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Chapter 8b: DC motor selection for anelectric vehicle

0908531: Mechatronics System Design

Source URL: http://www.ju.edu.jo/sites/Academic/l.sharif/Material/Forms/AllItems.aspxSaylor URL: http://www.saylor.org/courses/me302

Attributed to: [Dr. Lutfi R. Al-Sharif] www.saylor.org of 1

Chapter 8b DC Motor Selection of an Electric VehicleDr. Lutfi R. Al-Sharif (Revision 2.0, 17/5/2008)

1. IntroductionThis example shows the methodology for selecting a permanent magnet dc motor foran electric vehicle. It is based on the final year graduation project for EngineerRasha Khaleel [1]. More details about electric vehicles can be found in [2].

2. Problem“Select a suitable DC permanent magnet motor from the datasheet at the end of thisChapter that satisfies the performance requirements stated in section 3 below”.

3. Performance RequirementsThe total mass of the vehicle (including live load and dead load) is 1300 kg. Theelectric vehicle must meet the following requirements:

Case I: On a level track. Acceleration: it should be able to accelerate from 0 to 60 mph in 6 s.Top speed: It should be able to achieve a top speed of 100 mph.

Case II: Climbing at 30° Acceleration: It should be able to accelerate from 0 to 60 mph in 10 s.Top speed: It should be able to achieve a top speed of 75 mph.

Assume the following:

• Assume an overall system efficiency of 88%.• Assume that the vehicle is fitted with tyres that have a diameter of 17 inches

(432 mm).• Assume that 1 mile = 1.6 km.• Take the acceleration due to gravity (g) as 9.81 m·s-2.

4. Basic equationsThere are four forces that need to be overcome when driving the vehicle:

4.1 Acceleration forceIn order to accelerate the masses, a force needs to be applied. The data given only

includes translational masses. So in order to account for the rotational inertias, itshall be assumed that they represent a fixed percentage of the total translationalmasses (5% in this case).

where:F a is in Nm is the mass in kga is in m·s-2

4.2 Climbing force







When climbing an incline, an extra force is needed to overcome the component ofgravity that is parallel to the incline:

Where:F c is in Nm is the mass in kgg is the acceleration due to gravity in m·s

-2

! is the angle of inline to the horizontal

4.3 Aerodynamic drag forceThe vehicle will face air resistance. This depends on the density of the air, theeffective area and the square of the speed.

Where:F cd is the aerodynamic drag force in NC w is the relative wind factor at wind speed of 75 mph (dimensionless) taken here as

0.062C d is the drag coefficient (dimensionless) taken here at 0.3 A is the effective area in m2 , taken here as 2 m2 " is the density of air in kg·m

-3taken here at 1.2 kg m

-3

! is the angle of inline to the horizontal which is 30 degrees in this problem

v is the speed in m·s-1

4.4 Rolling resistance force Although the tyres have full traction on the surface and thus do not incur any friction,there is still friction incurred within the vehicle inside the bearings when moving. Thisis referred to as rolling resistance. It calculated as follows:

Where:F r is the rolling resistance in Nm is the mass in kgg is the acceleration due to gravity in m·s-2 ! is the angle of inline to the horizontalC r is the coefficient of rolling resistance (dimensionless) and is speed dependentv is the speed in m·s-1

5. Motor specificationThe vehicle will use four motors, each mounted directly onto one of the wheels. Thisimproves the efficiency of the system by reducing transmission. Then you have to

select a motor from the following three motors:







All three motor have a top rotational speed of 2000 rpmThey have rated torques of:

750 N·m500 N·m350 N·m

More details about the motors are shown in the datasheet at the end of this Chapter.

REFERENCES & BIBLIOGRAPHY[1] “Electric Vehicle Technology Explained And Design”, 20/5/2007, a Dissertation

in Electrical Engineering, Submitted by Rasha Khaleel Noful, MechatronicsEngineering Department, Faculty of Engineering & Technology, University ofJordan.

[2] “Electric Vehicle Technology Explained”, James Larminie, Oxford Brookes

University, Oxford, UK, John Lowry, Acenti Designs Ltd., UK, 2003 John Wiley& Sons Ltd.







Datasheet for DC Motors

8b motor selection for an electric vehicle rev 2 080517 ccupload

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