OMU-332VEHICLE COMPONENT DESIGN

Asst.Prof. Özgür ÜNVER December 31st, 2019

HYDRAULIC SYSTEMS

Application Areas

Benefits of Hydraulic Systems;• Extensively used for driving high-power machine tools,

• They can deliver a higher amount of power while being relatively small in size(high power density).

• Very large amount of power that can be transferred through small tubes and flexible hoses,

Hydraulics used in many applications:• Excavators

• Cranes

• Heavy duty machines

• Construction machinery

• Mining machinery

• Etc..

FLUID SYSTEMS

A fluid is a substance which flows (liquid or gas).

• Gases (such as air) are often treated as compressible

• Liquids (such as water and oil) are usually considered incompressible.

• A force applied to a fluid produces a reaction force

Conservation of mass is represented by the continuity equation,

• total ingoing mass flow rate = total outgoing mass flow rate

CONSERVATION OF MASS

For compressible fluids, the density (𝜌) varies!

For incompressible fluids density, 𝜌, is almost constant, therefore, the continuity equation can be written as;

𝐴1𝜐1 = 𝐴2𝜐2

Videoshttp://www.youtube.com/watch?v=uYIzWI12T8g

http://www.youtube.com/watch?v=mgkyabWnZFw

http://www.youtube.com/watch?v=M4rJO6QzDWA

http://www.youtube.com/watch?v=wwGTZIkh42E

http://www.youtube.com/watch?v=SwqM8zpmAD8

http://www.youtube.com/watch?v=6C7fZKHQPN4

BASIC PRINCIPLES• Liquids:

• Have no Shape

• Are (almost) incompressible

• Transmit force in all directions, equally

FUNDAMENTAL FEATURES

If a hydraulic rotary pump with the displacement 10 cc/rev is connected to a hydraulic rotary motor with 100 cc/rev, the shaft torque required to drive the pump is 10 times less than the torque available at the motor shaft, but the shaft speed (rev/min) for the motor is 10 times less than the pump shaft speed.

Advantages & Disadvantages of Hydraulics

Advantages:

• Flexibility

•Multiplication of Force

•Compact(actuator)

•Economy

• Safety

Disadvantages:

•Efficiency(compared to electric motors)

•Cleanliness

FLUID (HYDRAULIC) SYSTEMS

FLUID (HYDRAULIC) SYSTEMS

The components of a hydraulic systems are:

• Motor: main power supply (electric/ICE/steam/turbine)

• Pump: hydraulic power generation system

• Fluid: transfers the power between the various circuit elements

• Pipes: for connecting the various components of the actuation system

• Filters: to filtering the hydraulics

• Accumulators: damping, storing, compansating

• Reservoirs (tanks): storing liquid

• The valve: hydraulic power regulator

• The actuator (piston): the element which converts hydraulic power into mechanical power

• The sensors and transducers

• The system display and control devices

HYDRAULIC FACTS

Oil takes the path of least resistance

A pump does not create pressure, it creates flow.

Pressure is caused by resistance to flow.

These can produce the same power:

• High pressure & low flow

• Low pressure & high flow

PUMP TYPES

• Pumps transform electrical or mechanical energy into hydraulic energy. • They constitute the fluid flow generator of the hydraulic system, • Pressure is determined by the system (not the pump)• Eficiency = Volumetric efficiency x Mechanical efficiency

A positive-displacement pump;

• has a small clearance between the stationary and rotating parts.

• able to push a definite volume of fluid for each cycle of pump operation at any resistance encountered.

• only by varying the speed of the pump can the output of the pump be changed.

• hydraulic delivery in a variable pump can be changed by altering the physical relationship of the pump elements and keeping the speed at a constant level.

Non-Positive-Displacement Pumps;

• has a large clearance between the rotating and stationary parts.

• the total volume of the fluid displaced from the pump depends on its speed and resistance faced at the discharge side of the pump unit.

• In applications which deal with a low-pressure and high-volume flow situation.

PUMP TYPESCentrifugal pumps:http://www.youtube.com/watch?v=iygacPUfuRAhttp://www.youtube.com/watch?v=V3aPHmZ97yMhttp://www.youtube.com/watch?v=BaEHVpKc-1Q

Gear pumps:http://www.youtube.com/watch?v=xPC5uFja1pYhttps://www.youtube.com/watch?v=TIGSBEUGYeUhttps://www.youtube.com/watch?v=JR-j0D5YwoI

Rotary vane:http://www.youtube.com/watch?v=AFHogF-9eGAhttp://www.youtube.com/watch?v=BnvzPoNSXCghttp://www.youtube.com/watch?v=pAARwR3hCqw

Piston pumps:http://www.youtube.com/watch?v=2mh902AP7Ywhttp://www.youtube.com/watch?v=OsYk27A7A_Mhttp://www.youtube.com/watch?v=KpWbJxtgs3Uhttp://www.youtube.com/watch?v=a58zzqfF5N0

Pump Type Pressure

(bar)

Flow Rate

(l/min)

Rotational Speed

(rpm)

Viscosity

(cSt)

Efficiency

(%)

External Gear Pump

Unbalanced 40-200 300 500-3000 40-80 60-80

Balanced 100-200 200 500-6000 40-80 80-90

Internal Gear Pumps

Balanced 150-300 100 500-2000 40-80 80-90

Lobe Pumps 30-50 200

Screw Pumps 50-160 100 500-3000 80-200 70-80

Vane Pumps

Balanced,fixed

displacement

100-200 300 500-3000 20-160 80-90

Variable

Displacement

40-160 125 500-2000 20-160 70-80

Piston Pumps

Radial 0-700 125 1000-3000 10-200 85-90

Axial - Bent axis 0-400 10-2000 500-3000 20-50 85-90

Axial - Swash Plate 150-350 10-2000 1000-3000 30-50 85-90

GEAR PUMPS• Work well at 150 bar and below

• Less expensive to manufacture than piston type pumps

• Very simple (work with a minimum moving parts),

• Reliable,

• Relatively cheap

• Less dirt sensitive

• The meshing of the teeth prevents the oil flowing back

• To prevent cavitation minimum absolute pressure: 0.8 bar or 80 kPa

• Vane pumps are applied if the pressure is below 200 bars,

• The advantage: pulse free delivery

• The advantage: low level of noise.

