VCM = Variable Cylinder Management [flexible Zylinderabschaltung]

Einen Vorläufer des Systems zur flexiblen Zylinderabschaltung (VCM) führte Honda beim Civic Hybrid im Jahre 2003 in ein Serien-Modell ein.

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Civci Hybrid 2003:

VTEC Controlled Cylinder Idling System
A major aspect of regenerative braking is to reclaim as much energy as possible during deceleration. Since the electric motor, which also acts as an electric generator, is attached directly to the crankshaft of the engine, the engine needs to provide as little resistance as possible during deceleration to allow the generator to produce high levels of electricity and charge the batteries. In a traditional engine, the pumping action of the cylinders will actually provide a moderate amount of resistance, or "engine braking," during deceleration (except in neutral or when the clutch is engaged in a manual transmission). The Cylinder Idling System effectively reduces engine drag by closing the intake and exhaust valves on up to three of the four cylinders and allowing the pistons to move more freely within the cylinders, thus allowing the generator to provide maximum resistance (instead of the engine) and, consequently, produce more electricity.

The system uses Honda's patented VTEC (Variable Valve Timing and Lift Electronic Control) technology to close the intake and exhaust valves on up to 3 of the 4 cylinders at rpms as low as 1000 to reduce the pumping action in the engine. Whereas traditional applications of VTEC engage an alternative cam profile at high rpm and high oil pressure for improved performance, this VTEC system engages at low rpm and low oil pressure to close the valves for a different kind of improved performance - reduced engine resistance during deceleration.

Accord Hybrid 2005:

i-VTEC Engine with Variable Cylinder Management

One major improvement new to this engine is the implementation of the advanced version of Honda's variable valve-timing and lift electronic control (VTEC) system or i-VTEC. i-VTEC adds a level of "intelligence" to the legendary VTEC system by adding a Variable Cylinder Management (VCM) system that switches between six- and three-cylinder combustion. When high output is required, such as during startup and acceleration or when climbing hills, the engine operates on all six cylinders to deliver superior performance. During cruising and at low engine loads, the system idles the rear bank of three cylinders for improved fuel efficiency and reduced emissions. Further, the idled cylinders remain sealed, alleviating the pumping losses associated with intake and exhaust and giving fuel economy a further boost.

Variable Cylinder Management helps maximize fuel efficiency by making the Accord Hybrid's 3.0L V-6 engine effectively run on only three cylinders when the power needs are minimized, yet it can still seamlessly provide the full power of all six cylinders during hard acceleration or other high load situations. When full power is needed, i-VTEC instantly opens the valves and sends fuel to the three previously idled cylinders. When combined with the IMA motor, output peaks at 255 horsepower.

The Accord Hybrid's VCM system is similar to the VTEC-controlled Cylinder Idling System used on Civic Hybrid, but is more sophisticated. Where the Civic Hybrid's cylinder idling deactivates three of the engine's four cylinders during deceleration only to help improve regenerative braking efficiency, the Accord's VCM system, is able to deactivate the engine's rear bank of three cylinders during a variety of driving situations, including steady-speed cruising, light acceleration and braking. Thus, improving fuel efficiency, reducing emissions and making regenerative braking more efficient.

VCM Operation

The Accord Hybrid's i-VTEC V-6 engine features a Variable Cylinder Management (VCM) system that improves fuel economy by idling three of the Odyssey's six cylinders during cruising and deceleration. VCM deactivates the rear bank of cylinders by using the VTEC (Variable Valve-Timing and Lift Electronic Control) system to close the intake and exhaust valves while cutting fuel at the same time.

The rear bank of cylinders was chosen for deactivation because the front bank is best positioned for cooling performance. Idling the rear bank also helps to maintain the temperature of the catalytic converter beneath the cylinder heads, helping to maintain optimum emissions performance. The Accord Hybrid's spark plugs continue to fire even when the cylinders are deactivated. This minimizes plug temperature loss and prevents fouling induced from incomplete combustion during cylinder re-activation. Further, sparking in air alone results in higher voltages than in a fuel-air mixture because of the higher insulation resistance. Therefore, iridium-tipped spark plugs are used for their high resistance to wear at high voltages.

i-VTEC VCM System Designed for Rapid Switching at Low Engine Speeds

In a conventional VTEC system, hydraulic pressure pushes a single synchronizing piston, which is in turn pressed back by a return spring. The VTEC system locks the valvetrain's rocker arms to allow additional valves to open and increase engine breathing. Such systems require relatively high engine speeds since hydraulic pressure is used to push the spring. VCM, however, demands switching at low rpm. This is achieved by creating a hydraulic circuit with two systems, each capable of providing the hydraulic pressure required to push the synchronizing piston in the required direction. This design thereby allows switching from six cylinders to three cylinders in low-speed ranges. To achieve responsive switching to six cylinders when the driver quickly opens the throttle under hard acceleration or driving up hill, the system employs a new three-way solenoid spool valve to control the oil pressure for switching. These enhancements result in highly responsive VCM switching regardless of engine speed.

VCM monitors throttle position, vehicle speed, engine speed, automatic-transmission gear selection, and other factors to determine if the vehicle is cruising or decelerating. During cruising and deceleration, VCM deactivates the three cylinders on the rear bank of the engine. To further enhance control, the system also simultaneously determines whether engine oil temperature is suitable for VCM switching and whether catalytic converter temperature will remain in the proper range. While idling the cylinders, the system controls ignition timing, and turns the torque converter lock-up on and off, thereby suppressing torque-induced jolting during the switch from six to three cylinder operation. The result is a smooth, seamless switch between three and six cylinder modes that is nearly unnoticeable to the driver.

For cylinder deactivation operation, the synchronizing piston moves to isolate the valve-lift rocker arms from the deactivated cylinders' rocker arms. The deactivated cylinder rocker arms are operated by zero-lift cams that deactivate the cylinders by closing the intake and exhaust valves.

Active Control Engine Mount System (ACM)

Due to the inherent increase in engine vibration when VCM has deactivated the rear bank of cylinders, an Active Control Engine Mount system (ACM) is used to minimize the effects of engine vibration. The system uses sensors that alert the Electronic Control Unit (ECU) to direct ACM actuators to move in synch with the vibration, thereby eliminating the vibration being transmitted to the passenger compartment. Additionally, an Active Noise Control system (ANC) works in cooperation with the ACM. An ANC controller with front and rear microphones in the passenger cabin detects the booming noise associated with cylinder deactivation and instructs the audio system's speakers to emit an opposite sound wave. (See the Interior section for more information on ANC.)


Variables Zylinder-Management im Accord 2007