Patent Description:
Gear trains according to the state of the art as used in transmissions, gearboxes, axles, differentials, steering gears, or power take offs have housings (also known as casings) that combine the function of mounting and supporting the moving parts and the function of encapsulating the moving parts in one structure. That is, a housing not only performs the job of encapsulation with a continuous skin, but it also carries out the structural tasks. This principle is usually adopted by any system in which rotating gears transmit mechanical power or positional definition. <CIT> discloses an encapsulated gear train according to the preamble of claim <NUM>.

One drawback of such a construction is that this continuous skin encapsulates the entire transmission and thus provides a large surface that is very efficient at noise radiation. Since it is also a structural part, this same housing is subjected to vibrations that may be caused by the gears due to transmission error, leading to the generation of airborne vibration.

A further drawback relates to the freedoms of how the transmission can be designed. Since both functions, support and encapsulation, usually come with restrictions of their own kind, the designer is required to find some compromise.

Therefore, the invention provides an improved gear train. The invention allows for the provision of a stiffer, more robust, lighter, and quieter gear train.

This is achieved by a constructional separation of the function of structural support and the function of encapsulation of the gear train.

The invention relates to an encapsulated gear train as defined in claim <NUM>.

In some embodiments, the encasement is, in terms of substance, a separate item from the support frame.

In some embodiments, the encasement is, at least for the most part, made of a non-metal material.

In some embodiments, the gear train further comprises a lubricant distribution system configured to distribute lubricant inside the encasement.

In some embodiments, at least one of (a) an interior of the encasement, (b) the support frame, and (c) a lubricant guiding element arranged on the encasement or the support frame is part of the lubricant distribution system and configured to guide the lubricant towards at least one of (i) the gears and (ii) bearings, said gears and bearings being mounted on the input shaft or the output shaft which are rotatably mounted in the support frame.

In some embodiments, the encasement is configured to encapsulate the whole support frame and to further encapsulate a portion of the structure.

In some embodiments, the support frame is produced by at least one of casting, sintering, forging, machining, moulding, or additive manufacturing.

In some embodiments, the support frame is designed based only or mainly on mechanical requirements.

In some embodiments, the gear train further comprises a locating element arranged between the encasement and the support frame.

In some embodiments, the gear train further comprises an air ventilation system with an air inlet, an air outlet, and an air accelerator, wherein the air inlet and the air outlet are arranged on the encasement.

In some embodiments, the machine is a vehicle, an aircraft, a ship, a train, or a wind turbine. In particular, the vehicle is an electric vehicle.

In some embodiments, the encapsulated gear train is a single-speed two-stage transmission. In particular, the machine is an electric vehicle and the encapsulated gear train is a single-speed two-stage transmission.

In some embodiments, the support frame is mounted to a gas turbine, an electric motor, an engine, or a generator.

The invention further relates to an electric powertrain comprising a gear train according to the disclosure herein and an electric motor, wherein the encasement is configured to further encapsulate the electric motor.

By way of example only, preferred embodiments of the invention will be described more fully hereinafter with reference to the accompanying figures, wherein:.

<FIG> shows a gear train <NUM>, in particular a gear box or transmission, according to the state of the art, having a housing <NUM> that combines in itself the structure for mounting the transmission shafts and the encapsulation to seal up the transmission gears. By mounting this comprises providing structural support against loads such as gravity and separating forces generated by the gears when power is passed through a meshing gear pair. By encapsulation this comprises containing the lubricant within the transmission and preventing ingress of dust, dirt and water. Such a typical transmission housing is also shown in <FIG>.

Further with reference to <FIG>, the input shaft <NUM> driven by the motor <NUM> is mounted in the housing <NUM> and is supported with a bearing <NUM>. Of course, the motor <NUM> could have a rotor shaft that is directly fixed to the input shaft <NUM>, but for the sake of simplicity it is shown as one shaft here.

In this example, the motor <NUM> and the housing <NUM> are connected by bolted joints <NUM>. The gear <NUM> arranged on the input shaft <NUM> drives the gear <NUM> arranged on the intermediary shaft <NUM> to achieve a first reduction. Said intermediary shaft <NUM> is mounted in the housing <NUM> by the bearings <NUM>. A further gear <NUM> is arranged on the intermediary shaft <NUM> to drive the gear <NUM> arranged on the output shaft <NUM> to achieve a second reduction. Said output shaft <NUM> is mounted in the housing <NUM> by the bearings <NUM>. Seals <NUM> prevent particles (e.g. dust, dirt, or water) from entering the housing <NUM> and lubricant to leave the housing <NUM> at the point at which the output shaft transmits power out of the transmission. The output shaft <NUM> drives the drive shafts <NUM> via universal joints <NUM>.

