[TusharK]

MAN Trucks India has launched its new CLA BS-IV compliant bus chassis range in India. It is available in two variants - 18.250 (4X2) and 22.300 (6X2) multi-axle. The CLA range adopts a front-engine layout and will be manufactured at the company's Pithampur facility in Madhya Pradesh.



The CLA bus chassis are designed for intercity application. MAN has partnered with three bus body builders in order to offer different body design to customers.

The buses are powered by a BS-IV compliant MAN D-0836 engine mated to a 6-speed gearbox. The turbocharged, intercooled, common rail direct injection diesel engine comes with Selective Catalytic Reduction (SCR) technology for reduced emissions. The engine is offered in two states of tune - the 4X2 version has 245 BHP while the engine in the multi-axle version has been tuned to 296 BHP.

The bus rides on rear air suspension and has air actuated drum brakes with ABS. It also comes with a retarder and an engine valve brake system.

Link to Team-BHP News

[norhog]

Grateful if some one can explain what a retarder and engine valve brake system is?

[blackwasp]

Originally Posted by norhog

Grateful if some one can explain what a retarder and engine valve brake system is?

Retarder - heavy vehicles like buses and trucks have a secondary brake to improve the life of the conventional friction brakes.
AFAIK there are 2 types-
1. Hydraulic - here oil (or hydraulic fluid) is pumped into a chamber with vanes. This causes additional drag slowing down the driveshaft. These are silent.
2. Electric / Magnetic - Electromagnetic induction is used to slowdown the drive / axle by supplying it with an electric current. The current can be supplied from the vehicle batteries. Basically current is used to generate a magnetic field in the stator attached to the chassis which slows down the rotor fixed to the drive / axle. There is no contact between stator and the rotor and no fluid is used.

Engine valve brake - Here, the one exhaust valve is kept open in the compression and the expansion stroke to slowdown the engine. A short video I found can explain better.

https://www.youtube.com/watch?v=CfDL5SNSKwM

[honeybee]

Originally Posted by blackwasp

Retarder - heavy vehicles like buses and trucks have a secondary brake to improve the life of the conventional friction brakes.
AFAIK there are 2 types-
1. Hydraulic - here oil (or hydraulic fluid) is pumped into a chamber with vanes. This causes additional drag slowing down the driveshaft. These are silent.
2. Electric / Magnetic - Electromagnetic induction is used to slowdown the drive / axle by supplying it with an electric current...

Engine valve brake - Here, the one exhaust valve is kept open in the compression and the expansion stroke to slowdown the engine...

So these basically work by increasing the engine braking?

The first two seem to be independent of the actual internal combustion process and more to do with the drive shaft rotations. By reducing these rotations, the drive power supplied to the wheels is greatly reduced which should help lose speeds quickly.

If that is correct, what happens when the retarder swings into action while the engine is still rotating at higher RPMs? Or does this all work only with the foot off the accelerator?

Regarding the exhaust valve, does it mean that the exhaust gasses are retained or fed back into the combustion chambers to retard the combustion process itself? If so, any ill effects on the engine?

[silversteed]

Originally Posted by honeybee

If that is correct, what happens when the retarder swings into action while the engine is still rotating at higher RPMs? Or does this all work only with the foot off the accelerator?

Think of the retarder as an additional brake lever/pedal. Hydrodynamic or Electromagnetic, the retarder works independently of the engine RPM. Newer systems provide the status to the vehicle's EMS so that the fuelling etc can be adjusted accordingly.

Originally Posted by honeybee

Regarding the exhaust valve, does it mean that the exhaust gasses are retained or fed back into the combustion chambers to retard the combustion process itself? If so, any ill effects on the engine?

AFAIK, the exhaust gases won't be fed back into the engine unless there's an EGR system. The system in effect causes a slight loss of compression and provides braking force.