A METHOD AND A DEVICE FOR REGULATION OF A TURBO-CHARGING DEVICE

Abstract: The invention concerns a method and a device for regulating a turbo-charging device in an internal combustion engine. The turbo-charging device comprises a first turbo unit (1) and a second turbo unit (2) arranged to be regulated in response to the rotational speed of the engine (11), to pressure levels (p1, p2, p3, p4), and to the engine fuel composition.

Description: A METHOD AND A DEVICE FOR REGULATION OF A TURBO- CHARGING DEVICE The subject invention concerns a method for regu- lation of a turbo-charging device of the kind comprising a first and a second turbo unit. The invention also concerns a device for effecting such regulation. The demands on future engines will increase as concerns less fuel consumption, reduced exhaust emission, lighter weight, reduced space requirements, longer life and increased power concentration. One way of obtaining this is to use a smaller stroke-volume, supercharged engine instead of a larger aspirating engine. By using alternative fuels, preferably engine-grade alcohol of methanol (MlOO alternatively M85 where 100/85 conventionally indicate the proportion of methanol in the fuel), it becomes possible to make use of the properties of the high octane number of these fuels in order to increase the compression ratio of the engine for higher efficiency. Furthermore, in a supercharged engine the charging pressure may be increased without resulting in uncontrolled combustion (knocking). Of particular interest is the possibility to increase the amount of supercharge at low rotational speeds, as well as the response, to achieve higher torque. This is normally not possible in conventional engines on account of the risk of knocking when petrol is used as fuel. In-line engines, for example (other cylinder con¬ figurations are also possible), of combustion type which preferably are fuelled by methanol (MlOO or M85) offer unique possibilities to combine well-functioning turbo- charge conditions with excellent fuel economy and reduced exhaust emission. In sequentially arranged turbo-supercharge devices it is possible to obtain optimal efficiency conditions within a wide range of rotational speeds. A small turbo unit configured to be efficient at low rotational speeds may be combined with a larger unit which is adapted primarily for higher rotational speeds, up to the level of the full-power range of the engine. By using methanol fuels, as well as more efficient charging, the gas mixture and the cylinder are heated to less high levels and the formation of nitrogen oxide compounds (NOx-compounds) is reduced. By means of electronically controlled charging, it becomes possible to outline the charging pressure level for both methanol fuel and pure petrol operational con¬ ditions (lower charge pressure on account of the lower octane number). If a fuel consumption sensor is also used it also becomes possible to register and make use of the intermediary fuel mixture (qualities/octane number), and the charging pressure level may be adjusted to the possi¬ bilities of each individual fuel qualities. Controlled charging to approach a torque-related set value, the use of methanol fuels and of sequential turbo- supercharging combine to provide high torque throughout practically the entire range of rotational speeds. In this way, performance characteristics may be obtained, allowing a large aspiration engine to be replaced by a supercharged engine of equal power, as outlined above. The advantages obtained are that the engine operates under a higher specific load for a given load output, with consequential reduced pumping losses and frictional losses. The result is improved specific fuel consumption and lower absolute consumption (corresponding to the smaller engine, since the basic compression may remain slow on account of the octane number of the methanol f el). With the aid of torque-controlled regulation (set value as a function of the number of revolutions) and of regulating valves of a particular design, transition from the small turbo unit to the larger one may be made without dips in the charging pressure and in the torque. In-line engines also provide unique favourable possi¬ bilities for incorporating sequential supercharging by means of installing one small and one larger turbo unit having short exhaust and air ducts in a highly compact manner. The invention comprises a method and a device for regulation of turbo-charging devices and is characterized by the features defined in the characterizing clauses of claims 1 and 2. The invention will be described in closer detail in the following with reference to a preferred embodiment and to the accompanying drawings, wherein Fig. 1 illustrates schematically the structural design of a turbo unit operating in serial sequence, Fig. 2 is a block diagram of the regulating system of the invention, and Fig. 3 shows the principle of control of the two turbo units. Fig. 1 illustrates a turbo-charging arrangement in accordance with the invention. It comprises a first turbo unit 1 and a second turbo unit 2, the latter one being larger than the first one. However, the size difference is not necessary. On the air intake side of the unit is provided a first regulating valve 3 which may be electronically controlled but which in this case is a non¬ return valve. On the exhaust side is provided a second, electronically controlled regulating valve 4. A first waste-gate valve 5 is provided in the first turbo unit 1, and in the second turbo unit a second waste- gate valve 6, both of which are electronicaly controlled. Closely adjacent the induction duct of the engine a rotary intake valve 7, which valve is controlled in response to the function of the "ordinary" valve 8. In the customary manner, an exhaust valve 9 is provided at the cylinder head. It goes without saying that the invention may be used in engines having more than one exhaust and one intake valve per cylinder. Numeral reference 10 designates a sensor designed to measure the temperature of the exhaust gases. In addition, numeral reference 11 designates a revolution counter 11, and numeral reference 12 indicates the ordinary throttle valve. Fig. 2 illustrates in the form of a block diagram a regulating system intended for the subject invention. It comprises a control unit 13 which in the customary manner is provided with a micro processor, a memory unit and input and output means for control of various parameters of the process. To the central unit 13 are coupled con¬ nections for input and output signals. The input signals represent the magnitudes of four different pressure signals pi, p2, p3, and p4. How to define these pres- sures is shown in Fig. 1. The different pressures are measured with the aid of four different pressure sensors (not shown) of a conventional type which are positioned on the air side of the device in the positions indicated by references pi, p2, p3, and p4, respectively (see Fig. 1). To the control unit 13 are likewise connected the revolution counter 11, the exhaust temperature sensor 10 and an indicator 14 which is positioned in the fuel system (not shown) to provide information on the fuel quality. The indicator 14 issues a continuous signal, indicating the proportion of methanol in the fuel mixture. From the control unit 13 output signals are emitted to the regulating valve 4, the first waste-gate valve 5 and to the second wast-gate valve 6. Optionally, a heat exchanger may be provided somewhere on the air side of the turbo device. The regulation of the turbo charging pressure will be described in the following in closer detail. When the rotational speed of the engine is low (the engine may be an in-line engine, a V-engine, a diesel engine, a Wankel engine or other type of internal combustion engine), the first (smaller) turbo unit 1 will be operated to reach the desired charging pressure. This is desirable, since the smaller unit requires a comparatively low gas flow to achieve a high efficiency rate. In order to operate only the first turbo unit 1 (at low rotational speeds), the first regulating valve 4 must be kept closed while the second waste-gate valve 6 is maintained in open position. This process is governed by the control unit 13 with the aid of a computer programme of a kind known to the expert in the field. When the pressure differential "set value minus actual value of pressure p4" is regulated and, simul¬ taneously, the rotational speed n of the engine increases, a continuous "transition" takes place, whereby the operation of the first unit will gradually decrease while the second, larger turbo unit 2 will "take over" and be operated to an increasing extent. In the extreme situation, involving a high rotational speed and a large difference between the set value and the actual value of pressure p4, the small unit 1 will "compensate" for this pressure differential and to some extent be operated concurrently with the operation of the second unit 2. The manner in which the two turbo units 1, 2 will be operated may be illustrated with the aid of a diagram of the type illustrated in Fig. 3. The percentages illustrate the "proportion" (of 100%) of the turbo function that will apply to the first unit 1 as a function of the rotational speed n and the difference between set/actual values of the pressure. Owing to the subject invention, a high efficiency rate of the turbo function is achieved over a very large range of rotational speeds. An increase of the response (i.e. how quickly the pressure build-up occurs) is likewise obtained. With the aid of the fuel quality indicator 14 it becomes possible to control the amount of charge of the turbo units by calculating the set values of the charging pressure on the basis of the actual fuel composition at each instant. Once the set value has been established, the table of Fig. 3 is used as a guide for selection of which unit, 1 or 2, to be given priority. It should be pointed out that the invention is particularly well suited for use in connection with fuels containing methanol. By using commmonly known sensors it becomes possible to register continuously for instance the percentage of methanol in petrol (or vice versa). As regards the regulation of the set value of a turbo unit as such, i. e. the control of the valves 5 and 6, reference is made to the Swedish Patent 8101119-9 entitled "A device for control of the charging pressure in a turbo- charged internal combustion engine". Upon transition between operation of the first unit 1 and operation of the second unit 2 the following applies. Before the valve 4 is opened, a check (with regard to the duty-cycle of the valve 6) is made to establish whether the unit 2 has enough power to operate the engine at the desired pressure. The set value of the unit 2 is then increased by an amount equalling the existing pressure across the first unit 1 while at the same time the valve 4 begins to open. These operations are time-controlled. During the opening movement of the valve 4 the counter- pressure on the engine is reduced, for which reason the set value of pressure p4 is reduced in order to maintain the output torque of the engine. In this manner, a suc¬ cessive transition from one unit 1, 2 to the other is achieved (i.e. when the valve 4 opens) without alteration of the engine torque. One possible embodiment of the invention may be used in connection with the so called Atkinson/Miller process.

