Patent Publication Number: US-2016230735-A1

Title: Engine stop control device

Description:
TECHNICAL FIELD 
     The present invention relates to an engine stop control device that stops an engine if a vehicle speed is less than a prescribed vehicle speed and a booster negative pressure of a brake booster is greater than or equal to a prescribed negative pressure. 
     BACKGROUND ART 
     An engine stop control device that performs an economy running control to limit fuel consumption during idling, such as when a vehicle is in a stopped state waiting for a traffic light, is publicly known. In the economy running control, the engine is stopped when the vehicle is in a stopped state or is reducing the speed to stop, and the engine is restarted when the vehicle starts. Patent Document 1 discloses an engine stop control device. In the device, the above engine stop is performed under a necessary condition in which the negative pressure (booster negative pressure) of the brake booster is greater than or equal to a prescribed negative pressure to limit a shortage of the booster negative pressure. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Laid-Open Patent Publication No. 2011-064188 
     SUMMARY OF INVENTION 
     Technical Problem 
     In summer, in which the frequency of using an air conditioner is high, an engine load caused by a driving load of a compressor for an air conditioner increases. This reduces the intake pipe negative pressure so that a shortage of the booster negative pressure generated by introducing the intake pipe negative pressure is likely to be caused. When the driving loads of auxiliary machines other than the compressor for an air conditioner, such as an alternator, are high, the intake pipe negative pressure is reduced so that a shortage of the booster negative pressure is likely to be caused in the same way. Accordingly, as in the above document 1, if the condition in which the booster negative pressure is greater than or equal to the prescribed negative pressure is a necessary condition for performing the engine stop, the performing of the engine stop is likely to be inhibited due to the shortage of the booster negative pressure when the driving loads of the auxiliary machines are high. This reduces opportunities for performing the engine stop, so that the fuel consumption improvement effect by the engine stop control may be reduced. 
     An objective of the present invention is to provide an engine stop control device that properly ensures a booster negative pressure and opportunities for performing the engine stop. 
     Solution to Problem 
     To achieve the foregoing objective and in accordance with an aspect of the present invention, an engine stop control device that stops an engine if a vehicle speed is less than a prescribed vehicle speed and a booster negative pressure of a brake booster is greater than or equal to a prescribed negative pressure is provided. The engine stop control device includes: an ejector and a controller. The ejector increases the booster negative pressure. The controller is programmed to control the engine and the ejector. If a condition in which the vehicle speed is greater than or equal to the prescribed vehicle speed and a driving load of an auxiliary machine of the engine is greater than or equal to a prescribed load is satisfied, the controller drives the ejector. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ] 
         FIG. 1  is a diagram schematically illustrating a configuration of an engine stop control device according to one embodiment; 
       [ FIG. 2 ] 
         FIG. 2  is a flowchart illustrating a process of performing an ejector driving control routine performed in the engine stop control device of  FIG. 1 ; and 
       [ FIG. 3 ] 
         FIG. 3  is a time chart illustrating an example of a control mode before and after the stopping of a vehicle in the engine stop control device of  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an engine stop control device according to one embodiment will be described in details with reference to  FIGS. 1 to 3 . 
     The engine stop control device according to the present embodiment is applied to an engine  10  to be mounted on a vehicle. As shown in  FIG. 1 , a compressor  11  for an air conditioner, which compresses the refrigerant for cooling the passenger compartment, is connected to the engine  10 . The compressor  11  is one of auxiliary machines driven by the power of the engine  10 . An air cleaner  13 , an airflow meter  14 , a throttle valve  15 , and an intake pipe negative pressure sensor  16  are sequentially provided in this order from the upstream portion in an intake passage  12  of the engine  10 . The air cleaner  13  filters the intake air introduced into the intake passage  12  to remove dust. The airflow meter  14  detects the flow rate (intake air amount GA) of the intake air, which flows through the intake passage  12 . The throttle valve  15  adjusts the intake air amount GA by changing the flow passage area of the intake passage  12 . The intake pipe negative pressure sensor  16  detects the magnitude of the negative pressure (intake pipe negative pressure) generated in the downstream portion of the intake passage  12  from the throttle valve  15 . 
