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Int. J. Mech. Eng. & Rob. Res. 2014 Subhash Mishra and Sagar Janghu, 2014

BALANCE BAR DESIGN AND MOTION ANALYSISOF PUSHROD

Subhash Mishra1* and Sagar Janghu1

*Corresponding Author: Subhash Mishra, subhashmishra309@gmail.com

To execute the functioning and biasing of force acting on two master cylinder using single brakepedal a mechanical system, i.e., balance bar is used which is designed to divide the forceapplied by the driver on the brake pedal to the master cylinders. Moreover in master cylinderpushrod’s movement is critical for proper functioning of master cylinder. So to achieve linearmotion correct position and orientation of brake pedal and pushrod mounting is required. Aftermotion analysis and practical examination it is shown how to decide the mounting’s of pushrod.

Keywords: Balance bar, Disc brakes, Master cylinder, Pushrod

INTRODUCTIONIn vehicle when braking force is applied weightis transferred to the frontwheels, so to lock allthe wheels higher braking force is required onfront wheels then the rear wheels, also in caseof cornering weight is transferred from innerto outer wheels which again results in differentbraking force. In hydraulic braking system thebraking force is applied by means of hydrauliccylinder, i.e., master cylinder. As differentbraking force is required at front and rearwheels so biasing of input force to the twomaster cylinders is needed. Which can bedone with the help of mechanical balance bar.This adjusts the force acting on the pushrod

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Int. J. Mech. Eng. & Rob. Res. 2014

1 Netaji Subhas Institute of Technology, Delhi, India.

by changing the distance between pushrodmounting and pedal.

The force applied on the piston by pushrod,i.e., force is transmitted by pushrod. Themotion of pushrod is critical for completefunction of master cylinder. To transfer theapplied force with minimum loss, the pushrodshould move in a straight line and must goesmaximum inside the cylinder.

BALANCE BAR DESIGNBalance BarA balance bar (also called a bias bar) on dualmaster cylinder systems, divides the forcefrom the brake pedal to the two master

Research Paper

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Int. J. Mech. Eng. & Rob. Res. 2014 Subhash Mishra and Sagar Janghu, 2014

cylinders. It is called a “balance bar” becausethat is exactly what it does. The torque on oneside of the bar must balance the torque on theother side of the bar. Remember that a forceapplied over a distance causes torque.Therefore, the master cylinder closer to thepivot point on the bar has a shorter lever armand will receive a higher braking force.Balancing bars take force from one side andgive it to the other.

Design• It consists of a solid rod which is mounted

using bearings on its both the ends. Thebearings are attached to the frame ofvehicle.

• A slot of dimension 300*15*15 mm of cutout in the solid rod.

• A sleeve is put on solid rod with a clearanceof 2 mm between the two. The pedal iswelded to the sleeve.

• Two holes of diameter 15 mm are drilled inthe sleeve and a M15 nut is welded over

the two holes. The holes are made so thatM15 bolt can be screwed to the nut weldedon the hole up to the bottom surface of slotand a check nut is also put on screw toprevent it from unscrewing due to vibrations.

• In this way the sleeve gets fixed onto thesolid rod as bolt get stuck in the slot cut inthe solid rod. Hence, there is no relativemotion between sleeve (on which pedal iswelded) and the solid rod.

• Two strips are welded on the solid bar witha hole in them. The clamps of mastercylinder pushrods are attached to the stripsthrough nut and bolt. The master cylindersare fixed on the frame of the car.

• As a result, when the pedal is pressed, thesolid rod rotates along with pedalmovement. The strips welded on the solidbar move along an arc and since, the mastercylinders are fixed, the pushrods arepressed due to the movement of the strips.

• If the sleeve is in the centre of the slot, then,equal force is applied on both the pushrodsand hence, equal braking pressure iscreated in both master cylinders.

• However, in order to bias the force beingapplied on both pushrods, the bolts ofsleeve are loosened and the sleeve ismoved towards the master cylinder on whichmore force is needed, and the bolts istightened again. As a result, the pedal forceis unequally distributed and hence, unequalbraking pressure is created in the mastercylinders.

Advantage• In design, when the pushrod is fully pressed

into the master cylinder, the pushrod is

Figure 1: Layout of Braking System

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Int. J. Mech. Eng. & Rob. Res. 2014 Subhash Mishra and Sagar Janghu, 2014

parallel to it. As a result, maximum brakingforce is applied and no vertical componentof force acts on the pushrod, due to which ithas maximum service life.

• This setup needs less space because themaster cylinders are situated above thepedal and not in line with pedal (whichrequires more space).

• Easy to design, manufacture andinstallation.

• The bearing provides a twisting momentwhich helps in reversal of pedal once pedal

input force is removed. As a result, no needfor return spring.

MOUNTING ANALYSIS OFPUSHROD MOUNTAs pedal follows a circular profile about thepoint of pivot, such that the pushrod mountingfixed on balance bar also follows a circular arc,so the circular motion of mounting strip istransformed into linear motion of pushrod. Thepath followed by the pushrod depends on themounting position of strip. These mount stripcan be attached as:

Case 1: When mounting strip is mounted at 0degree angle with vertical. As force is appliedon the pedal the bearing will rotate inanticlockwise sense, so as the mounting stripfollowing the circular arc, this will movepushrod in the forward direction but the forceis not exactly in horizontal sense but inclineddownward.

The resultant downward force which will beact in horizontal direction will be less and alsothe component along thedownward Ydirectionwill tend to move the pushrod in downwarddirection and not exactly horizontal. This maydamage the master cylinder.

Figure 2: CAD Model of Balance Bar

Figure 3: Case 1 - Pushrod and Strip Vertically Mounted

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Int. J. Mech. Eng. & Rob. Res. 2014 Subhash Mishra and Sagar Janghu, 2014

Case 2: When the mounting strip of pushrodis mounted as show in Figure as the forceapplied on the pedal shaft on which strip isattached rotates in anticlockwise sense andhence the mounting strip will also move on acircular arc (shown by red dotted arc). Themounting strip is attached in same angle asthe angle of travel of pedal so that forcetransmitted via pushrod doesn’t goes indownward inclination.

Case 3: To obtain the completely horizontallytransmitted force in pushrod. The pushrodshould be attached to the mounting strip

making some angle (as shown in Figure), suchthat when mounting moves in circular arc theforce completely transmitted to pushrod.

BIBLIOGRAPHY1. http://sports.racer.net/brake_bias.htm

2. http://www.apracing.com/drawings/Balance%20Bar%20Systems.pdf

3. http://www.formula1-dictionary.net/brake_balance.html

4. h t t p : / / w w w. p f c b r a k e s . c o m . a u /techtips.php?pageId=23

Figure 4: Case 2 - Strip Inclined Mounted

Figure 5: Case 3 - Pushrod and Strip Inclined Mounted