The suspension installed in modern cars is a compromise between comfort, stability and handling. Suspension with increased rigidity, guarantees a minimum level of roll, respectively, guarantees comfort and stability.
Soft suspension is characterized by a smoother ride, while when performing maneuvers, the car sways, which leads to increased instability and poor handling.
Therefore, automakers are striving to develop the latest active suspension designs.
The term "active" means such a suspension, the main parameters of which change during operation. The electronic system introduced into it allows you to change the necessary parameters in automatic mode. The suspension design can be divided into its elements, for each of which the following parameters change:
Some types of construction use the impact on several elements at once. Most often, active suspension uses shock absorbers with a variable degree of damping. This suspension is called adaptive suspension. Often this type is referred to as a semi-active suspension, due to the fact that it does not contain additional drives.
To change the damping capacity of shock absorbers, two methods are used: the first is the use of electromagnetic valves, as well as the presence of a special magnetic rheological type fluid. The shock absorber itself is filled with it. The degree of damping of each shock absorber is controlled individually and is carried out by an electronic control unit.
Known suspension designs of the adaptive type described above are:
- Adaptive Chassis Control, DCC (Volkswagen);
- Adaptive Damping System, ADS (Mercedes-Benz);
- Adaptive Variable Suspension, AVS (Toyota);
- Continuous Damping Control, CDS (Opel);
- Electronic Damper Control, EDC (BMW).
The active suspension option, in which special elastic elements are implemented, is considered the most versatile. It allows you to constantly maintain the required height of the body and the rigidity of the suspension system. But in terms of design features, it is more rigid. Its cost is much higher, as well as repairs. In addition to traditional springs, hydropneumatic and pneumatic elastic elements are installed in it.
Suspension Active Body Control, ABC from Mercedes-Benz regulates the level of rigidity using a hydraulic actuator. For its operation, oil is injected into the shock absorber strut under high pressure, and hydraulic fluid acts on the coaxially located spring.
The shock absorber hydraulic cylinder control unit receives data from 13 different sensors, including sensors for longitudinal acceleration, body position, and pressure. The presence of the ABC system virtually eliminates the occurrence of body roll when cornering, braking and accelerating. With an increase in the speed of the car over 60 km / h, the system automatically lowers the car by 11 mm.
The air suspension is based on a pneumatically elastic element. Thanks to him, it becomes possible to change the height of the body relative to the roadway. Pressure is injected into the elements by means of a special electric motor with a compressor. The stiffness of the suspension is changed with the help of damped shock absorbers. It is on this principle that the Airmatic Dual Control suspension from Mercedes-Benz was created, it uses the Adaptive Damping System.
Elements of hydropneumatic suspension allow you to adjust the height of the body and the stiffness of the suspension. The suspension is adjusted with a high pressure hydraulic actuator. The hydraulic system is powered by solenoid valves. One of the modern examples of such a suspension is the third generation Hydractive system installed on Citroen cars.
A separate category of active type suspensions includes structures that include anti-roll bars. In this case, they are responsible for the stiffness of the suspension. Moving in a straight line, the stabilizer does not turn on, the suspension moves increase. Thus, handling on rough roads is improved. When cornering or rapidly changing direction, the stiffness of the stabilizer increases, thereby preventing the occurrence of body roll.
The most common types of suspension are:
- Dynamic Drive from BMW;
- Kinetic Dynamic Suspension System, KDSS from Toyota.
An interesting version of the active suspension is installed on Hyundai cars. This is an active geometry control suspension system (Active Geometry Control Suspension, AGCS). It implements the ability to change the length of the levers. They affect the performance of the convergence of the rear wheels. When driving straight and performing maneuvers at low speed, the system selects the minimum convergence. When performing maneuvers at high speed, it leads to an increase in convergence, which improves handling. The AGCS system interacts with the stability control system.