     The vehicle on which the above engine  10  is mounted includes a brake booster  50 . The inside of the brake booster  50  is sectioned by a diaphragm  17  into a negative pressure chamber  18  and an atmospheric pressure chamber  19 . The brake booster  50  uses the pressure difference between the negative pressure (booster negative pressure) introduced into the negative pressure chamber  18  and the atmospheric pressure introduced into the atmospheric pressure chamber  19  to boost and transfer the depressing force applied to a brake pedal  20  to a brake master cylinder  21 . This assists the braking operation of the driver. The brake booster  50  includes a booster negative pressure sensor  22 , which detects the booster negative pressure in the negative pressure chamber  18 . The brake pedal  20  is provided with a brake switch  20   a,  which is turned ON in accordance with the depressing of the brake pedal  20 . 
     The negative pressure chamber  18  of the brake booster  50  is connected through an intake pipe negative pressure introducing passage  23  to a portion of the intake passage  12  that is downstream of the throttle valve  15 . The intake pipe negative pressure introducing passage  23  is provided with a vacuum valve  24 , which serves as a check valve and is opened when the booster negative pressure is less than the intake pipe negative pressure. 
     The negative pressure chamber  18  of the brake booster  50  is also connected through an ejector suction passage  25  to the ejector  26 . The ejector  26  operates with the intake air as a driving gas to suction the air in the negative pressure chamber  18  to increase the booster negative pressure. The ejector  26  is provided in a bypass passage  27 , which connects the upstream portion and the downstream portion of the intake passage  12  with respect to the throttle valve  15 . An electromagnetic on-off valve  28 , which selectively opens and closes the bypass passage  27 , is provided in the bypass passage  27 . 
     The ejector  26  includes a nozzle  29 , a diffusor  30 , and a suction chamber  31 . The intake air flows from the upstream portion of the intake passage  12  with respect to the throttle valve  15  through the bypass passage  27  into the ejector  26 . The nozzle  29  constricts the flow of intake air into the ejector  26  and squirts the intake air into the suction chamber  31 . The diffusor  30  reduces the speed of the intake air squirted through the nozzle  29 , increases the pressure of the intake air, and discharges the intake air. The above ejector suction passage  25  is connected to the suction chamber  31 . 
     The above ejector  26  operates as follows. When the on-off valve  28  is opened in the state in which the differential pressure in the intake passage  12  between the upstream pressure and the downstream pressure of the throttle valve  15  (hereinafter, referred to as ejector differential pressure) is sufficiently high, the intake air flows from the upstream portion through the bypass passage  27  to the downstream portion with respect to the throttle valve  15 . At this time, the intake air that has flowed into the ejector  26  provided in the bypass passage  27  is accelerated according to the constriction of the nozzle  29 . This reduces the pressure of the intake air, and the intake air is squirted into the suction chamber  31 . The intake air is expanded and diffused in the suction chamber  31  and then flows into the diffusor  30 . After the speed of the intake air is reduced in the diffusor  30  and the pressure of the intake air is increased, the intake air is returned through the bypass passage  27  to the downstream portion of the intake passage  12  from the throttle valve  15 . In the suction chamber  31  at this time, a negative pressure is generated by a high speed and low pressure intake airflow squirted through the nozzle  29 . The air in the negative pressure chamber  18  of the brake booster  50  is drawn through the ejector suction passage  25  into the suction chamber  31  in which the negative pressure is generated, and then joins the intake air squirted through the nozzle  29 . As a result, the negative pressure in the negative pressure chamber  18  into which the air is drawn, i.e., the booster negative pressure is increased. 
     The engine  10 , which includes the above ejector  26 , is controlled by an electronic control unit  32 . The electronic control unit  32  includes a central processing unit (CPU), which performs an arithmetic processing for the engine control, a read only memory (ROM), which stores programs and data for the engine control, and a random access memory (RAM), which temporarily stores the arithmetic result of the CPU and the detection results of sensors. 
