192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
1999-08-24
2001-02-20
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S085060, C192S113350, C188S071600, C188S26400E
Reexamination Certificate
active
06189669
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, generally, to friction devices such as clutch or brake assemblies for use in transmissions, differentials or brake systems. More specifically, the present invention relate to a multi-disk friction clutch or brake system having selectively actuated lubrication for cooling the clutch on demand.
DESCRIPTION OF THE RELATED ART
Multi-disk friction devices are employed in a wide range of applications as clutches or brakes. For example, such friction devices are frequently used in land-based vehicles. Generally speaking, land vehicles require three basic components. These components include a power plant (such as an internal combustion engine), a powertrain and wheels. The powertrain's main component is typically referred to as the “transmission.” Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. Transmissions include one or more gear sets, which may include an inner sun gear, intermediate planet gears that are supported by their carriers and outer ring gears. Various components of the gear sets are held or powered to change the gear ratios in the transmission. The multi-disk pack clutch is a friction device, which is commonly employed as a holding mechanism in a transmission or differential. In addition, multi-disk friction devices also find use in industrial applications, such as wet brakes, for example, to brake the wheels on earth moving equipment.
The multi-disk pack clutch or brake assembly has a clutch sub-assembly including a set of plates and a set of friction disks, which are interleaved between one another. The plates and friction disks are bathed in a continual flow of lubricant and in “open pack” operation normally turn past one another without contact. The clutch or brake assembly also typically includes a piston. When a component of a gear set is to be held, as for example during a particular gear range, a piston is actuated so as to cause the plates and friction disks to come in contact with respect to one another. In certain applications, it is known to employ several multi-disk pack friction devices in combination to establish different drive connections throughout the transmission or differential to provide various gear ratios in operation, or to brake a component.
The confronting faces of the interleaved plates and friction disks are covered with frictional surfaces. When a friction device is engaged, kinetic energy is converted into thermal energy and a considerable amount of heat is generated. If the frictional surfaces get too hot, they can bum which damages the friction surfaces and degrades the clutch or brake operational effectiveness. Accordingly, the heat generated when a friction device is engaged must be dissipated.
Multi-disk friction clutches and brake systems have traditionally relied on a continuous “splash” supply of coolant, typically automatic transmission fluid (AFT), to remove the heat generated during operation. Coolant is supplied at or near the inner diameter of the disks and moves radially outward across the friction surface under the influence of centrifugal forces. While the centrifugal forces are important to move the coolant between the engaged friction disks, because the perimeter of the plates is larger at the outer diameter than the inner diameter, the coolant tends to break up into droplets which reduces wetting of the friction surfaces and concomitantly reduces the cooling capacity of the fluid.
When the disks are not engaged, little or no cooling is usually required. However, which conventional cooling schemes employed in the related art, unneeded coolant is often supplied to the open clutch or brake. When this occurs, the coolant in the friction device is sheared by the interleaved plates and friction disks due to the differential rotational speeds of the drive and driven members which the clutch or brake bridges. This condition reduces the efficiency of the transmission through viscous shear losses in the fluid and ultimately results in lower fuel efficiency.
Additionally, when coolant is directed toward a friction device operating in an open pack mode wherein coolant is not needed, the coolant is not being used by friction devices, which are engaged or otherwise require cooling. This also increases the volume of oil needed for a given transmission, differential or brake system and unnecessarily requires increasing the capacity of the associated pump.
It is known in the related art to selectively provide coolant to the clutch pack when the friction device has been engaged and to selectively interrupt coolant to the clutch pack when the friction device is disengaged. However, in general, the systems that have been proposed in the related art suffer from the disadvantage that they are overly complex in operation or are too difficult to be manufactured in a cost-effective manner. Examples of such arrangements are set-forth in U.S. Pat. Nos. 5,755,314; 5,791,447; 5,810,412 and 5,813,508.
Accordingly, there remains a need in the art for a friction device which may be selectively cooled on demand using forced coolant flow such as when the clutch or brake is engaged and wherein coolant to the clutch or brake may be selectively interrupted when not needed, such as when the clutch or brake is disengaged. Additionally, there is a need in the art for such a friction device having a cooling scheme wherein the friction disk are fully wetted when they are engaged.
In copending U.S. application Ser. No. 09/153,582, commonly assigned a clutch pack is interposed between the drive and driven members and is operable to connect and disconnect the drive and driven members for transferring and interrupting torque therebetween. A piston assembly is supported in the clutch housing and defines an expandable chamber between the piston assembly and the clutch housing. A source of pressurized fluid is in communication with the expandable chamber. The piston assembly is responsive to the pressure of fluid in the expandable chamber to move between disengaged and engaged positions thereby actuating the clutch pack to connect and disconnect the drive and driven members.
The piston assembly includes a main body having an outer ring annularly disposed about the main body. The outer ring includes at least one orifice extending through the outer ring. The outer ring is movable between a first position wherein the orifice is closed and the drive and driven members are disconnected and a second position wherein the orifice is open to allow flow of pressurized fluid through the orifice and into contact with the clutch pack thereby cooling the clutch pack when the drive and driven members are operatively connected through the clutch pack.
Thus, the piston assembly is operable to control the flow of coolant under pressure from the outer diameter of the clutch pack between the adjacent plates and disks to the inner diameter of the clutch pack to cool same when the drive and driven members are connected. Further, the piston assembly is also operable to stop the flow of pressurized coolant and to evacuate the clutch pack when the drive and driven members are disconnected.
In this way, the friction device provides coolant to the clutch pack when coolant is needed, such as when the clutch or brake is engaged, and interrupts coolant to the clutch pack when the coolant is needed, such as when the clutch or brake is disengaged. However, such an arrangement utilizes the piston apply fluid as the coolant fluid.
SUMMARY OF THE INVENTION
In order to isolate the piston apply function from the cooling function a separate supply of pressurized fluid is directed through a second supply line and control is by hydraulic piston motion to control flow from the separate supply of coolant to the clutch pack.
The advantages of such an arrangement is that actuation pressure for the clutch pack can be separated from coolant flow in a friction device such as a clutch or brake assembly thereby optimizing the control of clutch operation.
REFERENCES:
patent: 3292758 (19
Kremer John M.
Martin R. Keith
McCrary Paul T.
Borg-Warner Inc.
Dziegielewski Greg
Lorence Richard M.
Reising, Ethington, Barnes, Kisselle et al.
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