WO2011105917A1

WO2011105917A1 - Interaxial differential gear

Info

Publication number: WO2011105917A1
Application number: PCT/PL2011/000019
Authority: WO
Inventors: Krzysztof CIEŚLAK
Original assignee: Uniwersytet Mikołaja Kopernika
Priority date: 2010-02-24
Filing date: 2011-02-22
Publication date: 2011-09-01
Also published as: PL390534A1

Abstract

The subject of the application is the interaxial differential gear primarily used in wheeled vehicles, comprising of a mechanical assembly (A), the main housing (2) and the pitch lock assembly (B).

Description

Interaxial differential gear

The subject of the application is the interaxial differential gear primarily used in wheeled vehicles.

Several differential mechanisms have been recognised, amongst others in the following publications:

GB19880014226, GB19880016712, US19950495417, US19920969727, WO1993US08280 and US19910712667, WO1992US03518. The above mentioned solutions utilize a specific worm gear working principle - to be precise the one feature in question is the self-locking ability in a situation where teeth of interacting elements overlap at a certain angle. The angle of the teeth, which is utilized in the above mentioned solutions, is such that any rotational speed differences between individual elements cause reciprocal thrust interpenetration to occur, thus eliminating the drawbacks of the classical mechanism, which is the transfer of the entire torque onto the slipping wheel/axle.

However, as result of such operational characteristics, negative effects do occur, such as:

1) Constant levels of resistance of cooperating elements, resulting in partially increased fuel consumption and drive subassemblies wear.

2) The mechanism is unable to transfer up to 100% of the torque onto the non-slipping wheel/axle. This occurs in ratios ranging from 30 to 60%, whereas the higher value applies to the smaller torque transmission.

3) Constant levels of internal friction lead to surfaces degradation of the mating components resulting in reduction of the initially set parameters.

Surprisingly, the invention based solution yielded the following effects: 1) it does not differentiate rotational speeds of individual elements in a resistive manner, and thus does not impair the fuel economy or cause excessive wear on the torque transmitting elements,

2) it is capable of the transfer of up to 100% torque to the axle with better traction,

3) it does not modify the working parameters during operation.

According to the invention, the interaxial differential gear consists of the unified main housing 2 and ring gear 3 , whereby the ring gear 3 transfers power onto the main housing 2; consecutively the power is transferred to a mechanism consisting of bevel gears 4 and sun gears 5 and 6, which rotations correspond to the average rotational speed of the front and rear axles, where the sun gear 5 apportions the power to the front axle, whilst the sun gear 6 transfers power to the rear axle. Elements 5, 6, 7, 8, 9 and 10 are corotational, while sun gear 6, extended with the use of a shaft, is connected to the bell 8 by means of a screw thread 11; the thread orientation is such that the screwing in of the sun gear 6 into the bell 8 occurs at the same time as the transferring of the torque between elements 6 and 8, thus resulting in drawing them closer; spirally twisted springs 12 are employed in order to secure these elements in their original position; when torque transferred by the mechanism is significant enough to tighten the springs 12, the bell 8 is displaced towards the left, which in turn causes the tightening of the multi-plate friction clutch, which individual elements are fitted to the bell and to the housing 2; at the moment of clamping, and subsequently shifting, rod 13 shall also shift, which in turn moves pin 14 towards the left. Pin 14 is fitted with specially machined splines of an inclined working surface 6, which come in direct contact with their identical counterparts, that are an integral part of the clutch basket 15, responsible for keeping the balls wedged between the respective surfaces; the main housing 2 is attached to the mechanical assembly A, which comprises of two unidirectional clutches, one of which is a unidirectional ball clutch 17 with higher rotational capabilities used for driving bell 18 in relation to the sun gear 5, whereas the basket 15 is an integral part of the second unidirectional clutch, which prevents the bell 18 from yielding higher rotational speed ranges by wedging balls from basket 15 between the respective working surfaces of elements 5 and 18; additionally the differential gear is equipped with springs 19, which are fixed to the peripheral surface and connect the friction clutch plate and housing 2, furthermore the differential gear is equipped with a pitch lock assembly B, fitted with an oil pump 20, which collects the working fluid through channel 21 located in shaft 9; the oil pump 20 possesses a ring connected to element 9 and pressed against it with the use of a spring, whereby the ring is mounted in such a manner that causes it to move along the rippled peripheral area, which is integral with housing 2; the oil pump 20 provides working fluid to the actuator 22, which piston rod is directly connected to splines 23, that are equipped with friction plates, and drawn off to a neutral position with the use of spring 24, wherein the actuator 22 has a continuously open outlet, which allows for the release of working fluid at relatively low pressure levels; should fluid pressure rise above the permissible flow level of the outlet it will trigger a rapid accumulation of fluid resulting in the displacement of the piston rod together with the splines, which in turn will cause the clutch plates to tighten.

