Mechatronics LabMechatronics Lab

Design and characterization for regenerative shock absorbers

Candidate: Yijun XU

PhD in Mechanical Engineering Tutor: Prof. Nicola AMATI

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Outlines

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• Motivation and State of the Art

• Suspension assessment

• Design method for motor-pump unit

• Prototype assembly and efficiency assessment

• Experimental tests and results

• Conclusion and work in progress

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Motivation and State of the art

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Regenerative shock absorbers

Conventional suspensions

Conventional suspensions dissipate the kinetic energy as heat

waste, regenerative shock absorbers can convert the kinetic

energy into electrical energy.

Linear Ball screw Rack and pinion Electro-hydrostatic (EHA)

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Why EHA dampers?

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Advantages comparison with other solutions• Linear motors force density is limited, work inefficiently, additional heft to the vehicle

• Electromechanical technologies (Ball screw, rack and pinion…) are complex and difficult to integrate into the

suspension also with wear and fatigue issues

• Fluid-based EHA solution overcomes the main tribology of electromechanical systems, the fluid is used as

power transmission, the actuator offers better flexibility for its placement within suspension

No. Component

1 Battery

2 Power stage

3 Electric motor

4 Hydraulic pump

5 Pressure-relief valves

6 Check valves

7 Piston

8 Gas accumulator

9 Base

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Quarter car model

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Regenerative

damper

Reference vehicle:

Jeep Renegade

Parameter Symbol Front Rear

Sprung mass 𝑚𝑠 416.5 kg 256 kg

Unsprung mass 𝑚𝑢 40 kg 30 kg

Suspension stiffness 𝑘𝑠 23256 N/m 21739 N/m

Tire stiffness 𝑘𝑢 226 kN/m 206 kN/m

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Suspension assessment

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Road class Description Gr [m cycle] SCO2 [gCO2/km]

A Very good 1.60E-07 1.6E-01

B Good 6.40E-07 6.4E-01

C Average 2.56E-06 2.6E+00

D Poor 1.02E-05 1.0E+01

E Very poor 4.10E-05 4.1E+01

The emission reduction can be calculated by using

the following expression :

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Design method for the motor-pump unit

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Force-speed maps of the regenerative shock absorber

limited by damping, force and speed values

Ideal map

Expected map

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Hydraulic pump design

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2

3

1

3-node mesh refinement

1: Axial

clearance

2: Radial clearance

between inner gear

and shaft

3: Radial clearance

between outer gear

and pocket

Displacement: 3.572 cm3/rev.

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Pressure balance inside the case

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P1

P4

P2

P3

Pressure balance

𝑃1 = 𝑃2𝑃3 = 𝑃4𝑃2 > 𝑃3

Unbalanced condition

𝑃1 > 𝑃2 > 𝑃3 > 𝑃4

Forces due to

pressure unbalance

Case with groovesCase without grooves

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Electric machine design

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Magnetic

Design

Torque

maximization

Winding

Design

Fixed

parameters

Design

constraints

Design

Assessment

Final

configuration

Parameter Value Description

𝑅ro 10 mm Rotor outside diameter

𝑅m 15 mm Magnet diameter

𝑅si 29.5 mm Stator inside diameter

𝑅so 32 mm Stator outside diameter

𝑑 1 mm Tooth-winding gap

𝑔 0.5 mm Air gap

𝐿 30 mm Active length

𝑁m 10 Number of magnets

𝑁s 12 Number of slots

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Electric Machine assessment

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Hottest

point

Symbol Value Description

𝑁tc 14 Number of turns per coil

𝐾e 21.4 mVs/rad Back EMF constant

𝑅 20 mΩ Phase resistance

𝑆w 2.19 mm2 Wire cross section

𝜆𝑝 4.22 Wb Permanent magnet flux linkage

𝑝 5 Number of pole pairs

𝑘cp 0.3 Coil packing factor

𝐵r 1.3 T Magnet remanent flux density

𝐵sat 1.2-1.8 T Iron saturation flux density

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Control strategy

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Prototype layout

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No. Component

1 Pump port plugs

2 Pump cover manifold

3 Casing

4 Gerotor gear

5 Ball bearing x 2

6 Stator

7 Motor spacer

8 Wave spring

No. Component

9 Position sensor

10 Drain cap

11 Cable gland x 4

12 Motor cover

13 Permanent magnets x 10

14 Winding coil x 6

15 Key

16 Rotor shaft

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Prototype layout

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Main data Unit Value

Added mass per corner kg 2.1

Max diameter mm 88

Max axial size mm 84

Pump displacement cc/rev 3.57

Max e-motor torque Nm 0.67

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Efficiency assessment in static test rig

