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 lies in energy recovery: when “compressed”, the solenoid acts as a generator, storing energy in battery. Despite the success of the experiment, ECASS will remain a conceptual development - for series production technology is too complex.
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 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 AVS (Adaptive Variable Suspension) adjustable 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 stabilization system exchange rate stability. Their common sensors inform the computer about the development of slipping or the tendency of the body to roll over.
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.
On the rear axle LC Prado is equipped with pneumatic cylinders, allowing the driver to choose the height of the car. On rough roads, the car can be raised 4 cm above 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 stabilizer settings. roll stability, using the KDDS suspension kinetic stabilization 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 close the hydraulic circuit, rigidly connecting 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 knows what an adaptive suspension is and how it works, then you can safely close this page, who does not know - you are welcome. In this publication, we will try to understand the design of this system, its secrets and features that distinguish it from other similar designs.
First, let's deal with the essence and terminology. Main Feature adaptive suspension (by the way, it is sometimes called active) is that it can change the stiffness of shock absorbers, the so-called damping, depending on the condition of the roadway, driving style and other similar parameters.
It is clear that all major automakers would like to have such a system in their arsenal, because it is a real find for modern car. So it is, and every self-respecting company, knowing what an adaptive suspension is, considered it necessary to create its own version of this technology.
For instance:
- At Toyota, it is called Adaptive Variable Suspension, which is abbreviated as AVS (we already mentioned it);
- Mercedes-Benz has an Adaptive Damping System or ADS;
- Bavarian engineers from BMW have named their version of the adaptive suspension Adaptive Drive;
- Volkswagen Adaptive Chassis Control - DCC;
- Opel called Continuous Damping Control - CDS, and so on...
It is not uncommon to combine an adaptive circuit with an air suspension to achieve even greater levels of comfort, which, for example, a business class car needs. This is what Mercedes did with ADS technology, in addition, a similar system is used in Audi.
Adaptive suspension for top cars
Although the adaptive circuit has almost as many names as automakers, there are currently only two methods for adjusting damper stiffness:
- electromagnetic valves;
- magnetic rheological fluid.
The systems we listed above, namely AVS, ADS and Adaptive Drive, use solenoid valve technology.
How it works?
As you know, the shock absorber is filled with a special fluid, and depending on how freely it moves inside it, its stiffness will also change.
In this case, the shock absorber is adjusted by changing the flow section of the valves - the narrower they are, the worse the fluid circulates and the stiffer the suspension becomes. Accordingly, if you increase the cross section, the shock absorbers become softer.
The valves are controlled by electrical signals from the control unit, which sets them based on their calculations required level"squeezing".
Audi Q7 adaptive suspension system (pneumatics):
Shock absorbers with magnetic rheological fluid are less common. Such systems are used on some models of Cadillac, Chevrolet and Audi.
A liquid with such a complex name has one interesting property due to the metal particles that it contains - when a magnetic field is applied, these same particles line up in a certain order.
This allows you to adjust the flow sections in the shock absorbers without valves, the only thing you need is to find the source of the magnetic field, for which coils are used, through which an electric current flows.
As in the case of valves, fills them with work the electronic unit management.
Everything's under control!
As already mentioned, control over the operation of the adaptive suspension is assigned to the control unit. He is subordinate to a scattering of sensors that track the acceleration of the car in the vertical plane, as well as the magnitude ground clearance depending on suspension travel.
The system can perform some actions both automatically and controlled by the driver.
In the first case, it is allowed to change the level of suspension stiffness depending on the condition of the roadway, as well as maintain body stability in corners, during acceleration and braking.
The driver, as a rule, can manually set the degree of stiffness of the shock absorbers, and usually he is given a choice of three modes: comfortable (the softest), sporty (the most clamped) and normal (something in between the first two).
In conclusion, a few words about the pros and cons ... Although, what disadvantages can the adaptive suspension have, except for the high cost, otherwise there are only advantages, which is the reason for its use in the most expensive and luxurious cars.
That's all for the theoretical part, I tell you, until we meet again on the pages of our blog, friends! And you watch a few short videos (not in Russian) on this system.
Watch right here on the site without going to YuoTube!
AVS system from Toyota:
BMW Adaptive Drive System:
System from General Motors with magnetic rheological fluid:
Before you start talking about such a mechanism as an adaptive suspension, you need to understand what a suspension is. It was created in order to be a buffer between the car body and the road.
If the car did not have a suspension, then all the bumps, jumps and other irregularities would be transmitted directly to the body, which would have a very bad effect on the general condition of the vehicle.
Among the suspension elements there is a spring. When the wheels meet a bump, it takes on almost all of the energy from the collision and compresses. But once compressed, the spring will push the energy back, causing the car to wobble. And immediately after that, shock absorbers are included in the work, which are designed to, so to speak, absorb all the energy due to resistance. It is also worth mentioning that shock absorbers convert this energy into heat.
Features of the adaptive suspension
Manufacturers of different brands of cars produce a considerable number of suspensions, which are divided into various options for one function or another. Adaptive suspension is known to most motorists as active suspension. And what is the principle of operation of such a suspension? It can adapt to the conditions on the road.
