VP Fuel Pump Motor

8/11/2019 VP Fuel Pump Motor

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Introduction

Increases in the fuel cost and more concern for the environment are pressuring

automotive companies to redesign and optimize various components used in

automobiles. Initiatives focusing on weight reduction and efficiency are leading

automotive companies and their suppliers to consider and adopt bonded Nd-Fe-B

magnets for various motors used in the automobiles.

Due to an increased interest in alternative fuels fuel pump motors are being driven to

switch to brushless designs, and this trend is quickening the adoption of bonded Nd-

Fe-B for these motors. The fuel pump is usually located in the fuel tank or on the

frame rail and is run by the vehicles DC electrical power system. The fuel pump is a

submersible unit with a permanent magnet electric motor. Most current fuel pumps

use brush-type permanent magnet motors with sintered ferrite arcs used for the

magnets. However, because certain alternative fuels, especially ethanol, are more

caustic than gasoline, the brushes tend to corrode more quickly, causing the fuel

pump to fail at a much higher rate. Moreover, ferrite-based motors need to be larger

and heavier in order to deliver the required performance.

This specific issues of higher fuel price, need for better performance with compact

size and the corrosion of the brushes by the alternative fuels has lead to the need of

designing a compact, cost effective, high performance permanent magnet brushless

motor having similar torque-speed characteristics to that of the existing permanent

magnet ferrite based brushed DC motors.


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Methodology

Benchmarking of the Original Motor

The original brushed PM motor with sintered ferrite arcs was dismantled and various

physical parameters like the dimensions and weight of various components were

measured. Figure 1 shows the three dimensional view of the motor and Figure 2

shows the exploded view of the benchmarked PM brushed DC motor. Figure 3

shows the winding pattern for the benchmarked ferrite PM brushed DC motor.

Fig. 1 Three dimensional view of the benchmarked Ferrite PM brushed DC motor

Fig. 2 Exploded view of the benchmarked Ferrite PM brushed DC motor


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Fig. 3 Winding diagram for the benchmarked Ferrite PM brushed DC motor

Table 1 Physical Parameters of the benchmarked Ferrite PM brushed DC Motor

No. of slots = 8 Winding type = Lap

No. of magnet pole arcs = 2 Turns / Coil = 190 with Copper wire diameter =0.01275 inches (AWG size 29)

Armature core length = 22.2mm

Armature Outer diameter = 22.3 mm

Length of air gap = 0.6 mm Magnet outer diameter = 32 mmBack iron thickness = 1.65mm

Magnet inner diameter = 23.5 mm

Length of the motor = 30 mm Total motor weight = 165.9 gmOverall diameter = 35.3 mm Total copper weight = 12.17 gmMagnet length = 30 mm Total magnet weight = 38.18 gm

-3000

-2000

-1000

0

1000

2000

3000

0 60 120 180 240 300 360

B-field

(Gauss)

Rotor Position (deg)

(a) Set up for Flux scan (b) Variation of air gap fluxFig. 4 Flux Scan for the benchmarked Ferrite PM brushed DC motor


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To get the shape and the magnitude of the actual air gap flux density from the

magnet a flux scan was performed using a closed magnetic circuit of the magnet

with back iron and a solid steel piece replacing the armature. The complete set up

for the flux scan is shown in Figure 4 (a), and Figure 4 (b) shows the flux density

variation in the middle of the air gap for the actual air gap of 2.74 mm. From the flux

scan it is observed that the magnets are magnetized to achieve a radial flux pattern

in the air gap of the motor.

Fig. 5 Cogging torque measurement device and cogging torque scan for the benchmarkedFerrite PM brushed DC motor

The cogging torque produced due to the presence of the permanent magnet when

the windings are not excited is measured using the cogging torque set up as shown

in picture of Figure 5, and the cogging torque waveform is shown in the chart of

Figure 5. The peak to peak cogging torque measured is 21.886 mN-m.

A Two dimensional (2-D) finite element (FE) model of the motor was made and

analyzed to predict the performance of the motor. Figure 6 (a) and (b) show the flux

density and the flux line plot for the motor with only permanent magnet excitation,

from which it is observed that some part of the modelled stator back iron is saturated

with peak flux density in excess of 2.0 T. Figure 7 shows the FE predicted radial

component of the flux density at the mid of the motor air gap, from which it is

observed that the peak air gap flux density is 0.35 T.


