WO2008084311A1

WO2008084311A1 - Control device for securing booster negative pressure and control method thereof

Info

Publication number: WO2008084311A1
Application number: PCT/IB2007/003886
Authority: WO
Inventors: Shigemasa Hirooka
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-12-27
Filing date: 2007-12-13
Publication date: 2008-07-17
Also published as: JP2008163753A

Abstract

In a vehicle including a brake booster (22) to which an intake manifold negative pressure is supplied from an intake manifold (14), an ECU 1A used when catalyst warm-up control is performed includes a vehicle start detecting unit that detects starting of the vehicle, and a catalyst warm-up control inhibiting unit that inhibits the catalyst warm-up control. When the vehicle start detecting unit detects starting of the vehicle, the catalyst warm-up control inhibiting unit inhibits the catalyst warm-up control.

Description

CONTROL DEVICE FOR SECURING BOOSTER NEGATIVE PRESSURE AND

CONTROL METHOD THEREOF

FIELD OF THE INVENTION

[OOOl] The invention relates to a control device for securing a booster negative pressure, and a control method thereof. In particular, the invention is concerned with the control device and method for securing a booster negative pressure used when catalyst warm-up control is performed.

BACKGROUND OF THE INVENTION

[0002] Vehicles including brake boosters are generally known. The brake booster serves to assist in a braking operation performed by the driver so as to reduce the pedal effort. The brake booster receives or draws a negative pressure from an intake system (including, for example, an intake manifold and a surge tank) of the internal combustion engine, and uses the received negative pressure as a booster negative pressure. In the meantime, there has been a growing interest in environmental issues, such as global warning and atmospheric pollution, in recent years. With regard to vehicles, one of important problems is to reduce the amount of emissions, such as hydrocarbon (HC), contained in exhaust gas. One effective method for reducing the amount of emissions, such as HC, is to quickly raise the temperature of a catalyst disposed in an exhaust system of the engine to a reaction temperature. To this end, control for retarding the ignition timing of the engine is performed after cold start of the vehicle. At the same time, the throttle valve is controlled so as to hold the intake passage wide open to make up for a reduction in the torque, thereby to increase the amount of intake air. These controls will be called "catalyst warm-up control". With the catalyst warm-up control thus performed, an increased amount of air-fuel mixture is burned at a point in time close to the exhaust stroke, so that exhaust gas having an increased temperature can reach the catalyst. As a result, the catalyst can be activated quickly.

[0003] If the throttle valve is controlled so as to hold the intake passage wide open as described above, the negative pressure produced in the intake system of the engine is reduced. On the other hand, the brake booster draws the negative pressure from the intake system of the engine. Therefore, if the booster negative pressure is largely reduced due to a driver's braking operation while the negative pressure in the intake system is reduced, the booster negative pressure cannot be restored to a sufficiently large magnitude. To further perform a braking operation while the booster negative pressure is of a reduced magnitude, an increased pedal effort or force applied to the brake pedal will be required to provide substantially the same braking force as that of the case where a sufficiently large booster pressure is available. In other words, this condition makes the driver feel as if the application of the brakes is less effective. It is thus necessary to secure a sufficiently large booster negative pressure in order to improve the running stability of the vehicle. To this end, technologies or methods for securing a sufficiently large booster negative pressure when the catalyst warm-up control is performed have been proposed in, for example, Japanese Patent Application Publications No. 10-147161 (JP-A-10-147161) and No. 2002 327639 (JP-A-2002-327639). Other technologies that are considered to be pertinent to the present invention have been proposed in, for example, Japanese Patent Application Publications No. 2003-148194 (JP A-2003- 148194), No. 2001-003.787 (JP-A-2001-003787), No. 2006-170083 (JP-A-2006- 170083) and No. 2001-355494 (JP-A-2001-355494).

[0004] The technologies proposed in the above-identified Japanese Patent Application Publications No. 10-147161 and No. 2002-327639 have a common feature that the time at which the catalyst warm-up control is inhibited or restricted so as to secure a sufficiently large booster negative pressure is when a braking operation is performed. In this case, however, it takes a certain period of time from the time of inhibition or restriction of the catalyst warm-up control to the time when the negative pressure of the intake system is actually increased, and it also takes a certain period of time until the increased negative pressure is actually supplied to the brake booster. These periods of time, and the like, lead to a delay in response in the control for securing a sufficiently large booster negative pressure. With the proposed technologies, therefore, the securing of the booster negative pressure may not be achieved at an appropriate time, since the brake pedal is normally depressed in an extremely short time in typical braking operations.

