should be "firm.' In this regard, it should be noted that the primary differ
Many car manufacturers try to compromise these 55 ence between independent and linked suspensions is that
factors for off-highway (rougher roads) driving using while the independent suspension can be expected to
much more damping in rebound (two to six times) than have a single wheel hop resonance in the ten to twenty
in compression. This minimizes body motion velocity, hertz frequency range, the linked suspension exhibits a
but does not always maximize ride comfort. It also pair of resonances. Both the suspension spring and the
reduces the safety of the ride, especially at higher rubber suspension bushings play an important part in
speeds. the actual vibrational levels transmitted across the sus
Although the damper is a critical element in the safe pension and entering the vehicle chassis at higher fre
operation of a vehicle, previously it has not been easily quencies.
tested conclusively without completely removing it With respect to vibration of the vehicle chassis, for a
from the vehicle. Because of this, various methods have fully dressed vehicle, the resonant frequencies are lower
been proposed for testing the quality of a damper. One than for the free chassis due to the mass. The frequency
of these methods is for the mechanic to physically oscil range of vibration usually begins around ten hertz and
late the vehicle by hand and observe the resulting oscil can extend out through several hundred hertz. A vehi
 5,369,974 4.
3
cle chassis can possess a large number of different vibra ther includes the step of determining, as a function of
tional modes, some of which may have resonant fre the frequency of oscillation, the adhesion of the tire to
quencies in the range where wheel hop and other low the support and the phase angle of the response of the
frequency problems can occur. tire to the oscillation, and further determining from said
It is known that low frequencies in the 0.5 to 30 Hz phase angle at a single frequency the adequacy of the
range are felt tactually by the human body, while vibra damping of the damper under test.
tions in the range of from 20 Hz on up may be heard. BRIEF DESCRIPTION OF THE DRAWINGS
Human beings are most sensitive to tactile vibrations in
the range of four to eight hertz, but the sensitivity falls FIG. 1 is a diagrammatic representation of the masses
off rapidly as the frequency rises. Moreover, the greater 10 and forces involved in the suspension tester of the pres
the amplitude of the vibration, the greater the sensitiv ent invention;
ity of the person to that particular frequency of vibra FIG. 2 is a block diagram of damper tester apparatus
tion. of the present invention;
Although the EUSAMA system is an improvement FIG. 3 is a graph illustrating the phase angle used in
over prior methods, it can also be improved. The testing 15 the present invention; and
in the EUSAMA system is actually a test of the entire FIGS. 4A-6 are representative display outputs of the
suspension system, not a test of the adequacy of the apparatus of FIG. 2. Similar reference characters indi
damper alone, and even then only one parameter, adhe cate similar parts throughout the several views of the
sion, is considered. drawings.
Ideally a test of a vehicle suspension should examine 20
DESCRIPTION OF THE PREFERRED
not only adhesion, but also actual adequacy of the EMBODIMENT
damper under test, and the balance of adhesion from
side to side of the vehicle. Prior suspension testers are Mathematically, the suspension of a vehicle can be
not believed to test these various aspects of the accept modeled as a two-degree-of-freedom system under a
ability of the suspension. 25 sinusoidal forcing function as shown in FIG. 1. The
SUMMARY OF THE INVENTION lowest mass (labelled m3 on FIG. 1) is exposed to the
forcing function (labelled R), and represents the damper
Among the various objects and features of the present tester platform, while m1 and m2 represent the sprung
invention may be noted the provision of a damper tester and unsprung masses. The system is modeled by the
with improved performance. 30 following force-balance equations:
Another object is the provision of such apparatus
which tests more than one parameter of the suspension For mil: RIn1--Rc1--Rk1=0 (1)
under test.
A third object is the provision of such apparatus For in2: Rim2-Rc2--Rk2-Rk1-Rc1=0 (2)
which reduces the time heretofore needed to perform 35 For m3: Rim3--R-Rk2-Rc2 = 0 (3)
damper testing.
A fourth object is the provision of such an apparatus Where:
which provides reproducible test results.
A fifth object is the provision of such an apparatus Rm1, Rim2, and Rim3 are the forces due to accelera
which occupies a minimal amount of space. tion of the masses.
Other objects and features will be in part apparent Rc1 and Rc2 are the forces due to the dampers.
and in part pointed out hereinafter. Rk1 and Rk2 are the forces due to the springs.
