Lever applied solenoid clutch actuator

A electromagnetic clutch assembly for use in a vehicle is presented. More specifically, the clutch assembly comprises an input member; an output member; a friction clutch pack having a first plurality of clutch plates coupled for rotation with said input member and a second plurality of clutch plates interleaved with said first plurality of clutch plates and coupled for rotation with said output member; a solenoid coil; an actuator hub having an armature plate; and a cam lever assembly having a first end engaging said actuator hub and a second end engaging said friction clutch pack. When electrical current is applied to the solenoid coil, the armature plate moves the actuator hub, the actuator hub engages the cam lever and causes said cam lever to compress the interleaved first and second plurality of clutch plates, thereby, resulting in the coupling of the input and output members.

FIELD

This invention relates generally to electromagnetic clutch assemblies and more specifically to an electromagnetic clutch having a solenoid activated cam lever actuation arrangement.

BACKGROUND

In many vehicle powertrain applications it is desirable to engage a clutch pack as a result of inputting an electrical signal to an electromagnetic coil. The clutch pack may control torque between an input and an output. One design of a conventional electromagnetic clutch assembly consists of a friction clutch pack having a plurality of interleaved friction plates, a solenoid coil, an armature plate, and a ball ramp mechanism. In this type of electromagnetic clutch assembly, electrical current is applied to the solenoid coil, which generates a magnetic force that attracts the armature plate to the coil housing and causes the coil housing, armature plate, and one element of the ball ramp mechanism to rotate relative to a second element. Since the second element of the ball ramp mechanism is linked to the output side of the clutch pack, the ball ramp mechanism imparts a clamping force against the clutch pack, thereby, engaging the interleaved friction plates.

Several of the engineering parameters considered when designing an electromagnetic clutch include power consumption, the time necessary to engage/disengage the clutch, the magnitude of the torque transferred, and the ability to modulate torque transfer. It is desirable in the automotive industry to continually improve upon the design of an electromagnetic clutch assembly in order to lower manufacturing costs by either increasing the ease associated with manufacturing each component or by having fewer components to assemble. Accordingly, there exists a need in the industry to continually provide electromagnetic clutch assemblies that are economical to manufacture and to assemble.

SUMMARY

The present invention provides a clutch assembly for use in a vehicle powertrain application. One embodiment of a clutch assembly, constructed in accordance with the teachings of the present invention, generally comprises an input member; an output member; a friction clutch pack having a first plurality of clutch plates coupled for rotation with the input member and a second plurality of clutch plates interleaved with said first clutch plates and coupled for rotation with the output member; a solenoid coil; an actuator hub having an armature plate; and a cam lever assembly having a first end engaging said actuator hub and a second end engaging said friction clutch pack. When electrical current is applied to the solenoid coil, the armature plate moves the actuator hub, the actuator hub engages the cam lever and causes said cam lever to compress the interleaved first and second plurality of clutch plates, thereby, resulting in the coupling of the input and output members.

In another aspect of the present invention the clutch assembly further comprises a bell-shaped housing that engages a flux concentrating annular housing with said annular housing providing protection for the solenoid coil. The bell-shaped housing, flux concentrating annular housing, and solenoid coil are preferably stationary with the flux concentrating annular housing and solenoid coil being separated from the armature plate by an air gap. In addition, the input member may further comprise an input shaft and actively engage a flange that is coupled to either the universal joint or a secondary shaft in the vehicle.

In another aspect of the present invention, the armature plate is secured in place by a snap ring positioned in a groove integrally formed with the actuator hub. When electrical current is applied to the solenoid coil, the generated magnetic flux causes the armature plate to be attracted by and move towards the flux concentrating housing and the solenoid coil, thereby decreasing the width (w) of the air gap. The application of electrical current to the solenoid coil generates a compression energy, which is transmitted to the clutch pack as a packing force through the actuating hub and cam lever assembly. The transmitted packing force is preferably in a substantially linear relationship with the extent to which the interleaved clutch plates in the friction clutch pack are compressed.

