Variable Cam Control Tuning: Oil Considerations
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Oil Considerations
04.04
| 00:00 | - As we've learned so far, cam control systems are actuated by engine oil pressure so it shouldn't be too much of a stretch to understand that the oil you run in your engine can have a large impact on the operation of the cam control system. |
| 00:13 | This is usually less of a concern for switched cam control and VTEC style systems but it's a very real problem for continuously variable cam control systems. |
| 00:24 | Aside from the quality and cleanliness of your oil, an obvious consideration here would be the oil weight or viscosity chosen but even with a specific oil you'll find that the oil viscosity changes with oil temperature. |
| 00:38 | We can see the effect of this if we monitor oil pressure at a static engine RPM as the oil heats up. |
| 00:44 | We'll see that at low temperature the oil pressure is highest and as the temperature increases, the oil pressure drops. |
| 00:51 | This creates some control problems with any systems that relies on the oil or more specifically oil pressure. |
| 00:58 | Essentially the requirements of the control strategy are going to vary as the temperature and oil pressure fluctuate. |
| 01:05 | This can be tricky and often impossible to actually manage without some impact on the accuracy of the system. |
| 01:11 | Put simply, the settings for the PID control algorithm which we'll cover later in the course, will need to vary with respect to oil viscosity and hence oil temperature. |
| 01:21 | Settings that work well at normal operating temperature where the oil might be sitting in the range of 90-110°C are unlikely to give crisp or accurate control during cold starting, particularly if you live in a region which sees very cold winter temperatures. |
| 01:37 | The issue here is that particularly in aftermarket standalone ECUs that incorporate a single VE or fuel table and ignition table, the assumption is that the cam timing will always be hitting our desired target. |
| 01:50 | If this assumption doesn't hold true and the cam timing isn't on target, this will affect the engine's volumetric efficiency and in turn this changes the mass of air in the cylinders. |
| 01:59 | All the time though, the ECU is providing fuel to suit the amount of air it expects to be in the cylinder which is no longer accurate. |
| 02:08 | The result can be a severely rich or lean mixture and this can often be felt as a hesitation or erratic drivability. |
| 02:15 | In some instances, if the engine is operated at high RPM and high load, it could also potentially be dangerous. |
| 02:23 | We can also see a similar situation if we decide to run a different oil viscosity compared to what is recommended by the manufacturer. |
| 02:30 | It might sound strange to purposefully go against the manufacturer's recommendations but this isn't uncommon in a motorsport application. |
| 02:39 | Take for instance our Toyota FA20 development engine which runs a 0W20 oil in stock form. |
| 02:47 | On the racetrack at elevated temperatures this oil results in an oil pressure that's considered dangerously low and it's common to move to a thicker oil or heavier viscosity oil which gains oil pressure. |
| 02:59 | In our case, we've moved to a 10W40 oil to support the additional power being produced thanks to a turbo conversion where we're now making around twice the stock power. |
| 03:09 | A change this dramatic in the oil specification however does require the PID control settings to be adjusted in order to retain the crisp and accurate control that we need. |
| 03:20 | The bigger problem however can be at cold start where the ECU may not offer the ability to manipulate the PID settings with respect to temperature or regardless of what you do with the settings you may simply not be able to get satisfactory response. |
| 03:36 | In these instances it can be best to disable the cam control system until sufficient coolant or oil temperature has been achieved in order to get the cam control working properly. |
| 03:47 | This of course guarantees that the fuel and ignition maps that have now been optimised for an active cam control system will certainly be wrong however there are ways to work around this, as we'll soon see as we move futher through the course. |