Briefly, the apparatus of the present invention is de R is the force to the load cells (force sensing trans
signed for testing dampers of a motor vehicle without ducers).
removing the dampers from the vehicle. The apparatus 45 The sprung mass is made up of the vehicle frame,
includes a movable support for contacting the bottom body, and load. Vehicles with high sprung mass tend to
surface of a tire associated with a damper to be tested be more comfortable than lighter vehicles because the
and members for oscillating the movable support to larger mass requires a larger force to produce an un
impose vertical oscillations on the tire. Transducers comfortable acceleration. The unsprung mass is com
sense the force applied by the tire to the support during 50 posed of the components on a car that move with the
oscillation of the support means while the oscillating suspension as it deflects. These components include the
members are controlled to oscillate the support means wheel, tire, brakes, axle, suspension links, dampers, etc.
over a predetermined range of frequencies. Circuitry is Turning to FIG. 2, there is shown an apparatus 11 for
provided responsive to the transducers for determining, performing the present invention to test the dampers
as a function of the frequency of oscillation, the adhe 55 (not shown) associated with vehicle wheels 13 (only
sion of the tire to the support and the phase angle of the two of which are shown). The apparatus includes a pair
response of the tire to the oscillation. The circuitry of supports 15, although any number of supports can be
further determines from the phase angle at a single used up to the total number of tires of the vehicle. The
frequency the adequacy of the damping of the damper supports have associated therewith suitable transducers
under test. 60 (load cells) 17 for measuring the force applied by the
The method of the present invention includes the vehicle through the tires to the supports. Each support
steps of placing a tire associated with a damper to be is driven (as indicated by the arrows labelled “R” to
tested on a movable support, oscillating the movable oscillate vertically by a suitable motor M (and any de
support to impose vertical oscillations on the tire, and sired drive train, not shown).
sensing the force applied by the tire to the support The particular mechanism used to impart oscillatory
means during oscillation of the support means. The motion to the tires is not critical to the present inven
oscillations are controlled to oscillate the support over tion. It is preferred that the mechanism include a base,
a predetermined range of frequencies. The method fur eccentric shafts disposed with respect to the base to
 5,369,974
5 6
impose oscillatory motion on a pair of carriers, the Damper Mounting
motors, and a platform which moves with the carriers. Suspension and Damper Tolerances
By way of example, the counter-rotating eccentric However, the present invention is not limited to any
shafts are mounted in one set of bearings on the base and particular method of taking into account these various
another set of bearings mounted in the carrier. Each factors. It has been found, however, that to accurately
carrier is constrained so that it will move only in the assess the condition of the dampers it is very important
vertical direction and is preloaded by two springs. The to adjust the tires to the proper inflation pressure as
rotation of the eccentric shafts cause the carrier, load recommended by the vehicle manufacturer. This pres
cells, and top plate assembly to oscillate vertically. The sure is usually between 28-35 p.s. i. It is also important
effect of the mass of the platform assembly is subtracted 10 that wheels on the same axle have equal tire pressures.
from the load cell readings electronically by inertia Some improper mounting of the dampers can be de
compensation. It should be understood, however, that tected by the damper tester 11 by comparing the two
any number of other mechanisms for imparting oscilla wheels to each other. In the following table the top nuts
tory motion to the tires could be used instead. on stud-mounted front dampers were not properly
The outputs of load cells 17 are supplied through 5 tightened. These new aftermarket dampers failed the
suitable interface circuitry 19 to a computer 21, which phase angle criteria but did not fail the adhesion criteria.
may be any suitable microprocessor. The computer After proper installation the same dampers passed both
controls one or more output devices (such as the printer criteria.
23 and display 25 shown) to provide test information to
the mechanic. The computer also controls, through a 20 Mounting Adhesion (L/R) Phase Angle (L/R)
suitable motor control circuit 27, motors M. More spe Improper 56.3/44.9 28.1/20.2
cifically, the computer controls the motors to vibrate Proper 61.4/59.5 46.3/38.0
supports 15 over a frequency range. The frequency
range is approximately 25 Hz down to zero Hz. The
motors initially oscillate the platforms up to the desired 25 Using both phase angle and adhesion data it is possi
high frequency, such as 25 Hz, and the oscillations are ble to quantify the following:
then allowed to decrease in frequency. Measurements Suspension Performance
of magnitude and phase are taken as the frequencies Damper Performance
decrease from 25 Hz down to zero. Suspension Balance
Apparatus 11 is used to measure minimum adhesion 30 The suspension balance is the comparison of the two
(like conventional damper testers) and other suspension dampers on the same axle. They should both have virtu
parameters such as minimum phase angle, minimum ally identical characteristics. Excessive imbalance indi
adhesive phase angle, the adhesion curve, the phase cates that the dampers should be replaced as a pair.