     The electronic control unit  32  inputs detection signals of various sensors for detecting the operation state of the engine  10  and the running state of the vehicle including the above airflow meter  14 , the intake pipe negative pressure sensor  16 , and the booster negative pressure sensor  22 . The sensors include an accelerator pedal sensor  33 , which detects the amount of depressing of the accelerator pedal (amount of accelerator operation), a refrigerant pressure sensor  34 , which detects the pressure of the refrigerant compressed by the above compressor  11 , and a vehicle speed sensor  35 , which detects the vehicle speed. Strictly, the vehicle speed sensor  35  detects the rotation speed of the wheels. The vehicle speed is obtained through an arithmetic calculation from the detection result of the rotation speed of the wheels. 
     The electronic control unit  32  performs an engine stop control that stops the engine  10  as part of the engine control. That is, the electronic control unit  32  corresponds to a controller programmed to control the engine  10 . The stopping of the engine  10  through the engine stop control is performed when the amount of accelerator operation is zero, a brake switch  20   a  is ON, and the vehicle speed is lowered to be less than the prescribed stop permission vehicle speed Sa. In the present embodiment, the stop permission vehicle speed Sa corresponds to the prescribed vehicle speed and the first prescribed vehicle speed. 
     However, to ensure the operability of the vehicle brake, the engine stop through the engine stop control is inhibited when the booster negative pressure is not over the prescribed stop inhibition negative pressure Pb even if the amount of accelerator operation is zero and the vehicle speed is less than the stop permission vehicle speed Sa. To perform the engine stop control to stop the engine  10 , it is required that the vehicle speed be less than the stop permission vehicle speed Sa and that the booster negative pressure be greater than or equal to the stop inhibition negative pressure Pb. That is, these two conditions are necessary conditions for performing the engine stop control. The engine  10  stopped by the engine stop control is restarted when the condition for performing the engine stop fails to be met, such as when the depressing of the accelerator pedal is not zero, the brake switch is OFF, or the booster negative pressure is reduced. 
     Ejector Driving Control 
     The electronic control unit  32  also performs a driving control of the ejector  26  for ensuring the booster negative pressure. That is, the electronic control unit  32  corresponds to a controller programmed to control the ejector  26 . Hereinafter, the driving control of the above ejector  26  will be described in details. 
       FIG. 2  shows a flowchart of the ejector driving control routine for the driving control of the ejector  26 . The process of the routine is repeatedly performed by the electronic control unit  32  during the operation of the engine  10  for every prescribed control cycle. 
     If the process of the present routine is started, first in step S 100 , the electronic control unit  32  determines whether the above ejector differential pressure is greater than or equal to a prescribed ejector drivable differential pressure Pd. The minimum value of the ejector differential pressure required for driving the ejector  26  is set as the value of the ejector drivable differential pressure Pd. That is, the determination is performed to check whether the ejector  26  is in the drivable state. In the present embodiment, the ejector differential pressure is checked according to the detection result of the intake pipe negative pressure sensor  16  or the booster negative pressure sensor  22 , for example. 
     If the ejector differential pressure is less than the ejector drivable differential pressure Pd (S 100 : NO), the process proceeds to step S 101 . In step S 101 , the electronic control unit  32  closes the on-off valve  28  to stop the ejector  26 . After the on-off valve  28  is closed, the process of the present routine this time is ended. 
     In contrast, if the ejector differential pressure is greater than or equal to the ejector drivable differential pressure Pd (S 100 : YES), the process proceeds to step S 102 . In step S 102 , the electronic control unit  32  determines whether the booster negative pressure is less than the prescribed ejector driving negative pressure Pe. The value that is greater than the above stop inhibition negative pressure Pb is set as the value of the ejector driving negative pressure Pe. If the booster negative pressure is less than the ejector driving negative pressure Pe (S 102 : YES), the process proceeds to step S 105 . In step S 105 , the electronic control unit  32  opens the on-off valve  28  to drive the ejector  26 . After the on-off valve  28  is opened, the process of the present routine this time is completed. 
