Patent Description:
Forklift trucks including a chassis (or frame), a mast pivotally mounted on the chassis and a fork slidably mounted on the mast are known in the art. The fork is used to lift a load, for example for transporting ware in a store. The mast can be tilted with respect to the chassis to facilitate loading and unloading of the ware.

It is also known to provide an electric motor for the traction of the wheels of the forklift truck. The electrical motor can be mounted e.g. on the front axle of the truck for the traction of the front wheels. In order to cool the electrical motor, a cooling system has been proposed in the prior art, wherein an air fan ventilates the outer surface of the electrical motor housing. However, in this configuration the cooling system can have failures due to the deposition of dust on the blades of the air ventilator and can produce disturbing noise for the driver of the truck. Furthermore, the air cooling system may not be capable of properly dissipating the heat generated by the power electronics module (such as an inverter) incorporated in the truck for the control of the currents to be fed to the electrical motor. An industrial truck according to the preamble of claim <NUM> is known from <CIT>.

In view of the above, it is an object of the present invention to provide an industrial truck which ensures an efficient and improved cooling of the electrical traction motor.

It is a further object of the present invention to provide an industrial truck which ensures an improved cooling of the electrical traction motor and of the power electronics module associated to the electrical motor.

It is a further object of the present invention to provide an industrial truck which is less prone to failures of the cooling system compared to the conventional systems.

It is a further object of the present invention to provide an industrial truck which can ensure an improved cooling of the electrical motor while minimizing the complexity of the cooling system, in particular by minimizing the overall number of components to be foreseen in the combined system "axle structure/motor cooling system".

In view of the above object, the present invention proposes an industrial truck including:.

The arrangement according to the invention allows to achieve a symmetrical distribution of the stress on the front axle structure, while obtaining a uniform and efficient dissipation of the heat generated by the electrical motor and by the power electronic module. Concentrated peaks of temperature can be avoided in the proximity of the power electronic module, thus enhancing reliability of the motor control. In addition, by using cooling ducts embedded in the front axle structure, the cooling system is less noisy and less prone to failure compared to conventional air cooling systems. Since the housing of the electrical motor and the gap between stator and rotor of the electrical motor form the cooling ducts for cooling both the electrical motor and the power electronic module, an efficient cooling of the heated components is ensured without the need of an additional cooling circuit. Furthermore, since the cooling ducts in the housing are formed only in the region between the motor and the power electronic module, the motor housing can be advantageously dimensioned to withstand the bending stresses without the need of forming holes in the whole periphery of the housing, especially in the lower part. The heat generated in the axle structure can thus be efficiently removed while an advantageous distribution of the bending stress on the axle is achieved, since the supports of the lifting assembly are formed on the lateral left and right portions.

The above and other advantages of the present invention will be illustrated with reference to an example embodiment of the invention, described with reference to the appended drawings listed as follows.

<FIG> shows a schematic representation of an industrial truck <NUM> according to an embodiment of the present invention, e.g. a forklift truck. The industrial truck <NUM> includes a frame <NUM>, a mast <NUM> pivotally mounted on the frame <NUM> and lifting element <NUM> (e.g. a fork, even though also other material handling devices can be mounted on the truck) for lifting a load <NUM>; the lifting element <NUM> is mounted on the mast <NUM> in a slidable manner along the mast <NUM>; in <FIG> the lifting element <NUM> is shown in a lowered position. The mast <NUM> is pivotally mounted on the chassis <NUM> around a pivot, which is preferably located close to the front axle of the truck <NUM>; however, the mast <NUM> and the lifting assembly could be positioned also close to the rear axle of the truck. The mast <NUM> may be tilted over a range of directions encompassing a vertical direction. The mast <NUM> forms part of a lifting assembly <NUM>, which is configured to lift the lifting element <NUM> to lift a load. The lifting assembly <NUM> includes actuating means (not shown) for causing the lifting element <NUM> to slide along the mast <NUM>; the actuating means can be implemented according any known configuration in the art. The industrial truck <NUM> is electrically driven. Further, the industrial truck <NUM> might include two wheels on the front axle and one or two wheels on the rear axle, as well as steering wheels for steering the truck while driving.

The truck <NUM> further includes a control unit <NUM> (schematically represented in dashed lines in <FIG>) configured to control the lifting actuator and a mast tilting actuator. The control unit <NUM> may control also further actuators of the truck, i.e. a wheel drive system. The wheel drive system may include one or more motors for driving the wheels of the truck and a braking system. The motor can be an electrical motor such as a reluctance, induction or permanent magnet motor, or the like.

