MoTeC M1 Software Tutorial: Camshaft Control
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Camshaft Control
16.45
| 00:00 | Many modern performance engines are now equipped with continuously variable cam control, allowing the cam position to be adjusted throughout the rev and load range for optimum performance. |
| 00:11 | Continuously variable cam control should not be confused with older, switched positions cams, where the cam only had two positions - Either fully retarded or fully advanced such as on twenty valve 4AGEs or early Mitsubishi 4G92 MIVEC engines. |
| 00:30 | The M1 ECU has the ability to control the position of up to four camshafts across two banks of cylinders and in this module we will look at how the ECU deals with the configuration and control. |
| 00:43 | If you are familiar with MoTeC’s hundred series ECUs, the cam control aspect was dealt with as a separate system to the Ref/Sync setup. |
| 00:52 | This meant that provided the engine had a synchronisation sensor, it would still run, even without the cam position sensors configured. |
| 01:01 | This also meant that extra work was required to correctly configure and calibrate the camshaft position sensors. |
| 01:08 | In the M1, the cam control configuration is written as part of the engine speed reference or Ref/Sync mode. |
| 01:16 | The mode tells the ECU how many variable camshafts it will be operating as well as what data to expect from the cam position sensors and where in the engine cycle this data should occur. |
| 01:28 | The M1 can also synchronise engine position off any of the available camshaft position sensors which means the M1 can achieve synchronisation and cycle lock faster during initial startup. |
| 01:42 | Since the cam control information is now part of the engine speed reference mode, the M1 can only control variable cam control in engines that have a mode written for them. |
| 01:53 | A range of popular engines are already supported and the list of supported engines is growing daily but it is worth consulting with MoTeC or your MoTeC dealer to make sure your particular engine is supported if you wish to use cam control. |
| 02:08 | One aspect of the M1 terminology that is important to understand is the way the inputs are named is very particular. |
| 02:16 | For example the M1 has inputs for camshaft position as well as an engine synchronisation input. |
| 02:23 | In the older hundred series ECUs, often the synchronisation position sensor also the cam position data. |
| 02:33 | In the M1 this isn’t always going to be the case and for example if we were setting up a quad cam engine that had four camshaft position sensors, the M1 will be expecting to see these inputs defined as camshaft position sensors, so in this case the synchronisation input is not used. |
| 02:52 | Configuring an input as engine synchronisation in this case would actually result in a configuration conflict in the M1 . |
| 03:01 | This won’t be the case for some engines such as Honda’s K series however where the engine has a single variable inlet camshaft with a position sensor, but it also includes an engine synchronisation sensor on the exhaust camshaft. |
| 03:15 | The easiest way to think of it is, if the trigger teeth for a sensor move with the variable cam then it is a “cam position” sensor, if it doesn't move with the cam then it’s synchronisation. |
| 03:28 | Where a separate synchronisation sensor exists, it should be connected and configured as the Engine Synchronisation input. |
| 03:37 | Configuring an engine with variable cam control actually starts in the ‘Ref/Sync’ worksheet in the ‘Initial Setup’ work book which we have already looked at, and the first step is to choose the engine speed reference mode relevant to your particular engine. |
| 03:52 | Also it must be decided if the Engine Speed Reference Mode uses the Engine Synchronisation input or just Cam Shaft Position sensor inputs. |
| 04:03 | In this module we will look at the remainder of the setup which can be found in the ‘Initial Setup 2’ workbook. |
| 04:09 | Worksheets exist for both inlet and exhaust cam control but for simplicity we will look at configuring just the inlet cam control. |
| 04:17 | The same techniques can be applied to configuring the exhaust cam control if necessary. |
| 04:24 | Let’s start with the configuration for the inlet cam control on bank 1. |
| 04:28 | We are going to deal with this list of parameters a little out of order and we will split the list up into three separate areas - Camshaft position setup, actuator output setup, and the PID setup. |
| 04:42 | First we will look at configuring the camshaft position input. |
| 04:47 | We can begin by configuring a resource for the ‘Inlet Camshaft Bank 1 Position Resource’ to define which input pin the sensor has been wired to. |
| 04:57 | Each camshaft position sensor will also require the parameters for ‘Pullup Control’, ‘Active Edge’, ‘Hysteresis’ and ‘Debounce’ parameters to be configured. |
| 05:08 | These parameters mirror those we have already discussed in the Ref/Sync setup module so if you need further clarification, check that section. |
| 05:17 | We have two more parameters under the camshaft position setup that we won’t be able to configure until the engine is actually running, but we will discuss them now. |
| 05:27 | The first of these is the ‘Position Offset’ parameter which defines where the camshaft position is zeroed, this can basically be thought of as the cams own reference offset or CRIP in old terms. |
