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資料來(lái)源： True Four Wheel Drive System For Vehicle Four Wheel Drive System For Vehicle真正的四輪驅(qū)動(dòng)車輛ABSTRACTA drive train for a four wheel drive vehicle including a front difforential engaged with a front drive shaft and front axles through a front differential gear set. The front differential includes a front bi-directional overrunning clutch that con-trols transmission of torque transfer between the front drive shaft and the front axles. A rear differential is engaged with rear axles and the transmission through a rear differential gear set. The rear differential includes a rear bi-directional over-running clutch that controls torque transfer between the trans-mission and the rear axles. The differentials are configured with a gear ratio that is within five percent of a l: 1 gear ratio.TRUE FOUR WHEEL DRIVE SYSTEM FOR VEHICLERELATED APPLICATIONThis application is related to and claims priority from U.S. Provisional Application 61/677,820, the disclosure of which is incorporated herein by reference in its entirety.FIELD OF THE INVENTIONThe invention relates to drive systems and, more particularly, to an improved drive system designed to provide substantially true four wheel drive capability.BACKGROUNDprovide four wheel drive capability. Those systems are all designed to engage all four wheels but also allow a speed differential across the axle. However, many of those systems do not provide true four wheel drive where each wheel pro-vides substantially the same speed during all drive conditions. Instead, the systems permit some degree of slippage. Current Four Wheel Drive Bi-Directional Overrun-ning Clutch Systems I illustrates the drive system for a conventional four wheel drive vehicle with a front bi-directional over-rul111ing clutch. The drive system includes four wheels. The rear left wheel RLW is connected to a rear differential RD through a rear left axle RLA. The right rear wheel RRW is com1ected to the rear differential RD through a rear right axle RRA. The front left wheel FLW is col111ected to a front dif-ferential FD through a front left axle FLA. The front right wheel FRW is connected to the front differential FD through a front right axle FRA.mission T through a rear drive shaft RDS. The front differen-tial FD is connected to the transmission T through a front drive shaft EDS. Straight Line Operation: During straight line driving while the vehicle is in a four wheel on demand mode (i.e., four wheel drive engages only when needed) both rear wheels RLW, RRW are the primary drive wheels and are co1111ected through the rear differential RD to rotate at the same speed. In a non-slip condition of the rear wheels, the front drive shaft FDS is engaged to the front differential FD, but the front axles FLA, FRA are not engaged with the front differential. That is, the front axles FLA, FRA and front wheels FLW, FRW are gen-erally in an overrun condition such that the front differential FD is not driving the front axles FLA, FRA and, therefore, not transmitting any torque to the front wheels. This means that the front wheels FLW. FRW are free to rotate at their actual ground speeds. In order for the front wheels to be engaged, the rear wheels must slip (break traction) or spin increase speed approximately 20% faster than the front wheels. While driv-ing in a straight line, once the rear wheels slip 20%, the overrunning condition in the front differential ED is over-come and both front axles are engaged. This results in the transmission T transmitting