angle curve, and the ride comfort. As discussed above, The goal of the pass-fail criteria of computer 21 is to
adhesion is a non-dimensional number representing the 35 classify dampers as good, bad, or marginal. The primary
minimum percentage of remnant vertical tire force to criteria used in the present invention for the evaluation
the pavement. The frequency at the minimum adhesion of the dampers was the phase angle. By examining the
is called the wheel-hop frequency. This is the natural phase angle of the output measured with respect to the
frequency of the unsprung mass, and in extreme cases excitation, computer 21 can calculate the damping
the wheel can break contact with the platform during a value of the damper under test. This damping value,
test, thereby reading zero adhesion and giving an inac unlike the adhesion value, which is also obtained with
curate phase angle. the present apparatus, directly reflects the quality of the
This testing procedure was designed to eliminate the damper under test. A minimum phase angle under thirty
need for previous vehicle specifications. Looking at the (30) degrees indicates that the damper should be re
sinusoidal waveform of the load on the shock absorber 45 placed.
tester platform vs. time, adhesion is found by dividing Since the minimum phase angle reading can give
the minimum load (measured by the load cells) by the unexpectedly high minimum phase angles on vehicles
weight at the wheel. Conceptually, this number states with extremely low adhesions, adhesion is also analyzed
how well the tire stays in contact with the ground. with the present apparatus. On vehicles with adhesion
The phase angle is calculated by finding the angular 50 lower than some percentage depending on the weight of
difference between the position of the top plate and the vehicle and other test parameters, the damper is
magnitude of the load as shown in FIG. 3. The phase considered to fail. Typical values for adhesion lower
angle represents the strength of the damper, with firm limits would vary from 18-28% or so depending upon
dampers having a large phase angle. The minimum car weight, axle, etc.
phase angle is determined by apparatus 11 at the lowest 55 The present invention, therefore, examines up to two
point of the phase angle curve, usually occurring be aspects of the dampers to determine whether the damp
tween 8 and 14 Hertz. Phase angle quantifies the rela ers are acceptable.
tionship of the strength of the suspension damper. The present invention is more clearly illustrated by
Acceptable dampers generally have a minimum phase way of a series of examples, shown in FIGS. 4-6. These
angle of at least thirty (30) degrees, whereas firm damp figures represent the output of printer 23 or display 25,
ers have phase angles over sixty (60) degrees. which are used by the mechanic to determine whether
It should be understood that the tests of adhesion and a damper under test has passed. Although these outputs
phase angle performed by apparatus are affected by the are shown in graphical form, it should be realized that
following parameters: the output could include alphanumeric information in a
Vehicle Weight 65 form readily understood by the user. The exact form of
Tire Effect the output constitutes no part of the present invention.
Damper Type and Conditions FIGS. 4A and 4B illustrate the damper test informa
Suspension Type tion provided by the present invention for a new vehi
 5,369,974 8
7
cle, in this case a Citation. FIG. 4A contains the display said determining means determining the damping value
of information for the front tires in graphical form, of the damper under test from the time response of the
although it is understood that additional alphanumeric vehicle to the oscillation, said determining means com
information may also be displayed. This information paring the determined damping value with the damping
would include the pass/fail results calculated as de- 5 value threshold to determine whether the damper under
scribed above. For example (see FIG. 6), the minimum test passes.
adhesion required for a damper to pass is 34.3% (this 4. The apparatus as set forth in claim 1 wherein the
number is illustrative only). FIG. 4B reveals that the left determining means further includes means for calculat
front damper had a passing minimum adhesion of 72.0% ing the balance of damping for left and right dampers
and the right front damper had a passing minimum 10 for the same vehicle, and a balance threshold which a
adhesion of 67.6%. pair of dampers under test must meet for the pair of
The present invention also provides for failing damp dampers to pass, the determining means determining the
ers if the dampers are not balanced within ten percent balance of damping for left and right dampers for the
for adhesion (when weight is taken into account). The same vehicle and comparing the determined balance
new dampers of FIG. 4 easily pass this test. In addition 15 with the balance threshold to determine whether the
the phase angle can be used to estimate the damping pair of dampers under test pass.
