GB2256458A - Control of i.c.engine supercharging. - Google Patents

Abstract

A source 1 of compressed air feeds two branches 2 and 3 leading to a wastegate actuator 14. Each branch comprises a boost control solenoid 4, 6 and on/off valve 5, 8 all under the electrical control of an ECU 15 via an interface 16. The branch 3 additionally has a one-way valve 7 and by-pass 9 containing a throttle 10 and a reservoir 11 which delay pressure build-up at the actuator 14 when the branch is operative. <IMAGE>

Description

INTERNAL COMBUSTION ENGINES The present invention relates to pressure charging apparatus for internal combustion engines.

The pressure charging apparatus may be a turbocharger or a supercharger in which, typically, in one known arrangement, engine boost level is controlled by a pneumatically controlled wastegate mechanism. The engine boost level is defined as the pressure level, relative to atmospheric, to which the turbocharger or supercharger compresses the air charge in the inlet manifold. The wastegate position, which controls the boost level is in turn controlled by a controlling pneumatic pressure which is regulated by a boost control solenoid. The boost control solenoid, which is fitted between the wastegate actuator mechanism and a pressure source (or reservoir), is actuated by an electrical control signal. This may be in the form of a voltage, frequency or duty cycle.The boost control solenoid is of a type where the full supply pressure is diverted to the wastegate actuator to open it fully (causing low engine boost) when a 'low' signal is supplied to the solenoid. The full supply pressure is diverted to vent away and no pressure reaches the wastegate actuator (causing high engine boost), when a 'high' signal is supplied to the solenoid. The solenoid operation is infinitely variable between these two extremes.

The signal to the boost control solenoid is usually supplied from an Electrical Control Unit (ECU), which may use engine speed, boost pressure and engine load amongst the incoming parameters. This enables the boost pressure to be controlled as desired via the action of the boost control solenoid. The ECU is pre-programmed to provide the desired boost levels dependent upon the incoming parameters. Additional safeguards may be incorporated into the inputs to the ECU, such that a low signal is sent to the boost control solenoid under conditions of engine stress (vibration or combustion detonation as examples) or for reasons of vehicle safety inhibits (cruise control operation, vehicle braking and gearchange operation are examples).

The existing arrangement is such that when a change is made to the electrical signal to the boost control solenoid, there is a delay before the wastegate actuator assumes the new position. This delay is dependent upon the control dynamics of the system such as the length of pipes and volume of the wastegate actuator and is generally engineered to be small. Under conditions of a changing signal to the boost control solenoid, there may also be a tracking error present that is to say the difference between the required and actual signal levels.

This may occur under conditions of engine acceleration.

The existing arrangement does not permit the control dynamics to be altered in response either to the nature of the inputs to the ECU or to the state of the output from the ECU to the boost control solenoid.

According to the present invention there is provided pressure charging apparatus for internal combustion engines comprising means for supplying air under pressure to the engine inlet, a wastegate, wastegate actuator for closing and opening the wastegate in order to alter the pressure in the engine inlet, means for pneumatically connecting the means for supplying air to the wastegate actuator, said means for connecting comprising two branches comprising respective boost control means and valve means, one of the branches comprising means for delaying the transmission of pressure therethrough and electrical control means for controlling the boost control and valve means whereby to provide for two different wastegate response rates.

In a preferred embodiment of the invention, the means for supplying air comprises an air compressor. Each boost control means may comprise a boost control solenoid operative to vent the branch in which it is disposed to atmosphere. The valve means may comprise an on/off valve disposed in each branch. Alternatively, the valve means may comprise a two-way valve means connecting both branches. In one position, the valve means opens one branch to the wastegate actuator and closes the other and in the other position the valve means opens the other branch to the wastegate actuator and closes the first mentioned branch. The means for delaying may comprise a one-way valve disposed to permit flow only in the direction from the wastegate actuator to the boost control means. This one-way valve is bypassed and a restrictor is disposed in the bypass and a volume is connected to it.By varying the size of restrictor and volume, the delay may be altered as desired.

In order that the invention may be more clearly understood, one embodiment thereof will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically a pressure charging apparatus according to the invention, and Figure 2A, 2B and- 2C respectively show variation of duly cycle, wastegate actuator position and engine boost level with time.

Referring to Figure 1, the apparatus comprises a pressure source 1 such as for example an air compressor.

The output from the pressure source feeds two branches respectively referenced 2 and 3. Branch 2 comprises an engine boost control solenoid 4 and an on/off valve 5.

Branch 3 comprises an engine boost control solenoid 6, one-way valve 7 and on/off valve 8. The one-way valve 7 is bypassed by a sub-circuit 9 which comprises a restrictor 10 and volume 11. Vent pipes 12 and 13 lead respectively from boost control solenoids 4 and 6.

