Exhaust valve control method and control device for fuel vapor processing device

Abstract

A fuel component purified from a filter tank (3) of an evaporated fuel treatment device is introduced as a purified gas into an intake passage (7) of an internal combustion engine (1). The purification passage (5) has a pair of exhaust valves (8A, 8B) alternately opened and closed, and each is subjected to duty cycle control. An intake stroke interval based on the number of cylinders is set to ΔREF, and the opening period of each exhaust valve (8A, 8B) is an odd multiple of ΔREF, and the opening period of each is offset by half a period. For example, the initial opening period of the first exhaust valve (8A) includes an interval in which the intake pulsation waveform falls from a peak to a trough, and the initial opening period of the second exhaust valve (8B) that follows includes an interval in which the intake pulsation waveform rises from a trough to a peak. Therefore, the influence of intake pulsation is at least partially cancelled out.

Description

Technical Field

[0001] This invention relates to an evaporative fuel treatment apparatus utilizing a filter canister, and more particularly to the control of an exhaust valve located in a purification passage between the filter canister and the intake passage of an internal combustion engine. Background Technology

[0002] Currently, a widely used evaporative fuel treatment device temporarily adsorbs evaporative fuel generated in the vehicle's fuel tank onto a filter canister using adsorption materials such as activated carbon, preventing it from flowing out. Then, during the operation of the internal combustion engine, the fuel components are purified from the filter canister and introduced into the engine's intake system through the introduction of fresh gas. The exhaust valve located in the purification passage is typically controlled by a duty cycle at an appropriate drive frequency to control the flow rate of purified gas introduced into the engine's intake passage.

[0003] In this evaporative fuel treatment device, the purified gas is measured based on the pressure difference across the exhaust valve in the purification passage and the valve's opening time (i.e., duty cycle). However, in the intake passage connected to the purification passage, there are periodic intake pulsations related to the number of cylinders. The effect of these intake pulsations is smaller when the average pressure in the intake passage is sufficiently low, such as when the internal combustion engine load is low, and when the pressure difference across the exhaust valve is large.

[0004] However, in the turbocharging region of turbocharged internal combustion engines and the high-load region of naturally aspirated internal combustion engines, the pressure difference (average pressure difference) across the exhaust valve decreases, while the impact of intake pulsation increases relatively. Therefore, there is a problem where the purified gas flow rate fluctuates due to the relationship between intake pulsation and the opening period of the exhaust valve.

[0005] Patent documents 1 and 2 disclose a technique in which multiple exhaust valves are arranged side-by-side so that the phases of their opening periods are staggered, thereby shortening the overall opening and closing cycle. However, these documents do not describe problems such as the influence of intake pulsation or their solutions.

[0006] Patent Document 1: Japanese Utility Model Application Publication No. 5-10767

[0007] Patent Document 2: Japanese Patent Application Publication No. 5-332205 Summary of the Invention

[0008] The present invention relates to an exhaust valve control method for an evaporative fuel treatment apparatus, wherein one or more exhaust valves controlled by duty cycle are installed in a purification passage between a filter canister and the intake passage of an internal combustion engine.

[0009] The opening cycle of the aforementioned exhaust valve is synchronized with the rotation of the internal combustion engine, and...

[0010] The intake stroke interval, defined by the number of cylinders, is ΔREF, and the interval between the start of one opening period and the start of the next opening period is (an odd multiple of ΔREF / 2).

[0011] In addition, if the number of cylinders is set to C, the above odd number is (2·C+1).

[0012] The period of intake pulsations generated within the intake passage is determined by the number of cylinders connected to the intake passage, and the pressure within the intake passage repeatedly increases or decreases in relation to the intake stroke of each cylinder. For example, in a simplified intake pulsation waveform, the interval between two adjacent peaks is ΔREF. The interval between the start of one opening period and the start of the next opening period is staggered by (an odd multiple of ΔREF / 2), so that, for example, if an opening period begins at a peak of the intake pulsation waveform, the next opening period begins at a trough of the intake pulsation waveform.

[0013] Therefore, the effects of intake pulsation are at least partially offset, enabling a stable flow of purified gas corresponding to the duty cycle. Attached Figure Description

[0014] Figure 1 This is a structural illustration of the evaporative fuel processing apparatus involved in the present invention.

[0015] Figure 2 It is a timing diagram showing the relationship between the waveform of intake pulsation and the opening periods of the first and second exhaust valves.