torque to the front wheels thru the front drive which is geared in a way that decreases the vehicles ground speed. When the ground speed has increased so as to cause the rear wheel speed to be rotating less than 20% faster than the ground speed, or the speed of the rear wheel has decreased so as to be rotating less than 20% faster than the ground speed, the front wheels will start to overrun again and no torque will be transmitted to the front wheels. Turning Operation: In a comer all four wheels are trying to rotate at different speeds, This is shown on the chart in FIG. 4 which depicts wheel revolutions vs. turning radius for all four wheels. For a vehicle with alocked rear axle or solid axle (i.e., an axle where the rear axles RLA, RRA are connected, either physically or through gearing, such that they always rotate at the same speed) the ground speed is dictated by the rear outside wheel due to vehicle dynamics (i.e., the rear outside wheel has to cover more circumferential distance than the rear inside wheel when turning around a common axis.) Since both rear wheels are rotating at the same speed and the rear outside wheel is the drive wheel the rear inside wheel is beginuing to scrub or drag on the ground. This can cause inefficiencies, turf wear and/or tire wear. The primary reason conventional bi-directional ovemnming clutch four wheel drive systems have a 20% under drive is for turning. With the rear outside wheel dictat-ing ground speed the front inside wheel will go slower than the rear outside wheel as shown in FIG. 4. If there is no under drive the bi-directional oveITllllling clutch for the front inside axle would engage and begin to drive torque. This would cause the front inside wheel to travel at an incorrect speed and would create inefficiencies, turf wear, tire wear and, more importantly, torque steer.As mentioned above, during a tum the rear outside wheel is dictating ground speed, the rear inside wheel is scrubbing or dragging, and the front wheels are overrunning. Referring to FIG. 5 which depicts the percentage difference between the front and rear wheel speeds versus the turning radius of a locked rear axle, once the rear outside wheel slips or spins a certain percentage, dictated by vehicle geometry and turning radius. the bi-directional overru1ming clutch con-trolling the transfer of torque to the front inside wheel will engage and drive torque through the front inside wheel At this time both rear wheels and the front inside wheel are driving torque and their speed is dictated by the drive line, not ground speed. The front outside wheel is still ovemmning allowing it to spin at the rotational speed dictated by ground speed and vehicle geometry. When both rear wheels and the front inside wheel slip a certain percentage, again dictated by vehicle geometry and the turning radius, the bidirectional clutch con-trolling torque transfer to the front outside wheel will engage and torque will be transmitted to all four wheels, even though three of the wheels would be slipping. Wedging The existing drive system is prone to a condition called wedging. Wedging occurs when torque is being driven through the bidirectional over-numing clutch and a rapid direction change occurs. This can cause the rollers in the clutch to be positioned or locked on the wrong side of the clutch profile preventing the output hubs from overru1ming. The effect causes the front drive to act like a solid axle, but with the 20% speed difference in the drive line it results in scrubbing of the front tires. This condition can