DESIGN OF NEW TYPE OF MASTER CYLINDER TO AVOID THE UNDESIRABLE BLEEDING IN THE DISC BRAKE SYSTEM RAHUL SINGH & PRASHANT NAUSRAN Department of Mechanical Engineering, K. I. E. T, Delhi, Muradnagar, Ghaziabad, India ABSTRACT A designed of new type of master cylinder containing air vessel, to minimize or eliminate the undesirable bleeding and some other problems related to disc brake system of vehicle, and method of locking of all four wheels simultaneously. It would involve the explanation of all factors responsible and time delay in the application of force to stop the vehicle and release brake pads contact with braking disc after the force if removed, due to involvement of compression of air when pedal force is applied along with their solutions. KEYWORDS: Master Cylinder, Bleeding, Air Vessel INTRODUCTION Braking system is one of the most important parts of our vehicle required to have a better control on vehicle and to stop it within a safe stopping distance. Master cylinder is a control device that converts non-hydraulic pressure (commonly from a driver's foot) into hydraulic pressure. This is used, for stopping vehicle. Braking Bleeding: Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. As known air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. PROBLEM IN PRESENT DESIGN Use of two different chambers (or slave cylinder) and so many accessories in present master cylinder, to make it working, decreases master cylinder's efficiency. And due different spring system for different slave cylinder in master cylinder, there are different forces on different tire, and there is a Bleeding problem present design. Also, a vacuum is created when pedal force is removed, which pull liquid present in brake wiring back in master cylinder, hence decrease brake efficiency. Another port (by pass port) is used to minimize this effect of vacuum. Hence, make the system complex. Figure 1: Master Cylinder INNOVATION Here is designed of new type of master cylinder containing air vessel, to minimize or eliminate undesirable bleeding and some other problems, and a new method for locking of all four wheels simultaneously. International Journal of Automobile Engineering Research and Development (IJAuERD) ISSN 2277-4785 Vol. 3, Issue 4, Oct 2013, 73-78 © TJPRC Pvt. Ltd.74 Rahul Singh & Prashant Nausran Figure 2: Isometric and Side View of New Design DESIGN CONSIDERATION The maximum height of air vessel should be less than or equal to minimum height of brake fluid tank, to get air almost completely compressed in the air vessel (fluid will rise to the same height in the adjacent chamber when they are connected), and working of brake system efficiently. Figure 3: Diagram Showing Level of Fluid in Container Diameter of air vessel and master cylinder should be kept between 25.5mm to 26.5 mm to get minimum stopping (it is decided according to the calculation below). There is a pressure relief valve at top of air vessel, which can use to maintain pressure in the air vessel. While servicing, inside air pressure can be measured and can be regulate with the help of pressure relief valve. CALCULATION AND WORKING Figure 4: New Master Cylinder Line DiagramDesign of New Type of Master Cylinder to Avoid the Undesirable Bleeding in the Disc Brake System 75 NOTE: The white bars on piston are piston holes Considering system at constant temperature, Area at section aa and xx are Aaa and Axx respectively. Pressure at section oo, Poo = P0 + ρgy (1) P0 is the atmospheric pressure, ρ density of brake oil, y is distance from the top of fluid to bottom point in oil tank. Pressure at section xx due to fluid, which would be used to compress air, PTxxf = P0 + ρg(y +/- b) (2) Where b is the distance between oo and xx axis b is positive(+) when xx is below oo b is negative(-) when xx is above oo But according to design consideration, b will always be positive Total force acting at section xx (which is the diaphragm bet air and fluid) due to fluid FTxxf = PTxxf* Axx (3) Now, finding the change in volume of air due compression by pressure PTxxf We have bulk modulus for real gas, B = - (dP / (dV/V)) dP = PTxxf – P Initial in the chamber (4) There was air, initially in the chamber at atmospheric pressure so, P Initial in the chamber = P0 dV = - ((dP*V)/B) (5) dV = V´- V Where, V´ and V are final and initial volume of air, in vessel respectively. dV = (ᴫ/4) d2 (h´-h) (h´-h) = dV / ((ᴫ/4) d2) d is the diameter of air vessel (h´-h) this quantity would come negative, since dV is negative h and h´ are height measure from the top of air vessel to the diaphragm between air and water, when air is normal state and at the compressed state due to fluid force respectively. s= (h-h´) (6) Where, s is maximum displacement of air, present at the diaphragm of air and water, in air vessel, in the direction of the applied fluid force. The air gets almost compressed completely by fluid force and can be calculated from equation.76 Rahul Singh & Prashant Nausran This brake oil apply certain force on caliper pistons, but this force is not good enough to stop the vehicle even this force is not enough to make the contact between caliper pad and disc brakes, but it minimizes the force which is to be applied to stop the vehicle. This force is, PTxxf = FTxxf * Axx F3 = PTxxf*A1 (7) F3 is the force applied by fluid on piston of caliper. A1 is the area of caliper piston. (This relationship assumes 100% hydraulic efficiency of all components in the caliper body) The air vessel work over the principle of liquid hammer effect from built up liquid pressure, and use this pressure, which has been created by a liquid source above the master cylinder .to