Claims: CLAIMS 1. A method of regulating a turbo-charging device in an internal combustion engine, said turbo-charging device comprising a first turbo unit (1) and a second turbo unit (2), c h a r a c t e r i z e d by regu¬ lating the continuous transition between operation of the first unit (1) and the second unit (2) by means of a control unit (13) in response to the rotational speed (n) of the engine and to the existing engine pressure levels (pi, p2, p3, p4). 2. A method as claimed in claim 1, c h a r a c ¬ t e r i z e d in that the regulation of the turbo- charging device is affected by information on the composition (14) of the engine fuel. 3. A regulating device as claimed in claim 1 or 2, c h a r a c t e r i z e d b y a central unit (13) to which are connected means sensing the rotational speed (n) of the engine, the temperature (T) of the exhaust gases, and the composition (14) of the engine fuel, and by valves (4, 5, 6) positioned adjacent respectively said first and said second turbo unit and controlled by said central unit (13).

Inventors: BACKLUND OVE, DAHLGREN MATS, RYDQUIST JAN-ERLING, SANDBERG LARS, BACKLUND, OVE, DAHLGREN, MATS, RYDQUIST, JAN-ERLING, SANDBERG, LARS
Applicants: VOLVO AB, AB VOLVO
Application year: 1991
Main classification: F02B37
IPC codes: F02B33, F02B37, F02D41