| 05:40 | This offset is already defined fairly thoroughly inside the engine speed reference mode, so the M1 already knows where to expect the camshaft position sensor inputs already. |
| 05:51 | With production tolerances between engines, or the minor differences that may arise from the head or block being machined in an engine, the cam position on each engine will vary slightly. |
| 06:03 | The Position Offset parameter is included to account for these small discrepancies and should only need to be a relatively small number. |
| 06:13 | To adjust the ‘Position Offset’, disconnect the camshaft actuator and run the engine. |
| 06:18 | You can then adjust the offset until the measured camshaft position reads zero. |
| 06:23 | You should find that the offset ends up very close to zero, and it should certainly be within the range of plus or minus five to ten degrees. |
| 06:33 | As a recommendation there should be about one degree of clearance from the cam mechanism mechanical stop so that the offset should really be set so that an inlet cam should be minus one with the cam solenoid unplugged. |
| 06:46 | This means when we ask for zero degrees, there will be a physical gap to the mechanical stop. |
| 06:52 | A closed loop system will try to press the cam actuator against the mechanical stop if this is what is requested, this can result in a slight lag in response the next time the cam aim table asks for, say, ten degrees. |
| 07:06 | We also have a parameter called ‘Position Smooth’ which is a kind of filtering that can be applied to the camshaft position input. |
| 07:14 | This can be used to reduce the noisy nature of some camshaft position signals, particularly on engines with strong valve train harmonics, aggressive cam profiles or production tolerances in trigger tooth profiles. |
| 07:28 | This can result in a ‘spiky’ camshaft position input that can make it difficult for the feedback control to perform its job well. |
| 07:36 | In these cases a small amount of smoothing may be added in to reduce this noise. |
| 07:42 | Remember that filtering by its nature will slow the response of the signal and this can also affect the control system. |
| 07:49 | In general we want to use as little filtering as we can. |
| 07:54 | Once we have configured the position sensor, we also need to configure an output for the camshaft actuator. |
| 08:01 | The actuator is the part of the cam control system responsible for physically advancing and retarding the cam position. |
| 08:09 | The ECU uses closed loop control to change the duty cycle signal to the actuator solenoid, this changes the path of engine oil to advance or retard the cam. |
| 08:19 | Generally each camshaft will have a single actuator which will be a two pin solenoid supplied with twelve volts and ground. |
| 08:27 | Our first step in setting up the actuator is to assign an output resource from the drop down menu as usual. |
| 08:34 | If we move back up the list a little, we have ‘Actuator Drive’ which defines if the output will switch to ground or a positive voltage. |
| 08:42 | Most cam actuators will permanently be supplied with 12v from the engine wiring loom and the connection to the ECU will be the ground side (low side drive). |
| 08:53 | Some examples have the cam actuator wired permanently to chassis ground which means the ECU would have to supply the 12v in this situation which would be a high side drive. |
| 09:06 | ‘Actuator Reference Voltage’ is a setting used to maintain stable and consistent cam control as battery voltage varies. |
| 09:14 | As with any mechanical device, there is an inherent latency or lag in the operation of the cam control solenoid and this will vary with voltage. |
| 09:23 | This is very similar to the dead time in a fuel injector. |
| 09:27 | The M1 provides a background adjustment that normalises the output as voltage changes with the aim of maintaining consistent cam control. |
| 09:37 | The reference voltage should be set to the voltage at which the setting tests were performed - Normally fourteen volts with the engine running. |
| 09:45 | The Reference Voltage also works in conjunction with the ‘Voltage Filter’ parameter here at the bottom of the parameter list. |
| 09:52 | This filters changes in the battery voltage and can be used to reduce noise or spikes in the battery voltage signal that can affect the M1’s background compensation for actuator duty cycle. |
| 10:03 | In most instances this can be set to twenty five to fifty. |
| 10:08 | ‘Actuator Polarity’ defines whether increasing duty cycle will retard the cam position which is ‘Normal’, or advance the camshaft, which is ‘Inverting’. |
| 10:19 | The ‘Normal’ setting is typical for an exhaust camshaft, while ‘Inverting’ is typical for an inlet camshaft. |
| 10:26 | This is because inlet and exhaust cams generally operate in opposing directions of travel. |
| 10:33 | ‘Actuator Minimum’ and ‘Actuator Maximum’ define the useful duty cycle range of the camshaft actuator. |
| 10:39 | as we have already discussed, control valves can have “dead bands” at the low and high end of the duty cycle range. |
| 10:47 | For example a valve may not have any reaction from zero through to about fifteen percent duty cycle and be fully open at eighty five percent duty cycle so 85-100% duty cycle nothing happens. |
| 11:02 | In this situation it is useful to configure the ECU to not use duty cycle values outside the range of 15-85%. |
| 11:11 | ‘Output Frequency’ defines the operating frequency (number of pulses per second) of the camshaft actuator. |