An example of the invention has been presented on the drawings, where Figure 1 represents the cross-sectional view of the interaxial differential gear, while Figure 2 a diagram of the mechanical assembly A.

The interaxial differential gear revolves around axle 1, whereby it is driven by the primary source of power, which is transferred onto the main housing 2 via the ring gear 3, that is uniform with the main housing. Subsequently the power is transferred to a mechanism consisting of bevel gears 4 and sun gears 5 and 6, which rotations correspond to the average rotational speed of the front and rear axles. The first sun gear 5 apportions the power to the front axle, whilst the sun gear 6 transfers power to the rear axle. Elements 5, 6, 7, 8, 9 and 10 are corotational, which means that most of the time they have an identical rotational speed. Sun gear 6, extended with the use of a shaft, is connected to the bell 8 by means of a screw thread 11. The thread orientation is such that the screwing in of the sun gear 6 into the bell 8 occurs at the same time as the transferring of the torque between elements 6 and 8, thus resulting in drawing them closer. To secure these elements in their original position spirally twisted springs 12 are employed. When torque transferred by the mechanism is significant enough to tighten the springs 12, the bell 8 is displaced towards the left, which in turn causes the tightening of the multi-plate friction clutch, which individual elements are fitted to the bell and to the housing 2. At the moment of clamping, and subsequently shifting, rod 13 shall also shift, which in turn moves pin 14 towards the left. Pin 14 is fitted with specially machined splines of an inclined working surface 16, which come in direct contact with their identical counterparts, that are an integral part of the clutch basket 15, responsible for keeping the balls wedged between the respective surfaces.

The construction and operational principle of the mechanical assembly A is such that it consists of two unidirectional clutches. Clutch 17 is a standard unidirectional ball clutch, which allows for higher rotational speed used for driving bell 18 in relation to the sun gear 5. The second unidirectional clutch, an integral element of which is the clutch basket 15, prevents the bell 18 from yielding higher rotational speed ranges by wedging balls from basket 15 between the respective working surfaces of elements 5 and 18. Should the clutch with the basket 15 be engaged, then it is impossible for element 18 to move at any other rotational speed than that of element 5. Should the clutch basket 15 be drawn away from the wedging surface, than only clutch 17 will be operating between elements 5 and 18, which shall allow the bell 18 to reach higher rotational range, thus also allowing the same for the front axle. This is inevitable, because after engaging the multi-plate clutch a rigid connection is made between element 6, which is the rear axle drive, and housing 2, which rotates at an identical rate to that of primary drive. Should the vehicle travel along a bend there is an inevitable difference in rotational speed between separate axles, and in such a situation the above described locking mechanism shall transfer the torque onto the rear axle, whilst the front one, inevitably revolving at higher rotational speed, shall be released by the clutch 17, resulting in a lack of any overloading of the mechanism. Should the rear axle wheels slip then clutch 17 shall connect both assemblies responsible for propelling the axles and the power shall be transmitted to all the wheels. When the specified value of transmitted torque falls below a certain level springs 12 unblock the system and the power will then be distributed by the differential gear assembly. Springs 19 are responsible for smooth transition back into the initial position; they are mounted peripherally and consist of a friction clutch plate and main housing 2. The friction clutch clamping system works in such a way that the individual plates are initially integrated, but with an existing frictional force that is too weak, afterwards the springs 19 are tightened, which allows for the entire clutch to be displaced to the left, and only when the springs 19 are fully clamped shall the entire transferred tightening torque be used to permanently engage the clutch. Such a functional system is necessary, because at the moment of engagement of the unidirectional clutch with the clutch basket 15 in section A the mechanism can not operate without thrust. This is due to specific situations typical to vehicle operation.

Should the specified turning moment fall below the required value then the locking of the mechanism shall not occur. The pitch lock assembly B prevents such an event from happening. It is equipped with an oil pump 20 collecting the working fluid through channel 21 located in the shaft 9. The above fluid is fed in by any possible route. An integral part of the pump is a special ring attached onto the elongated element 9 and pressed against it with the use of a spring, which initiates reciprocating movement alongside element 9, when there is a rotational difference between element 9 and the main housing. This is achieved by moving the ring along the rippled peripheral area, which is integral with housing 2. The oil pump 20 provides working fluid to the actuator 22, which piston rod is directly connected to splines 23, that are equipped with friction plates, and drawn off to a neutral position with the use of spring 24. The actuator 22 has a continuously open outlet, which allows for the release of working fluid at relatively low pressure levels. Should fluid pressure rise above the permissible flow level of the outlet it will trigger a rapid accumulation of fluid resulting in the displacement of the piston rod together with the splines, which in turn will cause the clutch plates to tighten. The operational basis for the pitch lock B lies in the known principle that if an excessive rotational speed difference exceeds a certain limit, then the working fluid pressure generated by such a difference shall cause the system to lock, but should the rotational speed difference drop as a result of locking, then a corresponding drop in fluid pressure in the actuator 22 shall be observed. Thus, the system, for which a correct ratio between the friction surfaces on the one hand and the existing pressure present under any load on the other was calculated during the design stage, will self-regulate, but if the rotational speed difference drops below the pitch value then there will be no friction. The pitch is determined for each particular vehicle pursuant to its maximum turning radius and the speed at which it can then travel. The higher the speed the greater the rotational speed difference within the mechanism, thus resulting in greater fluid pressure per time unit. The scenario where the mechanism has not exceeded the flow capacity shall be treated as usual operating conditions, but should the capacity limit be exceeded then the mechanism shall treat this is an unnatural situation and react as above.

