Test Drive
Subaru Forester
Drive is everything!
Potapkin Alexander ( 26.05.2017
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Photo: PushCAR
Any person in our country and abroad who is at least a little familiar with cars, having heard the phrase - "Symmetrical all-wheel drive", will immediately remember Subaru cars. This is a kind of rule - we say Subaru, we mean symmetrical all-wheel drive, and vice versa - we say symmetrical all-wheel drive, we mean Subaru. And, of course, Subaru cars are legendary boxer engines. Subaru cars are a tradition of four-wheel drive and boxer engines, which the manufacturer has remained true to throughout its history.
To date, Subaru offers only four models in Russia. But the main model of the brand was and remains the Forester, it is the main locomotive of all sales. The new, fourth generation Forester with the SJ index appeared in 2013, and has already gone through two small restylings. After all, minor, but frequent, changes in appearance are designed to maintain interest in the model and in the brand as a whole.
It's no secret that all Japanese manufacturers have recently become very fond of continuously variable transmissions, in other words, a variator. Among them was Subaru. Abandoning traditional automatic transmissions, the developers put their own development, the Lineartronic CVT, on the new generation. On the one hand, the variator is a smooth ride and fuel economy. On the other hand, this is a lot of wear on the parts of the box and a quick “overheating” on the road. After all, any crossover, especially with all-wheel drive settings like Subaru's, sooner or later simply has to go off-road - "knead" the dirt and transfer heavy loads. And it seems that the CVT is simply not suitable for such trips, but Subaru engineers managed to destroy this statement. The Lineartronic box is capable of withstanding enormous loads. You can get stuck and skid for five or ten minutes, and in the end, you won’t see the box or clutch overheat indicator on the dashboard. Of course, if you wish, you can overheat the variator and clutch on the Forester, but if you compare it with competitors, then Forik is one of the leaders in terms of endurance. Branded symmetrical all-wheel drive, as before, differs depending on the transmission. With a manual transmission comes a more advanced all-wheel drive system with a self-locking center differential. That is, the version on the "mechanics" has a permanent four-wheel drive. A simplified system comes with the variator, which automatically distributes torque between the axles, and a multi-plate clutch is responsible for blocking the center differential. And the X-Mode off-road assistance system gives the Forester permanent all-wheel drive, if the speed is not higher than 40 km / h, and helps to automatically maintain the set speed on the descent.
But, even with a simpler all-wheel drive and without the X-Mode system, the Forester on the roads will be able to compete with a couple of cars in this class. The main rivals of the Subaru Forester in terms of cross-country ability, all-wheel drive and its settings can be considered the new Jeep Cherokee or Land Rover Discovery Sport.
And, if with the technical component of the transmission and all-wheel drive, which complements the ground clearance of 22 cm, everything is very good and there is simply nothing to complain about. And this, one might say, is the main trump card of the Forester, on which the manufacturer focuses, but for the rest, namely, comfort, quality of materials and assembly, there are still questions and comments. Of course, if we draw an analogy with the previous generation, then the new Forester is made much better. But, nevertheless, there are still many shortcomings in it, which simply should not be in a car for more than two million. And the first thing you notice in the car's interior is simplicity, archaism and meager quality of materials. Many are accustomed to the fact that Subaru is primarily handling and technology, but comfort and ease of movement are secondary things, and here they are not particularly needed. To be honest, I personally can’t understand this, and it’s a little wild for me to see a car for 2 million with a penny, for example, without rear parking sensors, I’m already silent about the front ones. Yes, there is a rear-view camera, but according to all modern trends, it simply must be supplemented with parking sensors. And there are no parking sensors in any version! Or a multimedia system with six speakers, which, apparently, is here simply because it is necessary, and no one has been involved in its settings at all. The head unit is completely touch-sensitive, and it is worth giving it its due, the “head” itself works very quickly. I was also surprised by the simply disgusting work of the light sensor. Sometimes he did not understand when he needed to turn on the dipped beam, and when to turn it off. Plus, the optotronic instrument panel “attached” to it works in just two stages, that is, there is no smooth transition of the backlight, in other words, there is no dimmer. It just switches to dim or bright. And it is worth noting that now you will not find such minor flaws even in budget cars for 600 thousand rubles. And you should not forget about the main "trick" of most Japanese manufacturers - only two power windows, and sometimes one, which operate in automatic mode.
