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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 8, Issue 5, May 2017, pp. 33–41, Article ID: IJMET_08_05_004
Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=5
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
DESIGN AND ANALYSIS OF A HYDRAULIC
BRAKE CALIPER
Rathin Shah
Department of Mechanical Engineering,
Vishwakarma Instititute of Techonology, Pune, Maharashtra, India
Chinmay Shah
Department of Mechanical Engineering,
Vishwakarma Instititute of Techonology, Pune, Maharashtra, India
Swapnil Thigale
Department of Mechanical Engineering,
Vishwakarma Instititute of Techonology, Pune, Maharashtra, India
ABSTRACT
Effective braking is a critical factor determining the performance of any vehicle.
With enhancement in the performance, need of an effective braking system increases.
Brake caliper being the heart of a braking system, the whole system is built
considering its strength. An optimized design of a brake caliper thereby ensures
reduced size of wheel assembly, reduced weight and effective braking. This paper
studies a conceptual design of a brake caliper for an All-Terrain Vehicle (ATV),
primarily focusing on reducing the size and weight without compromising its strength,
stiffness and low piston drag. Computer aided design model of a brake caliper is
created in Creo 2.0 and analyzed for stress and deformation in ANSYS Workbench
14.0.
Key words: FEA, Brake Caliper, Braking System, Piston Drag, ATV, Piston
Retraction, ANSYS Workbench 14.0, Braking Torque, Pressure, Braking Force
Cite this Article: Rathin Shah, Chinmay Shah and Swapnil Thigale, Design and
Analysis of a Hydraulic Brake Caliper. International Journal of Mechanical
Engineering and Technology, 8(5), 2017, pp. 33–41.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=5
1. INTRODUCTION
In braking, a brake caliper plays a very important role as the final clamping force on a brake
rotor is applied by the friction pads held by caliper. When driver applies brakes, pressure is
applied on the back side of piston pushing the friction pads against brake rotor resulting in
frictional force on brake rotor and slows the vehicle down. A general layout of a double piston
floating caliper is shown in Figure1.
Design and Analysis of a Hydraulic Brake Caliper
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Figure 1 Exploded View of a Brake Caliper
1.Fluid Inlet
2.Caliper Body
3.Friction pads
4.Scrapper seal
5.Piston
6.Retraction seal
7.Bleed nipple port
A brake caliper which is mounted on upright mainly holds the friction pads, while the
clamping force is applied by the piston. The pressure distribution over the friction pads must
be uniform so as to ensure even pad wear and heat distribution. Braking torque generated
being the key parameter in braking, must be greater than the torque required to stop the
vehicle. This is achieved by applying clamping force on the brake rotor which causes reactive
forces thereby inducing stresses in the caliper body. The applied clamping force results in
frictional force and generates heat which is dissipated by rotor and pads i.e. the kinetic energy
of a vehicle is converted into heat which increases the disc temperature. This heat may be
transferred to the caliper body through the brake pads causing thermal deformation.
2. TYPES OF CALIPERS
2.1. Depending on Working Mechanism
Floating Caliper
Fixed or Opposed Piston Caliper
2.2. Floating Caliper
In a floating caliper, piston is on the inboard side of the caliper while the caliper is mounted
on a guiding pin which acts as a cylindrical support. The guiding pin allows linear movement
of the caliper along its axis. The friction pads on the outboard side are continuously in contact
with the brake rotor which prevents the bending of the rotor. When brake pedal is actuated,
the pressure is applied on back side of the piston which forces the friction pads against the
rotor. The reaction force forces the caliper to slide over the guide pin leading to clamping of
the rotor.
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2.3. Fixed Caliper
Fixed type caliper has pistons on both sides of the rotor and can be directly fixed to the
mountings on the uprights. Pistons from both the sides force the friction pads to apply force
on brake rotor. Fixed caliper does not require extra mounting bracket which is necessary in
floating type caliper for sliding. The major advantage of fixed caliper over a floating caliper is
the even wear of the friction pads.
2.4. Depending on Number of Pistons
Number of pistons in a caliper significantly affects its performance. Calipers can be made
with single or multiple pistons depending upon torque requirement and space availability. For
vehicles requiring less braking torque, single piston can be used. But, with increasing torque
requirement the bore diameter becomes considerably large increasing the size of the caliper.
Hence, the number of pistons needs to be switched to two or three depending upon the
requirement. The only disadvantage of using double or triple piston caliper is added number
of leakage sources.
