After the 4WD schemes used on Toyota were considered in some detail in previous materials, it turned out that there is still an information vacuum with other brands. Let's start by taking four-wheel drive 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, Subaru mechanics have had an honest all-wheel drive with three differentials (the center differential is blocked by a closed viscous coupling). From negative aspects it is worth mentioning the overly complicated design, resulting from the combination of longitudinal installed engine and 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, there is also a highly advanced manual transmission with an "electronically controlled" center differential, 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.
1. Active AWD
This option has long been installed on the vast majority of Subaru (with automatic transmission type TZ1). In fact, this "full" drive is as "honest" as Toyota's V-Flex or ATC - the same plug-in rear wheels and the same TOD (Torque on Demand) principle. There is no center differential, and the rear-wheel drive is switched on by a hydromechanical clutch in the transfer case - it goes back from ~ 10% of the effort in normal conditions(if you do not attribute this to internal friction in the coupling) up to almost 50% in the limit state.
Although the Subar scheme has some advantages in the working algorithm over other types of plug-in 4WD. Albeit small, but the moment at A-AWD operation(unless the system is forcibly disabled) is still transmitted back constantly, and not only when the front wheels slip - this is more useful and efficient. Thanks to hydromechanics, it is possible to redistribute the force (although it is too loudly said to "redistribute" - just select a part) more accurately than in the electromechanical ATC - A-AWD is able to work out slightly both in turns and during acceleration and braking, and it will be structurally stronger. Reduced the likelihood of a sharp spontaneous "appearance" rear wheel drive in a turn followed by an uncontrolled "flight" (there is such a danger for cars with a viscous coupling for connecting the rear wheels).
To improve the "all-terrain" qualities, Subaru often installs in rear differential models with A-AWD automatic locking mechanism (viscous clutch, "cam differential" - see below about it).
2. VTD AWD
The VTD (Variable Torque Distribution) scheme is used on less massive versions with automatic boxes type TV1 (and TZ102Y, in case Impreza WRX GF8) - as a rule, the most powerful in the range. Here, everything is in order with "honesty" - the four-wheel drive is really permanent, with an interaxle differential (blocked by a 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).
Every VTD flyer states that "Torque is split 45/55 between the front and rear wheels." And wow, many are actually beginning to believe that they are driven forward along the track by 55% rear-wheel drive. You need to understand that these figures are an abstract indicator. When the car moves in a straight line and all wheels rotate at the same speed, the center differential, of course, does not work out, and the moment is clearly divided between the axles in half. What do 45 and 55 mean? Only gear ratios in the planetary gear set of the differential. If the front wheels are forcibly stopped completely, then the differential carrier also stops, and gear ratio between the rear drive shaft and input shaft razdatki will just be the same 55/100, that is, 55% of the moment developed by the engine will go back (the differential will work as an overdrive). If the rear wheels freeze, then 45% of the torque will go forward through the differential carrier in the same way. Of course, the presence of blocking is not taken into account here, and indeed ... In reality, the distribution of moments is a constant floating value and is far from unambiguous.
Subaru usually attaches quite advanced technology to the VTD. VDC system(Vehicle Dynamic Control), in our opinion - the system exchange rate stability. When starting it 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 works on the go dynamic stabilization. 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.
3. "V-Flex"
Probably worth mentioning is 4WD, which is used on small models with CVTs (like the Vivio and Pleo). Here the scheme is even simpler - constant front-wheel drive and the rear axle "connected" by a viscous coupling when the front wheels slip.
About the cam differential
1 - separator, 2 - guide cams,
3 - thrust bearing, 4 - differential housing, 5 - washer, 6 - hub
We have already said that in English language all self-locking differentials fall under the concept of LSD, however, in our tradition, this is usually called a system with a viscous coupling. Often used on subaru rear The LSD differential is built differently - it can be called "friction, cam type". 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, and the "lock" is inherent in the very principle of operation.
The separator rotates with the differential housing. The "keys" fixed on the separator can move in the transverse direction. The protrusions and cavities of the cams (let's call them that) together with the keys form a transmission of rotation, like a chain.
If the resistance on the wheels is the same, then the keys do not slip and both axle shafts rotate at the same speed. If the resistance on one wheel is noticeably greater, then the keys begin to slide along the cavities and protrusions of the corresponding cam, still trying to turn it in the direction of rotation of the separator. Unlike a planetary type differential, the speed of rotation of the second half-axle does not increase (that is, if one wheel is stationary, the second will not spin twice as fast as the differential housing).