<FIG> shows the frame <NUM>, <NUM> of the industrial truck and the front axle structure <NUM> connected to the frame, wherein the wheels are removed in the drawing and the lifting assembly <NUM> is shown detached from the frame <NUM>, <NUM>. The front axle structure <NUM> includes a housing <NUM> for receiving the electrical motor for the traction of the front wheels, and a left portion <NUM> on which supporting means <NUM> are formed to support the lifting assembly <NUM> (a right portion of the front axle structure is described later). The left portion <NUM> is also connected to the frame <NUM> and supports the wheel carrier element 22b.

<FIG> shows the front axle structure <NUM> according to an embodiment of the invention. The front axle structure <NUM> is connected to the frame <NUM> of the truck by means of flanges <NUM>. The front axle structure is constituted by a left portion <NUM>, a right portion <NUM> and a housing <NUM>, <NUM>, <NUM> of the electrical motor joined together with each other. The housing <NUM>, <NUM>, <NUM> is interposed between the left portion <NUM> and the right portion <NUM>.

The left portion <NUM> and the right portion <NUM> may be directly joined to the housing <NUM>, <NUM>, <NUM>, i.e. without the interposition of other elements, although other arrangement may be possible. Each of the left portion <NUM> and the right portion <NUM> comprises supporting means <NUM> (e.g. flanges) for supporting the lifting assembly <NUM>. Furthermore, preferably each of the left portion <NUM> and the right portion <NUM> includes a flange <NUM> for the connection to the frame <NUM>, preferably a vertical flange formed on the upper part of the front axle structure <NUM>. The left portion <NUM> and the right portion <NUM> are each formed preferably as a single integral piece, e.g. made of cast iron.

The housing <NUM>, <NUM>, <NUM> of the electrical motor includes cooling ducts (described later more in details) and is configured to withstand a bending stress induced in the housing by the weight of the lifting assembly <NUM>.

In one embodiment, the right portion <NUM> includes a circular flange <NUM> for connection to the housing <NUM>-<NUM> by means of a plurality of fastening means <NUM>. The left portion <NUM> include a similar flange for the connection the housing of the motor.

Preferably, opposite to the housing <NUM>-<NUM>, the left portion <NUM> is connected to a further element 22a which supports the wheel carrier element 22b in a rotatable manner. Similarly, the right portion <NUM> is connected to a further element 21a which supports the wheel carrier element 21b.

The housing of the electrical motor includes, preferably, a longitudinally hollow body <NUM> forming the recess for accommodating the electrical motor and two end pieces <NUM>, <NUM>. The longitudinally hollow body <NUM> circumferentially surrounds the electrical motor. Each of the longitudinally hollow body <NUM> and two end pieces <NUM>, <NUM> are formed as a single integral piece. The two end pieces <NUM>, <NUM> are attached respectively to opposite longitudinal open ends of the longitudinally hollow body <NUM>. The longitudinal hollow body <NUM> is preferably substantially cylindrical. The two end pieces <NUM>, <NUM> have the shape of a circular plate. The two end pieces <NUM>, <NUM> are connected to the longitudinally hollow body <NUM> by means of a plurality of fastening means <NUM> distributed along the outer circumference of the end pieces <NUM>, <NUM>.

The housing includes an outer surface <NUM> on which a power electronic module <NUM> (e.g. an inverter for feeding the currents to the electrical motor) for controlling the electric motor is mounted. Preferably, the outer surface <NUM> for mounting the power electronic module is formed on the hollow body <NUM> of the housing, most preferably on the upper part of the front axle structure <NUM>, i.e. the power electronic module <NUM> is placed above the front axle structure <NUM>. Preferably, the outer surface <NUM> is planar.

In one preferred embodiment, the components of the housing <NUM>, <NUM>, <NUM> are formed by cast iron, most preferably by ductile cast iron. Ductile cast iron is preferred to achieve a desired mechanical resistance, e.g. resistance in case of collisions. However, although cast iron is the preferred material, the components forming the housing <NUM>-<NUM> could be also formed with aluminium, in case of very low nominal loads of the industrial truck.