     In above step S 102 , if the booster negative pressure is determined to be greater than or equal to the prescribed ejector driving negative pressure Pe (S 102 : NO), the process proceeds to step S 103 . In step S 103 , the electronic control unit  32  determines whether the ejector driving request due to failure is made. If the ejector driving request due to failure is made at this time (S 103 : YES), the process proceeds to above step S 105 , and the ejector  26  is driven. In contrast, if the ejector driving request due to failure is not made (S 103 : NO), the process proceeds to step S 104 . 
     The ejector driving request due to failure is made when a failure that causes a reduction of the intake pipe negative pressure occurs. The failure includes a throttle failure, an intake VVT advanced ignition failure, an exhaust VVT retarded ignition failure, an intake pipe negative pressure sensor failure, and an NE sensor failure, for example. 
     The throttle failure occurs when the intentional control of the opening degree of the throttle valve  15  (throttle opening) fails. At this time, the fail-safe measures that set the opening degree of the throttle to an opening degree for an evacuation travel that can be set by only hardware are taken. Since a sufficient intake pipe negative pressure is not generated in this case, the booster negative pressure is ensured by driving the ejector  26 . 
     The intake VVT advanced ignition failure occurs when the intake VVT, in which the valve timing of the intake valve is variable, fails so that retardation of the valve timing of the intake valve fails. The exhaust gas VVT retarded ignition failure occurs when the exhaust VVT, in which the valve timing of the exhaust valve is variable, fails so that advancement of the valve timing of the exhaust valve fails. At the time of occurring of the failures, the amount of air to be introduced into the combustion chamber is out of the intentional control. This may cause an unstable combustion especially in the low load region of the engine  10 . Accordingly, when the failures occur, the fail-safe measures that increase the idling rotation speed of the engine  10  are taken to avoid misfire. In this case, the opening degree of the throttle at the time of the idling operation is increased to be greater than the opening degree in the normal operation so that the intake pipe negative pressure that occurs at the time of the idling operation is less than the intake pipe negative pressure that occurs at the time of the normal operation. Accordingly, the booster negative pressure is ensured by driving the ejector  26 . 
     The intake pipe negative pressure sensor failure occurs when the intake pipe negative pressure is not correctly determined due to a failure of the intake pipe negative pressure sensor  16 , for example. The NE sensor failure occurs when the engine rotation speed is not correctly determined due to factors such as the failure of the NE sensor, which detects the engine rotation speed. Since the combustion state of the engine  10  is not correctly determined at the time of occurring of the failures, the fail-safe measures that increase the idling rotation speed of the engine  10  are also taken at this time to more reliably maintain the combustion of the engine  10 . Accordingly, the booster negative pressure is ensured by driving the ejector  26  at the time of the failures as well. 
     As described above, in the ejector driving control, if the booster negative pressure is reduced to be less than the ejector driving negative pressure Pe, the booster negative pressure is recovered by driving the ejector  26 . This reduces the frequency in which the engine stop by the engine stop control is inhibited due to the shortage of the booster negative pressure. When a sufficient intake pipe negative pressure is not generated due to the failure, the booster negative pressure is ensured by driving the ejector  26 . 
     Further, in the present embodiment, the electronic control unit  32  drives the ejector  26  in the following cases as well. That is, in the above ejector driving control routine, if the booster negative pressure is not less than the ejector driving negative pressure Pe (S 102 : NO), or if the ejector driving request due to failure is not made (S 103 : NO), the process proceeds to step S 104 . In step S 104 , the electronic control unit  32  determines whether a pre-vehicle stop driving condition is satisfied. If the pre-vehicle stop driving condition is satisfied (S 104 : YES), in above step S 105 , the electronic control unit  32  opens the on-off valve  28 , and drives the ejector  26 . 
