PRESENTATION ON SOLAR CAR(TECHNICAL SPECIFICATIONS, DESIGN, BRAKING AND SUSPENSION)

Presented by:

Abhishek Thakur

Akshay Mistri

Anirudh Pratap Singh

Sarthak Anand

Guided by:

Mr. P.N Vishwakarma

GROUP DETAILS

Name Enrollment number

Abhishek Thakur A2305411201

Akshay Mistri (Slides 3,4,5,6) A2305411185

Anirudh Pratap Singh A2305411135

Sarthak Anand A2305411198

BASIC ASSUMPTIONS MADE

• Gross weight of the vehicle including two passengers: 400 Kg

• Max velocity to be achieved: 30 Km/hr or 8.334 m/sec or 2.54 ft/sec

• Wheel diameter: 16 inches or 40.64 cm

• Max gradient climb: 5 degrees

• Surface friction factor: 0.02 ()

• Time taken to achieve max speed: 3 seconds

TORQUE SPECIFICATIONS

These torque calculations are made by the help of a paper from University of Florida.

Condition Torque requirements (N-m)

 

Per wheel torque

Transmission torque

required (2 × per

wheel torque)

To just start motion of vehicle 8.93 17.86

To start and accelerate (without any

gradient climb) 20.671 41.343

To move on a 5º gradient 59.59 119.18

MOTOR SPECIFICATIONS

• DC Series motor will be used

• Max torque : 8 or 9 N-m

• Continuous (Average) Torque : 6 N-m

• Voltage : 60 Volts (max)

• Since, we will vary the motor current, Horsepower and RPM conditions will have to adjusted according to the motors available in the market.

GEAR REDUCTION SYSTEM

• Needed to multiply the motor output torque.

• Feeds multiplied torque into the differential.

• (N-m, Max) =

Motor Torque (N-m, Continuous) × Gear Reduction × Differential Efficiency

• 41.343 = 6 × Gear Reduction × 0.5 (or 50%)

• Gear Reduction = = 13.781 or 14

BRAKING SYSTEM

• Braking system will consist of two disc brakes for front wheels and two drum brakes on the rear wheels.

• It will also include a parking brake or a handbrake.

BRAKING ANALYSIS

• Braking power is analyzed in such a way that it is maximum enough to brake the car but not misbalance it.

• Brakes used will have an effective braking radii of 130 mm.

• This analysis gives the following outputs:

Braking time 1.213 seconds

Minimum Braking distance (d) 5.0571 m

Deceleration achieved 6.867 m/

Effective Brake radii 130 mm or 0.13 m

Braking Force 2746.8 N

Max. Braking torque 357.084 N-m

Max Braking torque (per wheel)

89.271 N-m

PARKING BRAKE

In cars, the parking brake, also called hand brake, emergency brake, or e-brake, is a latching brake usually used to keep the vehicle stationary. It is sometimes also used to prevent a vehicle from rolling when the operator needs both feet to operate the clutch and throttle pedals. Automobile hand brakes usually consist of a cable directly connected to the brake mechanism on one end and to a lever or foot pedal at the driver's position. The mechanism is often a hand-operated lever (hence the hand brake name), on the floor on either side of the driver, or a pull handle located below and near the steering wheel column, or a (foot-operated) pedal located far apart from the other pedals.

SUSPENSION • Suspension is the system of springs, shock absorbers and linkages that connects a vehicle to

its wheels and allows relative motion between the two. Suspension systems serve a dual purpose — contributing to the vehicle's road holding/handling and braking for good active safety and driving pleasure.

• Why double wishbone in the front?

• Double wishbone suspension system satisfies the above objective. It has the following advantages-

• It gives more flexibility in designing the suspension system i.e. we can control roll centre variation and roll centre height as per the requirements of vehicle.

• It is sturdy and hence easily sustains the large bumps, frequent impacts that is desirable for front suspension.

• Even if this suspension requires large space, it is suitable as we have enough space in the front.

