[dracul]

Originally Posted by Rahul Rao

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A PTO sources it's energy from the gearbox, whenever the engine is declutched, it stops rotating, and as soon as the clutch is engaged again it starts rotating after this momentary stop and this start loads the entire chain from compressor, drive shaft to PTO to gearbox to clutch, and finally engine.
A belt driven system sources energy from crank pulley which is rotating continuously. Even when compresser cuts off after achieving set temperature, it restarts after a minimum of 3 to 5 minutes.

Rahul

PTO can be attached directly to the engine itself. Prime examples are transit mixers without separate engine. Most truck and bus engines have the provision.
In my opinion the manufactures must move towards inverter type compressors running by dc. It may increase the efficiency and reduce the complexity of belt drive and magnetic clutch.

[Rahul Rao]

Originally Posted by dracul

PTO can be attached directly to the engine itself. Prime examples are transit mixers without separate engine. Most truck and bus engines have the provision.

Good to know this, I will try to see this arangement.

Originally Posted by dracul

In my opinion the manufactures must move towards inverter type compressors running by dc. It may increase the efficiency and reduce the complexity of belt drive and magnetic clutch.

Inverter type is more effecient, and it will be effective in series hybrid buses, but for buses with conventional diesel and normal gearbox, or parallel hybrid it is converting mechanical energy to electrical and back to mechinacal with loss of effeciency in both conversions. Here use of variable stroke compressors to control capacity will be more effecient.

Rahul

[Ashley2]

Originally Posted by Rahul Rao

A PTO to drive a Ac compressor doesnt work, it has been tried before without success. A Ac compressor needs a high starting torque, and comparatively low running torque to keep it rotating. Once compressor cuts off, it needs about 2 Min for pressures on both sides to equalise. If restarted without equilising the needed torque will go up considerably.
If you see pressures on R 134a Ac system, while running the suction side is between 30 and 40 psi, while discharge side is between 180 and 250 psi. After equilising both sides have something between 90 to 120 psi depending on ambient temperature.
A PTO sources it's energy from the gearbox, whenever the engine is declutched, it stops rotating, and as soon as the clutch is engaged again it starts rotating after this momentary stop and this start loads the entire chain from compressor, drive shaft to PTO to gearbox to clutch, and finally engine.
A belt driven system sources energy from crank pulley which is rotating continuously. Even when compresser cuts off after achieving set temperature, it restarts after a minimum of 3 to 5 minutes.

Rahul

Rahul, I was referring PTO system only for engine cooling and not for AC. This is a common feature in all the modern day rear engine chassis like B11R, B13R and recently launched B8R.

A PTO sources it's energy from the gearbox, whenever the engine is declutched, it stops rotating, and as soon as the clutch is engaged again it starts rotating after this momentary stop and this start loads the entire chain from compressor, drive shaft to PTO to gearbox to clutch, and finally engine

It doesn't stop rotating. It rotates constantly with the engine speed as its connected with idler shaft and its rotation is independent of clutch. Also I guess PTO driven AC compressors are used in Double Decker AC's