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Toyota Prado four-wheel drive system
Toyota Prado (PRADO) Toyota Land Cruiser family's latest SUV. The new development of the next-generation SUV, equipped with Toyota's new 4.0LV6 engine emissions meet Euro Ⅲ standard. Prado (PRADO) advanced engine provides strong power output, together with the sturdy frame and enhanced suspension system so bumpy road to become comfortable and smooth. As a sport utility vehicle, four-wheel drive system can be described as a top priority. This article will introduce you to focus Prado (PRADO) equipped with full-time four-wheel drive system
For ordinary bevel gear differentials, whether inter-wheel differential or intermediate differential, because the planetary gear speed difference in the absorption due to internal friction generated by the rotation is very small, if not to limit it or lock only, if one side (or a shaft) wheel slip, the other wheels (or axles) is also the driving force is limited to the side of the wheel slip (or axis) of the driving force is equal to the tire can not be fully grip, affect the car's off-road. Prado (PRADO) chassis system uses a full-time drive mode, the layout of the three differentials: front, rear differential bevel gear differentials using ordinary, non-differential limiting and locking device, left and right both sides of the wheel slip through the TRC / VSC braking system to limit; intermediate differential use childcare Sen (TORSEN) T-3-type limited-slip differential. Domestic FAW Toyota Prado (PRADO) using 4BM actuator, can be achieved electronically controlled differential lock.
Full-time four-wheel drive system, the basic structure
Toyota Prado(PRADO)four-wheel drive system consists of the mechanical part of the transmission, actuator (available electronically controlled locking differential), front and rear drive shaft and front and rear differential sand other components.
Theel ectronically controlled four-wheel drive in part by the brake control ECU, the engine ECU, inter mediate differential locking button, parking and neutral position switch, 4WD control ECU and splitter electric actuator sand other components .Splitter electric actuator so perate according to the driver's wishes(center differential lock button), brake status, state of the engine operating speed, transmission gear status signal splitter for the differential lock stop control. The purpose of doing so is to facilitate the driver's operation, to ensure the transmission of switching actuator accurately and efficiently, avoid mechanical damage caused by misuse.
Splitter electric actuators
FAW Toyota Prado (PRADO) engine model 1GR-FE, transmission model A750F, its sub-actuators using improved VF4BM. Shown in Figure 2, actuator has two gear L and H, the transmission ratios of 2.566 and 1.000, L, H gear manually by the driver. According to road conditions and the driver to switch the "intermediate differential locking button" to carry on the differential lock, thus enabling H4F-H4L-L4F-L4L shift mode. H4F and L4F splitter for the corresponding high and low gear differentials "F" (free) mode, H4L and L4L was "L" (lock) mode. Other types of sub-actuator shown in Table 1, wherein VF2A splitter 2700 models used in the Prado, TORSENLSD the optional component.
Coming from the power transmission through the splitter and a subtransmission L or H gear spread differential gear casing, and then by the differential transmission mechanism within the power to the front, rear axle, 4WD control ECU for the splitter electric actuator control, drive "middle differential lock fork shaft" to achieve the intermediate differential lock switch.
TORSENLSD slip differential structure
TORSENLSD structure mainly by the differential housing, the planetary gear carrier, the planetary gear, a sun gear, a ring gear engaging gear, the sun gear wheel engaging the clutch disc, and four other components. The structure has eight planets and the sun gear and the ring gear external teeth meshing with each other, their mutual tooth meshing gears are TORSENT-3 type. When the ring gear and the sun gear of the speed ranges when (a drive shaft with slip tendency), will be forced to produce planetary rotation movement, this movement will lead to rotation with the ring gear or the sun gear relative axial movement. Axial movement of the pressure within the device installed in the clutch pressure plate, resulting in internal friction, thus limiting the relative movement, also limits the movement of the drive shaft to slip, and increase the torque of the drive shaft does not slip; sun wheel engaging with the sun gear wheel pair with each other, so that the sun wheel to the front coming from the PTO shaft. And put the ring gear engaging the ring gear teeth to the rear PTO shaft, thus engaging the teeth actually used for transmission of power transmission gear. As long as the front and rear wheels due to the adhesion surface due to changes in the torque changes, the differential will immediately produce than ordinary differential (non-limiting type) to a much larger internal friction torque. This method is also called differential limit torque-sensitive type.
Different driving conditions TORSENLSD torque distribution
The splitter switch to H4F or L4F mode, the differential is in "free mode", TORSENLSD have the following four operating states.
