JP2012097631A - Engine brake system of internal combustion engine and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine brake system of an internal combustion engine which increases the maximum absorption torque in the range from an engine middle speed rotation region to an engine high speed rotation region, and to provide a method of controlling the engine brake system of an internal combustion engine.SOLUTION: The engine brake system 20 of an internal combustion engine 10 includes: an intake throttle 24 and a mechanical supercharger 21 in an intake passage 12 of the internal combustion engine 10; an exhaust brake valve 25 in an exhaust passage 16; a bypass passage 22 which bypasses the mechanical supercharger 21; and a flow rate control valve 23 in the bypass passage 22. In the engine brake system 20, such a supercharging operation as to increase driving loss of the mechanical supercharger 21 is performed by controlling the valve opening degree of the flow rate control valve 23 in such a manner that the operation pressure ratio of the mechanical supercharger 21 does not exceed the limit upon the engine brake operation, and the valve opening degree of the intake throttle 24 is adjusted and controlled so as to provide a supercharging pressure providing a suction and exhaust pressure difference at which pump loss becomes maximum.

Description

  The present invention relates to an engine brake system for an internal combustion engine that can increase a maximum absorption torque in an engine medium speed rotation range and an engine high speed rotation range by using a mechanical supercharger and an exhaust brake valve together and using an intake throttle, and It relates to the control method.

  The use of exhaust brakes, compression release brakes, retarders, etc. as auxiliary brake systems has become commonplace, mainly for large trucks, for the purpose of reducing the running cost of brakes and avoiding a decrease in braking force due to fading. Yes. In particular, in recent years, the required amount of engine braking force has been increasing due to laws and regulations, and there is a strong demand for enhancement of engine braking force.

  On the other hand, from the viewpoint of improving fuel efficiency, reduction of the displacement of the internal combustion engine is required, but this displacement greatly affects the engine braking force. Therefore, it is important to ensure a large engine braking force even with a small exhaust amount in order to downsize the internal combustion engine accompanied by a reduction in the exhaust amount, that is, to realize engine downsizing.

  In a diesel engine, as a means to effectively enhance the engine braking force, a method of increasing the pump loss by increasing the intake / exhaust pressure difference (exhaust pressure> intake pressure) using an exhaust brake, or using a compression release brake is used. A method of obtaining a negative work in the compression / expansion stroke of an internal combustion engine has become common. Moreover, as a power absorbing device provided outside the internal combustion engine, a retarder or the like has been put into practical use.

  The compression release brake is being adopted because it is easy to secure a large braking force, but it is necessary to add a valve system component for the internal combustion engine, and the strength of the head body is ensured when this valve system component is additionally installed. Since it is essential to do this, it is often necessary to redesign around the head. As a result, there is a merit that a large amount of cost is required for adoption, and because the compression release brake itself only contributes to the enhancement of the engine braking force, there are few benefits obtained for the large cost of adopting this system There is a problem.

  Therefore, as an engine brake system for a commercial vehicle, it is inexpensive and the use of an exhaust brake system is the most common. In this exhaust brake system, when the braking force is required, the exhaust brake valve provided in the exhaust pipe is closed to reduce the flow area of the exhaust pipe, thereby increasing the pressure inside the exhaust manifold, and the internal combustion engine. The pump loss (pumping loss) is increased and the engine braking force is increased. In this exhaust brake system, the pump loss increases and the engine brake force increases as the pressure inside the exhaust manifold increases.

  However, since the shutter used for the exhaust brake used for exhaust throttling is placed in the exhaust pipe and exposed to high-temperature and high-pressure exhaust gas, it has a complicated shape in consideration of cost, operational reliability and durability. It becomes difficult to do. For this reason, pressure-regulating flow control valves that can change the flow in multiple stages, such as those used for general intake throttles, are not used, and with a few exceptions, a constant leak opening that is only ON / OFF operation. An on-off valve having an effective area is used.

  Therefore, in the case of using the exhaust brake system, it is necessary to narrow down a certain area of the flow path area without adjusting the flow path area between the engine low speed rotation range and the engine high speed rotation range. The effective diameter of the opening is set so as to be the maximum structurally acceptable exhaust pressure at the maximum engine speed (rated speed), so that there is a problem that sufficient exhaust pressure cannot be obtained in the engine low speed engine speed range. is there.

