It took a number of years of effort working on prototype vehicles and subsequent road testing in order to get to the stage when the algorithm was finally ready for a production vehicle. British auto racing driver Chris Goodwin was the one who got to test the McLaren 720S and the simulation results from the beginning were very positive – we knew we were on to a winner!

Professor Malcolm Smith

Hosted by Gonville & Caius College in celebration of Professor Smith's 60th birthday, the July 5 Workshop on Networks and Control was organised by the Department of Engineering and sponsored by McLaren. It included presentations from Cambridge academics, former students, as well as experts from universities in Japan, the United States and Germany.

Malcolm Smith, Professor in Control Engineering and a Fellow of Caius, is well known for his invention of a vehicle suspension device called an inerter, which is now a standard component in Forumla 1 suspensions and widely used in motorsport.

Revealed at the workshop was Professor Smith's contributions to a different technology; one which has been utilised in the latest McLaren supercar – the 720S. The suspension system on the car is termed 'semi-active' since it makes use of continuously adjustable dampers which are controlled by a computer in real time. The system employs a new algorithm, which Professor Smith developed with his former PhD student Dr Panos Brezas. In honour of his 60th birthday, the McLaren 720S was displayed at the College during the workshop.

Although semi-active systems are not new in themselves, the algorithm developed by Professor Smith and Dr Brezas has achieved a big step forward in performance by simultaneously optimising the car's ride and handling response. The ride behaviour is the car's response to undulations in the road, whereas the handling behaviour is the response to driver inputs such as steering, accelerating and braking.

Here Professor Smith explains the research which led to the algorithm discovery and why getting there proved to be a challenge:

"When Panos began his PhD under my supervision back in 2008, we looked carefully, in collaboration with our sponsor McLaren, at the problem of controlling the car under arbitrary and simultaneous excitation from both types of exogenous inputs: road undulations and driver inputs. The inputs have different character, and affect the vehicle in different ways. We modelled the road inputs stochastically and the driver inputs deterministically.

The challenge

"The most difficult part of the control problem is that the control input (the adjustable damper rate) enters the problem non-linearly. Nevertheless, we did succeed in deriving a control law for a suitable performance criterion that incorporated all the important attributes: body accelerations, tyre forces etc.

"The next challenge arose because our algorithm relied on 'state feedback', but not all components of the car's state are directly measurable. An observer of special type had to be developed to take account of the two types of disturbance on the vehicle.

"Putting this all together on a prototype vehicle was not straightforward. We were very fortunate to work with a former Cambridge PhD student Dr Will Hoult (who was supervised by Dr David Cole) who took charge of the algorithm development at McLaren.

The solution

"It took a number of years of effort working on prototype vehicles and subsequent road testing in order to get to the stage when the algorithm was finally ready for a production vehicle. British auto racing driver Chris Goodwin, who is currently Chief Test Driver for McLaren Automotive, was the one who got to test the car and the simulation results from the beginning were very positive – we knew we were on to a winner!

"The 720S was also tested by McLaren in a wide range of motoring conditions, ranging from Death Valley and the snows of Colorado and the Alps to a bumpy roundabout near Woking. The roundabout offered a combination of demanding handling and an uneven road surface, permitting testing of the algorithm’s ability to find a balance between comfort and control."

Speaking about the new and improved performance of the 720S earlier this year, Chris Goodwin said: “The biggest leap has come in the software that controls that suspension system. It’s an intelligent system that successfully balances the requirements of ride, comfort, and body control and handling, dealing with road surface changes, challenging corners in a way that we’ve never seen before.”