cause exces-sive tire wear and turf wear. This also effects steering effort and stability of the vehicle. The vehicle will try to maintain a straight line due to the effect of the front drive acting like a solid axle.Because of the wedging condition in the current systems precautions are put into place to help reduce wedging. One of these precautions is the use of a cut-off switch so that when the vehicle is shifted from the forward direction to the reverse direction so as to automatically disengage the bi-directional overrum1ing clutch (for example, shutting off the coil that is indexing the roll cage). This system also uses the cut-off switch when transitioning from the reverse direc-tion to the forward direction. Another way to reduce wedging is the use of a switch, when the brakes are applied, that will interrupt power to the 4 wheel drive system. Many other methods can be used to reduce wedging, but none are 100% percent effective with the 20% difference in drive line speeds. Conventional Drive Systems:A common conventional drive system would have the same vehicle layout as in FIG. 1, but the mechanisms in the front and rear differentials would be different. Most com-mon drive systems have an open differential with the ability to be locked into a solid axle in both the front and rear differen-tials. The drive line in a conventional system would also be using a drive line that is geared to a 1: 1 ratioStraight Line Operation: During straight line driving while the vehicle is in four wheel drive and all the axles are unlocked, all four wheels are rotating at the same speed. This is due to the drive line being geared at 1:1 ratio and the front and rear differen-tials are being driven at the same speed and no differentiation is needed across the axles. This is also the case when any or both of the front and rear differentials are in a locked position creating a solid axle. Turning operation:Conventional four wheel drive systems will nor-mally have the rear differential locked and the front drive will be in the open state until the solid axle mode is selected by the user. During turning with a solid axle in the rear differential and an open differential in the front, only one tire is turning at the correct ground speed. Due to vehicle dynamics the rear outside wheel is considered the drive wheel and is turning at ground speed. The inside rear wheel is being driven at the same speed as the rear outside, but the ground speed is slower. This causes the inside rear wheel to scrub or slip during a tum. (0023] Since the two front wheels are connected to an open differential, they are allowed to differentiate across the axle, However, the differential is being driven at an incorrect speed. That is, the front open differential takes the input speed and averages it across the axle. In a normal non slip condition the average speed across the axle is centered about the middle of he vehicle. Since the rear outside wheel is traveling at a different speed ( or arc) than the average of the two front wheels, both front wheels are scrubbing when in a tum caus-ing un-needed drive line torque or drive line bind. Once the operator selects the solid axle mode of the vehicle, both front wheels are locked together and they now rotate at the same speed. When turning, the outside front wheel is going slower than what ground speed dictates, thus causing the wheel to scrub. At the same time the inside front wheel is going faster than the ground speed dictates causing it to, likewise, scrub. Due to the wheels being driven at the wrong speeds