Home-Differentials explained
Differentials explained
Copied this from the jeepfan.com who copied it from somewhere on the web. :D The HRV has Conventional or Open Differentials which are good On Road and poor Off Road. Before anyone asks, ARB don't (currently?) make an Air Locker for either the HRV or the CRV. DIFFERENTIALS - WHAT'S THE DIFFERENCE? When a vehicle is negotiating a corner, the outside wheel has to travel a greater distance than the inside wheel. Therefore, the outside wheel must turn faster than the inside wheel. The differential is the device within the axle assembly which, in addition to transmitting the power to each axle shaft/wheel, allows one wheel to turn at a different speed than the other. What types of Differentials are there? Conventional or Open Limited Slip Automatic Locking Manual Locking Conventional differential uses two side gears inside the differential case. Each gear is splined to accept an axle shaft. These side gears are in turn driven by a set of spider gears. The spider gears, also inside the differential case, ride on a shaft which is pinned into the differential case and through which all the power is transmitted. The case is driven by the ring gear which is bolted fast to the case. The conventional differential is fitted as standard equipment on most vehicles. On paved roads this system is very successful, giving predictable handling, even tire wear and requiring very little maintenance. However, in off road situations where traction surfaces vary greatly, this type of differential has a major limitation. When one wheel has greater traction than the other, all the power will be directed to the wheel with the least traction. For example, if one wheel is in the air and the other wheel is still on a hard surface, then all the power will be transferred to the wheel in the air. No power will go to the one on the ground and the vehicle will not move. Limited slip differentials (LSD's) come in a variety of designs. Most use friction plates, cones and/or gears to reduce slippage between each of the tires. these units have a dual power path from the differential case to the axle shafts. some power is transmitted through the spider gears to the side gears in the conventional manner. The remainder is transmitted by friction between the differential case and the clutch plates and the side gears. A certain amount of "clutch preload" is built into the unit in a static condition. Then, as load is applied to the differential, the separation forces between the spider gears and the side gears increases this clutch loading. This increase in friction provides for a good positive power flow from the case directly to the side gears. When traction is available to both wheels, the power going to the differential causes the plates to bind tightly together, giving even power to both wheels. However, in a situation where there is little or no traction available to either one wheel or the other, the amount of power that can be transmitted to the other wheel which has traction is dependent on the friction or "preload" in the clutch plates. High levels of "clutch preload" will result in good torque transfer but some chattering of the clutches during cornering may occur. Lower levels of preload results in minimal chatter but reduced levels of torque transfer to the wheel with traction. Because LSD's restrict true differential action, tire wear is accelerated. Changes in vehicle handling may also occur, particularly in short wheelbase vehicles. Wear rates on limited slip differentials are generally higher than on other types due to the reliance on friction to reduce wheel slippage. Also, special lubricants may be required to minimize rough and noisy operation. Despite their limitations, LSD's are popular as original equipment options as well as an aftermarket replace because: Some traction improvement off road is provided Vehicle handling idiosyncrasies are not excessive Installation is simple Cost is reasonable Automatic locking differentials transmit power to each wheel through a pair of dog clutches. Differential action, such as when cornering is provided by automatically disengaging the appropriate clutch when one wheel rotates faster than the other. This results in differential action which occurs in ratcheting stages rather than being smooth and progressive. Power received by the differential is automatically directed to the wheel with greater traction. Therefore, if one wheel is lifted off the ground, the other wheel will receive the total power applied to the differential to maintain vehicle mobility. Traction is far superior to conventional and limited slip differentials. While automatic locking differential provide excellent performance off road, vehicle handling, particularly on highway, is sacrificed. Unlocking during cornering can be sudden, resulting in a rapid change of direction, particularly in short wheel based vehicles. During sharp cornering an audible racheting sound usually occurs as differential action takes place and a loud banging noise may be heard when the unit locks up again. Tire wear usually increases. On 4WD vehicles, installation is normally considered for the rear axles only. Front axle installations can cause extreme difficulties in steering. Manually lockable differentials use a conventional differential in conjunction with a mechanical locking device which can be operated at the drivers's discretion. when locked, both axles will then turn at the same speed irrespective of the road surface. When it is unlocked, the differential functions as a conventional differential giving predictable handling, long service life and no increase in tire wear. It can be installed in both the front and rear axles without compromising on-road performance. Although manually lockable differentials are available in tractors and some military style vehicles, the installation in mass produced recreation type vehicles have been restricted by high cost and complexity of installation. The ARB Air Locker has allowed this situation to be