Sensors, ECUs, Actuators To Boost Suspension Performance

Written by  Sameer Kumar | 10 February 2017 | Published in February 2017 ( Technology )

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Suspension. A bunch of springs and dampers, and some control arms. How hard can it be, right? Wrong. Suspension on modern cars has come a long way from the cheap-and-cheerful leaf springs and basic 'shocks' found on many vehicles earlier. These days, it's all about variable spring rates, active damping and computer-controlled movement that can react and adjust to the terrain in real time. Here, we take a look at some emerging trends and technologies in the world of automotive suspension.

NEW OBJECTIVES

Until a few decades ago, the sole objective of having suspension on cars was to keep its occupants isolated from the jarring effects of riding over bumps and potholes on the road. Of course, ride comfort still remains as one of the most important considerations when designing an automotive suspension system, but now the suspension system must also help with driving dynamics – provide extra grip, more agility, improved cornering ability and, with the advent of electronics, the ability to 'understand' terrain and adapt to it in real time by automatically varying damping characteristics. The idea is to isolate the springing and damping functions from wheel location and position, thereby ensuring that the suspension keeps operating at maximum efficiency in all kinds of driving conditions, and at all speeds. That's a tall order, yes, but suppliers and OEMs have been working hard at achieving all of this, with a great deal of success.

When it comes to choosing a specific type of suspension system, automotive OEMs have a fair number of options to choose from, these days. There are fully hydraulic systems, air-assisted systems and, finally, computer-controlled semi-active and fully-active systems that provide a superlative mix of ride comfort and dynamic ability. The latter is the future of automotive suspension technology and even though such suspension is currently expensive and hence found only on high-end cars, costs are likely to come down progressively over the next few years, which should hopefully lead to wider deployment of such systems. Let's take a closer look at some of the more recent innovations in this space, from various global OEMs.

MECHANICAL INNOVATION

One recent innovation that comes to mind when we speak of modern suspension, is Ford's integral link rear suspension configuration, which made its debut on the European-spec Mondeo two years ago. This new design boasts improved ride comfort, better lateral stiffness for enhanced steering feedback and handling, self-levelling capability for maintaining optimal ride height, and even allows the wheels to move rearwards on impact with bumps, for reduced NVH. The mechanical system is complemented with the addition of an active control system, which manages torque vectoring, pull-drift compensation and torque steer reduction.

French carmaker, Citroën is known for its 'magic carpet' ride, due to the hydropneumatic suspension system used on its mid-1950s DS. Today, with its 'Citroën Advanced Comfort' programme, the company aims to deliver the ultimate in ride comfort on all its cars, not just high-end ones, with its new progressive hydraulic cushion suspension system. This system has been tested extensively with the Citroën C4 Picasso, which is based on the PSA Group's EMP2 platform. Instead of conventional shock absorbers, springs and mechanical stops, Citroën's system uses two progressive hydraulic cushions (one each for compression and rebound) at both ends of each suspension unit.

With this system, occupants are almost entirely isolated from bumps and irregular road surfaces, with the hydraulic cushions gradually slowing suspension movement, rather than abrupt stops at the extremes of compression and rebound. Unlike conventional mechanical systems that absorb energy and then partially return it, the hydraulic cushion simply absorbs and dissipates energy, improving ride comfort in a very big way.

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ACTIVE & SEMI-ACTIVE SUSPENSION

While OEMs and suppliers continue to innovate in the area of mechanical suspension, the holy grail these days is active, computer controlled suspension that achieves maximum dynamic performance, without compromising ride comfort. Such systems primarily consist of a set of sensors, that can 'feel' the terrain and 'recognise' road surfaces, and an ECU for analysing the data collected and provided by the sensors, and based on that data, provide 'instructions' to the suspension system on how to modify spring and damper rates in real time. There are also electrical servos and actuators, which carry out the ECU's commands and adjust the actual, physical suspension hardware on the fly by utilising advanced hydraulics.