Whether or not a car with such a differential can “drive on one wheel” is determined by the current balance between the resistance on the axle shaft, the speed of rotation of the body, the amount of force transmitted back and the friction in the key-cam pair. However, this design is certainly not "off"-road.
To date, there are many all-wheel drive systems for cars. Consider the two most common versions using the example of Subaru cars, because some of them have common name and designation. There are several different versions all-wheel drive Subaru AWD.
All such models (except rear-wheel drive Subaru BRZ coupes) have a standard symmetrical full AWD drive. The name is common, but four modifications are used all-wheel drive systems.
Standard all-wheel drive system based on center self-locking differential and viscous coupling (CDG)
Most people believe that this category of systems is associated with all-wheel drive. It is very common in cars of a similar brand, which has mechanical box gears. This model is a symmetrical all-wheel drive configuration, under normal conditions, the torque is in the ratio of the front and rear axles 50 to 50.
When the car slips, the differential, which is located between the axles, is able to send up to 80% of the torque to the front axle, this function provides good grip tires with the road surface. A viscous coupling is used by such a differential so that it can respond to a mechanical difference in tire grip with the road without the participation of a computer.
Type of all-wheel drive cdg you can see on the car Subaru Forester having six-speed box gears.
Such a drive has been used for a long time, and the appearance new version next year only means that it will not disappear soon. The model is a reliable and simple all-wheel drive system that can provide very safe driving using available traction.
It should be noted that you can see the type of all-wheel drive cdg on cars Subaru Impreza 2014 with a two-liter engine, as well as on the XV Crosstrek with a five-speed manual transmission, on the Ouback and Forester with a six-speed gearbox.
All-wheel drive system with variable torque distribution for vehicles with automatic transmission (VTD)
It is very important to note that concern Subaru started translating most of his Vehicle from standard automatic to continuously variable transmission(CVT). At the same time, now you can still find cars with such a system.
Symmetrical all-wheel drive, which involves the use of variable torque distribution, can be found on the Tribeca (with a 3.6i engine and 6 cylinders, as well as a 5-speed gearbox), Outback and Legacy. Here there is a torque shift towards the rear axle in the proportion of 45 to 55. Instead center differential with a viscous coupling, a multi-plate hydraulic clutch will be used here, which will be combined with a planetary variant differential.
When slip is detected, signals will be sent from sensors that are installed to measure wheel slip, as well as braking force and throttle position located near the throttle. In this case, the torque will be distributed evenly along the axes (50 to 50) to ensure maximum adhesion of the wheels to the asphalt surface.
A fully mechanical viscous coupling is much simpler and more flexible. The VTD system has the advantage that it has an active rather than a reactive component, this achieves a high speed of torque transfer between the axles, mechanical system can't boast like that.
All-wheel drive system with active torque distribution (ACT)
Subaru's new models are already using the third option for all-wheel drive systems. In particular, it has many similarities with previous version- also implies the use of an electronically controlled multi-disc system in a ratio of 60 to 40 with a torque shift to the front axle.
All-wheel drive type act is used on models Subaru Legacy 2014
Also, this AWD has an active torque distribution called ACT. Thanks to the original multi-plate electronically controlled torque transmission clutch, the distribution of torque between the axles in real time corresponds to the driving conditions of the vehicle.
Such an all-wheel drive system allows you to increase both the stability and efficiency of the machine. All-wheel drive type act is used on Subaru models XV Crosstrek, Legacy 2014, Outback 2014, WRX and WRX STI 2015.
All-wheel drive system with multi-mode center differential (DCCD)
In addition to the all-wheel drive systems described above, Subaru used other variants of symmetrical all-wheel drive, which are no longer used. But latest system, which we will mention today, is the system that is used on the WRX STI.
This system uses two center differentials. One is electronically controlled and provides on-board computer Subaru good control over the distribution of torque between the axles. The other one is mechanical device, which can respond more quickly to external influences than its electronic "colleague". The driver's benefit, ideally, is to use the best of the electronic proactive and mechanical reactive "world".
Generally speaking, these differentials naturally exploit their differences - being harmoniously combined planetary gear- but the driver can shift the system towards any of the center differentials using electronic system Driver control Controlled Center Differential (DCCD) - Driver Controlled Center Differential.
The torque distribution for DCCD systems is 41:59 offset towards the rear axle. This all-wheel drive system, focused on providing maximum running characteristics, for serious sports.
