New comment. What is a hub and how does it work? What does the hub do?
Many people are interested in the question of what hubs are and what they are used with. Now let's look at this issue. In general, a hub is a node in a network. This term has different meanings in different industries.
Using the hub in various industries
For example, in transport, hubs are transfer or transshipment nodes, hub airports. In the energy industry, this is a kind of special center in which one route is divided into several. On SUVs, this word refers to the freewheel installed on the front axle. Various Internet networks also use hubs. What is this on the Fidonet network? Here, a hub is a node that serves to transmit mail. In the Direct Connect file sharing network, this is the name of the network server.
But the concept is most widely used in computer technology and the Internet. A specific set of network equipment is based on the tasks assigned to the designed network and the costs of implementing a specific solution. An important element of such tasks is the choice of devices, among which routers, switches and hubs play the main role. What is this, we will try to figure it out.
Hubs in computer networks
Construction technologies are constantly evolving. The devices that underlie them and are used to organize communication between computers are called differently: hub, switch and router. We will look at what this is in more detail.
Each of the listed devices plays its role in organizing communication between network computers. Externally, they may look the same: small metal boxes with a number of ports or connectors where an Ethernet cable is connected. As for such concepts as switch, hub, hub, router, they are often used as synonyms, but this is a mistake. These are all different devices.
Hub
One of the first network devices are hubs. What kind of devices are these? The term is of English origin. The word hub means center of activity. Hub, or designed to connect computers into a simple peer-to-peer network. The device has a number of ports to which you can connect all personal computers on the network. Most often, twisted pair cables, which are crimped in a special way, are used for this purpose.
How the hub works
Let's consider the principle of operation of a network hub. When any computer on a network equipped with a hub attempts to access another PC, the first device sends a special block of information called a packet to the address of the network hub.
Let's try to figure it out using an example of a circuit with three computers. Let's say computers PC1, PC2 and PC3 are connected to the device. The role of the hub is to replicate the data packet from PC1 by transmitting it to other devices connected to the local network, that is, PC2 and PC3. At the moment the signal arrives at PC3, for which it was intended, the latter sends a response packet to the hub. The network hub again sends this packet to all network computers until the response from PC3 returns to the sending computer PC1.
This is an approximate diagram of the interface of computers connected to a local network with a hub. The main disadvantage of such networks is that too much information is sent. A network hub continuously sends data packets to all devices on a computer network, even if the destination is one specific PC. At the same time, computers receive blocks of information that they often do not need at all. The technology turns out to be very expensive. This is why network hubs are now almost obsolete. Instead, more intelligent devices were developed - network switches, which are commonly called switches.
Switch
The term is of English origin and means a switch, or network switch. Like a hub, a switch is required to connect computers on the same local network. The circuit for connecting it to computers is no different from the circuit with a network hub. Instead of a hub, PCs are simply connected to a switch.
While outwardly very similar to a network hub, the switch has fundamental differences from it, consisting in the method by which information is transferred between computers on the local network.
After receiving a packet of information from a computer, a network switch, unlike a hub, does not forward it to all PCs participating in the network, but organizes the sending of the packet to the address of the computer for which the package is intended. For example, when PK1 sends a packet of information to computer PK3, the switch organizes the transfer to it, bypassing PK2. The network switch also returns the response packet from PK3 only to the sender of the information packet - PK1.
The switch has the ability to remember the addresses of all computers that are connected to its ports, and thanks to this it can work as a traffic controller, transmitting information only to the recipient’s PC and ignoring others.
The operation of the network switch is based on a table of special MAC addresses of users’ network equipment in the external and internal networks. As a result, the information packet arriving at each of the ports is compared with the routing table and sent to the port address where the corresponding equipment is located.
Router
The name "router" gave rise to the English router. This is a router that can organize the transfer of information between two or more different local networks. In addition, the router has ports that are required to connect some other devices to it using a cable.
How the router works
Just like a network switch stores a table of registered MAC addresses, a router stores a table of IP addresses as its routing table. The router's main job is to store this data and ensure that other routers know about changes in the network configuration. It is solved by using it to coordinate with other routers. When packets arrive at a router, the router uses different protocols and criteria to determine the best path to forward the packet of information to the destination.
The router can be programmed to enable multi-level rules that are determined by the content of the information packets that arrive at it. The router is programmed to enable network equipment security, translate network NAT addresses, and provide DHCP network services.