The outer surface <NUM> can be formed with raw cast iron to avoid an expensive machining process after casting. In this case, a layer <NUM> of thermally conductive material is applied to the outer surface <NUM> and the power electronic module <NUM> is mounted on the layer of conductive material <NUM>, which is interposed between the power electronic module <NUM> and the outer surface <NUM>. Preferably, the layer of conductive material <NUM> is made of graphite and is formed with a Pyrolytic Graphite Sheet, PGS. This allows to ensure a proper thermal conduction from the power electronic module <NUM> to the housing <NUM>-<NUM> even if the outer surface <NUM> is not machined after casting. In the figure, the layer of conductive material <NUM> and the power electronic module <NUM> are shown in exploded schematic view. Preferably, the outer surface <NUM> has a rectangular elongated shape extending along a longitudinal direction of the axle. The power electronic module <NUM> has advantageously a planar shape and covers at least <NUM>% of the outer surface <NUM> when mounted on the housing <NUM>-<NUM>. The layer <NUM> occupies the whole space between the power electronic module <NUM> and the outer surface <NUM>.

Alternatively, the planar outer surface <NUM> could be processed by machining to obtain a smooth surface; in this case, the layer <NUM> could be omitted and sufficient thermal conduction may be achieved via a smooth machined surface <NUM>.

<FIG> shows the front axle structure of <FIG> in which the hollow body <NUM> and the stator <NUM> of the electrical motor <NUM> are removed and only the rotor <NUM> of the electrical motor <NUM> is shown. <FIG> is a cross section of the housing <NUM>-<NUM>, in which the motor <NUM> is shown. <FIG> shows the hollow body <NUM> taken alone.

As well illustrated at <FIG>, <FIG>, <FIG> and <FIG>, the longitudinally hollow body <NUM> includes cooling ducts <NUM> that are in communication with a first manifold duct <NUM> formed in the end piece <NUM> and with a second manifold duct <NUM> in the end piece <NUM>. However, also a single cooling duct <NUM> could be present. In the preferred embodiment, three ducts <NUM> are present in the body <NUM>, as visible in <FIG>. In the present disclosure, with "longitudinal" it is intended in a direction parallel to the longitudinal extension of the front axle structure <NUM>. Furthermore, the end piece <NUM> may include a first manifold duct <NUM> and the end piece <NUM> may include a second manifold duct <NUM> for feeding cooling liquid in the gap <NUM> between the rotor <NUM> and the stator <NUM> of the electrical motor. Preferably, the manifold ducts <NUM> and <NUM> may have an annular shape; the annular shape may be closed (i.e. without interruption) or may be open (i.e. with an interruption). For example, the first manifold duct <NUM> and the second manifold duct <NUM> may be formed as a groove in the end pieces <NUM> and <NUM>, respectively. The groove may be open in the direction facing the hollow body <NUM> to allow supply and collection of the coolant to/from the cooling ducts (or paths) formed between the stator <NUM> and rotor <NUM> the gap therebetween.

As shown in <FIG>, in one embodiment, the manifold duct <NUM> has a circular shape. The manifold duct <NUM> in the end piece <NUM> (shown in <FIG>) has a similar shape and arrangement as duct <NUM>. The end pieces <NUM> and <NUM> include a hole in a central position to allow the shaft <NUM> connected to the rotor <NUM> of the motor <NUM> to pass through the end pieces <NUM>, <NUM> and transmit the wheel traction motion. The end piece <NUM> includes a plurality of longitudinal holes <NUM> formed between the outer rim of the end piece <NUM> and the manifold duct <NUM> for receiving fastening means for connecting the end piece <NUM> to the hollow body <NUM>. The end piece <NUM> includes a similar arrangement of longitudinal holes for connection to the hollow body <NUM>. The end piece <NUM> includes an inlet <NUM> for feeding cooling liquid into the manifold <NUM>. The end piece <NUM> includes an outlet <NUM> for the collection of liquid exiting the housing through the manifold <NUM>. The inlet <NUM> and the outlet <NUM> are preferably formed on the upper part of the front axle structure. The inlet <NUM> and the outlet <NUM> are preferably formed adjacent to the outer surface <NUM>. The manifold ducts <NUM>, <NUM> are in communication with rotating cooling ducts <NUM> formed between the stator <NUM> and the rotor <NUM> of the electrical motor. The ducts <NUM> arranged close to the outer surface <NUM> for cooling the power electronic module may be in communication with respective ducts 83a, 84a in the end pieces <NUM>, <NUM> that connect the inlet/outlet <NUM>, <NUM> with the respective manifold ducts <NUM>, <NUM>. The ducts 83a and 84a extend advantageously along a substantially vertical direction. The inlet <NUM> and the outlet <NUM> are connected to an external hydraulic circuit (not shown in <FIG>) configured for the circulation of the cooling liquid inside the manifolds <NUM> and <NUM>, the gap <NUM> between stator and rotor of the motor and the ducts <NUM> in the hollow body <NUM>. The cooling liquid circulates in the front axle structure only in the motor housing <NUM>, <NUM> and <NUM> and in the gap <NUM> between the rotor and the motor. The cooling liquid does not circulate in the left and right parts <NUM>, <NUM> of the front axle structure <NUM>.

