Description

The application refers to an electric machine, comprising a hollow driveshaft for supporting a rotor rotatable relative to a stator, the driveshaft and being rotatably supported in a housing about an axis of rotation, and a hydraulic system for circulating a fluid inside the housing, having a supply line leading to an axial bore of the driveshaft.

From US 2019/0081537 A1 , a cooling system for a rotary electric machine is known for driving a vehicle. The cooling system includes a first pump, to be driven accompanying with running of the vehicle to supply lubricant to the rotary electric machine, and a second pump driven by a second drive source to supply the lubricant to the rotary electric machine. The first pump is configured to supply the lubricant, through a first passage, to an inside of a rotary shaft of a rotor core of the rotary electric machine. The second pump is configured to supply the lubricant, through a second passage, to a coil of a stator of the rotary electric machine.

WO 2015/058788 A1 discloses a drive assembly for a motor vehicle with a first gear and a second gear drivingly connected to one another, and a lubricant filling which, in a static built-in condition of the drive assembly, defines a lubricant level. A first reservoir is arranged above the lubricant level which can be filled with lubricant as a result of the rotation of the first gear. A second reservoir is arranged above the lubricant level which can be filled with lubricant as a result of the rotation of the second gear. The first reservoir serves to lubricate a first bearing region, whereas the second reservoir serves to lubricate a second bearing region of the drive assembly.

CN 1 1 1441926 A discloses a hybrid gearbox driving motor cooling electric oil pump system and a control method. The system comprises a suction filter, an oil pump, an oil pump motor and an oil pump motorcontroller, wherein the suction filter is used for sucking oil at the bottom of a hybrid gearbox; the oil pump is used for pumping out the oil sucked by the suction filter; and the oil pump motor is used for providing speed and torque for the oil pump, supplying power to the oil pump, and supplying the oil as a cooling medium to the hybrid gearbox.

CN 107565756 A discloses an oil pump motor, a gearbox and a vehicle; the oil pump motor comprises the following units: a housing with an oil inlet and an oil outlet; a motor and an oil pump arranged in the housing, wherein the motor is used for driving the oil pump, the oil pump is provided with an oil inlet chamber and an oil outlet chamber mutually connected, and the oil outlet chamber is connected with the oil outlet; a cooling channel arranged in the housing and outside the motor and the oil pump, the cooling channel pipe wall makes contact with the motor and the oil pump, the cooling channel has an inlet and an outlet, the inlet is connected with the oil inlet, and the outlet is connected with the oil inlet chamber. The gearbox oil liquid circulates in the oil pump motor and flows in the cooling channel; the cooling channel pipe wall makes contact with the motor and the oil pump, so the gearbox oil liquid in the cooling channel can cool down the motor and the oil pump, thus providing cooling and heat radiation effects without immersing the oil pump motor in the gearbox oil liquid.

A performance of an electric machine is thermally limited in operation. Inherent losses may occur in the copper, iron and magnets of electric motors, where material properties limit the temperatures of the respective components and structures. Effective cooling is necessary to achieve adequate performance. However, if cooling fluid is evenly conveyed independent of a speed or operation point of the electric machine, the efficiency is negatively affected due to churning losses of the electric machine and/or a gearbox. Direct oil cooling solutions for the active parts thus require complex hydraulic circuits to provide an adequate pressure and flow rate of the oil.

It can be an objective to propose an electric machine with an efficient and less complex hydraulic system for cooling the electric machine.

The objective is achieved by an electric machine according to claim 1 . Embodiments are described in the dependent claims. The electric machine comprises a hollow driveshaft for supporting a rotor rotatable relative to a stator, the driveshaft being rotatably supported in a housing about an axis of rotation, and a hydraulic system for circulating a fluid, having a supply line leading to an axial bore of the driveshaft. A control valve is arranged in the axial bore for controlling a flow of the fluid into the driveshaft, the control valve being actuated by centrifugal force.

The centrifugal force acting on the control valve inside the rotating driveshaft will advantageously open and close the valve in dependence of the rotational speed of the driveshaft. The control valve is a mechanical part of low complexity, which allows an effective control of the flow of the fluid into the driveshaft. At low rotational speed the closed control valve reduces the flow rate, thus reducing churning losses of the electric machine. At high rotational speed the control valve opens and increases the flow rate, which may further result in a reduced fluid level in a gearbox potentially reducing churning losses of the gears at high speed. The driveshaft comprises radial bores connecting the axial bore to the rotor.