in a comer, conventional drive systems are not very efficient. They cause severe turf damage or wear due to the tires scrub-bing. They also cause tire wear due to the scrubbing. The tires being driven at the wrong speeds also cause issues with steer-ing and turning performance of the vehicle. The difference between ground and actual wheel speed results in the wheels trying to straighten the vehicle out. This cause's increased wear in steering components, as well as rider fatigue since increased input is needed to maintain the vehicle in the tum. Many manufacturers have added power steering to try to minimize operator input when cornering because of the four wheel drive operations. A need therefore exists for an improved four wheel drive system that incorporates bi-directional overrunning clutches in a drive system that minimizes scrubbing in all wheels while permitting 1.1 or near 1: 1 gear ratio between the front and rear axles. SUMMARY OF THE INVENTIONThe present invention is directed to drive train for a four wheel drive vehicle. The drive train includes a front drive shaft connected to a transmission. Two front axles with each axle connected to a corresponding front wheel. A front dif-ferential is engaged with the front drive shaft and the front axles through a front differential gear set. The front differen-tial includes a front bi-directional overrunning clutch that controls transmission of torque transfer between the front drive shaft and the front axles. The front bi-directional ovemmning clutch includes a front clutch housing connected to the front drive shaft so as to be rotatable by the front drive shaft, the front clutch hous-ing including an inner cam surface. A front roller assembly is located inside the front clutch housing and adjacent to the cam surface. The front roller assembly includes a roll cage with a plurality of rollers arranged in two sets within slots formed in the roll cage, the rollers are rotatable inside the slots. A plurality of springs are arranged in the roll cage to position the rollers within the slots. The roll cage is rotatable within the front clutch housing. (0029] Two front hub are located in the front clutch hous-ing. Each hub is positioned radially inward from a set of the rollers located between an outer surface of the front hub and the im1er cam surface. Each front hub is engaged with an axial end of one of the front axles so as to rotate in combination with the axle. The front hubs are independently rotatable within the roll cage and the front clutch housing. A front engagement control assembly is located within the housing and controls engagement and disengage-ment of the front bi-directional overrunning clutch. The front engagement control assembly includes an electromechanical device that is controllable for impeding rotation of the roll cage relative to the front clutch housing so as to index the roll cage relative to the front clutch housing. When the engagement control assembly is activated and the roll cage is indexed relative to the clutch housing, the front bi-directional overrunning clutch is configured to trans-mit torque from the front drive shaft to the front axles when the front clutch housing is rotating faster than the front axles. Also, when the vehicle is traveling straight the front differen-tial is configured to begin to transmit torque from the front drive shaft to the front axles at a first speed. The gear train including two rear axles, each axle com1ected to a corresponding rear wheel. A rear differential is engaged with the rear axles and