Another factor that affects performance of a caliper is pad wear. It seems that pressure
exerted by the pads is even over the pad area but it does not happen in practice. The side from
which the rotor enters the caliper is called the leading side, while the side from which the
rotor exits the caliper is the trailing side as shown in Figure 2
Figure 2 Leading and Trailing Side
When the pads are pressed against the rotor, it tries to turn the pads as well because o f
which the area on the leading side experiences larger forces. This causes excessive heat
generation in the leading area of the friction pad resulting in more wear. Single piston caliper
shows least uneven wear pattern throughout the friction pad, which can be further reduced by
providing a small offset between the axes of the piston and the friction pad on the leading
side. In calipers with multiple pistons, pad area is greater along the circumference of disc
resulting in significant uneven wear. In multi-piston calipers the pistons are different in
diameter such that the smaller piston is on the leading side and the greater one on the trailing
side.
2.5. Depending on Caliper Body
Brake caliper can be made as a single body called monobloc caliper or in two parts called split
type caliper. The major problem in a caliper being deflection under the application of
clamping force, the caliper is made in two parts and then joined together by bolts. The
position of these bolts must be close to the piston centerline so that the deflection is minimal.
But if one decides to use a monobloc caliper, the part joining the inboard and outboard side
Design and Analysis of a Hydraulic Brake Caliper
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i.e. the bridge between the two, must be strong enough to sustain the forces. Casting or
vertical machining center (VMC) are the general manufacturing methods used for a brake
caliper. A split type caliper is always easy to manufacture as compared to monobloc caliper as
two separate parts can be machined or casted independently and can be easily joined together
or separated with the provision ofbolts.
3. BORE DIAMETER CALCULATIONS
When the driver applies brake, pedal force is converted into pressure by a master cylinder.
This pressure is carried by the brake fluid to the wheel i.e. the caliper side where the pressure
is converted into the clamping force. Magnitude of this force depends upon the bore diameter
and number of pistons. The clamping force presses the friction pads against brake rotor
generating a frictional force between them which is responsible for braking torque. The
generated braking torque must be greater than the required braking torque to stop the vehicle.
Required braking torque on a particular wheel is calculated from the load on the
corresponding axle. Thus, the piston diameter and the bore diameter are calculated according
to required braking torque. The clamping force required is
given by equation (1).
Where,
= Clamping force(N) (1)
= Braking torque required(N-m)
=Effective radius of brake rotor (m)
µ = Coefficient of friction between brake rotor and friction pad
This magnitude of clamping force is applied on the rotor by the piston. The diameter and
number of pistons can be iterated according to equation (2) depending upon the rim size i.e.
space availability.
(2)
Where,
D = Diameter of piston (mm)
n = Number of pistons
The piston diameter is nothing but the bore diameter of caliper. There is clearance fit
between the piston and the caliper bore in absence of any seals. A step is provided at the
bottom of bore to prevent the back side of piston from touching the bottom surface of caliper
and to increase the space for fluid to apply pressure.
4. SEAL GROOVE ASSEMBLY
With the actuation of brakes, piston moves out, which needs to be retracted from the brake
rotor surface after releasing the brake pedal so that there will not be any piston drag. Also, the
brake fluid must not leak. The distance between the brake rotor and the friction pad is around
0.006 inch after the application of brakes. The seal performs both the functions of piston
retraction and leakage prevention. Retraction seal deforms and stores energy as the piston
moves out. With release of the pedal, it pulls piston back, releasing the energy. It indicates
that the amount of retraction depends upon the deformation of seal, and should be considered
while selecting the seal groove. Piston drag and piston displacement are directly dependent on
the piston retraction. If the piston retraction is small, piston drag is induced. Piston drag is the
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residual torque on brake rotor even after releasing the brakes. Greater the piston drag, greater
is the energy loss and fuel consumption. Larger piston retraction causes larger piston
displacement which in turn increases braking time and stopping distance due to larger pedal
travel. This also disturbs the brake pedal response (feel). Considering these factors, the
deformation of the seal and hence the groove geometry must be optimized. Deciding a groove
geometry depends on the experience of prototype testing. General groove geometry is as
shown in Figure 3.
Figure 3 Seal Groove Geometry
In Figure 3, groove denoted by 1 shows the piston retraction seal groove in which front
taper angle allows deformation of the seal, while the bottom taper angle ensures easy insertion
of the piston. After the installation of seal, inner diameter of the groove is less than outer
diameter of seal which provides the necessary radial squeeze. At the front corner, a chamfer is
given, called corner break, to allow excessive deformation of seal. One more groove is
provided in the front, given by 2 in above figure for scrapper seal, which prevents the dirt
from entering into the bore. A radial squeeze of around 12%-18% is provided in the seal for
the prevention of leakage.