Packed with intelligence, routers are among the most sophisticated network devices. In addition to the ability to redirect information packet traffic, routers can be used to control traffic on the network. In addition, they have the ability to respond to changes in the network, dynamically detecting them, protecting it with packet filtering, calculating packets for blocking or passing.
USB hub
In addition to Ethernet network hubs, the term "hub" is used to refer to USB technologies. The development of new equipment places increased demands on the level of development of user interfaces of computer equipment. The wide variety of computer peripherals that connect via USB require a special device that allows you to connect multiple devices simultaneously via USB. It's called a USB hub. What is the principle of its operation?
It is a small device with several ports. Connect it through the computer socket. It allows you to connect multiple USB devices to one USB port on your PC.
USB hub device
The design and arrangement of the hubs are not very complicated. They are designed to switch signals and provide supply voltage. In addition, they monitor the status of peripherals connected to them, making the host aware of changes.
The hub includes two modules - a controller and a repeater. A repeater is a managed switch that connects the input and output ports. It has the ability to reset and pause signal transmission. The controller includes registers that allow you to interact with the host. Registers are controlled using special commands that allow you to configure the hub, monitor the status and change the parameters of downstream ports. It is possible to use a daisy chain hub when devices are connected sequentially.
Types of USB hubs
One such type is an internal card on the system bus. It is used to connect USB devices to the motherboard. This is done using a USB PCI card installed in the free space of the PCI bus located directly on the motherboard. This type of USB hub is best used by those who are familiar with the structure of a computer. For those who do not have experience, it is better to choose another type.
Another type is an external USB hub without power. Such a device is simple and relatively inexpensive. This type of USB hub connects to the USB port of your computer. This device is great for laptop owners. For home computer users, it is also possible to use such a USB hub, but you must take into account that a number of devices connected to the computer require power supplied through the USB port. This type of hubs is not capable of powering several similar devices at once. In this situation, it is best to use powered hubs. What are these devices and how do they differ from devices without power?
A powered USB hub operates in exactly the same way as an unpowered hub. The difference is that it can be plugged into an outlet. This allows you to provide adequate power to all devices that are connected via USB. The largest USB hubs are seven-port.
Another type of such device is a USB computer board. This device is suitable for laptop users. It connects to a special USB port located on the laptop body and makes it possible to use two ports instead of one.
We tested five types of hubs for the UAZ carText: Evgeny Konstantinov
Photo: Alexander Davidyuk, Andrey Khorkov, Alexander Ivanov
Having placed an advertisement for the hubs of the Brazilian company AVM in our magazine, we suddenly wondered: what kind of South American beast is this, and is it really that good? What if we, without suspecting it, are deceiving our readers? But this is all poetry... However, the “physical” side of the “obscene” question is also not idle. Especially for those who drive UAZs. Indeed, despite the fact that several types of hub couplings are produced today for this brand, they are not recognized as ideal by the “UAZ community”. Moreover, among the owners of Ulyanovsk all-terrain vehicles, hub locks are considered one of the most decent topics for small talk...
As a result of market research, we focused on five types of hubs for the UAZ vehicle (we only considered options that can be found on the open market). One is, one might say, historical. To turn it on and off you need two keys and a few minutes of time. The rest of the hubs are much simpler to control: just turn the outer handle less than half a turn from the 4x2 to 4x4 position, and everything should happen right away. This is in theory. But in life, everything depends on how clearly the hidden mechanism with a spring, two splined bushings and two groups of guides works. By the way, despite the fact that all four models are designed according to the same principle, they differ greatly in details and manufacturing features.
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The oldest hub produced by UAZ, dating back to the GAZ-69. Such “switches” are still standardly installed on trucks. The engagement includes small sharp splines on the coupling body and on the inner sleeve. The latter is put on the axle shaft along the internal splines and screwed with a special bolt. Thanks to him, everything works. This coupling option is the most accessible, both in terms of availability in stores and in price (500 rubles per pair). |
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Nowadays, Simbirs and Hunters are equipped as standard with ELMO couplings made in Sterlitamak. They are the most common among UAZ “quick switches” and are much more often found on the open market than others. ELMO is produced in two versions: with and without a decorative metal cap. There are no differences between them, with the exception of this very cap and the price (920 and 960 rubles per pair, respectively). |
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The STED hubs, which are produced in Ufa, are very similar in appearance to the previous version, but if you look closely, it’s easy to notice the differences in design and careful manufacturing. They are rarely found on sale, but they are a little cheaper - they ask for 850 rubles for a pair. |
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You can’t buy STELM couplings in any store either. They differ from all others in their cone-shaped body and light gray color. In addition, it was noticeably lighter than other subjects. They are produced, like the previous version, in Ufa, but they have a noticeable difference in price. For a couple they asked us for a simply apocalyptic sum - 666 rubles. |
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The only foreign-made hubs in our collection are easy to recognize at first glance. It's not even about the letters AVM. The “foreign quality” is visible from the polished lid and other pleasant little details. You can feel the designer’s meaningful work. The Brazilian hubs are sold in a sealed cardboard box that contains two hubs, instructions, a set of screws for the cover and two cardboard hub spacers. The price of the set is $180, which translates to just over 5 thousand rubles. |
“And all around is aluminum, aluminum...”
