Field of Invention

The invention relates to an electromagnetic jaw clutch, in particular for large transmissions such as ship transmissions, particularly hybrid electric-diesel transmission.

Prior art

Electromagnetic jaw clutches transmit torque mechanically but are activated electrically. Basically, electromagnetic jaw clutches are of two types. In the first type, the torque is transmitted when the electromagnet is electrically excited, and in the second type, the torque is transmitted when the electrical excitation of the electromagnet is interrupted. Electromagnetic jaw clutches are suitable for transmitting large torques that occur e.g. in ship transmissions, at relatively low speeds. Hybrid transmissions are known from prior art, in which working element (e.g. a ship propeller) can be driven by an electric motor or by a diesel engine. Prior art transmissions do not allow clutch engagement at high revolutions, much less at non-synchronous revolutions, as this would damage the teeth of the jaw clutch. Prior art transmissions allow clutch engagement at low synchronous revolutions (max. 50 rpm) and at higher revolutions due to special tooth design, where the transmission torque is significantly reduced due to active engagement.

A crown gear electromagnetic coupling disclosed in U.S. Patent Application 2011/0290055 A1 is known from prior art. In this coupling, the torque is transmitted when the electromagnet is electrically excited. When the excitation of the electromagnet ceases, the spring separates the crown gears from each other and the torque ceases to be transmitted. The coupling comprises an electromagnetic winding arranged within a housing, on which the first crown gear is mounted. The electromagnet can attract a second crown gear that is prestressed by a spring by pushing the crown gears one from the other when the electromagnet is not electrically excited. When one or both crown gears are damaged when using the coupling, the drive must be dismantled and the entire coupling disassembled so that the damaged crown gear can be replaced. This is time consuming, and in the case of large transmissions also physically demanding and strenuous.

Technical problem

The technical problem is how to provide an electromagnetic jaw clutch, especially for large hybrid transmissions, that will allow synchronisation and clutch engagement at diesel engine idling speeds and electric motor revolutions almost identical to those of the diesel engine, deviating from the diesel engine revolutions by +/- 50 rpm, and providing an unreduced torque over the entire revolution range of the whole system.

A further technical problem is how to provide an electromagnetic jaw clutch which will allow its quick and easy replacement in the event of damage to the crown gear.

Solution to the technical problem

The technical problem is solved with an electromagnetic jaw clutch, in particular for hybrid ship transmissions, comprising:

- a first part of a clutch connectable to a drive/output shaft,

- a first crown gear that is detachably connected to the first part,

- a second part of a clutch connectable to an output/drive shaft,

- a second crown gear that is detachably connected to the second part and arranged in such a way to engage in a form-fit manner the first crown gear to transmit torque, - a third crown gear arranged coaxially with the first crown gear and detachably connected to the first part and having a plurality of teeth in the form of ring segments, the tips of which are formed as flat faces, and

- a fourth crown gear arranged coaxially with the second crown gear and in a way to frictionally engage the third crown gear to transmit torque and detachably connected to the second part and having a plurality of teeth in the form of ring segments, the tips of which are formed as flat faces,

- wherein the tooth tips of the third crown gear extend beyond the tooth tips of the first crown gear and/or the tooth tips of the fourth crown gear extend beyond the tooth tips of the second crown gear, and

- the teeth of the third crown gear and the fourth crown gear being formed by a clearance fit,

- wherein the number of teeth of the first and second crown gears is a multiple of the number of teeth of the third and fourth crown gears, and

- wherein the guiding flanks of each tooth of the third or fourth crown gear are substantially aligned in the radial direction with the centre lines of the gaps between the teeth of the first or second crown gear, respectively.

The advantage of the electromagnetic jaw clutch according to the invention over known clutches is that, when the clutch is coupled at high revolutions, the first and second parts of the clutch are synchronised before the teeth of the first and second crown gears come into engagement, thereby preventing damage to the teeth of the first and second crown gears.

Figure 1: Electromagnetic jaw clutch

Figure 2: First part of the clutch with a first and third crown gear Figure 3: Teeth of the first and third crown gears in radial view Figure 4: Teeth of the first and third crown gears in radial view The technical problem is solved with an electromagnetic jaw clutch 1, in particular for hybrid ship transmissions, comprising:

- a first part 2 of a clutch connectable to a drive/output shaft,

- a first crown gear 4 that is detachably connected to the first part 2 of the clutch,

- a second part 3 of the clutch connectable to an output/drive shaft,

- a second crown gear that is detachably connected to the second part 3 of the clutch and arranged in such a way to engage in a form-fit manner the first crown gear to transmit torque,

- a third crown gear 5 arranged coaxially with the first crown gear and detachably connected to the first part 2 of the clutch and having a plurality of teeth 7 in the form of ring segments, the tips of which are formed as flat faces, and

- a fourth crown gear arranged coaxially with the second crown gear and in a way to frictionally engage the third crown gear to transmit torque and detachably connected to the second part and having a plurality of teeth in the form of ring segments, the tips of which are formed as flat faces,

- wherein the tooth tips of the third crown gear extend beyond the tooth tips of the first crown gear and/or the tooth tips of the fourth crown gear extend beyond the tooth tips of the second crown gear, and

- the teeth of the third crown gear and the fourth crown gear being formed by a clearance fit,

- wherein the number of teeth of the first and second crown gears is a multiple of the number of teeth of the third and fourth crown gears, and

- wherein the guiding flanks of each tooth of the third or fourth crown gear are substantially aligned in the radial direction with the centre lines of the gaps between the teeth of the first or second crown gear, respectively.

