Patent ID: 12249892

DETAILED DESCRIPTION

A cooling jacket for cooling the permanent magnet synchronous electric motor (PMSM) in order to increase the heat transfer from the electric motor to the coolant, increase the heat transfer coefficient and decrease the overall temperature of the electric motor cooling system according to an embodiment of the invention will be described in detail below.

As shown inFIGS.3-10, the permanent magnet synchronous electric motor (PMSM) is provided with the cooling jacket in order to increase the heat transfer from the electric motor to the coolant, increase the heat transfer coefficient and decrease the overall temperature of the electric motor cooling system according to this embodiment of the invention comprises a stator outer housing2substantially in the form of a hollow cylinder surrounding the cooling jacket1according to the invention which is also substantially in the form of a hollow cylinder; a stator core3in the form of a hollow cylinder located inside the cooling jacket1and made of steel sheets, a plurality of electrical wires wound about the stator core3to form electrical windings; and a rotor4is rotatably mounted inside the stator core3.

The stator outer housing2has an end portion configured to form a bearing housing22of the motor. According to another embodiment, the bearing housing22may be manufactured as a separate unit. The concave groove23is formed in the inner surface of the stator outer housing2to guide the coolant toward the front surface of the bearing housing cooling portion A.

Cooling jacket1comprises a bearing coolant guiding channel10, and a stator coolant guiding channel14located between the cooling jacket1, and a stator outer housing2and the O-rings5,6, and6′ that seals the coolant. The stator outer housing2has an inner surface that is configured to contact with the outer surface of the cooling jacket1. The configuration of the cooling jacket1will be described in more detail below.

As shown inFIGS.5-10, the cooling jacket1for cooling the permanent magnet synchronous electric motor (PMSM) in order to increase the heat transfer from the electric motor to the coolant, increase the heat transfer coefficient and decrease the overall temperature of the electric motor cooling system according to the embodiment of the invention comprises a bearing housing cooling portion A and a stator cooling portion B and O-rings5,6, and6′.

The bearing housing cooling portion A is disposed to surround the bearing housing22of the stator outer housing2and manufactured separately from the stator cooling portion B, this separately manufacturing is for the purpose of decreasing the noise and vibration. The bearing housing cooling portion A is secured with the stator cooling portion B to form an unitary unit with two O-ring6and6′ that seals between the bearing housing cooling portion A and the stator cooling portion B to prevent the coolant from being leaked. The number of O-rings is not limited to this embodiment and the number of O-rings other than two may be used.

The bearing housing cooling portion A has an outer wall9located on the outer end side (i.e., the left side in the figure) and the bearing coolant guiding channel10. According to the preferred embodiment shown inFIGS.3-14, the outer wall9may have the same height as that of the bearing coolant guiding channel10. Referring toFIG.14, the bearing coolant guiding channel10may pass across the outer wall9toward the front surface102A of the bearing housing cooling portion A. The front surface102A of the bearing housing cooling portion A is provided with an arc-shaped groove101A so that the coolant, after flowing across the outer wall9toward the front surface102A of the bearing housing cooling portion A, may flow into the arc-shaped groove101A to increase the bearing housing22cooling effect. The concave groove23in the inner surface of the stator outer housing2, the circumferential surface103A of the bearing housing cooling portion A, the front surface102A of the bearing housing cooling portion A, and the arc-shaped groove101A together forming the bearing coolant guiding channel10. The coolant, after flowing through the bearing coolant guiding channel10, may be discharged to the outside through the coolant discharging pipe19.

However, the present invention is not limited to this embodiment. According to an embodiment, the bearing coolant guiding channel10is a portion that has a lower height than that of the outer wall9, and is disposed between the outer wall9and the inner wall12of the stator cooling portion B. The bearing coolant guiding channel10runs along the circumference of the bearing housing cooling portion A.

Referring toFIGS.6-8, the stator cooling portion B comprises an outer wall11located on the outer end side (i.e., the right side in the figure) and an inner wall12located on the inner end side, the partition wall15extends in the spiral shape around the circumference of the stator cooling portion B, and is connected with the outer wall11and the inner wall12at one end151and the other end152, respectively, wherein the partition wall15is in hermetically contact with the inner surface of the stator outer housing2so that the coolant cannot pass through and together forming a stator coolant guiding channel14.

The stator coolant guiding channel14extends from the coolant inlet7to the coolant outlet8. The outlet of coolant8is connected with the bearing coolant guiding channel10of the bearing housing cooling portion A. The middle section of the stator coolant guiding channel14is enlarged, at the middle of the enlarged section there is provided a flow splitter16having a shape that corresponds to the enlarged middle section. According to an embodiment, the middle section of the stator coolant guiding channel14is enlarged, the enlarged section is substantially in the diamond form when being viewed in the radial direction. At the middle of the enlarged section there is provided a flow splitter16that is substantially in the diamond form when being viewed in the radial direction. However, the present invention is not limited to this embodiment, and any other shapes, such as ellipse, may be used. The flow splitter16has a height equal to the height of the partition wall15, the upper surface of the flow splitter16is curved to hermetically contact with the inner surface of the stator outer housing2, thus the coolant cannot pass through (see the cross-section taken along I-I′ inFIG.4).

At the middle of the stator coolant guiding channel14there is provided a middle rib13that extends in the spiral shape around the circumference of the stator cooling portion B. The middle rib13comprises two portions which are a front rib portion and a rear rib portion. The front rib portion extends substantially parallel with the partition wall15from the coolant inlet7to a position located between the partition wall15and a side surface of the flow splitter16. The rear rib portion extends substantially parallel with the partition wall15from a position located between the partition wall15and an opposite side surface of the flow splitter16to the coolant outlet8.