According to an embodiment, the control valve has a plurality of cantilevered beams arranged circumferentially about the axis of rotation and connected to a ring fitted into the axial bore, the cantilevered beams being biased axially inwards. The centrifugal force urges the cantilevered beams radially outwards. The cantilevered beams may form a nozzle with an orifice for the fluid to flow through, wherein an area of the orifice depends on the respective position of the cantilevered beams. The area of the orifice increases upon an increasing rotational speed of the driveshaft.

According to a further embodiment, at a rotational speed of the driveshaft of zero RPM an oil flow rate through the control valve is between zero and 20 percent of a reference oil flow rate through the axial bore without the control valve. For example, the oil flow rate through the control valve at zero RPM is ten percent of the reference oil flow rate. The reference oil flow rate is the flow rate through the axial bore without the control valve that occurs if all other parameters like pressure, density or temperature are identical. The rotational speed of the driveshaft can be identical as well, though it is does not affect the reference oil flow rate. The person skilled in the art is aware that at low rotational speeds of the driveshaft the oil flow is strongly reduced. For example, at a rotational speed of the driveshaft of 20 percent of the maximum rotational speed, the oil flow rate through the control valve can be between 15 and 25 percent of the reference oil flow rate. At a maximum rotational speed of the driveshaft, the oil flow rate through the control valve is more than 75 percent of a reference oil flow rate through the axial bore (18) without the control valve, for example about 80 percent.

According to a further embodiment, the area of the orifice is composed of a radial orifice area and a longitudinal orifice area. The area of the orifice at a rotational speed of the driveshaft of zero revolutions per minute (RPM) may be between zero and two percent of a cross-sectional area of the axial bore. The area of the orifice at a maximum rotational speed of the driveshaft may be more than five percent, particularly more than ten percent of the cross-sectional area of the axial bore. The radial orifice area is a circular opening in a plane perpendicular to the axis of rotation formed at a free end of the cantilevered beams. The longitudinal orifice area is formed by tapered slots between the cantilevered beams. A diameter of the radial orifice area may increase from zero RPM to the maximum rotational speed of the driveshaft by 15 percent to 25 percent of an axial length of the cantilevered beams. Longer cantilevered beams provide an increase in the total area of the orifice.

According to a further embodiment, each of the cantilevered beams comprises a balancing weight at a tip end. Particularly, the cantilevered beams may each have a resilient segment formed of a flat material and being connected to the ring, and a head segment forming the balancing weight. The head segment may have a higher mass than the resilient segment, in particular at least 1 .5 times the mass of the resilient segment.

According to a further embodiment, the resilient segment has a neck portion, wherein the flat material of the neck portion is undulated, having at least one S-form. Wave crests and wave troughs of the undulated waveform or S-form extend circumferentially with respect to the axial direction. The flat material of the neck portion may have multiple S-Forms concatenated. The higher the number of S-Forms, the lower the stress and the bigger the resulting area of the orifice. According to a further embodiment, the hydraulic system has a fluid reservoir, the supply line hydraulically connecting the fluid reservoir and the axial bore. The fluid reservoir may provide a constant fluid pressure, which may be maintained by a pump. The fluid reservoir may be located in a higher position than the axial bore with regard to a direction of gravitational force, allowing the fluid to be passively conveyed to the axial bore. In particular, the fluid may be conveyed to the fluid reservoir by rotating elements of the electric machine, in particular from an oil sump by gearwheels of a transmission connected to the driveshaft.

Embodiments of the electric machine will be illustrated with reference to the drawings, wherein

Figure 1 shows an embodiment of the electric machine in a longitudinal section with a control valve in a closed position;

Figure 2 shows a detail B of Figure 1 ;

Figure 3 shows the detail B of Figure 1 in a different perspective;

Figure 4 shows the embodiment of Figure 1 with the control valve in an open position.