As for the cabin as a whole, he loves to creak very much, especially on bumps and bumps, and he is not happy with loud music either. In general, the Japanese have much to strive for. Nevertheless, if these little things, let's call them that, are ignored, then a very large and spacious cabin in the class opens up before us. A large trunk (maximum volume with the rear sofa folded down is 1548 liters), a spacious rear row, and seats that are very loyal to the back endow the Forester with the practicality that many appreciate and that they look at first of all when choosing a car. But if you continue to find fault with the little things, then for myself I noted the insufficient adjustment of the driver's seat. Personally, I did not have enough vertical adjustment, and I wanted the chair to go lower.
In terms of management, the Forester is a typical representative of this class. But it does have a slight advantage - the boxer motor, which keeps the center of gravity lower, which gives it an advantage in corners. Plus all-wheel drive, which constantly distributes torque between the wheels and axles, depending on the steering wheel. The car on our test was with a 2.5 liter engine. This motor is a kind of golden mean for the Forester. 171 hp engine produces a peak torque of 235 Nm. According to measurements and sensations, he goes a little faster than the declared characteristics. Even more powerful engines of the same volume cannot boast of such agility and responsiveness. The motor confidently pulls the car even after 140 km / h, and acceleration to 100 km / h takes just over 9 seconds. But due to insufficient sound insulation of the engine compartment and wheel arches, you don’t want to “turn” the engine at all, and at high speed a lot of aerodynamic noise penetrates into the cabin. Of the minuses can be noted too sensitive gas pedal. This will be especially noticeable in city traffic. Even at the slightest pressure on the gas, the car immediately reacts with a jerk forward. The panacea in traffic jams will only be the "reduced" L mode, which puts the box in a simulated first gear.
In terms of suspension and handling, the Forester didn't just take a step forward, it took a big leap. The joint platform, on which the junior XV model is also based, has MacPherson-type struts in front with an anti-roll bar, the rear is independent, spring-loaded on double wishbones. And the suspension here is really tuned for bad roads. You can safely drive at speed along a broken country road or along a “concrete” that has seen a lot, and at the same time, just marvel at the minimal buildup of the body, the absence of breakdowns, and enjoy the pleasant and quiet operation of the racks.
Subaru Forester gets better and better with every generation. His main trump card in front of his classmates was and will be the technical component - the engine and all-wheel drive. But the interior (performance, design and quality) loses almost all competitors on the market. Most car buyers need convenience, comfort, modern active safety systems and various electronic assistants. Off-road capabilities are of little concern now. After all, few in the city crossover storm ravines, overcome fords or simply drive on muddy ground. Therefore, placing great emphasis on the cross-country ability of the car and investing heavily in its development is not quite the right move. Nevertheless, Subaru brand cars will always find their buyer and will never be left without attention.
The cost of the car Subaru Forester (2.5 CVT) from 2,197,900 rubles.
"Tell me about Subaru's all-wheel drive, namely the 60x40 torque distribution. How does it work?"
It is good that the author of the question indicated the ratio (60/40), although it would be better if he also specified the model, as well as the years of its release. After all, despite the common brand name Symmetrical AWD, completely different all-wheel drive transmissions are used on Subaru cars, depending on the model, year of manufacture and sales market!
In order not to confuse readers and not overload the answer with a listing and description of all possible variations, we will briefly go over the four-wheel drive circuit diagrams used on modern Subaru, and dwell a little more on the one that, we think, is of interest to the author of the question.