5. LUBRICATION
Lubrication plays a vital role in the performance of a brake caliper, especially in case of a
floating caliper. Before installing seals and other parts, caliper bore and guide pins (in floating
calipers) must be lubricated. The surface of bore should not be highly polished as it will not
hold the lubricant and hence the surface roughness should be around 5-10 micro-inches. Semi
solid, amber colored barium grease which has specific gravity less than 1 with flash point
around 435o C is majorly used for the lubrication. Red rubber grease can also be used as a
substitute
6. MATERIALS
The material of a brake caliper body must be rigid to allow less deflection, and should be light
to reduce the final weight of assembly. But, most important property considered for selection
of the material is the modulus of elasticity as, for a caliper, stiffness is more important than
strength. Most of the commercial vehicles use brake calipers made of cast iron because of low
cost, high modulus of elasticity (200-210 GPa) and good machinability. The only
disadvantage of cast iron is its density, which is much higher than other materials. Aluminium
can also be used for the manufacturing of caliper considering its lower weight, but modulus of
elasticity in this case is less (72-80 GPa). Also, metal matrix composite (MMCs), with base
material as Aluminium or Beryllium, reinforced with ceramic fibers which are aligned in
proper direction to obtain required strength and stiffness along that particular direction. These
Design and Analysis of a Hydraulic Brake Caliper
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MMCs have modulus of elasticity of about 180G Paand lower density as compared to all
other materials, but are most costly.
Pistons can be made of Aluminium alloys. But, thermal conductivity of Aluminium is
high, around 200-250 W/mK, which causes the heat generated due to the friction between
rotor and friction pads to be transmitted through piston. This leads to decrease in disc
temperature, but as the heat is transmitted to the brake fluid, it may increase the temperature
of fluid. Higher fluid temperatures may cause changes in compressibility and evaporation of
the brake fluid. To overcome this problem, small titanium blocks can be used in between the
backing plate of friction pad and the piston surface. Along with this, the contact surface
between backing plate and piston surface can be reduced by making a hole at the center of the
piston. Pistons can also be made of Titanium or Phenol formaldehyde, but are avoided due to
their high cost as compared to Aluminium.
While deciding the material for seals inside the caliper bore, the factors considered are its
compatibility with brake fluid, temperature operating range, fluid pressure range, hardness,
working conditions (static or dynamic), tensile strength, compressibility and failure modes.
The properties of seals vary with time and temperature. Various materials available for seals
are Thermoplastic elastomers, Rubber, Rigid thermoplastics, etc. From the aspect of brake
fluids, which are polyalkylene glycol based (DOT 3, DOT 4) or silicone based (DOT 5),
rubber is best suited material for the seals. Rubber seals such as nitrile rubber (NBR) and
hydrogenated nitrile rubber (HNBR) are generally used as the material for seals and can
operate up to 150 bar. Nitrile rubbers can work within the range of -40o C to 130o C and have
tensile strength up to 2000 psi. Hydrogenated nitrile rubbers works in wider range of
temperature in between -35o C to 150o C. As the seal deforms due to the motion of piston,
failure may occur. For this, its hardness should be within 60-70 in durometer scale, so that it
does not require too excessive or negligible force to deform. So after referring the seals
design, following o rings were decided-
Table 1 Specificaion of o rings
NO O ring Specification
1 Retraction Seal ring /%
Compression
ISO 3601-218
/5.2
2 Scrapper seal ISO 3601-124
7. FINITE ELEMENT ANALYSIS
After doing calculations and deciding the parameters like bore diameter, seal groove,
mounting, etc. a 3D model was created using a CAD software like Catia. This model was
analyzed by applying the forces and pressure. Static structural analysis of the CAD model was
carried out in ANSYS 14.0. This paper studies the analysis of a fixed caliper
7.1. Material Properties
Material: Al 7075 Density: 2700 kg/m3 Young’s Modulus: 72GPa
Yield Tensile Strength: 503 MPa
Ultimate Tensile Strength: 590 MPa
Rathin Shah, Chinmay Shah and Swapnil Thigale
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7.2. Meshing
The different mesh parameters like aspect ratio, skewness and jacobian were considered to
improve the mesh quality. An average mesh quality of 0.8 and above is considered acceptable.
In order to achieve this mesh quality, different meshing techniques were used. Out of the
different element types like hex dominant, sweep etc. tetra elements were the most suitable as
they capture the curvatures more accurately than in any other method.