It is another objective of the present invention to provide an electromagnetically activated clutch assembly comprising a rotatable input member; a rotatable output member; an actuator hub positioned proximate to the input member; a solenoid coil; a flux concentrating annular housing positioned proximate to the solenoid coil; an armature plate coupled to the actuator hub and separated from the flux concentrating annular housing and solenoid coil by an air gap; a cam lever assembly having a first end engaging said actuator hub and a second end engaging a friction clutch pack; and a friction clutch pack having a first plurality of clutch plates coupled for rotation with said input member and a second plurality of clutch plates interleaved with said first plurality of clutch plates and coupled for rotation with said output member.

When electrical current is applied to the solenoid coil, the magnetic flux so generated attracts the armature plate towards the flux concentrating housing and solenoid coil, thereby reducing the width (w) of the air gap and generating compression energy. Preferably, the width of the air gap decreases upon the application of electrical current to the solenoid coil by about 90%. The compression energy is transmitted as a packing force through the actuator hub and the first and second ends of the cam lever assembly to the friction clutch pack. The transfer of the packing force to the friction clutch pack causes the plates within the clutch pack to compress, thereby, coupling the input member to the output member. This packing force is preferably in a substantially linear relationship with the extent to which the clutch pack is compressed.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description and drawings, corresponding reference numerals indicate like or corresponding parts and features.

The present invention generally provides a clutch assembly for use in a vehicle. The clutch assembly generally comprises: an input member; an output member; a friction clutch pack having a first plurality of clutch plates coupled for rotation with said input member and a second plurality of clutch plates interleaved with said first plurality of clutch plates and coupled for rotation with said output member; a solenoid coil; an actuator hub having an armature plate; and a cam lever having a first end engaging said actuator hub and a second end engaging said friction clutch pack. When electrical current is applied to the solenoid coil, the armature moves the actuator hub, the actuator hub engages the cam lever and causes said cam lever to compress the interleaved first and second plurality of clutch plates, thereby, resulting in the coupling of the input and output members.

One benefit associated with the clutch assembly of the present invention is a reduction in manufacturing cost due to a decrease in the number of components that must be manufactured and assembled to form the clutch assembly. In particular, the clutch assembly of the present invention eliminates several components currently utilized in conventional electromagnetic clutch assemblies, such as a ball ramp actuator, among others. A thorough description of a conventional electromagnetic clutch assembly having a solenoid type operator is found in U.S. Pat. No. 6,905,008 issued to Kowalski et al., the entire contents of which are hereby incorporated by reference.

Referring toFIG. 1A, the electromagnetic clutch assembly1includes a bell-shaped, clutch assembly housing5that has a continuous flange or a plurality of flanges10. These flanges may be adapted to receive fasteners used to attach the clutch assembly1to the housing of a secondary differential assembly (not shown) in a vehicle. An O-ring15or toric joint may be utilized in coordination with the flange10to provide an effective seal between the clutch assembly housing5and the secondary differential assembly. The clutch assembly housing5is designed to engage a ball bearing assembly20, which in turn supports a cylindrical input member25.

The input member25further comprises an input shaft30that defines a positive drive means. The input member25includes a feature, such as but not limited to male splines, keyways, and hexagonal flats, which engage a complimentary feature integrally formed with a flange35that is part of the universal joint or another secondary shaft (not shown). A nut40may be used to position and retain the flange35proximate to the input shaft30.

Similarly, the input member25also supports the positioning of an output hub45and an actuating hub83. The cylindrical wall of the output hub45further forms a plurality of spines or teeth50. Oil seals55are typically utilized to provide fluid tight seals between the various components of the clutch assembly1, while rolling element thrust bearings57are used to allow differences in speed by various rotating or moving elements. The input and output members may rotate independently of each other when the clutch assembly is not actuated.