     The pre-vehicle stop driving condition is satisfied if the following conditions (1) and (2) are satisfied. That is, the condition (1) refers to a state in which the vehicle speed is greater than or equal to the above stop permission vehicle speed Sa and less than the pre-vehicle stop driving vehicle speed Sb, and the condition (2) refers to a state in which the power loss of the engine  10  for driving the compressor  11  for an air conditioner, i.e., the load of the air conditioner is greater than or equal to a prescribed ejector driving request load Le. The air conditioner load is obtained based on the detection result of the refrigerant pressure sensor  34 . A value that is greater than the stop permission vehicle speed Sa is set as the pre-vehicle stop driving vehicle speed Sb in the above condition (1). In the present embodiment, the pre-vehicle stop driving vehicle speed Sb corresponds to a second prescribed vehicle speed. 
     If the pre-vehicle stop driving condition fails to be met (S 104 : NO), in above step S 101 , the electronic control unit  32  closes the on-off valve  28 , and stops the ejector  26 . 
     Effect 
     Next, the effect that occurs in the operation state of the vehicle as a result of performing the above ejector driving control routine will be described. 
       FIG. 3  shows an example of changes of the operation state of the vehicle to which the engine stop control device according to the present embodiment is applied before and after the vehicle stop when the compressor  11  is driven with an air conditioner load that is greater than or equal to the above ejector driving request load Le.  FIG. 3  shows the changes of the operation state of the vehicle when the driving of the ejector  26  in accordance with the satisfaction of the pre-vehicle stop driving condition is not performed with dashed lines as a comparative example. 
     When the speed is reduced to stop the vehicle, the vehicle speed is reduced so that the engine rotation speed is reduced. This reduces the intake pipe negative pressure. This reduces the booster negative pressure of the brake booster  50 , which is generated by introducing the intake pipe negative pressure, as well. In the comparative example, at a time point t 2  when the booster negative pressure is less than the ejector driving negative pressure Pe, the on-off valve  28  is opened and the driving of the ejector  26  is started. In this case, if the air conditioner load is low, the booster negative pressure is promptly recovered after the start of driving the ejector  26 . This avoids a phenomenon in which the booster negative pressure is less than the stop inhibition negative pressure Pb. 
     However, if the air conditioner load is high, the engine load is increased as well. This reduces the intake pipe negative pressure. This delays the recovery of the booster negative pressure after the start of driving the ejector  26 . Accordingly, if the driving of the ejector  26  is started at the time when the booster negative pressure is less than the ejector driving negative pressure Pe, the booster negative pressure is not recovered before the vehicle speed is reduced to be less than the stop permission vehicle speed Sa. Therefore, the performing of the engine stop by the engine stop control is likely to be inhibited due to the shortage of the booster negative pressure. As a result, the opportunities for performing the engine stop is reduced so that the improvement effect of the fuel efficiency by performing the engine stop control is likely to be reduced. In the case of the comparative example shown in  FIG. 3 , even after the vehicle stop, the condition for performing the engine stop fails to be met and the operation of the engine  10  continues even in the period in which the vehicle is in the stopped state. 
     In contrast, in the present embodiment, if the air conditioner load is greater than or equal to the ejector driving request load Le, the pre-vehicle stop driving condition is satisfied at a time point t 1  when the vehicle speed is reduced to be less than the above pre-vehicle stop driving vehicle speed Sb, and the on-off valve  28  is opened. This starts the driving of the ejector  26  earlier than in the case of the comparative example so that the booster negative pressure that is greater than or equal to the stop inhibition negative pressure Pb is easily ensured until the vehicle speed is reduced to be less than the stop permission vehicle speed Sa even if the air conditioner load is high and the recovery of the booster negative pressure is delayed. Accordingly, in the case of the present embodiment, at a time point t 3  when the vehicle speed is less than the stop permission vehicle speed Sa, the condition for performing the engine stop is satisfied and the engine  10  is stopped. Accordingly, in the engine stop control device of the present embodiment, the condition in which the sufficient booster negative pressure is ensured is necessary for performing the engine stop. This limits the shortage of the booster negative pressure and the reduction of the opportunities for performing the engine stop caused by the shortage of the booster negative pressure. 
     The above described engine stop control device according to the present embodiment has the following advantages. 