Having collected such a rich collection of hubs, it was impossible not to become interested in their internal structure... First of all, we unscrewed the covers from the cases. And what? The mechanisms of the three Russian products turned out to be practically interchangeable (both in whole and in parts). But for the Ufa couple, everything turned out to be absolutely the same. But the “Brazilian” and the “Soviet veteran” demonstrated bright individualism and originality, resulting in one hundred percent uniqueness of the components.
As for the materials used, what surprised us most was STELM, which hides a “strategic reserve of silumin” under neat gray paint. Both the body (directly involved in the transmission of torque!) and the cover are cast from an alloy whose “strength” is legendary. Here is the answer to why the “gray” (meaning color) hub weighs only 800 grams. And this despite the fact that for the rest this parameter fluctuates around the 1100 gram mark, and the STED reaches all of 1200. However, we even found silumin in it - the parts of the switching mechanism are made from it. In ELMO, a cover was added to the number of light alloy parts. True, it does not carry any load. The AVM also had a cover made of aluminum alloy, and the switching mechanism was made of plastic. However, the splined bushings in all five cases turned out to be steel (as well as the springs). The only hub lock made entirely of iron and its derivatives is the old-style UAZ hub.
In terms of the thoroughness of surface treatment and general production culture, the “Brazilians” took first place. However, remembering how much AVMs cost, there was no point in doubting this. True, even here there was a small fly in the ointment. One of the screws for securing the cover turned out to be... without a thread. More precisely, instead of threads, its surface was covered with smooth circular grooves.
Oddly enough, silumin STELMs distinguished themselves by the greatest accuracy of processing from Russian hubs. This surprised us very much. Especially when you consider that exactly the same parts inside the “steel Ufa” turned out to be extremely poorly processed. Burrs, rust, scale... Burrs and poorly polished surfaces were also found in Sterlitamak couplings (the most expensive of the Russian ones), but the quality of processing here is still higher. True, one of the new couplings had a broken thread, due to which the cover could be tightened with five screws out of six.
It is difficult to spoil anything in old-style couplings, as well as to surprise with high technology. But we note that the inner bushing of the specimen we received, it seems, was not processed on a machine, but was chewed by some goblins with their teeth! We also found extraneous marks and dents on the working surfaces of the splines. Against this background, the slightly knocked-down thread on the lid was perceived simply as an innocent prank by the manufacturer.
But don’t think, we didn’t just disassemble and examine the internal structure of the “locks”, we were constantly twisting something with our playful little hands. Well, in the end we got it... First, a splined bushing on one of the STEDs got stuck in a seat on the body, and then a similar problem happened with the ELMO. In general, in order not to disrupt the end of the experiment, they had to be completely disassembled and, marveling at the “quality” of the rubbing surfaces, put back together. However, such a nuisance is not fatal. When working on a car, all rubbing surfaces will break in over time.
To the departing fields!
To identify the pros and cons of hubs in real use, we take the entire collection and go out into a snowy field. The program is simple: we install a pair of test hubs on the front axle, ride on virgin soil and try to turn them on after the rear wheels have skidded. Moreover, to collect statistics, we carry out a series of such inclusions.
And our work was not in vain: many interesting things emerged. So, for example, to install AVM hubs, you need a 1/8-inch hex wrench (to first unscrew and then screw back the shiny caps after tightening the hub bolts). This tool is not included in the kit, and it is not easy to find on sale. But, on the other hand, non-standard cover screws partly serve as “secrets” for beautiful imported couplings. Otherwise, the “Brazilians” did not cause any trouble. During installation, everything (including our own gaskets) fit just perfectly. They showed exemplary clarity in their work. Thanks to the small splines with clearly defined entries, the Brazilian clutches turn on and off instantly, just turn the handle to the appropriate position. Of all the test participants, not a single misfire occurred with them.