• The stator ring is circular and is held in an eccentric position.

• The amount of eccentricity determines the displacement of the pump (flow rate).

• When eccentricity is zero, the displacement of the pump becomes 0 cm3

• To prevent cavitation minimum absolute pressure: 0.8 bar or 80 kPa

VANE PUMPS

Variable displacement vane pump

AXIAL PISTON PUMP

• The axial piston pump with rotating swashplate

• The most commonly used pump type above 200 bar

• The swashplate is driven by the shaft

• Angle of the swashplate determines the stroke of the piston (flow/rotation).

• Can be driven in both directions

• Cannot be used as a hydromotor.

ENERGY MODULATION DEVICES (VALVES)The energy modulation devices in fluid power systems control;

• pressure,

• direction,

• Flow rate (l/min).

http://www.youtube.com/watch?v=vY_bguSNgSc

http://www.youtube.com/watch?v=eKqfP2F_Pl0

Pressure Control Valves

Relief valves:

• mainly protect/limit the circuit from maximum pressure.

• can be considered as safety valves (electricity: fuse)

• have to be large enough to handle the entire volume flow. http://www.youtube.com/watch?v=8gvfCj57Fj8

http://www.youtube.com/watch?v=b2KQVkdAGzQ

valve closed symbol valve open

Pressure Control Valves

Unloading valves:

• to permit a pump to operate at a minimal load.

• it needs an external signal.

• fluid delivery is shifted through the secondary port back to the main reservoir whenever sufficient pilot pressure is applied

Pressure Control ValvesSequence valves• are used to control the order of the flow in

a particular order. • caused by requiring the inlet pilot pressure

to reach a set pressure level • The actuation of the valve is caused by fluid

pressure that is generated separately.

Counterbalance valves• To prevent the free fall of a load held by the

actuator and to develop some line of resistance.

• restricts fluid flow to maintain a pressure level sufficient to balance a load

• fluid is held under pressure until pilot action overcomes the spring force setting or the counterweight in the valve.

Pressure Control Valves

Regulator valves

• known as pressure-reducing valves.

• provide a constant pressure at the outlet port, regardless of the pressure at the inlet port

http://www.youtube.com/watch?v=sFAYW_D3G_g

Pressure switch

• used whenever an electrical signal is required

• The electric signal can be relayed to a solenoid valve to change the direction of flow or to actuate a pump.

Directional Control Valve

Directional Control Valve

Used to direct the flow of fluid to the various places in the system.

• blocks the flow completely,

• guides the flow to various branches

They may be used for;

• energizing or de-energizing a fluid power circuit

• isolate the fluid power circuit from a part of the circuit

• reverse the direction of the flow

• combine the flow

• separate the flow

Directional Control Valve

Check Valves for Directional Control

• allow free flow of fluid in one direction and restrict in the opposite direction.

• The pilot-operated check valve allows the free flow in one direction and will only allow fluid flow in the opposite direction (normally blocked) if pilot pressure is applied at the pilot pressure port of the valve.

http://www.youtube.com/watch?v=Aa-LhKtZYoc

Directional Control ValvePosition Valves for Directional Control

• used to direct fluid to one or more different flow lines,

• Depending on the position of the valve, the interconnection of the external ports produces various combinations of flow direction.

• Port number/position number

• Position determines the number of alternative flow conditions the valve can provide.

• These are made possible by the configuration of the spool or the passages of the valve body.

Symbol of a 4/3-direction control valve

This is a 4/3-direction control valve • 4 line connections • 3 positions

Directional Control Valve

• http://www.youtube.com/watch?v=vY_bguSNgSc

• http://www.youtube.com/watch?v=3CIeLBvUA-o

• http://www.youtube.com/watch?v=_Ae77QL46_4

• http://www.youtube.com/watch?v=ZZY_KyLaGvk

Volume Control Valve

Volume Control Valve

• The volume-control valves are used to monitor the rate

of fluid flow to various parts of a fluid power circuit.

• Volume-control valves have the role of regulating the

speed

Needle Valves:

• based on a long, tapered point that seats in the valve

• permits a very gradual opening and closing of the

passage The needle valve is not pressure compensated

Volume Control Valve

Fixed-Volume, Pressure-Compensated, Flow-Control Valves:

• Keeps a constant flow regardless of the variations in the inletflow to the valve.

• If the inlet flow rate rises, the mechanism partly closes the pressure-compensated valve in order to reduce the outlet flow.

• Due to this mechanism, the total volume of fluid through the valve always remains fixed.

Volume Control Valve

Variable-Volume, Pressure-Compensated, Flow-Control Valves:

• Uses an adjustable volume-control device to adjust the orifice area.

• Some of the components used in the valves are tapered slots or meteringspools.

• These types of valves maintain a constant flow with varying inlet and outlet pressures.

Flow-Divider Valves

• to synchronize the movements of two or more cylinders without having mechanical interconnections between them.

• This valve handles the flow of fluid in a line and fans out to two or more lines so that each has the same flow rate.