A possible example of a clutch application is in ship transmission. When a ship sails off, an electric motor is used, e.g. rotating at 2500 rpm. After the ship has sailed off, the electric motor revolutions lower to e.g. 1250 rpm. A diesel engine rotates at e. g. 1200 rpm. When the clutch 1 is engaged, the first part 2 of the clutch and the second part 3 of the clutch approach each other. The non- synchronous rotation of the first and second parts of the clutch causes the tooth 6 tips of the third crown gear to come in contact with the tooth tips of the fourth crown gear. The clutch acts as a friction clutch at this point, as the torque of the transmission portion is transferred to the output portion through friction between the tooth tips. The clutch therefore allows torque to be transmitted by friction while the first and second parts of the clutch rotate in a non- synchronous manner. When the rotation of the first and second parts of the clutch is synchronous or nearly synchronous, the teeth of the third and fourth crown gear, respectively, slip into the gaps between the teeth of the fourth and third crown gear, respectively. At the same time, the teeth of the first and second crown gears come into contact, transferring the torque from the driving portion to the output portion by means of a form-locked connection. However, the teeth of the third and fourth crown gears do not transmit torque due to a clearance fit in the gaps between the teeth of the opposite crown gear.

The number of teeth 6 of the first crown gear and second crown gear, respectively, is an integer multiple of the number of teeth 7 in the form of ring segments of the third and fourth crown gear, respectively.

The first and second crown gears are fitted with Hirth teeth.

The radial edges of the teeth in the form of ring segments of the third and fourth crown gears, respectively, are formed by chamfering or rounding with a second radius

The tips of the teeth of the first and second crown gears, respectively, are formed in the radial direction by rounding with a first radius Ri, where R ₂ < Ri. The radial flanks of the teeth in the form of ring segments of the third and fourth crown gears, respectively, are formed at an angle b with respect to the radial plane perpendicular to the plane of the clutch. The radial flanks of the teeth of the first and second crown gears, respectively, are formed at an angle a with respect to the radial plane perpendicular to the plane of the clutch, wherein b = a - (1° to 3°).

The tooth tips of the third crown gear extend beyond the tooth tips of the first crown gear and/or the tooth tips of the fourth crown gear extend beyond the tooth tips of the second crown gear by at least 0.05 mm.

The first part of the clutch may comprise an electromagnet holder and an electromagnet which can be electrically excited, while the other part of the clutch acts as an anchor, the first and/or second part being formed of two pieces which are movably arranged relative to each other in axial direction of the clutch by an intermediate arrangement of a spring means, the electromagnetic jaw clutch transmitting torque when the electromagnet is electrically excited.

Alternatively, the first part of the clutch may be formed as a hub and the second part of the clutch comprises an anchor and an electromagnet holder with an electromagnet which can be electrically excited, the anchor and the electromagnet holder being movably arranged relative to each other in axial direction of the clutch by an intermediate arrangement of a spring means, and the transmission of the torque from the first to the second part being interrupted when the electromagnet is electrically excited.

The first, second, third and fourth crown gears may further be divided into n segments and have a number of teeth that is an integer multiple of n, wherein n > 2, preferably n > 3, and wherein the crown gears are connected with the first and the second part, respectively, with fastening means arranged in the radial direction of each crown gear. The crown gears are divided into segments in the area of the gap between the teeth.

The fastening means are formed by screws, preferably socket head screws with a hexagonal inner hole, and washers. Each segment is tightened with at least 4 screws.

Between the adjacent screws, in the radial direction of each crown gear, a cylindrical pin is arranged so that it extends through the crown gear to the depth of the first and second part of the clutch, respectively. Each segment is provided with at least two cylindrical pins. The cylindrical pin serves to better position the segment of the crown gear on the first and the second part of the clutch, respectively, and safer operation during the operation of the clutch, as the torque can be transmitted from a part of the clutch via the crown gear even in the event of screws falling out. Each cylindrical pin is secured against falling out by a spring pin. The cylindrical pin is preferably formed by a threaded borehole in the axial direction of the cylindrical pin. The purpose of the threaded borehole is to screw in the screw when removing the crown gear, by means of which the cylindrical pin together with the spring pin is pulled out of the hole.

The crown gears are made of steel or bronze.

In the event of damage to the crown gear, the fastening means of the crown gear and individual damaged segments of the crown gear are removed in the radial direction and replaced with new ones.

A further advantage of the electromagnetic jaw clutch according to the invention over known clutches is that in the event that the first or second crown gear nevertheless gets damaged it is not necessary to dismantle the drive and disassemble the entire clutch, which facilitates work and allows quick replacement of a damaged crown gear with a new one.