Variable Cam Control Tuning: Inside a Variable Cam Actuator
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Inside a Variable Cam Actuator
03.24
| 00:00 | - We've already discussed the fact that the continuously variable cam control system relies on engine oil pressure to advance or retard the cam and while it's not strictly necessary to understand how this system works from a mechanical perspective in order to tune it, I believe it's still very helpful knowledge to have, giving you a more complete understanding of the system. |
| 00:20 | While there are a variety of subtle differences in the various cam control systems from different manufacturers most work on a similar principle whereby the cam wheel or cam pulley is essentially 2 piece. |
| 00:33 | The inner section is attached and keyed onto the camshaft itself and this is free to move within our outer section of the cam wheel which is driven by the cam belt or cam chain. |
| 00:44 | Inside the cam wheel, you'll typically find a series of lobes on the inner section of the cam wheel which can move back or forth within chambers that are machined into the outer section. |
| 00:55 | The chambers are wider than the lobes and this is what allows the cam to be advanced or retarded with respect to the outer section of the cam gear. |
| 01:03 | The amount of cam movement that can be achieved is mechanically limited by the relationship between the width of the chambers and the lobes. |
| 01:11 | And it's pretty typical for these systems to allow 40-50° of movement which is a significant amount. |
| 01:18 | As already discussed, this can prove problematic with larger cam profiles where the factory range of movement may allow interference between the components at extremes. |
| 01:29 | An advanced technique here is to actually disassemble the cam wheel and add mechanical stops internally to artificially limit the cam travel. |
| 01:38 | This is something that needs to be completed during the assembly of the engine and may not be possible on every cam control engine type. |
| 01:45 | Generally you'd be able to receive advice from the cam manufacturer as to whether this technique is required or even possible for the particular engine and cam profile that you're considering. |
| 01:58 | We've talked about the inner workings of the cam wheel but of course we need a way of actually moving the cam and this is achieved with a supply of high pressure oil. |
| 02:07 | A cam control engine will have a reasonably complex path of oil galleries through the camshaft which leads to the advance and retard chambers inside the cam wheel. |
| 02:17 | The flow of oil into these galleries is then controlled by a solenoid that the ECU switches at high frequency. |
| 02:24 | In one position the solenoid will supply oil to the retard chamber in the cam wheel and simultaneously allow oil that's already in the advance chamber to drain out. |
| 02:33 | When switched to the opposite position, the flow is reversed and the advance chamber is pressurised while the retard chamber is drained. |
| 02:42 | At this point the system sounds very much like a switch cam control system that's only capable of being in the full advance or full retard position. |
| 02:50 | However with the control strategy already discussed, the ECU can pulse width modulate the solenoid to move the cam to a specific target and then hold it there while the engine's running. |
| 03:02 | Since a continuously variable cam control system relies on oil pressure to move the cam, hopefully it should be pretty apparent that the effectiveness of the system will depend to an extent on the oil being used and the temperature of the oil. |
| 03:16 | We'll be taking a closer look at oil considerations in an upcoming module. |