value of the damper under test. 5. Apparatus for testing suspension and dampers of a
FIG. 4B shows the results in graphical form for all motor vehicle without removing the dampers from the
four dampers. As can be readily seen from the graphs, vehicle comprising:
all four dampers of this new vehicle have essentially the a movable support for contacting the bottom surface
same response to the test. of a motor vehicle tire associated with a damper to
Turning to FIGS. 5A and 5B, the same output is be tested;
shown for a similar car, with the rear dampers com means for oscillating the movable support to impose
pletely missing. The results of FIG. 5A, for the front vertical oscillations on the tire;
dampers, are essentially the same as those of FIG. 4A. 25 means for sensing the force applied by the tire to the
However, the results for the rear dampers are very support during oscillation of the support means;
different. Examination of the graphs of FIG. 5B clearly means for controlling the oscillating means to oscil
illustrate the defective nature of the (non-existent) rear late the support means over a predetermined range
dampers. FIG. 6, a summary output for the test of FIG. of frequencies;
5, illustrates the point clearly. While the front dampers 30 means responsive to the sensing means for determin
easily pass all three tests, the rear dampers fail the adhe ing, as a function of the frequency of oscillation,
sion test, and almost fails the left/right balance test. the time response of the vehicle to the oscillation,
From the above, it can be seen that the present inven said determining means further determining from
tion readily and easily performs multiple damper tests, said time response the adequacy of the damping of
any of which can be used to fail the damper under test. 35
the damper under test, said determining means
Of course, the examples given herein are illustrative including a minimum phase threshold which the
only and are not to be taken in a limiting sense. damper must meet for the damper to pass, said
What is claimed is:
1. Apparatus for testing suspension and dampers of a determining means comparing the time response of
motor vehicle without removing the dampers from the 40 the vehicle with the minimum phase threshold to
vehicle comprising: determine whether the damper under lest passes;
a movable support for contacting the bottom surface said determining means estimating the damping value
of a motor vehicle tire associated with a damper to of the damper under test from the time response at
be tested; a single frequency.
means for oscillating the movable support to impose 45 6. Apparatus for testing suspension and dampers of a
vertical oscillations on the tire; motor vehicle without removing the dampers from the
means for sensing the force applied by the tire to the vehicle comprising:
support during oscillation of the support means; a movable support for contacting the bottom surface
means for controlling the oscillating means to oscil of a motor vehicle tire associated with a damper to
late the support means over a predetermined range 50 be tested;
of frequencies; means for oscillating the movable support to impose
means responsive to the sensing means for determin vertical oscillations on the tire;
ing, as a function of the frequency of oscillation, means for sensing the force applied by the tire to the
the time response of the vehicle to the oscillation, support during oscillation of the support means;
said determining means further determining from 55 means for controlling the oscillating means to oscil
said time response the adequacy of the damping of late the support means over a predetermined range
the damper under test, said determining means of frequencies;
including a minimum phase threshold which the means responsive to the sensing means for determin
damper must meet for the damper to pass, said ing, as a function of the frequency of oscillation,
determining means comparing the time response of 60 the time response of the vehicle to the oscillation,
the vehicle with the minimum phase threshold to said determining means further determining from
determine whether the damper under test passes. said time response the adequacy of the damping of
2. The apparatus as set forth in claim 1, wherein the the damper under test, said determining means
predetermined frequency range is from zero hertz to including a minimum phase threshold which the
over twenty hertz. 65 damper must meet for the damper to pass, said
3. The apparatus as set forth in claim 1 wherein the determining means comparing the time response of
determining means includes a damping value threshold the vehicle with the minimum phase threshold to
which the damper under test must meetin order to pass, determine whether the damper under test passes;
 5,369,974
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said determining means including means for deter placing a tire associated with a damper to be tested on
mining as a function of the frequency of oscillation a movable support;
the adhesion of the tire to the support and further oscillating the movable support to impose vertical
including an adhesion threshold which the damper oscillations on the tire;
under test must meet in order to pass. sensing the force applied by the tire to the support
7. The apparatus as set forth in claim 6 wherein the means during oscillation of the support means;
minimum measured value of adhesion for a damper controlling the oscillations to oscillate the support
under test must meet the adhesion threshold for the over a predetermined range of frequencies;
damper to pass. electronically determining, as a function of the fre
8. Apparatus for testing suspension and dampers of a 10 quency of oscillation, the time response of the vehi
motor vehicle without removing the dampers from the cle to the oscillation, and further electronically
vehicle comprising: determining from said time response at a frequency
a movable support for contacting the bottom surface the adequacy of the damping of the damper under
of a motor vehicle tire associated with a damper to test, said determining step including comparing the
be tested; 15
time response of the vehicle with a minimum phase
means for oscillating the movable support to impose threshold to determine whether the damper under
vertical oscillations on the tire; test passes.