     (1) In the present embodiment, if the air conditioner load is greater than or equal to the ejector driving request load Le, the ejector  26  is driven at a vehicle speed that is greater than or equal to the stop permission vehicle speed Pb. Accordingly, even if the air conditioner load is high and it takes some time to recover the booster negative pressure by driving the ejector  26 , the inhibition of performing the engine stop by the engine stop control due to the shortage of the booster negative pressure is less likely to be performed. This suitably ensures the booster negative pressure and the opportunity for performing the engine stop. 
     (2) In the present embodiment, the condition in which the vehicle speed is less than the pre-vehicle stop driving vehicle speed Sb that is set greater than the stop permission vehicle speed Sa is a further condition for driving the above ejector  26 . Accordingly, the ejector  26  is driven only if the necessary condition on the vehicle speed for performing the engine stop by the engine stop control is likely to be satisfied. This limits the unnecessary driving of the ejector  26 . This limits the power consumption of the electromagnetic driving type on-off valve  28 , to which a current is supplied to be opened when driving the ejector  26 . This limits the degradation of the fuel cost of the engine due to the increase of the power generation load in turn. 
     The above embodiment may be modified as follows. 
     In the above embodiment, an upper limit (pre-vehicle stop driving vehicle speed Sb) is set for the vehicle speed in which the ejector  26  is driven in accordance with the satisfaction of the pre-vehicle stop driving condition. However, the ejector  26  may be driven without setting the upper limit of the vehicle speed. That is, the above condition (1) may be relaxed to only a condition in which the vehicle speed is greater than or equal to the above stop permission vehicle speed Sa. Even in this case, the advantage of the above condition (1) is obtained. Further, even in this case, if the upper limit condition of the booster negative pressure or the intake pipe negative pressure is added to the pre-vehicle stop driving condition, the unnecessary driving of the ejector  26  is limited. 
     In the above embodiment, it is determined whether the booster negative pressure is over the prescribed stop inhibition negative pressure Pb to determine whether the performing of the engine stop in the engine stop control is inhibited. If the booster negative pressure sensor  22  is not provided, the determination may be made by using the intake pipe negative pressure detected by the intake pipe negative pressure sensor  16  in place of the booster negative pressure. Further, the determination of step S 101  in the ejector driving control routine in  FIG. 2  is performed by using the intake pipe negative pressure in place of the booster negative pressure in the same way. 
     A pressure sensor that detects the absolute pressure of the downstream portion of the intake passage  12  from the throttle valve  15  or the absolute pressure in the negative pressure chamber  18  of the brake booster  50  may be used in place of the intake pipe negative pressure sensor  16  and the booster negative pressure sensor  22 . In this case, the same engine stop control and the same ejector driving control are performed as in the above embodiment by obtaining the intake pipe negative pressure and the booster negative pressure from the atmospheric pressure and the detection results of the sensors. Assuming that the atmospheric pressure is constant, the detection values of the absolute pressure are used as index values of the intake pipe negative pressure and the booster negative pressure. In this case, the size relation of the comparison expression used for the determination between the right and left sides is inverted. 
     In the above embodiment, the vehicle speed is obtained from the detection result of the vehicle speed sensor  35 , which detects the rotation speed of the wheels. Alternatively, the vehicle speed may be obtained from the detection result of the rotation speed of the output shaft of the transmission and the differential gear ratio, or the vehicle speed may be obtained from the detection result of the rotation speed of the input shaft of the transmission and a set of the transmission ratio and the differential gear ratio. 
     In the above embodiment, the electromagnetic driving type valve is employed for the on-off valve  28 . However, an on-off valve of another type may be employed. 
     In the above embodiment, the ejector  26  is driven if the vehicle speed is greater than or equal to the stop permission vehicle speed Sa and the air conditioner load is greater than or equal to the ejector driving request load Le. However, the determination whether the above driving of the ejector  26  is necessitated may be performed by using the driving load of an auxiliary machine other than the compressor  11  or the sum of the driving loads of a plurality of auxiliary machines in place of the above air conditioner load.