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(a) Flux density plot (b) Flux line plotFig. 6 Flux density and Flux line plot from FE analysis of the benchmarked Ferrite PM brushed

DC motor

Fig. 7 FE predicted variation of the flux density at the mid of air gap for only PM excitation

Fig. 8 FE predicted cogging torque for thebenchmarked Ferrite PM brushed DC motor

Fig. 9 FE predicted developed torque forthe benchmarked Ferrite PM brushed DCmotor at different armature currents


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Figure 8 shows the FE predicted cogging torque variation for different rotor position,

from which it is observed that the cogging torque cycle is 2 /Nrdegree electrical,

where Nris the number of teeth on the armature. The peak to peak cogging torque

predicted using the FE analysis is 13.2 mN-m. This is less than the actual measured

value of 21.886 mN-m, and the difference appears to be mostly due to misalignment

in the cogging torque measurement device. This conclusion is drawn because the

measured peak to peak cogging can be seen to vary from ~15 to ~21mN-m as the

shaft is rotated.

Considering the linear commutation of the coils and the winding pattern as shown in

Figure 3, the current in various coils at different rotor positions was worked out, and

the developed torque of the motor was predicted for armature currents of 5 A and 8

A. These are shown in Figure 9. Table 2 gives the value of the average torque and

torque ripple for both currents. For the brushed PMDC motor with ferrite magnet arcs

it is normal design practice to provide higher magnet length compared to the

armature length, this will increase the average torque by about 10% in the motor by

utilizing the end leakage flux. To accommodate this end leakage flux effect the

average torque values achieved using the 2-D FE analysis are corrected and also

shown in Table 2.

Table 2 Measured and Predicted average torque at different armature currents

Armature current (A) 5.00 8.00Average Torque from 2D FEA (mN-m) 47.10 75.23Predicted average Torque considering the end leakge flux(mN-m)

52.29 83.51

Measured Average Torque (mN-m) 51.00 87.00Predcited Torque Ripple (%) 46.05 40.74


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Fig. 10 Dyno test setup Fig. 11 Performance characteristics of the benchmarked PMbrushed DC motor

The actual performance characteristics of the motor were measured by connecting

the motor to a dyno as shown in Figure 10. Figure 11 shows various performance

characteristics of the benchmarked brushed PMDC motor from which it is observed

that the peak efficiency of the motor is 47%. The measured average torque for the

armature current of 5 A and 8 A are given in Table 2, which is in very close

agreement with the predicted values resulting from the FE analysis after considering

the effect of end leakage flux.

Redesigning the PMBLDC Motor

To overcome the difficulty of brush corrosion in the case of the PMDC motor working

with fuels such as Ethanol, brushless motor design alternatives are proposed. The

brushless motors are designed to achieve the same torque-speed characteristics of

the benchmarked ferrite brushed PMDC motor but with the minimum possible overall

volume and weight and also without much increase in the raw material cost from the

benchmarked one.


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Bonded Neo Solution # 1

Table 3 Comparison of physical parameters and performance of benchmarked ferritePM DC brushed motor and redesigned PM BLDC motor with MQP-B2+ magnet and

0.6 mm air gap

Different design solutions using MQP-B2+

Magnet for PM BLDC motor with 0.6 mm air

gap

Parameter

Benchmark

PMDC

motor

Motor A

BLDC-MQP-

B2+

0.6 mm Gap

(featured in

Brochure)

Additional

Solution 1

Additional

Solution 2

Type of Magnet FerriteCompression

Moulded

Compressio

n Moulded

Injection

Moulded

Total motor weight (gm) 165.9 75.1 82.9 85

Length of the motor

(mm)30.0

22.022.0 22.0

Overall diameter (mm) 35.3 26.2 27.5 28.0

Total copper weight (gm) 12.17 19.2 22.1 23.8

Total magnet weight

(gm)38.18

7.58.9 9.5

Length of Air gap (mm) 0.6 0.6 0.6 0.6

Current at 30 mN-m (A) 4.07 3.00 2.60 3.00

Current at 60 mN-m (A) 6.47 5.10 4.40 5.20

Efficiency at 30 mN-m

(%)47.0

62.067.5 63.0


(%)36.0

55.065.0 60.5

Normalized Volume 1 0.404 0.445 0.46

Normalized Weight 1 0.453 0.499 0.512

Normalized Diameter 1 0.742 0.779 0.793

Normalized Length 1 0.733 0.733 0.733

While maintaining the same air gap as the benchmarked ferrite fuel pump motor and

utilizing the magnetic strength of MQP-B2+ powder, Radially magnetized

compression moulded and injection moulded magnets are used to design brushless


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PM motor solutions.. Table 3 shows the comparison of key physical parameters and

performance of three PMBL DC motor alternatives to the benchmarked ferrite PM

brushed DC fuel pump motor.

