WO2015075133A2

WO2015075133A2 - A hydraulic disc coupling

Info

Publication number: WO2015075133A2
Application number: PCT/EP2014/075176
Authority: WO
Inventors: Kristoffer Nilsson
Original assignee: Borgwarner Torqtransfer Systems Ab
Priority date: 2013-11-20
Filing date: 2014-11-20
Publication date: 2015-05-28
Also published as: WO2015075133A3

Abstract

A hydraulic wet disc coupling for a vehicle is provided. The disc coupling comprises a set of inner discs rotationally connected to a first axle, a set of outer discs rotationally connected to a second axle, and an actuator configured to arrange the sets of discs in a connected mode, whereby torque is transmitted from the first axle to the second axle, as well as in a disconnected mode in which the set of inner discs is separated from the set of outer discs, wherein at least one disc of the set of inner or outer discs is provided with a spring for biasing the disc away from an adjacent disc.

Description

TITLE: A HYDRAULIC DISC COUPLING

TECHNICAL FIELD

The present invention relates to a hydraulic disc coupling for an AWD vehicle.

BACKGROUND

There is an increasing demand for disconnect driveline systems, i.e. driveline systems that can be completely deactivated when not in use to reduce losses and thereby fuel consumption and C02 emissions. As the main objective is to reduce the overall losses a key property of the disconnect system is low losses in the disconnected mode. One of the main contributors of losses in the disconnected mode is normally the disc pack, where the input shaft will be rotating while the output shaft is stationary, creating a high differential speed over the disc pack.

Two of the main methods to reduce the drag torque of the coupling in such conditions are to reduce or eliminate the oil flow and to separate the discs.

For separation of the discs there are two main categories, separation of the complete disc pack as described in WO2012/125096, and individual disc separation as described in for example DE102006029163A1. The complete c disc separation is normally desired due to the lower cost.

One problem with the complete disc pack separation is the drag in the lower speeds regions, when there is not enough centrifugal force to evacuate the oil from the disc pack, leading to high drag torque.

An example of individual disc separation is shown in US20100274456,

Here, each one of the outer discs is provided with a separate spring urging the outer discs away from the adjacent inner discs. However, the discs will always be in contact in order to force the actuating piston away from its engaging position. Further to this, the springs will apply a force to the discs due to the height of the springs. Therefore, drag losses will still be a major problem with this solution.

Another example is shown in DE102007038155. Such solution, wherein every second inner disc is spring biased away from its adjacent inner disc, will also be subject to drag losses since the outer discs will be positioned arbitrary, in practice most likely in contact with one of the inner discs. SUMMARY

It is an object of the invention to overcome the above-mentioned drawbacks by providing a hydraulic disc coupling, as well as a method for connecting a hydraulic disc coupling.

The proposed solution combines the benefits of individual disc

separation and complete disc pack separation while maintaining a low cost.

An idea of the present invention is to provide at least one disc of the inner set of discs or the outer set of discs with a spring, such that the spring urges the associated disc away from the adjacent disc of the other set of discs,

According to first aspect, a hydraulic wet disc coupling for a vehicle is provided. The coupling comprises a set of inner discs rotationally connected to a first axle, a set of outer discs rotationally connected to a second axle, and an actuator configured to arrange the sets of discs in a connected mode, whereby torque is transmitted from one of said axles to the other one of said axles, as well as in a disconnected mode in which the set of inner discs is separated from the set of outer discs. At least one disc of the set of inner and/or outer discs is provided with a spring for biasing the disc away from an adjacent disc.

The set of inner discs and/or the set of outer discs may be spring biased for urging the set of inner discs and/or the set of outer discs towards the disconnected mode.

When in the disconnected mode, the set of inner discs may be separated from the outer discs by a first axial clearance, and the at least one disc may be spring biased away from an adjacent disc by a second axial clearance, wherein the first axial clearance is greater than the second axial clearance.

The first axial clearance may be approximately 0,09mm, and the second axial clearance may be approximately 0,05mm.

The spring of the at least one disc may be provided as an elongated member arranged circumferentially and being tilted in an axial direction relative the plane of the disc.

The spring of the at least one disc may be provided as an elongated member arranged circumferentially and having an increased thickness.

In some embodiments the elongated member is arranged at the outer and/or inner periphery of the disc.

