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Boost Control: Internal vs External Wastegate Actuators

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Internal vs External Wastegate Actuators


00:00 - Before we move on and look at the options available for numerically connecting the wastegate actuator to a boost control solenoid, we need to discuss the different configurations of wastegate actuator.
00:13 What I'm talking about here, is wastegate actuators with a single boost pressure port, and those with dual ports.
00:20 Loosely these can be usually broken down into internal wastegate actuators which normally have single ports, and external wastegate actuators, which normally have dual ports.
00:32 While this is typical, it's not a hard and fast rule as occasionally you may come across an internal wastegate actuator with dual ports or an external wastegate with a single port.
00:45 Regardless of the type actuator, or the number of ports, if we understand what's going on inside the actuator, it's easy to decide how it will function and more importantly, how to connect it to a boost control system.
01:01 In a single-port port actuator, there's a single sealed chamber, as you can see here.
01:08 This is common on an OEM wastegate actuator and usually the actuator will be sealed and nonadjustable.
01:16 In this type of actuator, the sealed chamber includes a fixable diaphragm and this is connected to the wastegate valve.
01:24 On the other side of the diaphragm is the spring which holds the wastegate closed.
01:30 Occasionally in some applications, the style of actuator will actually have two ports, just to confuse matters.
01:38 But in this case both ports are connected to the same side of the sealed chamber, and hence they achieve the same thing.
01:45 With this time of wastegate actuator, providing boost pressure to the port on the wastegate will pressurise the chamber, and hence open the wastegate.
01:55 Increasing boost pressure requires that the pressure signal to the chamber is reduced either electronically or pneumatically.
02:04 In a dual-port wastegate, we have two chambers, as you can see here.
02:10 In this type of actuator, the springs usually house on the top of the wastegate, which is removable to facilitate easy and quick changes of spring rate.
02:20 The port on the other side of the actuator closest to the valve, should be connected to boost pressure and when the lower chamber is pressurised, the pressure will work against the spring and lift the valve off it's seat.
02:35 With this type of wastegate, there are two techniques we can use to increase boost pressure, we can either reduce the pressure reaching the bottom of the wastegate, the same way we did with the single port actuator, or we can supply boost pressure to the top port of the waste gate.
02:53 The first technique is more common when using an pneumatic control valve, and the second technique is more common when using electronic control.
03:03 We'll look at these techniques in detail shortly, so don't worry too much just now.

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