US007695075B1

(12) United States Patent

(10) Patent N0.:

Mackiewicz
(54)

(75)

(45) Date of Patent:

DISC THICKNESS VARIATION

COMPENSATION

Inventor:

John Edmund Mackiewicz, Niles, Ml

US

Notice:

Apr. 13, 2010

2005/0264102 A1 *
2005/0269875 A1 *

12/2005
12/2005

TeZuka ..................... .. 303/152

Maki et a1. ..
303/152

2008/0067867 A1 *

3/2008

Taguchi .................... .. 303/167

* Cited by examiner

Primary ExamineriChristopher P Schwartz

Assigneej Robert Bosch

(*)

US 7,695,075 B1

Stuttgart

AZZOIIIEy, Agent, 01'' FirmiMaginot, Moore & Beck

Subject to any disclaimer, the term of this

(57)

$12318 11S5ZXleILdeg3O5 adjusted under 35

A vehicle braking system of the type having individually

' ' '

( ) y

ays'

ABSTRACT

controlled brakes With respective angularly ?xed (17, 19) and

rotatable (11) friction surfaces urged into contact by an opera

(21) Appl' NO" 11/856747

(22) Filed,
sep_ 18, 2007

tor initiated (35, 65) braking force for each of a plurality of

rotatable vehicle Wheels has braking torque variations Within

(51)

a Wheel revolution alleviated for each Wheel by sensing varia

tions in braking force (45, 71) as a function of Wheel angular

Int CL

3601' 8/32

(200601)

position (49, 77) during a complete vehicle Wheel revolution

us. Cl. ................................... .. 303/191; 188/18 A

and initiating (59) a reduction in braking force during a Sub

(58) Field of Classi?cation Search ............. .. 188/18 A

188/158_ 303/3 7 20 191_ 324/161

sequenFYvheel revolutio. priorlo the Wheel reaching an angu'

lar pos1t1on (87) at vvhlch an lncrease 1n braking force Was

(52)

See application ?le for complet sarcil history'

sensed during a prev1ous Wheelrevolut1on.A part1cular Wheel

U'S' PATENT DOCUMENTS

4,8711 13 A
10/1939 Taig

angular position may be identi?ed as a reference position and

data indicative of the sensed variations stored (51, 75) as a
function of Wheel angular position relative to the reference
position. This stored data is then utiliZing (63, 59) to deter
mine the angular position (85) at Which braking force reduc

6,087,826 A *

tion is initiated. Identi?cation of a reference position may be

(56)

References Cited

6,322,160 B1

7/2000 Donaih ,,,,,,,,,,,,,,,,,,,,, __ 324/161

11/2001 Loh et a1.

directly done by sensing an angular anomaly (49) generated

6,375,281
6,378,669 B1 *

4/2002 Angerfors
Kumsako et.................
a1~
.. 303/176

6,607,252 B2 :

8/2003 Weng et a1. ................. .. 303/87

20023620129533;

giglitral'

" 1881/5;E 5);II;

2004/0046444 A1 *

3/2004 Heubner' 8'; 11121111111: ' 303/1135

2004/0104618 A1 *

6/2004

2005/0067233 A1 *

3/2005 Nilsson et a1. ............ .. 188/158

datathe
indicative
Wheel Speed
of thesensors
sensed variations,
or indirectly
analyzing
Storing
(55, 83) the
Stored data to identify any established patterns Within the

data, and identifying a particular Wheel angular position as a

reference Position based on an identi?ed repetitive Pattern

Yamamoto et a1. .......... .. 303/20

4 Claims, 3 Drawing Sheets

BRAKE

35

COMMAND J

\1
MASTER

37

CYLINDER

59 \

\ll

INITIATE

41

PRESSURE

r9 CORRECTIVE
ACTION

MODULATOR
/

/|\
?gcslgg?