Figure 12 shows the three dimensional view, and Figure 13 shows the exploded view

of the re-designed BLDC motor-A which utilizes MQP-B2+ magnets. Figure 14

shows the flux density and the flux line plot, while figure 15 shows the phase current

waveforms for the redesigned motor-A at torque of 80mN-m. From these it can be

observed that two phases are conducting at any time, and each phase is conducting

for 120 electrical in half cycle. Figure 16 shows the cogging torque variation, from

which it is observed that the peak-to-peak cogging torque is 16mN-m and the period

for one cycle of cogging torque is 60 electrical.

Fig. 12 Three dimensional view of the redesigned PMBL DC motor-A with MQP-B2+ magnetand 0.6 mm air gap


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Fig. 13 Exploded view of the redesigned PMBL DC motor-A with MQP-B2+ magnet and 0.6 mmair gap

(a) Flux density plot (b) Flux line plotFig. 14 Flux density and flux line plot for the redesigned PMBL DC motor-A with MQP-B2+

magnet and 0.6 mm air gap

Fig. 15 Phase currents for 80 mN-m torquefor the redesigned PMBL DC motor-Ahaving MQP-B2+ magnet and 0.6 mm airgap

Fig. 16 Cogging torque for the redesignedPMBL DC motor-A having MQP-B2+magnet and 0.6 mm air gap


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Fig. 17 Performance Characterisitcs of the Benchmarked ferrite PM Brushed DC andredesigned PMBL DC motor-A with MQP-B2+ magnet and 0.6 mm air gap

Figure 17 shows the comparison between the performance characteristics of the

redesigned PMBL DC motor-A and the benchmarked ferrite brushed DC motor, from

which it is observed that for all torques the new redesigned motor draws less current

from the battery and also gives higher efficiency and thus consumes less fuel. Table

3 also gives the comparison of the weight and volume of the original benchmarked

motor and new redesigned motors. It is to be noted that for the benchmarked

ferrite PM Brushed DC motor the length of the motor and the overall diameter is the

magnet length and diameter of the magnet return ring respectively. For the

redesigned PM Brushless motor the length of the motor is defined by the magnet

length, and this is identical to the stator lamination stack length. The overall diameter

of the redesigned PM brushless motor is defined by the outside diameter of the stator

back iron.Considering this active magnetic circuit length and the diameter the

overall volume is calculated in both the cases and it is found that for the new


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redesigned motor the volume and the weight of the motor is reduced by over

50%. It is observed from Table 3 that the motor with injection moulded magnets

needs higher weight/volume of the magnet and motor compared to the motor with

compression moulded magnets. It is also observed that for both the injection

moulded and the compression moulded motors the current drawn from the battery is

lower and efficiency is higher compared to benchmarked ferrite brushed PM DC

motor. The highest reduction in volume and weight for the redesigned PMBL DC

motors with compression moulded magnets is 60% and 55% respectively. Here two

designs are presented with compression moulded magnets to indicate that the

lowest size or weight of the motor does not always results in to the highest efficiency.

There is a trade of between the size\volume of the motor and the motor efficiency.


To provide protection to the magnet against corrosion when the fuel pump is used for

an alternative fuel like ethanol, a non magnetic over-moulding layer needs to be

provided on the magnet. In general the presence of non magnetic over-moulding

layer increases the physical air gap of the motor by 0.4 mm, so considering the

presence of this non magnetic over moulding layer alternative designs are provided

for the motor with air gap of 1.0 mm. Table 4 shows the comparison of key physical

parameters and performance of PMBL DC motor alternatives with 1.0 mm air gap to

the benchmarked ferrite PM brushed DC fuel pump motor. Figures 18 and 19 show

the three dimensional and exploded views of the redesigned PMBL DC motor-B

which utilizes MQP-B2+ magnets.