DISCLOSURE OF THE INVENTION

[0005] It is therefore an object of the invention to provide a control device for securing a booster negative pressure, which device is able to favorably secure a booster negative pressure when catalyst warm-up control is performed.

[0006] A first aspect of the invention is concerned with a control device for securing a booster negative pressure. The control device for securing a booster negative pressure is used when catalyst warm-up control is performed, in a vehicle including a brake booster to which a negative pressure is supplied from an intake passage in an intake system of an internal combustion engine. The control device includes a vehicle start detecting unit that detects starting of the vehicle, and a catalyst warm-up control restricting unit that restricts the catalyst warm-up control when the vehicle start detecting unit detects starting of the vehicle. According to the first aspect of the invention, the control device restricts the catalyst warm-up control by executing the catalyst warm-up control within the bounds of securing a sufficiently large booster negative pressure. By restricting the catalyst warm-up control in this manner, it is possible to prevent a delay in activation of the catalyst and a resulting increase of exhaust emissions, while at the same time assuring a sufficiently large booster negative pressure.

[0007] The catalyst warm-up control restricting unit may inhibit the catalyst warm-up control when the vehicle start detecting unit detects starting of the vehicle. In this aspect, the negative pressure of the intake system can be increased to a sufficiently large magnitude when the vehicle starts, and therefore, a sufficiently large booster negative pressure can be secured beforehand as a preparation to a later braking operation required for stopping or decelerating the vehicle. Namely, the control device according to this embodiment is able to favorably secure a sufficiently large booster negative pressure beforehand for the required braking operation.

[0008] The catalyst warm-up control may be control for retarding the ignition timing of the engine in relation to normal ignition timing, and increasing the amount of intake air drawn into the engine.

[0009] The vehicle start detecting unit may detect starting of the vehicle based on a distance traveled when the vehicle starts. More specifically, it is preferable to detect starting of the vehicle by determining the distance the vehicle has traveled when starting. The starting of the vehicle may be detected when, for example, the distance traveled when the vehicle starts becomes larger than a predetermined value.

[0010] The vehicle start detecting unit may detect starting of the vehicle based on the vehicle speed of the vehicle.

[OOll] The catalyst warm-up control may be inhibited or restricted under a further condition that the catalyst warm-up control is performed so that the negative pressure of the intake system becomes smaller than a predetermined value. In this connection, inhibiting or restricting the catalyst warm-up control is not desirable from the viewpoint of reduction of exhaust emissions. Therefore, the catalyst warm-up control is inhibited or restricted only when the catalyst warm-up control is performed so that the negative pressure of the intake system becomes smaller than the predetermined value. In this manner, the catalyst warm-up control is not inhibited or restricted to a larger extent than necessary, which is advantageous in terms of reduction of exhaust emissions.

[0012] The vehicle may include an automatic transmission, and the catalyst warnrup control may be inhibited or restricted under a further condition that the automatic transmission is shifted to a drive range. When the automatic transmission is shifted to the drive range (hereinafter referred to as "D range"), the load of the automatic transmission is applied to the engine. At this time, the amount of intake air drawn into the engine is increased so as to produce sufficient torque for dealing with the load of the automatic transmission. At the same time, the engine speed is set to a low speed so as to suppress creeping force of the vehicle. Therefore, when the automatic transmission is shifted to the D range, the negative pressure in the intake system is likely to be largely reduced particularly under catalyst warm-up control. On the other hand, since there are no restrictions as described above when the automatic transmission is placed in the neutral range (hereinafter referred to as "N range"), it is possible to keep the negative pressure of intake system sufficiently large while performing catalyst warm-up control. Thus, if the catalyst warm-up control is inhibited or restricted only when the automatic transmission is placed in the D range as described above, the catalyst warm-up control is not inhibited or restricted to a larger extent than necessary, which is advantageous in terms of reduction of exhaust emissions.

[0013] The vehicle may further include a negative-pressure boosting device that supplies the brake booster with a negative pressure that is larger than the negative pressure to be supplied from the intake passage of the intake system. Even in the case where the vehicle includes the negative-pressure boosting device, a sufficiently large booster negative pressure can be favorably secured beforehand as a preparation to necessary braking operations.

