load sensing technologies - robert bosch gmbh€¦ · load sensing technologies. dcsn/slm-dk |...

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Load sensing technologies



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What is load sensing?“Sensing the load pressure downstream of an orifice and…

“Lastunabhängige Durchflussverteilung”

…adjusting the pump flow rate to maintain a constant pressure drop across the orifice…

…meaning a constant flow is achieved regardless of a change in load pressure”

Non-compensated and compensated valves‒ Load dependent and load independent with multiple functions

Types of compensation‒ Pre compensated (Load sensing) & Post compensated (Flow-sharing / LUDV)



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What is load sensing?Open Center LS Closed Center LS



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What is load sensing?Open Center LS Closed Center LS



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Flow Equation

A

QV

∆p

QV = α x A x ∆ p2ρ

α x = K2ρ

QV = K x A ∆ p

QV = f (A, ∆ p) ∆ p = const. QV = f (A)

QV = FlowA = Opening area of orifice∆ p = Differential pressureα = Flow coefficientρ = Oil- Density

Load- dependent System (Open Center Control)

Load- independent System(Load Sensing Control)

0

20

40

60

80

0

20

40

60

80

100

0

5

10

15

20

25

300 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

105

110

115

120

125

130

135

140

145

150

155

160

165

170

175

180

185

190

195

200



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Under-saturation condition∆p

qpump

Avalve

[mm

²][l/

min

][b

ar]

∆p

qpump

qrequired [l/min]

Avalve50 l/min

18,5 mm²

20 bar

100 l/min

36,9 mm²

20 bar

100 l/min

55,3 mm²

8,9 bar

73,8 mm²

100 l/min

5 bar

20 bar

Max 100 l/min



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Pre- and post-compensation – basic circuits

Load sensing pump

Pressure compensator(normally open)

Metering element(main spool)

Actuator(cylinder or motor)

Load signal check

Biasspring

Load signal check

Metering element(main spool)

Pressure compensator(normally closed)

Load sensing pump

Actuator(cylinder or motor)

No bias spring

Pre-compensated Post-compensated



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Pre-compensation - basic circuit

• Start of movement load-/flow-independent

• Fine control range load-independent but flow-dependent

• Independent movement during parallel operation



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Pre-compensation - saturated conditionLoad50 bar

Load250 bar

50 bar 250 bar

250 bar270 bar 270 bar

57 bar 257 barBias spring 7 bar

Bias spring 7 bar

FR = 20 bar

∆p 213 bar

∆p 7 bar

∆p 13 bar

∆p 7 bar

Max flow = 100 l/min

Required flow60 l/min




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Pre-compensation - under-saturated conditionLoad50 bar

Load250 bar

50 bar 250 bar

250 bar251,1 bar 251,1 bar

57 bar 251,1 barBias spring 7 bar

Bias spring 7 bar

FR = 20 bar

∆p 194,1 bar

∆p 7 bar

∆p “0” bar

∆p 1,1 bar




Actual flow80 l/min

Actual flow20 l/min

∆p =Qv2 � ρ

A2 � α2 � 2

A = Qv

α� 2ρ �∆p

50 l/min

7 bar

31,2 mm²

20 l/min

= 31,2mm²

= 1,1 bar

Load sensing – pre-compensated circuit


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Consumer flows with reduced pump flow



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LS pressure limitation • Function analogue to pressure cut-off• Limitation of the LS-signal, therefore

nearly free of losses• Local as well as global pressure

limitation is possible

Local LS pressure limiters

Global LS pressure limiter



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LS unloading • LS unloading is realized through the main spool



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Example: M4-12 High pressure load sensing control block

Flow sharing (LUDV) – post compensated circuit


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Basic circuit

• Start of movement load-/flow-independent

• Fine control range load/flow-independent • Independent movement during parallel

operation



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Saturated condition

Load50 bar

Load250 bar

50 bar

270 bar

250 bar

∆p 20 bar

∆p 200 bar



270 bar

250 bar

250 bar

∆p 20 bar

∆p “0” bar

250 bar

FR = 20 bar




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Undersaturated condition

Load50 bar

Load250 bar

50 bar

261,8 bar

250 bar

∆p 11,8 bar

∆p 200 bar



261,8 bar

250 bar

250 bar

∆p 11,8 bar

∆p “0” bar

250 bar

FR = 20 bar


Actual flow61,5 l/min

Actual flow38,5 l/min

020406080

020406080

10005

1015202530

0 10 20 30 40 50 60 70 80 90 100

110

120

130

140

150

160

170

180

190

200

11,8 bar

130 l/min



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Flow sharing Consumer 1Qrequired = 80,0 l/minQactual = 61,5 l/minRatio = 1 : 0,77

Consumer 2Qrequired = 50,0 l/minQactual = 38,5 l/minRatio = 1 : 0,77

PumpQrequired = 130,0 l/minQmax = 100,0 l/minRatio = 1 : 0,77



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Consumer flows with reduced pump flow



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End stop condition

Ppump = PLS

No flow can pass through compensator

∆p = 0

300 bar

300 bar 300 bar

FR = 20 bar

DR = 300 bar



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LS pressure limitation

FR = 20 bar

DR = 300 bar LSRV = 280 bar

300 bar

280 bar280 bar

∆p 20 bar



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Port pressure limitation • Local port pressure limitation only possible via full flow shock valves

• High loss and heating• Only global LS pressure limitation is

possible



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LS unloading

Post compensated circuit (LUDV)


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Example: M7-22 High pressure flow sharing control block

Combination circuit


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LS and LUDV – checklist

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2

3

1) Check valve from pre-compensated LS-signal to common LS-signal

2) LS copy valve (if necessary)

3) No valves in the LS line between pump and LUDV valve

4) Main relief valve (or PC)5) LS relief valve setting = pump

standby pressure below the MRV (or PC)

6) LS unloading valve

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LS (pre compensated) LUDV (post compensated)

Combination circuit


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LS and LUDV – system features• LS circuit will have priority over the

LUDV circuit in under-saturated condition

• LUDV circuit will share the remaining flow when the required LS functions are saturated

LS (pre compensated) LUDV (post compensated)



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Summary of featuresLS (pre-compensation) Good fine-control Start of movement load-independent Load-independent parallel operation of several

actuators under saturated condition Possibility for local LS pressure limitation

Load-dependent under under-saturated condition, i.e. system reacts like throttle control

Sensitive against oscillations, therefore intensive prototype commissioning may be necessary

LUDV (post-compensation) Good fine-control Start of movement load-independent Load-independent parallel operation of several

actuators also under under-saturated condition

No possibility for local LS pressure limitation Sensitive against oscillations, therefore intensive

prototype commissioning may be necessary


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Thanks for your attention

load sensing technologies - robert bosch gmbh€¦ · load sensing technologies. dcsn/slm-dk |...

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