| 11:19 | The output frequency will affect the Actuator Max/Min settings so should be set once and not changed. |
| 11:27 | Now we are going to move up further and discuss the settings for the actual camshaft control. |
| 11:32 | The first of these is ‘Dead Band’, which defines a range of camshaft position that the ECU will accept as meeting our target, generally this will be about 0.2 -0.3 degrees. |
| 11:44 | For example if the inlet cam position aim is twenty degrees and the deadband is set to zero point two degrees, any value in the range nineteen point eight through to twenty point two degrees will be accepted and the error will be considered to be zero. |
| 12:00 | In this instance the control system will not attempt to make changes. |
| 12:05 | The dead band is used so that the control system is not trying to make too many, minute changes. |
| 12:11 | The dead band can be modified during tuning to see how it affects control, as long as control remains stable the smallest number possible should be used. |
| 12:23 | ‘Feed Forward’ is the actuator duty cycle that allows the cam to remain in one fixed position. |
| 12:29 | To move the cam, the duty cycle is either raised or lowered, depending on if it’s being advanced or retarded, from the Feed Forward Duty cycle. |
| 12:37 | Once it reaches its desired position the duty cycle goes back to the Feed Forward value to stop the cam moving . |
| 12:44 | Generally a value somewhere around fifty percent will tend to hold the cam position stable with no advance or retard movement. |
| 12:53 | Every engine is different and this parameter needs to be adjusted to provide stable control. |
| 12:59 | This can be tested with the engine running. |
| 13:02 | Simply start at zero percent Feed Forward with the P,I, and D parameters also set to zero, and use the “page up” key to start adding duty cycle. |
| 13:13 | Once you get slightly above the Feed Forward duty cycle needed, the cam position channel will start to move. |
| 13:20 | The cam will move quite quickly with only a couple of percent duty cycle over what is needed for Feed Forward. |
| 13:27 | Use the page up and page down buttons to try to hold the cam at any advance that is not against the mechanical stops - Say 10 degrees. |
| 13:35 | The duty cycle that roughly holds the cam in one position is the number needed for the Feed Forward. |
| 13:42 | This test procedure can be used as a systems check if you think there is a problem with the cam control actuator or wiring pin out. |
| 13:50 | It should be noted at this stage that in general nearly all variable cam motorsare designed to be “non-interference” Any race engine that has larger cams should be checked at the time of building to make sure there is no possibility of valves clashing with the pistons. |
| 14:06 | It is not the job of the cam control function to guard against an incorrect engine mechanical combination. |
| 14:12 | Generally larger camshafts will need the mechanical stops in the cam actuators modified, this is quite common. |
| 14:20 | Remember if there is a fault in one of the cam actuators or a wiring short nothing but a mechanical stop can save the engine. |
| 14:29 | Next we have the ‘Proportional’, ‘Integral’ and ‘Derivative’ gains which define how the M1 will control the cam actuator in response to an error between cam aim position and the actual cam position. |
| 14:42 | These parameters need to be configured in order for the closed loop control system to be able to provide accurate control of the cam position. |
| 14:50 | The P,I and D duty cycles are added or subtracted to the Feed Forward duty cycle to make the cam move. |
| 14:57 | The principles of PID tuning are beyond the scope of this course, however MoTeC or your MoTeC dealer should be able to provide suitable parameters for the more popular cam control systems. |
| 15:09 | We have now covered the configuration of a single continuously variable inlet camshaft. |
| 15:15 | If we have a V configuration engine, we can use the ‘Inlet Camshaft Bank 2’ parameters to configure the control of other inlet camshaft, and likewise we can use the ‘Cam Control Exhaust’ worksheet to configure a continuously variable exhaust camshaft. |
| 15:31 | Be aware that due to the ever present production tolerances the Feed Forward should be checked for each cam to make sure there are no differences bank to bank. |
| 15:41 | The Feed Forward for the left inlet cam may be slightly different to the right inlet cam, and each cam will work better if its mechanical differences are accounted for in the ECU setup. |
| 15:53 | While we have discussed the configuration, the actual calibration of the camshaft position is done from the ‘Camshaft’ worksheet in the ‘Tuning’ workbook. |
| 16:02 | This simply has a table for the exhaust and intake cam aim positions. |
| 16:08 | By default these are just a single value, however clicking on the table itself and then pressing ‘A’ to bring up the ‘Axis Setup’ menu will let us configure a two dimensional or three dimensional table with engine speed and manifold pressure as the available axis options. |
| 16:25 | The time graph on the bottom of the worksheet is a great place to track the performance of the cam control system and we can watch how the inlet and exhaust cam positions from each bank are tracking against the camshaft position target. |
| 16:38 | The time graph is a critical element in the configuration and optimisation the PID control parameters. |