A flux concentrating annular housing60, which engages the bell-shaped housing5, is used to house and provide protection for the solenoid coil65. Electrical power is supplied to the solenoid coil through a conductor cable70. An air gap75proximate to the solenoid coil65and annular housing60separates the coil and housing from an armature plate80. The armature plate80engages the actuator hub83and is secured in place using a snap ring67positioned in a groove integrally formed with the actuator hub83.

When the solenoid coil65is energized, the generated magnetic field causes the armature plate80to be attracted by and move towards the flux concentrating annular housing60and solenoid coil65. This attraction and movement effectively decreases the width (w) of the air gap75between the annular housing/solenoid coil arrangement and the armature plate80. Since parts are moving relative to one another, the width, w, of the air gap75preferably remains at a value greater than zero (i.e., a clearance gap remains). The attraction and movement of the armature plate80further causes the actuator hub83to move along the surface of the input member25thereby engaging and transmitting a force through thrust bearing56to the first end100of a cam lever assembly85. This cam lever assembly85, which pivots around a pivot point or fulcrum87, in turn reversibly engages a primary friction clutch pack90through its second end101. The force transmitted through the cam lever assembly85to the clutch pack90, causes the plates within the clutch pack90to compress against one another. One skilled in the art will understand that more than one cam lever assembly85may be incorporated into the clutch assembly1in order to more evenly distribute the force transmitted to the clutch pack90.

Referring toFIG. 1Bthe mechanical advantage provided by the cam lever assembly85is dependent upon the magnitude of the force transferred through the thrust bearing56to the first end100of the assembly85, the distance (D1) for the lever or effort arm between the first end100at its contact point with the thrust bearing56and the pivot point87in the assembly, and the distance (D2) for the effort arm between the pivot point87and the second end101of the assembly where it contacts plate105. Under a condition of static equilibrium, the input force (Fin) transferred to the first end100multiplied by the distance, D1will be equivalent to the output force (Fout) multiplied by the distance, D2. In general, the cam lever assembly85acts a force multiplier with the output force, Fout, being greater than the input force, Fin, due to the difference in distances D1and D2. Preferably D1is greater than the distance, D2. One skilled in the art will understand that the distance, D2may change based on the shape of the bottom of the second end101that makes contact with plate105. Another aspect of the present invention is that the direction of the output force, Fout, is opposite that of the input force, Fin.

One advantage of the present invention is that the clutch can be used in a preemptive manner. In other words, the force transmitted through the cam lever assembly85to the clutch pack90does not rely upon the relative difference in motion between the first end100and second end101of the cam lever assembly85, but rather simply the energization of the solenoid coil65. Thus the cam lever assembly85may engage the clutch pack9in the absence of any movement or rotation of the input member25or the output hub45. In comparison, the rotation of one element relative to a second element in a conventional ball ramp mechanism is necessary for the mechanism to impart a clamping force against the clutch pack.

One skilled in the art will understand that the curved geometry of the cam lever assembly85between the first end100and second end101is a design feature that can impact the magnitude of the transferred force. As shown inFIG. 1B, when the lever is caused to move by the transfer of Finat the first end100, the point of contact established between the second end101and the clutch pack9in order to transfer Foutwill change, thereby, modifying the output packing force, D2. In addition, the cam assembly may be spring loaded and/or configured to mitigate the effect of speed or centrifugal forces. Thus when the solenoid coil65is not energized, the cam lever assembly85will not engage the clutch pack9by dynamic forces.

The motion of the lever may be physically restricted through the use of a mechanical stop102. The use of such a stop102prevents over energization of the clutch assembly1. One important design consideration in determining the geometry of the cam lever assembly85and the clearances between the various moving parts in the clutch assembly1is to insure that the clutch assembly1does not self-engage or become self-locked during engagement, but rather is capable of exhibiting a modulated output (e.g., transfer torque) in direct response to a modulated input signal (e.g., current applied to a solenoid).