the transmission through a rear differential gear set. The rear differential including a rear differential housing and a rear bi-directional overrunning clutch that controls torque transfer between the transmission and the rear axles. The rear bi-directional overrunning clutch includes a rear clutch housing located within the rear differential !mus-ing and rotatable by the transmission, the rear clutch housing including an inner cam surface. A rear roller assembly is located inside the rear clutch housing and adjacent to the cam surface. The rear roller assembly includes a roll cage with a plurality of rollers arranged in two sets within slots formed in the roll cage. The rollers are rotatable inside the slots. A plurality of springs are arranged so as to position the rollers within the slots. The roll cage is rotatable within the rear clutch housing.Two rear hubs are located in the rear clutch housing. Each hub is positioned radially inward from a set of the rollers located between an outer surface of the rear hub and the im1er cam surface. Each rear hub is engaged with an axial end of one of the rear axles so as to rotate in combination with the axle. The rear hubs are independently rotatable within the roll cage and the rear clutch housing.The rollers in each set of the rear roller assembly are adapted to wedgingly engage the corresponding rear hub to the rear clutch housing when one of either the rear hub or rear clutch housing is rotating faster than the other so as to trans-mit torque from whichever is faster to whichever is slower. The differentials are configured such that when the vehicle is traveling straight and the rear differential is trans-mitting torque to the rear axles. The rear differential is con-figured to rotate the rear axles at a second speed, and where the difference between the first speed and the second speed is five percent or less. In one preferred embodiment, the differ-ence between the first speed and the second speed is less than about three percent. In another embodiment there is substan-tially no difference between the first speed and the second speed.In one embodiment, the front bi-directional over-running clutch includes an armature plate that is engaged or connected with the front roll cage such that the armature plate rotates with the roll cage. The front engagement control assembly impedes rotation of the roll cage relative to the front clutch housing by engaging the amiature plate so as to index the roll cage relative to the clutch housing.Preferably the hubs are substantially coaxially aligned with each other within the housing. and are adapted to rotate about a common axis within the housing. In one embodiment, the rear differential is part of a transaxle which is engaged with the transmission. 。In another embodiment the front differential is part of a transaxle which is engaged with the transmission. The foregoing and other features of the invention and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments, as illustrated in the accompanying figures. As will be realized, the invention is capable of modi-fications in various respects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive.摘要一種用于四輪驅(qū)動(dòng)車輛的傳動(dòng)系統(tǒng)，包括與前驅(qū)動(dòng)軸接合的前差速器和通過(guò)前差速齒輪組的前軸。 前差速器包括前雙向超越離合器，其控制前驅(qū)動(dòng)軸和前軸之間的扭矩傳遞的傳遞。 后差速器通過(guò)后差速齒輪組與后軸和變速器接合。 后差速器包括控制變速器和后軸之間的扭矩傳遞的后雙向超越離合器。差速器構(gòu)造成具有百分之五內(nèi) 1：1 的齒輪比誤差比。真正的四輪驅(qū)動(dòng)系統(tǒng)車輛相關(guān)申請(qǐng)本申請(qǐng)與美國(guó)臨時(shí)申請(qǐng) 61 / 677,820 相關(guān)并要求其優(yōu)先權(quán)，其公開(kāi)內(nèi)容通過(guò)引用整體并入本文。