Vehicle braking control

A method of operating an engine for a vehicle having at least a first cylinder, the method comprising:

• operating the first cylinder to provide at least one of compression braking and expansion braking by holding one of an intake valve and an exhaust valve of the first cylinder closed while opening, closing, and opening the other of the intake valve and the exhaust valve during a cycle of the first cylinder and during a first vacuum level of an intake manifold upstream of the first cylinder;
• and
• operating the first cylinder to provide at least one of compression braking and expansion braking by operating both the intake valve and the exhaust valve of the first cylinder during a cycle of the first cylinder to allow at least some air to flow through the first cylinder during a second vacuum level of the intake manifold.

A method of operating an engine having a plurality of cylinders, comprising:

• during an increased vacuum level request, increasing a vacuum level of an intake manifold by increasing a number of cylinders providing at least one of compression braking and expansion braking by operating at least one intake valve and at least one exhaust valve to allow at least some air to flow through the first cylinder in response to reduced vacuum;
• and
• during a decreased vacuum level request, decreasing the vacuum level and decreasing air flow through the engine by increasing a number of cylinders providing at least one of compression braking and expansion braking by holding closed one of an intake valve and an exhaust valve while opening, closing, and opening the other of the intake valve and the exhaust valve in response to increased vacuum.