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 lifting 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 influence the vehicle'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
Adaptive Suspension (other name semi-active suspension) - a type of active suspension, in which the degree of damping of the shock absorbers varies depending on the condition of the road surface, driving parameters and driver requests. The degree of damping is understood as the rate of damping of oscillations, which depends on the resistance of the shock absorbers and the magnitude of the sprung masses. In modern designs of adaptive suspension, two methods are used to control the degree of damping of shock absorbers:
- using solenoid valves;
- using magnetic rheological fluid.
When regulating with an electromagnetic control valve, its flow area changes depending on the magnitude of the acting current. The greater the current, the smaller the valve flow area and, accordingly, the higher the degree of damping of the shock absorber (rigid suspension).
On the other hand, the lower the current, the larger the valve flow area, the lower the degree of damping (soft suspension). A control valve is installed on each shock absorber and can be located inside or outside the shock absorber.
Shock absorbers with electromagnetic control valves are used in the design of the following adaptive suspensions:
Magnetic rheological fluid includes metal particles that, when exposed to a magnetic field, line up along its lines. The shock absorber filled with magnetic rheological fluid does not have traditional valves. Instead, the piston has channels through which fluid passes freely. Electromagnetic coils are also built into the piston. When voltage is applied to the coils, the particles of the magnetic rheological fluid line up along the lines of the magnetic field and create resistance to the movement of the fluid through the channels, thereby increasing the degree of damping (suspension stiffness).
Magnetic rheological fluid is used in the design of adaptive suspension much less often:
- MagneRide from General Motors (Cadillac, Chevrolet);
- Magnetic Ride from Audi.
The damping degree of shock absorbers is controlled by an electronic control system, which includes input devices, a control unit and actuators.
The following input devices are used in the operation of the adaptive suspension control system: ground clearance and body acceleration sensors, operating mode switch.
Using the mode switch, the degree of damping of the adaptive suspension is adjusted. The ride height sensor records the amount of suspension travel in compression and rebound. The body acceleration sensor detects the acceleration of the vehicle body in the vertical plane. The number and range of sensors varies depending on the design of the adaptive suspension. For example, Volkswagen's DCC suspension has two ride height sensors and two body acceleration sensors in front of the vehicle and one at the rear.
The signals from the sensors enter the electronic control unit, where, in accordance with the programmed program, they are processed and control signals are generated for the actuators - control solenoid valves or electromagnetic coils. In operation, the adaptive suspension control unit interacts with various vehicle systems: power steering, engine management system, automatic transmission and others.
The design of the adaptive suspension usually provides for three modes of operation: normal, sporty and comfortable.
Modes are selected by the driver depending on the need. In each mode, the degree of damping of shock absorbers is automatically controlled within the set parametric characteristic.
The readings of the body acceleration sensors characterize the quality of the road surface. The more bumps on the road, the more actively the car body sways. In accordance with this, the control system adjusts the degree of damping of the shock absorbers.
Ride height sensors monitor the current situation when the car is moving: braking, accelerating, turning. When braking, the front of the car drops below the rear, while accelerating - vice versa. To ensure the horizontal position of the body, the adjustable degree of damping of the front and rear shock absorbers will differ. When turning the car, due to the inertial force, one of the sides is always higher than the other. In this case, the adaptive suspension control system regulates the right and left shock absorbers separately, thereby achieving cornering stability.
Thus, based on the sensor signals, the control unit generates control signals for each shock absorber separately, which allows for maximum comfort and safety for each of the selected modes.
Subject: adaptive suspension
Example: Toyota Land Cruiser Prado
For a modern SUV, active suspension is not a prestigious option, but an urgent need. If terminological accuracy is observed, then most modern pendants with the word Active in the name should be classified as semi-active. The operation of the active system is not based on the energy of the interaction of the wheels with the road. For example, the hydraulic active suspension proposed by Colin Chapman, the founder of Lotus, adjusted the height of each wheel using hydraulic cylinders and individual high-speed pumps. Tracking the slightest changes in the position of the body with the help of sensors, the car raised or put out its “paws” in advance. The suspension was tested on a 1985 Lotus Excel car, but did not go into production due to extreme complexity and energy gluttony.