The gears <NUM>, <NUM>, <NUM>, <NUM> and shafts <NUM>, <NUM>, <NUM> are subject to gravitational loading. Additionally, as power is transmitted through the meshing gears the gears force themselves apart. These gravitational forces and gear loads are passed through the bearings <NUM>, <NUM>, <NUM>, into the housing <NUM> and through mounts <NUM> to the structure <NUM>. This can be described as the load path. The motor <NUM> is mounted on the chassis <NUM> with another isolating mount <NUM>. The housing <NUM> consists of two halves that are connected by bolted joints <NUM>. Lubricant that is needed for reducing friction and wear and removing heat from the rolling/sliding contacts of the gears is kept inside the system because the housing <NUM> assumes - in addition to the function of structural support - the encapsulation function that also prevents the ingress of dust, dirt and water.

<FIG> shows a gear train <NUM> for a machine as an embodiment of the invention. Specifically, the gear train <NUM> is a transmission comprising a non-encasing support frame <NUM>, which is indicated as the bold-lined structure. "Non-encasing" means open so that the shafts and gears are not sealed by the support frame. Oil is able to pass through the support frame and no protection is provided by the frame from dust, dirt or water. An input shaft <NUM> is rotatably mounted in the support frame <NUM> by bearing <NUM>, and an output shaft <NUM> is rotatably mounted in the support frame <NUM> by bearings <NUM>. An optional intermediary shaft can be provided as in <FIG>. Gears <NUM> and <NUM> (and the optional gears on the intermediary shaft) are provided to operatively connect the input shaft <NUM> with the output shaft <NUM>. An encasement <NUM> encapsulates the input shaft <NUM>, the output shaft <NUM>, the gears <NUM> and <NUM>, and at least a portion of the support frame <NUM>. The support frame <NUM> is immediately mounted on the structure <NUM> of the machine such that the support frame <NUM> does not pass any structural loads on to the encasement <NUM>. For example, the support frame <NUM> is mounted via isolating mounts <NUM> (=fixing point) and <NUM> on the structure <NUM>.

The shown configuration is one example of how the support frame can be mounted on a structure of the machine, i.e. in this embodiment, the structure is in part the chassis <NUM> and in part the motor <NUM>, and the machine may be a vehicle. In further embodiments of the invention, the structure may be only the chassis or only the motor or any other part of a vehicle, tractor, aircraft, train, ship, or wind turbine.

Thus, an important difference between the inventive transmission and the prior art is that the encapsulating part (prior art: housing; present invention: encasement) is not in the load path between the shafts and gears and the structure. In accordance with embodiments of the invention, the encapsulating part is resting totally on the shaft support frame and is isolated from it by antivibration elements. The encapsulating part (=encasement) has thus merely or mostly the function of (a) keeping the lubricant within its dimensions, i.e. inside its interior where the moving parts (shafts, gears) are located as well as (b) preventing of dust, dirt and water ingress. The encasement is not affected by gravitational forces or gear loads coming from the support frame.

The support frame <NUM> may be attached to the motor <NUM> by at least one bolted joint <NUM>, and the motor <NUM> may be mounted on the structure <NUM> by isolating mount <NUM>. The mounts <NUM> and <NUM> provide freedom of movement between the transmission and the structure. The structural loads (flex due to torque applications, temperature changes, external shock loads) pass through these mounts, and since the mounts are provided with a degree of flexibility, the gearbox moves relative to the environment/vehicle.

<FIG> shows the support frame <NUM> isolated from all other components of the transmission <NUM>. Because the support frame <NUM> can transfer all the load caused by the weight of the shafts and gears and by operating the transmission (gear loads) into the structure <NUM>, the encasement <NUM> can be configured to carry nothing but its own weight. Thus, the encasement <NUM> can be manufactured from a light-weight material and be optimized for size and/or shape. In particular, plastic is lightweight and has excellent acoustic damping properties compared to cast iron, aluminium, or magnesium, which are the metals that state of the art transmission housings are usually made from.