Versions with a manual transmission have an "honest" permanent four-wheel drive. As a rule, this is a CDG scheme with a symmetrical center differential, which is blocked using a viscous coupling. Consider pure mechanics, supplemented by hydraulics, without any electronic control. Some models, in particular the Forester, are also equipped with a rear cross-axle differential, which is blocked with a viscous coupling. In addition, a reduction gear is used on a number of models.
But the "charged" WRX STi are equipped with an asymmetric differential, which provides a redistribution of torque in favor of the rear wheels. The ratio depends on the generation of "verses", but is at the level of 41:59 - 35:65. In this case, the "center" has a variable (forced or automatic) degree of blocking using an electromagnetic clutch. This system is known as Driver Controlled Center Differential (DCCD). On the rear axle, in addition, a "self-block" is installed.
For "charged" versions of Subaru with automatic transmission (the same Impreza WRX STi, as well as Forester S-Edition and Legacy GT), a scheme called Variable torque distribution AWD (VTD) was once proposed. It uses an asymmetrical planetary differential (45:55 in favor of the rear wheels), which is locked using an electronically controlled multi-plate clutch. As an option, a viscous coupling can also be installed in the rear axle differential.
Finally, Subaru with automatic transmissions and Lineatronic CVTs are equipped with the Active torque split AWD (ACT) all-wheel drive system. Apparently, it is about her that our reader asks. Depending on the generation and year of manufacture, there are certain design differences, but the principle of operation of ACT remains unchanged.
Unlike the above schemes, there is no center differential here; an electronically controlled clutch is responsible for transmitting torque to the rear wheels. Well, and most importantly - such Subaru have a more "front-wheel drive" character on how many surfaces, since the ratio in normal conditions is 60:40 in favor of the front wheels!
At the same time, the redistribution of traction depends on a number of parameters (the selected gearbox mode, the speed of rotation of the front and rear wheels, the position of the "gas" pedal, etc.), on the basis of which the control unit "decides" how hard to clamp the clutches and how much torque transfer to the rear axle. Therefore, the ratio changes in real time and can vary between 90:10 - 60:40 in favor of the front axle. By the way, the rear cross-axle differential on a number of models can also be equipped with a viscous coupling as an automatic lock.
To say that Subaru with ACT have a "fake" four-wheel drive is impossible: unlike many models of other brands with a connected rear axle, traction is always supplied to the rear wheels. But things still don’t reach the “equal” ratio of 50:50, in general, on slippery surfaces, such cars are controlled somewhat differently than versions with a mechanical differential. However, all these features are revealed in far from standard driving modes, and in “civilian” modes, even an experienced driver is unlikely to determine which of the Symmetrical AWD variations is used.
Ivan KRISHKEVICH
website
You have questions? We have answers. The topics you are interested in will be expertly commented on by either specialists or our authors - you will see the result on the website.
I wanted to add useful information about Subaru's symmetrical drive and specifically my Legas. Maybe for someone who still doubts whether or not to take this car, this information will be useful and important for making the right decision.
In those. characteristics, I indicated that the drive is permanent full and this is so, but it is also symmetrical. What does it mean?
The entire system is perfectly symmetrical about the longitudinal axis of the vehicle. Evenly distributed on all four wheels, the load provides exceptional stability during movement and maneuvering.
Any road, especially in Russia, has an uneven surface. Pits found on the asphalt, slippery areas, and just puddles when driving at high speed can cause loss of control of the car. AWD all-wheel drive avoids loss of control by controlling the grip of each of the wheels every moment. When one of the wheels slips, the car reacts to prevent skidding. Increased directional stability when driving at high speeds, the car does not "scour" on bumps or ruts.
In difficult weather conditions, the grip of the tires with the road deteriorates noticeably. A slippery road covered with freshly fallen snow is an almost insurmountable obstacle for a two-wheel drive car. If any of them gets stuck, the driver is practically doomed to seek outside help. The AWD all-wheel drive system installed in Subaru cars gives even exclusively city cars the power and off-road capability. If any of the wheels loses traction, the load is redistributed to the rest and the car continues to move.
