Crankcase ventilation system

Abstract

To provide a crankcase ventilation system capable of properly ventilating the inside of a crankcase with a necessary minimum constitution without using a concentration sensor.SOLUTION: A crankcase ventilation system 1 includes an engine 2, a ventilation device 3, and a control device 7. The engine 2 has a crankcase 21, and a piston 22 disposed inside of the crankcase 21, and is constituted to mixedly burn hydrocarbon and hydrogen as a fuel F. The ventilation device 3 is constituted to ventilate the inside of the crankcase 21 by the outside air B supplied into the crankcase 21. The control device 7 has a concentration estimation portion 72 for estimating concentration of a combustible gas in the crankcase 21 on the basis of a mixed fuel burning ratio of hydrogen in the fuel F in the engine 2, and a control portion 73 operating the ventilation device 3 according to the concentration of the combustible gas by the concentration estimation portion 72.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a crankcase ventilation system.

Background Art

[0002] The crankcase of an engine houses a piston, a connecting rod, a crankshaft, etc. Although the inside of the crankcase is separated from the combustion chamber where the mixture of fuel and air burns via the piston, it is known that blow-by gas containing unburned fuel leaks from the combustion chamber into the crankcase. In particular, when hydrogen, which has a wider flammable range than gasoline, natural gas, etc., is contained in the fuel, there is a risk that the hydrogen in the blow-by gas will catch fire, and thus the blow-by gas is ventilated.

[0003] For example, in the four-stroke engine of Patent Document 1, it is described that a ventilation fan for forcibly discharging blow-by gas containing hydrogen from the inside to the outside of the crankcase is arranged in a ventilation flow path provided in the crankcase. And by ventilating the blow-by gas containing hydrogen in the crankcase with the ventilation fan, it is possible to prevent hydrogen from catching fire in the crankcase.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the four-stroke engine described in Patent Document 1, a concentration sensor is used to measure the hydrogen concentration inside the crankcase, and a ventilation fan is driven when the hydrogen concentration exceeds a predetermined threshold. In other words, a concentration sensor is always required to measure the hydrogen concentration. Therefore, further ingenuity is needed to ventilate the hydrogen-containing blow-by gas inside the crankcase without using a concentration sensor.

[0006] This invention has been made in view of the above problems, and aims to provide a crankcase ventilation system that can properly ventilate the inside of the crankcase with the minimum necessary configuration without using a concentration sensor. [Means for solving the problem]

[0007] One aspect of the present invention is, An engine having a crankcase and a piston positioned within the crankcase, configured to co-combust hydrocarbons and hydrogen as fuel, A ventilation device that ventilates the inside of the crankcase by supplying outside air into the crankcase, The crankcase ventilation system comprises a concentration estimation unit that estimates the concentration of combustible gas in the crankcase based on the hydrogen co-firing ratio in the fuel of the engine, and a control device that controls the operation of the ventilation device according to the concentration of combustible gas determined by the concentration estimation unit. [Effects of the Invention]

[0008] The crankcase ventilation system according to one embodiment described above, when using an engine configured to co-combust hydrocarbons and hydrogen, uses a concentration estimation unit to estimate the concentration of combustible gas in the crankcase based on the hydrogen co-combustion rate in the engine's fuel. The crankcase ventilation system then uses a control unit to control the operation of the ventilation device according to the combustible gas concentration estimated by the concentration estimation unit. The hydrogen co-combustion rate in the engine's fuel is determined based on the amount of hydrocarbons and hydrogen supplied to the engine, etc. Examples of hydrocarbons used as fuel include city gas, gasoline, and propane.

[0009] The crankcase ventilation system, by having a concentration estimation unit, can detect the concentration of flammable gases inside the crankcase without using a concentration sensor and activate the ventilation device when ventilation is necessary. Therefore, according to the crankcase ventilation system of this embodiment, the inside of the crankcase can be properly ventilated with the minimum necessary configuration without using a concentration sensor. [Brief explanation of the drawing]

[0010] [Figure 1] An explanatory diagram showing the configuration of a crankcase ventilation system according to Embodiment 1. [Figure 2] An explanatory diagram showing the electrical configuration of a crankcase ventilation system according to Embodiment 1. [Figure 3] A graph showing the relationship between the hydrogen co-firing ratio in the fuel and the concentration of combustible gas in the crankcase, according to Embodiment 1. [Figure 4] A flowchart illustrating a control method for a crankcase ventilation system according to Embodiment 1. [Modes for carrying out the invention]