[0014] The control device for securing a booster negative pressure may further include a boosting device abnormality detecting unit that detects an abnormality of the negative-pressure boosting device, and the catalyst warm-up control may be inhibited or restricted when the boosting device abnormality detecting unit detects an abnormality of the negative-pressure boosting device. In the case where the negative-pressure boosting device is provided, the negative-pressure boosting device is basically used for securing a sufficiently large booster negative pressure, and it is thus preferable to minimize the likelihood of inhibiting or restricting catalyst warm-up control. Where the negative-pressure boosting device is provided, therefore, the catalyst warm-up control is inhibited or restricted only when the negative-pressure boosting device is at fault, for example, so that a sufficiently large booster negative pressure can be favorably secured while assuring early activation of the catalyst.

[0015] The control device for securing a booster negative pressure may further include a braking operation counting unit that counts the number of braking operations, and the catalyst warm-up control may be inhibited or restricted under a further condition that the number of braking operations counted by the braking operation counting unit before the vehicle start detecting unit detects starting of the vehicle is larger than a predetermined number. While the booster negative pressure is reduced through braking operations, the booster pressure is reduced down to an insufficient level only after the braking operation is performed a plurality of times if the booster pressure is initially sufficiently large. Accordingly, it is preferable to inhibit or restrict the catalyst warm-up control only when the booster negative pressure is reduced down to an insufficient level, from the viewpoint of reduction of exhaust emissions. With the arrangement as described above, the catalyst warm-up control is prevented from being inhibited or restricted to an extent greater than necessary, and therefore, a sufficiently large booster negative pressure can be favorably secured while assuring early activation of the catalyst.

[0016] A second aspect of the invention is concerned with a control method of a control device for securing a booster negative pressure. The control method of the control device for securing a booster negative pressure is used when catalyst warm-up control is performed, in a vehicle including a brake booster to which a negative pressure is supplied from an intake passage in an intake system of an internal combustion engine. The control method includes a step of detecting starting of the vehicle, and a step of restricting the catalyst warm-up control when starting of the vehicle is detected.

[0017] According to the invention, the control device for securing a booster negative pressure and its control method make it possible to favorably secure the booster negative pressure when catalyst warm-up control is performed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein^:

FIG. 1 is a view schematically showing an ECU IA along with various constituent components of the vehicle;

FIG. 2 is a view schematically showing a principal part of a driving system of the vehicle;

FIG. 3 is a view schematically showing an example of method of detecting the distance traveled when the vehicle starts and detecting starting of the vehicle;

FIG. 4 is a view showing a flowchart illustrating a process performed by the ECU IA;

FIG. 5 is a view showing a flowchart illustrating a process performed by an ECU IB;

FIG. 6 is a view schematically showing an ECU 1C along with various constituent components of the vehicle;

FIG. 7 is a view schematically showing the internal structure of an ejector!

FIG. 8 is a view showing a flowchart illustrating a process performed by the ECU 1C;

FIG. 9 is a view showing a flowchart illustrating a process performed by an ECU ID. DETAILED DESCRIPTION OF EMBODIMENTS

[0019] The best mode for implementing the invention will be described in detail with reference to the drawings.

[0020] Referring to FIG. 1 through FIG. 4, a first embodiment of the invention will be described. FIG. 1 schematically shows a control device, in the form of an ECU (Electronic Control Unit) IA, for securing a booster negative pressure according to the present embodiment, along with constituent components of the vehicle. The constituent components, including an internal combustion engine 50, as shown in FIG. 1 are installed on the vehicle (not shown). An intake system 10 of the engine 50 has an air cleaner 11, air flow meter 12, electrically operated throttle 13, intake manifold 14, intake port 52a that communicates with a combustion chamber N, intake pipes 15a, 15b disposed as needed between these components, and so forth. The air cleaner 11 is arranged to filter intake air supplied to each cylinder of the engine 50, and communicates with the atmosphere via an air duct (not shown). The air flow meter 12, which serves to measure the amount of intake air, produces an output signal responsive to the amount of intake air.