39

43

WHEEL

wmam. SPEED

/| CYLINDER

SENSOR

PRESSURE

TRANSDUCER

FLUCTUA'I'ION

\_45
63

47

49

AC/DC
EPARATOR

STORE AC COMPONENT AS A
FUNCTION OF ANGULAR POSITION

I \-5 l

US. Patent

Apr. 13, 2010

Sheet 1 of3

US 7,695,075 B1

mm

o02o2.w8n2.

mmc02o2w3n3

2:30:m

23P59.h30

Q.

con-8w

.9.co

P55

US. Patent

Apr. 13, 2010

Sheet 2 0f 3

BRAKE

US 7,695,075 B1

35

COMMAND

Fig. 4
MASTER

37

CYLINDER

59

\ll

41

PRESSURE
MODULATOR

4-3\

WHEEL
CYLINDER

39/

WHEEL SPEED
SENSOR

PREssURE

ANTICIPATE

/ ANGULAR

TRANSDUCER

PRESSURE

FLUCTUATION

POsmON '_

\_45
63

47

49

AC/DC

V'SEPARATOR
STORE AC COMPONENT AS A
FUNCTION OF ANGULAR POSITION

\5 l

3S

Flg- 5

BRAKE
COMMAND

61

37

\d WHEEL sPEED

MASTER _/

sENsOR

59 \ .

J1

INITIATE

CYLINDER

41

PRESSURE

WHhhL

CORREcnvE

/ MODULATOR

ACTION

_/

CYLINDER

39

ANTICIPATE A
PRESSURE
57

PRESSURE
TRANSDUCER

FLUCTUATION

/|\

55

COMPARE CURRENT
AND PRIOR VALUES

45
47

AC/Dc

\JYSEPARATOR
STORE AC
COMPONENT VALUES *~/

53

US. Patent

Apr. 13, 2010

65

US 7,695,075 B1

BRAKE
.

67

Sheet 3 of3
6

COMMAND

COMMANDED
(TARGET)
CLAMPING FORCE

INITIATE

ELECTRIC

CORREC'HVE

ACTUATOR

ACTION

79

WHEEL SPEED

\J

'|\

SENSOR

ANGULAR

ANTICIPATE
PREssURE

POSITION
MEAsURED

ELUcTUAnoN

CLAMPING

COMPARE

FORCE
71

77d

_/

73

sToRE VARIA'HON VALUES As

A FUNCTION OF ANGULAR POSITION

\ 75

'

Flg' 7

BRAKE

65

COMMAND

67
COMMANDED

(TARGET)
CLAMPING FORCE

WHEEL sPEED

SENSOR

lNI'?A'?-I

m ,E _____>

(30122511014

ANTICIPATE

PREssURE

FLUCTUATION

\I, /69

ELECTRIC

AcruAToR

91

MEASURED

CLAMPING
FORCE

'1

COMPARE CURRENT

71 .1

coMPARE

73/

AND PRIOR vALUEs \

)F

83
81

STORE VARIATION
vALUEs

US 7,695 ,075 B1
1

DISC THICKNESS VARIATION

COMPENSATION

pected vibration that the driver of the vehicle feels through the
steering Wheel, brake pedal and seat track. The vibration
associated With brake roughness can be transmitted to the

driver of the vehicle, causing the driver to feel the vibrations.

They concluded the prior art hydraulic brake system With a
DTV less than 6 microns did not experience signi?cant brake
torque variation, but When the DTV of the prior art rotor is 30
microns, the brake torque variation can become signi?cant.
The solution suggested in this patent involves a circular

BACKGROUND OF THE INVENTION

The present invention relates to vehicle braking systems

and more particularly to compensation techniques for prob
lems created by irregularities in braking surfaces, such as disc
thickness variations in electrically or hydraulically actuable
disc brakes, to reduce braking surface induced braking torque

enlarged drum in Which a pressure Wave in the ?uid entering

the substantially circular enlarged ?oW chamber from a ?uid
line Will be forced to move in a substantially circular path and
re?ect off of the peripheral Wall at a plurality of points to
thereby dissipate the pressure Wave. These tWo patented sys
tems attempt to react to pressure changes When those changes

variations.
DESCRIPTION OF THE RELATED ART

Both drum and disc brakes are commonplace on todays

vehicles. Drum brakes have an annular drum ?xed to a Wheel

occur.

