The present teachings generally include a hydraulic power transfer unit assembly including a disconnect mechanism using automatic transmission line pressure for an all-wheel drive vehicle.
Power transfer units (PTUs) are used in some vehicles to distribute driving torque provided from an engine and transmission to the right front wheel and both rear wheels of a vehicle. In some other arrangements the right side half shaft passes through the PTU and is not considered part of the PTU. For example, some power transfer units only transfer torque from a transverse transmission differential to a propeller shaft, which then drives rear half shafts through a rear differential. A hypoid gear set is often used to accomplish the 90 degree turn in the direction of drive between the front differential carrier axis of rotation and the propeller shaft axis of rotation. The torque ratio that the hypoid gear set can provide is dependent on the relative tooth counts of the hypoid ring gear and the pinion gear. The diameters of these gears are limited by available packaging space.
One aspect of the disclosure provides a power transfer unit assembly for selectively transferring torque from a powertrain to a driven member of a vehicle to a driven member. The power transfer unit assembly includes an input shaft, a transfer shaft, a propeller shaft, and a disconnect mechanism. The input shaft is configured to be rotatably driven by an output shaft of the powertrain, about a first axis of rotation. The transfer shaft concentrically surrounds the input shaft. The transfer shaft has a first bevel gear. The first bevel gear is configured to be meshingly engaged with the driven member to selectively rotatably drive the driven member about a second axis of rotation. The disconnect mechanism is disposed between the input shaft and the transfer shaft. The disconnect mechanism is configured to selectively drive the transfer shaft by the input shaft. The input shaft is disconnected from the transfer shaft and torque is not transferred to the driven member when the disconnect mechanism is disengaged. Likewise, the input shaft is operatively connected to the transfer shaft and torque is transferred from the input shaft to the driven member when the disconnect mechanism is in the engaged position.
Another aspect of the disclosure provides a powertrain for a vehicle. The powertrain includes a transmission, a front differential, a helical gear, a propeller shaft, and a power transfer unit assembly. The transmission includes an output member. The front differential includes a differential carrier. The helical gear is operatively attached to the differential carrier of the front differential such that the transmission output member is configured to rotate in unison with the differential carrier. The differential carrier is rotatable about a first axis of rotation. The power transfer unit assembly includes an input shaft, a transfer shaft, and a disconnect mechanism. The input shaft is configured to be rotatably driven by the differential carrier about a first axis of rotation. The transfer shaft concentrically surrounds the input shaft. The transfer shaft has a first bevel gear. The first bevel gear is meshingly engaged with the propeller shaft to selectively rotatably drive the propeller shaft about a second axis of rotation. The disconnect mechanism is disposed between the input shaft and the transfer shaft. The disconnect mechanism is configured to selectively drive the transfer shaft by the input shaft. The input shaft is disconnected from the transfer shaft and torque is not transferred to the propeller shaft when the disconnect mechanism is disengaged. Likewise, the input shaft is operatively connected to the transfer shaft and torque is transferred from the input shaft to the propeller shaft when the disconnect mechanism is in the engaged position.
This arrangement significantly reduces drag and noise, vibration, and harshness (NVH). The input shaft is disconnected from the first bevel gear such that torque is not transferrable from the input shaft to the first bevel gear when the disconnect mechanism is in the disengaged position. The input shaft is operatively connected to the first bevel gear to enable torque transfer from the input shaft to the first bevel gear when the disconnect mechanism is in the engaged position.
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the several views, a vehicle 10 having a powertrain 12 is shown in
Referring now to
Referring again to
Accordingly, the power transfer unit assembly 38 enables driving torque ultimately provided by the engine 14 through the front differential 26 to front wheels to also be directed to rear wheels via the propeller shaft 40, such as in an all wheel-drive mode of operation.
As discussed further herein, the power transfer unit assembly 38 includes an input shaft 44, a bevel gear set with a first bevel gear 46 and a second bevel gear 48, and a stationary housing 50 surrounding and supporting the bevel gears 46, 48. The bevel gears 46, 48 may be hypoid spiral gears but are not limited to such. As used herein, the first bevel gear 46 is referred to as a hypoid ring gear 46 and the second bevel gear 48 is referred to as a pinion gear 48.
The power transfer unit assembly 38 is arranged with torque transfer components concentric with and rotatable about a single axis (the first axis of rotation 36). Because the components are arranged about a single axis of rotation 36, the overall radial dimension of each of the power transfer unit assembly 38 may be kept relatively small, enabling packaging into a fixed available packaging space adjacent the engine block 15.
Referring again to
Referring to
The hypoid ring gear 46 is engaged with (i.e., meshes with) the pinion gear 48. The pinion gear 48 meshes with the hypoid ring gear 46 in a different plane than the cross-section through the center of the hypoid ring gear 46. In other words, the pinion gear 48 is offset from the hypoid ring gear 46 so that the second axis of rotation 42 does not intersect the first axis of rotation 36. In
The cover housing 64 provides a location for an annular double lip seal 88A that seals between the shaft portion 56 of the hypoid ring gear 46 and the cover housing 64. Another annular double lip seal 88B seals between the shaft portion 58 of the hypoid ring gear 46 and the housing 66. A passage 90A is provided in the cover housing 64 in communication with the lip seal 88A. An end of the passage 90A can be at a location at the underside of the power transfer unit assembly 38 that is easily accessed for inspection. The passage 90A can be referred to as a weep hole, as it provides an indication of leakage past the lip seal 88A if fluid weeps through the passage 90A. A similar passage 90B is provided in the housing 66 in communication with the lip seal 88B to provide an indication of leakage past the lip seal 88B.
