Relación entre el plano emocional, interpretacional - cognitivo y las afecciones auditivas y de equilibrio

39 system is completely surpassed by the gain in performance due to the power addition accompanying the f- RBS. Hence an analysis was performed to calculate how the mass addition affects the performance of the racecar. As a measure for performance, the minimum time taken to travel 75 m. starting from rest (t75) is used. Using the calculations and a Matlab code created by the Formula SAE team (Jayhawk Motorsports), to this purpose, the following plot is generated.

Figure 16: Effect of mass addition in the performance of the vehicle

This plot shows how the t75 varies with the addition of mass. The default point in green shows the time for the vehicle mass of 650 lbs. which is the assumed base mass of the vehicle with driver and without the addition of the f-RBS system. This curve doesn’t include the improvement in performance due to the f-RBS power. The Matlab code calculated the t75 with the help of the Torque curve of the engine, also considering the gear shift RPM etc. The Matlab code was developed based on the following equations [41]: (8) (9) 4.1682 4 4.1 4.2 4.3 4.4 4.5 600 620 640 660 680 700 720 M in im u m Tim e fo r 7 5 m d a sh sta rtin g a t ze ro m p h (t 75 ) [s]

Mass of the Vehicle [lbs] Mass vs. Performance

40

(10)

( ) ₍₁₁₎

where, Fx : Tractive force at the wheels obtained from the engine

τe : Engine Torque

Ntf : Combined ratio of transmission and final drive

r : radius of the wheels

Flim.traction : maximum or limiting traction due to limiting coefficient of static friction

µs,lim : Limiting or peak coefficient of static friction

W : Weight of the vehicle

Wrear : Weight on the drive wheels (rear)

Wr,s : Static Weight distribution- rear

Faero,down : Aerodynamic Downforce

Based on Figure 16), around 70-80 lbs. seems to be a good mass constraint for the flywheel system as vehicle time t75 doesn’t get affected drastically with the addition of 80-90 lbs. The t75 goes from 4.1682s at default mass of vehicle at 650 lbs. to 4.3215s at 740 lbs.

41 For the current application, the CVT/Variator design needs to operate in a particular manner:

1. The CVT continuous ratio change should be externally controllable 2. The rated power rating should match that required by the f-RBS 3. It should have a wide ratio so as to affect size reduction of flywheel

The reasoning for the above points – as per kinetic energy equation of the flywheel – equation (2), the amount of energy stored in a flywheel is directly proportional to the Moment of inertia I and the square of the rotational velocity ω. So, either a flywheel can be designed to be of less mass and operate at higher velocities or vice versa. For the given application and due to limit set by available maximum range of CVT (explained later) and safety concerns, a requirement of lower operating speeds of flywheel was decided upon. This automatically implied that the flywheel design needs to compensate on moment of inertia and hence the mass of the flywheel. As mentioned, CVT design/selection sets a limit on the design of the flywheel. Since the available energy is a function of moment of inertia, the maximum flywheel speed pertaining to the maximum energy available varies. The CVT range is the constraining factor to the maximum speed flywheel can achieve and hence to the maximum energy it can capture out of the available energy. In order to maximize capturing either the mass/moment of inertia needs to be increased or the range needs to increase.

Mechanical Variators/CVTs, presently used in the industry, are of different design and operational capabilities due to the varying needs of the applications. They are known by different nomenclature depending on the application. One of the types of CVTs are the ones used in the automotive sector, the ‘Torque converters’ or ‘Belt-CVTs”- these CVT’s used in the scooters, tractors etc. are designed either for high performance or for high fuel economy. The common belt CVTs used in scooters or ATVs are designed to automatically shift from the low to high ratio and vice versa depending upon the output torque load or speed load with the help of springs, weights and other torque/speed sensing equipment. In

42 case of heavy duty industrial application (machines utilizing electric motors etc.,) the CVTs better known as ‘Variable Speed Drives’, are designed to vary output speed(driven shaft) continuously for a constant speed of electric motor(driver shaft), either manually controlled or with automatic operation on the basis of load. [42, 43]

The need of the present system is as follows: as mentioned before in the system operation, at the need of regen-braking or Accel-boost mode initiation, the CVT ratio needs to be set so as to synchronize the speeds of the driver and driven i.e., the wheel and flywheel or vice versa. And once they are engaged through the clutches, the gear ratio needs to be switched continuously from the current value to either a higher or lower gear, so as to initiate an energy transfer. Hence, for this operation the CVT needs to be externally controllable as per need.

After examining all the variator/CVT/Variable speed drive options available, it was decided that either of the options given below are suitable for the present application:

1. A Variable speed drive of ‘Fixed Center type Drive’ design e.g., Speed Selector Fixed center variable pulley drive – series 45 which has a manually controllable pulley. [42]

2. A modified design of torque converter/CVT system used in ATVs and scooters e.g., a Comet Symmetric 40 series Torque converter.[44]

In case of the Variable Speed Drives, the advantages are that these systems are available in the power rating required for the f-RBS system and also that they can be externally controlled. But, on the downside, they are heavy in construction and are designed for a system in which the driver (usually an electric motor) operates at constant RPM and driven varies, whereas in the context of the f-RBS in this thesis both the driver and driven operate at varying RPM. This fact needs to be examined while selecting a variable speed drive.

A modified design of a CVT/Torque converter is desirable, as they are simple in construction, lighter weight and available in the power rating required.

43 A typical torque converter and clutch system or a CVT system used in ATVs and scooters is of similar design as to the diagram shown above. It is a Variable diameter pulley (VDP)-type CVT using rubber (Kevlar reinforced or polyester reinforced) V-belt. The operation of the original system is as follows: Initially the belt sits at the lowest on the left pulley (say driver pulley) and at the highest point on the right pulley (say driven pulley) to give a lower gear ratio. On the back of one driver pulley plates are roller or spring weights, which with increase of rotational speed push the pulley plate into the other driver pulley plate (due to centrifugal forces) and hence the belt moves up on the driver pulley. When the belt position changes on the driver pulley, the belt position on the other (driven pulley adjust itself), due to the tension maintained in the belt with the help of spring at both pulleys. And in the process pushes the driven pulley plates away from each other. So, with increase of rotational speed at the driver the belt position moves from a lower to a higher on the driver and vice versa on the driven pulley, and consequently the gear ratio changes from lower to a higher gear continuously, smoothly and automatically. [44]

Figure 17: Example of a ‘Torque Converter-Clutch’ type CVT used in ATVs- Comet System [44]

Modified Torque Converter Design