Vehicle Power Requirements

Power Needs during Constant Speed Cruising 

The power needs of a particular vehicle depend on the velocity, the acceleration rate, the slope angle, and the road conditions. Unless otherwise stated, the following discussion is for situations on a flat surface, i.e., the slope angle is 0 degrees (or radian). 

The second scenario is that the vehicle passes other vehicles during highway driving. If the velocity at the end of passing is 110 km hr -, and the acceleration rate during the passing is 5 km h s (around 1.4 m s ), then the passenger car needs about 85 kW of power. 

The third scenario is that a passenger car accelerates from 0 to 100 km h i in 10 seconds. If the acceleration rate is constant at 10 km h i s (i.e., 2.8 m s ) during the 10 seconds, then the power need at the end of acceleration (when the velocity reaches 100 km h i) will be around 141 kW, as shown in Table 6.3. 

Power needs versus cruising velocity for cars, buses, and tourist carts. 

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Electric power output of the reactor module Is one of the most important requirements because it ultimately drives system mass and volume. While thrusting, the majority of electric power is used to drive the ion propulsion thrusters. Minimum acceptable thrust (and thus power) was determined to be driven by the complex gravity fields around the Jovian moons, where a minimum thrust level is required to achieve stable orbit and de-orbit of the moons. Due to the high mass of the JIMO vehicle, driven in part by the systems required to support the high voltage ion propulsion thrusters, the xenon propellant, the 1500 kg science payload, and the reactor module, an output power of 130 kWe for propulsion is required. The 200 kWe reactor module power output listed in Table 1-1 results after accounting for propulsion unit efficiency of 72%, conversion losses, transmission losses, and other vehicle power requirements. Explicitly stated, the required reactor output is estimated as follows [(130 kWe thruster output / 0.72 Propulsion Power Units Efficiency) + 5 kWe Vehicle Operation] / 0.95 Power Conversion and Distribution (PCAD) efficiency = 195 kWe ( 200 kWe). 

In the United States, in particular, recent legislation has mandated sweeping improvements to urban air quality by limiting mobile source emissions and by promoting cleaner fuels. The new laws require commercial and government fleets to purchase a substantial number of vehicles powered by an alternative fuel, such as natural gas, propane, electricity, methanol or ethanol. However, natural gas is usually preferred because of its lower cost and lower emissions compared with the other available alternative gas or liquid fuels. Even when compared with electricity, it has been shown that the full fuel cycle emissions, including those from production, conversion, and transportation of the fuel, are lower for an NGV [2]. Natural gas vehicles offer other advantages as well. Where natural gas is abundantly available as a domestic resource, increased use... 

The product of force F and the rolling radius (R) of the tires on the drive wheels is the wheel torque (T). Power depends on both torque and rotational speed (N). By definition, power is given by P = 2tiNFR = 27tNT. Wlien driving at constant speed, the driver adjusts the accelerator pedal so the drive-wheel power exactly matches the power required (P,) to overcome the resistance of the vehicle (discussed later in this article). To accelerate the vehicle, the driver further depresses the accelerator pedal so that the power available at the drit c wheels (PJ exceeds P,.. 

For maximum vehicle acceleration, the driver depresses the accelerator pedal to the floorboard and the engine operates with a tvide-open throttle. The power required curve traces the power needed by the car as a function of vehicle velocity when it is operated at constant speed in still air on a level road. At any given speed, the difference between these curves, Pa-Pr in Equation 1, is available for accelerating and hill climbing. 

The force of aerodynamic drag opposing foiward motion of the vehicle depends on its drag coefficient (Cj), its frontal area (A,), the air density (p), and the velocity of the wind with respect to the vehicle. In still air, this velocity is simply the vehicle velocity (V.). If driving into a headwind of velocity V , however, the wind velocity with respect to the vehicle is the sum of these two. Multiplying the aerodynamic drag force by vehicle velocity provides the aerodynamic power requirement (PJ. 

Vehicle maximum speed is indicated in Figure 1 by the intersections of the power available and power required cuiwes. It is seen to fall from more than 120 mph to 90 mph in going from conditions of Figure la to Figure Ic. In the early days of the automobile, top speed was of greater importance than today. The Panhard Levassor of 1886 was capable of only 12 mph. In about 1900, cars with a top speed of about 40 mph had become available, which may have been adequate for existing roads. When the first concrete road appeared in 1909, the Olds Limited could reach... 

Vehicle fuel economy is normally measured in miles per gallon. At any given instant, it depends on the energy content of a gallon of fuel (Qf), the vehicle velocity (V.,) and power required (P,-5q), the thermal efficiency with which the engine converts fuel energy into useful output work (rj,.), and the mechanical efficiency with which the driveline delivers that work to the vehicle wheels (r j). Specifically,... 

Though sodium-sulfur batteries have been under development for many years, major problems still exists with material stability. It is likely that the first commercial uses of this batteiy will not be for electric vehicles. Sodium-sulfur storage batteries may be more well-suited for hybrid electric vehicles or as part of a distributed energy resources system to provide power ill remote areas or to help meet municipal peak power requirements. 

Any problems in the setup, startup, and operation of the CBMS also were recorded in the course of the field tests. These observations are important to improving the system before it goes into production. The field tests revealed three problems. The protective screens over electronics cooling air inlets and outlets on the CBMS II housing were damaged by operator activities in the vehicles and required reinforcement. The ground probe head, which protrudes outside the vehicle hull, required more power to maintain the correct temperature under colder or wetter weather conditions. Finally the automated mass and frequency calibration procedure was not reliable in the field and required modification. These problems have been corrected and are being incorporated in the LRIP units. 

Test cells using the above graphite materials were evaluated in PC-based electrolytes. For this work, the hybrid pulse power characterization (HPPC) test was performed on cells with the different graphite anodes and PC-based electrolytes to evaluate their high power capabilities. These electrochemical experiments indicate that cells containing the surface-modified natural graphite can meet the power requirement set by the FreedomCar partnership for the hybrid vehicle applications. 

In conclusion, the surface modified natural graphite has good performance in PC based electrolyte and also meets the power requirements for hybrid electrical vehicle applications. Surface carbon coated natural graphite SLC1015 is a very promising material in high power Li-ion batteries with lower cost, reasonable safety, and low irreversible capacity. 

High-power lithium-ion batteries are promising alternatives to the nickel metal hydride batteries which are currently used for energy storage in hybrid electric vehicles (HEVs). Currently, Li(Ni,Co)02-based materials are the most widely studied cathode materials for the high-power lithium-ion batteries [1-4]. Although Li(Ni,Co)02-based materials meet the initial power requirement for the HEY application, however, it has been reported that they... 

The modular design of the HyPM fuel cells allows scaling for higher power requirements using a variety of configurations, such as series and parallel systems. Potential applications for the technology include vehicle propulsion, auxiliary power units (APU), stationary applications including backup and standby power units, combined heat and power units and portable power applications for the construction industry and the military. 

DOD is interested in new or novel advanced power and propulsion systems that will reduce fuel consumption, improve performance, extend vehicle range, reduce emissions, and reduce support costs. The Navy and Army are considering hybrids for ships, land vehicles, helicopters, and battlefield power requirements. 

When designing an electric vehicle, the first question is the dimensions of the electric motor(s) in relation to the required performance. With that in mind, in Figure 4.4 the iso-power lines refer to the total nominal power required at the motors to reach a speed of 120 km h. The typical peak power of an electric motor could be as much as 2-3 times the nominal power and the graph should then be used for... 

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