GB2256459A - Control of i.c.engine supercharging. - Google Patents

Abstract

A source 1 of compressed air is connected via a boost control solenoid 2 and three separate branches 4, 5 and 6 to a wastegate actuator 11. Branch 4 comprises an on/off valve 7, branch 5 a throttle 8 in series with a reservoir 9 and branch 6 a one-way valve 10. An electrical control unit 12 is connected via an interface 13 to the solenoid 2 and valve 7. With valve 7 closed the branch 5 provides a delay in pressure build-up at the actuator 14. A further on/off valve (14, Fig. 2) may be provided in branch 5. <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 fully 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, a 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 and boost control means disposed upstream of said two branches, valve means being disposed in one of said branches and means for delaying the transmission of pressure being disposed in the other 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. The boost control means comprises a boost control solenoid operative to vent to atmosphere. The valve means may comprise-an on/off valve. The means for delaying may comprise a restrictor and a volume. A one-way valve may be disposed in parallel, with the means for delaying. A further on/off valve may be disposed in series with the restrictor and volume. Varying the size of the restrictor and volume varies the delay. The one-way valve enables a delay in correcting overboost to be achieved without a delay in correcting underboost. 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. The further on/off valve enables the use of a potentially unreliably small restrictor to be avoided when a wastegate delay is required with the first mentioned on/off valve shut which in order of magnitude is greater than the case with that on/off valve open.

In order that the invention may be more clearly understood, two embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically one form of pressure charging apparatus according to the invention, Figure 2 shows diagrammatically other forms of pressure charging apparatus according to the invention, and Figures 3A, 3B and 3C 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 1 leads to a boost control solenoid 2 having a vent pipe 3. The output from the boost control solenoid 2 is split into three separate branches respectively referenced 4,5 and 6. Branch 4 incorporates an on/off valve 7, branch 5 a restrictor 8 in series with a volume 9 and branch 6 a one-way valve 10. The three branches recombine upstream of a wastegate actuator 11. An electrical control unit 12 is connected via an electrical interface 13 to the boost control solenoid 2 and on/off valve 7.

Figure 2 illustrates an arrangement similar to that of Figure 1 except that an additional on/off valve 14 is incorporated in branch 5 downstream of volume 9. The components of this arrangement bear the same reference numerals as those of the arrangement of Figure 1 which correspond.

In the arrangement of Figure 1, when a fast response is required (on/off valve 7 open), the signal pressure is presented not only to the volume 9, ,but also directly to the wastegate actuator 11. This will enable a quicker response than when the only connection to the wastegate actuator 11 is via the volume 9.

To enable this quicker response to be comparable with that of the existing arrangement, it would be necessary to employ a very small volume 9. The volume size is required to be of the same magnitude as the pipework volume (typically a few cubic centimetres), to avoid excessive damping of the wastegate actuator 11.

In order to produce a wastegate delay (with the on/off valve 7 shut) which is orders of magnitude greater than the case with the on/off valve 7 open, it is likely that the restrictor 8 would become unreliably small, recalling that the volume 9 must be small.

The problem of the volume 9 causing excessive damping of the wastegate actuator 11, in the case where the on/off valve 7 is open, can largely be resolved by the addition of valve 14 as shown in Figure 2.

In the arrangement of Figure 2, on/off valve 7 is configured to be open when on/off valve 14 is shut and vice versa. A faster wastegate response is achieved when branch 4 is in operation than when branch 5 is in operation. This is electrically configured to occur in response to a low signal from the ECU 12 to the boost control solenoid 2.

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, whereby the boost control ECU 12 feeds a duty cycle (fixed voltage, fixed frequency) to the boost control solenoid 2 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 13 is used which is designed to do the following: a) Open on/off valve 7 ) In response to a duty Shut on/off valve 14 ) cycle of less than 40% b) Shut on/off valve 7 ) In response to a duty Open on/off valve 14 ) cycle of more than 60% 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 7 is open allowing an unrestricted signal pressure between the boost control solenoid 2 and the wastegate actuator 11. On/off valve 14 is shut which prevents the control pressure at the wastegate actuator from being damped by the volume 9. If the restrictor 8 is sufficiently small then damping of the control pressure between on/off valve 7 and boost control solenoid 2 is minimal.

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) On/off valve 7 is shut. Branch 4 is therefore totally unable to affect the wastegate actuator 11.

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 8 and volume 9 will have reached the same level. The wastegate actuator 11 is therefore supplied with the same pressure as controlled just downstream of-boost control solenoid 2.

Under conditions of a rising signal pressure in response to a lowering duty cycle, the one-way valve 10 prevents a direct connection to the wastegate. The wastegate actuator still responds to the pressure in the volume 9. The restrictor 8 allows flow into the volume 9 thereby slowly increasing the pressure both in the volume and at the wastegate actuator 11. The wastegate actuator pressure therefore lags behind the pressure just downstream of boost control solenoid 2.

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 2. 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 8 and volumes 9 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 3a and variation of wastegate actuator position in Figure 3b.

Engine boost level variation for both the existing and inventive arrangements are shown in Figure 3c. 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 3a, 3b and 3c the inventive variation is shown in dashed line and the existing variation in full line. In Figure 3a, duty cycle varies between high at the top and low at the bottom. In Figure 3b wastegate actuator position varies between shut at the top with progressive opening towards the bottom. In Figure 3c 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.

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 embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention.

Claims (8)

1. Pressure charging apparatus for internal combustion engines comprising means for supplying air under pressure to the engine inlet, a wastegate, a 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 and boost control means disposed upstream of said two branches, valve means being disposed in one of said branches and means for delaying the transmission of pressure being disposed in the other 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 the boost control means comprises a boost control solenoid operative to vent to atmosphere.

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

5. Pressure charging apparatus as claimed in claim 1,2,3 or 4, in which the means for delaying comprises a restrictor and a volume.

6. Pressure charging apparatus as claimed in any preceding claim in which a one-way value is disposed in parallel with the means for delaying.

7. Pressure charging apparatus as claimed in claim 5, in which an on/off valve is disposed in series with the restrictor and volume.

8. Pressure charging apparatus substantially as hereinbefore described with reference to Figure 1 or to Figure 2 of the accompanying drawings.