What does a hub not turn on look like? Yes, disgusting... You drive into the snow and stop (the rear wheels begin to slip). Get out, turn the handles on the front hubs to the 4x4 position, get back behind the wheel, engage the front axle with the lever and, having engaged the appropriate gear, step on the gas pedal. But instead of the expected movement, a crash is heard from somewhere in the area of the front wheel, and the car remains in place (the rear wheels are slipping). What to do in this case? In essence, nothing supernatural. Depress the clutch and try to start again. Usually everything works out. At least we always left on the second try.
The leader in failures to operate the first time was STED. With him, unnecessary body movements had to be made in more than half of the attempts. The ELMOs did not turn on on the first try a little less often, but also almost every other time. But the cheap STELM, to everyone’s amazement, almost caught up with the expensive “Brazilians”. They did not deign to turn on instantly only two times out of several dozen attempts!
Analyzing the results, we concluded that, first of all, for the clarity of inclusion, the shape of the splines involved in the engagement is important, and with the same shape, the cleanliness of the surface treatment. However, among the subjects there was also a model for whom all this was completely unimportant. Old-style clutches are always engaged, and also visibly. True, this process is quite tedious, but by tightening the bushing 13 turns, you can be sure that the clutch is tightly engaged. True, it is also possible that a tooth hits a tooth and no engagement occurs. It is useless to twist it by force. As the experiment showed, the teeth will press into each other, but will not engage. It is much more effective to slightly release the tightening and use your fingers to turn the sleeve into the desired position. Or spin the front driveshaft. The only position in which it is impossible to turn on the ancient structure is under water or in liquid mud. The fact is that an unscrewed cap allows free access of liquid inside the coupling and further to the bearings and into the bridge.
And a few more observations. The easiest to switch are steel Ufa couplings, whose rotary handle allows you to grasp it with your bare hand in 15-degree frost without experiencing discomfort. Exactly the same switches on silumin ones turned noticeably tighter, and on one of the hubs there was no clear fixation in the 4x4 position. The most “unpleasant” switches are equipped with ELMO: their silumin handles with sharp edges require the greatest force to turn. As for AVMs, they have the clearest handle fixation in extreme positions, while the handle itself is comfortable and requires a little more effort than the STED.
As I already said, with the installation of all types of hubs on the axle, with the exception that the spacers purchased at the store slightly did not match the size of the hub flange, and a special key for AVM was required, we did not have any difficulties. But during removal, STELM threw up a problem: the centering belt on their flange, apparently, turned out to be thicker than necessary, and it got jammed in the hub.
Chilling horrors
Hubs are not only valuable fur... In the sense that, among other things, they must serve as reliable end caps for the bridge, preventing water from entering when passing through fords. Are our experimental subjects up to the task? As a water barrier, we took... a bucket and, adjusting the level in it with the help of a mug, took turns lowering the hub couplings into the font up to the very flange. Then they were switched several times without removing them from the water, and finally they were left alone for 10 minutes. It is worth mentioning that we did not carry out any additional treatment with lubricant.
I’ll say right away that only STED came out completely dry. No matter how we twisted it, in 10 minutes it did not gain a drop. This, fortunately, compensates for one of its design features: like the “veteran”, its internal space freely communicates with the bridge. In other hubs, the water flow will still have to overcome the narrow gap between the body and the rotating inner sleeve. By the way, the “military switch” can also be considered 100% waterproof: when the lid was screwed on by hand along a dry thread, it began to let water in (drop by drop) only by the end of the tenth minute. Obviously, when the threads are lubricated and tightened with a wrench, water does not get inside at all.
The other three types of hubs draw water through a switch knob. STELM began to leak after nine minutes. But the results of AVM and ELMO were unpleasantly surprising. These hubs begin to leak when switched underwater. At first glance, they do this slowly, but after 10 minutes the “Brazilian” was half full, and ours was almost completely full. If you don’t switch the hubs, then the Sterlitamak tank starts leaking after 2 minutes, and the AVM starts leaking after 2 and a half. And one more observation. Unlike Russian products, the Brazilian one has through holes in the case for the lid screws. Therefore, it is very important that all these screws are completely screwed in and tightened well. Otherwise - flood!