  In order to secure the engine braking force from the low engine speed range, a system using a mechanical supercharger in addition to the exhaust brake is very effective. By operating this mechanical supercharger, the intake air pressure is increased from the low engine speed range to increase the exhaust pressure, and the intake / exhaust pressure difference is increased to increase the pump loss and the mechanical supercharger drive loss is reduced. This is because, in addition to the shaft output, the absorption power as an engine brake is increased accordingly.

  As an example of using this mechanical supercharger in combination with an exhaust brake, when the mechanical supercharger is driven via a continuously variable transmission on the crankshaft of an internal combustion engine and the engine braking force is desired to be secured, An engine with a supercharger has been proposed in which the effect of exhaust braking force is increased by increasing the boost ratio and increasing the supercharging pressure (see, for example, Patent Document 1).

JP 09-104259 A

  However, even when this mechanical supercharger and the exhaust brake are used in combination, there are problems with the pressure resistance and heat resistance of the turbine of the exhaust turbocharger (turbocharger) provided in the exhaust pipe. Since there is a pressure limit also in the system gasket, EGR cooling system, etc., it is difficult to extremely increase the pressure inside the exhaust manifold, and there is a limit to the enhancement of the engine braking force by the exhaust brake.

  That is, since the maximum exhaust pressure is determined by the structural limit, the intake / exhaust pressure difference decreases as the supercharging pressure increases. As a result, pump loss is reduced and the resulting braking torque is reduced. In the engine high-speed rotation range, the exhaust pressure easily reaches the maximum exhaust pressure due to the increase in the intake air amount. Therefore, in order to reduce the supercharging pressure, it is necessary to reduce the operating pressure ratio of the mechanical supercharger.

  On the other hand, the present inventor closed the exhaust brake valve when the engine brake was operated to provide a mechanical braking force augmentation system that can be used for various purposes at a lower cost. The turbocharger is operated to increase the engine braking force, and the opening of the variable flow valve (flow control valve) provided in the bypass passage that bypasses the mechanical supercharger This flow rate control is performed by controlling the pressure sensor arranged on the outlet side of the supercharger or the detection value of the supercharging pressure sensor to be a target value set in advance with respect to the rotational speed of the internal combustion engine. An engine braking system for an internal combustion engine that increases the engine braking force while controlling the operating pressure ratio of the mechanical supercharger so that the exhaust pressure does not exceed the structural (endurance) limit by adjusting the valve opening degree; I thought of the control method.

By using the engine brake system of the internal combustion engine and its control method, the pump loss can be greatly increased during engine braking, and the engine braking force can be greatly increased particularly in the engine low speed rotation range. In addition, by adjusting the valve opening of the variable flow rate valve in the bypass passage and performing supercharging operation with the mechanical supercharger even in the middle speed range of the engine, the drive loss of the mechanical supercharger is reduced by the engine absorption power. In part, the engine braking force can be increased.
However, in this system and its control method, the operating pressure ratio of the mechanical supercharger decreases in the high engine speed range and the driving loss decreases, so the absolute amount of braking torque is reduced under the engine high speed condition. There is a problem that it is difficult to greatly increase.

  The present invention has been made in view of the above-described situation, and an object of the present invention is to eliminate the reduction in pump loss in the engine medium speed rotation region and to increase the maximum braking torque and to increase the maximum braking torque. And an engine braking system for an internal combustion engine capable of increasing the maximum absorption torque in the range of the medium-speed rotation range and the high-speed rotation range of the engine by increasing the driving force of the mechanical supercharger in the high-speed rotation range of the engine and its control It is to provide a method.

  In order to achieve the above object, an engine brake system for an internal combustion engine of the present invention comprises a mechanical supercharger in an intake passage of the internal combustion engine, an exhaust brake valve in an exhaust passage, and the mechanical supercharger. In an engine brake system for an internal combustion engine having a bypass passage that bypasses the engine and provided with a flow control valve in the bypass passage, an intake throttle between the intake manifold of the internal combustion engine in the intake passage and the mechanical supercharger And the control device for controlling the mechanical supercharger, the exhaust brake valve, the flow rate control valve, and the intake throttle has a limit on the operating pressure ratio of the mechanical supercharger when the engine brake is operated. In order not to exceed the supercharging operation to increase the drive loss of the mechanical supercharger by controlling the valve opening of the flow control valve, It constituted the valve opening of the serial intake throttle so that the pump loss is adjusted controlled to boost pressure as the intake and exhaust pressure difference becomes maximum.