1 front axle rear axle speed equal to speed
When the car is driving in a good straight road, the front and rear wheel speed close to equal, that the sun wheel and the ring gear is equal to the angular velocity, the power of the transmission line shown in Figure 6. Shown in Figure 7, the sun wheel and the ring gear speed is equal, the planet gears not rotation movement, the internal friction differential is 0, the radius of the sun wheel and the ring gear ratio of 2:3, the torque of the front axle and the rear axle ratio of 2:3. Normal driving, the rear axle 60% of the torque obtained, to obtain 40% of the torque of the front axle. This torque distribution and quality of the car distribution corresponds to favor the use of the rear axle when the vehicle speed is greater than the front axle load cases, enhance vehicle tire grip to increase stability of the vehicle.
2 speed rear axle front axle speed is greater than
When the steering wheel or because of slippery roads lead to slip, the vehicle speed is greater than the front axle rear axle appears the situation. Ring sun gear wheel speed is greater than speed, relative movement between the forced rotation of the planetary gears. But because it is the ring gear and the sun gear meshing with each other, meshing with great friction profile angle, and the planetary gear carrier and it will produce friction between, so the rotation of the planetary gear over the friction force by , squeeze the 4th clutch disc. On the other hand, the ring gear is axially leftward movement, squeezing the 1st clutch disc. On the 4th friction clutch plate, limiting the high-speed continues to increase the rotational speed of the sun gear, the No. 1 of the friction clutch plate, put the power differential housing directly transmitted to the ring gear. From the above, the planetary gear and the clutch plate friction autobiography constitutes the friction torque of internal friction, thereby increasing the driving force of the rear axle. Before the rear axle torque distribution ratio can be up to 29:71, thus reducing the front axle torque, putting more driving force distribution to the rear axle attachment good condition. When the vehicle to achieve this torque distribution, the steering axle drive torque reduction, increased lateral adhesion, reduces steering skidding tendency operational stability has been improved, but also improve the car on slippery roads when through sex.
3 speed rear axle front axle speed is less than
