Automotive Engineering-Brake System - Report Example

Automotive Engineering- Brake System The Operation of a Master Cylinder The master cylinder consists of a brake fluid inside a barrel. This is the simple arrangement that enables the explanation of the operation of the master cylinder towards the halting of vehicles (Dixon, 2010). The master cylinder starts and spreads the breaking effect to the pads located in the wheels of the vehicles. It operates a dual breaking system that ensures that the failure of a system does not sabotage the whole system. If one system fails, the other operates. The two systems may be separated as front and rear. In other complicated cases, they are separately diagonally with reference to the location of wheels. During the operation, a push of the pedal causes the movement of the primary piston located inside the master barrel (Barnett, 2004). This activates one of the dual systems. The primary piston is tied to another secondary piston by a spring. The motion of the primary piston causes the movement of the secondary piston opening up openings that allow the fluid in front of it to build pressure. The pressure is evenly spread to the pads. The pads are connected to the rotor in the tires. The pads press against the rotor causing the tires to halt. Defects in the Master Cylinder The master cylinder brake system is a system that is effective the in the braking of vehicles. However, the brake system has its flaws that are pressure related. The flaws are caused by the leakages that occur in the master cylinder that inhibit the actions of the brake fluid (Knowles, 2005). These leakages may be due to the contamination of the break fluids. Leaks in the master cylinder have various effects on the brake fluid and master cylinder. Leaks cause the inclusion of air in the master cylinder which affects the operation of the break system. The cracks in the brake cylinder may be so great that it leads to the loss of the brake fluid. Brake fluid is a vital component in the operation of the breaking system of the car. The loss of the beak fluid can render the breaking system ineffective in the transmission of the breaking pressure to the tires of the cars. The fluid is necessary to transmit the force on the pedals to the brake pads through the fluid principle of pressure transmission. Considerations in design of a master cylinder Several considerations must be considered before designing master cylinder, in the recent past most manufacturers have settled on the use of cast iron in the master cylinder design because of the low costs incurred. The use of cast iron have been outdated overtime by the continuous research in finding better materials for use in the design of master cylinder (Barnett, 2004). Research findings relate the weight of master cylinder to the mileage of the vehicle, finding lighter materials improved the mileage of the vehicles. The use of composite master cylinder significantly reduces the weight of the master cylinder compared to the use of cast iron; the composite comprises alluminium body integrated with a plastic reservoir, the master cylinders are then coated with hard oxide to protect the alluminium surfaces. Calculation The brake pedal ration can be altered with the aid of the lever geometry or an corresponding adjustable angle between the brake pedal force (Fp) and the actuation force directed to the master cylinder (FHZ,B). Therefore, redirection of the actuation force as in the vehicle realized BRC08 results to a high bearing load at the brake pedal via the force Fp,larger Fp,larger = Fp + FHZ,B Main brake cylinder directional control force is valid: FHZ,Bet = Fp . L1/ ( cos α . L2) For the force to brake master cylinder cylinder with l= l1+ l2 follows from the equilibrium conditions on the balance beam: FHZ,Bet(1)= FHZ,Bet . l2/ l FHZ,Bet(2)= FHZ,Bet . l1/l FHZ,Bet(1) = Fp . L1. l1/ ( cos α . L2 . I FHZ,Bet(2) = Fp . L1. I1/( cos α . L2. I Because of the choice to a front/ rear axle distribution an easy-to-implement basic brake pressure distribution can be made by means of a separate dimensioning of main brake cylinder piston diameter ( dHZ(X)). In summary it is valid for the association amidst the brake circuit pressure: P1 = I2/d2HZ(2) × 4 FP . L1/ [ Π . cos α . L2 . I] P2 = I1/ d2HZ(2) × 4 FP . L1( Π. Cos α. L2. I) Determining the line pressure of a master cylinder Line pressure= leg effort × pedal ratio ÷ piston area of the master cylinder Given a 1” bore master cylinder with a leg effort of 200 lbs. piston area of 0.785 square inches and the pedal ratio of 7:1. The line pressure can be determined from the formula Line pressure=200×7÷0.785=1784 psi. Determination of master cylinder pushrod input force Master cylinder pushrod input force= Driver foot input force/ 2 × pedal ratio Estimation of the weight transfer under maximum deceleration or G stopping force Vehicle Mass, M= Static Front + Rear Weight Weight transferred= Mass ×rate of deceleration in negative Gs × Height of C.G/ Wheel base Estimating dynamic axle loading Dynamic Front axle weight during maximum-G stop= Static Rear Weight + ∆W Dynamic Rear Axle Weight during maximum –G stop= Static Rear Weight -∆W Axle brake force portion the adhesion limits takes: ɸ= FB,h/ [FB,h+ FB,v] = FB,h/ ( z× FG) = FB,h/( z× m×g) Front axle: Zv=µ. ( 1-Ψ)/ ( 1-µ.X-ɸ) or µv = FB,v/ FG,V,dyn = 1-ɸ/( [1-Ψ]/z + X) = FB,v /[m.g(lh/l +z. hg/l)] Rear axle: Zh= µ×Ψ/(µ.X+ ɸ) or µh = FB,h/ FG,h,dyn = ɸ/( Ψ/z- X) = FB,h/ [ m.g( lv/l- z. hg/l)] Maximum individual front and rear torque required Torque front= Tfront ( Nm) = Dynamic front axle weight(N)/2× Tire Rolling diameter (m)/2× Maximum deceleration rate Torque rear = Trear (Nm)= Dynamic rear axle weight (N)/2 × (Tire Rolling Diameter/2)× Maximum deceleration rate Torque output of the