Lotus City Car
Download PDF
Purchases of city cars are on the rise as consumers downsize their vehicles and engines to save money and fuel.
The renewed interest in these urban vehicles has seen a fresh approach from Lotus Engineering, who has looked at what is in store for the city car of the future. For Automotive Engineer, one of the most prominent engineering magazines in Europe, Lotus undertook a challenging project study, with only two weeks to come up with sketches, layout ideas and plenty of innovative thinking to redefine the city car. The results show how future vehicles could become much more tightly focused on their real purpose.
The Lotus ethos of performance through light weight is now more prevalent than ever and is equally important for city cars. Current city cars carry too many tonnes of metal and cubic metres of space that is simply not needed.
The first aspect to be decided was number of occupants, with the Lotus city car carrying four people or two people with luggage. The seating position is also high to allow improved visibility. Because the car must be small, safe and maneuverable, rear wheel drive is best, with the steering angle at the front.The car, shorter and taller than normal, will have 12” wheels, always challenging for the design team, who strive for a cool looking car. To give the car a tiny turning circle of 6.5m, there is a large steering backlog of 55º. The front passenger sits further forward than the driver, with the front seat travel longer than usual. The seat slides completely forward to touch the steering wheel to let you climb in the back. The door is lightweight to make it easier to handle with just enough inertia to shut in. The side window links to the front and rear lights to create a graphic that’s longer than the cars side. Similarly, the windscreen extends into the solar panels on the roof.
The car is also surrounded with soft rubber trim, protecting it from low-impact knocks in cities where they engage in tactile parking. The strip along the sill is the sandwich floor, but by turning it into a black panel, it cuts down the visual height. The rear seats fold down to create extra space for storing luggage and shopping. The instrument panel is a simple, one-piece moulding with airbags at the top. A common vent runs across it and there’s a useful tray and a cup-holder. There’s also a head-up display to link the satnav and speed, quite useful in a city environment.
The platform has a sandwich floor that holds the batteries, inverter and power electronics and keeps the centre of gravity low. With the need for a lightweight vehicle, it uses an extruded aluminium spaceframe with a flat sheet underbody. The body would be pressed aluminum or composite depending on volumes.
A diecast magnesium or aluminium unit with a pressing on the exterior is used. Metallic parts are also specified for around the door to ensure the dimensional accuracy for the sealing and a quality feel. The simple bonded aluminium lower structure can be stretched for other versions of the vehicle. The bulkhead structure in front of the occupants holds the steering column and offers somewhere for the door hardware.
The crash structure comprises sacrificial composite energy absorbers that can be replaced cheaply. These drawings are a result of just two weeks work. A typical concept phase at Lotus lasts between three and six months. In that time, the engineers would devise a package for the stylists to put some lines around it. They would then build a seating buck to check the CAD assumptions on the internal package. This would then feed back into the mechanical package, improving the ergonomics and fine-tuning the styling. This isn’t the finished item, but shows massive advances in a short space of time.
More than half of all journeys in the UK are less than 11 km. City journeys are even shorter so a range of little more than 22 km would meet most of our requirements.
The city car will offer good acceleration from 0 to 65 km/h but a top speed of 105 km/p is adequate. Given that power consumption of 200 W is typical in a small car, a 10 kW battery would give a range of 50 km, which would weigh around 100 kg. Recharging that with a standard 13A plug that delivers 3 kW would take three-and-a-half hours.There are two blocks of four batteries, each with a capacity of 10 kWh. The first block provides the basic 50 km range, the second is bought or leased for winter use or extra range. The batteries are air-cooled, not water-cooled. The air comes in the front of the vehicle through the composite crash structure, through the air-conditioning condenser, and then along a tunnel in the floor section between the batteries. This cools the cells and assists the water-cooled e-motor in the summer. In the winter, the air flow is blocked so instead warm air from the motor’s radiator is pumped the other way up the tunnel to keep the batteries at an efficient operating temperature. Other heat generated is also allowed to pass through the floor to the interior.