Mesh quality obtained using the default settings (i.e. a coarse mesh with element size=
4mm) was 0.619 as shown in Figure 4. Hence, in order to refine the mesh, settings were
suitably changed. Proximity and curvature was used in order to ensure finer mesh along the
curved regions and varying cross sections. A fine mesh of average quality 0.84 with element
size of 0.6 mm was obtained consisting of 706573 nodes and 458263 elements which can be
seen in Fig.
Figure 4 Default Mesh
Figure 5 Refined Mesh
8. FORCE CALCULATIONS
Caliper body is subjected to mainly following three loads
Reaction on caliper due to the pressure applied at the back of piston
Reaction on the caliper body due to clamping force
Frictional force on pad, transmitted to the friction pad mounts.
These forces are calculated to stop a vehicle weighing (m) 250 kg with a weight
distribution of 40% at front and 60% at rear. Considering the pedal force (F) applied by driver
to be 300 N, magnitudes of above quantities are calculated as follows: Pedal leverage (L) =
5,Diameter of Master cylinder (d) = 19.05 mm, Pressure at the piston (P) = F*L*(Π/4)*d2 =
Design and Analysis of a Hydraulic Brake Caliper
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5262738.42 Pa , Diameter of piston (D) = 25.4mm , No. of pistons (n) = 1 , Total area of
pistons (A) = n*(Π/4)*D2 = 506.71 mm2 ,Clamping force (Fc) = P*A = 2666.63 N
,Coefficient of friction between rotor and friction pad (µ) = 0.35,Frictional force = Fc*µ =
933.335N
9. SUPPORTS
Depending upon the caliper type, different supports are given for the mountings. In a floating
caliper without mounting bracket, cylindrical support is given at the mountings. If a mounting
bracket is provided for floating, the holes of the bracket are fixed and forces are applied. In a
fixed type caliper, the mounting holes of the caliper are constrained as opposed to floating
calipers. These constraints and direction of forces are shown in Figure 6.
B:Clamping force
C:Pressure force
D:Frictuinal force
Figure 6 Loads and Supports
10. RESULTS
Results obtained from static structural analysis with ANSYS Workbench 14.0 are as shown in
following figures:
Figure 7 (a) Stress Distribution (b) Deformation
Figure 7 shows the stress distribution and deformation of a single side of the fixed caliper
which weighs around 398 grams. It can be seen from the above figures that these models are
Rathin Shah, Chinmay Shah and Swapnil Thigale
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over designed as there are some areas where stress induced is very less and can be optimized
by removing material from those areas.
11. CONCLUSION
This paper studies in detail, conceptual design, analysis and optimization of a brake caliper
system. In this paper, an attempt was made to design a fixed brake caliper considering various
parameters and was analyzed for its performance at normal conditions neglecting the thermal
effects which may contribute to deformation in smaller extent. Piston retraction behavior was
rigorously studied on the basis of seal groove geometry, seal material and operating
temperatures which contributes in determination of piston displacement, piston drag and
hence the performance of caliper.
Furthermore, other components of brake caliper system were modified to lower the
manufacturing cost, reduce weight and increase stiffness. Lubrication and selection of proper
materials was done taking into account the performance needs of the vehicle. In analysis,
mesh quality more than 0.8 was obtained for optimum discretization. Also, stresses generated
were maintained upto a limit considering a reasonable factor of safety
REFERENCES
[1] Stolarski.T, Nakason.Y &Yoshimoto (2006). Engineering Analysis with ANSYS
Software. Elsevier Butterworth-Heinemann.
[2] Limpert Rudolf (2011). Brake Design and Safety. Society of Automotive Engineers, Inc.
[3] Joseph R. David (1993). ASM Specialty Handbook: Aluminium and Aluminium Alloys.
ASM International.
[4] Dinzburg B. (2001). The Selection of Elastomer Compounds through Correlation of
Rubber Properties to Seal Life. SAE Technical Paper 2001-01-0686.
[5] Walker.J (2005). The Physics of Braking System. Stop Tech: High Performance Braking
System.
[6] Okon D. Anwana, Hao Cai (2003). Analytical Prediction of the Brake Caliper Seal-
Groove Performance. SAE 2002-01-0927
[7] BOSCH Automobile Handbook (1996). 4th edition
[8] R. D. Cook (1995). Finite Element Modeling For Stress Analysis, John Wiley &Sons Inc.
[9] Dattatraya K Chavan, Anish S Gorantiwar, Kunal R Nalamwar and Rites h G Deokar, A
Comparative Study and Analysis of the Performance of Various Regenerative Braking
Systems. International Journal of Mechanical Engineering and Technology , 8(3), 2017,
pp. 66 –76