The middle rib13has a lower height than the height of the partition wall15. Preferably, the middle rib13has a lower height than the height of the partition wall15by 0.5 mm. Thereby, when the stator outer housing2is mounted to surround the cooling jacket1, the radial distance from the top of the middle rib13to the inner surface of the stator outer housing is 0.5 mm.

The O-ring5form a seal between the stator cooling portion B and the stator outer housing2to prevent the coolant from being leaked.

FIGS.11-14is schematic views showing the flow path of the coolant through the cooling jacket according to the embodiment of the invention. InFIGS.11-14, the physical components of the cooling jacket1such as the outer walls9and11, the inner walls12, the partition wall15, and the flow splitter16have been omitted, only the flow path of the coolant is shown for ease of understanding.

As shown inFIGS.11-14, when the permanent magnet synchronous electric motor using the cooling jacket1according to the invention operates, the coolant is introduced from the coolant feeding pipe17, flows through the inverter cooling path18to the coolant inlet7of the cooling jacket1, follows the stator coolant guiding channel14to the coolant outlet8in order to flow through the bearing coolant guiding channel10to the outside through the coolant discharging pipe19.

According to an embodiment, the coolant exits the coolant outlet8of the stator cooling portion B, follows the bearing coolant guiding channel10. Referring toFIG.14, the coolant follows the bearing coolant guiding channel10may flow across the outer wall9toward the front surface of the bearing housing cooling portion A, flows into the arc-shaped groove101A to increase the bearing housing22cooling effect, then continues to flow along the concave groove23in the front surface of the bearing housing cooling portion A and flows to the outside through the coolant discharging pipe19. The fluid passage circulates in the aforementioned manner allows the coolant to flow from inlet to outlet with optimal velocity according to this configuration and takes away the heat via forced convection heat transfer mechanism.

The flow splitter which is substantially in the diamond form16is a very important aspect in the design of the cooling jacket for cooling the permanent magnet synchronous electric motor according to the invention. The shape of the flow splitter16that is substantially in the diamond form when being viewed in the radial direction is intended to enhance the turbulence level in the design with minimum pressure drop. The flow splitter16is in contact with the stator outer housing2while the middle ribs15are not. If the flow splitter16substantially in the diamond form when being viewed in the radial direction is not provided, the coolant guiding channel will become uneven. The enlarged coolant guiding channel generates the unenen flow distribution, results in higher pressure drop with the same heat transfer coefficient, thus consumes more power for pumping the coolant. In order to form an even coolant guiding channel, more partition walls is required, which results in the number of loops of the spiral guiding passage increasing, results in the higher pressure drop with the same heat transfer coefficient, thus consumes more power for pumping the coolant.

The middle ribs disclosed in the Chinese Utility Model No. CN208862672U and the Chinese Patent Application Publication No. CN105990945A are entirely different as compared to the design of the middle rib of the cooling jacket for cooling the permanent magnet synchronous electric motor according to the invention. The cooling jacket in the Chinese Utility Model No. CN208862672U has three middle ribs while the design of the cooling jacket for cooling the permanent magnet synchronous electric motor according to the invention has only one middle rib. In the Chinese Patent Application Publication No. CN105990945A, the middle ribs has different heights, which will give an entirely different effect on the heat transfer coefficient and pressure drop. All the coolant jackets substantially have the same design but the pressure drop and heat transfer coefficient makes them distinct, as the results of the number of cooling channels, channel width, channel height, and flow splitter.

The height of the middle rib of the cooling channel has a direct impact on pressure drop and turbulence level. Low height creates low turbulence level and less pressure drop. Higher height of the middle rib creates more turbulence due to smaller guiding passage and less cross-flow velocity and thus, the higher height of the middle rib increases the pressure drop. The pressure drop affects the pump capacity which affects the current drawn from the battery and hence affects the operation range of the vehicle. In fact, if the middle rib is going to be in contact with the stator outer housing then the pressure drop will be nearly double. The 0.5 mm gap from the top of the middle rib to the inner surface of the stator outer housing also affects the cross flow, due to small guiding passage, the increasing cross flow velocity enhances the heat transfer. The 0.5 mm gap is determined after many iterations of simulations and is selected such that it meets the pressure drop (pump capacity) requirement.

The middle rib is also disposed to increase the contact surface area with the coolant and hence increases the heat transfer and decrease the temperature. Through practice, the temperature by using the cooling jacket for cooling the permanent magnet synchronous electric motor according to the invention is reduced by 6° C. as compared to when using the known cooling jacket. The other concern is the pressure drop, the pressure drop will be certainly increased if the middle rib is also contact with the inner surface of the stator outer housing. Instead of creating a seal connection of the middle rib with the stator outer housing, a 0.5 mm gap is provided. Therefore, by providing such additional middle rib, the pressure drop will be maintained nearly same as when using the known cooling jacket.

According to the invention, a cooling jacket is provided for cooling the permanent magnet synchronous electric motor, thus increase the heat transfer from the electric motor to the coolant, increase the heat transfer coefficient and decrease the overall temperature of the electric motor cooling system. With the design of the cooling jacket for cooling the permanent magnet synchronous electric motor, the temperature of the motor is reduced by 6° C. by means of the more even flow path and the heat transfer coefficient.