Side torque distribution
Until we figured out how modern Subaru distribute torque between the front and rear axles, but what about the distribution of torque between the wheels, between the left and right side? On both front and rear axles, you will usually find a standard diff. open type(i.e. not subject to blocking). More powerful models(such as the WRX and Legacy 3.6R models) are often fitted with a limited slip differential on the rear axle to improve traction on the rear axle when cornering.
The WRX STI is also equipped with a limited slip differential on the front axle to maximize all-wheel traction. Latest WRX The 2015 and 2015 WRX STI also use brake-based torque distribution systems that brake the inside wheel when cornering to transfer power to the outside when cornering and reduce the turning radius.
Quick jump to sections
world premiere crossover Subaru XV, created on the basis of the Subarovskoy Impreza model, took place in 2011 and today this car has firmly established itself in the ranks of urban SUVs.
There is never too much ground clearance, especially in our conditions.
Therefore, it is worth getting acquainted with the crossover, and which has the maximum ground clearance. This new Subaru XV, having a clearance of 220 mm. This car, like the Subaru Forester, is built on the platform of the new Impreza. He is a little smaller than the "forester", but ground clearance he has exactly the same. Plus the mandatory all-wheel drive. It's a Subaru!
Why does a car need such an impressive distance between the road and the body? Ask those who live outside the city and every day overcome kilometers of not the best roads. Also, this question will be answered by those who live in the city, but on those streets where there is no asphalt.
Alternative option
However, ground clearance is not the only criterion when choosing universal car. After all, if this were the case, then there simply wasn’t an alternative to an equal SUV, but there is such an alternative. Subaru XV in terms of off-road capabilities can give odds to many framers, and as for behavior on asphalt and fuel consumption, almost any comparison will be in favor of a crossover.
In order to better understand the dimensions of the Subaru XV, we present the data of the Forester. XV is 15 cm shorter and 12 cm lower, and here wheelbase they are practically the same. In fact, no one will feel the difference of 5 mm in practice, and therefore the interior of the Subaru XV is almost as spacious as that of the Forester.
Specifications
- Length: 4450 mm
- Width: 1780 mm
- Height: 1615 mm
- Wheelbase: 2635 mm
- Curb weight: 1415 kg
- Ground clearance: 22 cm
- Trunk volume: 310 / 1210 liters
The difference in length is noticeable only in the volume of the trunk. If the Forester has 505 liters, then the Subaru XVI has only 310. On the other hand, for most compact five-doors it is quite a normal figure. Of course, the trunk can be quadrupled if folded rear seats. For a car with all-wheel drive, there is always overall luggage with which you need to make an excursion to nature.
Yes, the backs of the rear sofa are not adjustable in terms of the angle of inclination. But the landing here is lighter than on the Forester, and this allows you to move on asphalt with more confidence. This Subaru is capable of cornering at speeds worthy of the finest premium car brands.
The fact that the car has a ground clearance of 22 cm is absolutely not felt. And it's understandable why. The boxer engine traditionally allows you to make the center of gravity lower than other cars. Plus, permanent all-wheel drive and a very well-tuned system of exchange rate stability.
As for engines, we have Subaru XV available with two engines, both petrol. The volume of the base unit is 1600 "cubes". It has 114 hp.
But much more interesting, of course, is a two-liter engine, in which one and a half hundred autohorses. With it, acceleration from standstill to the first hundred takes 10.5 seconds, and fuel consumption in the combined cycle is less than 8 liters per 100 km. And here's what's interesting: this indicator for the version with automatic transmission is better than for a car with a 6-speed manual.
Engines:
- 1.6 liter petrol
- Power 114 hp
- Torque: 150 Nm
- Maximum speed: 179 km/h
- Acceleration time to 100 km/h: 13.1 sec
- 2 liter petrol
- Power 150 hp
- Torque: 198 Nm
- Maximum speed: 187 km/h
- Acceleration time to 100 km/h: 10.7 sec
- Average fuel consumption: 6.5 liters per 100 km
Features of the variator
The reason is simple: here, as on the new generation Forester, there is no classic machine, and the Lineartronic variator. That is, there is no gear shifting, as such, but there is constantly unrelenting traction in almost the entire rev range. There is some howling characteristic of the variator, but it is drowned in the specific pleasant sound of the boxer engine. Especially if this motor is spinning.
By the way, if desired, the variator provides the ability to shift gears in manual mode, moreover, not only with a selector, but also with paddle shifters. Although, to be honest, the CVT does a great job even without driver prompts.