After the water procedures, we sent the experimental subjects to the freezer for several hours. And what? You won't believe it, but all the switches were covered in ice! They didn't want to turn around at all. The ice had to be chipped, but even then, of all the switches, only AVM was turned by hand. True, its frozen mechanism did not work instantly - it was necessary to make several turns of the inner sleeve before the characteristic closing click was heard. Domestic hubs froze inside, apparently not so much, and turned on immediately. But in all cases I had to turn the handles with pliers. They just didn't give in. It took two people to turn ELMO around.
Hub model
Outer sleeve
Inner sleeve
Knowledge is power
Well, almost everything is clear. All that remains is to determine the strength of the hubs and the hardness of the working surfaces of the splined bushings using special instruments.
We started with a hardness tester. We, of course, expected that the metal of the spline bushings would be different, but to such an extent... The hardest steel was found in the Brazilian product. STED splined bushings have almost the same hardness. The bushings on ELMO are slightly inferior to them. But the steel of the old-style couplings turned out to be raw. But the worst thing was the metal of STELM. The nails are even harder! So, with a standard Rockwell hardness measurement, the device showed a solid zero on the splines of the inner sleeve! To get at least some result, I had to measure it according to Brinell. Meanwhile, this method is usually used for soft non-ferrous metals. However, in this case, we had iron in front of us, unless, of course, the magnet lied...
The strength test required the development and manufacture of a special device, in general terms resembling a massive lathe with a lever. They fixed an axle shaft with a hub on it in the device, fixed it with a special drum and began to tighten the resulting system, observing how the load on the dynamometer increased...
We started with the gray “Ufa resident” (obviously the weak link). No one doubted that this coupling would break. But how did she do it! Until the very last moment, she did not give anything away. The load grew evenly and confidently, but as soon as the dynamometer readings reached 3500 Nm, there was... an explosion (there was even smoke coming from the hub). Imagine our surprise when, having disassembled the system, we took out the coupling with the body falling apart. The material turned out to be not just silumin, but low-quality silumin (chips exposed an abundance of shells of different sizes).
We “tucked” the Brazilian hub into the machine with approximately the same feeling with which Siberian men stuck a rail under a Japanese chainsaw. But the result was completely unexpected. We knew something wouldn't hold up. But hub or axle shaft? At a load of 4100 Nm, the first light “crunch” was heard. Let's keep spinning. And at around 4250 there is a crackling, whistling and ringing of broken glass. She cut off 8 hardened M8 bolts holding... the hub on the stand drum! Their fragments were fired, causing slight destruction in the room. The axle shaft remained intact, the hub was also not damaged, but there was nothing to carry out “destructive” tests of the remaining samples...
Tsar Bell and others
Are you probably waiting for conclusions and results? This time everything is obvious. Apparently, a special shelf will have to be allocated for the gray hub so that it can stand there like the Tsar Bell. You should laugh in vain, STELM is basically not good for anything else - it will fail you at the most crucial moment.
The old-style coupling, despite the quality of the material and workmanship, is reliable. But at the same time it is very inconvenient to switch. Installing it on a car only makes sense for very hard-working people (or if this UAZ constantly drives with a connected axle).
As for the rest of the couplings, they all require improvement, albeit to varying degrees. AVMs turned out to be the closest to ideal. With them, everything is simple: check all the screws for the presence of threads, purchase an hex wrench and, after disassembling the switch, lubricate its parts with a thin layer of greasy waterproof lubricant.
ELMO also require the same waterproofing. In addition, in order to achieve a clearer connection, this coupling will have to be completely disassembled into individual parts and the working surfaces must be sanded with a velvet file and sandpaper. True, the model will still have one fatal inconvenience - the switch is tight and unpleasant to the touch.
STED needs sanding even more (this process will take longer than sanding along with waterproofing in the previous case). In addition, you will have to put in order the internal seating belt for the spring on the large bushing. Due to its chipped surface, we were unable to properly assemble the coupling, which had been disassembled into screws, and make it work.
A hub is a very broad concept. It is used not only in network terminology. Also, for example, there is the concept This is a device that
Used to connect several different USB devices to one port. But this is not the entire range of possibilities for using concentrators of various natures.
In any developing project in the information market segment, sooner or later the task arises of combining a certain number of disparate data processing devices. A well-built network can easily solve this problem. There are quite a large number of technologies to implement this task. When you start planning the construction of your network, you must immediately determine which devices for aggregating information flows will be used in the process of maintaining the functionality of network connections. (hub) is one such device.