When the ring gear speed is greater than the sun wheel speed, then the planetary gear also produces rotation, rotation time with the ring gear, the sun gear and the tooth will produce friction between the frame; while planetary gear axially to the left, the ring gear and the sun gear respectively, to the left, to the right to make axial movement, still squeezing the 1st ring gear clutch plate, squeeze the 2nd planetary gear clutch disc, sun wheel squeezing the 4th clutch disc, so high-speed rear axle by the 1st and 2, the friction clutch constraints while powered by the planetary gear carrier through the friction clutch plate 4 directly to the sun wheel, increasing the output torque of the front axle. By the internal friction of the differential 1, 2, 4, rotation of the planetary gear friction components, the front, the rear axle reaches the maximum torque distribution ratio 53:47.
4 locking center differential
If a smaller front wheel traction, slip trend emerged, automatically limits its slip differential, front-wheel drive is automatically reduced to 29%. If the wheel continues to decrease adhesion, but this time the front wheel drive force can be further reduced, not the rear axle slip torque is assigned to only 71%, at this time, the driver should locking differential, which kind of situation generally occurs in the morass of extraordinary bad road. If the front wheels off the ground (floating), the driving force of the wheel to 0, then if not locking differential, rear axle can only be assigned to 71% of the maximum driving force, but if locking the differential, rear axle can be assigned to 100% of the drive force.
豐田普拉多全時(shí)四驅(qū)系統(tǒng)
豐田普拉多（PRADO）是豐田陸地巡洋艦系列中的最新款SUV。這款全新開發(fā)的新一代SUV，配備了豐田全新4.0LV6發(fā)動機(jī)，排放達(dá)到歐Ⅲ標(biāo)準(zhǔn)。普拉多（PRADO）先進(jìn)的發(fā)動機(jī)提供強(qiáng)勁的動力輸出，配以堅(jiān)固的車架以及強(qiáng)化的懸架系統(tǒng)，使坎坷的路途變得舒適順暢。作為一款越野車，四輪驅(qū)動系統(tǒng)可謂是重中之重。本文將著重為您介紹普拉多（PRADO）裝備的全時(shí)四驅(qū)系統(tǒng)。
對于普通的錐形齒輪式差速器，不論是輪間差速器還是中間差速器，由于行星齒輪在吸收轉(zhuǎn)速差時(shí)因自轉(zhuǎn)而產(chǎn)生的內(nèi)摩擦力很小，假如不對其進(jìn)行限制或鎖止，只要有一側(cè)（或一軸）車輪滑轉(zhuǎn)，則另一車輪（或車軸）的驅(qū)動力也會被限制到與滑轉(zhuǎn)一側(cè)車輪（或一軸）的驅(qū)動力相等，不能充分發(fā)揮輪胎的抓地力，影響汽車的越野性。普拉多（PRADO）的底盤系統(tǒng)采用了全時(shí)驅(qū)動方式，布置了3個(gè)差速器：前、后差速器采用普通錐形齒輪式差速器，無差速限制和鎖止裝置，左、右兩側(cè)車輪的滑轉(zhuǎn)通過TRC/VSC系統(tǒng)以制動方式來限制；中間差速器采用托兒森（TORSEN）T-3型限滑差速器。國產(chǎn)的一汽豐田普拉多（PRADO）采用4BM分動器，可以實(shí)現(xiàn)對差速器的電控鎖止。
全時(shí)四驅(qū)系統(tǒng)的基本構(gòu)成
豐田普拉多（PRADO）四驅(qū)傳動系統(tǒng)的機(jī)械部分主要由變速器、分動器（可電控鎖止差速器）、前后傳動軸及前后差速器等組成。
四驅(qū)的電控部分由制動控制ECU、發(fā)動機(jī)ECU、中間差速器鎖止按鈕、駐車及空擋位置開關(guān)、4WD控制ECU和分動器電控執(zhí)行器等組成。分動器電控執(zhí)行器根據(jù)駕駛員的操作意愿（中間差速器鎖止按鈕）、汽車制動狀態(tài)、發(fā)動機(jī)運(yùn)行轉(zhuǎn)速狀態(tài)、變速器擋位狀態(tài)等信號對分動器內(nèi)的差速器進(jìn)行鎖止控制。這樣做的目的是為了便于駕駛員操作，確保分動器內(nèi)的傳動切換準(zhǔn)確有效，避免由于誤操作而造成的機(jī)件損壞。
分動器電控執(zhí)行器