  An engine brake system control method for an internal combustion engine of the present invention for achieving the above-described object includes a mechanical supercharger in an intake passage of the internal combustion engine, an exhaust brake valve in an exhaust passage, In a control method for an engine brake system of an internal combustion engine, wherein a bypass passage that bypasses the mechanical supercharger is provided and a flow rate control valve is provided in the bypass passage, an intake manifold of the internal combustion engine in the intake passage and the mechanical supercharger An intake throttle is provided between the flow control valve and the opening of the flow control valve so that the operating pressure ratio of the mechanical supercharger does not exceed a limit when the engine brake is operated. The turbocharger is operated to increase the driving loss of the mechanical supercharger, and the valve opening of the intake throttle is set to a supercharging pressure that is the intake / exhaust pressure difference that maximizes the pump loss. It is a method and adjusting control to so that.

  According to these configurations, when the engine brake is operated, the boost pressure can be increased to increase the intake amount, the exhaust pressure can be increased, the pump loss (pumping loss) can be increased, and the braking torque can be increased. . That is, in an exhaust brake system using an exhaust brake valve (exhaust shutter) with a constant opening, pump loss, that is, engine brake force, can be increased by supercharging operation with a mechanical supercharger to increase braking torque.

  In particular, by driving the mechanical supercharger during engine braking, the reduction in pump loss in the medium and high engine speed ranges is reduced, and the flow control valve (pressure By controlling the valve opening degree of the ratio control valve), it is possible to increase the driving force of the engine-type supercharger and secure the driving loss and increase the maximum absorption torque. At the same time, the supercharging pressure is controlled by the intake throttle so that the decrease in the intake / exhaust pressure difference due to the increase in the supercharging pressure and the decrease in the pump loss associated therewith are minimized under the exhaust pressure condition where the maximum pressure is defined. The combination of the two increases the braking torque.

  In addition, in the engine braking system for the internal combustion engine, when the mechanical supercharger and the output shaft of the internal combustion engine are connected via a transmission having a constant speed increase / decrease ratio, the internal combustion engine In the engine brake system control method, when the mechanical supercharger is driven at a constant speed increase / decrease ratio with respect to the output shaft of the internal combustion engine, a continuously variable transmission having a complicated speed increase ratio mechanism becomes unnecessary. Compared with the case of adopting a continuously variable transmission, the arrangement space of the transmission becomes easier and the cost is reduced.

  According to the exhaust brake system for an internal combustion engine and the control method thereof according to the present invention, in order to further increase the maximum braking torque when the engine brake is operated, the reduction in the pump loss in the medium-speed rotation range of the engine is eliminated, By increasing the mechanical supercharger driving force in the engine medium speed rotation region and the engine high speed rotation region, the maximum absorption torque can be increased in the range from the engine medium speed rotation region to the engine high speed rotation region.

It is a figure showing composition of an engine brake system of an internal-combustion engine of an embodiment concerning the present invention. It is a figure which shows the other example of a structure of the engine brake system of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows the other example of a structure of the engine brake system of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows the relationship between an engine speed and the absorption torque of an engine brake. It is a figure which shows each loss part in an engine medium speed rotation area. It is a figure which shows each loss part in an engine high speed rotation area.

  As shown in FIGS. 1 to 3, an engine brake system 20 for an internal combustion engine according to an embodiment of the present invention is a mechanical supercharger 21 from an upstream side to an intake passage 12 connected to an intake manifold 11 of the engine 10. A bypass passage 22 for bypassing the mechanical supercharger 21, a flow control valve 23 provided in the bypass passage 22, an intake throttle 24 provided between the mechanical supercharger 21 and the intake manifold 11, And an exhaust brake valve 25 provided in the exhaust passage 16 connected to the exhaust manifold 15.

