Electromagnetic inertia brake for a multiple-ratio power transmission

1. Field of the Invention

The invention relates to power transmission mechanisms with a clutch brake for overcoming inertia during ratio changes.

2. Background Art

A typical powertrain for a road vehicle comprises an engine and a multiple-ratio power transmission together with a master disconnect clutch for establishing and disestablishing a power flow path from the engine through the transmission. Transmission ratio shifts are accomplished during a ratio shift interval in which the vehicle operator disengages the master clutch. A torque input shaft for the transmission must decelerate during a transmission ratio shift so that the relative speeds of gearing elements of the oncoming torque flow path are generally in synchronism. The time required to accomplish a ratio shift and to improve shift quality is dependent on deceleration rate of a transmission power input shaft. It is known design practice to increase the rate of deceleration by using an inertia brake for the power input shaft during a shift interval, thereby improving shift quality.

An example of a transmission input shaft inertia brake with an electromagnetic brake actuator is disclosed in U.S. Pat. No. 7,000,748. That patent is assigned to the assignee of the present invention. The brake includes an armature that frictionally engages a stationary friction surface on a transmission housing thereby retarding rotation of the transmission torque input shaft at the onset of a ratio shift.

Another example of an electromagnetic inertia brake is disclosed in U.S. patent publication 2007/0095625, which also is assigned to the assignee of the present invention. An armature hub disclosed in that publication is drivably connected to the power input shaft of the transmission, such as by a spline or keyway and key connection. An armature plate is secured to the armature hub by a flexible drive plate. When the electromagnetic coil windings are energized, the flexible drive plate allows the armature to frictionally engage a friction surface for the transmission housing. The braking capacity of the electromagnetic brake of the patent publication is determined by the friction torque developed on a single side of the armature.

The inertia brake of the present invention is capable of substantially increased braking capacity for the power input shaft of a multiple-ratio transmission. Unlike the design of the '625 patent publication, the armature of the inertia brake of the present invention does not rotate with the power input shaft of the transmission. Rather, it is fixed to the transmission housing. Provision is made for allowing the armature to adjust axially in the direction of the transmission power input shaft, although it is prevented from moving rotatably relative to the transmission housing. The armature may be biased in an axial direction, which tends to separate the armature from the transmission housing. A reaction plate is situated between the movable, non-rotating armature and the transmission housing. The reaction plate, in turn, is connected to a reaction plate hub. A driving connection, such as a spline or keyway, connects the hub to the transmission power input shaft. An annular friction surface of the reaction plate frictionally engages a friction surface on the transmission housing and another friction surface of the reaction plate frictionally engages the movable non-rotating armature. The dual friction surface feature improves braking capacity.

According to one aspect of the invention, the non-rotating armature is spaced from the transmission housing and the reaction plate is located in the space between the transmission housing and the armature. Electromagnetic coil windings are disposed in the housing at an interface of the reaction plate and the transmission housing. The coil windings create a flux field that causes a clutch engaging force on the armature.

In another embodiment of the invention, the housing has a main housing portion and a second housing portion that are spaced apart, the non-rotatable armature and the reaction plate being disposed between the housing portions. The coil windings are located in the second housing portion. This facilitates repair and servicing of the brake without fully disassembling the brake assembly.

According to another feature of the invention, a torsional damper is disposed between the reaction plate and the power input shaft to attenuate or dampen torsional oscillations as the inertia brake is applied.