一汽豐田普拉多（PRADO）的發(fā)動機(jī)型號為1GR-FE，變速器型號為A750F，其分動器采用經(jīng)過改進(jìn)的VF4BM。如圖2所示，分動器有L和H兩個(gè)擋位，傳動比分別為2.566和1.000，L、H擋位由駕駛員手動操作。駕駛員根據(jù)路面狀況切換“中間差速器鎖止按鈕”對差速器進(jìn)行鎖止，因而可實(shí)現(xiàn)H4F-H4L-L4F-L4L的換擋模式。H4F和L4F為分別對應(yīng)分動器高、低擋的差速器“F”（自由）模式，H4L和L4L則為“L”（鎖止）模式。其他類型的分動器如表1所示，其中VF2A分動器在普拉多2700車型上使用，TORSENLSD為選裝部件。
由變速器傳來的動力經(jīng)分動器的副變速L或H齒輪傳到差速器外殼齒輪，再經(jīng)差速器內(nèi)的傳動機(jī)構(gòu)把動力傳到前、后軸，4WD控制ECU對分動器電控執(zhí)行器進(jìn)行控制，驅(qū)動“中間差速器鎖止撥叉軸”實(shí)現(xiàn)中間差速器鎖的切換。
TORSENLSD防滑差速器結(jié)構(gòu)
TORSENLSD的結(jié)構(gòu)，主要由差速器外殼、行星齒輪架、行星齒輪、太陽輪、環(huán)形齒輪接合齒、太陽輪接合齒及4個(gè)離合器盤等組成。結(jié)構(gòu)中有8個(gè)行星齒輪與環(huán)齒和太陽輪齒內(nèi)外相互嚙合，它們之間相互嚙合齒輪的齒形屬于TORSENT-3型。當(dāng)環(huán)齒與太陽輪的轉(zhuǎn)速不等時(shí)（某一驅(qū)動軸有打滑趨勢），行星齒輪會被迫產(chǎn)生自轉(zhuǎn)運(yùn)動，這個(gè)自轉(zhuǎn)運(yùn)動又會導(dǎo)致與環(huán)齒或太陽輪的軸向相對運(yùn)動。軸向運(yùn)動的壓力對安裝在裝置內(nèi)的離合器盤施加壓力，產(chǎn)生內(nèi)摩擦力，因此限制了相對運(yùn)動，也就限制了打滑的驅(qū)動軸的運(yùn)動，而增加不打滑的驅(qū)動軸的扭矩；太陽輪與太陽輪接合齒相互配對，以便把太陽輪傳來的動力輸出到前驅(qū)動軸。而環(huán)形齒輪接合齒則把環(huán)齒的動力輸出到后驅(qū)動軸，因此接合齒實(shí)際上是用于傳遞動力的過渡齒輪。只要前、后驅(qū)動輪因地面附著力的變化而導(dǎo)致扭矩的變化，差速器會立即產(chǎn)生比普通差速器（非限制式）要大得多的內(nèi)摩擦扭矩。這種差速器的限制方式也叫扭矩敏感式。
不同行駛狀態(tài)TORSENLSD的扭矩分配
把分動器切換到H4F或L4F模式時(shí)，差速器處于“自由模式”，TORSENLSD有如下的4種工作狀態(tài)。
1.前軸轉(zhuǎn)速等于后軸轉(zhuǎn)速
當(dāng)汽車在良好路面直線行駛時(shí)，前輪與后輪的轉(zhuǎn)速接近相等，即太陽輪與環(huán)齒的角速度也相等，動力的傳動路線如圖6所示。如圖7所示，太陽輪與環(huán)齒轉(zhuǎn)速相等，行星齒輪不做自轉(zhuǎn)運(yùn)動，差速器的內(nèi)摩擦為0，太陽輪與環(huán)齒半徑之比為2:3，前軸與后軸的扭矩比為2:3。正常行駛時(shí)，后軸得到60%的扭矩，前軸得到40％的扭矩。這種扭矩分配方式與汽車的質(zhì)量分配相對應(yīng)，有利于利用車輛加速時(shí)后軸載荷大于前軸的情況下，提升車輛輪胎的抓地力，增加車輛的穩(wěn)定性。
2.前軸轉(zhuǎn)速大于后軸轉(zhuǎn)速
當(dāng)汽車轉(zhuǎn)向或因濕滑路面導(dǎo)致前輪打滑時(shí)，車輛則會出現(xiàn)前軸轉(zhuǎn)速大于后軸的情況。太陽輪轉(zhuǎn)速大于環(huán)齒轉(zhuǎn)速，兩者的相對運(yùn)動使行星齒輪被迫自轉(zhuǎn)。但是由于它與環(huán)齒和太陽輪齒相互嚙合，嚙合的齒形角產(chǎn)生很大的摩擦力，同時(shí)它與行星齒輪架之間也會產(chǎn)生摩擦力，因此行星齒輪的自轉(zhuǎn)受到以上摩擦力的作用，擠壓4號離合器盤。另一方面，環(huán)齒則沿軸向向左運(yùn)動，擠壓1號離合器盤。4號離合器盤的摩擦力，限制了高轉(zhuǎn)速的太陽輪的轉(zhuǎn)速繼續(xù)增加，1號離合器盤的摩擦力，則把差速器外殼上的動力直接傳遞到環(huán)齒。由上可知，行星齒輪自傳的摩擦力和離合器片的摩擦力構(gòu)成了內(nèi)摩擦力矩，從而增加了后軸的驅(qū)動力。前、后軸的扭矩分配比最大可達(dá)到29:71，從而減小前軸的扭矩，把更多的驅(qū)動力分配到附著狀況好的后軸。當(dāng)車輛實(shí)現(xiàn)這種扭矩分配后，轉(zhuǎn)向時(shí)前軸驅(qū)動扭矩降低，增加了側(cè)向附著力，可減小轉(zhuǎn)向側(cè)滑的趨勢，操作穩(wěn)定性得到了改善，同時(shí)也提高了汽車在濕滑路面行駛時(shí)的通過性。
3.前軸轉(zhuǎn)速小于后軸轉(zhuǎn)速
當(dāng)環(huán)齒轉(zhuǎn)速大于太陽輪轉(zhuǎn)速，此時(shí)行星齒輪也產(chǎn)生自轉(zhuǎn)，自轉(zhuǎn)時(shí)與環(huán)齒、太陽齒和齒架之間會產(chǎn)生摩擦阻力；同時(shí)行星齒輪沿軸向向左運(yùn)動，環(huán)齒和太陽輪分別向左、向右做軸向運(yùn)動，環(huán)齒仍然擠壓1號離合器盤，行星齒輪擠壓2號離合器盤，太陽輪擠壓4號離合器盤，因此，后軸的高轉(zhuǎn)速受到1號和2號離合器片摩擦力的限制，同時(shí)動力由行星齒輪架通過4號離合器盤的摩擦力直接傳遞到太陽輪，增加了前軸的輸出扭矩。差速器的內(nèi)摩擦力由1號、2號、4號和行星齒輪自轉(zhuǎn)摩擦力組成，使前、后軸的扭矩分配比最大達(dá)到53:47。
4.中間差速器的鎖止
假如前輪的地面附著力較小，出現(xiàn)了滑轉(zhuǎn)趨勢，差速器自動限制其滑轉(zhuǎn)，前輪驅(qū)動力自動降低到29％。若前輪附著力繼續(xù)減小，而此時(shí)前輪驅(qū)動力不能再降低，未滑轉(zhuǎn)的后軸所分配到的扭矩只能達(dá)到71％，此時(shí)，駕駛員應(yīng)該鎖止差速器，這種情況一般發(fā)生在非凡惡劣的泥沼路面。如前輪離開地面（懸空），該車輪的驅(qū)動力降為0，此時(shí)假如未鎖止差速器，后軸只能分配到71％的最大驅(qū)動力，但假如鎖止了差速器，后軸則可分配到100％的驅(qū)動力。