  The mechanical supercharger 21 is driven by being connected to the engine 10 by a normal gear, a belt, or the like (belt 21a in FIGS. 1 to 3), or driven by an engine generator and an electric motor. To do. In the embodiment of FIGS. 1 to 3, a particularly complex planetary gear is configured with a fixed speed increasing ratio that keeps the speed increasing / decreasing ratio between the mechanical supercharger 21 and the output shaft 10 a of the engine 10 constant. And continuously variable transmissions are not used. A clutch (not shown) is provided between the mechanical supercharger 21 and the output shaft 10a of the engine 10 so that the mechanical supercharger 21 can be turned ON / OFF.

  Further, the flow rate valve control 23 is formed by a valve whose flow rate can be adjusted so that the flow rate of the intake air A passing through the bypass passage 22 can be adjusted, while the exhaust brake valve 25 is compared to withstand the exhaust gas G of high temperature and high pressure. It is formed by an open / close valve with ON / OFF operation that does not adjust the flow rate.

  The intake throttle 24 is formed of a flow control valve that can adjust the amount of intake air that passes through the intake passage 12.

  In addition, a compressor 13 a and an intake air cooler (intercooler) 14 of an exhaust turbocharger 13 are disposed in the intake passage 12. The compressor 13a may be arranged on the downstream side of the mechanical supercharger 21 as shown in FIG. 1, or may be arranged on the upstream side as shown in FIGS.

  Further, as shown in FIG. 2, the intake air cooler (intercooler) 14 may be disposed at a position downstream of both the mechanical supercharger 21 and the compressor 13a as shown in FIGS. Alternatively, it may be disposed between the mechanical supercharger 21 and the compressor 13a.

  1 to 3, the intake throttle 24 is disposed immediately before the intake manifold 11. However, the intake throttle 24 is disposed between the intake manifold 11 and the mechanical supercharger 21. All you have to do is

  Further, a turbine (west gate turbine) 13 b of the exhaust turbocharger 13 is disposed in the exhaust passage 16 upstream of the exhaust brake valve 25. Further, a pressure sensor 26 is attached to the outlet side of the mechanical supercharger 21 as necessary, and a supercharging pressure sensor 27 is provided at or near the intake manifold 11.

  Then, the detection values of the pressure sensor 26 and the supercharging pressure sensor 27 are inputted, the ON / OFF operation of the mechanical supercharger 21, the valve opening adjustment of the flow control valve 23, the valve opening adjustment of the intake throttle 24, and the exhaust. A control device (not shown) for controlling the ON / OFF operation of the brake valve 25 is provided. Normally, this control device is built in a control device called an ECU (Engine Control Unit) that controls the overall operation of the engine 10.

  The EGR system is not particularly shown in FIGS. 1 to 3, but is provided as necessary. The present invention can be applied to an internal combustion engine with an EGR system and an internal combustion engine without an EGR system. Further, even when the EGR system is provided, the position for taking out the EGR gas and the position for returning to the intake system are not particularly limited.

  Next, a control method in the engine brake system 20 of the internal combustion engine having the above configuration will be described.

  In the engine brake system 20 of the internal combustion engine, when the exhaust brake is operated, the exhaust brake valve 25 provided in the exhaust passage 16 is closed in accordance with a conventional scheme. Subsequently, the clutch of the mechanical supercharger 21 is connected to operate the mechanical supercharger 21.

  If supercharging operation by the mechanical supercharger 21 is performed during the engine braking operation, the exhaust flow rate increases excessively, and the exhaust system pressure may exceed the structural limit of the engine 10. This possibility is particularly high in the high engine speed range. Therefore, the control of the valve opening degree of the flow control valve 23 and the control of the intake throttle 24 are combined. That is, after the operation of the mechanical supercharger 21, the supercharging operation by the mechanical supercharger 21 is performed by controlling the valve openings of the flow control valve 23 and the intake throttle 24.

  In the engine low-speed rotation region, the supercharging operation is performed by controlling the valve opening degree of the flow control valve 23 to operate the mechanical supercharger 21 at the allowable maximum pressure ratio. At this time, the intake throttle 24 is opened and the boost pressure adjustment by the intake throttle 24 is not performed. As a result, the boost pressure is maximized, the intake air amount is increased, the exhaust pressure is increased, the pump loss (pumping loss) is increased, and the braking torque is increased. That is, the pumping torque that is insufficient, that is, the engine braking force is increased by the supercharging operation by the mechanical supercharger to increase the braking torque.