With a set of brake shoes Which expand outWardly upon

application of hydraulic pressure to a Wheel cylinder to

US. Pat. No. 6,378,669 recogniZes it is dif?cult to set the

rotating axis of a Wheel perfectly perpendicular to a brake
disc. Therefore, it is often the case that a brake disc slightly
Wobbles While rotating. If brake pads are pressed against a
brake disc turning in a Wobbling state, there occurs a slight
Wall thickness variation in a circumferential direction of the
brake disc. Occurrence of such a variation in Wall thickness
may become a cause of vibrations of the Wheel during brak
ing, or may cause the reaction force exerted on the brake pedal
to ?nely ?uctuate, and may give a disagreeable feel to a driver
of the vehicle. The patented system utiliZes an ECU, pressure
sensors for measuring the oil pressures in the Wheel cylinders
and the Wheel speed sensors for detecting the rotational posi

engage the drum interior thereby braking the Wheel. Disc

brakes have a rotatable disc or rotor ?xed to a Wheel and a 20

spanning caliper unit supporting friction pads near each disc

face. Application of hydraulic pressure to a Wheel cylinder
applies a clamping force causing the jaWs of the caliper to
close toWard one another forcing the pads to engage the

opposite disc faces braking the Wheel.

These braking systems are typically hydraulically operated

25

and often include an antilock (ABS) feature. Many neWer

vehicles provide additional features knoWn as electronic sta

bility programs (ESP) to enhance vehicle stability. These

knoWn ABS and ESP systems typically have an electronic

30

control unit (ECU) Which receives signals from individual

Wheel speed sensors and other transducers for controlling
hydraulic pres sure modulators to release and reapply braking
forces to the Wheels. Some braking systems are electrically
actuated. For example, US. Pat. No. 4,877,113 teaches an
electric disc brake Where a vehicle operator commanded
clamping force enables an electric actuator to brake the
Wheel.

stored in correspondence to the rotational position (angle) of

the brake disc. The brake pads are placed in contact With the
increased Wall thickness portion of the brake disc by a strong
35

Drum or disc eccentricities or other irregularities may

induce undesirable vibrations during braking. For example,

40

Disc Thickness Variation (DTV) of a rotor directly causes

that the Wear of the brake disc can be reduced. The state of
contact betWeen the brake disc and the friction member may
45

increase and thereby increases the brake torque.

US. Pat. No. 6,322,160 recogniZed that operational char
acteristics of a brake could cause changes in hydraulic ?uid
pressure inducing vibrations. The patentees introduced a

spring-loaded hydraulic damper in the brake line in an

attempt to attenuate tactile vibration caused by hydraulic ?uid
pressure changes induced in a hydraulic brake system by a
characteristic of a hydraulic -operated brake When the brake is
being actuated to apply brake torque to a rotating object.
US. Pat. No. 6,607,252 recogniZed the existence of disc
thickness variations and the accompanying brake torque
variations and attempted to dissipate hydraulic pressure
Waves in an enlarged circular chamber. The patentees point
out that vehicles having a hydraulic brake system have expe
rienced brake torque variation due to disc thickness variation
(DTV) in the rotor of disc brakes or insu?icient cylindricity of
the drum in drum brakes. The forces created by the brake
torque variation are transmitted to the tire of the vehicle and
cause the tires of the vehicle to vibrate in the longitudinal
direction of the tire. This vibration is thereafter transmitted to
the brake system and chassis of the vehicle and results in
brake roughness. Brake roughness is de?ned as the unex

pressing force, and are placed in contact With the relatively

small Wall thickness portion of the brake disc by a Weak
pressing force, so that the Wall thickness variation of the brake
disc is quickly eliminated. The oil pressure control eliminates
the Wall thickness variation of a brake disc by planing (i.e.,
removing material from) an increased Wall thickness portion
of the brake disc, and avoids contact of the brake pads With a
relatively small-Wall thickness portion of the brake disc, so

Brake Torque Variation (BTV). As the thicker portion of the

rotor passes through the disc brake caliper/brake pads, the
resistance of the brake to open up to accommodate the addi
tional rotor thickness causes the clamp force of the caliper to

tions of the brake discs to function as a Wall thickness varia

tion detector. A state of the Wall thickness of the brake disc is

be controlled While a vehicle is not under braking. Therefore,

since the control for eliminating (suppressing) a variation in
the Wall thickness of the brake disc is performed While the
vehicle is not under braking, the state of contact betWeen the
brake disc and the friction member can be set to an optimal

