Autonomous corner modules as an enabler for new vehicle chassis solutions

Journal article, 2006

Demands for new functions and refined attributes in vehicle dynamics are
leading to more complex and more expensive chassis design. To overcome this, there has
been increasing interest in a novel chassis design that could be reused in the development
process for new vehicle platforms and mainly allow functions to be regulated by software.
The Autonomous Corner Module (ACM) was invented at Volvo Car Corporation (VCC) in
1998. The invention is based upon actively controlled functions and distributed actuation. The
main idea is that the ACM should enable individual control of the functions of each wheel;
propulsion/braking, alignment/steering and vertical wheel load. This is done by using hubmotors
and by replacing the lower control arm of a suspension with two linear actuators,
allowing them to control steering and camber simultaneously. Along with active
spring/damper and wheel motors, these modules are able to individually control each wheel's
steering, camber, suspension and spin velocity. This provides the opportunity to replace
mechanical drive, braking, steering and suspension with distributed wheel functions which, in
turn, enable new vehicle architecture and design.
The aim of this paper is to present the vehicle dynamic potential of the ACM solution, by
describing its possible uses and relating them to previous research findings. Associated work
suggests chassis solutions where different fractions of the functions of the ACM capability
have been used to achieve benefits in vehicle dynamics. For instance, ideas on how to use
active camber control have been presented. Other studies have reported well-known
advantages, such as, good transient yaw control from in-wheel motor propulsion and stable
chassis behaviour from four-wheel steering, when affected by side wind. However, this
technology also presents challenges. One example is how to control the relatively large
unsprung mass that occurs due to the extra weight from the in-wheel motor. The negative
influence from this source can be reduced by using active control of vertical forces. The
implementation of ACM, or similar technologies, requires a well-structured hierarchy and
control strategy. Associated work suggests methods for chassis control, where tyre forces can
be individually distributed from a vehicle path description. The associated work
predominately indicates that the ACM introduces new opportunities and shows itself to be a
promising enabler for vehicle dynamic functions.