reversed. This unique air operated unit incorporates its activating mechanism totally inside the differential center. This avoids the need to have complicated piston arrangements hanging off the axle housing. Locking action is controlled by the drive with a push button switch inside the cab. Installation involves a bolt in replacement of the original equipment differential center, a 12 volt air compressor with reservoir and an in-vehicle mounted switch. Original equipment axles, bearings, etc. are retained. Locking/Unlocking of the unit is extremely rapid approximately 0.1 seconds) and may be achieved at any vehicle speed. No special maintenance is required and servicing of other vehicle components is unaffected. Standard lubricants are used. The ARB Air Locker is the ultimate differential for almost any vehicle providing 100% drive to each wheel, without handling problems, or additional wear problems. How would you thnk we, H and C owners, could make up for the lack of differencial locks? From my little experience, I would say CR-V's relatively good accelation may work in some cases. That's to day, speed. Would you have any other suggestions? my experience says, that the only thing to compensate the lack of locking diff is to choose a direction where you can estimate at least 3 wheels to stick to the ground. it needs some 3D thinking capabilities but it works. and if the surface is too slippery - pick another route. speeding may turn out completely wrong on terrain. How would you think we, H and C owners, could make up for the lack of differencial locks? IMO you can't 'make up for lack of differential locks'. Either you have them when you need them, or you don't (which is our case). :( Having said that, I agree with mrtn that carefully choosing exactly where you drive ensuring at least three tyres stick to the ground decrease the inconvenience on rocky/uneven terrain, however this doesn't help when driving in mud or sand. From my little experience, 'little experience' = bulls**t. :D I've seen your website and 'little' is not the word I'd use to describe the amount of off-road driving you do. :D I would say CR-V's relatively good accelation may work in some cases. That's to say, speed. I agree with this statement. Would you have any other suggestions? The following provides an indication of how I drive when off road. Sand/muddy roads/dirt roads = relatively fast (2nd gear and above). Very rocky/uneven surface = slowly (1st and 2nd gear). As mrtn says carefully choosing exactly where you drive ensuring at least three tyres stick to the ground. Water 20cm+ = slowly (Higher revs 1st and exceptionally 2nd gear). Remember that neither the HRV or CRV are hardcore 4WDs, there are (some) 2WDs that are better off road. mrtn and freelnce, thanks for your valuable comments! This Sunday I had a chance of going through a heavily muddy trail with a Nissan Terrano. The trail was of a typical W-form. As snow had started melting, the bottoms of the two V-forms that were pressed by tires became very muddy. Yet, on the middle of the trail there still remained a relatively hard mountain-like zone, as the earth had been more or less iced. In the course of one or two kilometers on the trail, my V got stuck once, while the Terrano stopped nearly ten times. Terrano has an LSD, and of course a full-time 4WD. Both vehicles were on M/T tires. Whenever the Nissan got stuck and the driver tried to get out, it looked to me that all of the 4 wheels were spinning very slowly at the same speed. I would understand this is thanks to LSD and/or a low gear? Yet, Terrano never made it to get out itself. Why? Because the vehicle had got always comfortably sitting on the middle mountain-like zone, i.e. being blocked at the lowest points (central differentials?). And why my V was almost able to get through, being stucked just once? The only reason I can think of is that my V is more lifted up than the Terrano. From my "little" experince, when a vehicle gets stuck and loses traction on one or more tires, very often the vehicle itself is more or less "blocked", being "raised" on something, e.g. mud, sand. In such a situation, whether the activation of diff. lock will make a big difference, which is my honest question. I don't want to be arrogant. Still I am yet to be convinced that the availability of diff. lock is so significant that the lack of it can not be compensated by means of other measures, like M/T tires, lifting up. From my "little" experince, when a vehicle gets stuck and loses traction on one or more tires, very often the vehicle itself is more or less "blocked", being "raised" on something, e.g. mud, sand. In such a situation, whether the activation of diff. lock will make a big difference, which is my honest question. I don't want to be arrogant. Still I am yet to be convinced that the availability of diff. lock is so significant that the lack of it can not be compensated by means of other measures, like M/T tires, lifting up. Wataken this is a good question. I'll explain this to the best of my ability, I'm happy for others to correct or elaborate on the following. Lets do some hypotheticals based on the following vehicles which are the same make and model. VEHICLE1 has a 3 inch lift and large MT tyres. VEHICLE2 has differential lockers, but is standard in all other respects (no lift and has road tyres). VEHICLE3 has differential lockers, a 3 inch lift and large MT tyres. Example 1. VEHICLE1 and VEHICLE2 do the same trip you did with the Terrano. VEHICLE1 gets stuck once. VEHICLE2 having insufficient ground clearance (like the Terrano) would get stuck more often with all tyres spinning in the air. In this case you are correct that additional ground clearance and MT tyres were more beneficial than the differential lockers on a vehicle with less ground clearance. Example 2. VEHICLE1 and VEHICLE3 do the same trip you did with the Terrano. VEHICLE1 gets stuck once. VEHICLE3 (having the same ground clearance as VEHICLE1) doesn't get stuck as even if it has lost traction on 3 tyres, the 4th