The housing <NUM>-<NUM> of the electrical motor is thermally coupled with a stator <NUM> of the electrical motor <NUM>, whereby in the cooling ducts <NUM> and in the gap <NUM> a cooling liquid flows to cool the electrical motor during the operation of the industrial truck. Specifically, as shown in <FIG>, the stator <NUM> of the motor is formed with resin cast so as to adhere to the inner wall <NUM> of the hollow body <NUM> of the housing. The stator <NUM> is formed by casting resin in the housing to incorporate the stator windings.

The rotor <NUM> is fixed on the hollow shaft <NUM> which passes through the central holes in the end pieces <NUM> and <NUM>. The shaft <NUM> is supported by bearings carried by the left and right portions <NUM>, <NUM> of the front axle structure <NUM>.

Preferably, the motor <NUM> is a permanent magnet motor. In this embodiment, the rotor <NUM> includes a plurality of magnets <NUM> forming the magnetic poles of the rotor. In a preferred embodiment, the rotor <NUM> includes a plurality of lobes <NUM> along its circumferential surface. The lobes <NUM> are preferably eight. Each lobe <NUM> is associated to a respective magnet <NUM> embedded in the lobe. Among two adjacent lobes <NUM>, a groove <NUM> is formed, that in turns forms a cooling duct through which the cooling liquid circulates. In the preferred embodiment, eight cooling ducts <NUM> (or cooling paths) are formed between the successive eight lobes <NUM>. However, also a different number of lobes <NUM> can be considered. The outer shape of the lobes <NUM> may correspond to a segment of a circumference. In operation, the cooling paths <NUM> rotate as the rotor <NUM> rotates, so as to uniformly cool the whole periphery of the stator <NUM>.

As well shown in <FIG> and <FIG>, in a region of the housing <NUM>-<NUM> between the outer surface <NUM> and a recess <NUM> configured to accommodate the electric motor <NUM>, the housing <NUM>-<NUM> (and specifically the hollow body <NUM> of the housing in the embodiment shown in the figures) includes at least one power electronic module cooling duct <NUM> positioned between the stator <NUM> and the outer surface <NUM> for cooling the power electronic module during the operation of the industrial truck. According to a preferred embodiment, the housing includes cooling ducts <NUM> only in the region between the outer surface and the recess <NUM>; more generally, the hollow body <NUM> of the housing does not include cooling ducts in the lower part of the housing, opposite to the outer surface <NUM> for supporting the power electronic module. The cooling ducts <NUM> in the housing have the purpose to cool the power electronic module mounted on the surface <NUM>. The cooling liquid circulating in the gap between the rotor and the stator of the motor <NUM> (and, more specifically, in the paths <NUM> formed between the lobes <NUM> of the rotor <NUM> and the stator <NUM>) serve for cooling the electric motor <NUM>. Accordingly, an efficient cooling of the motor and of the power electronic module can be achieved, while providing cooling ducts in the housing only on the upper part close to the outer surface <NUM>, so that no void parts is present e.g. in the lower part of the housing. This allows to achieve a desired mechanical strength to the bending stresses induced in the housing <NUM>, <NUM> and <NUM> during operation of the industrial truck <NUM>, while reducing the overall dimensioning of the parts of the housing <NUM>, <NUM> and <NUM>.

The power electronic module cooling ducts <NUM> are preferably more than one, most preferably three as shown in the <FIG>. All the power electronic module cooling ducts <NUM> are positioned between the recess <NUM> and the outer surface <NUM> in the example shown in <FIG>. The hollow body <NUM> has a substantially cylindrical shape and the ducts <NUM> extend along a longitudinal direction of the hollow body <NUM>, which in turn corresponds to the direction of the longitudinal axis of the front axle structure.