  Further, in the middle speed range of the engine, the operating loss of the mechanical supercharger 21 is controlled while controlling the valve opening degree of the flow control valve 23 so that the operating pressure ratio of the mechanical supercharger 21 does not exceed the limit. Increase. At the same time, the intake throttle 24 is throttled, the valve opening degree is adjusted, the supercharging pressure is adjusted, and the optimum control is performed so that the intake / exhaust pressure difference is optimized, that is, the pump loss is maximized. To do. In other words, the drive loss is ensured by the supercharging operation of the mechanical supercharger, and under the exhaust pressure condition where the maximum pressure is regulated, the intake / exhaust pressure difference is reduced due to the increase of the supercharging pressure and the pump loss is reduced accordingly. The supercharging pressure is controlled by the intake throttle 24 so as to minimize the pressure.

  Further, in the engine high speed rotation range, the opening degree of the flow control valve 23 is controlled so that the operating pressure ratio of the mechanical supercharger 21 does not exceed the limit, and the drive loss of the mechanical supercharger 21 is reduced. To increase. At the same time, the intake throttle 24 is throttled and the valve opening degree is adjusted to adjust the supercharging pressure, and the supercharging pressure is controlled so that the exhaust pressure does not exceed the structural limit. In other words, in the high engine speed range, the pump loss amount is specified with the upper limit of the exhaust pressure. On the other hand, by using the intake throttle 24 in combination, the mechanical supercharger 21 is driven within the range of the operation limit pressure ratio of the supercharger, and the supercharging pressure is appropriately set while ensuring the maximum drive loss. Adjust and control the exhaust pressure to be below the limit.

  Thereby, the driving loss of the mechanical supercharger can be added to the engine braking force by the exhaust brake, and the absolute amount of the braking torque amount can be greatly increased.

  In the control of the flow control valve 23, the operating pressure of the mechanical supercharger 21 is adjusted by controlling the valve opening degree of the flow control valve 23 and adjusting the flow rate of the intake air A flowing into the mechanical supercharger 21. The ratio is adjusted, thereby controlling the supercharging pressure. In this control, the opening degree of the flow rate control valve 23 is set to the detected value (signal) of the pressure sensor 26 attached to the outlet side of the mechanical supercharger 21 or the supercharging pressure provided at or near the intake manifold 11. Based on the detection value (signal) of the sensor 27, control is performed so that one of the pressure values becomes a target value set in advance with respect to the engine speed.

  As for the control of the valve opening degree of the flow control valve 23, a control determined to be a value determined based on map data prepared in advance and a measured intake air amount obtained from an intake air amount sensor (MAF sensor: not shown) By combining one or both of the controls for setting the target intake air amount that is set in advance with respect to the speed with the control based on the pressure on the intake side, it is possible to secure more safety.

  As a result, the supercharging work of the mechanical supercharger 21 is added to the engine braking force, and the intake air flow rate and the exhaust flow rate can be secured from the engine low speed rotation region by supercharging by the mechanical supercharger 21. Therefore, even if the exhaust brake valve 25 is an open / close valve having a constant opening degree, it becomes possible to ensure a high exhaust pressure from a lower engine speed range. As a result, a high exhaust braking force can be secured from the engine low speed rotation range.

  With these controls, the mechanical supercharger 21 and the exhaust brake valve 25 are used in combination to allow a significant increase in exhaust brake force and intake air flowing into the mechanical supercharger 21 using the intake throttle 24. By introducing the control for adjusting the amount, it is possible to secure a large engine braking force from the engine low speed rotation range while adjusting the intake pressure to prevent the exhaust pressure from becoming excessive.

  In FIG. 4, when the clutch is turned off and the mechanical supercharger 21 is not used together (conventional example: dotted line A), the clutch is turned on and the mechanical supercharger 21 is used, but the intake throttle 24 is open. (Reference example: dotted line B) and the case where the clutch is turned on and the mechanical supercharger 21 is used together and the valve opening of the intake throttle 24 is adjusted and controlled (example: solid line C). The relationship between the engine speed and the absorption torque of the engine brake is illustrated. In FIG. 4, the upper part of the drawing indicates that the absorption torque is large and the engine braking force is large. According to FIG. 4, in the engine high-speed rotation region, the absorption torque in Example C is increased by about 17% compared to Reference Example B.