FIG. 1 is a schematic diagram of a typical heavy-duty master clutch, a transmission with multiple-ratio gearing and a clutch release bearing for engaging and disengaging the master clutch;

FIG. 2 is a cross-sectional view of the electromagnetic brake of the invention as seen from the plane of section line 2 - 2 of FIG. 2 a;

FIG. 2 a is an axial view of the electromagnetic brake as seen from the left side of the transmission illustrated schematically in FIG. 1 ;

FIG. 3 is a cross-sectional view of the electromagnetic brake of the invention including damper springs as seen from the plane of section line 3 - 3 of FIG. 3 a;

FIG. 3 a is an axial view of the electromagnetic brake of the invention as seen from the left side of the transmission seen in FIG. 1 ;

FIG. 4 is a cross-sectional view of the electromagnetic brake of the invention wherein the electromagnetic coil is relocated relative to the coil location of FIG. 3 ;

FIG. 5 is a cross-sectional view of an alternate embodiment of the invention as seen from the plane of section line 5 - 5 of FIG. 5 a;

FIG. 5 a is an axial view of the alternate embodiment of the invention of FIG. 5 as seen from the left side of the transmission illustrated in FIG. 1 ; and

FIG. 6 is another alternate embodiment of the invention wherein the armature reaction plate is frictionally engageable with a multiple disk clutch assembly connected to the transmission housing.

FIG. 1 shows in schematic form a vehicle powertrain comprising an engine 10 , a multiple-ratio power transmission 12 having multiple-ratio gearing 14 and a master clutch 16 with a driver-actuated clutch release bearing. The master clutch can be opened and closed by a vehicle operator to establish and disestablish a mechanical power flow path from engine 10 to transmission power input shaft 18 and to the transmission gearing 14 .

The transmission has a power input shaft 18 , which is drivably splined to an engine crankshaft through master clutch 16 .

A transmission mainshaft 20 delivers driving torque to a transmission power output shaft, which is drivably connected to vehicle traction wheels through a driveshaft and a differential and axle assembly. Reference may be made to U.S. patent publication 2007/0095625 for a description of a typical master clutch that can be used in this environment.

FIG. 2 is a cross-sectional view of the inertia brake of the present invention. A portion of the transmission housing, shown at 22 , has an annular space that receives coil windings of an electromagnetic solenoid brake coil 24 . An annular reaction brake plate 26 is situated adjacent an annular friction brake surface 28 on housing portion 22 . An armature plate 30 is secured to housing portion 22 by a plurality of studs 32 , which extend through oversize openings in armature plate 30 and through openings in annular cover plate 33 . Sleeves 34 surrounding studs 32 serve as spacers between the armature plate 30 and the housing portion 22 . The spacers are surrounded by coil springs 36 , which establish a calibrated separation force between the housing portion 22 and the armature plate 30 . The armature plate 30 thus is non-rotatable, but it is movable axially.

Reaction plate 26 engages the annular friction surface 38 on the non-rotatable armature plate. The reaction plate 26 is secured, as shown, to an internally splined hub 40 , which is splined to a splined transmission input shaft corresponding to shaft 18 in the prior art construction shown in FIG. 1 . Reaction plate 26 thus rotates with the transmission power input shaft on the torque flow downstream side of the master clutch.

When coil 24 is energized, the armature plate is drawn toward the reaction plate 26 . A retarding force on the transmission torque input shaft is created by the friction torque on each annular surface of the reaction plate 26 . This essentially doubles the reaction torque that would be available in an inertia brake design of the type disclosed in U.S. patent publication 2007/0095625 and U.S. Pat. No. 7,000,748. This will make it possible to increase the rate of deceleration of the input shaft during a ratio shift event, which reduces the ratio shift time. The inertia effect of the rotating mass of a clutch and armature assembly of the type shown in these references is not present in the design of the present invention. The only rotating mass of the inertia brake of the present invention is the mass of the rotating reaction plate 26 . This feature also contributes to a reduction in the time required to execute a ratio change.

The inertia brake retarding force occurs when the electric coil assembly is excited or energized. This generates a magnetic field, which pulls the non-rotating armature into frictional engagement with the rotating armature plate and the armature plate is brought into frictional engagement with the friction surface of the housing portion 22 .