The housing 66 and the cover housing 64 define a first cavity 92A that contains the hypoid ring gear 46 and the pinion gear 48. The cover housing 64 and the lip seals 88A, 88B substantially isolate the first cavity 92A from the second cavity 92B. This enables the use of different fluids in the two cavities. For example, the first cavity 92A can be filled with hypoid gear lubrication fluid that has a relatively high viscosity. A lower viscosity fluid, such as automatic transmission fluid (ATF) can be provided from the transmission 16 and differential housing 28 to the second cavity 92B through an annular passage 94A between the hypoid ring gear 46 and the input shaft 44, and through an annular passage 94B between the input shaft 44 and the half shaft 34B. By using lower viscosity transmission fluid in the second cavity 92B and isolating the higher viscosity gear lube in the first cavity 92A, spin losses are reduced. The lip seals 88A, 88B serve an additional function of increasing the drag on the rotating hypoid gear 46 to help keep it stationary about the first axis of rotation 36 when in a front-wheel drive mode. Lip seal 67 seals between the cover housing 64 and the half shaft 34B, and is the only seal at which there is relative motion when a disconnect clutch 80 (described in detail below) is disengaged. An alternative method to separate the two cavities 92A, 92B would be to place seals between the rotating hypoid ring gear 46 and input shaft 44, and between the input shaft 44 and half shaft 34B. In such an embodiment, the housing 66 would have an opening with a drain and fill plug to allow the cavity 92B to be filled with fluid.
With continued reference to
The disconnect mechanism 80 is hydraulically actuated. The disconnect mechanism 80 may be configured to move from the disengaged position 100, as shown in
The disconnect mechanism 80 includes a selectively engageable torque transmitting device 110, a piston 112, and a return spring 114. The torque transmitting device 110 may be a clutch, such as a dog clutch and the like, that is axially movable along the shaft portion 56, by the piston 112. The torque transmitting device will be referred to from herein as a clutch 110. Referring to
The cover housing 64 defines a pocket 118 radially surrounding the first axis of rotation 36. The piston 112 is operatively disposed to be at least partially within the pocket 118 such that the piston 112 is axially adjacent and in contact relationship with a first side 126 of the clutch 110. The piston 112 includes a pressure side 130 and an apply side 132, opposite the pressure side 130. The pressure side 130 faces the pocket 118 and the apply side 132 faces the first side 126 of the clutch 110. As will be explained in more detail below, the piston 112 is configured to move axially from a first position 122 to a second position 124, in response to a pressure force F1 applied to the pressure side 130 of the piston 112 within the pocket 118, by pressure of fluid received in the pocket 118, from the transmission 16.
The return spring 114 is axially disposed adjacent the clutch 110 such that the spring 114 axially acts on a second side 128 of the clutch 110, opposite the first side 126. Therefore, the return spring 114 continuously applies a spring force F2 to the second side 128 of the clutch 110, while the pressure force Fl is applied to the first side 126 of the clutch 110, via the piston 112. The clutch 110 selectively moves from the disengaged position 100, as shown in
The cover housing 64 also defines at least one inlet opening 120 that fluidly connects the pocket 118 with the transmission 16. Therefore, when fluid is selectively drawn from the transmission 16, via the pump 106 and the like, to the pocket 118, fluid pressure within the pocket 118 increases such that the fluid, under pressure, applies the pressure force F1 to the pressure side 130 of the piston 112. Since the apply side 132 of the piston 112 is in contact relationship with the first side 126 of the clutch 110, this pressure force F1 is transmitted axially from the piston 112 to the clutch 110.
The piston 112 may also include a valve 134, such as a bleed valve and the like, that provides fluid communication from the pocket 118 to the second cavity 92B via a bleed circuit 105. As such, the fluid will be slowly released from the pocket 118 to the second cavity 92B. The pressure within the pocket 118 is defined by a balance between the rate and pressure fluid is applied and the size of the orifice through which the fluid flows into the pocket 118. Therefore, the fluid mixes with the fluid already in the second cavity 92B. This fluid would then flow back to the transmission 16 through the annular passage 94A between the hypoid ring gear 46 and the input shaft 44, and through the annular passage 94B between the input shaft 44 and the half shaft 34B.
Alternatively, the fluid feed circuit 103 may also include a dump circuit configured to improve the speed at which the piston 112 could be returned to the disengaged position 100, illustrated in
The power transfer unit assembly 38 may be modular, as the assembly 38 has a base of a housing 66, an input shaft 44, a hypoid ring gear 46, and a pinion gear 48. Using common components such as the hypoid ring gear 46 and pinion gear 48, and maintaining the components that accomplish the additional torque reduction concentric with a single axis (the first axis of rotation 36) may reduce weight, cost, and packaging space requirements in comparison to a two-axis torque reduction arrangement.
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/934400, filed Jan. 31, 2014, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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61934400 | Jan 2014 | US |