Cadillac Magnetic Ride Control struts and shock absorbers are designed to improve handling and improve ride comfort on a variety of road surfaces. The system appeared a long time ago and turned out to be so effective that many other European and German automakers later repeated it, but initially it appeared on the Escalade, SRX, STS models.
Operating principle
In general, the system works quite simply. Unlike traditional shock absorbers, shock absorbers of this type do not use oil or gas, but a magnetic rheological fluid that reacts to a magnetic field created by a special electric coil located in the body of each shock absorber. As a result of the impact, the density of the liquid changes, and, accordingly, the stiffness of the suspension.
The Magnetic Ride Control system works very quickly, data from various sensors comes at a speed of up to a thousand times per second, instantly responding to changes in the road surface. Sensors measure the buildup of the body, vehicle acceleration, loading and other data, on the basis of which the current strength is calculated, which is supplied separately to each of the shock absorbers at the moment.
In fact, everything happens exactly as the manufacturer describes, good handling is combined with a high level of comfort. But there is also a significant drawback when operating in our country.
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It begins in the mid-50s of the last century, when the French company Citroen installed hydropneumatics on the rear axle of the representative Traction Avant 15CV6, and a little later - on all four wheels of the DS model. On each shock absorber there was a sphere divided by a membrane into two parts, in which there is a working fluid and a pressurized gas supporting it.
In 1989, the XM model appeared, on which Hydractiv active hydropneumatic suspension was installed. Under the control of electronics, she adjusted to the traffic situation. Today, Citroen is running the third generation Hydractiv, and along with the regular version, they offer a more comfortable one with the Plus prefix.
In the last century, hydropneumatic suspension was installed not only on Citroens, but also on expensive executive cars: Mercedes-Benz, Bentley, Rolls-Royce. By the way, cars crowned with a three-beam star still do not avoid such a scheme.
Active Body and other systems
The Active Body Control system (active body control) differs in design from Hydractiv, but the principle is similar: by changing the pressure, the suspension stiffness and ground clearance are set (hydraulic cylinders compress the springs). However, Mercedes-Benz also has air suspension chassis options (Airmatik Dual Control), which set the ground clearance depending on speed and load. The stiffness of the shock absorbers is monitored by ADS (Adaptive Damping System - adaptive damping system). And as a more affordable option, Mercedes buyers are offered the Agility Control suspension with mechanical devices that regulate stiffness.
Volkswagen calls the damper control system DCC (aDaptive Chassis Control - adaptive suspension control). The control unit receives data from the sensors on the movement of the wheels and the body and accordingly changes the rigidity of the chassis. Characteristics are set by electromagnetic valves mounted on shock absorbers.
A similar adaptive suspension is used by Audi, however, on some models, the original Audi Magnetic Ride system is installed. The damping elements are filled with a magnetoresistive fluid that changes viscosity under the influence of a magnetic field. By the way, a design that works on the same principle was first used by Cadillac. And the name of the "Americans" is consonant - Magnetic Ride Control. Fitting into this family, Volkswagen is in no hurry to part with proper names. Porsche's intelligent chassis with electronically controlled shock absorbers and, on some models, also air suspension, bears the designation PASM (Porsche Active Suspension Management - active suspension control). Another nominal weapon PDCC (Porsche Dynamic Chassis Control - dynamic chassis control) helps to effectively deal with rolls and pecks. Anti-roll bars with hydraulic pumps practically do not allow the body to bow from side to side. Opel has been installing IDS (Interactive Driving System - interactive driving system) on production models for almost a decade. Its main component is CDC (Continuous Damping Control - continuous damping control), which adjusts the shock absorbers depending on road conditions. By the way, other manufacturers, such as Nissan, also use the CDC abbreviation. In new Opel models, tricky electronic and mechanical devices are called "flexes". The suspension was no exception - it was called FlexRide.
BMW has another cherished word - Drive. Therefore, it is quite logical that the adaptive suspension is called Adaptive Drive. It includes Dynamic Drive roll suppression and EDC (Electronic Damper Control) damper control. The latter will probably soon also come up with a designation with the word Drive.Toyota and Lexus use common names. The stiffness of the shock absorbers is monitored by the AVS system (Adaptive Variable Suspension - adaptive suspension), the ground clearance is regulated by the AHC (Active Height Control) air suspension. The KDSS (Kinetic Dynamic Suspension System), which controls the hydraulic actuators of the stabilizers, allows you to take turns with minimal roll. Nissan and Infinity have an analogue of the latter - the original HBMS system (Hydraulic Body Motion Control - hydraulic control over the movement of the body), which changes the characteristics of the shock absorbers and thereby reduces the car's rocking from side to side.