As described above, operational characteristics of the mechanism consist of two planes. For the medium and high grip range of the vehicle wheels (on dry or wet roadway), especially during start-up, high torque values are being transmitted onto the wheels. High grip of all drive wheels is required in such situations to most efficiently utilize the power. Under low grip conditions (non-hardened terrain, mud, ice) or during high speeds, the high torque values can not be transferred by the mechanism, and subsequently grip loss of any of the axle wheels can occur. In such situations with power being excessively diverted away to one of the axles, the mechanism shall immediately engage the pitch self-locking system.

The main applications of the mechanism based on the above invention are in regards to sport-utility vehicles, for which the utilization of an all-wheel drive is required, but implementation of solutions such as rigid coupling of all drive axles is not possible because of the required need of being equipped with a constant all-wheel drive, which can be engaged automatically if necessary.

Rigid coupling is a professional solution applicable to heavy haulage equipment, or to off-road sports, where extreme operational conditions in unhardened terrain can occur. This is unlike sport-utility vehicles, with which drivers require high quality steering, for example in regards to a dynamic start, or traction reliability on sharp comers. Up until now only mechanical systems fitted with highly advanced sophisticated electronic control systems were able to meet these expectations.

Claims

Claim

The interaxial differential gear, wherein consisting of the uniform solid main housing 2 and ring gear 3, whereby the ring gear 3 transfers power onto the main housing 2; consecutively the power is transferred to a mechanism consisting of bevel gears 4 and sun gears 5 and 6, which rotations correspond to the average rotational speed of the front and rear axles, where the sun gear 5 apportions the power to the front axle, whilst the sun gear 6 transfers power to the rear axle, elements 5, 6, 7, 8, 9 and 10 are corotational, while sun gear 6, extended with the use of a shaft, is connected to the bell 8 by means of a screw thread 11; the thread orientation is such that the screwing in of the sun gear 6 into the bell 8 occurs at the same time as the transferring of the torque between elements 6 and 8, thus resulting in drawing them closer; spirally twisted springs 12 are employed in order to secure these elements in their original position; when torque transferred by the mechanism is significant enough to tighten the springs 12, the bell 8 is displaced towards the left, which in turn causes the tightening of the multi-plate friction clutch, which individual elements are fitted to the bell and to the housing 2; at the moment of clamping, and subsequently shifting, rod 13 shall also shift, which in turn moves pin 14 towards the left, whereas pin 14 is fitted with specially machined splines of an inclined working surface 16, which come in direct contact with their identical counterparts, that are an integral part of the clutch basket 15, responsible for keeping the balls wedged between the respective surfaces; the main housing 2 is attached to the mechanical assembly A, which comprises of two unidirectional clutches, one of which is a unidirectional ball clutch 17 with higher rotational capabilities used for driving bell 18 in relation to the sun gear 5, whereas the basket 5 is an integral part of the second unidirectional clutch, which prevents the bell 18 from yielding higher rotational speed ranges by wedging balls from basket 15 between the respective working surfaces of elements 5 and 18; additionally the differential gear is equipped with springs 19, which are fixed to the peripheral surface and connect the friction clutch plate and housing 2, furthermore the differential gear is equipped with a pitch lock assembly B, fitted with an oil pump 20, which collects the working fluid through channel 21 located in shaft 9; the oil pump 20 possesses a ring connected to element 9 and pressed against it with the use of a spring, whereby the ring is mounted in such a manner that causes it to move along the rippled peripheral area, which is integral with housing 2; the oil pump 20 provides working fluid to the actuator 22, which piston rod is directly connected to splines 23, that are equipped with friction plates, and drawn off to a neutral position with the use of spring 24, wherein the actuator 22 has a continuously open outlet, which allows for the release of working fluid at relatively low pressure levels; should fluid pressure rise above the permissible flow level of the outlet it will trigger a rapid accumulation of fluid resulting in the displacement of the piston rod together with the splines, which in turn will cause the clutch plates to tighten.