The support frame <NUM> on the other hand can be designed to have optimized strength and/or stability while omitting material that does not contribute to the strength. Therefore, the invention allows for a lighter and more stable construction that is, in particular, based on mechanical (static, dynamic, and fatigue) requirements. A first iteration of such optimization can be seen by stepping from <FIG> (which shows a part of a conventional transmission housing that combines the structural support and the encapsulation of the shafts and gears) to <FIG> (which is the support frame <NUM> of the invention). The support frames shown in <FIG> correspond to the same gear train arrangement as does the housing shown in <FIG>. For example, the static and dynamic loads that the structure will be exposed to can be determined with a simulation algorithm such as finite element analysis. When generating a 3D model of the optimized support frame structure, further restrictions can be taken into account such as the mounting spots (for attaching the support frame to the structure) or the joint spots <NUM> that are used to connect further parts of the support frame.

In a further iteration, the structure of the support frame can be further simplified, especially when, as shown in the example of <FIG>, determining that the amount and position of the joint spots is free to be chosen by the simulation algorithm. The optimized support frame assumes what resembles an "organic" shape which may be difficult to manufacture with conventional production methods. Therefore, in an embodiment of the invention, the support frame may be produced by additive manufacturing. Casting and sintering may be alternatives to this manufacturing method and, when altering the optimized support frame to suit the method, even forging may be an option. These named manufacturing methods require very little finishing processes (optimally, only machining the bearing seats and bolting surfaces). Another manufacturing method allowing to use the full potential of the inventive construction is moulding composite materials, e.g. fibre-reinforced plastic. The different manufacturing methods can also be combined to form a hybrid system, whereby e.g. some parts of the support frame are made by forging and machining and then additive manufactured structure is added. Other combinations of the aforementioned manufacturing methods may apply as well.

The separation of the two functions (structural support and encapsulation) further effects a separation of noise abatement, i.e. abatement of air borne noise being assigned to the encapsulation function (encasement) and abatement of structure borne noise being assigned to the structural support function (support frame).

Furthermore, vibration isolating seals could be provided wherever the encasement <NUM> may be in contact with the support frame <NUM>. <FIG> shows such a seal <NUM> surrounding the structural mount <NUM> that is intended for connecting the support frame to the structure. In this example, two parts <NUM> and <NUM> are joined to form the encasement <NUM>, wherein the mount <NUM> protrudes the encasement <NUM> at the seam between the two parts <NUM> and <NUM>. The seam however does not have to necessarily run through the hole for the mount <NUM> - different seam locations may be provided.

<FIG> shows an embodiment of the transmission further comprising a lubricant distribution system <NUM> for distributing lubricant <NUM> inside the encasement <NUM>. Lubricant guiding elements <NUM> are arranged on the encasement <NUM> to guide the lubricant towards the gears and/or either side of the bearings, including the outer side, which would normally, i.e. in a transmission housing according to the state of the art, not be reached by lubricant as they would face the outside of the housing.

In the shown example, the lubricant guiding elements <NUM> are incorporated in, e.g. machined, cast or mounted into, the interior of the encasement <NUM>. The lubricant distribution system may consist of a channel array <NUM> with a pump <NUM> that lets the lubricant <NUM> circulate within the encasement <NUM>. Instead of providing lubricant guiding elements <NUM>, the said channels or pipes may alternatively be curved to reach the respective target places for the lubricant. In any case, the lubricant distribution system <NUM> may in particular be configured to (evenly) spread the lubricant <NUM> over the target places, which may imply the use of nozzles, sprinklers, or the like. <FIG> shows the support frame <NUM> in a highly abstracted way. The mount <NUM> diverting from a main body of the support frame exits the encasement <NUM> so that the fixing points <NUM> can be affixed to the structure of a machine. It is further noted that only part of the shafts, support frame, and gears is shown in <FIG>.

Another embodiment of the invention with a lubricant distribution system merely comprises lubricant guiding elements (such as the elements <NUM> in <FIG>). In this case the lubricant may be distributed simply by splashing. i.e. the lubricant settles to the bottom of the encasement and then the gears turn around and fling the lubricant around to be captured and fed onto the gears and bearings. This is referred to as splash lubrication or wet sump, whereas the embodiment of <FIG> is referred to as a fed lubrication or dry sump. Even with splash lubrication there may still be features such as guide elements <NUM> that correspondingly control the flow of the lubricant to the desired gears and bearings.

