250 otherwise the hybrid powertrain will operate in the engine only mode at step 260 the powertrain regenerating brake control flowchart is shown in fig1 a the ecu 60 a reads a deceleration command input at step 310 and calculates the deceleration torque requirement based on vehicle speed and other operating parameters engine brake torque and the motor brake torque at step 320 if the required deceleration torque is greater than the motor regenerative brake torque which is determined at step 330 then engine braking will be activated in combination with the motor regenerating brake as shown at step 340 otherwise the vehicle will operate in the motor regenerating brake only mode at step 370 during the engine braking mode the engine brake noise will be checked in order to comply with local noise regulations as indicated by step 350 if the braking noise level is not acceptable the engine valve timing can be varied to reduce the brake noise as shown in step 360 0046 fig1 b shows a control strategy related to catalyst temperature for reducing engine exhaust emissions at step 400 the operating parameters of the diesel engine are read thereafter step 430 compares the exhaust gas temperature with the temperature required for effective catalyst operation if the exhaust gas temperature is lower than the required temperature the exhaust valve timing will be adjusted through variable valve actuation vva device to increase the temperature as indicated in step 410 step 440 determines the hydrocarbon concentration of the exhaust gas since a proper hydrocarbon concentration is required for effective nox adsorption and lean nox catalyst operations if the hydrocarbon concentration is lower than specified post injection or auxiliary exhaust manifold injection is required to add hydrocarbons into the exhaust gas stream in step 420 the.