[0016] Figure 3 This is a main flowchart of the exhaust valve control in one embodiment.

[0017] Figure 4 This is a flowchart of the control of the timing of the second exhaust valve.

[0018] Figure 5 This is an explanatory diagram showing examples of the on-time when the duty cycle is different. Detailed Implementation

[0019] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1This is an explanatory diagram schematically showing the structure of an evaporative fuel treatment device for a vehicle equipped with an internal combustion engine 1. The evaporative fuel treatment device treats the evaporative fuel generated in the vehicle's fuel tank 2 during vehicle parking to prevent it from flowing out. It is primarily composed of a filter canister 3 filled with adsorbent material such as activated carbon for temporary storage of the evaporative fuel. The filter canister 3 has a pressurization port 3a and a purification port 3b at one end of its internal flow path, and a discharge port 3c at the other end. The pressurization port 3a is connected to the upper space of the fuel tank 2 via a pressurization passage 4, while the purification port 3b is connected to the intake passage 7 of the internal combustion engine 1 via a purification passage 5. The discharge port 3c is open to the atmosphere via a discharge passage 6. Furthermore, a discharge shut-off valve (not shown) may sometimes be installed in the discharge passage 6 for leak detection, etc.

[0020] Evaporated fuel generated during, for example, vehicle parking or fuel supply is introduced into filter canister 3 via pressurization passage 4. During its flow through the adsorbent material toward discharge port 3c, it is adsorbed by the adsorbent material in each part. During operation of internal combustion engine 1, atmospheric air is drawn in through discharge passage 6 by negative pressure generated in the intake system, thereby purifying the adsorbed evaporated fuel from the adsorbent material. The purified fuel is then introduced into the intake system of internal combustion engine 1 via purification passage 5, and finally combusted in the combustion chamber of internal combustion engine 1 together with fuel from the fuel injection valve.

[0021] The internal combustion engine 1 in the illustrated example is a 4-stroke spark-ignition internal combustion engine, such as a turbocharged internal combustion engine with 3 cylinders in series. Therefore, the intake passage 7 of this internal combustion engine 1 has a compressor 11 with a turbocharger, and a throttle valve 12 is arranged downstream of the compressor 11. Additionally, an intake valve 13, consisting of a butterfly valve for generating negative pressure within the intake passage 7, is arranged upstream of the compressor 11 in the intake passage 7. The front end of the purification passage 5 is connected to the intake passage 7 between the intake valve 13 and the compressor 11. Therefore, even in the pressurized region, a certain degree of negative pressure can be generated by the intake valve 13, enabling purification by the filter canister 3 based on the pressure difference between the filter canister 3 and the atmospheric pressure on the exhaust passage 6 side, i.e., the introduction of purified gas into the intake passage 7.

[0022] In the purification passage 5, a pair of exhaust valves 8, consisting of solenoid valves, are provided to control the flow rate of the purified gas. Specifically, a portion of the purification passage 5 branches into a pair of parallel purification passages 5a and 5b, each equipped with a first exhaust valve 8A and a second exhaust valve 8B. That is, the two exhaust valves 8A and 8B are arranged side by side. Here, it is preferable that the lengths of the branched purification passages 5a and 5b are equal, and it is particularly preferable that the portions of each purification passage 5a and 5b closer to the intake passage 7 than the exhaust valves 8A and 8B are equal in length. In other words, the passage lengths from the front opening of the purification passage 5 connected to the intake passage 7 to each exhaust valve 8A and 8B are equal. Thus, the effect of intake pulsation reaching each exhaust valve 8A and 8B is equivalent.

[0023] The duty cycle of exhaust valves 8A and 8B is controlled by controller 9. Controller 9 is configured as part of an engine controller that performs various controls on internal combustion engine 1 (including fuel injection control, ignition control, throttle valve 12 opening control, intake valve 13 opening control, etc.).

[0024] Regarding the duty cycle control in this embodiment, the opening cycle of exhaust valves 8A and 8B is synchronized with the rotation (crankshaft angle) of the internal combustion engine 1. In other words, it is configured such that the drive frequency of the duty cycle control varies according to the rotational speed of the internal combustion engine 1, and a drive pulse signal is output at a specified crankshaft angle.