The cooling liquid enters the from the inlet <NUM> into the conduit 83a in the end piece <NUM>, which distributes the cooling liquid to all cooling ducts <NUM> in the hollow body <NUM> and to the cooling paths <NUM> in the gap between the rotor and the stator of the electrical motor via the manifold duct <NUM>. The cooling ducts <NUM> may be fed by the separate duct 83a. The cooling liquid is then collected by the manifold duct <NUM> in the end piece <NUM> and exits the housing of the electrical motor via the outlet <NUM>. As above discussed, the liquid from the cooling ducts <NUM> may be collected by a duct 84a separate from the manifold <NUM>.

The industrial truck according to the invention further comprises a lifting assembly hydraulic circuit <NUM> for feeding liquid (e.g. oil) to one or more hydraulic actuators configured to move the lifting element <NUM> of the lifting assembly <NUM>. Advantageously, the liquid circulating in the lifting assembly hydraulic circuit <NUM> is the same as the cooling liquid. According to one embodiment, the hydraulic circuit includes a first main pump <NUM> for pumping the oil to the oil control valves of the actuators of the lifting assembly <NUM> and a second pump <NUM> to send oil to the cooling circuit including the ducts formed in housing <NUM>-<NUM> of the electric motor in the front axle structure <NUM>. Both pumps <NUM> and <NUM> may be driven by the same motor. Furthermore, both pumps <NUM>, <NUM> draw oil from a common oil tank <NUM> via a suction filter <NUM>. Before reaching the ducts in the housing <NUM>-<NUM> of the motor in the front axle structure, the oil pumped by the pump <NUM> circulates in an oil cooler <NUM> for cooling the liquid. After circulating in the circuit of the lifting assembly actuators and in the cooling circuit of the front axle structure, the oil is collected into the common oil tank <NUM>.

The above description of embodiments applying the innovative principles of the invention is provided solely for the purpose of illustrating said principles and must thus not be considered as limiting the scope of the invention claimed herein.

For example, although a preferred embodiment involves the use of the oil circulating in the hydraulic circuit of the lifting assembly as refrigerant, also another liquid could be used. For example, also water could be used as refrigerant. In this case, an independent hydraulic circuit would be included in the industrial truck, separate from the hydraulic circuit for operating the actuators of the lifting assembly.

Furthermore, although in the above embodiments the front axle structure has been described, the same axle structure could also be implemented in the rear axle structure. In addition, cooling paths defined by the rotor and the stator in the gap therebetween may also have different shapes and numbers compared to the example described above. For example, the the number of lobes formed on the outer surface of the rotor can be between <NUM> and <NUM>, whereby accordingly the cooling ducts or paths formed between adjacent lobes can be from <NUM> to <NUM>. The grooves formed on the outer circumferential surface of the rotor can also have different shapes, e.g. a rectangular section.

Claim 1:
An industrial truck including:
- a frame (<NUM>, <NUM>),
- a lifting assembly (<NUM>) including a movable lifting element (<NUM>) for lifting a load (<NUM>),
- at least an electrical motor (<NUM>) for the traction of wheels of the industrial truck, and
- an axle structure (<NUM>) connected to the frame (<NUM>) of the truck by means of flanges (<NUM>) and constituted by a left portion (<NUM>), a right portion (<NUM>) and a housing (<NUM>, <NUM>, <NUM>) of the electrical motor, the housing (<NUM>, <NUM>, <NUM>) being interposed between the left portion (<NUM>) and the right portion (<NUM>), the housing (<NUM>, <NUM>, <NUM>) being joined to each of the left portion (<NUM>) and the right portion (<NUM>), wherein each of the left portion (<NUM>) and the right portion (<NUM>) comprises supporting means (<NUM>) for supporting the lifting assembly (<NUM>), and the housing of the electrical motor is configured to withstand a bending stress induced in the housing by the weight of the lifting assembly,
characterized in that
the housing includes an outer surface (<NUM>) on which a power electronic module (<NUM>) for controlling the electric motor is mounted,
wherein a circumferential portion of the housing (<NUM>) surrounding the electrical motor around a motor axis includes one or more cooling ducts (<NUM>) only in a region between a recess (<NUM>) of the housing configured to accommodate the electric motor (<NUM>) and the outer surface (<NUM>) for cooling the power electronic module during the operation of the industrial truck, and wherein a gap (<NUM>) between a stator (<NUM>) and a rotor (<NUM>) of the electrical motor forms a cooling path for the circulation of cooling liquid to refrigerate the electrical motor.