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Hydraulic

calculations

MobileMachines

IHA

2307

JanneUusi

Heikkil

janne.uusihiekkila@tut.fi

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Behaviour

of

simplified

hydraulic

power

transmission

Thefigurepresentssimplifiedhydraulic

powertransmission.Thefigureshows

twomainpartsandauxiliarypump.

Parametersof

the

system:

Hydraulicpump:

Electricmotor:

Hydraulicmotor:

Overallpressurelossinpipelinesis8bar.

Totalefficiencyofthesystemis60%

(includingelectricmotor).

IHA2307 2

%90

/revm1080V

vol

36

p

%89

rev/min1000n

tot

m

93%

87%

vol

mec

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Behaviour

of

simplified

hydraulic

power

transmission

Stateofthesystem:

1. Relativedisplacementofthepumpissetobe50%.

2. Constantload

of

the

hydraulic

motor

is12kW.

3. Efficienciesisassumedtobeconstantontheoperatingrange.

Calculate:

a) Outletpressureofmainpump

b) FlowrateQ1c) Loadwhenpressurereliefvalve

opens

d) Displacementofthemotorwhenrotationalspeedofthemotoris200

rpme) Supplypowerofelectricmotor

f) Mechanicalefficiencyofthemainpump

IHA2307 3

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Behaviour

of..:

a)

Outlet

pressure

of

main

pump

Pressureatinletofthe

motor:

Outletpressureofpump:

247bar+8bar=255bar

IHA2307 4

s

cmrev 600

min

l360.9

rev

l

1000

80

min

10000.5Q

Vn%50Q

p

volpp

bar247

0.870.93

10600

1012

QPp

6-

3

volmecp

inlet

s

m

W

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Behaviour

of..:

b)

Flow

rate

Q1

LeakflowQ1:

Leakageofthepump:

Leakageof

the

motor:

Totalleakage:

Ql =Qpl+Qml=(4+2.52)l/min=

6.52l/min

IHA2307 5

min

l4

rev

cm80

min

rev10000.50.9)1(

Vn0%5)(1Q pvolpl

min

l2.52

min

l36)93.01(

Q)(1Q pvolml

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Behaviourof..:c)Loadwhenpressurereliefvalveopens

Maximumofthepressure

ontheoutlet ofthe

pump is270

bar.

>pressure difference

over themotor can be:

270bar 8

bar =

262

bar

IHA2307 6

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Behaviourof..:d)Displacementofthemotorwhen

rotational

speed

of

the

motor

is

200

rpm

Flowequation

IHA2307 7

volpmmmm QVC n

revcm167

min

rev200

%0.93min

l36Cm

m

volp

m

n

QV

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Behaviour

of..:

e)

Supply

power

of

electric

motor

Totalefficiencyofthe

hydraulicsystemwas60%

IHA2307 8

kW20%60

kW12Pp

kW22.5%89

kW20Pem

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Behaviourof..:f)Mechanicalefficiencyofthemainpump

Equationofpowerandtorque

andtonumbers

IHA2307 9

mec

p

p

p

p

1

2

Vp0.5

PM

%85

601020

10001080102555.02P

2nVp0.52P

Vp0.5

3

65

pp

pp

mec

sW

revrev

mPa

mec

CM,MP

p

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Variabledisplacementpumpisusedtocontrolfixed

displacement

motor

Propertiesofthepump

Propertiesofthemotor

IHA2307 10

%85

bar)/(sm100.9

motor)electrictofixed(constant,rev/s25n/revm10164V

mec

36

p

36

p

2

m

mec

36m

36

m

mkg1.0J

85%

bar)/(sm100.9

/revm1065V

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Variabledisplacementpumpisusedtocontrolfixed

displacement

motor

Compressibilityofthefluidand

pressurelosses inthepipeline

areneglected.

Calculate:

a) accelerationofthehydraulic

motor,whenitsrotational

speedis

33

rev/s

and

pump

displacementis60%.

b) requiredpowerofelectric

motorwhen

system

state

is

samethaninquestiona).

IHA2307 11

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Variabledisp..:a)accelerationofthehydraulicmotor,whenits

rotational

speed

is

33

rev/s

and

pump

displacement

is

60

%.

IHA2307 12

pVnpVnQ mmmppp

178bar100.9)(0.9

106533101640.625

)(

VnVnp

6

66

mp

mmpp

dt

dJM mm

2

V

p

M2

m

mm_mec

2

65mm_mecm

s

rad156

1.02

1065101780.85

2J

Vp

dt

d

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Variabledisp..:b)requiredpowerofelectricmotorwhen

system

state

is

same

than

in

question

a).

IHA2307 13

51.4kW0.85

101640.62510178

Vpn

)V(n

p

pQ

P

65

p_mec

pp

p_volpp

p_tot

p_totem

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One

former

exam

question:

Thereisbelowthehydraulicdiagramofthehydrostaticpowertransmission

(aclosedloophydraulicsystem).Namethenumberedcomponentsofthe

hydraulicsystemandexplaintheiroperationinthesystembriefly.

IHA2307 14