Simplifying smart cars

Delta, 14 April 2010

Cars are becoming increasingly stuffed full of sensors, electronics and software that mainly function independently and sometimes contradictorily. Newly appointed professor Edward Holweg pleads for an integrated approach.

Professor Edward Holweg was as intrigued as everyone else by the recent controversy surrounding Toyota’s apparently malfunctioning brakes and sticking throttles. “The confusion with the brakes concerned the hybrid Prius”, he explains. “In an emergency brake the pedal felt strange, while the automated system switched from the regenerative electromagnetic brake to the mechanical one. The other defect, the stuck throttle, was more serious. Modern throttle systems are electro-mechanical, meaning the gas pedal and the engine’s throttle are only electronically connected. When the brake is activated, the system should be intelligent enough to reset the throttle automatically. But apparently that did not always happen. These cases are illustrative of the present state of built-in automotive control systems, whereby each system not only functions independently of the others, but also sometimes even counteract each other. This is what the newly appointed professor of intelligent automotive systems (Mechanical, Maritime and Materials Engineering) aims to change with an integrated approach.
In his inaugural lecture, which he will deliver next Friday, prof. Holweg will show how cars – starting with the Model T Ford a century ago – have evolved from purely mechanical systems, via hydraulics (1922) and electro-hydraulics (1971: first anti-lock braking system), to electro-mechanical (drive-by-wire) systems. Holweg believes this trend is unstoppable. Yet, there is a limit to the growing complexity. “Increasing complexity is simply not a sustainable direction to follow”, he argues. “My view is therefore focused on simplifying the current vehicle architecture in order to counter the increasing complexity.” He thinks the principle of Global Chassis Control could
make cars both better and simpler.
What is Global Chassis Control?

“It means you have one set of sensors, connected to one control system that uses one set of actuators to control the entire vehicle.”

What role do actuators play?

“In the driving direction, the actuators are the traction and brake systems; in the lateral direction, the steering; and vertically, the suspension of the car.”
Given the fact that you also work part-time at SKF, a bearing manufacturer, I presume the sensors are placed in the bearings?

“That’s correct. Although the best place would be in the tires, because you’d want to measure the x,y,z-forces from the road onto the tires. But since measuring at the tire-road interface is hard to realise, measuring forces in the wheel bearing is second best option. We can actually calculate the three forces on the tire from the three forces and three angular moments we measure in the bearing.”
Is Global Chassis Control functioning yet?

“Not yet. At SKF, we have a modified BMW that features sensors in the wheel bearings and estimators that calculate the forces. We’re currently developing and testing ABS software on the wheel test bench at TU Delft. Results so far indicate that the breaking distance is shorter than with conventional ABS-systems, which use the rotation of the tire as an input. In late summer we intend to demonstrate the system in a BMW on a test track where there is lots of asphalt around.”
Will industry adopt the concept?

“It’s still early days, but BMW for example is working on an integration of subsystems like ABS and ESP [electronic stability control, ed.], having both systems share the same sensors.”

What will the research at TU Delft focus on?

“We want to improve the sensors in the bearings, including the estimators to calculate the forces. Perhaps we will also need to modify the bearings to allow for better measurements. Another research focus will be on the development of an electro-mechanical wheel suspension. That’s a project we’ll be doing in collaboration with TU Eindhoven.”

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