front and rear brake system= values for stopping event at maximum deceleration Torque output for front brakes Tfront = Apfront,total area of pistons for 1.5 of slider caliper design the total area of pistons of front caliper× Rfront, effective radius for the front brake × µ, the pad friction coefficient × 2( two sides to the rotor and pad interfaces) × Pf, the circuit pressure Front circuit pressure = Pfront( N/mm2 or psi) = Tfront/ (Apfront /Rfront/µfront/ 2) Rear circuit pressure = Prear ( N/mm2 or psi) Trear/ (Apfront /Rfront/µfront/ 2) Theoretical Relationship of Brake Efficiency and Master/Wheel Cylinder Ratio The efficiency of the braking system is the determinant of the safety of the break system. It determines the safe distance of stopping for a vehicle. The efficiency of a braking system of a vehicle varies with the various breaking conditions (Barnett, 2004). The ratio between the mass cylinder and the wheel cylinder has an effect on the brake efficiency of a braking system (Dixon, 2010). The brake efficiency increases with an increase in the mass/wheel cylinder ratio. This relationship is theoretically illustrated by mathematical formulas relating the force on the petal, the efficiency and the diameter of the master and the wheel cylinders. Brake efficiency ƞ = a(Mc/Wc)2 + b(Mc/Wc) + c Where Mc and Wc are the master cylinder and the wheel cylinder respectively. a, b and c are real constants. The constants above show that the relationship is non-linear. The correlation between the braking efficiency and the master/wheel cylinder ratio represented in a chart depicts an almost linear relationship. Break efficiency can also be expressed with regard to the force on the pedal. At a constant mass/wheel cylinder ratio, the efficiency of the brakes is incremental with the force applied in the pedal and is related in the formula below. Ƞ = (r1/r2)(Mc/Wc)2 { Fa m2/(0.25m2 – (ϻR)2)}(1/Fp) × 8 Where Fp = Force applied on the control pedal Ƞ = Braking efficiency Fa = the force initiating the mechanism r1/r2 = the ratio of radii of pedal ϻ = coefficient of friction of the material R = radius of the braking drum M = the initiating mechanism The efficiency of the braking system is thus dependent on the force on the pedal and the mass/wheel cylinder ratio. A residual pressure valve is normally utilized when the master cylinder is mounted within the lower horizontal plane than the corresponding calipers (Gilles, 2005). In the prevention of the fluid from partially draining the calipers by the gravity feeding back to the master cylinder, a residual valve is normally plumbed within the brake line amidst the calipers and the corresponding master cylinder (Knowles, 2005). Moreover, this normally holds residual pressure within the lines and calipers when is released. Residual valves pressure are offered within the two pressure sizes entailing 2lb and 10 lb valves are solely utilized for cars with rear drum brakes and ought to be never utilized on the four wheeled disc system. Valves within the master cylinder mainly retains minimum brake line pressure to aid in eliminating excessive pedal travel in both disc and drum systems (Gilles, 2005). Moreover, valve is utilized in disc brake applications where the master cylinder is mounted on the horizontal plane of the calipers where the fluid drain mark results from the gravity and vibration. This subsequently causes piston retraction and thus a relatively longer pedal stroke to regain the pedal (Knowles, 2005). Adjustment of the balance bar Screw Heim joints into the position on the balance on the balance bar accomplish equivalent spacing of the master cylinder (Gilles, 2005). The tow pushrods ought to be parallel to each other. Determination of the two master cylinders mainly requires the longest stroke to fill its underlying assigned calipers. This normally based on the cylinder bore size, caliper piston size and corresponding number of the caliper pistons. Master cylinder mainly utilizes larger bore which requires more stroke (Knowles, 2005). This also requires most of the stroke to adjust the balance bar to the bias that master cylinder. The lengthening of the pushrod on the master demands relatively longer stroke or shortening of the pushrod on the master that requires the least stroke. The use brake bias gauges are essential brake turning tools that are normally tentatively mounted for checking the gauges of a car. Inspection of the master brake cylinder entails determination of the distance of the brake pedal the moves when particular pressure is applied. The brake hoses and assemblies ought to be observed from the beneath (Barnett, 2004). Moreover, inspection of the fourth brake locations demands either removal of the wheel or performance of the brake analyzer or corresponding road test. Brake hoses and braking bleeding Brake line plumbing is demanded to move along with the suspension that mainly require flexible hose. It mainly utilizes stainless steel braid reinforced Telflon-lined hose that is exceedingly preferred (Dixon, 2010). Air inside the underlying hydraulic system causes a mushy pedal which uses a pure fluid transmission from the master to the corresponding caliper pistons that operates the prevailing pistons immediately with no lag time that would correspondingly cause trapped air via compression. References Dixon, J. (2010). Modern diesel technology: Preventive maintenance and inspection. Clifton Park, NY: Delmar. Gilles, T. (2005). Automotive chassis: Brakes, suspension, and steering. Clifton Park, N.Y: Thomson Delmar Learning. Barnett, G. J. (2004). Automotive fire analysis: An engineering approach. Tucson, AZ: Lawyers & Judges Pub. Co. Knowles, D. (2005). Tech one: Basic automotive service and maintenance. Clifton Park: Thomson Delmar Learning. Read More