means for sensing the force applied by the tire to the 11. The method as set forth in claim 10 wherein the
Support during oscillation of the support means; predetermined frequency range is from zero hertz to
means for controlling the oscillating means to oscil over twenty hertz.
late the support means over a predetermined range 12. The method as set forth in claim 10 wherein the
of frequencies; damping value is electronically calculated from the time
means responsive to the sensing means for determin response.
ing, as a function of the frequency of oscillation, 3. The method as set forth in claim 10 further includ
the time response of the vehicle to the oscillation, 25
ing failing a damper under test unless it meets a damping
said determining means further determining from value threshold.
said time response the adequacy of the damping of 14. The method as set forth in claim 10 further includ
the damper under test, said determining means ing electronically calculating the balance of damping
including a minimum phase threshold which the for left and right dampers for the same vehicle axle, and
damper must meet for the damper to pass, said 30 failing a pair of dampers unless they meet a damping
determining means comparing the time response of balance threshold.
the vehicle with the minimum phase threshold to 15. A method of testing suspensions and dampers of a
determine whether the damper under test passes;
said determining means including means for deter motor vehicle without removing the dampers from the
mining the adhesion of the tire to the support. 35 vehicle, said method comprising the steps of:
9. Apparatus for testing suspension and dampers of a placing a tire associated with a damper to be tested on
motor vehicle without removing the dampers from the a movable support;
vehicle comprising: oscillating the movable support to impose vertical
a movable support for contacting the bottom surface oscillations on the tire;
of a motor vehicle tire associated with a damper to sensing the force applied by the tire to the support
be tested; means during oscillation of the support means;
means for oscillating the movable support to impose controlling the oscillations to oscillate the support
vertical oscillations on the tire; over a predetermined range of frequencies;
means for sensing the force applied by the tire to the determining, as a function of the frequency of oscilla
support during oscillation of the support means; 45 tion, the time response of the vehicle to the oscilla
means for controlling the oscillating means to oscil tion, and further determining from said time re
late the support means over a predetermined range sponse at a frequency the adequacy of the damping
of frequencies; of the damper under test, said determining step
means responsive to the sensing means for determin including comparing the time response of the vehi
ing, as a function of the frequency of oscillation, 50 cle with a minimum phase threshold to determine
the time response of the vehicle to the oscillation, whether the damper under test passes; and
said determining means further determining from failing the damper under test unless it meets an adhe
said time response the adequacy of the damping of sion threshold.
the damper under test, said determining means 16. The method as set forth in claim 15 wherein the
including a minimum phase threshold which the 55 minimum measured value of adhesion for a damper
damper must meet for the damper to pass, said under test Inust exceed the adhesion threshold for the
determining means comparing the time response of damper to pass.
the vehicle with the minimum phase threshold to 17. A method of testing suspensions and dampers of a
determine whether the damper under test passes; motor vehicle without removing the dampers from the
said determining means further including means for 60 vehicle, said method comprising the steps of:
calculating the balance of adhesion for left and placing a tire associated with a damper to be tested on
right dampers for the same vehicle axle, and an a movable support;
adhesion balance threshold which a pair of damp oscillating the movable support to impose vertical
ers under test must meet for the pair of dampers to oscillations on the tire;
paSS. 65 sensing the force applied by the tire to the support
10. A method of testing suspensions and dampers of a means during oscillation of the support means;
motor vehicle without removing the dampers from the controlling the oscillations to oscillate the support
vehicle, said method comprising the steps of: over a predetermined range of frequencies;
 5,369,974 12
11
determining, as a function of the frequency of oscilla failing a pair of dampers unless they meet an adhesion
tion, the time response of the vehicle to the oscilla balance threshold.
tion, and further determining from said time re 18. The method as set forth in claim 17 further includ
sponse at a frequency the adequacy of the damping ing failing a damper unless it meets an adhesion balance
of the damper under test; 5 threshold which is a function of vehicle weight.
determining, as a function of frequency, the adhesion 19. The method as set forth in claim 17 further includ
of the tire to the support; ing failing a pair of dampers unless it meets an adhesion
calculating the balance of adhesion for left and right balance threshold which is a function of tire axle.
ck k :k k sk
dampers for the same vehicle; and
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