It is also noteworthy that, if necessary, for the driver, the stiffness of this suspension can be changed using the control unit, which is located in the cabin.
It is worth saying that the avs abbreviation is used only by brands such as Lexus and Toyota. But this does not mean at all that other brands do not produce this movement. They simply call these suspensions in their own way, and this is important to consider, because motorists often get confused in such a situation.
By itself, this mechanism is very complex in terms of design. The best specialists are selected for its creation. And if something goes wrong with such a suspension, then it is better to go to the service and contact the specialists.
Suspension Options
And now we need to consider the most interesting options for such a suspension. And the first in line will be the shock absorber damping system. Now in stores they sell the suspension in two versions:
- magnetic rheological fluid;
- solenoid valve with regulation.
The liquid-containing option is based on the action of an electric current. You need to buy a special liquid, namely the one in which there are small particles of metal. And when an electromagnetic field is created, these metallic elements will line up in a strict order. And in the second case, when the impact on the valve begins, the passage holes will either decrease or increase, thus changing the stiffness of the suspension.
The second option is an adaptive suspension from the BMW brand. It's called Dynamic Drive. If this mechanism is installed on a BMW, then the comfort indicators will be very good, but it is not certain that it will be just as good on other car brands. Sensors that are located both in front and behind the body can react in a split second and adjust the desired rack. And this, in turn, will completely remove pecks when braking or strong inclinations during a turn. Tests have shown that this system responds very well during any emergency stop. In the process of driving, the driver can choose one of three options for movement: normal, comfortable and sporty.
Another noteworthy option is the dynamic control system. Such a system is most often seen on Opel cars. It is noteworthy that it is possible to adjust each rack individually. In new generations of cars, the adaptive suspension from this manufacturer provides 4 options for movement: soft, sporty, dynamic and comfortable. It is also worth saying that when changing modes, the system changes not only the shock absorber characteristics, but also the dynamic stabilization along with the steering.
Active suspension was created for Porsche cars. It, in comparison with the previous ones, is very "smart", because it completely connects all the mechanisms with the main computer. Active system, before making a performance decision, takes into account readings from all sensors, speed, steering angle and even tire pressure. After all the information is collected, the system gives a command to the valves on the racks.
Adaptive Suspension (other name semi-active suspension) - variety 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.
Adjusting the degree of damping of shock absorbers provides electronic system control, which includes input devices, 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 ensures maximum comfort and safety for each of the selected modes.
Since the day the first car appeared, engineers have not stopped for a second in an attempt to create the perfect car. At the same time, one of the main tasks that confronted great minds was the development of a safe and versatile suspension that can adapt to road conditions. And the efforts were rewarded. In 1954, it was possible to produce the first car equipped with a hydropneumatic (adaptive) suspension.
Purpose
What is hydropneumatic suspension for? Engineers have created an adaptive mechanism that can adapt to the surface and driving style. The main components of the device are hydropneumatic units, which are characterized by increased elasticity. The elements are the working fluid and gas under pressure in the containers intended for them.
The adaptive suspension makes the car move smoothly and, if necessary, changes the position of the body in relation to pavement. Hydropneumatic suspension is often "mixed" with other types of suspension. A striking example is the car of the French company Citroen C5. Two suspensions coexist in it - an adaptive and classic MacPherson strut (front) and a multi-link rear suspension type.
History
As already mentioned, the first car with an adaptive suspension was created in 1954, and a year later the novelty appeared at the Paris Motor Show. The design of the knot made a splash among connoisseurs automotive world. For those times, a car with hydropneumatic suspension seemed like a miracle. Regardless of the number of passengers or the filling of the trunk, the car retained its original ground clearance and showed smooth movement. It became possible to hang the wheels without using a jack.
The function that makes it possible to adjust the clearance of the car also deserved attention. For France, with its country roads, this option was very useful. The adaptive suspension has increased the level of safety even when driving over hard bumps.
The appearance of a new device was the beginning of the journey. Citroen engineers did not stop, and in 1989 they created the Hydractive 1 adaptive suspension, which is still used today. The advantage of the new design is the presence of an electronic "stuffing" that allows you to control the traffic situation and adapt to it.
Four years have passed and the brand's cars were equipped with the updated Hydractive 2 suspension. Seven years later (in 2000), the world saw the Hydractive 3 adaptive suspension. New design had unique characteristics and was shared with braking system(in the second "part" the brakes and suspension interacted with each other).
Hydropneumatic suspension is installed not only on Citroen cars. Brands such as Rolls-Royce, Bentley, Mercedes and others have also intercepted the new technology. In the last 5-10 years, this list has been replenished with a number of other models.
Device
The adaptive suspension consists of a group of nodes, each of which carries its own functional load:
1. Hydroelectronic block (the second name of the node is hydrotronic). The task of the device is to supply the required volume of the working composition and guarantee the necessary pressure. This node contains the following elements:
- electric motor;
- ECU ("brains" of the adaptive suspension);
- axial piston pump;
- solenoid valves that regulate the clearance of the car;
- protective valve;
- stop valve. The task is to protect the body from a decrease in ground clearance in a non-working position.