There are many suspension systems in this space, each using slightly different set of proprietary technologies, but essentially working on the same principle. Among some notable systems out there is Tenneco's next-generation semi-active 'Kinetic H2/CES' and ACOCAR fully-active suspension systems that are both currently in production. Kinetic H2/CES combines advanced mechanical and hydraulic systems with intelligent electronics, for improved vehicle dynamics. With this system, the front and rear anti-roll bars and all four shock absorbers have been replaced with four double-acting hydraulic cylinders and two integrated CES (Continuously Controlled Electronic Suspension System) damper valves, two roll accumulators, an automatic pressure maintenance unit (APMU), and interconnected hydraulic lines. Two CES damper valves at each corner restrict the flow between cylinders and accumulators to electronically control roll, bounce and pitch, allowing decoupling of ride comfort and handling performance, and improving both in the process.

Moving on to fully-active systems, Tenneco's ACOCAR system features the addition of hydraulic pumps to shock absorbers, for improved control of suspension movement. With oil constantly circulating through its shock absorbers (with damping valves that can each be closed independently), a car fitted with ACOCAR can compensate for dips and bumps on the road, by articulating the movement of each wheel independently and keep the car 'flat' at all times. The system is able to substantially reduce or even eliminate undesired roll, pitch and weave, thereby pushing the vehicle's performance envelope further.

Similarly, Audi recently announced their new 48-volt damper system-based eROT technology, which enhances ride comfort and also allows for energy recuperation. With this system, horizontally arranged electric motors replace conventional shock absorbers, while electromechanical rotary dampers boost ride comfort in a significant way. The guiding principles behind this active suspension technology is to prevent kinetic energy (induced by constant suspension movement in a car) from being wasted in the form of heat, quickly adapt to road surfaces and the driver's driving style and maximise traction and grip at all times. With damper characteristics defined by software, and electric motors used in place of telescopic shock absorbers, the system does away with rebound and compression strokes being dependent on each other, and allows each to function independently. Plus, there is the aforementioned energy recuperation – a lever arm constantly absorbs the motion of the wheel carrier, transmitting this force via a series of gears to an electric motor, which converts it into electricity. Every little bit helps, right? Of course, it's not just Audi – all high-end European and Japanese OEMs offer some variation of active/semi-active suspension on their high-end models, with minor differences in functionality but largely the same guiding principles.

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THINKING BEYOND SUSPENSION

It's one thing to make the suspension unit itself as good as possible, using computers and technology to ensure that it responds to the terrain flawlessly. However, there is another approach, one that Jaguar has recently tried. It's a new connected car technology that allows a vehicle to identify the location and severity of potholes and other road surface irregularities, and adjust suspension characteristics accordingly, in real time, for best response. Not just that, the system is also able to share road surface data to the 'cloud,' whereby other vehicles can also have access to that data, and when driving in the area, can be pre-prepared to adjust their suspension settings.

This technology is a sort of 'add-on' to cars already connected to the web (which would allow them to receive road surface data in real time) as well as fitted with some form of active suspension, so that they can use the data received to instantly adjust settings accordingly. And while this technology has the potential to help improve ride comfort as well as grip/traction for enhanced performance, it also has the potential to prevent damage to a vehicle's wheels, tyres and suspension components, thereby saving large amounts of money in the context of repairs. In the future, pothole-sensing (for the want of a better term!) systems could also help with autonomous driving, since the data accumulated could be shared with self-driving cars, which would use the data for safer navigation.

On the subject of cars 'reading' road conditions and automatically adjusting suspension characteristics accordingly, we must also make mention of the Mercedes-Benz F 700 concept car of a decade ago, which featured 'active PRE-SCAN' suspension, which used two laser-guided sensors in its headlamps to produce a precise image of the road ahead. The car's on-board ECU could interpret the image created by the sensors and using the vehicle's 'active body control' system, adjust damping on each wheel individually to provide the best possible response to the terrain on which the car is being driven. While the F 700 never made it to production, this example serves to illustrate that manufacturers have been working on road sensing technologies, to complement active suspension, for a very long time. And now, with better sensors and vastly more powerful microprocessors, such systems could not only be production ready very soon, they could also find their way to more affordable, mainstream cars in the short- to mid-term future.

TEXT: Sameer Kumar

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