[0011] A preferred embodiment of the crankcase ventilation system described above will be explained with reference to the drawings. <Embodiment 1> As shown in Figures 1 and 2, the crankcase ventilation system 1 of this embodiment comprises an engine 2, a ventilation device 3, and a control device 7. The engine 2 has a crankcase 21 and a piston 22 arranged inside the crankcase 21, and is configured to co-combust hydrocarbons and hydrogen as fuel F. The ventilation device 3 is configured to ventilate the inside of the crankcase 21 with outside air B supplied into the crankcase 21. The control device 7 has a concentration estimation unit 72 that estimates the concentration of combustible gas inside the crankcase 21 based on the co-combustion rate of hydrogen in the fuel F in the engine 2, and a control unit 73 that controls the operation of the ventilation device 3 according to the concentration of combustible gas determined by the concentration estimation unit 72.

[0012] The crankcase ventilation system 1 of this configuration will be described in detail below. The crankcase ventilation system 1 installs a ventilation device 3 around the engine 2 and receives information on the hydrogen co-firing ratio in the fuel F from the engine 2 to control the operation of the ventilation device 3.

[0013] (Engine 2) As shown in Figure 1, the engine 2 of this embodiment is configured to co-combust city gas (natural gas) and hydrogen (hydrogen gas) as hydrocarbons. The engine 2 has a plurality of cylinders in which combustion chambers 25 are formed. The engine 2 has a plurality of pistons 22 that move in double motion within the cylinder 210, a plurality of connecting rods 23 that are rotatably connected to each piston 22, a crankshaft 24 to which the plurality of connecting rods 23 are rotatably connected and which outputs the power from the reciprocating motion of the plurality of pistons 22 as rotational force, and a crankcase 21.

[0014] The crankcase 21 houses multiple pistons 22, multiple connecting rods 23, and a crankshaft 24. A cylinder 210 on which the pistons 22 slide is connected to the crankcase 21. The crankcase 21 has an outside air inlet 211 for supplying outside air B into the crankcase 21 and an outside air outlet 212 for discharging the outside air B from inside the crankcase 21.

[0015] In the engine 2 of this embodiment, a supercharger 4 is connected. The supercharger 4 utilizes the energy of the exhaust gas G exhausted from the combustion chamber 25 of each cylinder of the engine 2 to compress the air-fuel mixture M of the fuel F and the combustion air A supplied to the engine 2. The exhaust pipe (exhaust manifold) 62 that exhausts the exhaust gas G from the combustion chamber 25 of each cylinder is connected to the turbine 41 of the supercharger 4, and the intake pipe (intake manifold) 61 that supplies the air-fuel mixture M to the combustion chamber 25 of each cylinder is connected to the compressor 42 of the supercharger 4. A throttle valve 611 is disposed in the intake pipe 61.

[0016] The compressor 42 of the supercharger 4 is supplied with an air-fuel mixture M of a hydrocarbon and hydrogen as the fuel F and the combustion air A via a supply pipe 51. The mixing of the hydrocarbon and hydrogen and the mixing of the mixed fuel and the combustion air A are performed upstream of the supply pipe 51.

[0017] (Ventilation device 3) As shown in FIG. 1, the ventilation device 3 of this embodiment is composed of a first blower 31 connected to the outside air inlet 211 of the crankcase 21 and a second blower 32 connected to the outside air outlet 212 of the crankcase 21. The first blower 31 and the second blower 32 are configured to perform operations of blowing air and stopping the blowing air in response to a command from the control device 7. The first blower 31 and the second blower 32 are configured to operate simultaneously to ventilate the inside of the crankcase 21 with the outside air B.

[0018] The first blower 31 is configured to introduce the atmosphere as the outside air B into the crankcase 21. The second blower 32 is configured to discharge the outside air B containing blow-by gas from the crankcase 21. The blow-by gas contains combustible gas. A confluence pipe 52 is connected to the discharge port of the second blower 32 and merges with the supply pipe 51 of the air-fuel mixture M. When the first blower 31 and the second blower 32 operate, the outside air B containing blow-by gas in the crankcase 21 is discharged into the confluence pipe 52 and mixed with the air-fuel mixture M flowing through the supply pipe 51 from the confluence pipe 52. Then, the outside air B containing blow-by gas is utilized for combustion in the engine 2. By refluxing the outside air B containing blow-by gas to the supply pipe 51 as the air supply system, the supercharging capacity of the supercharger 4 is assisted.