A more elegant solution was tested on the HMMWV. The ECASS electromagnetic suspension consists of four solenoids, each of which pushes the wheel down or allows it to rise up. The beauty of ECASS is energy recovery: when “compressed”, the solenoid works like a generator, storing energy in the battery. Despite the success of the experiment, ECASS will remain a conceptual development - the technology is too complicated for mass production.
Semi-active suspension is built according to the traditional scheme. The elastic elements are springs, springs, torsion bars or pneumatic cylinders. Electronics controls the characteristics of the shock absorbers, making them softer or stiffer in a split second. The computer alternately opens or closes the valves in the hydraulic system. The smaller the holes through which fluid passes inside the shock absorber, the more it dampens suspension vibrations.
hydraulic orchestra
The Toyota LC Prado SUV is equipped with an adjustable AVS (Adaptive Variable Suspension) adaptive suspension that allows the driver to select the operating mode: soft Comfort, medium Normal or hard Sport. In each of the three ranges, the computer constantly changes the characteristics of each shock absorber. The system responds to orders from the electronics in 2.5 ms. This means that at a speed of 60 km / h, the characteristics of the suspension change completely every 25 cm of the path. The suspension works in close cooperation with the stability control system. Their common sensors inform the computer about the development of slipping or the tendency of the body to roll over.
For large SUVs, adaptive suspension is vital. On serious off-road, the jeep needs large suspension travel, which means soft springs. On the contrary, a tall car needs tight settings in order not to fold on the highway.
Pneumatic cylinders are installed on the rear axle of the LC Prado, allowing the driver to choose the height of the car. On rough roads, the vehicle can be raised 4 cm above the rear axle by increasing the ground clearance (Hi mode). The machine can be lowered by 3 cm (Lo mode) to make it easier to get on or off the ground. Hi mode is designed for driving at low speeds, upon reaching 30 km / h, the car will automatically switch to Normal.
However, clearance adjustment is not the main task of pneumatic cylinders. Firstly, the gas inside them has a more pronounced progressive characteristic than a steel spring, and at small strokes the suspension works much softer.
Secondly, the pneumatic cylinders automatically compensate for vehicle loading, always maintaining the same ground clearance.
Toyota engineers also abandoned the traditional compromise in the field of anti-roll bar settings, using the KDDS kinetic stabilization suspension system. Each LC Prado stabilizer is connected to the frame via a hydraulic cylinder. The cylinders are connected into a single hydraulic circuit. As long as the liquid circulates freely inside the circuit, the stabilizers practically do not work. In this mode, the suspension demonstrates the maximum travel required for off-road use. In high-speed turns, the valves shut off the hydraulic circuit, rigidly linking the stabilizers to the body and preventing roll. On a straight line, a hydraulic accumulator included in the circuit helps the suspension hide small bumps in the road.
Who is poor is stupid.
Japanese proverb
Turn on the locks, transfer the "razdatka" to a lower row, slightly touch the gas pedal. The newest Land Cruiser Prado with a 4-liter gasoline engine and pneumatic rear suspension slowly and with dignity crawls into a deep track, rolled out in autumn, generously powdered with snow ...
What's the price
You know, it happens that everything coincides. A long-awaited test drive, a great car and perfect weather. Everything matched. Well, about the weather, you yourself see everything from the photographs, but about the car, let me enlighten you a little.
On a ten-point scale, I would put the car 7-8 points. But you need to remember that this is a subjective assessment - based on my personal preferences. In general, the car is good - although I personally lack dynamics a little. But it is very comfortable and it is a real "rogue"! For its purpose, the car is very good, especially since the price is reasonable. But I would not consider Prado as my next car, at least not yet - I have not yet found an approach to Japanese cars, although they have a number of undeniable advantages - quality, price, reliability.