Figure 5 shows a detail C of Figure 4;

Figure 6 shows the detail C of Figure 4 in a different perspective;

Figure 7 shows a further embodiment of the electric machine in a longitudinal section;

Figure 8 shows a detail D of Figure 7;

Figure 9 shows a further embodiment of the electric machine in a longitudinal section;

Figure 10 shows a further embodiment of the electric machine in a longitudinal section; Figure 1 1 shows a further embodiment of the electric machine in a sectional perspective view;

Figure 12 shows the control valve in three different positions.

In Figure 1 , an embodiment of the electric machine is depicted in a longitudinal section. The electric machine comprises a hollow driveshaft 11 for supporting a rotor 10 rotatable relative to a stator 17, the driveshaft 1 1 being rotatably supported in a housing 1 about an axis of rotation A. The rotor 10 is fixed to the driveshaft 1 1 and rotates inside the stator 17, which is connected to the housing 1 . A hydraulic system for circulating a fluid has a supply line 14 leading to an axial bore 18 of the driveshaft 1 1. Inside the axial bore 18, a control valve 12 is arranged, which controls a flow of the fluid into the driveshaft 11 . From the axial bore 18 the fluid flows through radial bores 16 to the rotor 10. The control valve 12 being actuated by centrifugal force.

The control valve 12 is in a closed position. The detail B with the control valve 12 in the closed position is illustrated schematically in Figures 2 and 3 in different views. The control valve 12 has a plurality of cantilevered beams 2 arranged circumferentially about the axis of rotation A and connected to a ring 8, which is fitted into the axial bore 18. The cantilevered beams 2 are biased axially inwards towards a closed position, which is shown in Figures 2 and 3.

In Figure 4, the embodiment of Figure 1 is shown with the control valve 12 in an open position. The detail C with the control valve 12 in the open position is illustrated schematically in Figures 5 and 6 in different views. The centrifugal force urges the cantilevered beams 2 radially outwards gradually opening the control valve 12. The cantilevered beams 2 generally form a nozzle with an orifice for the fluid to flow through, wherein an area of the orifice depends on the respective position of the cantilevered beams 2. The area of the orifice is composed of a radial orifice area 3 and a longitudinal orifice area 4. The radial orifice area 3 is a circular opening in a plane perpendicular to the axis of rotation A formed at a free end of the cantilevered beams 2. The longitudinal orifice area 4 is formed as tapered slots between the cantilevered beams 2. The area of the orifice continually increases from the closed position of Figures 2 and 3 to the open position of the cantilevered beams 2 upon an increasing rotational speed of the driveshaft 1 1 , as shown in Figures 5 and 6. The illustrations of the control valve 12 are schematic. The area of the orifice in the closed position of the cantilevered beams 2, i.e. at a rotational speed of the driveshaft of zero RPM may be between zero and two percent of a cross-sectional area of the axial bore 18. In a maximum opened position of the cantilevered beams 2, i.e. at a maximum rotational speed of the driveshaft, the area of the orifice may be more than five percent, in particular more than ten percent of the cross-sectional area of the axial bore 18. Depending on the control valve design, a cross-sectional area of the axial bore 18 of up to 20 percent is feasible.

In Figure 7, a further embodiment of the electric machine is shown in a longitudinal section. The electric machine is depicted partially with a part the housing 1 and the hollow driveshaft 1 1 . The rotor and stator have been omitted. A detail D showing the closed control valve 12 inside the axial bore 18 controlling the fluid flow from the supply line 14 is shown in Figure 8. Each of the cantilevered beams 2 comprises a balancing weight 5 at a tip end 6. Further, each of the cantilevered beams 2 has a resilient segment 7 formed of a flat material and being connected to the ring 8. A head segment 9 forms the balancing weight 5. The head segment 9 may have a higher mass than the resilient segment 7, in particular at least 1 .5 times the mass of the resilient segment 7. The resilient segment 7 has a neck portion 19, wherein the flat material of the neck portion 19 has an undulated or S-form facilitating the opening of the control valve 12.

In Figure 9, a further embodiment of the electric machine is shown in a longitudinal section. The electric machine is depicted partially with the hollow driveshaft 1 1. The control valve 12 inside the axial bore 18 controls the fluid flow from the supply line 14. The hydraulic system has a fluid reservoir 15, which is hydraulically connected to the axial bore 18 via the supply line 14.