50

state for eliminating (suppressing) the Wall thickness varia

55

tion of the brake disc. The patentees are, in essence, introduc

ing intentional Wear, preferably When the brakes are not being
applied, to true-up (reduce or eliminate Wobble of) a rotor. It
is desirable to lessen or avoid the adverse effects of manufac
turing imperfections, Wear or heat induced Warping or distor

tion, off-axis mounting and other irregularities in braking

surfaces.
SUMMARY OF THE INVENTION
60

The present invention provides an anticipatory corrective

action for a recurring braking surface anomaly by recogniZ

ing a repeated pattern and providing a prepared synchroniZed
65

response.
The invention comprises, in one form thereof, a method of

alleviating disc brake rotor induced braking torque variations

by applying a relatively constant braking force to the rotor

US 7,695 ,075 B1
3

and observing ?uctuations of the relatively constant braking

force. The rotor angular position is monitored, and the

thicker portion from betWeen the pads Will be accompanied

by a reduction in braking torque and loWering of the hydraulic
cylinder pressure.

observed braking force ?uctuations and monitored rotor

angular position utiliZed to anticipate a future ?uctuation in

An illustrative pro?le for rotor 11 is shoWn in FIG. 2 Where

the thickness begins increasing from some standard or refer

braking force. The applied braking force is relieved if the

anticipated braking force ?uctuation is an increase and
increased if the anticipated braking force ?uctuation is a
decrease to moderate the adverse effects of irregularities in
disc thickness.
Also in general, and in one form of the invention, a method
of compensating for irregularities in disc brake rotor thick
ness in a vehicle disc braking system includes monitoring

ence thickness at Zero degrees reaching a maximum deviation

near the midpoint of its revolution and returning to the stan

dard thickness near the end of one complete revolution. The
greatest thickness variation 29, of course occurs as the thick

est region 23, 25 passes betWeen the pads of FIG. 1. For the
disc thickness variation pattern shoWn in FIG. 2, a relatively
constant braking force command Would result in a nearly
identical braking force torque variation pattern as shoWn at 33

applied braking force during a braking event throughout at

least one complete rotor revolution and recording variations

in FIG. 3.
As shoWn in FIG. 2, the measurement and discernment of
increment 27 is di?icult as it is very small, Whether measured
in DTV or its corresponding BTV. Measurement 29 is much
easier to measure and recogniZe as a departure from normal

in the monitored braking force throughout the complete rotor

revolution. Sub sequent variations in applied braking force are
compared With the recorded variations to establish a rotor

angular reference position, and the applied braking force

anticipatively varied to ameliorate the adverse effects of rotor
thickness variations.
An advantage of the present invention is that a more uni

20

higher brake torque. In the illustrations of FIGS. 2 and 3, the

form braking torque is provided throughout complete Wheel

control response time 31 is shoWn as about one-sixth of one

rotations.
BRIEF DESCRIPTION OF THE DRAWINGS

Wheel revolution. The system needs to alloW for the control

25

example of the multitude of possible variation patterns.

rotor and spanning friction pads;

30

Wheel cylinder 41 to brake Wheel rotation. The pressure

35

40

FIG. 6 is a block diagram illustrating one technique of

compensation for disc thickness variations in an electric disc

braking system; and

45

braking system.

50

Referring noW to the draWings and particularly to FIG. 1,

there is shoWn a cross-sectional vieW of a portion of a disc
55

sure to a conventional Wheel cylinder (not shoWn). The cali

per supports respective friction pads 17 and 19 Which are
forced into braking engagement With the rotor 11 upon appli
60

tion is nonuniform With the greatest thickness depicted

betWeen points 23 and 25. If the rotor section depicted is
moving betWeen the pads 17 and 19 in the direction of arroW

direct method.
The direct method uses anABS Wheel speed sensor 43 With
a special tooth or other indicia to denote a synchronizing point
on the rotor. The tooth can be con?gured to provide a larger
voltage signal or a prolonged one sensed at 49. Other suitable
techniques for identifying an angular rotor reference such as
counting a knoWn number of Wheel speed sensor teeth may be
employed. In this Way, the pressure variations may be stored
at 51 as a function of the rotor angular orientation. Either