On a freeway, overcoming even not very steep, at first glance, turns, a car with a two-wheel drive can suddenly break into a skid. This is due to the gradually and imperceptibly increasing centrifugal force acting on it during the maneuver. The perfect balance of all Subaru all-wheel drive system designs and the force that is transmitted to each wheel make it possible to perfectly follow the chosen trajectory of movement. For the first time, a city car acquires the dynamics and handling of a racing car. It was after Subaru that many other auto manufacturers began to equip their cars with all-wheel drive systems, but this company retains leadership in the quality of its developments.
The system combines a fairly low center of gravity, which is inherent in Subaru boxers, and the complete lateral symmetry of the transmission. This solution combines excellent vehicle weight distribution and perfect balance, thanks to which the AWD (All Wheel Drive) all-wheel drive provides excellent stability and excellent traction of the wheels with the road surface in absolutely any conditions. The big advantage of this system is the placement on the same line of all components: engine, transmission, rear differential and universal joint, forming a symmetrical design in a horizontal plane. This solution is very important for the ideal weight distribution of the car along the length and width, which gives a neutral balance, which ensures a more comfortable and safer driving.
In confirmation of all this, I suggest watching the video at the link below. The topic of ice in Russia is more relevant than ever. Personally, when buying a car, I made a big bet on safety, because. my family's life is important. And since we have winter for six months, then the choice was obvious in favor of all-wheel drive. Only here on Subari he is really the best. WHAT CAR DO YOU THINK WAS CLIMBING THIS SLIDE? The question will be removed at the end of the video!
https://rutube.ru/tracks/3786687.html?v=aaf61c7931770df4820410f172d4b397.
Even at the very beginning of its history, Subaru made a bet on all-wheel drive versions of its models, a technology that at that time was available mainly on special vehicles. In 1972, Subaru introduced its first four-wheel-drive model, the Leone Estate Van 4WD, and since then, more than half of the company's sales have come from all-wheel drive vehicles. It is also important that Subaru's symmetrical all-wheel drive was not adapted to cars with a single axle drive, but was immediately created for use on cars with four-wheel drive. As for the all-wheel drive Subaru Symmetrical All Wheel Drive with axle shafts of the same length, coupled with a longitudinally located boxer Subaru Boxer engine and a transmission shifted to the wheelbase, this arrangement allows, in addition to close to ideal weight distribution along the axes, to ensure efficient implementation of engine power and a good grip balance wheels with the road on any type of surface. That is, the optimal distribution of torque between all wheels, and hence a high level of controllability.
Torque is optimally distributed to all wheels, resulting in near-neutral steering
Symmetrical all-wheel drive confidently counteracts both the drift of the front axle and the skid of the rear
There are four types of all-wheel drive Symmetrical AWD. The first of them, VTD, is not represented on the Russian market today, but was previously used on Legacy GT models 2010–2013, Forester S-Edition of the same period, Outback with a 3.6-liter engine 2010–2014, Tribeca, WRX and WRX STI 2011–212 This system uses a planetary type center differential, which is blocked by an electronically controlled multi-plate hydraulic clutch.
The original 45:55 torque distribution is constantly monitored by Vehicle Dynamic Control and automatically adjusted according to road conditions, road profile and topography. The second system is ACT with active torque distribution. Here, through a multi-plate electronically controlled clutch, the torque, depending on the condition of the road, is dosed to the front and rear wheels up to a ratio of 60:40 in real time. On the Russian market with this type of all-wheel drive, Forester, Outback and XV models with Lineatronic transmission are presented.
For mechanical transmissions, the CDG all-wheel drive system with a self-locking differential is designed. In its design, an interaxle differential with bevel gears, blocked by a viscous coupling, is used. At the same time, under normal driving conditions, the distribution of traction between the front and rear wheels occurs in a ratio of 50:50. This system is very well suited for sports driving, so it is not surprising that it was previously used on the WRX model with a manual transmission, and today the Forester and XV models with a manual transmission are on the Russian market. The fourth type of all-wheel drive Subaru - DCCD has in its arsenal an electronically controlled active limited slip differential, and it is fully focused on sports driving enthusiasts, those who love the Subaru brand for its cars with a racing character.