The spring of the at least one disc may be provided as an elongated member extending radially and being tilted in an axial direction relative the plane of the disc. The spring of the at least one disc may further be provided as an elongated member extending radially and having an increased thickness.

The elongated member may extend towards the outer and/or inner periphery of the disc.

In an embodiment, the spring is integrally formed with the disc.

According to a second aspect a vehicle is provided, comprising a hydraulic wet disc coupling according to the first aspect.

According to a third aspect, a method for connecting a hydraulic wet disc coupling having a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle, is provided. The method comprises the step of controlling an actuator to arrange the sets of discs in a connected mode, whereby torque is transmitted from one of said axles to the other one of said axles and whereby a spring, provided on at least one disc of the set of inner and/or outer discs for biasing the disc away from an adjacent disc, is compressed.

According to a fourth aspect a method for disconnecting a hydraulic wet disc coupling having a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle, is provided. The method comprises the step of controlling an actuator to arrange the sets of discs in a disconnected mode, whereby the set of inner discs are separated from the set of outer discs to prevent torque transfer from between the sets of discs, and whereby a spring, provided on at least one disc of the set of inner and/or outer discs is biasing the disc away from an adjacent disc.

DRAWINGS

The invention will be described in further detail below under reference to the accompanying drawings, in which

Fig 1 is a diagram showing a typical drag torque with complete disc pack separation,

Fig 2 is a diagram showing a typical drag torque for a hydraulic disc coupling according to an embodiment,

Fig 3 shows a cross-sectional view of a hydraulic disc coupling according to an embodiment,

Fig. 4 shows a hydraulic scheme of a hydraulic disc coupling according to an embodiment, Fig. 5 is a cross-sectional view of the coupling pack of a hydraulic disc coupling according to an embodiment,

Fig 6 shows a side view of a friction disc for use with a hydraulic disc coupling according to an embodiment, and

Fig. 7 shows a side view of a friction disc for use with a hydraulic disc coupling according to a further embodiment.

DETAILED DESCRIPTION

Starting with Fig. 1, a diagram showing a typical drag torque with complete disc pack separation is shown. The diagram shows the drag torque on the Y-axis, and the differential speed on the X-axis, i.e. the speed difference between the input shaft and the output shaft. Three relationships are shown for different temperatures. As can be seen the drag torque is higher at low

differential speed, which results due to the fact the centrifugal force, experienced at the low speed, is not sufficient to drain the oil from the disc pack. Further to this, drag torque is increased for lower temperatures, as the oil experiences a higher viscosity for lower temperatures.

Now turning to Fig. 2, a diagram showing a typical drag torque with complete disc pack separation (dashed line) as well as for a hydraulic disc coupling according to an embodiment (solid line) is shown. As can be seen, the hydraulic disc coupling according to the embodiments presented herein

significantly decreases the drag torque, especially at lower speeds.

In order to describe the hydraulic disc coupling, reference is made to Figs. 3-5.

The complete coupling pack may for example be separated as described in WO2012/125096. Another example of complete coupling pack separation will be described with reference to Figs. 3 and 4. While Fig. 3 is a cross-sectional view of a disc coupling 4, Fig. 4 shows a hydraulic scheme of the disc coupling 4 shown in Fig. 3. Shown are thus the coupling 4 with its disc package 12 actuated in a cylinder 14 by a working piston 13 with its piston rod 13' and a return spring 15. Further shown are an electric motor 16, an actuator pump 17, a drive shaft 18, a centrifugal regulator 19, a pressure overflow valve 20, a reservoir 21 , and hydraulic lines 22-24.

The function of this pump actuator system is as described in

WO2014/131531 by the same applicant.

As it is illustrated in Fig 4 with hydraulic symbols, an auxiliary piston 40 is shown as connected to the working piston 13. The piston area of the auxiliary piston 40 is much smaller than that of the working piston 13. The working piston 13 and the auxiliary piston 40 together may form a ring step piston.

The auxiliary piston 40 is applied by oil in a hydraulic line 41 with the same pressure as in the hydraulic line 23.

Further, in the hydraulic line 23 there is a 3/2 directional solenoid valve

42. This valve 42 is normally held in the position shown in Fig. 4 by a

compression spring 43 but may be switched-over to its second position by means of a solenoid 44.