本發(fā)明涉及驅(qū)動(dòng)系統(tǒng)，更具體地，涉及一種設(shè)計(jì)成提供基本上真實(shí)的四輪驅(qū)動(dòng)能力的改進(jìn)的驅(qū)動(dòng)系統(tǒng)。背景提供四輪驅(qū)動(dòng)能力。 這些系統(tǒng)都被設(shè)計(jì)成接合所有四個(gè)車輪，但也允許在車軸上有速度差。 然而，這些系統(tǒng)中的許多不提供真正的四輪驅(qū)動(dòng)，其中每個(gè)輪在所有驅(qū)動(dòng)條件期間提供基本相同的速度。 相反，系統(tǒng)允許一定程度的滑動(dòng)。正確的四輪驅(qū)動(dòng)雙向超越離合器系統(tǒng)圖 1 示出了用于具有前部雙向超越離合器的常規(guī)四輪驅(qū)動(dòng)車輛的驅(qū)動(dòng)系統(tǒng)。 驅(qū)動(dòng)系統(tǒng)包括四個(gè)輪子。 后左輪 RLW 通過(guò)后左輪軸 RLA 連接到后差速器 RD。 右后輪 RRW 通過(guò)右后輪 RRA 連接到后差速器 RD。 前左輪 FLW 通過(guò)左前車軸 FLA 與前差速器 FD 連接。右前輪 FRW 經(jīng)由右前輪 FRA 與前差速器 FD 連接。單元 T 通過(guò)后傳動(dòng)軸 RDS。 前差速器 FD 通過(guò)前驅(qū)動(dòng)軸 EDS 連接到變速器 T.直線操作在車輛處于四輪按需模式（即，四輪驅(qū)動(dòng)僅在需要時(shí)接合）的直線行駛期間，兩個(gè)后輪 RLW，RRW 都是主驅(qū)動(dòng)輪，并且通過(guò)后差速器 RD 聯(lián)接以旋轉(zhuǎn) 以相同的速度。 在后輪的防滑狀態(tài)下，前驅(qū)動(dòng)軸 FDS 接合到前差速器 FD，但是前軸 FLA，F(xiàn)RA 不與前差速器接合。 也就是說(shuō)，前軸 FLA，F(xiàn)RA 和前輪 FLW，F(xiàn)RW 通常處于超速狀態(tài)，使得前差速器 FD 不驅(qū)動(dòng)前軸 FLA，F(xiàn)RA，因此不向前輪傳遞任何扭矩。 這意味著前輪 FLW。 FRW可以以其實(shí)際地速度自由旋轉(zhuǎn)。為了使前輪接合，后輪必須滑動(dòng)（斷開(kāi)牽引）或旋轉(zhuǎn)增加速度比前輪快大約 20％。 當(dāng)在直線上行駛時(shí)，一旦后輪滑動(dòng) 20％，則克服前差速器 ED 中的超速狀況，并且兩個(gè)前軸接合。 這導(dǎo)致變速器 T 通過(guò)以減小車輛地速的方式來(lái)使變速的前驅(qū)動(dòng)器將扭矩傳遞到前輪。 當(dāng)?shù)厮僭黾右灾率购筝喫俣缺鹊厮俚男D(zhuǎn)小于 20％，或者后輪的速度已經(jīng)減小以便比地速更快地旋轉(zhuǎn)小于 20％時(shí) ，前輪將再次開(kāi)始超速，并且沒(méi)有扭矩將被傳遞到前輪。轉(zhuǎn)向操作：在角落中，所有四個(gè)輪子都試圖以不同的速度旋轉(zhuǎn)。這在圖 1 中的圖表上示出。 圖 4示出了所有四個(gè)車輪的車輪轉(zhuǎn)數(shù)對(duì)轉(zhuǎn)彎半徑。 對(duì)于具有鎖定的后軸或?qū)嵭妮S（即，其中后軸 RLA，RRA 被物理連接或通過(guò)齒輪連接，使得它們總是以相同的速度旋轉(zhuǎn)的軸）的車輛，地速由后外側(cè) 由于車輛動(dòng)力學(xué)（即，當(dāng)圍繞公共軸線轉(zhuǎn)動(dòng)時(shí)，后外輪必須覆蓋比后內(nèi)輪更多的圓周距離） 。由于兩個(gè)后輪以相同的速度旋轉(zhuǎn)，并且后外輪是驅(qū)動(dòng)輪 后內(nèi)側(cè)輪開(kāi)始在地面上擦洗或拖曳。 這可能導(dǎo)致效率低下，草皮磨損和/或輪胎磨損。主要原因是傳統(tǒng)的雙向四通離合器四輪驅(qū)動(dòng)系統(tǒng)力的 20%用于轉(zhuǎn)向。 由于后外輪確定地速，前內(nèi)輪將比后外輪慢，如圖 3 所示。 如果沒(méi)有低于驅(qū)動(dòng)，用于前內(nèi)軸的雙向偏心離合器將接合并開(kāi)始驅(qū)動(dòng)扭矩。 這將導(dǎo)致前內(nèi)側(cè)車輪以不正確的速度行駛，并且將產(chǎn)生低效率，草皮磨損，輪胎磨損，并且更重要的是，扭矩轉(zhuǎn)向。如上所述，在轉(zhuǎn)彎期間，后外輪輪流地面速度，后內(nèi)輪是擦洗或拖曳，并且前輪是超速的。參考圖 1。圖 5 示出了一旦后外輪滑動(dòng)或旋轉(zhuǎn)一定百分比（由車輛幾何形狀和轉(zhuǎn)彎半徑?jīng)Q定）時(shí)，前后車輪速度相對(duì)于鎖定后車軸的轉(zhuǎn)動(dòng)半徑的百分比差異。控制到前內(nèi)輪的轉(zhuǎn)矩傳遞的雙向超越離合器將接合并通過(guò)前內(nèi)輪驅(qū)動(dòng)轉(zhuǎn)矩。此時(shí)，后輪和前內(nèi)輪都是驅(qū)動(dòng)轉(zhuǎn)矩，并且它們的速度由驅(qū)動(dòng)線決定，不是地速。前外輪仍然是超速的，允許其以由地速和車輛幾何形狀決定的旋轉(zhuǎn)速度旋轉(zhuǎn)。當(dāng)兩個(gè)后輪和前內(nèi)輪滑動(dòng)一定百分比，再次由車輛幾何形狀和轉(zhuǎn)彎半徑?jīng)Q定時(shí)，控制到前外輪的扭矩傳遞的雙向離合器將接合，并且扭矩將被傳遞到所有四個(gè)車輪中，即使其中的三個(gè)車輪將滑動(dòng)。楔入現(xiàn)有的驅(qū)動(dòng)系統(tǒng)傾向于稱為楔入的狀態(tài)。 當(dāng)扭矩通過(guò)雙向超越離合器被驅(qū)動(dòng)并且發(fā)生快速方向改變時(shí)，發(fā)生楔入。 這可能導(dǎo)致離合器中的輥定位或鎖定在離合器輪廓的錯(cuò)誤側(cè)上，從而防止輸出輪轂過(guò)度磨損。 該效果使得前驅(qū)動(dòng)器像實(shí)心軸一樣起作用，但是在驅(qū)動(dòng)線中具有 20％的速度差，這導(dǎo)致前輪胎的擦洗。 這種情況可能導(dǎo)致過(guò)度的輪胎磨損和草皮磨損。 這也影響車輛的轉(zhuǎn)向力和穩(wěn)定性。 由于前驅(qū)動(dòng)器像實(shí)心軸一樣作用的效果，車輛將試圖保持直線。由于當(dāng)前系統(tǒng)中的楔入條件，采取預(yù)防措施以幫助減少楔入。 這些預(yù)防措施之一是使用切斷開(kāi)關(guān)，使得當(dāng)車輛從正向轉(zhuǎn)換到相反方向時(shí)，以便自動(dòng)地脫離雙向旋轉(zhuǎn)離合器（例如，關(guān)閉正在分度的線圈 滾動(dòng)保持架） 。 當(dāng)從反方向轉(zhuǎn)換到正方向時(shí)，該系統(tǒng)也使用截止開(kāi)關(guān)。 減少楔入的另一種方式是在應(yīng)用制動(dòng)器時(shí)使用開(kāi)關(guān)，其將中斷對(duì)四輪驅(qū)動(dòng)系統(tǒng)的供電。 許多其他方法可以用于減少楔入，但是沒(méi)有一種方法對(duì)于驅(qū)動(dòng)線速度的 20％差異是100％有效的。傳統(tǒng)驅(qū)動(dòng)系統(tǒng)：常見(jiàn)的傳統(tǒng)驅(qū)動(dòng)系統(tǒng)將具有與圖 1 中相同的車輛布局，但前差速器和后差速器中的機(jī)構(gòu)將是不同的。最常見(jiàn)的驅(qū)動(dòng)系統(tǒng)具有打開(kāi)的差速器，其具有鎖定到固體中的能力 在傳統(tǒng)系統(tǒng)中的驅(qū)動(dòng)線也將使用傳動(dòng)比為 1：1 比率的驅(qū)動(dòng)線直線操作：在車輛處于四輪驅(qū)動(dòng)并且所有車軸都被解鎖的直線行駛期間，所有四個(gè)車輪以相同的速度旋轉(zhuǎn)，這是由于驅(qū)動(dòng)線以 1:1 的比率傳動(dòng)，并且前部和 后差速器以相同的速度被驅(qū)動(dòng)并且不需要跨越軸的差異，當(dāng)前差速器和后差速器中的