Anyone who had the opportunity to ride in, drive, or worse yet, repair one of the Cadillac 4-6-8 engines from years past, will no doubt be forgiven a certain skepticism when it comes to the current spate of cylinder deactivation technologies.
However, turbochargers were once thought to be short-lived, and automatic transmissions were once considered the sole preserve of the luxury set and not crisp-shifting enough to handle performance driving aspirations–please tell this to Porsche AG–so things can change.
With the seemingly contradictory consumer desire for more horsepower as well as better fuel economy, the new age of cylinder deactivation has been ushered in.
There are a number of systems out there, probably the most familiar being that currently used in the Chrysler Hemi 5.7 litre engine.
The Multi-Displacement System (MDS) shuts down four of the eight cylinders (two inboard, two outboard). The system is relatively simple, but utilizes some sophisticated controls. Powered by the E38 32-bit engine controller, algorithms that control the systems and the use of Electronic Throttle Control–Chrysler’s first use of the technology in a rear-drive vehicle–allow the transition from eight cylinders to four in 40 milliseconds (0.040 seconds).
Since the 90-degree V8 engine uses a pushrod design, the system operates by deactivating eight valve lifters on four cylinders. The roller lifters have an inner and outer sleeve that locks into position under normal use, and can be unlocked to allow the roller to freewheel on the cam when that cylinder is deactivated. This keeps the valves in four of the cylinders closed, and there is no combustion. In addition to stopping combustion, no energy is lost by pumping air through these cylinders.
The system uses electro-hydraulic technology adapted from transmission controls by Eaton Corp. to route oil to activate the system.
Customers will experience estimated fuel economy gains of up to 20% under various driving conditions, and a projected 10% aggregate improvement.
General Motors also has its version, called Displacement On Demand (DOD), which operates in a similar fashion.
This system differs from the aforementioned Cadillac V8 engine in 1981 in that the detachment of the cam profile and cam input from the valve on the Cadillac occurred at the fulcrum of the rocker arm. Also, the mechanism on the Cadillac was a rotational solenoid.
On the new systems, sensors also tell the PCM what the engine is doing at any point in its cycle; for example, which cylinder has fired, and where the valvetrain is located at that particular point. The module interprets the information to control complex functions such as fuel injection, electronic spark control, and electronic throttle control. The PCM also monitors driver commands, several engine sensors, and mathematical models to determine the right time in the engine cycle to initiate the process. Aided by DOD algorithms, it then controls spark advance, fuel injectors, electronic throttle, and four valvetrain control solenoids in precise coordination, to achieve a seamless transition between V4 and V8 operation. The sequential reactivation of cylinders to increase engine output happens so quickly that there is an immediate increase in engine output.
In addition, DOD leverages an existing oil pump system to provide hydraulic pressure to control the system. The mechanical actuators are special hydraulic lifters, each with a spring-loaded locking pin. In normal operation, when the camshaft rotates against the hydraulic lifter, it opens and closes either an intake or exhaust valve.
The special lifter, developed by Eaton Corp., is designed so that one section can collapse, or telescope, into the other section. The two sections can be either coupled or uncoupled by means of the locking pin. When cylinder deactivation is initiated, hydraulic pressure is used to dislodge the locking pin and collapse the lifter, thus closing the valve. In reactivation mode, the removal of hydraulic pressure causes the locking pin to return to its latched position to restore the lifter’s normal function.
The activated state of the special lifters is the default mode. In V4 mode, every other cylinder in the firing order is deactivated. Thus, in a V8 engine, the process would affect the outer two cylinders on one bank and the inner two on the opposite bank. The cylinder deactivation-reactivation operation is accomplished in a fraction of a second, making the transition seamless and transparent to the driver.
Of course, shutting down cylinders in a way that makes it seamless to the driver involves more than quick solenoids; a V4 doesn’t sound or feel the same as a V8 and when you take a V6 and make it an inline three-cylinder, as Honda has done, noise, vibration, and harshness (NVH) concerns must be addressed.
Honda’s Variable Cylinder Management (VCM) technology is found in the 3.5L V6-equipped Odyssey EX and Touring models. The addition of VCM to the variable valve timing engine disconnects the intake and exhaust valves in the three cylinders in the rear cylinder bank of the transversely mounted engine.
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 operates the accelerator pedal, the system employs a new three-way solenoid spool valve to control the oil pressure for switching.
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.
Of course, an inline three-cylinder engine is not as inherently balanced as a V6, so the system employs Active Noise Control and an Active Control Engine Mount.
When three of the V6’s cylinders are idled, a computer sends a signal to an active control engine mount that counteracts any vibration. And to make the transition entirely seamless, an audio speaker creates an opposite phase sound, providing a noise-cancelling effect and leaving the driver unaware of the changes underhood.
That, of course, was only a dream for the old Cadillac system. But one can only wonder, with the number of systems which must operate, and stop operating, to make the new reality of cylinder deactivation seamless, whether it might be a nightmare in store for those called in when things go wrong.
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