By class standards, the Subaru XV has enough spacious salon. Especially when compared with crossover competitors. Here you immediately feel the advantage that the car is built on the basis of passenger car. And the landing is more comfortable, and the controls are all at your fingertips.
The interior, of course, is not as elegant as that of the Forster, but the quality of the finishing materials is also at its best. Front panel made of soft plastic. The seats, although they seem ordinary, are actually very tenacious to keep the driver and passengers in corners.
Audio system, climate control, power windows - all this is already "in the database". But keyless entry to the salon, engine start button, leather upholstery seats, rain and light sensors, as well as dual zone climate control Relies only on the top configuration. In it, the place of a monochrome display will also be taken by a multi-functional color one, the same as on the Forester, with a dynamic picture and a plug-in rear view camera.
All-wheel drive system
Subaru XV is only all-wheel drive. True, the “four by four” scheme here can be different. It all depends on the engine and transmission. The most off-road, oddly enough, version with a 1.6-liter engine and manual transmission. It has an interaxle self-locking differential and a downshift is provided. So, if you plan to take real mud baths more or less regularly, it is better to opt for this version.
Cars with a CVT have their own symmetrical all-wheel drive scheme, with active torque distribution. By default, 60% of the drive is sent to the front wheels and 40% to the rear. But for better grip wheels with the road and better handling this ratio can change almost instantly and very flexibly. This is precisely the reason for the feeling of confidence that every driver gets behind the wheel of a Subaru.
Mandatory for all versions of the XV is the stability control system. By the way, in all configurations, except for the most basic, Subaru XV is equipped with front side and curtain airbags. On European tests This crossover received the highest rating - five stars. Moreover, it was this car that was named "the safest for passengers' children."
Subaru XV really universal machine, which is equally good at almost all the tasks that cars face when operating in our conditions. It is comfortable in the city, rulitsya chic on the highway and is not afraid of moderate off-road.
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 "sport" versions 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 - drive shaft oil pump, 5 - torque converter clutch housing, 6 - oil pump, 7 - oil pump housing, 8 - gearbox housing, 9 - speed sensor turbine wheel, 10 - 4th gear clutch, 11 - clutch reversing, 12 - 2-4 brake, 13 - front planetary gear set, 14 - 1st gear clutch, 15 - rear planetary gear set, 16 - 1st gear and reverse brake, 17 - gearbox output shaft, 18 - mode gear " P", 19 - front drive gear, 20 - rear output shaft speed sensor, 21 - rear output shaft, 22 - shank, 23 - A-AWD clutch, 24 - front drive driven gear, 25 - overrunning clutch, 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" in this scheme is not achieved - 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 inclusion 1st gear (selector), clutches are immediately pressed to the maximum possible pressure- thus, as it were, "difficult all-terrain conditions" are determined and the drive is kept the most "permanently complete".
5) With the "FWD" fuse plugged into the socket high blood pressure is not supplied to the clutch and the drive is always carried out only on the front wheels (distribution "100/0").
6) With the development of automotive electronics, slippage has become more convenient to control according to standard ABS sensors and reduce the degree of clutch lockup during cornering or ABS activation.
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 - gearbox housing, 9 - speed sensor turbine wheel, 10 - 4th clutch, 11 - reverse clutch, 12 - 2-4 brake, 13 - front planetary gear set, 14 - 1st gear 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 movement, the right and left wheel rotate at the same speed, the differential cup and the side gears move together and the torque 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 API class 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.
Friction differential cam type was first used by Subaru in 1996 on turbo Imprezas, then it appeared on Forester versions STi. The principle of its operation is well known to most from our classic trucks, "shishigam" and "UAZ".
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):
"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. Indeed, despite the common brand name Symmetrical AWD, on cars brands Subaru Depending on the model, year of manufacture and market, completely different all-wheel drive transmissions are used!
In order not to confuse readers and not to overload the answer with a listing and description of all possible variations, we will briefly go over circuit diagrams all-wheel drive, used on modern Subaru, and a little more detail 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 by 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 "charged" WRX STi 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 electromagnetic clutch. This system 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, for transmitting torque to rear wheels responds to an electronically controlled clutch. 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 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.
It is impossible to say that Subaru with ACT have a "fake" all-wheel drive: unlike many models of other brands with plug-in rear axle here the thrust to the rear wheels is always supplied. But things still do not reach the "equal" ratio of 50:50, in general, 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, but in "civilian" even experienced driver is unlikely to determine which of the Symmetrical AWD variations is used.
Ivan KRISHKEVICH
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