[0019] A flow rate adjustment valve 53 for adjusting the flow rate of the outside air B containing blow-by gas mixed from the confluence pipe 52 into the supply pipe 51 is arranged in the confluence pipe 52. By operating the flow rate adjustment valve 53, a part of the outside air B containing blow-by gas may be discharged outside the confluence pipe 52.

[0020] Note that, without using the supercharger 4, the air-fuel mixture M may be supplied to the combustion chambers 25 of the respective cylinders of the engine 2 via the intake pipe 61. In this case, the outside air B containing blow-by gas is mixed with the air-fuel mixture M in the supply pipe 51 and supplied to the combustion chambers 25 of the respective cylinders of the engine 2 without passing through the supercharger 4.

[0021] Also, the outside air B containing blow-by gas in the crankcase 21 may be dissipated into the atmosphere. In this case, for example, the second blower 32 may not be connected to the confluence pipe 52, and the discharge port of the second blower 32 may be opened to the atmosphere.

[0022] (Control device 7) As shown in Figures 1 and 2, the control device 7 of the crankcase ventilation system 1 has a combustion ratio receiving unit 71 that receives information on the combustion ratio of hydrogen in the fuel F in the engine 2 from the engine control device 70. The concentration estimation unit 72 estimates the concentration of combustible gas in the crankcase 21 based on the information on the combustion ratio of hydrogen in the fuel F received by the combustion ratio receiving unit 71.

[0023] The control device 7 of the crankcase ventilation system 1 may be integrated with the engine control device 70. In this case, the co-firing ratio receiving unit 71 and the concentration estimation unit 72 are configured as parts that perform a series of operations.

[0024] In engine 2, it is known that blow-by gas containing combustible gases leaks from the combustion chamber 25 into the crankcase 21 via the piston rings. In particular, hydrogen has the lowest density of all gases and is prone to leaking from the combustion chamber 25 into the crankcase 21 in engine 2. Therefore, when hydrogen is present in fuel F, the higher the proportion of hydrogen in fuel F (combustion ratio), the higher the concentration of combustible gas in the crankcase 21.

[0025] The hydrogen co-firing ratio in fuel F in engine 2 is determined based on the supply amounts of hydrocarbons and hydrogen to engine 2. The hydrogen co-firing ratio in fuel F is determined based on the ratio of the heat energy of hydrocarbons supplied to engine 2 per unit time (referred to as the heat energy of hydrocarbons) to the heat energy of hydrogen supplied to engine 2 per unit time (referred to as the heat energy of hydrogen). The hydrogen co-firing ratio in fuel F should be the heat energy of hydrogen in the sum of the heat energy of hydrocarbons and the heat energy of hydrogen. Hydrocarbons used as fuel F include natural gas such as city gas, as well as gasoline, propane, etc. Fuel F is supplied to engine 2 as fuel gas, and hydrogen is supplied as hydrogen gas.

[0026] Figure 3 shows the relationship between the hydrogen co-firing ratio in fuel F and the concentration of combustible gas in the crankcase 21. It is shown that the higher the hydrogen co-firing ratio in fuel F, the higher the concentration of combustible gas in the crankcase 21. When the concentration of combustible gas in the crankcase 21 is C [vol%], the hydrogen co-firing ratio in fuel F is φ [vol%], and the coefficients are a, b, and c, the relationship is given by C = a·φ 2 It is expressed as +b·φ+c. The concentration estimation unit 72 estimates the concentration of the combustible gas in the crankcase 21 such that the higher the co-firing ratio of hydrogen in the fuel F, the higher the concentration of the combustible gas in the crankcase 21.

[0027] The control unit 73 is configured to control whether to operate or stop the first blower 31 and the second blower 32, which constitute the ventilation device 3, according to the concentration of the flammable gas determined by the concentration estimation unit 72. The control unit 73 can control the operation of the first blower 31 and the second blower 32, which constitute the ventilation device 3, based on various conditions.