When the arrangement as shown in Fig. 4 is to go from the AWD mode or connect mode to a FWD mode or disconnect mode, the motor 16 is stopped. Oil will remain at the smaller piston 40, whereas the oil at the larger piston 13 becomes non-pressurized.

When the arrangement is to go back to AWD mode or connect mode, the electric motor 16 is started, and the solenoid 44 is energized. The small piston 40 will be applied (to the right in the drawing) by hydraulic pressure through the line 41 , whereas oil from the reservoir 21 may be sucked into the compartment at the larger piston 13. Hereafter the solenoid is de-energized.

The disc package 12 comprises a first set of discs 12a rigidly attached to a first axle 50, and a second set of discs 12b rigidly attached to a second axle 60. When the coupling 4 is activated to provide four-wheel drive to the vehicle, the sets of discs 12a, 12b are pressed towards each other whereby torque from the driven axle 50 will be transmitted to the other axle 60.

The sets of discs 12a, 12b are further shown in Fig. 5. The inner axle 50 is provided with the inner set of discs 12a, while the outer axle 60 is provided with the outer set of discs 12b. Each set of discs 12a, 12b comprises a series of individual discs 120 spaced apart by a pre-determined clearance when the coupling is in a disconnected mode.

The total clearance can for example be 0,09 mm per friction surface. The disc pack separation is combined with a spring feature on the outer or inner discs. As is shown in Fig. 5, the discs of the outer set of discs 12b is provided with springs 130 integrally formed with the disc 120. The height of these

springfeatures 130, i.e. the axial length, is lower than the clearance per friction surface, which means it does not create any force over the discs 120 which would lead to higher drag torque. However the height of these spring features 130 is enough to create a small separation between the disc surfaces to reduce the drag torque. The height of these spring features 130 can for example be in the range of

0,05 mm per disc surface. The force of the springs 130 can be very low since it is not needed to separate the whole disc pack and thereby move the piston, etc. A low spring force reduces the energy needed to compress the disc pack once the coupling is to be activated. The disc separation can be combined with elimination or reduction of the oil flow to reach the lowest drag torque.

The spring feature 130 can be placed in the outer discs or the inner discs or possibly both. The spring feature 130 can be realized in many ways, for example as described below or by bending the discs 120 for example 0.05 mm from the flat condition. To further reduce the drag torque it may be desirable to place the spring contact surfaces on the smallest possible diameter (in opposite to the discs shown below, where it's place on the outer diameter).

Now turning to Fig. 6, an example of a friction disc 120 is shown. The spring feature 130 is realized by providing the outer periphery of the disc 120 with one or more elongated members 132 extending in the circumferential direction and being separated radially, as well as circumferentially, from the surrounding parts of the disc 120. The elongated members 132 are further displaced axially, i.e. away from the plane of the disc surface, such that they experience a height compared to the remaining disc surface. The elongated members 132 thus form spring features 130. Preferably, the spring features 132 are disposed at equal angular distance from each other. The spring features 130 may be arranged at the outer periphery, as is shown in Fig. 6, and/or at the inner periphery of the disc 120. Hence, the thin elongated members 132, forming "fingers", are slightly bent to give for example 0,05 spring function in each direction. The spring function can also be achieved by keeping the steel body flat and make the material of the disc 120, which may be sinter bronze, for example 0.05 mm thicker on the tip of the elongated member 132. This might be more suitable for normal friction disc manufacturing processes.

In Fig. 7, another example of a friction disc 120 is shown. The spring feature 130 is realized by providing the outer periphery of the disc 120 with one or more elongated members 132 extending in the radial direction and being separated circumferentially from the surrounding parts of the disc 120. The elongated members 132 are further displaced axially, i.e. away from the plane of the disc surface, such that they experience a height compared to the remaining disc surface. In a preferred embodiment, every second elongated member 132 is bent for example 0.05 mm in one direction and every other the same distance in the other direction. The elongated members 132 thus form spring features 130. Preferably, the spring features 132 are disposed at equal angular distance from each other. The spring features 130 may be arranged at the outer periphery, as is shown in Fig. 6, and/or at the inner periphery of the disc 120. Hence, the thin elongated members 132, forming radially extending "fingers", are slightly bent to give for example 0,05 spring function in each direction. The spring function can also be achieved by keeping the steel body flat and make the material of the disc 120, which may be sinter bronze, for example 0.05 mm thicker on the tip of the elongated member 132. This might be more suitable for normal friction disc manufacturing processes.