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Input

power

GEROTOR

PUMP

Hydrauli

c losses

Mechanical

powerELECTRIC

MOTOR

Electric

powerPOWER

STAGE

Electric

power

AC 3-phase DC

Mechani

cal

losses

𝜂h 𝜂m 𝜂e

Electric

losses

𝐷in11.47

cm3

rev

𝐷g3.57

cm3

revM M

Q

P1

P2

Power

module

DC bus

battery

High-side pressure

sensor

Flow meter

Low-side pressure

sensor

Input angular

speed

Output angular

speed

DC bus voltage

and current

Input motor-

pump group

Output motor-pump

group (RSA)

Input motor

(speed-driven)

Output motor

(damping control)

Accumulator

Hydraulic efficiency

𝜂h =𝐷gΩg

𝑄

Mechanical efficiency

𝜂m = 1 −𝑐mΩg

𝐷gΔ𝑃

Electric efficiency

(motor and power stage)

𝜂e = 1 −2(𝑅 + 𝑅on)𝑇em

3𝐾e2Ωg

Total efficiency

𝜂tot = 𝜂e𝜂m𝜂h =𝑉dc𝑖dcΔ𝑃𝑄

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Static test results

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No. Description

1 Motor-pump prototype

2 Power stage

3 Driving motor-pump unit

4 Current probe

5 Hydraulic lines

6 Hand pump to fill the circuit

No. Description

7 Battery array

8 Data logging PC

9 Driving motor switchboard

10 Control PC

11 Gas-loaded accumulator

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Static test results

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0.139

0.172

0.289

0.4

Proto 2

0.167

0.274

0.163

0.395

Proto 3

0.148

0.315

0.12

0.417

Proto 4

0.193

0.148

0.268

0.391

Proto 5

Legend

Power terms (normalized with

respect to the total input power)

Hydraulic loss

Mechanical loss

Electrical loss

Regenerated power

0

0.2

0.4

0.6

0.8

1

hydraulic mechanical electrical total

Peak efficiency in the characterized area

proto 2 proto 3 proto 4 proto 5

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Damper characterization on the test bench in Marelli

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Final prototype assembly on the vehicle

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Front axle reg. power monitoring

Rear axle reg. power monitoring

Front-left damper Front-right damper

Rear-left damper Rear-right damper

MPPM Front axle

MPPM Rear axle

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Testing track and setup

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The testing was carried out inside Magneti Marelli

(shown in green)

The Fiat 500X is equipped with 4 regenerative

shock absorbers which are controlled by 2 ECUs

(Front and Rear)

The tests are performed under 3 different

conditions with damping values of 920, 2760 and

6135 [Ns/m]

• Position 1 : road with rush downhill

• Position 2 : where perform “S” maneuver

• Position 3 : road with step

compression forces exerted

to the right wheels of the car

①②

③

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Testing result – phase current and power regenerated

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Damping value: 6135 [Ns/m] Phase current Iu, Iv and Iw for front right corner Passing through position3 (Step)

Maximum 42.2 [A]

Max. power regenerated 120[w]

Damping value: 920 [Ns/m] Power regenerated for the rear axle Passing through position1 (Downhill)

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Conclusions and work in progress

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• The method adopted for designing the motor-pump unit for hydraulic shock absorbers

guarantees the damping functionality and maximize the energy regeneration capability of the

system.

• The results shows the role of different components on the total conversion efficiency and it turns

out that the hydro-mechanical losses were identified as the most critical aspect of the design.

• Next step is to evaluate comfort ,handling and regeneration on a test track with different road

profiles.

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The End

Thank You for Your Attention