build a hydram(hydraulic ram) type system. The vessel must be located at an elevation lower than the liquid source. The kinetic energy of the liquid running down from oil tank through the pipe and builds up pressure because of liquid hammer effect. The air vessel is then able to use this built up pressure to pump the braking fluid through a smaller diameter brake wiring over a greater distance at small flow rate. More than 50% of the energy of the driving flow can be transferred to the delivery flow. The remaining 50% of the energy is absorbed by air during liquid hammering. When the master cylinder is completely filled with brake oil and gas inside is completely compressed then air will try to expand and would apply built up pressure back over fluid. Air would not be able to send brake oil, back to oil tank. So, liquid has no way to escape, except going inside brake wiring. This fluid will apply certain amount of force on the caliper piston (when present in brake wiring) but would not be able to move the piston. Now, for stopping the car, what we only need is, to apply required pressure. Fluid is already present in the brake wiring; there we will be only time lag due to compression of air by pedal force. But, by using bulk modulus equation it can be calculated that air get almost completely compressed due fluid force applied initially, there will be very negligible amount of time lag(approximately .000879 s from calculation when all the parameter in taken as constant) due to pedal force. Now calculating the force F1, This is the force on the push rod and F2 is the pedal force, Figure 5: Pedal Force Diagram Where, F2= Force Applied, F1= Force at the push rod, r2 = Distance of the pedal from pivot, r1 = Distance of push rod from pivot, Q = Angle rotated, T = Travel of the Pedal, V.S. = Vertical Shift in push rod, L = Overall length of pedalDesign of New Type of Master Cylinder to Avoid the Undesirable Bleeding in the Disc Brake System 77 F1:F2 is known as the Mechanical Advantage. It is equal to the ratio of r2:r1. F1 = F2*(r2:r1) Force at section aa due to the pedal force is given by, Faa= F1 Force at section xx due to the pedal force is given by, Faa/Aaa=Fxxp/Axx F xxp = Faa/Aaa* Axx F xxp = Paap* Axx (Since, Faa/Aaa= Paap) The air in the air vessel is almost getting compressed by fluid force which is very less in amount then pedal force. Hence, there will be no or very less delay in braking by application of braking force, involves compression of air in air vessel. The force on piston of caliper due to pedal force is given by F4 = Pxxp*A1 (8) Now, calculating force at caliper piston is, F cp = F3 + F4 (9) (This relationship assumes 100% hydraulic efficiency of all components in the caliper body.) Since there are two pistons per caliper so the Net Force = 2*Fcp (this relationship assumes 100% mechanical efficiency of all components in the caliper assembly. In practical application, mechanical deflection & i Ffriction = Net force * coefficient of friction between brake pads and disc (This relationship assumes 100%effiency of all components at the brake pad interface. In practical application, mechanical deflection of the brake pad material and friction found between brake pad and the caliper body components prevents this condition. In addition, it should be noted that the coefficient of friction between the brake pads and the disc is not a fixed value, but rather changes dynamically with time, temperature, pressure, wear etc.) Ffriction = Fcp * µ´ µ´ = coefficient of friction between brake pads and disc Td (Torque available at the disc) = Ffriction * Reff Where, R eff = the effective radius (effective moment arm) of the rotor (measured from the rotor center of rotation to the center of pressure of the caliper pistons) Tt(torque available at the tires) = Td (this relationship assumes 100% mechanical efficiency of all components at the wheel end. In practical application, mechanical deflection and relative motion between the rotating components prevents this condition.) Ftire = Tt/Rt(radius of the tire) Ftotal = Ftire*4(for all four tires)78 Rahul Singh & Prashant Nausran Deceleration of vehicle in motion due to brake pads, a y = Ftotal/mv Friction force between tire and road, f1 = µ * N N = W = m * g Now deceleration due to friction between road and tires (ax) = (µ * N)/mv Total deceleration (av) = ax + ay Stopping distance = v2/2*av BRAKE EFFICIENCY Figure 6: Brake Efficiency in Present and New Design Brake efficiency is constant in the present design as no air bubble will get trapped in brake wiring because of presence of air vessel in the system, if any air bubble will appear in the system due its less density it will mix with air in air vessel, there would be less losses due to thermal expansion of fluid (causes due to flowing fluid friction) because fluid in this case is not flowing, it is already present in wiring, only pressure is being transferred CONCLUSIONS The above new design will eliminate, bleeding and some other problems in disc brake system. The earlier used master cylinder had much complex structure and moving parts compare to this innovation, so cost of this new master cylinder would be less or may be same compare to earlier used master cylinder (in between $200 to$300) and this design will eliminate the undesirable bleeding and some other problem in disc brake system and would work efficiently. REFERENCES 1. R. K. Rajput, automobile engineering, laxmi publication 2. Frank M. White, fluid mechanics 3. Bruce Roy Munson, Donald F. Young, Theodore Hisao Okiishi, Fundamentals of fluid mechanics 4. John A. Roberson, Clayton T. Crowe, Engineering fluid mechanics