[0025] Figure 2 This is a timing diagram showing the relationship between (a) the waveform of the intake pulsation in intake passage 7 and (b) the opening periods of exhaust valves 8A and 8B (1st and 2nd exhaust valves). In the diagram, "PCV1" and "PCV2" represent exhaust valves 8A and 8B (1st and 2nd exhaust valves), respectively. Additionally, "#1", "#2", and "#3" are cylinder numbers. Here, ignition occurs in the order of "#1→#2→#3".

[0026] Intake pulsation is generated by the intermittent intake strokes of each cylinder in the internal combustion engine 1, and its period or frequency is determined by the number of cylinders sharing the intake passage 7. In a tandem 3-cylinder internal combustion engine with a 4-stroke cycle, the intake stroke occurs every 240°CA of crankshaft rotation, therefore... Figure 2 As shown in (a), intake pulsations with pressure waveform peaks are generated every 240°CA. Therefore, if the intake stroke interval ΔREF is expressed in terms of crankshaft angle, it is 240°CA. Furthermore, Figure 2(a) The waveform of the intake pulsation is simplified for ease of understanding. The crankshaft angle of the internal combustion engine 1 is detected by a so-called crankshaft angle sensor or cam angle sensor (not shown). Based on its output signal, a REF signal is obtained every 240°CA of crankshaft angle, which serves as the reference for fuel injection timing control and ignition timing control of each cylinder. In other words, the intake stroke interval ΔREF is the interval from the REF signal of a certain cylinder (e.g., cylinder #1) to the REF signal of the next cylinder in the firing order (e.g., cylinder #2). Figure 2 The dashed lines in the diagram represent the timing of the REF signal for each cylinder. The REF signal is output, for example, relative to the top dead center of the compression stroke of each cylinder before a certain crankshaft angle. Furthermore, in this invention, the intake stroke interval ΔREF can be processed based on the actual time, rather than the crankshaft angle.

[0027] The first exhaust valve 8A and the second exhaust valve 8B are driven at intervals that are odd multiples of ΔREF. That is, the period of the drive pulse signal is an odd multiple of ΔREF. More preferably, the number of cylinders is set to C, and the above-mentioned odd number is (2·C+1). For example, in one embodiment of a tandem 3-cylinder internal combustion engine, the period of the drive pulse signal for each of the first exhaust valve 8A and the second exhaust valve 8B is 7 times ΔREF.

[0028] Furthermore, the rising edge of the drive pulse signal for the first exhaust valve 8A differs from the rising edge of the drive pulse signal for the second exhaust valve 8B by half of the aforementioned period. That is, in the embodiment of a tandem 3-cylinder internal combustion engine, the phase difference between the respective drive pulse signals for the duty cycle control of the first exhaust valve 8A and the second exhaust valve 8B is (ΔREF×7 / 2). Therefore, for the entire purification system comprising the two exhaust valves 8A and 8B, the interval between the start of one opening period and the start of the next opening period is (ΔREF×7 / 2).

[0029] Figure 2 (b) represents the opening periods of the first and second exhaust valves 8A and 8B based on the drive pulse signal. For ease of understanding, a small duty cycle is used as an example. Preferably, the first exhaust valve 8A and the second exhaust valve 8B are driven with equal duty cycles. As described above, the starting point of the opening period of the first exhaust valve 8A and the starting point of the opening period of the second exhaust valve 8B differ by half a cycle of each opening cycle (an odd multiple of ΔREF). Therefore, as shown, for example, the initial opening period of the first exhaust valve 8A includes a section descending from the peak to the trough of the intake pulsation waveform, and the subsequent initial opening period of the second exhaust valve 8B includes a section ascending from the trough to the peak of the intake pulsation waveform. Therefore, the effect of the intake pulsation on the purified gas flow rate is substantially canceled out in the first exhaust valve 8A and the second exhaust valve 8B, which depends on the pressure difference before and after the exhaust valves 8A and 8B.

[0030] That is, when the intake pulsation relative to REF deviates somewhat before and after, if the purified gas flow rate decreases during the opening period of the first exhaust valve 8A (the interval from the peak to the trough of the intake pulsation waveform), then the purified gas flow rate increases during the subsequent opening period of the second exhaust valve 8B (the interval from the trough to the peak of the intake pulsation waveform); conversely, if the purified gas flow rate increases during the opening period of the first exhaust valve 8A, then the purified gas flow rate decreases during the opening period of the second exhaust valve 8B. Furthermore, the intake pulsation relative to REF varies to some extent depending on factors such as the propagation speed of the pressure wave (the speed of sound within the intake passage).