It is with this type of drive that we have presented the Subaru WRX STI car. This design is a symbiosis of electronic and mechanical center differential locks that respond to changes in torque. First, a faster mechanical interlock is activated, then the electronic interlock is activated. The torque between the front and rear wheels is distributed in a ratio of 41:59, and the operation of the entire system is focused on the optimal use of maximum driving characteristics. The design of the differential provides for the possibility of "preload", that is, the mode of pre-setting its characteristics. By quickly realizing high torque, such a system strikes a good balance between sharpness and precision of control and vehicle stability. Of course, in this type of drive, a manual transmission control mode is also provided.
The low center of gravity of a compact boxer engine, symmetrical all-wheel drive with equal drive lengths and transmission variations... All this ensures excellent handling on any kind of surface.
And in conclusion, a few well-known postulates about the benefits of all-wheel drive. In this case, the symmetrical all-wheel drive Subaru Symmetrical AWD. Thanks to the fact that the torque is distributed to all four wheels, the car demonstrates stable behavior both on the turning arc on asphalt pavement and when driving on uneven roads. The advantage of an all-wheel drive car is especially noticeable when driving on winter roads. Secondly, an all-wheel drive car is more prone to neutral steering than its two-wheel drive counterparts. Thus, his driver is much less likely to go past the turn. And, of course, a four-wheel drive car, as a rule, has good acceleration dynamics: the torque transmitted to all four wheels allows you to better realize the capabilities of high-power engines.
10.05.2006
After the 4WD schemes used in Toyota were examined in some detail in previous materials, it turned out that there is still an information vacuum with other brands ... Let's first take the four-wheel drive of Subaru cars, which many call "the most real, advanced and correct."
Mechanical boxes, by tradition, are of little interest to us. Moreover, everything is quite transparent with them - since the second half of the 90s, all Subaru on the mechanics have an honest all-wheel drive with three differentials (the center differential is blocked by a closed viscous coupling). Of the negative sides, it is worth mentioning an overly complicated design obtained by combining a longitudinally mounted engine and the original front-wheel drive. As well as the refusal of the Subarovites from the further mass use of such an undoubtedly useful thing as a downshift. On single "sports" versions of the Impreza STi, there is also an advanced manual transmission with an "electronically controlled" center differential (DCCD), where the driver can change the degree of its blocking on the go ...
But let's not digress. There are two main types of 4WD used in automatic transmissions currently operated by Subaru.
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1.1. Active AWD / Active Torque Split AWD |
Permanent front-wheel drive, without center differential, connection of the rear wheels with an electronically controlled hydromechanical clutch
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1 - torque converter lock-up damper, 2 - torque converter clutch, 3 - input shaft, 4 - oil pump drive shaft, 5 - torque converter clutch housing, 6 - oil pump, 7 - oil pump housing, 8 - transmission housing, 9 - speed sensor turbine wheel, 10 - 4th clutch, 11 - reverse clutch, 12 - 2-4 brake, 13 - front planetary gear set, 14 - 1st clutch, 15 - rear planetary gear set, 16 - 1st brake gear and reverse, 17 - transmission output shaft, 18 - "P" mode gear, 19 - front drive gear, 20 - rear output shaft speed sensor, 21 - rear output shaft, 22 - shank, 23 - clutch A- AWD, 24 - front drive driven gear, 25 - freewheel, 26 - valve block, 27 - sump, 28 - front output shaft, 29 - hypoid gear, 30 - impeller, 31 - stator, 32 - turbine. |
E this option has long been installed on the vast majority of Subaru (with automatic transmission type TZ1) and is widely known from the Legacy model of 89. In fact, this four-wheel drive is as “honest” as the fresh Toyota Active Torque Control - the same rear-wheel drive and the same TOD (Torque on Demand) principle. There is no center differential, and the rear-wheel drive is activated by a hydromechanical clutch (friction package) in the transfer case.
