2103483 Automotive System Design (2022/2)

Accumulator

Accumulator Detail Design

Battery Cell

We choose Melasta Battery Model Number SLPB8763124 for its Light Weight and High Energy Density.

With have specifications:

Nominal Voltage: 3.7 V

Current: 7.5 A

Max Discharge: 20 C

Continuous Discharge: 15 C

Max Charge: 4 C

Nominal Energy: 27.75 Wh 99.9 kJ

Mass: 151 g

Battery Amount Decision

Maximum Motor Voltage Operation is 490 V. So, we will use 132 Battery Cells in series connection to get 132x3.7 = 488.4 V (Almost 490 V as possible to get Lower Current). But it will have energy only 488.4x7.5/1000 = 3.663 kWh where our target is 7.676 kWh. So, we will use 2 parallel connection.

Finally, our Accumulator have 488.4x(7.5x2)/1000 = 7.326 kWh almost our target but if we increase more parallel connection is will be over target and too much weight.

Conclusion: Battery Cell Amounts is 132x2 = 264 cells

Battery Segment Decision

Now we have 264 cells, 39.864 kg and 7.326 kWh

The Regulation:

EV.6.1.2 each segment must not exceed 120 V and 6 MJ
F.10.3.2 each segment must not exceed 12 kg

So we decide to divide it into 6 segment which each segment contain: 44 Battery Cells (22S2P Connection), 81.4 V, 6.644 kg and 1.221 kWh (4.3956 MJ)

Battery Module Specification

1 Battery Module contains:

44 Battery Cells

Connections:

22 Series Connection

2 Parallel Connection

Specifications:

Voltage: 81.4 V

Current: 15 A

Energy: 1221 Wh (4.3956 MJ)

Mass: 6.644 kg

Battery Rack Specification

Material: Aluminium alloy

Dimension (weight x length x height) : 133 x 266.5 x 128.8 mm (include mounting part)

Slot dimension (weight x length) : 8.7 x 63.5 mm

Wall between slot : 2 mm

Weight : 0.943 kg

Battery Layout Decisions

For No.1&2 Layout, the battery is exceed available area. While No.3 Layout air gap in front of container is too small its maybe Bad Air Flow in the Red Zone or it will not have Air Flow. So it will cause 1st Row of 1st Floor overheat.

So we decide to ask structure team to increase longitudinal space for Accumulator Container and get more 60 mm in longitudinal space.

Accumulator Container

Specifications:

Width: 540 mm

Length: 430 mm

Height: 370 mm

Material: Aluminum Alloy

Mass: 62.505 kg (without Bolt & Fans)

Mounting:

Width: 40 mm

Length: 45 mm (Side, Upper), 27.3 mm (Front)

Thickness: 5 mm

Hole Diameter: 12 mm

Accumulator Mounting

Accumulator Installation

Use Lifting Sling attach to four Mounting as left picture.

Then put down vertically on the Bracket.

Front Bracket | Upper Bracket | Side Bracket

Bracket Material

Bracket Material we use is 3mm Strenx 700 MC that can which has Yield Strength of 700 MPa

Wiring

The Regulation:

EV.7.3.2 All Tractive System wiring must:

a. Be marked with wire gauge, temperature rating and insulation voltage rating.

b. Have temperature rating greater than or equal to 90°C.

EV.7.3.3 Sizing of the conductors for the ‘continuous Tractive System current’ may consider the:

a. RMS or average electrical current that will be used

b. Anticipated duration of time at maximum electrical current

Calculation:

Max Power draw is 80 kW

Max Motor Operate Voltage is 490VDC

So, Peak Current is 80000/490 = 165A

Then, change to RMS by divide by √2 equal to 347Vrms 117Arms.

So we use 25 mm^2 Cross-section area that has weight 470 g/m

From picture left side, The Red line represent DC and The Rainbow line represent AC.

We have four 25 cm DC and six 20 cm AC, So total length of wire is 2.2 m while total weight is 470x2.2 = 1034 g

Energy Consumption

Parameter in Energy Simulation

Driving Cycle in Energy Simulation

Drive by Phasit Phucharoen in Assetto Corsa

Mod by UCM 2016 Formula Student

Result

Total Time = 1347.7 s

Total Energy Used = 5575.51 Wh

Total Energy Regen = 1761.89 Wh

Net Energy = 3813.62 Wh

Simulate by MATLAB

Future Improvement

From Energy Consumption Simulation Net Energy is 3813.62 Wh. So we can reduce Battery Capacity to 4.884 kWh.