In general, the encasement <NUM> may be made of a non-metal material, either fully or at least for the most part. For example, an encasement <NUM> made of (fibre-reinforced) plastic has the advantages of weight reduction and increased vibration abatement.

In some embodiments, which are not shown in the figures, the encasement is configured to encapsulate the whole support frame and to further encapsulate a portion of the structure, namely the part of the structure connected to the fixing points <NUM>. In this example, support frame <NUM> needs to be mounted onto the structure first, before the encasement <NUM> can be mounted. This allows for providing lubricant at the locations where the support frame <NUM> is mounted to the structure as well, so that in some embodiments, the lubricant distribution system <NUM> is configured to distribute lubricant to the fixing points <NUM>. Alternatively or additionally, the encasement <NUM> could further surround the motor <NUM> and/or the mounting places <NUM>/<NUM>. And advantage of such an embodiment would be the supply of lubricant further to the motor and/or the mounting places.

If the motor is included in the encasement, said motor may have its own structural frame or may also be embodied without any encapsulation as this function is then also provided by the overall encasement.

In some embodiments, as can be seen in <FIG>, the transmission further comprises a locating element <NUM> arranged between the encasement and the support frame. This can increase the support of the encasement <NUM>. The locating element <NUM> does not sit in the load path between the gears and the structure. It is designed to take no load except for the weight of the encasement <NUM>. The locating element <NUM> may be made of or contain material that dampens vibration, e.g. rubber.

As the invention allows much more possibilities / freedom to design the encasement, in some embodiments, which are not shown in the figures, the transmission further comprises an air ventilation system with an air inlet, an air outlet, and an air accelerator, wherein the air inlet and the air outlet are arranged on the encasement. The air inlet and the air outlet are located at spots where no lubricant impends to leave the encasement. In particular, at the location where the air inlet and/or air outlet are placed, the encasement could have protection shields that hinder the lubricant to come near the inlet/outlet. An air accelerator could be embodied as a fan or impeller. The air ventilation system would further improve the transmission as it would effectively dissipate heat generated in the transmission.

<FIG> shows a support frame <NUM> in accordance with an embodiment of the invention with motor <NUM> attached by bolted joints <NUM>. In this example, the support frame <NUM> is made of two main pieces that are connected at the joint spots <NUM>. The shown system has points <NUM> (provided on the motor)
and <NUM> (provided on the support frame) for being mounted to the structure of a machine. On the back side (the view is blocked in this figure), the system may have more such protruding fixing points. Axis A1 is the axis of the input shaft <NUM>, axis A2 is the axis of the intermediary shaft, and axis A3 is the axis of the output shaft <NUM>. For a better illustration of the support frame <NUM>, the shafts (as well as the gears) are hidden here.

<FIG> shows the system from <FIG> with the gear train wrapped by an encapsulating encasement <NUM>. In this example, the encasement <NUM> consists of two pieces connected along a seam. For assembly, the first half is put over the gear train so that the connecting points <NUM> are sliding in holes provided in the encasement <NUM>, said holes equipped with rings that seal the oil and provide vibration dampening. The second half is put over the gear train so that the output shaft <NUM> is sliding in a hole provided in the encasement <NUM>, said hole again equipped with a ring that seals the oil and provides vibration dampening. In particular, the encasement <NUM> also has sealing elements to seal between the motor <NUM> and the inside of the encasement <NUM>.

Claim 1:
An encapsulated gear train (<NUM>) for a machine comprising
a support frame (<NUM>), which is non-encasing,
an input shaft (<NUM>) rotatably mounted in the support frame,
an output shaft (<NUM>) rotatably mounted in the support frame,
gears (<NUM>,<NUM>) configured to operatively connect the input shaft with the output shaft, and
an encasement (<NUM>) configured to encapsulate the input shaft, the output shaft, the gears, and at least a portion of the support frame,
wherein
the support frame is configured to be mounted on a structure (<NUM>) of the machine such that the support frame does not apply any loads onto the encasement,
the support frame (<NUM>) comprises a fixing point (<NUM>) protruding from a main body of the support frame, and the support frame is configured to be mounted on the structure (<NUM>) by the fixing point,
the encasement (<NUM>) is configured to encompass said fixing point (<NUM>) and to seal the encapsulated components (<NUM>,<NUM>,<NUM>,<NUM>),
characterized in that
a vibration isolating seal (<NUM>) is arranged between the encasement (<NUM>) and fixing point (<NUM>).