tyre keeps pushing the vehicle forward. In this case, the vehicle with the differential lockers will be stuck less often in mud (or sand) due to all 4 tyres driving the vehicle. Example 3. VEHICLE1 and VEHICLE3 go driving in very rocky uneven terrain. Whenever VEHICLE1 has two tyres loosing traction it will cease moving (ie a front tyre on a rock lifting the opposite tyre and a rear tyre over a pot hole). Whenever VEHICLE3 has two tyres (or even three if on a ledge) loosing traction, it will keep moving. Once again in this example the vehicle with the differential lockers has the advantage over the vehicle without. In conclusion I agree that to a certain extent a vehicle can be set up (i.e. lift and better tyres) to compensate for the lack of differential locks. However, I don' think you can deny that if there are two vehicles the same, with only one having differential lockers, the one with the differential lockers will go alot further off road than the one without. The following links might also help explaining differential lockers. http://www.safari4x4.com.au/80scool/george_couyant/diffs/diffs.html http://www.pocuk.com/faq/4x4explained.htm In conclusion I agree that to a certain extent a vehicle can be set up (i.e. lift and better tyres) to compensate for the lack of differential locks. However, I don' think you can deny that if there are two vehicles the same, with only one having differential lockers, the one with the differential lockers will go alot further off road than the one without. Yes, of course, you are right. I will never deny the advantage of a vehicle with the diff. lock. The fact is, though, mine (also yours) is without one, and despite that I've been more and more fascinated with driving where you could not on a normal car like Accord, which I had possessed before. Since CR-V is my only vehicle, and since I have nothing to complain about its utility as an everyday vehicle, the sole question I have is to what extent I can enjoy going off road on it. Please take a look at the below two pictures. They are a record of my failure or I would say DEFEAT from last Sunday. I reached the point on the second picture THREE times, and yet the result was that I was winched out. I confess that this was really shocking to me. I think it was a good example where disadvantages of the CR-V were demonstrated: -- the lack of real 4WD -- the lack of a low gear -- the lack of a differential lock -- too short strokes, etc. The surface was so uneven that the vehicle was hardly on a full traction of the four wheels. Yet, I would rather say the reason was basically due to my still POOR driving skill. The first failure immediately made me so nervous that I was never able to go back as much as I could have. Spectators cried I should go back further, but I failed to do so, simply I was in such a panic. The result was that I restarted on the middle of the slope. The vechile had no time to gain enough speed and was not able to pass the last point, where it was suspended. Maybe I am wrong. Maybe it was too much for the CR-V. Yet I would believe there still remains quite a lot for me to draw out the maximum potentiality of the vehicle. The second pic for the above post. I think it was a good example where disadvantages of the CR-V were demonstrated: -- the lack of real 4WD -- the lack of a low gear -- the lack of a differential lock -- too short strokes, etc. Yes... Maybe it was too much for the CR-V. Maybe...but at least you had a go. :) Yet I would believe there still remains quite a lot for me to draw out the maximum potentiality of the vehicle. I think you do very well off road with your CR-V. :) Question. Do you think more power would have helped you get up that hill? The big tyres on your CR-V decrease its torque, would a Supercharger have helped...? :D Also, maybe you are now reaching the off road limits of what the CRV is capable. If you want to continue off roading in more and more difficult terrain, it might be time to consider buying a 'real' 4X4? Question. Do you think more power would have helped you get up that hill? The big tyres on your CR-V decrease its torque, would a Supercharger have helped...? :D Frankly sepaking, I don't know. I would assume that it was more because of the above mentioned disadvantages of the CR-V plus my poor driving skill than because of the lack of power. Yet, if something like a Supercharger can be mounted on it, I will be very interested. Will you have a concrete suggestion? Also, maybe you are now reaching the off road limits of what the CRV is capable. If you want to continue off roading in more and more difficult terrain, it might be time to consider buying a 'real' 4X4? Negative background: I still have three years to pay off the credit for my CR-V and have no money to clear it now! :? Positively speaking, I believe it is too early to make a final evaluation. I am sure that CR-V's off road capability is much better than it is said generally, but where could be the limits? This is an interesting question. Coming back to your initial issue of the thread, no doubt that Vehicle 3 is superior to Vehicle 1. I can never be more than of the Vehicle 1 level. Yet, between Vehicle 1 and Vehicle 3 levels there can be a lot of variations, and this is where we can make a fun. For instance, there can be a question. Which is better permorming on mud, CR-V with M/T tires or Land Cruiser with A/T tires? I have been involved in such a situation several times and so far I have no reason to say the latter is better. BTW, why don't you post some pictures from your off-roading? I'll be happy to see HR-V off-roading in Australia :) Wataken, As we are starting to deviate from this topic thread, I've answered your post under 'HRV:General Opinions, Commentaries, and Observations' under the new topic heading of 'General off roading discussion'. Here's the link. http://www.hondasuv.com/main2/viewtopic.php?p=15958#15958 Cool! Thanks to everybody! All of yout info is highly appreciated by my HR-V! |
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