An interesting idea was implemented by Hyundai by installing the AGCS (Active Geometry Control Suspension) rear suspension on the new Sonata. Electric motors drive the traction by changing the angles of the wheels. Thus, the electronics help the stern steer in turns. By the way, in some cars, electric motors that obey active steering change the steering angle along with the front ones. For example, RAS (Rear Active Steer - active rear wheels) for Infinity or Integral Active Steering for BMW.
Handbook of pendants: what are we standing on?
Until recently, only types of suspensions were distinguished - dependent, MacPherson, multi-link. The obscure names came about as the chassis learned to adapt to road situations and terrain. Let's clarify the situation.
Handbook of pendants: what are we standing on?Let's first deal with the concepts, since various terms are now in use - active suspension, adaptive ... So, we will consider that the active chassis is a more general definition. After all, changing the characteristics of suspensions in order to increase stability, controllability, get rid of rolls, etc. can be both preventive (by pressing a button in the passenger compartment or by manual adjustment) and fully automatically.
It is in the latter case that it is appropriate to speak of an adaptive running gear. Such a suspension, using various sensors and electronic devices, collects data on the position of the car body, the quality of the road surface, and the driving parameters in order to independently adjust its work to specific conditions, the driver’s piloting style or the mode he has chosen. The main and most important task of adaptive suspension is to determine as quickly as possible what is under the wheels of the car and how it rides, and then instantly rebuild the characteristics: change the clearance, damping degree, suspension geometry, and sometimes even ... adjust the rear wheel steering angles.
HISTORY OF ACTIVE SUSPENSION
The beginning of the history of active suspension can be considered the 50s of the last century, when outlandish hydropneumatic struts first appeared on a car as elastic elements. The role of traditional shock absorbers and springs in this design is performed by special hydraulic cylinders and hydraulic accumulator spheres with gas boost. The principle is simple: we change the fluid pressure - we change the parameters of the running gear. In those days, this design was very bulky and heavy, but it fully justified itself with a high smoothness of motion and the ability to adjust the ride height.
The metal spheres in the diagram are additional (for example, they do not work in hard suspension mode) hydropneumatic elastic elements, which are internally separated by elastic membranes. At the bottom of the sphere is the working fluid, and at the top is nitrogen gas.
Citroen was the first to use hydropneumatic struts on their cars. This happened in 1954. The French continued to develop this topic further (for example, on the legendary DS model), and in the 90s, the more advanced Hydractive hydropneumatic suspension debuted, which engineers continue to modernize to this day. Here it was already considered adaptive, since with the help of electronics it could independently adapt to driving conditions: it is better to smooth out shocks coming to the body, reduce pecking during braking, deal with rolls in corners, and also adjust the car’s clearance to the speed of the car and road wheel cover. The automatic change in the stiffness of each elastic element in an adaptive hydropneumatic suspension is based on the control of the pressure of liquid and gas in the system (to fully understand the principle of operation of such a suspension scheme, watch the video below).
VARIABLE SHOCK ABSORBERS
And yet, over the years, hydropneumatics has not become easier. Rather, on the contrary. Therefore, it is more logical to start the story with the most ordinary way of adapting the characteristics of the suspension to the road surface - individual control of the stiffness of each shock absorber. Recall that they are necessary for any car to dampen body vibrations. A typical damper is a cylinder divided into separate chambers by an elastic piston (sometimes there are several). When the suspension is activated, the liquid flows from one cavity to another. But not freely, but through special throttle valves. Accordingly, hydraulic resistance arises inside the shock absorber, due to which the buildup fades.
It turns out that by controlling the flow rate of the fluid, it is possible to change the stiffness of the shock absorber. So - to seriously improve the performance of the car by fairly budgetary methods. After all, today adjustable dampers are produced by many companies for a variety of car models. The technology has been worked out.
Depending on the device of the shock absorber, its adjustment can be carried out manually (with a special screw on the damper or by pressing a button in the cabin), as well as fully automatically. But since we are talking about adaptive suspensions, we will consider only the last option, which usually still allows you to adjust the suspension proactively - by choosing a specific driving mode (for example, a standard set of three modes: Comfort, Normal and Sport).
In modern designs of adaptive shock absorbers, two main tools for controlling the degree of elasticity are used: 1. a circuit based on electromagnetic valves; 2. using the so-called magnetorheological fluid.