[0028] In this embodiment, the control unit 73 is configured to operate the first blower 31 and the second blower 32, which are ventilation devices 3, when the concentration of the combustible gas estimated by the concentration estimation unit 72 exceeds the lower limit concentration C1 of the combustible gas ignition limit, which takes into account a predetermined margin. With this configuration, the crankcase 21 can be ventilated before the concentration of the combustible gas in the crankcase 21 reaches the concentration at which the combustible gas ignites. The lower limit concentration C1 can be set to a concentration that is a predetermined amount lower than the lower limit concentration C0 at which hydrogen as a combustible gas can ignite. The predetermined margin is set to a concentration that is a predetermined amount lower.

[0029] The control unit 73 is configured to maintain the pressure inside the crankcase 21 within a specified pressure range when operating the ventilation device 3. The specified pressure range can be defined as the range in which the pressure inside the crankcase 21 is higher than a predetermined pressure, which is higher than atmospheric pressure. In this embodiment, the pressure inside the crankcase 21 is maintained within the specified pressure range by appropriately setting the airflow rate of the first blower 31. Furthermore, by making the airflow rate of the first blower 31 (flow rate of outside air B) greater than the airflow rate of the second blower 32 (flow rate of outside air B including blow-by gas), it becomes easier to maintain the pressure inside the crankcase 21 within the specified pressure range.

[0030] (Control method) The control method for the crankcase ventilation system 1 will be explained with reference to the flowchart in Figure 4. When engine 2 is in combustion operation, the control device 7 of the crankcase ventilation system 1 receives information on the hydrogen co-firing ratio in fuel F from the engine control device 70 (step S101). Next, the control device 7 of the crankcase ventilation system 1 uses a concentration estimation unit 72 to estimate the concentration of combustible gas in the crankcase 21 based on the hydrogen co-firing ratio in fuel F (step S102). Then, the control unit 73 determines whether the concentration of combustible gas estimated by the concentration estimation unit 72 exceeds the lower limit ignition concentration C1 of the combustible gas, taking into account a predetermined margin (step S103).

[0031] If the concentration of the flammable gas determined by the concentration estimation unit 72 is less than or equal to the lower limit ignition concentration C1 of the flammable gas, the control unit 73 does not operate the ventilation device 3. Then, after waiting for a predetermined time to elapse (step S104), step S101 is executed again. On the other hand, if the concentration of the flammable gas determined by the concentration estimation unit 72 exceeds the lower limit ignition concentration C1 of the flammable gas, the control unit 73 operates the ventilation device 3 (step S105). Then, after waiting for a predetermined time to elapse (step S104), step S101 is executed again.

[0032] (Effects and Benefits) In this embodiment, when using an engine 2 configured to co-combust hydrocarbons and hydrogen, the crankcase ventilation system 1 uses a concentration estimation unit 72 to estimate the concentration of combustible gas in the crankcase 21 based on the hydrogen co-combustion ratio in the fuel F in the engine 2. The crankcase ventilation system 1 then uses a control unit 73 to control the operation of the first blower 31 and the second blower 32, which function as ventilation devices 3, according to the combustible gas concentration estimated by the concentration estimation unit 72.

[0033] The crankcase ventilation system 1, by having a concentration estimation unit 72, can detect the concentration of flammable gas in the crankcase 21 without using a concentration sensor, and can operate the first blower 31 and the second blower 32, which act as ventilation devices 3, when ventilation is necessary. Therefore, according to this embodiment of the crankcase ventilation system 1, blow-by gas in the crankcase 21 can be properly ventilated with the minimum necessary configuration without using a concentration sensor.

[0034] <Embodiment 2> This embodiment describes a crankcase ventilation system 1 in which the operation method of the ventilation device 3 by the control unit 73 of the control device 7 differs from that of Embodiment 1. In this embodiment of the crankcase ventilation system 1, the control unit 73 of the control device 7 is configured to determine whether the concentration of the flammable gas estimated by the concentration estimation unit 72 exceeds the lower limit ignition concentration C1 of the flammable gas, taking into account a predetermined margin. Furthermore, when the concentration of the flammable gas exceeds the lower limit ignition concentration C1, the control unit 73 is configured to operate the ventilation device 3 so that the amount of ventilation the inside of the crankcase 21 by the ventilation device 3 increases as the concentration of the flammable gas rises above the lower limit ignition concentration C1.