Double Wishbone Suspension System

A double wishbone (or upper and lower A-arm) suspension is an independent suspension design using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff and more.

Castor angle:  it’s defined as the angle created by the steering pivot point from the front to back of the vehicle. Caster is positive if the line is angled forward, and negative if backward. Typically, positive caster will make the vehicle more stable at high speeds, and will increase tire lean when cornering. This can also increase steering effort as well.

Camber angle:  Camber angle is the measure in degrees of the difference between the wheels vertical alignment perpendicular to the surface. If a wheel is perfectly perpendicular to the surface, its camber would be 0 degrees. Camber is described as negative when the top of the tires begin to tilt inward towards the fender wells. Consequently, when the top of the tires begin to tilt away from the vehicle it is considered positive.

Roll Centre:  "The point in the transverse vertical plane through any pair of wheel centers at which lateral forces may be applied to the sprung mass without producing suspension roll".

The lateral location of the roll center is typically at the center-line of the vehicle when the suspension on the left and right sides of the car are mirror images of each other.

The significance of the roll center can only be appreciated when the vehicle's center of mass is also considered. If there is a difference between the position of the center of mass and the roll center a moment arm is created. When the vehicle experiences angular acceleration due to cornering, the size of the moment arm, combined with the stiffness of the springs and anti-roll bars (anti-sway bars in some parts of the world), dictates how much the vehicle will roll. This has other effects too, such as dynamic load transfer.

DESIGN CALCULATIONS• To calculate spring rate:

• Starting with the basic equation from physics, relating natural frequency, spring rate, and

• mass:

• f= (K/M)^1/2*1/2π f = Natural frequency (Hz)

• K = Spring rate (N/m)

• M = Mass (kg)

• f = 1.5

• The spring rate of a coil spring may be calculated by a simple algebraic equation or it may be measured in a spring testing machine. The spring constant k can be calculated as follows:

• k = Gd^4/8ND^3

• k = 80*10^9*(0.008)^4/8*20(0.60)^3

• k = 9481.481 N/m

•  

• Wheel rate = k/MR^2 where MR^2 = motion ratio

• Wheel rate = 9.481N/mm

Natural frequency =1.5

Speed achieved = 2.54 ft/sec

Weight distribution at front = 55%

Total weight(kg) = 400

Sprung weight = 400

Spring length closed (mm) = 160

Spring deflection (mm) = 229.4

Energy stored (J) = 247.29

Spring stiffness (N/m) = 9.4*10^3

 Pitch of lead (mm) = 19.47

Shear stress (τ)(Pa) = 643*10^6

Angle of damper with vertical = 25

Motion Ratio = 1

Wheel Rate = 9.481

Spring compression = 52.578

Force in spring(front) = 2156

Spring Rate(N/m) = 9481.481

Force in spring (rear) = 1764

Compression of spring = 68.16549367

Required k (N/mm) = 9.481481

Knuckle:The most essential part of the vehicle is the KNUCKLE. Steering arm is attached to knuckle which provides steering moment, stub axle of the wheel is fitted inside the knuckle hole and it also supports two arms of the wishbones. The forces on the knuckle are calculated by using impulse-momentum equations for the vehicle which will strike the ground completely on one wheel for 0.1sec.

Wishbone design:

The upper and lower wishbones form the part of the four bar linkage and thus are subjected to compressive, tensile forces. These forces are calculated using static equations. The wishbones should be design in such a way that it easily carries these loads. By applying the principles of strength of materials the minimum dimensions of these wishbones are calculated.

Ball Joints:

 

The knuckle and the wishbones are connected using the ball-joints which allow a 3-dimensional movement of one part with respect to the other.

However the ball joints must carry the dynamic and static loads so that it functions properly. The static load on the ball joint is the reaction force given by the knuckle to the wishbone.

 

Rod ends:

The rod ends are used to allow the spring-damper system to move it relative to the fixed support on the roll cage. It should sustain the maximum dynamic and static conditions.