Strength Analysis of Disc Brake Assembly & Dynamic Pad Pressure Distribution

Strength Analysis of Disc Brake Assembly & Dynamic Pad Pressure Distribution Prasanna Chowdary Senior Engineer Mando Softtech India Pvt. Ltd. 1st Floo...
23 downloads 2 Views 564KB Size
Strength Analysis of Disc Brake Assembly & Dynamic Pad Pressure Distribution Prasanna Chowdary Senior Engineer Mando Softtech India Pvt. Ltd. 1st Floor, MPD Towers, Phase V Gurgaon-122002, India [email protected]

Keywords: Disc Brakes, Strength analysis, Pad Pressure distribution. Abstract The disc braking system which slows rotation of the wheel by the friction caused by pushing brake pads against a brake disc or rotor will result in forces both mechanical and hydraulic. These set of forces acting on brake caliper components result in deformations and stresses. Hence, structural Analysis of the Disc Brake assembly needs to be carried out aiming at evaluating the performance of brake components of an automobile under various braking conditions and there by assist in component design and analysis. The structural analysis is mainly used to determine the deformation and the Von Mises stress established in the brake components.

The hydraulic housing and piston assembly pushing the pads on to the brake disc results in pressure between the pad and disc interface. But, with the disc rotating, the pressure on the pad material is not always uniformly distributed. The pressure distribution across the pad surface vary depending on the braking conditions like pressure acting on the pads from the piston, braking torque, angular velocity of disc etc. By studying the pressure distribution on the brake pads, one can determine the wear pattern of the pads helping the automotive engineers to understand the dynamic characteristics and provide with better design of the automotive braking system.

In this paper we discuss about the performance analysis of automotive disc brake system by carrying out the strength analysis of the disc brake assembly and also to study the dynamic pressure distribution on the Pad surface at various braking conditions using RADIOSS and HyperMesh.

Introduction In general, the main functions of a brake system are to maintain a vehicle’s speed when driving downhill, to reduce a vehicle’s speed when necessary and to hold a vehicle when in parking. Today, most passenger vehicles are fitted with disc brake systems. A disc brake of floating caliper design typically consists of two pads, a caliper, a disc, a piston, a carrier bracket and two guide pins.

Along with achieving a afore mentioned functionalities, the brake caliper also need to withstand the forces and stresses raised in the components due to high hydraulic pressure and shear forces due to disc rotation and hence avoiding deformations in the caliper and to give maximum life.

Also one of the major requirements of the caliper is to press pads against the disc and it should ideally achieve as uniform interface pressure as possible. It is well known that uniform pad wear and brake temperature, and more even friction coefficient could only be achieved when pressure distributions between the pads and disc are uniform.

Simulate to Innovate

1

This paper investigates the stresses generated in the caliper components and contact (interface) pressure distributions at the rotor and piston-pad interface taking into consideration dynamic condition of the assembly .

Finite Element model A detailed finite element model is constructed taking into account all significant contact interfaces between disc brake components. Sliding frictional contact is analyzed to obtain the interface pressure distributions. The finite element model of the disc brake of floating caliper design being studied consists of a disc, two pads, caliper housing, carrier, piston, two guide pins, Knuckle and Hub as shown in Figure 1. The model uses up to about 160000 solid elements and a total of approximately 567136 degrees-of-freedom (DOFs).

Fig 1: Disc Brake Caliper FE Model

Since the Disc brake assembly being a complex system which involves large number of contacts between almost all of the components, contact problem is modelled by using element-based surfaces and surfacebased contact, and is analysed using small sliding interaction. Although element based surfaces have advantages over the node-based surfaces, owing to the complexity of the model, node based surfaces and edge contacts are also generated to obtain more accurate results in contact pressure and contact stresses.

Tie Contact

Sliding Contact Fig 2: Contact Interactions

Simulate to Innovate

2

Contact Analysis and Simulation Since the problem being dynamic with very time frame to apply loads and very large contacts, the FE model becomes highly non-linear. To obtain a desired solution Radioss explicit solver is used.