[0035] The higher the concentration of flammable gas in the crankcase 21, as estimated by the concentration estimation unit 72, is above the ignition lower limit margin concentration C1, the closer it gets to the ignition lower limit concentration C0 at which hydrogen as a flammable gas can ignite, increasing the risk of ignition of the flammable gas. Therefore, in this embodiment, when the concentration of flammable gas exceeds the ignition lower limit margin concentration C1, the higher the concentration of flammable gas is above the ignition lower limit margin concentration C1, the greater the ventilation rate provided by the ventilation device 3 to ventilate the crankcase 21. The ventilation rate provided by the ventilation device 3 is changed by changing the airflow rate provided by the first blower 31 and the second blower 32, which constitute the ventilation device 3.

[0036] Furthermore, the ventilation rate provided by the ventilation device 3 to the crankcase 21 is set to an amount that can maintain the concentration of flammable gas in the crankcase 21 at or below the lower ignition limit margin concentration C1. The ventilation rate provided by the ventilation device 3 may be determined in relation to the concentration of flammable gas in the crankcase 21, or in relation to the co-combustion rate of hydrogen in the fuel F.

[0037] In this configuration, the blow-by gas in the crankcase 21 can be ventilated more appropriately without using a concentration sensor by increasing the ventilation rate in the crankcase 21 as the concentration of the flammable gas increases.

[0038] The configuration of the control device 7, including the co-firing ratio receiving unit 71 and the concentration estimation unit 72, is the same as in Embodiment 1. The ventilation device 3 is composed of a first blower 31 and a second blower 32, as in Embodiment 1. Furthermore, the other configurations, functions, and effects are the same as in Embodiment 1. In this embodiment as well, the components indicated by the same reference numerals as those shown in Embodiment 1 are the same as the components in Embodiment 1.

[0039] The present invention is not limited to the embodiments described herein, and further different embodiments can be constructed without departing from the spirit of the invention. Furthermore, the present invention includes various modifications, modifications within the equivalent range, and so on. [Explanation of Symbols]

[0040] 1. Crankcase ventilation system 2 engines 21 Crankcase 211 Outside air inlet 212 Outside air outlet 22 pistons 3. Ventilation system 31 First Blower 32. Second Blower 4. Supercharger 41 Turbine 42 Compressor 51 Supply piping 52 Junction piping 7 Control device 70 Engine control unit 71 Co-firing ratio receiving unit 72 Concentration estimation part 73 Control Unit F fuel A Combustion air M fuel mixture B Outside air

Claims

1. An engine having a crankcase and a piston positioned within the crankcase, configured to co-combust hydrocarbons and hydrogen as fuel, A ventilation device that ventilates the inside of the crankcase by supplying outside air into the crankcase, A crankcase ventilation system comprising: a concentration estimation unit that estimates the concentration of combustible gas in the crankcase based on the hydrogen co-firing ratio in the fuel of the engine; and a control device that controls the operation of the ventilation device according to the concentration of combustible gas determined by the concentration estimation unit.

2. The crankcase ventilation system according to claim 1, wherein the control unit is configured to operate the ventilation device when the concentration of the combustible gas determined by the concentration estimation unit exceeds the lower limit concentration of the combustible gas ignition taking into account a predetermined margin.

3. The crankcase ventilation system according to claim 1, wherein the control unit is configured to operate the ventilation device to increase the amount of ventilation the ventilation device provides to the inside of the crankcase as the concentration of the combustible gas determined by the concentration estimation unit exceeds the lower limit ignition concentration of the combustible gas, taking into account a predetermined margin, as the concentration of the combustible gas determined by the concentration estimation unit rises above the lower limit ignition concentration.

4. The crankcase ventilation system according to any one of claims 1 to 3, wherein the control unit is configured to maintain the pressure inside the crankcase within a specified pressure range when the ventilation device is in operation.

5. The crankcase ventilation system according to any one of claims 1 to 3, wherein the ventilation device comprises a first blower connected to an outside air inlet for supplying outside air into the crankcase, and a second blower connected to an outside air outlet for discharging outside air containing blow-by gas from inside the crankcase.

6. The crankcase ventilation system according to any one of claims 1 to 3, wherein outside air containing blow-by gas in the crankcase is discharged into a confluence pipe that joins a supply pipe for supplying a mixture of fuel and combustion air to the engine.

7. The crankcase ventilation system according to any one of claims 1 to 3, wherein the outside air containing blow-by gas inside the crankcase is released into the atmosphere.

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