Both versions allow you to individually automatically change the degree of damping of each shock absorber depending on the condition of the roadway, vehicle movement parameters, driving style and / or preventively at the request of the driver. The chassis with adaptive dampers significantly changes the behavior of the car on the road, but in the control range it is noticeably inferior, for example, to hydropneumatics.
- How is the adaptive shock absorber based on solenoid valves arranged?
If in a conventional shock absorber the channels in the moving piston have a constant flow area for uniform flow of the working fluid, then in adaptive shock absorbers it can be changed using special solenoid valves. This happens as follows: electronics collects a lot of different data (damper response to compression / rebound, ground clearance, suspension travel, acceleration of the body in planes, mode switch signal, etc.), and then instantly distributes individual commands to each shock absorber: to dissolve or hold down for a certain time and amount.
At this moment, inside one or another shock absorber, under the influence of current, the flow area of the channel changes in a matter of milliseconds, and at the same time the intensity of the flow of the working fluid. Moreover, the control valve with the control solenoid can be located in different places: for example, inside the damper directly on the piston, or outside on the side of the housing.
The technology and settings of the adjustable solenoid dampers are constantly being improved to achieve the smoothest transition from hard to soft damping. For example, Bilstein shock absorbers have a special DampTronic central valve in the piston, which allows you to steplessly reduce the resistance of the working fluid.
- How does an adaptive shock absorber based on a magnetorheological fluid work?
If in the first case electromagnetic valves were responsible for adjusting the stiffness, then in magnetorheological shock absorbers this is controlled, as you might guess, by a special magnetorheological (ferromagnetic) fluid with which the shock absorber is filled.
What superpowers does she have? In fact, there is nothing abstruse in it: in the composition of the ferrofluid, you can find many tiny metal particles that react to changes in the magnetic field around the shock absorber rod and piston. With an increase in the current strength on the solenoid (electromagnet), the particles of the magnetic fluid line up like soldiers on a parade ground along the lines of the field, and the substance instantly changes its viscosity, creating additional resistance to the movement of the piston inside the shock absorber, that is, making it stiffer.
It was previously believed that the process of changing the degree of damping in a magnetorheological shock absorber is faster, smoother and more accurate than in a design with a solenoid valve. However, at the moment, both technologies are almost equal in efficiency. Therefore, in fact, the driver almost does not feel the difference. However, in the suspensions of modern supercars (Ferrari, Porsche, Lamborghini), where the reaction time to changing driving conditions plays a significant role, shock absorbers with magnetorheological fluid are installed.
Demonstration of the adaptive magnetorheological shock absorbers Magnetic Ride from Audi.
ADAPTIVE AIR SUSPENSION
Of course, in the range of adaptive suspensions, a special place is occupied by air suspension, which to this day has little to compete in terms of smoothness. Structurally, this scheme differs from the usual chassis in the absence of traditional springs, since their role is played by elastic rubber cylinders filled with air. With the help of an electronically controlled pneumatic drive (air supply system + receiver), it is possible to filigree inflate or lower each pneumatic strut, adjusting the height of each part of the body in an automatic (or preventive) mode over a wide range.
And in order to control the stiffness of the suspension, the same adaptive shock absorbers work together with the air springs (an example of such a scheme is Airmatic Dual Control from Mercedes-Benz). Depending on the design of the undercarriage, they can be installed either separately from the air spring or inside it (pneumatic strut).
By the way, in the hydropneumatic scheme (Hydractive from Citroen), there is no need for conventional shock absorbers, since electromagnetic valves inside the strut are responsible for the stiffness parameters, which change the intensity of the flow of the working fluid.
ADAPTIVE HYDRO-SPRING SUSPENSION
However, not necessarily the complex design of the adaptive chassis should be accompanied by the rejection of such a traditional elastic element as a spring. Mercedes-Benz engineers, for example, in their Active Body Control chassis simply improved the spring strut with shock absorber by installing a special hydraulic cylinder on it. And as a result, we got one of the most advanced adaptive suspensions in existence.
Based on data from a lot of sensors that monitor the movement of the body in all directions, as well as on readings from special stereo cameras (they scan the quality of the road 15 meters ahead), the electronics are able to finely adjust (by opening / closing electronic hydraulic valves) the stiffness and elasticity of each hydraulic spring rack. As a result, such a system almost completely eliminates body roll under a wide variety of driving conditions: turning, accelerating, braking. The design reacts so quickly to circumstances that it even made it possible to abandon the anti-roll bar.