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Table 4 Comparison of physical parameters and performance of benchmarked ferritePM DC brushed motor and redesigned PM BLDC motor with MQP-B2+ magnet and

1.0 mm air gap

Different design solutions using MQP-B2+

Magnet for PM BLDC motor with 1.0 mm air

gapParameter

Benchmark

PMDC

motorMotor-B

BLDC-MQP-B2+

1.0 mm Gap (featured

in Brochure)

Additional Solution

3

Type of Magnet Ferrite Compression Moulded

Total motor weight (gm) 165.9 80.5 93.0Length of the motor

(mm)30

22.022.0

Overall diameter (mm) 35.3 27.5 29.5

Total copper weight (gm) 12.17 20.20 28.60

Total magnet weight

(gm)38.18

7.5010.20

Length of Air gap (mm) 0.6 1.0

Current at 30 mN-m (A) 4.07 2.85 2.40

Current at 60 mN-m (A) 6.47 5.05 4.30

Efficiency at 30 mN-m(%)

47.0 62.5 68.0


(%)36.0

57.066.0

Normalized Volume 1 0.445 0.512

Normalized Weight 1 0.485 0.561

Normalized Diameter 1 0.779 0.834

Normalized Length 1 0.733 0.733


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Fig. 20 Enlarged view of the air gap for the redesigned PMBL DC motor-B having MQP-B2+magnet with non magnetic over-moulding layer

Figure 21 shows the flux density and the flux line plot for only permanent magnet

excitation for redesigned PMBL DC motor-B. The peak flux density in the stator

teeth, stator back iron and rotor back iron is 1.35 T, 1.60 T and 1.0 T respectively.

Figure 22 shows the redesigned PMBL DC motor-B phase currents for a torque of 25

mN-m at 6500 rpm - again each phase is conducting for 120 electrical for one half

cycle. Figure 23 shows the cogging torque profile for redesigned PMBL DC motor-B

from which it is observed that the peak-to-peak cogging torque is 8 mN-m, which is

less than the peak-to-peak cogging torque for the motor with 0.6 mm air gap. The

reduction in cogging torque is due to larger air gap.


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(a) Flux density plot (b) Flux line plotFig. 21 Flux density and flux line plot for the redesigned PMBLDC motor-B having MQP-B2+

magnet with non magnetic over-moulding layer

Fig. 22 Phase currents for 25 mN-m torquefor the redesigned PMBLDC motor-Bhaving MQP-B2+ magnet with nonmagnetic over-moulding layer

Fig. 23 Cogging torque for the redesignedPMBL DC motor-B having MQP-B2+magnet with non magnetic over-mouldinglayer


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Fig. 24 Performance Characterisitcs of the Benchmarked ferrite PM Brushed DC andredesigned PMBL DC motor-B having MQP-B2+ magnet with non magnetic over-moulding layer


redesigned PMBL DC motor-B and the benchmarked ferrite PM brushed DC motor.

From which it is observed that for all torque values the redesigned PMBL DC motor-

B draws less current from the battery and gives higher efficiency compared to the

benchmarked ferrite PM brushed DC motor. Table 4 also gives the comparison of

the weight and volume of the original benchmarked motor and new redesigned

motors.Again, the volume and the weight are both reduced by more than 50%.

This virtual design demonstrates that motor with Bonded Neo delivers

increased performance, while at the same time providing an additional level of

protection against corrosion and other wear.


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Magnetic powder MQP-14-12 is useful for applications needing higher flux with

higher temperature and corrosion resistance, and as PPS has already been

approved by automotive suppliers, a motor is designed with this cutting-edge high

temperature magnetic powder MQP-14-12 in an injection moulded PPS magnet.

