There are two main groups of active suspensions, the ones altering the suspension settings and the ones regarding the anti-roll systems.
The altering suspension setting types are the self-levelling and the height adjustable suspensions. These types of suspension systems aim to maintain the vehicle as flat as possible.
The self levelling suspension aims to counteract the difference in axle load between the front and the rear of the car due to loading of the vehicle, breaking or accelerating forces. The height adjustment suspensions cope with the problems of ground clearance and to some extent the stiffness of the suspension.
Inside the anti-roll systems there is another classification between active and semi-active anti-roll suspension.
Active anti-roll suspensions exert a force in the opposite direction of the rolling force to counteract the effect of the body roll, whereas the semi-active suspension opposes the body roll, usually by increasing the stiffness of the dampers.
Regarding the method used to achieve the anti-roll effect the suspensions can be also classified as hydraulic (active), electromagnetic (active), solenoid valve (semi-active) and magneto rheological (semi-active)
Michelin as a tyre manufacturer has developed its own suspension system. The system was exposed to the public for the first time in the Paris motorshow of 2008 and it is and a wheel onboard traction and suspension system as shown in the picture below.
Figure Michelin Active Wheel Picture, Press Kit 2008 Paris Motor Show
This suspension system is a combined traction and suspension electrical system. The Active wheel can incorporate only the suspension components or include an electric motor, and as Michelin claims it could be used in a four wheel drive or a two wheel drive layout depending on power demands.
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The main advantages of this system is that all the components necessary for the control of the suspension are assembled in the wheel, hence it would not interfere with package constrains or the geometry, and because of that, more cabin space can be fully utilized. Another of the advantages is that is a fully electrical system, so it can be utilized in hybrid cars as the drive of the wheels is done trough an electric motor installed on the wheels. This means that the use of this system could reduce the carbon emissions or fully eliminate them in an electric vehicle.
On the other hand, the system is fairly new and needs to be proven in real life situations. Other problems are that the drive must be necessarily done through electric motors, hence not really suitable for the use of a conventional engine alone, and although the costs of the system have not been published, it can be assumed that it would be fairly higher than a conventional active suspension based on the cost of research, development and price of the components alone.
Boseââ‚¬â„¢s approach to a active suspension is another peculiar one, as it is a cross between an in-wheel device and a conventional suspension. The way the mechanism works is by replacing the conventional shock absorbers and spring dampers by a single linear electromagnetic motor at each wheel. These electromagnetic motors are computer controlled to provide a soft suspension, but at the same time are set to self level the vehicle. Also because the electromagnetic motors are computer controlled suspension can be set to counteract the body roll and pitch angle of the vehicle during cornering, braking or acceleration.
Overall the system is not intrusive regarding the package constrains of the vehicle as it would be installed using the mounting points of a conventional coil-over spring damper. And in terms of weight, it would be similar to a conventional suspension. Another advantage is that the system would not require the extra weight added by using actuators and torque arms.
The main disadvantages are that the system is not a straight replacement as it needs the software to be set up for each vehicle in question, and the potential needs for a bigger battery to cope with the electromagnetic motors demand, and the power usage of recharging the battery.
MagneRide is the commercial name of the Magneto Rheological suspension developed by Delphi, and lately sold to BWI (Beijing West Industries) group.
The Magneto Rheological suspension is primarily a semi-active suspension that by altering the suspension properties of the fluid inside the dampers through electromagnets, changes the stiffness of the suspension. This system although being a semi-active suspension is able to perform almost as well as an active suspension. Unlike a semi-active suspension the control of the suspension stiffness can be changed none linearly to the input response, hence instead for example instead of opposing the body roll, it can be counteracted by further increase of the suspension stiffness.
Some of the disadvantages are the added weight and cost of the components compared to a conventional suspension, and that it cannot perform under certain conditions as well as a fully active suspension.
Originally this suspension was developed for General Motors, and used in the top end vehicles of the company such as Holden, Buick, Cadillac and Corvette models. Since the introduction of this suspension other companies have used this suspension in some of their performance range such as Audi, Ferrari and Acura.
The off-road applications of the MageRide have seen use of this system on the Cadillac SRX and Acura MDX.
This suspension system is currently being retrofitted to lightweight tanks and high mobility vehicles as well as in prototypes by the United States Army.