And of course, like pneumatic / hydropneumatic suspensions, the hydraulic spring circuit can adjust the position of the body in height, “play” with chassis rigidity, and also automatically reduce ground clearance at high speed, increasing vehicle stability.
And this is a video demonstration of the operation of the hydraulic spring chassis with the function of scanning the road Magic Body Control
Let us briefly recall the principle of its operation: if the stereo camera and the transverse acceleration sensor detect a turn, then the body will automatically tilt at a small angle to the center of the turn (one pair of hydraulic spring struts instantly relaxes a little, and the other one slightly clamps). This is done to eliminate the effect of body roll in a turn, increasing comfort for the driver and passengers. However, in fact, only ... the passenger perceives a positive result. Since for the driver, body roll is a kind of signal, information through which he feels and predicts one or another reaction of the car to a maneuver. Therefore, when the anti-roll system works, the information comes with a distortion, and the driver has to psychologically readjust once again, losing feedback from the car. But engineers are also struggling with this problem. For example, specialists from Porsche set up their suspension in such a way that the driver feels the development of the roll itself, and the electronics begin to remove undesirable consequences only when a certain degree of body inclination passes.
ADAPTIVE STABILIZER
Indeed, you read the subtitle correctly, because not only elastic elements or shock absorbers can adapt, but also secondary elements, such as, for example, an anti-roll bar, used in the suspension to reduce roll. Do not forget that when the vehicle is driving straight on rough terrain, the stabilizer has a rather negative effect, transmitting vibrations from one wheel to another and reducing suspension travel ... This was avoided by the adaptive anti-roll bar, which can perform a standard purpose, completely turn off and even "play" with its rigidity depending on the magnitude of the forces acting on the car body.
The active anti-roll bar consists of two parts connected by a hydraulic actuator. When a special electric hydraulic pump pumps a working fluid into its cavity, the parts of the stabilizer rotate relative to each other, as if raising the side of the machine that is under the action of centrifugal force
An active anti-roll bar is installed on one or both axles at once. Outwardly, it practically does not differ from the usual one, but it does not consist of a solid bar or pipe, but of two parts, joined by a special hydraulic “twisting” mechanism. For example, when driving in a straight line, it dissolves the stabilizer so that the latter does not interfere with the work of the suspensions. But in corners or with aggressive driving - a completely different matter. In this case, the stiffness of the stabilizer instantly increases in proportion to the increase in lateral acceleration and the forces acting on the car: the elastic element either works in normal mode or also constantly adapts to the conditions. In the latter case, the electronics itself determines in which direction the body roll develops, and automatically “twists” the parts of the stabilizers on the side of the body that is under load. That is, under the influence of this system, the car leans slightly from the turn, as on the aforementioned Active Body Control suspension, providing the so-called “anti-roll” effect. In addition, active anti-roll bars installed on both axles can affect the car's tendency to skid or skid.
In general, the use of adaptive stabilizers significantly improves the handling and stability of the car, so even on the largest and heaviest models like the Range Rover Sport or Porsche Cayenne, it became possible to “tumble” like on sports cars with a low center of gravity.
SUSPENSION BASED ON ADAPTIVE REAR ARMS
But the engineers from Hyundai did not go further in improving adaptive suspensions, but rather chose a different path, making adaptive ... rear suspension arms! Such a system is called Active Geometry Control Suspension, that is, active control of the geometry of the suspension. In this design, a pair of additional electrically actuated control arms are provided for each rear wheel, which vary toe-in depending on driving conditions.
Due to this, the tendency of the car to skid is reduced. In addition, due to the fact that the inside wheel turns in the turn, this tricky trick at the same time actively fights understeer, performing the function of the so-called all-wheel steering chassis. In fact, the latter can be safely written down to the adaptive suspensions of the car. After all, this system adapts in the same way to various driving conditions, helping to improve the handling and stability of the car.
FULL MANAGEMENT CHASSIS
For the first time, a fully controlled chassis was installed almost 30 years ago on the Honda Prelude, but that system could not be called adaptive, since it was completely mechanical and directly dependent on the rotation of the front wheels. Nowadays, everything is controlled by electronics, so each rear wheel has special electric motors (actuators), which are driven by a separate control unit.
PROSPECTS FOR THE DEVELOPMENT OF ADAPTIVE SUSPENSIONS
To date, engineers are trying to combine all invented adaptive suspension systems, reducing their weight and size. Indeed, in any case, the main task that drives automotive suspension engineers is this: the suspension of each wheel at any given time must have its own unique settings. And, as we can clearly see, many companies in this business have succeeded quite strongly.
Alexey Dergachev