[0031] Therefore, even when the pressure difference (average pressure difference) before and after the exhaust valve 8 is small, such as in the booster zone, the fluctuation of the purified gas flow caused by the intake pulsation can be suppressed, and the purified gas flow corresponding to the duty cycle can be stably obtained.

[0032] Specifically, in the above embodiment, taking into account the number of cylinders, a phase difference of (ΔREF×7 / 2) is assigned to the opening period of the two exhaust valves 8A and 8B in a tandem 3-cylinder internal combustion engine. Therefore, as Figure 2 For example, if the initial opening period of the first exhaust valve 8A includes a downward trough corresponding to cylinder #1, then the subsequent opening period of the second exhaust valve 8B includes a rising trough corresponding to the same cylinder #1, moving towards the peak of the next cylinder #2. That is, corresponding to the intake stroke of the next cycle of the same cylinder, even during transitions in the operating conditions (rotational speed and load) of the internal combustion engine 1, the impact of intake pulsation can be suppressed with higher precision. Furthermore, if the subsequent opening period of the first exhaust valve 8A includes a downward trough corresponding to cylinder #2, then the subsequent opening period of the second exhaust valve 8B includes a rising trough corresponding to the same cylinder #2, moving towards the peak of the next cylinder #3. Furthermore, the subsequent opening period of the first exhaust valve 8A includes a range from peak to trough corresponding to cylinder #3, and the subsequent opening period of the second exhaust valve 8B includes a range from trough to peak corresponding to the same cylinder #3. Thus, the opening periods of the first exhaust valve 8A and the second exhaust valve 8B change sequentially corresponding to cylinders #1 to #3, thereby smoothing out the effects of intake pulsation fluctuations between cylinders.

[0033] Figure 3This is a main flowchart illustrating the control of an exhaust valve in one embodiment. The main flowchart is executed synchronously with the REF signal output every 240°CA. In step 1, the count value N, representing the number of REF signals, is read in. In step 2, it is determined whether N is 1. If N is 1, the process proceeds to step 3, where the duty cycle of the first exhaust valve 8A is calculated based on the requested purge gas flow rate. This duty cycle is the proportion of the open period in one cycle, equivalent to... Figure 2 (b) shows the amplitude of one opening period. Furthermore, in a preferred embodiment, as previously described, the duty cycle of the second exhaust valve 8B also becomes the same value.

[0034] In step 4, the hysteresis T_delay between the start of the opening period of the first exhaust valve 8A and the start of the opening period of the second exhaust valve 8B is calculated. As mentioned earlier, in one embodiment, this hysteresis T_delay is (ΔREF × 3.5). Furthermore, proceeding to step 5, a drive instruction is issued to the first exhaust valve 8A. That is, one drive pulse signal is output to the first exhaust valve 8A. Thus, as... Figure 2 As shown in (b), the first exhaust valve 8A opens and closes.

[0035] In step 6, the count value N is incremented. In step 7, it is determined whether the count value N has reached 8. If the count value N is less than 8, the process ends. If the count value N reaches 8, the process proceeds to step 8, where the count value N is initialized to 1.

[0036] If N is not 1 in step 2, proceed from step 2 to step 6. Therefore, for the 7 synchronizations with the REF signal... Figure 3 The process only executes steps 3 to 5 once, thereby obtaining the opening cycle of the first exhaust valve 8A synchronized with the rotation of the internal combustion engine 1, and this cycle is (7 times ΔREF).

[0037] Figure 4 This is a flowchart of the timing control for the drive of the second exhaust valve, for example, executing the operation at minute intervals. Figure 4 The process is as follows. In step 11, it is determined whether a drive instruction has been given to the first exhaust valve 8A. If the result is NO, the process ends.

[0038] If there is a drive indication for the first exhaust valve 8A, then in step 12, timer T is started. In other words, timer T is initialized to 0. Furthermore, in step 13, it is determined whether the value of timer T is greater than or equal to the hysteresis T_delay calculated in step 4. Here, if it is NO, then the increment of the count value of timer T in step 14 is performed repeatedly.

[0039] If "T≥T_delay" is true in step 13, then proceed to step 15 and assign a drive instruction to the second exhaust valve 8B. That is, output one drive pulse signal to the second exhaust valve 8B. Thus, as... Figure 2 As shown in (b), the second exhaust valve 8B opens and closes with a half-cycle lag behind the first exhaust valve 8A.