Active Stabilizer Suspension System
The Active Stabilizer Suspension System is a joint venture between Toyota and Aisin Seiki Co. to develop an innovative suspension for Lexus (Toyotaââ‚¬â„¢s luxury range of vehicles). The system is a fully electrically controlled active suspension system. The way it works is similar to the one currently used by Jaguar-Land Rover, but instead of using a hydraulic system, is using brushless motors geared and connected to the stabilizer bars.
Toyota claims that this system is twenty times more energy efficient than a standard servo actuated hydraulic active suspension and its reaction time is also quicker, being considered to be within 20 milliseconds (Suzuki et all, 2006).
On the other hand the main disadvantages are the cost and development of the components.
This system is being currently offered as an optional extra throughout most of the Lexus range, and also offered in the crossover SUV Lexus RX 450h
The Hydractive system is a Citroen developed hydro-pneumatic suspension, in which the conventional coil springs and shock absorbers have been replaced by hydro-pneumatic shock absorbers. This system has suffered several revisions, being the current one Hydractive 3 being introduced in 2001. Early versions of the hydro-pneumatic suspension featured a self-levelling and ride height adjustment. The later versions of the Hydractive also feature options such as automatically lowering the ride height above certain speed to reduce fuel consumption or electronically controls that avoid the suspension dropping after the engine is switched off. Also another package, such as the Hydractive Activa suspension, combined the previous advantages with an active suspension eliminating body roll whilst cornering.
This suspension system is currently used by the PSA Peugeot Citroen group and at some point this suspension technology has been used by other manufactures and military vehicles.
The main advantages of this system are that independently of the load and load distribution, the car will always remain levelled. The system has at the same time a smooth and firm ride. This is due to the dual characteristic of the suspension. Firstly the pneumatic suspension provides a smooth ride because is not as stiff as a conventional spring, but at the same time the hydraulic suspension is less compressible than a conventional spring, providing a solid support when hard breaking or cornering happens. Overall the suspension is more progressive than a conventional coil-over system, being softer under bumps and harder under cornering.
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On the other hand this suspension has several drawbacks such as being a more complicated and expensive system, which requires specialized maintenance. Another concerning problem is that a system failure will result on ride height loss and a performance drop in the brake and power steering systems.
Air suspension works in a similar way as the hydro-pneumatic. In the air suspension the conventional coil-over spring dampers are replaced by air bags that are inflated through a compressor to stiffen the suspension when needed. Air suspensions offer similar advantages to the hydro-pneumatic such as self-levelling or an improved ride quality.
On the other hand the ride quality is not much greater than conventional coil-over suspensions, and the system suffers from a range of problems such as air bag, air line, compressor or dryer failures.
Most of the top end manufacturers and tuning aftermarket companies have developed their own air suspension systems such as Ford (Ford and Lincoln), Land Rover, Mercedes-Benz (Mercedes-Benz and Maybach), Rolls-Royce, SsangYong, Subaru, Toyota (Lexus) and Volkswagen (Volkswagen and Audi) to name a few.
The PASM is the trade name for Porsche Active Suspension Management. The PASM is an active air suspension, which is an air suspension as mentioned above that features self levelling and ride height adjustment as well as roll and pitch control.
This suspension is offered either as a standard or optional across the 911 and Cayenne ranges.
EDC (Electronic Damper Control) is the commercial name that BMW uses for its active suspension system. The ECD uses electronically controlled dampers to adjust the response of each of the wheels trough three different damper curve settings; soft, medium and hard. It is worth noting that there are other features that affect the suspension, but are not connected to the ECD such as the Cornering Brake Control or the Automatic Stability Control.
ABC (Active Body Control) is the trade name of Mercedes-Benz own active suspension.
The system features roll, pitch and roll control achieved through servo actuated hydraulics. In this respect the system is similar to the current used in the Range Rover, but this system instead of using actuators, uses a modified suspension strut. The ABC suspension strut replaces the conventional dampers with electronically controlled plunger cylinder dampers whilst retaining the coil-over. The mechanism woks in a similar manner, the sensors and accelerometers evaluate the situation and the oil pump send the pressure required to operate the suspension, but instead of using a single valve block and two actuators, the ABC system uses a front and rear servo-valves that in turn sent the oil to each of the four plunger cylinder dampers.
Society of Automotive Engineers (2006) ââ‚¬ËœDevelopment of Electric Active Stabilizer Suspension Systemââ‚¬â„¢. Paper no. 2006-01-1537. 2006 SAE World Congress Exhibition 3-6 April 2006, Detroit. Suzuki, S., Buma,S., Urababa, S., Nishihara, A., and Taneda, A Society of Automotive Engineers
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