, [0021] The electrically operated throttle 13 consists principally of a throttle valve 13a, a throttle body 13b, a valve stem 13c, and an electric motor 13d. The throttle valve 13a is arranged to control the overall flow rate of intake air supplied to the respective cylinders of the engine 50 by changing its opening. The throttle body 13b is in the form of a cylindrical member in which an intake passage is formed, and supports the valve stem 13c of the throttle valve 13a disposed in the intake passage. The electric motor 13d provided by, for example, a stepping motor is adapted to change the opening of the throttle valve 13a under control of the ECU IA. The electric motor 13d is fixed to the throttle body 13b, and the output shaft (not shown) of the motor 13d is coupled to the valve stem 13c. The ECU IA detects the opening of the throttle valve 13a, based on an output signal received from a throttle angle sensor (not shown) incorporated in the electrically operated throttle 13. The intake manifold 14 has a single intake passage at the upstream side thereof, and branch passages corresponding to the respective cylinders of the engine 50 at the downstream side, such that the branch passages branch off from the single intake passage. The intake manifold 14 serves to distribute intake air to the respective cylinders of the engine 50.

[0022] A brake system 20 includes a brake pedal 21, a brake booster 22, a master cylinder 23, a brake switch 24, a check valve 25 and wheel cylinders (not shown). The vehicle operator or driver operates the brake pedal 21 so as to restrict or inhibit rotation of the wheels. The brake pedal 21 is coupled to an input rod (not shown) of the brake booster 22. The brake booster 22 is arranged to produce assist force at a certain ratio with respect to the pedal effort so as to boost the force applied to the master cylinder 23. A vacuum chamber (not shown) defined in the brake booster 22 at one side close to the master cylinder 23 communicates with the intake passage of the intake manifold 14 via the check valve 25 and an air hose H. With this arrangement, a negative pressure of the intake system 10, more specifically, a negative pressure of the intake manifold 14 (which will also be called "intake -manifold negative pressure") in this embodiment, is supplied to the brake booster 22.

[0023] The brake booster 22 further includes an output rod (not shown) coupled to an input shaft (not shown) of the master cylinder 23. In operation, the master cylinder 23 produces a hydraulic pressure in accordance with the force applied from the brake booster 22, namely, the force obtained by adding the assist force to the pedal effort. The master cylinder 23 is connected to the respective wheel cylinders provided in disc brake mechanisms (not shown) of respective wheels via a hydraulic circuit, and each of the wheel cylinders produces braking force in response to the hydraulic pressure supplied from the master cylinder 23. In a hydraulic system of the brake system 20, there is provided a hydraulic pressure sensor 72 capable of detecting an increase in the hydraulic pressure responsive to a braking operation by the driver. The brake switch 24 is arranged to detect depression of the brake pedal 21 and produce an ON/OFF signal based on the result of the detection, and the check valve 25 is arranged to prevent reverse flow of air. It is to be understood that the brake booster 22 is not limited to any particular type but may be of a generally known type, provided that it is of a vacuum servo type.

[0024] The internal combustion engine 50 includes a cylinder block 51, cylinder head 52, piston 53, intake valve 54, exhaust valve 55, connecting rod 56, crankshaft 57, and so forth. The combustion chamber N is formed as a space defined or surrounded by the cylinder block 51, cylinder head 52 and the piston 53. The intake port 52a and exhaust port 52b, which communicate with the combustion chamber N, are formed in the cylinder head 52. Also, the intake valve 54 for opening and closing the intake port 52a and the exhaust valve 55 for opening and closing the exhaust port 52b are respectively mounted in the cylinder head 52. The reciprocating motion of the piston 53 is converted into rotary motion of the crankshaft 57 via the connecting rod 56. The engine 50 is provided with a crank angle sensor 41 for detecting the engine speed NE, a water temperature sensor 42 for detecting the water or coolant temperature, and various other sensors.

[0025] The internal combustion engine 50 is also provided with an air-conditioner compressor 58. The air-conditioner compressor 58 has a drive shaft whose pulley is coupled to a pulley of an output shaft of the engine 50 via a belt. In addition to the air-conditioner compressor 58 as an accessory machine, pulleys of a power- steering pump and a generator (not shown), for example, are also coupled to the pulley of the output shaft of the engine 50. The drive shaft of the air-conditioner compressor 58 is provided with an electromagnetic clutch (not shown). The electromagnetic clutch is engaged or disengaged under control of the ECU IA, depending upon the ON/OFF state of an air-conditioner switch 71 and the automatic temperature control function of the air conditioner, thereby to drive or stop the air-conditioner compressor 58.