The primary clutch pack90includes a plurality of smaller diameter plates104that engage the inner surface of the input member25. These smaller clutch plates104may be rotated along with the input member25. Similarly, interleaved between each pair of smaller clutch plates104is a larger diameter plate103that has an internal feature that can engage and mesh with a complimentary feature formed by the inner surface of the output hub45. Thus the larger diameter plates103are freely rotatable with the output hub45. The surface of each of the plates may include a suitable friction material. When the larger diameter and smaller diameter plates are compressed together the friction arising between the plates is enough to couple the input member25and the output hub45together. Thus allowing torque transfer through them.

The electrical characteristics exhibited by the solenoid coil65, the current applied to the coil65, the air gap75between the solenoid coil65and the armature80, and the mechanical characteristics exhibited by the cam lever assembly85represent important design considerations that may be used to insure that the clutch assembly does not self-engage. More specifically, the electrical characteristics of the solenoid coil65relate to the magnitude and strength of the magnetic flux generated, while the mechanical characteristics of the cam lever assembly85relate to the magnitude of the force ultimately transmitted to the plates in the clutch pack90. More specifically, the magnitude of the transmitted force is related to the overall length of the cam lever85and the angle established between the first100and second101ends of the lever. It is desirable that the electromagnetic clutch assembly1be capable of modulating the clamping of the friction clutch plates in the primary clutch pack90in response to the electrical input to the solenoid coil65. In other words it is desirable that the solenoid energy be either proportional to or substantially similar to the compressive energy to which the clutch pack90is subjected.

During operation the current flowing to the solenoid coil65is controlled by an electronic controller or other means known to one skilled in the art. Thus the current flowing through the solenoid coil65controls not only the generation of the magnetic field flux that attracts the armature plate80, but also the resulting movement of the actuating hub83and the force transmitted through the cam lever assembly85to the clutch pack90.

The following specific example is given to illustrate the invention and should not be construed to limit the scope of the invention.

An electromagnetic clutch assembly1was constructed in accordance with one embodiment of the present invention. The physical characteristics associated with the frictional clutch pack90incorporated into this clutch assembly1corresponded to nine small and large interleaved plates.

The magnitude of electrical current supplied to the solenoid coil65of the clutch assembly1was varied and the resulting energy generated and the compressive forces created along with the magnitude of compression within the clutch pack90were measured. InFIG. 2, the overall compression energy generated by the application of electrical current to the solenoid coil65is plotted as a function of the resulting magnitude of the compression that occurred within the clutch pack90. The non-linear relationship established shows a proportional relationship between the compression energy and the magnitude of the pack compression. As the amount of energy generated increases, the degree to which the clutch pack is compressed also increases. The compression energy is transmitted to the clutch pack90as a force transmitted through the actuating hub83and cam lever assembly85.

Referring now toFIG. 3, the magnitude of the force transmitted through the cam lever assembly85to the clutch pack90is plotted as a function of the resulting magnitude of the compression that occurred within the clutch pack90. The relationship between the applied force and the pack compression is substantially linear in nature as demonstrated by the constant slope of the line generated by the plotted data.

The applied force can be correlated back to the reduction in the width of the air gap75that occurs when the magnetic flux generated by the electrical current flowing through the solenoid coil65and flux concentrating annular housing60attracts the armature plate80. InFIG. 4, the magnitude of the force generated that can be transmitted through the actuating hub83and cam lever assembly85to the clutch pack90is plotted as a function of the width of the air gap75between the flux concentrating housing60and armature plate80. The non-linear relationship shown by the data demonstrates that the generated force increases as the width of the air gap decreases.

The overall magnitude of the compression energy that will be transmitted can be determined by calculating the area (A) under the force-gap curve (seeFIG. 4) over the distance that the gap has decreased. For example, inFIG. 4a decrease in the width (w) of the air gap from about 0.50 mm to about 0.05 mm results in a compression energy of about 2,042 N-mm (area under the curve). According to this one embodiment of the present invention the change in the width (w) of the air gap represents a reduction of about 90%. Referring once again toFIG. 2, a packing compression of about 0.45 mm is shown to correspond to the compression energy of about 2,042 N-mm as described above.