The Field of the Invention

This invention relates to an improved electrical compressor, in particular to an improved electrical compressor with a thrust bearing.

Background

Electrically driven compressors have become more and more common in recent years, particularly as the number of electric vehicles have increased. Such compressors are used to deal with heat management that is needed to cool not only the cabin of the vehicles but also the on-board electronics, such as batteries which generate a lot of heat and require cooling.

With their use in electric vehicles, energy efficiency has become a critically important factor in compressor design. Efficiency of centrifugal compressors when operating at relatively high pressure ratios and low mass flows is a particular issue. It is presently difficult to achieve a high isentropic efficiency of the compressor stage, whilst dealing with the thrust loads generated by the centrifugal compressor. Furthermore, control of tip gap between the compressor blades and the shroud is challenging at the high speeds desired for enhanced cooling.

The present invention has been devised with the foregoing in mind and aims to at least ameliorate the above mentioned issues.

Summary of the invention

According to an aspect of the present invention there is provided a compressor directly connected to an electric motor, said compressor comprising: a first stage connected to an electric motor, said first stage comprising a first stage inlet drawing air into the compressor over the electric motor; a second stage positioned adjacent to and opposite the first stage such that a second stage inlet draws air in an opposite direction to the first stage inlet; and a thrust bearing positioned between the first stage and the second stage.

Optionally an airflow path between the first stage inlet and the thrust bearing may comprise an airflow path and wherein no other thrust bearings are provided in the airflow path. Optionally the airflow path may comprise a clearance distance between an impeller blade of the first stage, said clearance distance.

The thrust bearing may comprise a thrust disc and a seal. By combining both a seal and a thrust disc at a single location the overall loss due to air leakage and winding losses may be reduced.

Optionally the first stage may be directly coupled to the electric motor, such that the compressor is mounted in position substantially by the thrust bearing. This allows for the tolerances between the compressor stages and the shroud or casing of the compressor can be more easily and tightly managed. This allows for the tip gap - namely the distance between the impeller blades of the compressor stages and the casing, to be minimized. This improves efficiency, particularly in high speed compressors that utilize a high pressure ratio and low mass flows.

The proposed design looks to use a two stage compressor design where the first stage inlet is facing the electric motor. The second stage is positioned back to back with first stage where the inlet is in opposite direction to that of the first stage. A thrust bearing is then positioned between the two stages.

By utilizing a thrust bearing to mount and separate the stages, the use of oil may be minimized or substantially eliminated.

The inlet for the first stage is typically drawn over the motor. As the thrust disc is positioned between the two compressor stages it substantially does not inhibit the flow to the first stage inlet. Also a contact seal is used between the two compressor stages - having an additional thrust bearing creates additional loss. By combining the two, this can reduce the overall losses.

The thrust bearing being locating between both compressor wheels also reduces the tolerance stack up between the wheels and the shrouds allowing for tighter control of the tip gap, this is important for the efficiency of the high pressure ratio low flow type machines.

Compressors are typically centrifugal compressors that operate at high speeds typically 10,000 rpm - 160,000 rpm. As an example, a 6kW oil-free compressor model may deliver a pressure ratio of 1.9 at 160,000 RPM and weigh less than 4kg. This high-speed motor and compact design can offer a power-dense solution. A 10kW oil-free compressor may provide a pressure ratio of 2.5 at 115,000 RPM, weigh 5.4kg, and may be configured to accept a wide range of input voltages (260-700V), allowing direct power in fuel cell applications without needing a separate DC/DC converter. A 25kW oil-free compressor typically features a pressure ratio of 3.0 at 95,000 RPM and weighs less than 10kg, providing a compact solution for higher power, continuous operation.

Figures

Figure 1 shows a cross-sectional view of a compressor and electric motor according to an existing design;

Figure 2a shows a cross-sectional view of a compressor and electric motor according to an embodiment of the present invention;

Figure 2b shows a close-up view of a portion of Figure 2a; and

Figure 2c shows a close up view of a portion of Figure 2a.

The figures are diagrammatic only and are used to illustrate aspects and embodiments of the present invention.

Description

Figure 1 shows a cross-section of an electric motor and compressor according to existing designs. The compressor cover and diffuser have been omitted from the image for simplicity. The figure shows a two stage compressor 10, a first stage 14 and a second stage 12. The stages are driven by an electric motor 30. The two stages are positioned in series and separated by a seal 18 that acts to reduce air leakage between the first stage and the second stage. The seal 18 can produce windage losses between the two stages due to the imprecise seating that typically occurs. Air is drawn into the first stage 14 via the first stage inlet 40. A thrust bearing 20 is provided before the first stage 14 to mount the compressor 10. The position of the thrust bearing 20 inhibits the flow of air into the compressor and can cause a reduction in efficiency due to the narrowing in the compressor air inlet passage 42 as it passes the shoulder 42a of the thrust bearing 20. There are also windage losses due to this configuration.

Figure 2a shows a corresponding cross-section according to the present invention. The design uses a two-stage compressor design 100. The compressor comprises a two-stage compressor 112, 114, with an inlet 140 for the first stage 114 that (directly) faces an electric motor 130. The second stage 112 is positioned back to back with the first stage 114, and the second stage inlet is in an opposite direction to that of the first stage inlet.

A thrust bearing 120 is positioned between the two stages. The thrust bearing 120 is described in greater detail with respect to Figure 2b. In particular, the bearing 120 comprises a bearing or thrust disc 122, with a contact seal 124. The inlet 140 for the first stage is drawn over the motor 130. As the thrust disc 122 is positioned between the two compressor stages it does not inhibit the flow to the first stage inlet 140. Also a contact seal 124 is used between the two compressor stages - having an additional thrust bearing creates additional loss, which is now omitted, leading to better air flow as shown in Figure 2c. By combining the two aspects into a single thrust bearing, and this reduces the overall losses.

The thrust bearing being locating between both compressor wheels also reduces the tolerance stack up between the wheels and the shrouds of the compressor, allowing for tighter control of the tip gap 118 of the compressor, this is very important for the efficiency of the high pressure ratio low flow type machines. This is shown in Figure 2b, where the tip gap 118 is the minimum clearance between the impeller blades and the shroud or casing. As shown in Figure 2b, by increasing the consistency of this distance, the efficiency of the compressor is improved, particularly for high speed compressors (50,000 rpm+).

Figure 2c shows how the airflow inlet between to the first stage inlet has a larger minimum distance 160 between the casing of the electric motor. By omitting the thrust bearing 20 of the existing design the flow of air is improved. Additionally, windage losses that may be generated in the prior art design are eliminated.