ECU and EM valves are components of the hydropneumatic suspension control system.
2. The container for the working mixture is located above the hydro-electronic unit. In cars with adaptive suspension Hydraktiv 3, LDS fluid is tried on, which has a bright orange color. Previously used green liquid LHM.
3. Front suspension strut - a device in which a hydraulic cylinder and a hydropneumatic elastic unit are combined. The structural elements are connected through a damping valve, which effectively dampens vibrations of the body part.
4. The elastic assembly, operating on the hydropneumatic principle, is a metal spherical structure. Inside is an elastic membrane, above which is nitrogen (compressed gas). Under the partition contains special compound transmitting pressure to the system. In this case, gas, as a filler, plays the role of an elastic element.
In the adaptive suspensions of the Hydractive 3+ series, one elastic unit is mounted on the wheel and an additional spherical structure on each of the axles. The use of the mentioned elements is an opportunity to expand the levels of suspension stiffness regulation. At the same time, the life of special spheres is 200 thousand kilometers or more.
Hydraulic cylinders - a group of units that guarantee the filling of elastic elements with liquid, as well as a change in the height of the body in relation to the road. The main device of the hydraulic cylinder is the piston. The rod of the latter is combined with "its" suspension arm. The hydraulic cylinders located at the front and rear are of the same design. The only difference is that the rear assembly is located at a slight angle to the road surface.
The stiffness regulator is a unit with which the stiffness of the suspension is adjusted. It consists of:
- EM valve for direct adjustment;
- additional damper valves;
- spool.
The stiffness regulator is mounted on both hangers. There are two possible modes:
- "soft" mode. In this case, the regulator combines hydropneumatic units in such a way as to ensure optimal pressure gas. At the same time, the EM itself remains without voltage;
- hard mode is activated when the node is energized. In this case, the rear cylinders, racks and auxiliary spheres are isolated from each other.
The adaptive suspension control system consists of the following units:
- input devices. This includes two mechanisms - a mode switch and a group of input sensors. The latter convert the measured characteristics into electricity. One of the main sensors of the system monitors the position of the body part (relative to the surface) and the steering wheel angle sensor.
In Citroen brand cars, 2-4 body position sensors are mounted. As for the second input device (the steering angle sensor), it transmits data on the speed of rotation and the direction of the steering wheel.
A special switch makes it possible to adjust the stiffness and height of the body manually;
- ECU - the "brains" of the system that collect signals from input nodes, process them and, taking into account the given algorithm, send commands to the executing bodies. In its work, the ECU interacts with the ABS and the control system of the power unit;
- executive nodes - devices that execute commands from the computer. These include EM valves for stiffness and height adjustment, an electric motor for the hydraulic system pump, and a headlight range control.
The electric motor is controlled by the control unit, changes the rotation speed, pump performance and pressure in the system. The adaptive suspension features four EM valves that adjust the height. The first pair lifts the front suspension and the second pair lifts the rear.
Operating principle
The structural elements interact according to the following algorithm:
- Hydropneumatic cylinders drive liquid to the elastic elements. The valve body controls the pressure and volume of the liquid. When oscillations occur, the liquid passes through the valve, which dampens the oscillation.
- Soft mode involves combining elements with each other and creating the maximum volume of gas. At this stage, rolls are compensated and the necessary pressure is maintained.
- When hard mode is required, the system is energized. After that, additional spheres and front suspension struts are separated from each other. At the moment of rotation, the stiffness changes for each specific node. In the process of rectilinear motion, the rigidity changes.
Alternatives
The hydropneumatic system from the Hydractive series is not the only development. Mercedes has introduced a similar design to the market - Active Body Control. The principle of operation is almost identical. Hydraulic cylinders press the springs, the pressure changes, the desired position and stiffness are set.
The adaptive suspension was also developed by Volkswagen. Its name is aDaptive Chassis Control. The node provides control settings through sensors and adjusts the rigidity of the chassis.
Advantages and disadvantages
Hydropneumatic suspension is not the epitome of ideal. It adds comfort and convenience, but it also has disadvantages.
Advantages:
- the ability to adjust the clearance manually increases the vehicle's cross-country ability, simplifies the process of parking, unloading and loading, as well as cleaning vehicle;
- the presence of some systematic adjustment makes operation more convenient;
- increasing the comfort of the trip, ensured by the smoothness of the ride. If you believe the reviews, then the car seems to be floating on water, and not moving on a hard surface;
- adjustment to driving style and road surface.
Cons of adaptive suspensions:
- the complexity of the design, which promises repair costs and an increase in the cost of a car upon purchase;
- the reliability of the adaptive suspension is less than that of classical designs.
- This type of suspension is distinguished by “tenderness”, therefore, it requires proper operation.
Results
Hydropneumatic (adaptive) suspension - a breakthrough in the automotive industry. With its appearance, it was possible to solve a lot of problems with handling, clearance and adjustment to the driving style. The main problem the price remains, due to which "budget" manufacturers still prefer affordable pendants.