analog or periodic digital sample values may be stored. An

21, the pads as Well as jaWs 13 and 15 Will be forced aWay

from one another by the approaching region of greatest thick

signal as indicated at 47. The DC portion of the signal repre

sents the mean apply pressure and the AC portion represents
the changes in brake pressure due to the DTV of the rotor. In
this Way, indirect detection of the rotor DTV is recogniZed
and recorded for each revolution of each rotor. The registra
tion or synchronization of this pressure/DTV mapping can be
made to the absolute rotor position by either an inferred or a

brake system. Wheel mounted rotor 11 is spanned by a brake

cation of hydraulic pressure. The thickness of the rotor sec

Will be recorded. The ABS or ESP ECU can monitor each of

these signals and separate the AC (transient) portion of the

signal from the DC (relatively steady state) portion of the

Corresponding reference characters indicate correspond

ing parts throughout the several draWing vieWs.

caliper having a pair of jaWs 13 and 15 Which may be urged

toWard one another by the application of hydraulic ?uid pres

ESP modulator 39 can record the hydraulic pressure applied

to Wheel cylinder 41. It Will be understood that there Will be at
least a pressure modulator, Wheel cylinder, Wheel speed sen
sor and pressure transducer for each of several different

vehicle Wheels and the hydraulic pressure applied to each

Wheel cylinder for each corresponding brake/brake channel

FIG. 7 is a block diagram illustrating another technique of

DETAILED DESCRIPTION OF THE INVENTION

control unit to alternately bleed and build Wheel cylinder ?uid

pressure upon sensing an imminent locking of the Wheel.
During a loW or moderate force brake apply, a signal from a
pressure transducer 45 located in or coupled to the ABS or

FIG. 5 is a block diagram illustrating another technique of

compensation for disc thickness variations in a hydraulic

compensation for disc thickness variations in an electric disc

In FIG. 4, When a vehicle operator depresses the brake

pedal, a brake command 35 enables the master cylinder 37 to
supply pressure ?uid by Way of pressure modulator 39 to the
modulator 39 and Wheel speed sensor 43 are conventional
ABS or ESP components Which cooperate With an electronic

antilock braking system;

antilock braking system;

response time by anticipating the need for correction. It Will

be understood that this is merely an illustrative rotor pro?le
and the illustrated rotor thickness variation is only one

FIG. 1 is a partial cross-sectional vieW of a brake system

FIG. 2 is a graph shoWing an illustrative rotor pro?le With

thickness variation as a function of relative angular position;
FIG. 3 is a graph comparing uncorrected and corrected
variations in braking torque as a function of relative angular
position for the illustrative rotor of FIG. 2;
FIG. 4 is a block diagram illustrating one technique of
compensation for disc thickness variations in a hydraulic

DTV or BTV. HoWever, by the time this threshold is reached,

the system cannot react fast enough to limit or reduce the

ness resulting in an increase in the cylinder hydraulic pres sure

angular position at Which an undesired change in the pres sure

Will occur and the current rotor angular position from sensor

and an increase in braking torque. Subsequent passage of the

43 alloW circuit 63 to anticipate that change. Knowing the

65

US 7,695 ,075 B1
5

system response time and current measured Wheel speed from

the BTV and hence the DTV of the rotor to be mapped and
stored at 75 as a function angular position as provided by the
sensor 77. Wheel speed sensor 79 and position or orientation

sensor 43, a corrective action (hydraulic pressure increase or

decrease) is initiated at 59.