  5 and 6 show changes in the breakdown of the braking torque in the engine medium speed rotation region and the engine high speed rotation region in the case of the conventional example A, the reference example B, and the example C of the above control. R1 indicates pump loss, R2 indicates friction loss, R3 indicates heat loss, and R4 indicates drive loss of the mechanical supercharger 21. X1 in FIG. 5 indicates an increase in exhaust pressure due to the mechanical supercharger 21 and an increase in pump loss associated therewith. 5 indicates an increase in braking torque due to optimization of pump loss, and X3 in FIG. 5 indicates an increase in braking torque due to control of the intake throttle 24. Further, X4 in FIG. 6 indicates an increase in braking torque as the operating pressure ratio of the mechanical supercharger 21 by the intake throttle 24 increases.

  Therefore, according to the engine braking system for an internal combustion engine having the above-described configuration and the control method therefor, in order to increase the maximum braking torque when the engine brake is operated, the reduction in pump loss in the medium-speed engine speed range is eliminated. At the same time, by increasing the driving force of the mechanical supercharger in the engine medium speed rotation region and the engine high speed rotation region, the maximum absorption torque can be increased in the engine medium speed rotation region and the engine high speed rotation region. .

  The exhaust brake system for an internal combustion engine and the control method thereof according to the present invention eliminates the loss of pump loss in the engine medium speed range when the engine brake is operated, and in the engine medium speed range and the engine high speed range. Since it is possible to increase the driving force of the mechanical supercharger and increase the maximum absorption torque in the medium-speed rotation range and high-speed rotation range of the engine, an exhaust brake system for an internal combustion engine such as a diesel engine mounted on an automobile and the like Applicable to the control method.

10 Engine (Internal combustion engine)
12 Intake passage 13 Exhaust turbo type turbocharger 16 Exhaust passage 20 Engine brake system 21 Mechanical supercharger 22 Bypass passage 23 Flow control valve 24 Intake throttle 25 Exhaust brake valve 26 Pressure sensor 27 Supercharging pressure sensor A Intake G Exhaust gas

Claims (4)

An internal combustion engine having a mechanical supercharger in an intake passage of an internal combustion engine, an exhaust brake valve in an exhaust passage, a bypass passage bypassing the mechanical supercharger, and a flow rate control valve in the bypass passage In the engine brake system of the engine,
An intake throttle is provided between the intake manifold of the internal combustion engine in the intake passage and the mechanical supercharger;
The mechanical supercharger, the exhaust brake valve, the flow rate control valve, a control device for controlling the intake throttle,
When the engine brake is activated,
In order that the operating pressure ratio of the mechanical supercharger does not exceed the limit, a supercharging operation is performed to increase the drive loss of the mechanical supercharger by controlling the valve opening of the flow control valve,
Further, the engine brake system for an internal combustion engine, wherein the opening degree of the intake throttle is adjusted and controlled so as to be a supercharging pressure that becomes an intake / exhaust pressure difference that maximizes pump loss.   2. The engine braking system for an internal combustion engine according to claim 1, wherein the mechanical supercharger and the output shaft of the internal combustion engine are connected via a transmission having a constant acceleration / deceleration ratio. An internal combustion engine having a mechanical supercharger in an intake passage of an internal combustion engine, an exhaust brake valve in an exhaust passage, a bypass passage bypassing the mechanical supercharger, and a flow rate control valve in the bypass passage In a method for controlling an engine brake system of an engine,
An intake throttle is provided between the intake manifold of the internal combustion engine in the intake passage and the mechanical supercharger;
When the engine brake is activated,
In order that the operating pressure ratio of the mechanical supercharger does not exceed the limit, a supercharging operation is performed to increase the drive loss of the mechanical supercharger by controlling the valve opening of the flow control valve,
Further, the control method of the engine brake system of the internal combustion engine, wherein the valve opening degree of the intake throttle is adjusted and controlled so as to become a supercharging pressure that becomes an intake / exhaust pressure difference that maximizes a pump loss.   4. The method of controlling an engine brake system for an internal combustion engine according to claim 3, wherein the mechanical supercharger is driven at a constant speed increase / decrease ratio with respect to the output shaft of the internal combustion engine.