Engineering & Technology · Vehicle Systems & Mobility Engineering
Vehicle requirements, missions and mobility contexts
The engineering problem is rarely just to move a vehicle. It may be to deliver people to a clinic, carry parcels through a dense district or move a load across rough ground. The useful outcome determines which vehicle characteristics matter.
Review mechanisms and machine design, fluids, electrical power and machines, and control and automation. Use newtons, joules and watts; 1 kWh=3.6 MJ. Speed in m/s equals speed in km/h divided by 3.6. These lessons provide engineering reasoning, not driving, repair or equipment-setting instructions.
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Turn a mobility need into measurable mission requirements and a fair comparison basis.
Describe the service before the machine
A mission states who or what must move, between which places, when, with what access and reliability. Payload is the people or goods carried; total moving mass includes the vehicle and everything on it. A compact delivery vehicle might meet an energy target yet fail a loading-space, accessibility or stopping-frequency requirement. A larger vehicle can be useful when its capacity is actually needed.
Translate broad intentions into observable criteria: carry a specified load, complete a route within a time window, fit a loading bay, accommodate a wheelchair interface, or retain a stated energy allowance at the end. Requirements need conditions and a method of verification. “Long range” is incomplete without payload, weather, route and the allowed remaining reserve.
Use a duty cycle and a service denominator
A drive cycle records speed against time. A duty cycle also includes working hours, stops, loading, waiting, climate control and charging or refuelling opportunities. Equal distance at equal average speed does not imply equal energy: repeated acceleration, hills and time spent using auxiliaries change the account. Conditions that rarely occur can still determine peak power, cooling or access requirements.
Vehicle-kilometres describe machine movement. Passenger-kilometres and tonne-kilometres describe transport service. Count empty repositioning in the energy total while keeping it out of useful passenger-distance. Report occupancy and route changes instead of treating a per-vehicle efficiency improvement as automatically the same improvement per useful journey.
Keep interfaces and uncertainty visible
A vehicle interacts with roads, kerbs, loading equipment, people, electricity or fuel supply and maintenance facilities. Queueing or an unavailable connector can defeat a mission even if the vehicle stores enough energy. Turning radius, usable entrances and service accessibility are system requirements rather than secondary cosmetic details.
Use measured route distributions and representative trials when available. Distinguish a typical case, an extreme case and the confidence in each. A small design margin based on uncertain energy input is different from a demonstrated ability to finish a mission. Compare alternatives against the same service, and retain unmet requirements alongside favourable results.
Count the trip that provides the service
In an original exercise, a vehicle carries four passengers 12 km and then returns 12 km empty. Supply constant energy use .24 kWh per vehicle-km for both legs. Total travel 24 km consumes 5.76 kWh. Useful service is 4×12=48 passenger-km, giving 5.76/48=.12 kWh/passenger-km. Counting only the outward energy would falsely halve the result.
A second arrangement carries two passengers on each of two outward trips, with an empty return after each. It provides the same 48 passenger-km but travels 48 km and consumes 11.52 kWh, or .24 kWh/passenger-km under the supplied model. Timetables, passenger access, loading and the possibility of combining journeys must determine whether either arrangement meets the actual need. The numbers are constructed, not fleet observations.
Try the reasoning
Does twice the seating capacity establish twice the useful service?
Show the answer and reasoning
No. Occupied distance, demand, access and the schedule determine delivered service.
Why include an empty return in energy but not passenger-distance?
Show the answer and reasoning
It consumes resources while delivering no passenger-distance in this exercise.
What is missing from a requirement that says “complete the route”?
Show the answer and reasoning
Conditions, payload, time, remaining energy and an acceptance method must be specified.
What to carry forward
Define useful movement, conditions and interfaces before optimising the vehicle.
References
Teaching resources and research supporting this lesson’s explanations and examples.