The inferred method is illustrated in FIG. 5 Which lacks the

sensor 77 are analogous to the sensor 43 and position detector

49 of FIG. 4. The anticipation and corrective action proceed

as discussed in conjunction With that ?gure except for the fact

angular position sensing function 49. Here, a BTV circum

ferential pro?le of the rotor is recorded at 53 and then syn
chroniZed to a selected point on the rotor circumferentially. A

that the corrective action is noW applied to the electric actua

comparison circuit 55 is designed to recogniZe a repetition of

tor 69 preferably by modifying the target clamping force 67.

a pattern previously stored at 53. As a simple example, if the

In addition to the absolute rotor position technique of FIG. 4,

rotor thickness varies sinusoidally, the ninety degree maxi

registration or synchronization can be made by an inferred

method as shoWn in FIG. 7. The results of comparison 73 are
stored at 81 and current comparison values compared to pre

mum or tWo hundred seventy degree minimum values are

easily identi?ed. After the tWo hundred seventy degree mini

sure Will occur. SomeWhat prior to Zero degrees, as deter

viously stored ones at 83. Changes in the commanded clamp

ing force 67 take place more sloWly than changes in the
measured force 71 alloWing rotor thickness induced varia

mined by the system response time and current measured

tions to be mapped over several Wheel revolutions and com

Wheel speed from sensor 61, the circuit 59 initiates a pressure

pared one revolution to another establishing the synchroniza

tion for pressure ?uctuation anticipation at 91.
In either FIG. 6 or 7, the mapping process provides the

mum, the next occurring Zero value Would be Zero degrees

Where circuit 57 recogniZes an undesired increase in the pres

reduction. In other Words, the logic can knoW Which portion

of the rotor is passing through the brake by constantly recog

niZing and syncing to the previously recorded pro?le. The

20

pressure records or mappings may all be stored in a common

memory and the functions of AC separation, comparison,

anticipation and initiation of corrective action all performed
for each Wheel by the ECU.
With either the method of FIG. 4, or of FIG. 5, or a com

reduction With enough lead time to be effective. As illustrated

in FIG. 3, torque reduction commences at 85 in anticipation of

the presentation of the thicker portion to the caliper pads at the

25

time shoWn at 87. In addition, the controlled pressure

increases and as a result, the mechanical resistance (stiction)
also increases and can be compensated by an additional con
trol pressure decrease. Thus the lead time 31 is set by knoWing

30

mean brake torque, and system voltage resulting in a cor

bination of the tWo, an ongoing algorithm can be used to

continually monitor and update the rotor DTV pro?le stored

at 51 or 53, as it Will change over the life of the rotor, but not
signi?cantly during a stop or a small series of stops. This

mapping process provides the WindoW of opportunity to pre

clude BTV by anticipating (57 or 63) the upcoming thicker
portion of the rotor and initiating torque reduction by use of
the ABS or ESP modulator 39 With enough lead time to be
effective. This is accomplished in the same manner of current
ABS. The modulator 39 decreases brake pressure and hence

system response time for the given conditions of rotor speed,

rected BTV as shoWn at 89.

Thus, While a preferred embodiment has been disclosed,

numerous modi?cations Will occur to those of ordinary skill
35

the brake torque by isolating the circuit and then decaying

brake ?uid from this isolated circuit. Increasing or restoring
brake torque is accomplished in the same manner except ?uid
is added back into the subject circuit by the modulator. The

lead time is set by knoWing system response time 31 (FIG. 3)

for the given conditions of rotor speed from sensor 43 or 61,
mean brake torque, and other system parameters. Therefore,
mapping of the rotor from a BTV standpoint, does provide a
solution as the larger threshold amount can be the trigger to
recogniZe the BTV problem and then prepare a control strat
egy to compensate for it for the next or a subsequent revolu

in this art. Accordingly, the scope of the present invention is to

be measured by the scope of the claims Which folloW.
What is claimed is:
1. In a vehicle braking system of the type having individu

ally controlled brakes having respective angularly ?xed and

40

45

rotatable friction surfaces urged into contact by an operator

initiated braking force for each of a plurality of rotatable
vehicle Wheels, a method of alleviating braking torque varia
tions Within a Wheel revolution, comprising, for each Wheel,
the steps of:
sensing variations in braking force as a function of Wheel
angular position during a complete vehicle Wheel revo

lution,

tion of the rotor. This recognition technique precludes the

need to measure and appropriately interpret small changes in
brake torque such as shoWn at 27 in FIG. 2 and also alloWs
adequate anticipation or reaction time to initiate a control