[0026] An exhaust system 60 of the engine 50 includes an exhaust manifold 61, three-way catalyst 62, muffler (not shown), exhaust pipes disposed as needed between these constituent components, and so forth. The exhaust manifold 61 is arranged to combine exhaust streams from the respective cylinders into a single stream, and has exhaust branch passages corresponding to the respective cylinders at the upstream side thereof, and a single exhaust passage at the downstream side thereof, such that the branch passages join into the single exhaust passage. The three-way catalyst 62 serves to clean exhaust gas by oxidizing hydrocarbon (HC) and carbon monoxide (CO) and reducing nitrogen oxides (NOx). In the exhaust system 60, an A/F sensor 63 for linearly detecting the air-fuel ratio based on the concentration of oxygen in the exhaust gas is disposed upstream of the three-way catalyst 62, and an oxygen sensor 64 for determining whether the air-fuel ratio is richer or leaner than the stoichiometric ratio based on the concentration of oxygen in the exhaust gas is disposed downstream of the three-way catalyst 62.

[0027] The ECU IA includes a microcomputer (not shown) that consists principally of CPU (Central Processing Unit), ROM (Read-Only Memory) and RAM (Random Access Memory), input and output circuits, and so forth. The ECU IA is configured to mainly control the engine 50, and also controls the electrically operated throttle 13 and the air-conditioner compressor 58 in this embodiment. Various objects to be controlled, as well as the electrically operated throttle 13 and the air-conditioner compressor 58, are connected to the ECU IA via drive circuits (not shown). To the ECU IA are also connected various switches and sensors, such as the throttle angle sensor, crank angle sensor 41, water temperature sensor 42, brake switch 24, air-conditioner switch 71, hydraulic pressure sensor 72 and a range switch 73.

[0028] The ROM stores programs in which various processes to be executed by the CPU are described. In the present embodiment, the ROM stores programs for controlling the engine 50, a program for performing catalyst warm-up control, a program for detecting the distance traveled when the vehicle starts, a program for detecting starting of the vehicle, a program for inhibiting catalyst warm-up control, etc. It is, however, to be understood that these programs may be combined as a single program. The program for detecting starting of the vehicle is created so as to detect starting of the vehicle based on the distance traveled when the vehicle starts. More specifically, the program is created so as to detect starting of the vehicle when determining that the distance traveled when the vehicle starts becomes larger than a predetermined value L. The program for inhibiting catalyst warm-up control is created so as to inhibit catalyst warm-up control specifically when starting of the vehicle is detected. In the present embodiment, the microcomputer and the above-mentioned programs provide various controllers, detecting units, determining units and others. In particular, the microcomputer and the program for detecting starting of the vehicle provide the above-indicated vehicle start detecting unit, and the microcomputer and the program for inhibiting catalyst warm-up control provide a catalyst warm-up control inhibiting unit.

[0029] Next, a method of detecting the distance traveled when the vehicle starts and detecting starting of the vehicle will be described in detail. FIG. 2 schematically shows a principal part of the driving system or power train of the vehicle. The driving system of the vehicle includes an automatic transmission (hereinafter referred to as "AT") 80 and a differential gear device 90. The AT 80 is coupled to the engine 50, and includes a torque converter 81 that functions as a fluid coupling, a clutch 82 that permits switching between power transmission and power cutoff, and a gear train 83 that transmits power at a certain gear ratio. A first pulse gear 85 is mounted on an input shaft 84 that couples the torque converter 81 with the clutch 82, and a turbine speed sensor 86 for detecting teeth formed on the first pulse gear 85 is mounted in the AT 80. Also, a second pulse gear 88 is mounted on an output shaft 87 of the gear train 83, and an output speed sensor 89 for detecting teeth formed on the second pulse gear 88 is mounted in the AT 80. [0030] The differential gear device 90 serves to transmit power received from the AT 80 to left and right wheels 92, respectively, and the wheels 92 are connected to the differential gear device 90 via suspensions (not shown) and shafts 91. An ABS rotor (not shown) that rotates with the corresponding wheel 92 and an ABS sensor 93 that detects teeth formed on the ABS rotor are mounted on each of the suspensions. The vehicle is also provided with an ECU (not shown) for the transmission, and the above-mentioned range switch 73 for detecting the range to which the shift lever is operated by the driver is connected to the transmission ECU. With this arrangement, the ECU IA may indirectly detect the output of the range switch 73 via the transmission ECU.