FIG. 3 discloses a modified design with a housing portion 42 , which corresponds to the housing portion 22 of FIG. 2 . A non-rotatable armature 44 is located on one side of rotating reaction plate 46 . Reaction plate 46 is positioned between a frictional annular surface on the armature 44 and a frictional annular surface of the housing portion 42 . The rotating reaction plate 46 frictionally engages the armature 44 and the annular surface of the housing portion 42 . Plate 46 is coupled to a reaction plate hub 48 by damper springs 50 , which are spaced about the axis of the hub 48 in tangential disposition with respect to the central axis of the brake assembly, as shown in FIG. 3A . This establishes a resilient connection between the transmission power input shaft and the plate 46 , which attenuates torsional disturbances upon engagement of the inertia brake.

Armature 44 is secured to housing portion 42 by a bracket 52 having a periphery that is secured to the outer periphery of the housing portion 42 . The periphery of the armature 42 is drivably and slidably connected, such as by interlocking spline elements, to the outer periphery of the bracket 42 . This connection permits the armature 44 to shift in the direction of the axis of the inertia brake, although rotary motion of the armature plate 44 is prevented. Upon excitation, the electric coil assembly generates a magnetic field that pulls armature plate 44 across an air gap.

FIG. 4 shows another modified design with a different arrangement for the electromagnetic coils of the electromagnetic brake. A housing portion 54 of FIG. 4 has a ring with an annular opening that receives the electromagnetic coil 24 ′. Housing portion 54 is joined to housing portion 58 by a bracket 60 . A non-rotatable armature 62 is located between housing portion 54 and housing portion 58 . The armature 62 is externally keyed or splined at 64 to bracket 60 to permit axial movement of the armature while preventing rotary motion of armature 62 relative to housing portions 54 and 58 . Reaction plate 56 is located between the armature 62 and housing portion 54 . Friction material can be provided on either, or both, of the annular friction surfaces of the armature reaction plate 56 .

The assembly illustrated in FIG. 4 can be secured to the transmission housing by mounting bolts or studs supported by a bearing support wall or a bearing cap of the type seen in the transmission illustrated in FIG. 1 at 65 .

FIGS. 5 and 5 a show a variation of the inertia brake design illustrated in FIG. 4 . Unlike the inertia brake of FIG. 4 , the housing portion 54 ′ seen in FIG. 5 has multiple electromagnetic clutch coil windings. A pair of coil windings is seen at 66 and 68 in FIG. 5 , and another pair is seen at 70 and 72 in FIG. 5 a . A different number of coil windings could be used as well. As in the case of the design of FIG. 4 , the electromagnetic coil windings create a magnetic field, which pulls the non-rotating armature 62 ′ toward the housing portion 54 ′. This creates frictional torque on the frictional surfaces for the rotating reaction plate that engage the armature 62 ′ and the friction surface of the housing portion 54 ′.

Elements of the electromagnetic brake of FIG. 5 have numerals that correspond to numerals for corresponding elements of the design of FIG. 4 , although prime notations are added to the numerals of FIG. 5 .

FIG. 6 shows another embodiment of the invention. A housing portion 74 has a bracket 76 that secures housing portion 74 to an annular housing portion 78 . Housing portion 78 has a circular cavity or opening that receives the coil windings 80 of the electromagnetic brake. Annular armature 82 is non-rotatably and slidably secured by a connection, such as by mounting studs or posts 77 , to housing portion 78 . The annular armature 82 engages a multiple disk brake assembly 84 , which comprises externally splined disks 86 connected to rotary reaction plate 85 , and internally splined disks 88 splined to housing portion 78 . When the electromagnetic coil windings are energized, armature 82 , connected slidably by posts 77 to housing portion 78 , engages the friction disks, thereby retarding the hub 90 , which is splined or otherwise secured to the transmission power input shaft. This design of FIG. 6 may provide increased braking capacity because of the multiple friction surfaces provided by the brake assembly 84 .

Although embodiments of the invention have been disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications and equivalents thereof are intended to be covered by the following claims.