The main distinguishing feature of a hub from a switch is its translation feature. All ports have the same rights. Therefore, having received an information flow through one of them, it ensures its broadcast to all other active ports. Roughly speaking, to understand what a hub is, you need to understand its essence. This is a repeater designed for a large number of ports and has a useful auto-segmentation function. Auto-segmentation is the process of automatically managing faulty ports (the process of transferring to a faulty port gives rise to another process - declaring the port inactive). Subsequently, if the fault is corrected, the port becomes active again.
This is the answer to the question of what a hub is and how it differs from a switch. The properties of a network hub can significantly increase the overall level of reliability and fault tolerance of the network. Moreover, resolving all conflicts that have arisen and ensuring general control over the state of connected channels is entrusted directly to the device itself without involving additional power, both software and hardware.
Hubs can be combined with each other, which allows you to build networks of absolutely any topology and size. They also allow for backbone connections between each other, thereby ensuring the implementation of the “bus” topology. But concentrators have one significant drawback: they strongly depend on the application in which they are used, that is, they are not universal. So, for each topology, their own types of concentrators are produced.
In general, in order to finally understand what a hub is, you need to understand one thing - it allows you to combine individual devices that are part of the network into one global (or rather local) workgroup.
We tried to understand in general terms what a hub is and “what it is eaten with.” Multifunctionality and wide applicability make concentrators widespread in the modern information technology market. With their help, you can solve the most complex construction problems and more.
A USB hub (or USB hub) is a device that can be used to expand a USB port to multiple available connection ports to a host system. A USB hub allows you to expand the possibilities of simultaneous use of various technologies when there is a lack of USB ports. It becomes possible to connect the maximum number of necessary devices, such as a computer mouse, scanner, keyboard, modem, external hard drive, coolers, lamps, etc.
The USB hub can be built-in or external, which determines the nature of the hub’s use. Most USB hubs are built-in and are part of a system device that connects any USB device to a USB PCI card (motherboard). In this case, the USB hub is installed in the PCI slot directly on the motherboard.
The built-in USB hub is used in laptops, which allows for additional USB connections. This can be a built-in computer card, which is an alternative to a USB hub, or an external USB hub. If the laptop's USB port is located in a hard-to-reach part of the system unit, then the USB hub is used with an extension cord.
An external USB hub can be unpowered (represents a regular splitter) and powered (equipped with a power supply from the mains, and can withstand current power up to 500mA). The latter is more practical, since most devices connected to USB ports require power, and a powered hub allows you to redistribute the voltage, which improves the operation of computers.
The principle of operation of a USB hub is quite simple. Depending on the distribution scheme from the exchange center, the hub allows the mechanisms included in it to work, both individually and in concert, depending on the access mode. The USB hub can expand the network to 127 ports.
If the operating principle of the hub chip has a physical “star” layout, then all USB connections will work autonomously from the center, without bridging each other. In the case of a serial connection from the center bus, the power supply may be bridged. There are also hubs designed according to the “octopus” and “squid” design, which allows you to connect different USB nodes that are located close to each other. Such connections, as a rule, do not have problems blocking each other.
Modern USB hubs are presented in many models: from classic functional hubs in the form of a box to stylish and original designer gadgets. All of them are characterized by high data transfer speeds, and also have additional functions that make it possible to improve the process of information transfer and the operation of the device itself.
These are end of frame timers, port controllers, PLL circuit, bit timing restorer, serial interface mechanism, MMU and on-chip RAM, I2C slave interface, GoodLink indicator, SoftConnect, overcurrent detectors, voltage converters. All this makes it easier for the PC user to work, as well as secure the process of information processing, transmission and storage.
Recently, the emphasis of prestige among car owners has been steadily shifting towards SUVs, some models of which are valued higher than the notorious Mercedes and BMW. This is understandable: a solid-looking car, moreover, perfectly adapted for our roads, which a person from abroad is unlikely to distinguish from off-road. But off-road vehicles also have disadvantages, especially those that cannot boast of permanent all-wheel drive. However, even those that are switched off when driving on the highway, the front axle remains loaded - this applies to axle shafts, the driveshaft, the gearbox, and the transfer case. All of them rotate “idle”, since they are rigidly connected to the front wheels. This increases the wear of the above components and leads to a noticeable increase. This problem is what the HUB, which is officially called a freewheel, is designed to solve.
How to choose HUBS for an SUV.Why do you need a HUB for an SUV?