In Figure 10, a further embodiment of the electric machine is shown in a longitudinal section. The electric machine is depicted partially with a part the housing 1 and the hollow driveshaft 1 1. The control valve 12 inside the axial bore 18 controls the fluid flow from the supply line 14. The fluid reservoir 15 is located outside of the housing 1 in a higher position than the axial bore 18 with regard to a direction of gravitational force to passively convey the fluid. In Figure 1 1 , a further embodiment of the electric machine is shown in a sectional perspective view. The electric machine is depicted partially with a part the housing 1 and the hollow driveshaft 1 1 . The control valve 12 inside the axial bore 18 controls the fluid flow from the supply line 14. The fluid reservoir 15 is integrated into the housing 1 in a higher position than the axial bore 18 with regard to a direction of gravitational force to passively convey the fluid. The fluid may be conveyed to the fluid reservoir 15 by rotating elements of the electric machine, in particular from an oil sump by gearwheels of a transmission connected to the driveshaft 11 .

In Figure 12, an exemplary embodiment of the control valve 12 is depicted in three different positions regarding its orifice opening, each in two side views. Position I is a maximum closed position, in which the control valve 12 has the lowest possible orifice opening formed by the radial orifice area 3 and the longitudinal orifice area 4. The control valve 12 actuated by centrifugal force is in position I when the electric machine stands still. A radius at the tip end 6 is 8.3 mm. The radial orifice area 3 has a diameter of 2.2 mm corresponding to an area of 3.8 mm ² . The longitudinal orifice area 4 is composed of eight slots and has a comparable area as the radial orifice area 3. The area of the orifice in the closed position I of the cantilevered beams 2 is about one percent of the cross-sectional area of the axial bore 18 of the driveshaft 11 , which is not depicted. At the rotational speed of the driveshaft of zero RPM, an oil flow rate through the control valve 12 can be ten percent of a reference oil flow rate through the axial bore 18 without the control valve 12 under otherwise identical parameters like pressure, density or temperature.

Position II is a slightly more opened position, in which the centrifugal force of about 3,000 RPM acting on the cantilevered beams 2 is in balance with the biasing force urging the cantilevered beams 2 inwards towards the position I. The radius at the tip end 6 is 0.65 mm higher than the 8.3 mm of position I. The radial orifice area 3 has a diameter of 3.4 mm corresponding to an area of 9.1 mm ² . At the rotational speed of the driveshaft of 3,000 RPM, which can be 20 percent of a maximum rotational speed, the oil flow rate through the control valve 12 can be 20 percent of the reference oil flow rate, which is unaffected by the rotational speed. Position III is a significantly more opened position, in which the centrifugal force of about 15,000 RPM acting on the cantilevered beams 2 is in balance with the biasing force urging the cantilevered beams 2 inwards towards the position I. The radius at the tip end 6 is 3.4 mm higher than the 8.3 mm of position I. The radius at the tip end 6 rises linearly with the rotational speed of the driveshaft 1 1 . The radial orifice area 3 has a diameter of 8.4 mm corresponding to an area of 55.4 mm ² . The diameter of the radial orifice area 3 has increased from position I at zero RPM to position III at the maximum rotational speed of 15,000 RPM by 6.2 mm, which is 20 percent of an axial length of the cantilevered beams 2 of 30 mm in this embodiment. The longitudinal orifice area 4 is composed of the eight tapered slots and has a comparable area as the radial orifice area 3. The area of the orifice in the open position III of the cantilevered beams 2 is about twelve percent of the cross-sectional area of the axial bore 18 of the driveshaft 11 , which is not depicted. At the maximum rotational speed, the oil flow rate through the control valve about 80 percent of the reference oil flow rate.

Reference Numerals

1 Housing

2 Cantilevered beams

3 Radial orifice area

4 Longitudinal orifice area

5 Balancing weight

6 Tip end

7 Resilient segment

8 Ring

9 Head segment

10 Rotor

11 Driveshaft

12 Control valve

14 Supply line

15 Reservoir

16 Radial bores

17 Stator

18 Axial bore

19 Neck portion A Axis of rotation