4 Modules (2x22s2p + 2x44s1p) can provide Peak Power = 97.68 kW and Max Continuous Power = 73.26 kW.

Can Reduce Weight 15.3 kg

Finite Element Method

Material used in Catia

Material used in Ansys

Bolt Torque used in Catia

-----------------------------------------------------Battery rack-------------------------------------------------------

The Regulation:

F.10.3.4 Cells and Segments

a. The cells and/or segments must be appropriately secured against moving inside the Container.

b. This mounting system design must withstand the following accelerations:

40 g in the longitudinal direction (forward/aft)

40 g in the lateral direction (left/right)

20 g in the vertical direction (up/down)

c. Calculations and/or tests proving these requirements are met must be included in the SES.

d. Any fasteners must be 6 mm or 1/4” minimum diameter

Battery rack FBD

20g in Z direction (Vertical:up)

At mounting part

At support mounting

20g in Z direction (Vertical:down)

At support mounting

Test 40g in Y direction (lateral)

At mounting part

At support mounting

Test 40g in x direction (longitudinal)

At mounting part

At support mounting

กดที่ ฺBattery rack FBD เพื่อดู FBD

Battery rack design condition

From Regulation the mounting system design must withstand the following accelerations:

40 g in the longitudinal direction (forward/aft)

40 g in the lateral direction (left/right)

20 g in the vertical direction (up/down)

A word "withstand" in regulation is not described what it means in details. So, We decide the testing result that the rack is not permanent deformation while taking the acceleration and the battery module is still in the rack. The rack is not permanent deformation, which means the stress on the rack as testing is not higher than the yield strenght of the aluminium alloy. Therefore, the rack is not fatique and permanent deformation.

Fix support at the frames

Insert M8 bolts at the mounting and M6 bolts at the supports

Meshing size is 0.05 m.

Note The supports consist of two beams, which are positioned to secure the batteries from an overhead perspective.

Test 40g in x direction (longitudinal)

Maxiumum deformation

At support 1.71 * 10^-5 m
At mount 3.35 * 10^-8 m

Maximum stress

At support 0.135 MPa
At mount 24.47 MPa

S.F = 280 MPa/ 24.47 MPa

= 11.44

Test 40g in Y direction (lateral)

Maximum deformation

At support 5.96 * 10^-6 m
At mount 1.25* 10^-7 m

Maximum stress

At support 0.094 MPa
At mount 10.7 MPa

S.F = 280 MPa/ 10.7 MPa

= 26.2

Test 20g in Z direction (Vertical:up)

Maximum deformation

At support 3.55 * 10^-6 m
At mount 1.11* 10^-7 m

Maximum stress

At support 0.147 MPa
At mount 7.46 MPa

S.F = 280 MPa/ 7.46 MPa

= 37.53

Test 20g in Z direction (Vertical: down)

Maximum deformation

At support 3.55 * 10^-6 m
At 2.72* 10^-6 m

Maximum stress

At support 0.158 MPa
At mount 7.46 MPa

S.F = 280 MPa/ 7.46 MPa

= 37.53

Conclusion

The rack has withstood all tested accelerations without exceeding 10^5 meters of deformation or surpassing the 280 MPa which is yield strength of the aluminum alloy. As a result, the rack is not permanent deformation and fatigue during testing in any accelerations. Furthermore, the batteries are still integrated into the rack. The outcomes align with the rack design condition.

-----------------------------------------------------Accumulator-----------------------------------------------------

The Regulation:

F.10.3.4 Cells and Segments

a. The cells and/or segments must be appropriately secured against moving inside the Container.

b. This mounting system design must withstand the following accelerations: 40 g in the longitudinal direction (forward/aft)

40 g in the lateral direction (left/right) 20 g in the vertical direction (up/down)

c. Calculations and/or tests proving these requirements are met must be included in the SES.

d. Any fasteners must be 6 mm or 1/4” minimum diameter

Accumulator Container FBD

Because it have too much component in Accumulator Container, I split into three FBD

First FBD contains 6xBMS and Horizontal Wall

Calculation

Second FBD contains 2xBattery Module, 2xRack and Vertical Wall

Calculation

Third FBD contains Primary Accumulator Container Frame and First & Second FBD Support Force

But its was over constraints or a redundant support FBD, so its too complex to calculate by hand.

It has only it weight (mass = 3.042 kg) in FBD that can calculation ==> 3.042*9.81*20 = 596.84 N

Fix Support (Welding)

M12 Bolt Support @142 Nm

M3 Bolt Support @2.2 Nm

M6 Bolt Support @16.8 Nm

M8 Bolt Support @41.0 Nm

M8 Bolt Support @Left side

M8 Bolt Support @Rack Connection

M8 Bolt Support @Right side

M8 Bolt Support @Horizontal Wall & Long Vertical Wall

40g [+X]

40g [+Y]

40g [-Y]

20g [+Z]

Conclusion: The Accumulator Container can withstand 40 g in the longitudinal & lateral direction and 20 g in the vertical direction. Moreover, it doesn't have any components moved to touch other components.