Branches 2 and 3 recombine downstream of on/off valves 5 and 8 before entering a wastegate actuator 14. Boost control solenoids 4 and 6 and valves 5 and 8 are electrically controlled from a boost control electrical control unit ECU 15 via an electrical interface 16. Unit 15 is connected to the interface 16 and the interface 16 to the solenoids 4 and 6 and on/off valves 5 and 8.

The operation of the above arrangement will now be described for an internal combustion engine having certain operational parameters for different operational regimes. Consider the example below, whereby the boost control ECU 15 feeds a duty cycle (fixed voltage, fixed frequency) to the boost control solenoid (4 and 6) with typical values as indicated.

i) Engine speed below 2000 rpm 100% duty cycle ii) Engine speed above 2000 rpm 60-70%* iii) Light engine stress (light detonation for example) 40% iv) Heavy engine stress (heavy detonation for example) 0% v) Vehicle brake application inhibit 0% vi) Vehicle cruise control inhibit 0% A 100% duty cycle received by the boost control solenoid (4 or 6) is one that is configured to fully shut the wastegate to provide maximum engine boost. A 0% duty cycle is similarly configured to fully open the wastegate to provide minimum engine boost.

An electrical circuit is used which is designed to do the following: a) Diverts the duty cycle from the ECU to control solenoid 4 ) In response to Opens On/Off valve 5 ) duty cycle of Shuts On/Off valve 8 ) less than 40% Supplies a 0% duty cycle to control solenoid 6 (achieved when open circuit) b) Diverts the duty cycle from the ECU to control solenoid 6 ) In response to a Opens On/Off valve 8 ) duty cycle or Shuts On/Off valve 5 ) more than 60% Supplies a 0% duty cycle to control solenoid 4 (achieved when open circuit) c) Allows a hysteresis period between changeover points at 40% and 60% duty cycles.

* This figure is adjusted in response to a boost level lower or higher than the value pre-programmed into the boost control ECU, in order to maintain a set point.

Operation under regime a) On/Off valve 5 is open with no restriction. Boost control solenoid 4 receives a 0% duty cycle and so cannot vent away any signal pressure. Since on/off valve 8 is shut, the signal pressure via branch 3 is prevented from reaching the wastegate 14. The wastegate is therefore controlled entirely via branch 2 by means of boost control solenoid 4.

Under dynamic conditions in this regime, the pressure upstream of boost control solenoid 4 may be very slightly different to the pressure upstream of the only boost control solenoid in existing arrangements, because some flow through boost control solenoid 6, via the restrictor 10 and into the volume 11 may take place.

However, the restriction into the volume 11 via this branch is much greater than the restriction to the flow via branch 2, which controls the wastegate. This means that operation under regime a) is 'effectively' the same as operation under existing arrangements.

If desired, operation could be made 'totally' the same by having a third on/off valve just upstream of boost control solenoid 6. This would need to be switched off and on at the same time as on/off valve 8, thereby totally isolating branch 3 when branch 2 was in operation.

Regime a) is therefore designed, like existing arrangements, to provide a quick acting wastegate response when the boost control ECU signal is low. In this example the occurrence of either iii), iv), v) or vi) as previously described, would result in a quick reduction of boost pressure as a result of a quick response from the wastegate to a low duty cycle output from the ECU.

Operation under regime b) described above: On/off valve 5 is fully shut. Boost control solenoid 4 receives a 0% duty cycle and so cannot vent away any signal pressure. Branch 2 is therefore totally isolated from the wastegate 14 and is unable to affect the operation of the wastegate 14.

Under steady state conditions (those under which the duty cycle valve output from the boost control ECU is constant), the same wastegate position (and therefore engine boost) is reached as would be achieved under existing arrangements. This is because the pressure either side of the restrictor 10 and volume 11 will have reached the same level. The wastegate actuator 14 is therefore supplied with the same pressure as controlled just downstream of boost control solenoid 6.

Under conditions of a rising signal pressure in response to a lowering duty cycle, the one-way valve 7 prevents a direct connection to the wastegate. The wastegate actuator still responds to the pressure in the volume 11. The restrictor 10 allows flow into the volume 11 thereby slowly increasing the pressure both in the volume and at the wastegate actuator 14. The wastegate actuator pressure therefore lags behind the pressure just downstream of boost control solenoid 6.

Under conditions of falling signal pressure in response to an increasing duty cycle, the one-way valve opens, permitting the wastegate actuator pressure to fall at the same rate as the signal pressure just downstream of boost control solenoid 6. This reduction in actuator pressure will occur at a similar rate to that achieved with existing arrangements.