The Subar scheme has some advantages in the working algorithm over other types of plug-in 4WD (especially the simplest ones, like the primitive V-Flex). Albeit small, but the moment during A-AWD operation is constantly transmitted back (unless the system is forcibly turned off), and not only when the front wheels slip - this is more useful and efficient. Thanks to hydromechanics, the force can be redistributed a little more accurately than in an electromechanical ATC. In addition, A-AWD is structurally more durable. For cars with a viscous coupling for connecting the rear wheels, there is a danger of a sharp spontaneous “appearance” of the rear drive in a turn, followed by an uncontrolled “flight”, but in A-AWD this probability, although not completely excluded, is significantly reduced. However, with age, as wear and tear, the predictability and smoothness of the connection of the rear wheels decreases significantly.
The algorithm of the system remains the same throughout the entire release period, only slightly corrected.
1) Under normal conditions, with the accelerator pedal fully released, the torque distribution between the front and rear wheels is 95/5..90/10.
2) As you press on the gas, the pressure supplied to the clutch package begins to increase, the discs gradually tighten and the torque distribution begins to shift towards 80/20 ... 70/30 ... etc. The relationship between gas and line pressure is by no means linear, but rather looks like a parabola - so that a significant redistribution occurs only when the pedal is pressed hard. With a fully recessed pedal, the friction clutches are pressed with maximum effort and the distribution reaches 60/40 ... 55/45. Literally, "50/50" is not achieved in this scheme - this is not a hard lock.
3) In addition, the speed sensors of the front and rear output shafts installed on the box make it possible to determine the slip of the front wheels, after which the maximum part of the moment is taken back regardless of the degree of gas supply (except for the case of a fully released accelerator). This function is active at low speeds, up to about 60 km/h.
4) When forced into 1st gear (selector), the clutches are immediately pressed with the maximum possible pressure - thus, as it were, "difficult all-terrain conditions" are determined and the drive remains the most "permanently full".
5) When the "FWD" fuse is plugged into the connector, no overpressure is supplied to the clutch and the drive is constantly carried out only on the front wheels (distribution "100/0").
6) With the development of automotive electronics, it has become more convenient to control slippage using standard ABS sensors and reduce the degree of clutch blocking when cornering or ABS is triggered.
It should be noted that all passport distributions of moments are given only in statics - during acceleration / deceleration, the weight distribution along the axes changes, so the real moments on the axes are different (sometimes "very different"), just like with different coefficients of wheel adhesion to the road.
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1.2. VTD AWD |
Permanent four-wheel drive, with center differential, electronically controlled hydromechanical clutch lock
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1 - torque converter lock-up damper, 2 - torque converter clutch, 3 - input shaft, 4 - oil pump drive shaft, 5 - torque converter clutch housing, 6 - oil pump, 7 - oil pump housing, 8 - transmission housing, 9 - speed sensor turbine wheel, 10 - 4th clutch, 11 - reverse clutch, 12 - 2-4 brake, 13 - front planetary gear set, 14 - 1st clutch, 15 - rear planetary gear set, 16 - 1st brake gear and reverse, 17 - countershaft, 18 - "P" mode gear, 19 - front drive gear, 20 - rear output shaft speed sensor, 21 - rear output shaft, 22 - shank, 23 - center differential, 24 - center differential lock clutch, 25 - front drive driven gear, 26 - overrunning clutch, 27 - valve block, 28 - sump, 29 - front output shaft, 30 - hypoid gear, 31 - impeller, 32 - stator, 33 - turbine . |
The VTD (Variable Torque Distribution) scheme is used on less mass-produced versions with automatic transmissions such as TV1 (and TZ102Y, in the case of the Impreza WRX GF8) - as a rule, the most powerful in the range. Here, everything is in order with "honesty" - the all-wheel drive is really permanent, with an asymmetric center differential (45:55), which is blocked by an electronically controlled hydromechanical clutch. By the way, since the mid-80s, Toyota 4WD has been working on the same principle on the A241H and A540H boxes, but now, alas, it has remained only on the original rear-wheel drive models (FullTime-H or i-Four all-wheel drive).