WindoW of opportunity to preclude BTV by anticipating the

upcoming thicker portion of the rotor and initiating torque

initiating a reduction in braking force during a subsequent

Wheel revolution prior to the Wheel reaching an angular
position at Which an increase in braking force Was
50

sensed during a previous Wheel revolution,

identifying a particular Wheel angular position as a refer
ence position,

response inclusive of the system response lag time. This

alloWs synchronization of the effects of the control to reduce
brake torque, to exactly correspond With the thicker portion of
the rotor passing through the brake caliper. The normal sys

storing data indicative of the sensed variations as a function

physical realiZation of amelioration control, can be overcome

of Wheel angular position relative to the reference posi

tion, and
utiliZing the stored data to determine the angular position at

by the mapping technique, knoWn timing of the subsequent

cycles, and application of the anticipatory control.

Which braking force reduction is initiated.

2. In a vehicle braking system of the type having individu

tem control lags of detection, computation of correction,

55

ally controlled brakes having respective angularly ?xed and

FIGS. 6 and 7 illustrate the application of the concepts

discussed so far to an electric disc brake system. The vehicle
operator issues a brake command 65 specifying a desired

60

brake caliper clamping force 67 Which is conveyed to an

electric brake actuator 69 applying a braking force to the
rotor. During a loW or moderate force brake apply, the electric
disc brake can provide a constant target clamp force and

simultaneously record the actual clamp force and/or brake

torque via onboard transducers 71. A comparison 73 alloWs

65

rotatable friction surfaces urged into contact by an operator

initiated braking force for each of a plurality of rotatable
vehicle Wheels, a method of alleviating braking torque varia
tions Within a Wheel revolution, comprising, for each Wheel,
the steps of:
sensing variations in braking force as a function of Wheel
angular position during a complete vehicle Wheel revo

lution,

US 7,695 ,075 B1
8

7
initiating a reduction in braking force during a subsequent
Wheel revolution prior to the Wheel reaching an angular

(d) storing data indicative of the sensed variations,

(e) analyZing the stored data to identify repetitive patterns
Within the data, and
Wherein step (c) includes identifying the particular Wheel

position at Which an increase in braking force Was

sensed during a previous Wheel revolution, and

identifying a particular Wheel angular position as a refer
ence position,
Wherein the vehicle braking system includes a Wheel speed
sensor for each Wheel, and the step of identifying includ

angular position as the reference position based on an

identi?ed repetitive pattern identi?ed in step (e).

4. In a vehicle braking system having individually con
trolled brakes each comprising a rotor ?xed to and rotatable
With a vehicle Wheel, a relatively ?xed caliper spanning a
portion of the rotor, a pair of friction pads, one on each side of

ing sensing an angular anomaly generated by the Wheel

speed sensor, and

the rotor and supported by the caliper, and a brake actuator for
urging the pads toWard one another to apply a braking force
and thus a braking torque to the rotor, the improvement com

Wherein the Wheel speed sensor includes a plurality of

equiangularly spaced indicia one of Which differs from

each of the others and provides the angular anomaly.

prising:

3. In a vehicle braking system of the type having individu

ally controlled brakes having respective angularly ?xed and

rotatable friction surfaces urged into contact by an operator
initiated braking force for each of a plurality of rotatable
vehicle Wheels, a method of alleviating braking torque varia
tions Within a Wheel revolution, comprising, for each Wheel,
the steps of:
(a) sensing variations in braking force as a function of

15

thickness variation indicative variations in the trans

ducer signal from relatively sloW operator applied brak

20

ing force indicative variations in the transducer signal;

a memory for storing relatively rapid signal variations over
a plurality of vehicle Wheel revolutions;
a circuit utiliZing the stored variations to anticipate future

25

a hydraulic pressure modulator responsive to the variation

Wheel angular position during a complete vehicle Wheel

revolution;
(b) initiating a reduction in braking force during a subse
quent Wheel revolution prior to the Wheel reaching an
angular position at Which an increase in braking force
Was sensed during a previous Wheel revolution,
(c) identifying a particular Wheel angular position as a

reference position,

a pressure transducer for monitoring applied braking force

and providing a signal indicative thereof;
a separating circuit for separating relatively rapid disc

braking force variations; and

anticipating circuit to moderate the anticipated varia

tions and resulting braking torque variations.

*