Regime b) is designed to give a quick acting wastegate when shutting in response to an increasing duty cycle signal at a similar rate to that achieved with the existing arrangement.

It is designed to give a slow acting wastegate when opening in response to a decreasing duty cycle signal.

The reaction rate, causing this slow action, is achieved by altering the restrictors 10 and volumes 11 sizes. It is the slowness of action under these conditions which allows a controlled overboosting to occur. This enables more engine power for a finite (transient) time period and consequently enhanced vehicle performance. The rate should not be so slow that too much overboosting occurs resulting in an engine stress condition, thereby engaging operation regime a).

Variation of duty cycle is shown in Figure 2a and variation of wastegate actuator position in Figure 2b.

Engine boost level variation for both the existing and incentive arrangements are shown in Figure 2c. All parameters are plotted against time for an operational condition of the type described above where high load engine acceleration is followed by a shut throttle deceleration. In Figures 2a,2b and 2c the inventive variation is shown in dashed line and the existing variation in full line. In Figure 2a, duty cycle varies between high at the top and low at the bottom. In Figure 2b wastegate actuator position varies between shut at the top with progressive opening towards the bottom. In Figure 2c pressure varies between high at the top and low at the bottom.

The above described arrangement will allow different control dynamics to be chosen based upon whether the state of the output from the ECU to the boost control solenoid is high or low. This can result in enhanced vehicle performance.

Typically the ECU will provide a lower signal (one which causes the wastegate to open further, lowering engine boost) under conditions of engine stress or safety inhibit, when compared to the signal resulting from excessive boost pressure or engine speed. Where this is the case, the described arrangement may be substituted for an existing arrangement with minimal interference to the ECU or vehicle wiring systems.

With this ECU strategy, the apparatus of the invention will allow the wastegate actuator to respond at a faster rate to engine stress or safety inhibits than to conditions of engine overboost or engine speed parameters. This makes possible a fast response to engine stress or safety inhibits (in a similar manner to the existing arrangement) . It allows a fast response to underboosting (in a similar manner to the existing arrangement). It provides a slow response to overboosting and those engine speed parameters which would tend to lower the state of the signal from the ECU to the boost control solenoid. A condition of overboost is said to exist when the engine boost pressure level is higher than the pre-programmed boost level which the ECU is attempting to control to, under a given set of engine input parameters. The converse applies under a condition of underboost.

An advantage of the described arrangement over the existing one, is that two different wastegate response rates are available and not only one. This new combination allows a controlled dynamic overboosting to occur, enhancing vehicle performance without affecting steady-state boost levels or the performance under conditions of engine stress or safety inhibits. The overboosting available may be used to compensate for the tracking error described above, or to temporarily provide higher engine boost levels than steady-state conditions would allow. Many turbocharged/supercharged engines will tolerate short periods of overboosting without producing any symptoms of engine stress.

It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.

Claims (10)

1. Pressure charging apparatus for internal combustion engines comprising means for supplying air under pressure to the engine inlet, a wastegate, wastegate actuator for closing and opening the wastegate in order to alter the -pressure in the engine inlet, means for pneumatically connecting the means for supplying air to the wastegate actuator, said means for connecting comprising two branches comprising respective boost control means and valve means, one of the branches comprising means for delaying the transmission of pressure therethrough and electrical control means for controlling the boost control and valve means whereby to provide for two different wastegate response rates.

2. Pressure charging apparatus as claimed in claim 1, in which the means for supplying air comprises an air compressor.

3. Pressure charging apparatus as claimed in claim 1 or 2, in which each boost control means comprises a boost control solenoid operative to vent the branch in which it is disposed to atmosphere.

4. Pressure charging apparatus as claimed in claim 1, 2 or 3, in which the valve means comprises an on/off valve disposed in each branch.

5. Pressure charging apparatus as claimed in claim 1, 2 or 3, in which the valve means comprises a two-way valve means connecting both branches.

6. Pressure charging apparatus as claimed in claim 5, in which in one position, the valve means opens one branch to the wastegate actuator and closes the other and in another position the valve means opens the other branch to the wastegate actuator and closes the first mentioned branch.

7. Pressure charging apparatus as claimed in any preceding claim, in which the means for delaying comprises a one-way valve disposed to permit flow only in the direction from the wastegate actuator to the boost control means.

8. Pressure charging apparatus as claimed in claim 7, in which the one-way valve is by-passed and a restrictor is disposed in the by-pass.

9. Pressure charging apparatus as claimed in claim 8, in which a volume is connected to the by-pass.

10. Pressure charging apparatus substantially as hereinbefore described with reference to the accompanying drawings.