Table 5 Comparison of physical parameters and performance of benchmarked ferrite

PM DC brushed motor and redesigned PM BLDC motor with MQP-14-12 magnetand 0.6 mm air gap

Parameter Benchmark PMDC motor

Motor-C

BLDC MQP-14-12 (IM)

0.6 mm Gap as par the

broacher

Type of Magnet Ferrite Injection Moulded

Total motor weight (gm) 165.9 85.0

Length of the motor (mm) 30.0 22.0

Overall diameter (mm) 35.3 28.0Total copper weight (gm) 12.17 23.80

Total magnet weight (gm) 38.18 9.50

Length of Air gap (mm) 0.6 0.6

Current at 30 mN-m (A) 4.07 2.75

Current at 60 mN-m (A) 6.47 4.75

Efficiency at 30 mN-m (%) 47.0 64.0

Efficiency at 60 mN-m (%) 36.0 59.0

Normalized Volume 1 0.46

Normalized Weight 1 0.512

Normalized Diameter 1 0.793Normalized Length 1 0.733

Table 5 gives the comparison of key physical parameters and performance of the

redesigned PMBL DC motor with MQP-14-12 magnet with 0.6 mm air gap (Motor-C)

to the benchmarked ferrite PM brushed DC fuel pump motor. Figure 25 shows the

phase currents of motor-C for torque of 70 mN-m at 4200 rpm, from which it is


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observed that each phase is conducting for 120 electrical for one half cycle with

single pulse mode. Figure 26 shows the cogging torque profile for motor-C, from

which it is observed that the cogging torque cycle is repeated after every 60

electrical and the peak-to-peak cogging torque is 4.4 mN-m.

Fig. 25 Phase currents for 70 mN-m torquefor the redesigned PMBL DC motor-Chaving MQP-14-12 magnet and 0.6 mm airgap

Fig. 26 Cogging torque for the redesignedPMBL DC motor-C having MQP-14-12magnet and 0.6 mm air gap

Fig. 27 Performance Characterisitcs of the Benchmarked ferrite PM Brushed DC andredesigned PMBL DC motor-C with MQP-14-12 magnet and 0.6 mm air gap


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redesigned PM BLDC motor-C and the benchmarked ferrite PM brushed DC motor.

From which it is observed that for all torque values the redesigned PMBL DC motor-

C draws less current from the battery and gives higher efficiency compared to the

benchmarked ferrite PM brushed DC motor. Table 5 also gives the comparison of

the weight and volume of the original benchmarked motor and new redesigned

motor.Again, the volume and the weight are both reduced by 50%.

Summary

Table 6 summarizes the key physical parameters and the performance of the

benchmarked ferrite PM brushed DC motor and the redesign PMBL DC motors.

The results presented here show that there are many possibilities and options

when making important decision about magnetic material. By selecting high

energy Bonded Neo material a drastic reduction in the weight and the volume

and increase in efficiency and overall performance of the motor can be

achieved. By making a more efficient motor, it would draw less battery current

and consume less fuel. In addition every 10% reduction in the weight of the

automobile yields 7% increase in the fuel efficiency. Therefore the reduction in

weight of the bonded Nd-Fe-B motor yields consequential results, and the

reduction in size would in turn allow automobile suppliers to shrink the size

and weight of the other related components.


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Table 6 Comparison of physical parameters and performance of benchmarked ferritePM brushed DC motor and different redesigned PMBL DC motors with Bonded Neo

Magnets

Parameter

PMDCFerrite

Benchmark

Motor-ABLDC-MQP-B2+ 0.6 mm

Air gap

Motor-BBLDC-MQP-B2+ 0.6 mm

Air gap

Motor-CBLDC-MQP-14-12 (IM)0.6 mm Air

gap

Type of Magnet FerriteCompression Moulded

CompressionMoulded

InjectionMoulded

Total motor weight (gm) 165.90 75.10 80.50 85.00

Length of the motor (mm) 30.0 22.0 22.0 22.0

Overall diameter (mm) 35.3 26.2 27.5 28.0

Total copper weight (gm) 12.17 19.20 20.20 23.80

Total magnet weight (gm) 38.18 7.50 7.50 9.50

Length of Airgap (mm) 0.6 0.6 1.0 0.6

Current at 30 mN-m (A) 4.07 3.00 2.85 2.75

Current at 60 mN-m (A) 6.47 5.10 5.05 4.75

Efficiency at 30 mN-m (%) 47.0 62.0 62.5 64.0

Efficiency at 60 mN-m (%) 36.0 55.0 57.0 59.0

Normalized Volume 1 0.404 0.445 0.46

Normalized Weight 1 0.453 0.485 0.512

Normalized Diameter 1 0.742 0.779 0.793

Normalized Length 1 0.733 0.733 0.733

VP Fuel Pump Motor

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