It turned out that for rear-wheel drive cars, which SUVs become when all-wheel drive is turned off, there is a fairly simple and elegant solution to disconnect the wheels from other transmission components. This is the answer to the question, what are HUBs on an SUV? Technically, implementing such a function is not that difficult. Indeed, such attempts have been made for quite a long time. In particular, before World War II, this could be done manually using a regular wrench. Of course, this was inconvenient, so the search for ways to more easily disable the front axle continued by many manufacturers of all-wheel drive cars (most of which by that time were concentrated overseas).
And in 1948, a freewheel appeared, designed by the famous innovator and inventor Albert Warne, which made it possible to give a second life to army jeeps that were decommissioned after the end of hostilities. When using such a device, no tools were required - it was enough to turn the clutch cover in the desired direction to disable or activate the overrunning eccentrics. It is not surprising that this inexpensive, technically simple and fairly reliable device was soon taken as a basis by many automakers. In addition to American companies (Jeep, Ford, Chevrolet), Japanese automakers - Toyota, Nissan, Mazda, Mitsubishi, Suzuki, and later Korean ones, as well as automakers from the Old World, became interested in the invention.
Classification of HUBs
In English, this word has several meanings, one of which is “hub”. And it is this value that has become commonly used in relation to the freewheel, which can be disconnected along with all-wheel drive when traveling on roads that do not require increased torque. However, despite the simplicity of the idea, many ways to implement it were invented. But currently the most common are three types of HUBs:
- with manual on/off;
- automatic;
- using a vacuum switching method.
Let's consider the operating principle of each of the listed HUBs, their main advantages and existing disadvantages.
Structurally, these are the simplest couplings, which is why they are said to be the most reliable. Here the hub is locked by means of a gear connecting the wheel to the hub. The gear is engaged - the front axle is loaded, if it is disengaged - the front wheels rotate exclusively on bearings, without transmitting force to the axle shaft and further along the chain. By turning on the manual HUB, you get a 100% guarantee that, regardless of external conditions, your front axle will not turn off. When driving downhill, you can rest assured that if the engine cannot cope with the task, it will not be turned off, as happens with other types of HUBs.
Despite their reliability, currently manual clutches are practically not installed on production cars, but you can equip your SUV with such a device yourself - this procedure is not much more complicated than removing a wheel. The most famous manufacturers of HUBs with manual shifting are the Brazilian company AVM and the American WARN, although such couplings are made in South Korea, Russia, and Ukraine. It is clear that American HUBs are of the highest quality, but they also cost much more than their analogues, although the operating principle of all such devices is almost the same. Recently, manual freewheels have become increasingly difficult to purchase, since most manufacturers prefer to produce automatic HUBs, which are much more popular. The main reason for this user misalignment is the main disadvantage of manual devices: to turn them on/off, you need to get out of it and manually engage the clutch if you are going to leave the track off-road, or do the opposite operation when entering the track.
HUBs supplied from foreign countries have two inscriptions: “Lock” and “Free”. The first indicates rigid engagement of the wheel with the hub, and only after the clutch is switched to this mode can all-wheel drive be engaged. If you have to drive on a paved road, when all-wheel drive is not needed, turn it off, and to reduce the load on the differentials, move the clutch to the “Free” position. In the latter case, after a long off-road drive, the HUB can become very hot, so you need to switch it with gloves or using a special key (some manufacturers include it in the delivery package).
As we wrote above, the operating principle of manual clutches is to use a spline connection. One of the gears is rigidly mounted on the axle shaft, the other, movable, on the hub. By turning the HUB switch to the “Lock” position, you use a powerful spring to move the movable splined sleeve towards the internal fixed gear, bringing the pair into engagement. By turning the switch to the “Free” position, you do the opposite operation. As you can see, the device is really extremely simple, and therefore very reliable - most likely, during the operation of the car you will be forced to change the hub rather than the clutch. The difference between products from the above manufacturers lies in the materials of manufacture and the features of the implementation of the basic principle. In particular, in Ukrainian HUBs, two springs are installed that act on cylindrical keys, while couplings from other manufacturers use one spring.
The vast majority of SUVs, the design of which includes a freewheel, are equipped with just such devices. The operating principle of automatic HUBS is that when the front-wheel drive is turned on, torque begins to be transmitted to the front driveshaft. This moment is captured by automatic clutches when the CV joints begin to rotate, which is a signal to block the clutch. The reverse operation is carried out after turning off the front drive. And although there is no need to leave the car and manually disengage the gears, to disengage the clutch you will need to perform a number of non-standard actions:
- stop the SUV;
- turn off the PP;
- engage reverse gear and drive a few meters (3-5).