[0040] Furthermore, the duty cycle control of the aforementioned exhaust valve 8 can be based on the crankshaft angle or on actual time.

[0041] Figure 5 This is an illustrative diagram showing an example of the opening period when the duty cycle is different. As mentioned earlier, the second exhaust valve 8B (PCV2) opens with a half-cycle lag relative to the first exhaust valve 8A (PCV1). Figure 5 The text only shows one or 1.5 cycles. As shown in "Duty Small," when the duty cycle is small, the opening periods of the first exhaust valve 8A and the second exhaust valve 8B do not overlap. As shown in "Duty Medium," if their respective duty cycles are 50%, the two opening periods alternate and are generally continuous. If the duty cycle is further increased, as shown in "Duty Large," the opening periods of the first exhaust valve 8A and the second exhaust valve 8B partially overlap. Additionally, "Full" indicates a duty cycle of 100%.

[0042] The above description focuses on an embodiment where a pair of exhaust valves 8A and 8B are alternately set to open. However, a structure with multiple exhaust valves 8 connected in parallel is also possible. Furthermore, the invention can be applied even if the purification passage 5 has a single exhaust valve 8. That is, if the period of the drive pulse of a single exhaust valve 8 is set to (an odd multiple of ΔREF / 2), for example (ΔREF × 3.5), the same utilization as in the above embodiment can be achieved. Figure 2 This explains the mutual cancellation effect of intake pulsations. That is, the interval between the start of one opening period and the start of the next opening period is (ΔREF×3.5), as shown below. Figure 2 As shown, for example, the initial opening period includes a range from the peak to the trough of the intake pulsation waveform, and subsequent opening periods, for the next cycle of the same cylinder, include a range from the trough to the peak of the intake pulsation waveform.

[0043] Furthermore, in the case of using a pair of exhaust valves 8A and 8B as shown in the aforementioned embodiment, the maximum purified gas flow is shared by the two exhaust valves 8A and 8B. Therefore, compared with the case of using a single exhaust valve 8, it is more advantageous in terms of being able to use a small-capacity solenoid valve with generally high responsiveness.

[0044] Furthermore, while the above embodiments described an example of a turbocharged internal combustion engine with a turbocharger, the present invention can also be applied to naturally aspirated internal combustion engines.

Claims

1. A method for controlling the exhaust valve of an evaporative fuel processing device, wherein, In an evaporative fuel treatment device, one or more exhaust valves controlled by duty cycle are located in a purification passage between a filter canister and the intake passage of an internal combustion engine. The opening cycle of the aforementioned exhaust valve is synchronized with the rotation of the internal combustion engine, and... The intake stroke interval, defined by the number of cylinders, is ΔREF. The interval between the start of one opening period and the start of the next opening period is (an odd multiple of ΔREF / 2). Let the number of cylinders be C, then the odd number mentioned above is (2·C+1).

2. The exhaust valve control method for the evaporative fuel processing device according to claim 1, wherein, The two exhaust valves are arranged side by side. The two exhaust valves are opened alternately in such a way that the interval between the start of the opening period of one exhaust valve and the start of the opening period of the next exhaust valve is an odd multiple of ΔREF / 2.

3. The exhaust valve control method for the evaporative fuel processing device according to claim 2, wherein, The two exhaust valves are driven with equal duty cycles.

4. The exhaust valve control method for the evaporative fuel processing device according to claim 2 or 3, wherein, The lengths of the purification passages from the aforementioned intake passages to each exhaust valve are equal.

5. The exhaust valve control method for the evaporative fuel processing apparatus according to any one of claims 1 to 4, wherein, Regarding the peaks and troughs of the intake pulsation waveform, one opening period contains a peak, and the next opening period contains a trough.

6. An exhaust valve control device for an evaporative fuel processing apparatus, the evaporative fuel processing apparatus comprising: A filter canister that adsorbs evaporated fuel; One or more exhaust valves are disposed in a purification passage between the filter canister and the intake passage of the internal combustion engine; and The controller performs duty cycle control on the aforementioned exhaust valve, wherein... The aforementioned controller synchronizes the opening cycle of the exhaust valve with the rotation of the internal combustion engine, and... The intake stroke interval, defined by the number of cylinders, is set as ΔREF. The exhaust valve is driven in such a way that the interval between the start of one opening period and the start of the next opening period is set to (an odd multiple of ΔREF / 2). Here, the number of cylinders is set as C, and the odd number mentioned above is (2·C+1).

Images