In the following, a brief description of methods for connecting and disconnecting the hydraulic wet disc coupling will be described. Starting with the method for connecting the coupling, it is assumed that the coupling has a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle. The method comprises the step of controlling an actuator to arrange the sets of discs in a connected mode, whereby torque is transmitted from one of said axles to the other one of said axles and whereby a spring, provided on at least one disc of the set of inner and/or outer discs for biasing the disc away from an adjacent disc, is compressed.

A method for disconnecting a hydraulic wet disc coupling will also be described. As for the method described above, it is assumed that the coupling has a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle. The method comprises the step of controlling an actuator to arrange the sets of discs in a disconnected mode, whereby the set of inner discs are separated from the set of outer discs to prevent torque transfer from between the sets of discs, and whereby a spring, provided on at least one disc of the set of inner and/or outer discs is biasing the disc away from an adjacent disc.

The invention has mainly been described with reference to a few embodiments. However, as is readily understood by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

Claims

1. A hydraulic wet disc coupling (4) for a vehicle, comprising

a set of inner discs (12a) rotationally connected to a first axle (50), a set of outer discs (12b) rotationally connected to a second axle (60), and

an actuator ( 13, 14) configured to arrange the sets of discs (12a, 12b) in a connected mode, whereby torque is transmitted from one of said axles (50) to the other one of said axles (60), as well as in a disconnected mode in which the set of inner discs (12a) is separated from the set of outer discs (12b), wherein

at least one disc ( 120) of the set of inner and/or outer discs ( 12a, 12b) is provided with a spring (130) for biasing the disc (120) away from an adjacent disc.

2. The disc coupling according to claim 1, wherein the set of inner discs

(12a) and/or the set of outer discs ( 12b) is spring biased for urging the set of inner discs ( 12a) and/or the set of outer discs ( 12b) towards the disconnected mode.

3. The disc coupling according to claim 1 or 2, wherein when in the disconnected mode the set of inner discs (12a) is separated from the outer discs (12b) by a first axial clearance, and wherein the at least one disc (120) is spring biased away from an adjacent disc by a second axial clearance, wherein the first axial clearance is greater than the second axial clearance.

4. The disc coupling according to claim 3, wherein the first axial clearance is approximately 0,09mm, and wherein the second axial clearance is approximately 0,05mm.

5. The disc coupling according to any one of the preceding claims, wherein the spring (130) of the at least one disc ( 120) is provided as an elongated member ( 132) arranged circumferentially and being tilted in an axial direction relative the plane of the disc (120).

6. The disc coupling according to any one of claims 1-4, wherein the spring (130) of the at least one disc ( 120) is provided as an elongated member (132) arranged circumferentially and having an increased thickness.

7. The disc coupling according to claim 5 or 6, wherein said elongated member (132) is arranged at the outer and/or inner periphery of the disc.

8. The disc coupling according to any one of claims 1-4, wherein the spring (130) of the at least one disc ( 120) is provided as an elongated member (132) extending radially and being tilted in an axial direction relative the plane of the disc.

9. The disc coupling according to any one of claims 1-4, wherein the spring (130) of the at least one disc ( 120) is provided as an elongated member (132) extending radially and having an increased thickness.

10. The disc coupling according to any one of claims 8 or 9, wherein the elongated member (132) is extending towards the outer and/or inner periphery of the disc.

11. The disc coupling according to any one of the preceding claims, wherein the spring (130) is integrally formed with the disc (120).

12. A vehicle, comprising a hydraulic wet disc coupling (4) according to any one of the preceding claims.

13. A method for connecting a hydraulic wet disc coupling having a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle, comprising the step of:

controlling an actuator to arrange the sets of discs in a connected mode, whereby torque is transmitted from one of said axles to the other one of said axles and whereby a spring, provided on at least one disc of the set of inner and/or outer discs for biasing the disc away from an adjacent disc, is compressed.

14. A method for disconnecting a hydraulic wet disc coupling having a set of inner discs rotationally connected to a first axle, and a set of outer discs rotationally connected to a second axle, comprising the step of:

controlling an actuator to arrange the sets of discs in a disconnected mode, whereby the set of inner discs are separated from the set of outer discs to prevent torque transfer from between the sets of discs, and whereby a spring, provided on at least one disc of the set of inner and/or outer discs is biasing disc away from an adjacent disc.