[0031] FIG. 3 schematically shows an example of method of detecting the distance traveled when the vehicle starts and detecting starting of the vehicle. FIG. 3 shows the respective conditions or states of the throttle, catalyst warm-up control, sensor output, counter and the vehicle speed. In this figure, the condition of the throttle indicates whether the engine 50 is running at idle or not, and the condition of the catalyst warm-up control indicates whether the catalyst warm-up control is inhibited or not. The state of the sensor output indicates the state of the output of the turbine speed sensor 86 or output speed sensor 89 or ABS sensor 93. The state of the counter indicates the number of counts made by the counter based on pulses of the sensor output, and the counter is implemented based on the program for detecting the distance traveled. In the present embodiment, the program for detecting the distance traveled is created so that the counter counts once each time the sensor output provides two pulses as one set. The program for detecting the distance traveled is further created so as to detect or determine the distance traveled when the vehicle starts, based on the number of counts made by the counter and data of the distance traveled upon start of the vehicle each time one tooth is detected (i.e., each time one pulse is generated). The data of the distance traveled for each pulse when the vehicle starts is stored in advance in the ROM. The distance traveled for each pulse when the vehicle starts is different from vehicle to vehicle, depending upon, for example, the gear ratio and tire radius set for the AT 80 and differential gear device 90.

[0032] In the example shown in FIG. 3, the sensor output represents the output of the ABS sensor 93. In the vehicle of this embodiment, where the output of the ABS sensor 93 provides the sensor output, the distance traveled when the vehicle starts increases by 42 mm for each pulse (i.e., each time one pulse is produced). Therefore, if the number of counts is three, namely, the counter counts three times, for example, the distance traveled when the vehicle starts is determined as 252 mm, according to the program for detecting the distance traveled. In the meantime, in the example shown in FIG. 3, the predetermined value L used for detecting starting of the vehicle is set to 250 mm. In this example, therefore, when the counter counts three times, the distance traveled upon start of the vehicle becomes larger than the predetermined value L (250 mm in this example), which means that starting of the vehicle is detected when the number of counts reaches three. As a result, the catalyst warm-up control is inhibited, and the throttle is brought into a condition where the engine 50 is not running at idle.

[0033] While the example of FIG. 3 is concerned with the case where the sensor output is provided by the output of the ABS sensor 93, the invention is not limited to this case, but the sensor output may be, for example, the output of the turbine speed sensor 86 or the output speed sensor 89. In the vehicle of this embodiment, for example, where the output of the turbine speed sensor 86 provides the sensor output, the distance traveled when the vehicle starts increases by 4 mm for each pulse (i.e., each time one pulse is produced). In the case where the output of the output speed sensor 89 provides the sensor output, the distance traveled when the vehicle starts increases by 8 mm for each pulse. In these cases, starting of the vehicle can be detected while the distance traveled when the vehicle starts is relatively small, provided that the ROM stores corresponding data concerning the distance traveled for each pulse. [0034] Since the distance traveled for each pulse when the vehicle starts can be acquired in advance, starting of the vehicle may be detected based on the number of counts during starting (or the number of pulses of the sensor output), rather than the distance calculated from the number of counts during starting. Namely, since the distance traveled when the vehicle starts is the result of conversion of the number of counts during starting into distance, detection of starting of the vehicle based on the number of counts (or the number of pulses of the sensor output) has the same meaning as detection of starting of the vehicle based on the distance traveled when the vehicle starts. Thus, the modified example where the number of counts or the number of pulses of the sensor output is used for detecting starting of the vehicle is covered by the present invention.

[0035] It is also possible to detect starting of the vehicle based on the vehicle speed. In this case, starting of the vehicle can be detected when the vehicle speed is found to be not equal to zero. It is, however, to be noted that the vehicle speed may be detected based on the output of the output speed sensor 89, more specifically, based on an average value of the number of counts within a predetermined period of time, and that an extremely low vehicle speed upon start of the vehicle is masked in view of the noise tolerance of the sensor. In the case where the vehicle speed is employed, therefore, the initial value of the vehicle speed during starting of the vehicle is equal to 0, as shown in FIG. 3, and thus detection of starting of the vehicle is delayed as compared with the case where starting of the vehicle is detected based on the distance traveled when the vehicle starts. As the detection of starting of the vehicle is delayed, a delay may arise in securing a sufficiently large booster negative pressure at the time when the vehicle starts. Thus, starting of the vehicle can be detected with higher accuracy based on the distance traveled when the vehicle starts, rather than the vehicle speed.