Subaru usually attaches a fairly advanced VDC (Vehicle Dynamic Control) system to the VTD, in our opinion - a system of exchange rate stability or stabilization. At the start, its component, TCS (Traction Control System), slows down the slipping wheel and slightly strangles the engine (firstly, by the ignition timing, and secondly, even by turning off part of the nozzles). Classic dynamic stabilization works on the go. Well, thanks to the ability to arbitrarily slow down any of the wheels, VDC emulates (simulates) a cross-axle differential lock. Of course, this is great, but you should not seriously rely on the capabilities of such a system - so far, none of the automakers has even managed to bring the "electronic lock" closer to traditional mechanics in terms of reliability and, most importantly, efficiency.
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1.3. "V Flex" |
Permanent front-wheel drive, no center differential, viscous coupling for rear wheels
Probably worth mentioning is 4WD, which is used on small models with CVTs (like the Vivio and Pleo). Here the scheme is even simpler - a permanent front-wheel drive and a rear axle "connected" by a viscous coupling when the front wheels slip.
We have already said that in English under the concept of LSD everyone gets self-locking differentials, but in our tradition this is usually called a system with a viscous coupling. But Subaru used a whole range of LSD differentials in different designs on their cars ...
2.1. Old style viscous LSD
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In the LSD differential, the right and left side gears are "connected" through a viscous coupling - the right splined shaft passes through the cup and engages with the clutch hub (the differential satellites are mounted cantilevered). The clutch housing is one piece with the gear of the left axle shaft. In a cavity filled with silicone fluid and air, there are discs on the splines of the hub and body - the outer ones are held in place by spacer rings, the inner ones are able to move slightly along the axis (for the possibility of obtaining a "hump effect"). The clutch works directly on the difference in speed between the right and left axle shafts.
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During rectilinear motion, the right and left wheels rotate at the same speed, the differential cup and side gears move together, and the moment is equally divided between the axle shafts. When there is a difference in the frequency of rotation of the wheels, the housing and the hub with the disks fixed to them move relative to each other, which causes the appearance of a friction force in the silicone fluid. Due to this, in theory (only in theory), there should be a redistribution of torque between the wheels.
2.2. New viscous LSD
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- Impreza WRX manual transmission until 1997
- Forester SF, SG (except FullTime VTD + VDC versions)
- Legacy 2.0T, 2.5 (except FullTime VTD + VDC versions)
Working fluid - transmission oil class API GL-5, viscosity according to SAE 75W-90, capacity ~0.8 / 1.1 l.
2.3. Friction LSD
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The next in line of appearance is the friction mechanical differential, used on most versions of the Impreza STi since the mid-90s. The principle of its operation is even simpler - side gears have a minimum axial play, a set of washers is installed between them and the differential housing. When there is a difference in the speed between the wheels, the differential works like any free one. The satellites begin to rotate, while there is a load on the gears of the axle shafts, the axial component of which presses the pack of washers and the differential is partially blocked.
The cam-type friction differential was first used by Subaru in 1996 on turbo Imprezas, then it appeared on the Forester STi versions. The principle of its operation is well known to the majority from our classic trucks, shishigs and UAZs.
There is actually no rigid connection between the drive gear of the differential and the semi-axes, the difference in the angular velocity of rotation is provided by slipping of one semi-axis relative to the other. The separator rotates together with the differential case, the keys (or "crackers") fixed on the separator can move in the transverse direction. The protrusions and cavities of the cam shafts, together with the keys, form a transmission of rotation, like a chain.
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Scope (on domestic market models):
- Impreza WRX after 1996
- Forester STi
The working fluid is an ordinary gear oil of API GL-5 class, viscosity according to SAE 75W-90, capacity ~ 0.8 l.
Eugene
Moscow
arco@site
Legion-Autodata
Information on car maintenance and repair can be found in the book (books):