If you simply disengage the front axle, the front driveshaft will be disconnected from the rear driveshaft, but the front axle will continue to rotate, driven by the wheels to which it is connected. Changing the direction of movement is precisely what is needed so that the automation recognizes that the CV joints have begun to rotate in the opposite direction. The automatic operation of the HUB is its main and, perhaps, only serious advantage. And now about the disadvantages:
- This design does not protect some parts from abrasion when driving with rear-wheel drive (for example, in Kia Sportage SUVs, the clutch engagement ring made of plastic, as well as the three-spike ring made of silumin, wear out quite quickly). As a result, at one point, when you try to engage all-wheel drive, you will fail, because the HUB simply does not have enough free play to engage between the wheel and the CV joint;
- The automatic clutch is not able to provide reliable locking. If, for example, you cannot climb a steep slope, the HUB will turn off when you put the SUV back in neutral. To turn it on, you will need to change the direction of movement to the opposite. But in some cases you simply cannot do this. For example, if you rolled onto an off-road area with mud or clay, and to turn on the HUB you need to drive forward a few meters.
However, those drivers who have already tried driving with an automatic clutch are unlikely to want to change it to a manual device, despite its absolute reliability. After all, HUB shutdowns occur infrequently, and getting out of an SUV to do this is “not comme il faut,” especially in bad weather.
Such devices are considered the most advanced types of automatic HUBs from a technical point of view. Here, their activation is ensured by electronics that respond to the inclusion of all-wheel drive. In the latter case, the vacuum pump is driven. Using the vacuum created in the inlet manifold, it sucks air through the piping system from the coupling, which causes the gear to engage and rigidly lock the wheel with the CV joint. If the four-wheel drive is turned off, the vacuum pump forces air into the line, acting on the movable gear in the opposite direction and disengaging it. Thus, the operating principle of the vacuum HUB eliminates the need to change the direction of movement to disengage the clutch - here everything happens automatically.
But there are a number of disadvantages here too. Firstly, the cost of such HUBs is significantly higher. Secondly, their independent installation is quite complicated, since it will require changes in the operation of many other components. Thirdly, the reliability of such devices is even less. than with conventional automatic couplings, since the operation of the vacuum HUB depends on the tightness of the corresponding pipelines and seals. As they wear out, dirt and water begin to get into the line, the vacuum pressure gradually drops, and at one not-so-wonderful moment you simply will not be able to turn the clutch on/off. That is, now you will have to regularly monitor the condition of pipelines and seals, preventing loss of tightness. Most likely, the combination of these three shortcomings became the reason for the low demand for vacuum hubs.
Pros and cons of using freewheels
Many SUV drivers don’t quite understand why HUBs are needed at all. Therefore, let us dwell in more detail on the main advantages and disadvantages of these devices:
- in the absence of a freewheel, disabling all-wheel drive does not mean that the front axle shaft will not rotate, but it transmits movement to both the cardan and the gearbox, which, in turn, causes the transfer case gears to rotate, and idle. In other words, the absence of a HUB leads to a decrease in the service life of the transmission (primarily) and the power unit;
- the ability to completely disconnect the hub from the CV joints allows you to improve the acceleration capabilities of the SUV, while at the same time significantly reducing friction when the vehicle is coasting;
- According to some estimates, HUBs are up to one liter of fuel for every 100 kilometers.
These devices also have obvious design flaws that are technically impossible to eliminate. The point is that in some situations you will not be able to engage all-wheel drive:
- driving off the asphalt onto a dirt road;
- when an SUV drives onto a high enough curb;
- if, while driving along the highway, dry areas alternate with snowy ones.
So you will have to decide whether you need a HUB after weighing all the above-mentioned pros and cons.
Nuances of choosing a HUB for an SUV
But if you are firmly convinced that your car needs a freewheel, you will have to solve another dilemma: which device to prefer, manual, automatic or vacuum. However, the specific model of the SUV also plays a role - not all of them have HUBs of a certain type. And yet, the main factor determining the choice is the operating conditions of the vehicle. If you live in a rural area and off-roading is your main method of transportation, it is better to give preference to manual clutches. For a city dweller who rarely travels outside the metropolis, there will be an automatic clutch.