-----------------------------------------------------Bracket-----------------------------------------------------

The Regulation:

F.10.5.7 Accumulator Attachment – Load Based

a. The minimum number of attachment points depends on the total mass of the container:

Total Mass > 40 kg must have minimum 10 Attachment Points

b. Any brackets which attach the Accumulator Container to the chassis must:

Be made of steel 1.6 mm minimum thickness or aluminum 4 mm minimum thickness
Have gussets to carry bending loads.

c. Each attachment point, including any brackets, backing plates and inserts, must be able to withstand 15 kN in any direction

d. Fasteners must spaced minimum 50 mm apart to be counted as separate attachment points.

Front Bracket

Conclusion: The Front Bracket can withstand 15 kN force in any direction.

The Most Stress: 570 MPa in -X direction (Backward of Formula).

Safety Factor: 700/570 = 1.228

Upper Bracket

Conclusion: The Upper Bracket can withstand 15 kN force in any direction.

The Most Stress: 501 MPa in X direction (Longitudinal of Formula).

Safety Factor: 700/501 = 1.397

Side Bracket

Conclusion: The Side Bracket can withstand 15 kN force in any direction.

The Most Stress: 475 MPa in -Z direction (Vertical Downward of Formula).

Safety Factor: 700/475 = 1.473

---------------------------------------------Cooling system----------------------------------------------

Regulation

EV.8.5.2 Temperatures (considering measurement accuracy) must remain below the lower of the two:

• The maximum cell temperature limit stated in the cell data sheet

• 60°C

EV.8.5.5 For lithium based cells

a. The temperature of a minimum of 20% of the cells must be monitored by the AMS

b. The monitored cells must be equally distributed inside the Accumulator Container(s)

F.10.4 Holes

Holes should be no larger than 10mm diameter, and slots are prohibited.

Once the lid is on, we expect each segment to be in its own room.

Use 10mm holes to reduce each face by up to 25%.

For the time being, sensible notches for connections between segments, connections outside the accumulator, or coolant tubes will not count towards the 25% limit. But no more fan-size holes for fans.

Objective

1.Find the hot spot to set the temperature sensors

2. To design a temperature battery management system

Flow design

First floor

Note 1.Requiring air flow from aeropart.

2.Requiring more air gap from accumulator.

3.Requiring more space from sturcture.

Second Floor

Fan

Fan can not be varied rpm
Focusing on CFM

Specification

3000 rpm

Air flow: 100 CFM

ref

6000 rpm

Air flow: 210 CFM

ref

6300 rpm

Air flow: 250 CFM

ref

7500 rpm

Air flow: 280 CFM

ref

Setting Fan

Environment

Set gravity

Set air temperature at 25C

The process of designing a temperature battery management

Heat Load(Loss power)

Q = I^2 x R

R: Internal resistance (Ohm)

I: Current (A)

Q: Heat load (Watt)

Internal resistance

R = V drop / I load

V drop: Difference Voltage at any load (V)

around 0.4 V

I load: Current at any load (A)

Loss power table

Simulation result

Loss power 22.95 watt at 70% power motor

On the second floor the temperature around 53C

Loss power 19.66 watt at 60% power motor

On the second floor the temperature around 49C

On the first floor the temperature around 58C

On the first floor the temperature around 51C

Setting temperature sensors

The temperature sensors are set up at the middle of the battery module. Because in these area the temperature are higher

All Results

Loss power 32.8 watt at 100% power motor

On the first floor the temperature around 71C

On the second floor the temperature around 66C

Loss power 29.5 watt at 90% power motor

on the first floor the temperature around 67C

On the second floor the temperature around 59C

Loss power 26.19 watt at 80% power motor

on the first floor the temperature around 62C

On the second floor the temperature around 59C

Loss power 16.38watt at 50% power motor

On the first floor the temperature around 41C

On the second floor the temperature around 40C

Loss power 16.38watt at 50% power motor

On the first floor the temperature around 35C

On the second floor the temperature around 36C

Loss power 13.15 watt at 40% power motor

On the first floor the temperature around 36C

On the second floor the temperature around 36C

Loss power 9.81 watt at 30% power motor

On the first floor the temperature around 32C

On the second floor the temperature around 33C

Loss power 6.54 watt at 20% power motor

On the first floor the temperature around 29C

On the second floor the temperature around 30C

Temperature table

Final Specification

Accumulator Capacity: 7.326 kW

Nominal Voltage: 488.4 V

Total Battery Weight: 39.9 kg

Total BMS Weight: 4.2 kg

Accumulator Container Weight (excluding Battery): 18.4 kg

Total Fan Weight: 2.8 kg

Total Bracket Weight: 1.3 kg

Total Bolt, Nut, Screw Weight: 1.9 kg

ECU + MCU Weight: 2 kg

Total Wire Weight: 1 kg

Accumulator Container Assembly Weight: 71.5 kg

Tractive Software

Gallery

The Accumulator

The Accumulator in the car

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