Sliding Cam Valve Lift System (if Equipped)

The Sliding Cam Valve Lift system (SCS) changes the camshaft lift profile of the intake and exhaust camshafts while the engine is running. The SCS has 4 intake camshaft profile actuators and 2 exhaust camshaft profile actuators. Each actuator consists of a actuator position sensor and two actuator solenoids, which control the guide pin activation. The guide pins are responsible for the axial movement of the Camshaft Lift Profile Sleeves on the Camshaft in response to electrical commands from the ECM. Each camshaft has 2 profile sleeves with different height cam lobes and each camshaft has a detent ball and spring under each sleeve that helps hold the profile sleeve into position. The SCS profile actuator solenoids push out an actuator guide pin into the shifting groove machined into the Camshaft Lift Profile Sleeve. When the guide pin engages the sleeve, it causes it to shift axially on the Camshaft causing unique sized cam lobes to be placed over the intake and exhaust valves and modify valve lift and duration. Once the Camshaft Lift Profile Sleeve has completed the shift, the guide pin is push back into the actuator by the profile sleeve, making contact with the magnet of the actuator solenoid. Modifying the valve lift during ever changing engine demand provides the following balance and benefits during the driving experience:

• Increased fuel economy
• Optimized engine power output
• Overall lower tailpipe emissions

The crankshaft position sensor and the Camshaft Position sensors are used to monitor the camshaft positions and provide input for the SCS system. 2 Intake and 2 Exhaust profile sleeve position sensors are used to monitor the Camshaft Lift Profile Sleeve positions axially on the Camshaft. The ECM uses the following information to calculate the desired camshaft lift:

• Barometric pressure sensor (BARO)
• Camshaft position sensors
• Crankshaft position sensor
• Engine load
• Engine speed
• Engine torque
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor

The Sliding Cam valve lift system has 3 unique sized cam lobes on each camshaft profile slider:

1. Power profile  - High lift - Full capacity, conventional lift and duration. When the driver needs the full capability of the engine then all 4 cylinders are active, all valves open to maximum lift.
2. Economizer profile  - Low lift - Reduced capacity (as little as 3 mm lift) changes the duration of the valve opening and closes the valve early. Under medium load conditions where the driver does not need the full capabilities of the engine power, like highway driving, the SCS system slides into low lift to start saving fuel. All 4 cylinders are still active with all intake valves now opening to a lower lift height.
3. Ultimate fuel economy  - AFM (Active Fuel Management) - Cylinder disable for increased fuel economy. For light load conditions, like highway cruising, when the driver does not need the full capability of the engine the SCS system slides into Ultimate Fuel Economy AFM mode and cylinders 2 & 3 are deactivated. The system first turns off #2 & 3 fuel injectors, then the exhaust valves and lastly the intake valves. This effectively traps a cylinder's worth of air with no fuel in the cylinder. This trapped air becomes an air spring helping the piston return in what would be the expansion stroke. Cylinders 1 & 4 are still active with their intake valves now opening to a lower lift height. The intake cam profile for the firing cylinders is the same low lift profile of the Economizer profile. The engine still produces the same power from the 2 cylinders but is now operating at half of the Economizer profile power.

Operation 

The sliding cam system profile actuators have the ability to individually push out each of the actuator's 2 shifting pins. The SCS actuators are single direction actuators (OUT only) and require a physical response to push back or retract the pins back into the actuator. Each of the actuators have 2 shifting pins with 2 completely independent shifting coils. Based on a PWM signal the shifting pins push out and engage the "shifting" groove of the sliding cam profile sleeve to the position requested. The first pin will be pushed out causing the camshaft profile sleeve to shift from High lift (Power profile) to Low lift (Economizer profile). The shifting groove is now aligned under the second pin and the position sensor confirms that the sleeve is in the requested position. The actuator profile position sensors operate the same as Cam sensors and provide a high signal when there is metal below them and a low signal when there is air below them. Each position, High lift, Low lift, and active fuel management (AFM) have a unique square wave profile allowing the position sensors to identify which mode it is in. When requested the second actuator pin will be pushed out to cause the profile sleeve to shift from Low lift to AFM mode. When the ECM requests moving back to a higher cam profile mode then the actuator on the neighboring cylinder is used to move the sliding cam profile sleeve in the opposite direction because the shift groove is pointing in the opposite direction. For the intake camshaft there are 2 profile sleeves covering 2 cylinders each (1&2 - 3&4). On the exhaust camshaft there are also 2 profile sleeves however they are smaller and only on cylinders 2 & 3.

Sliding Cam System Components 

Fig 1: Identifying Sliding Cam System Components

Courtesy of GENERAL MOTORS COMPANY