Hydraulic pressure on piston

Fig 3: Pressure on Piston & Housing

With the validated model, contact analysis was carried out to obtain the deflections on the caliper components and the pressure distribution between the disc and the piston pad, and between the disc and the finger pad. For the contact interface between the pads and the disc, a friction coefficient of µ = 0.4 was prescribed. The structure is carried out in three steps. First, the disc was rotated about the central axis at an angular velocity of 6-10 rad/s or equivalent to 60-95 RPM of Rotor. Second, a uniform pressure of 3.0 MPa was applied on the top of the piston and on top of caliper housing. In the third step again the pressure on top of piston and calliper housing is increased to 7.0 MPa. Lining Density (kg/mm3) Young’s modulus (GPa) Poisson’s Ratio

Back Plate

Disc

Piston

Carrier

Housing

Guide Pin

Knuckle

3050

7850

7167

7820

7050

7050

7820

7850

Orthotropic

210

125

210

172

172

210

200

0.29

0.29

0.29

0.29

0.30

0.30

0.29

029

Table: Material data of Disc brake assembly.

Simulate to Innovate

3

Fig 4: Vonmises Stress on Caliper Components

Simulate to Innovate

4

As mentioned earlier uniform pad wear and brake temperature, and more even friction coefficient could only be achieved when pressure distributions between the pads and disc are uniform. In addition, unevenness of the pressure distribution causes uneven wear and consequently shortens the life of pads. This might lead to dissatisfaction to the customers who need to visit their garage more frequently in order to replace tapered wear pads. Also it has been speculated that a non-uniform pressure may promote disc brake squeal.

Fig 5: Contact Pressure distribution in Ideal condition

One of the major improvements of both Pad wear and Brake Squeal is the change of the interface pressure distribution. Hence, higher and better the contact area of the pads, lower the squeal index and uneven Pad Wear.

It has been observed that higher pressure occurred on the leading side when the disc starts to slide, which again states that more wear appears on the leading side than the trailing side of the pad. So the study of dynamic pad pressure distribution helps in order to minimize and/or eliminate tapered wear in pads. Also the measurement of duration of speed reduction @ 3MPa and 7 MPa has been derived. With angular rotation at 10rad/sec dynamic pad pressure is obtained at 3MPa and 7Mpa pressure applied on to the Piston and Housing.

Fig 6: Contact Pressure distribution on Inner and Outer Pad

Simulate to Innovate

5

Altair Radioss can be used for Short duration events and capturing phenomena in detailed manner with fine time steps, Material and Rupture Models, Contacts frictions and solver scalability. Mando SoftTech India is Further Interested in Exploring Radioss capabilities for detailed Pad Failure phenomena with Rupture Modules. ACKNOWLEDGEMENT Thanks to Mr. Prashanth Kulkarni from Altair and Mr. Abhijit Kulkarni from DesignTech for their continuous support on above work and future Plans on establishing standard Radioss approaches.

REFERENCES 1.

Tamari, J., Doi, K. and Tamasho, T. Prediction of contact pressure of disc brake pad.

2.

Interface Pressure Distributions through Structural Modifications

Society of Automotive Engineering. Review 21, 133-141, 2000.

A. R. Abu Bakar, H. Ouyang and Q. Cao Department of Engineering, University of Liverpool Sae Technical Paper Series 2003-01-3332 3.

Prediction Of Disc Brake Contact Pressure Distributions By Finite Element Analysis Abd Rahim Abu Bakar & Huajiang Ouyang

4.

A Moving-Load Model for Disc-Brake Stability Analysis H. Ouyang and J. E. Mottershead. Department of Engineering, University of Liverpool, Liverpool L69 3GH, England.

5. 6.

https://www.researchgate.net/

https://www.researchgate.net/publication/271522399_A_critical_review_of_brake_squeal_and_its_treatment_in_practice.

Simulate to Innovate

6

Suggest Documents