[0036] Next, a process performed by the ECU IA according to the present embodiment will be described in detail, using the flowchart shown in FIG. 4. The CPU executes step SlI to determine whether the engine 50 is running at idle ("IDLE ON" in FIG. 3). If a negative decision (NO) is made in step SIl, no particular process is required in this embodiment, and therefore, the CPU once finishes the current cycle of the routine, and returns to step SlI to re-start the same routine. If an affirmative decision (YES) is made in step SIl, on the other hand, the CPU executes step S 12 to determine whether the amount by which the ignition timing is retarded under catalyst warm-up control (which will be called "catalyst warm-up retard amount") is larger than a predetermined value α. In this step, the CPU determines whether the catalyst warm-up control is being performed, and also determines whether the catalyst warm-up control causes the intake-manifold negative pressure to become smaller than a predetermined value, by determining whether the catalyst warm-up retard amount is larger than the predetermined value α. Alternatively, the CPU may determine in step S12 whether the intake air amount, for example, in place of or in addition to the catalyst warm-up retard amount, is larger than a predetermined value.

[0037] If a negative decision (NO) is made in step S12, it is determined that a sufficiently large booster negative pressure can be surely established in the brake booster 22. In this case, the CPU finishes the current cycle of the routine, and then returns to step SlI. If the catalyst warm-up control is performed at this time, the same control continues to be performed, thus assuring early activation of the catalyst. If an affirmative decision (YES) is made in step S12, on the other hand, the CPU executes step S13 to determine whether the distance traveled when the vehicle starts is larger than the predetermined value L. If a negative decision (NO) is made in step S13, no particular process is performed, and the CPU finishes the current cycle of the routine and returns to step SlI. In this case, the catalyst warm-up control continues to be performed, thus assuring early activation of the catalyst. If an affirmative decision (YES) is made in step S13, on the other hand, starting of the vehicle is detected, and the CPU carries out a process for inhibiting the catalyst warm-up control in step S14. With this control, the intake-manifold negative pressure is increased, and therefore, a sufficiently large booster negative pressure can be secured.

[0038] The ROM may store a program for restricting catalyst warm-up control, instead of the program for inhibiting catalyst warm-up control. The program for restricting catalyst warm-up control is created so as to restrict catalyst warm-up control when starting of the vehicle is detected. In this case, the catalyst warm-up control is restricted rather than inhibited in step S14. More specifically, in step S14, a process for reducing the catalyst warm-up retard amount or a process for controlling the throttle valve 13a toward the closed position (i.e., reducing the opening of the throttle valve 13a) is carried out in order to increase the intake-manifold negative pressure by a degree large enough to secure a sufficiently large booster negative pressure. In this case, since the catalyst warm-up control is not completely inhibited, it is possible to secure a sufficiently large booster negative pressure while at the same time avoiding or reducing a delay in the activation of the catalyst. Thus, the above-indicated catalyst warm-up control restricting unit is provided by, for example, the microcomputer and the program for restricting catalyst warm-up control.

[0039] In step S 14, a process for reducing the load applied to the engine 50 may be carried out in place of or in addition to the process for inhibiting or restricting catalyst warm-up control. More specifically, if the operation of, for example, the air conditioner and/or other accessories is stopped or restricted, the engine 50 is not required to produce torque for dealing with the load applied, and therefore, the throttle valve 13a is controlled toward the closed position by a degree proportional to the reduced torque. As a result, the intake-manifold negative pressure is increased. Thus, if the process for reducing the load applied to the engine 50 is carried out in step S 14, it is possible to secure a sufficiently large booster negative pressure without inhibiting or significantly restricting the catalyst warm-up control. Thus, a sufficiently large booster pressure and early activation of the catalyst can be both favorably achieved.

[0040] There are known a technology for inhibiting or restricting catalyst warm-up control when the booster negative pressure, which is directly detected by a negative pressure sensor, is reduced, and a technology for inhibiting or restricting catalyst warm-up control when the booster negative pressure, which is estimated based on the number of braking operations, is reduced. In the present embodiment, on the other hand, catalyst warm-up control is inhibited or restricted when starting of the vehicle is detected, so that a sufficiently large booster negative pressure can be secured with reliability in preparation for subsequent braking operation. Furthermore, the catalyst warm-up control is not particularly inhibited or restricted when the engine 50 is running at idle, thus favorably assuring early activation of the catalyst in the idling condition. Moreover, starting of the vehicle can be detected by using sensors, such as the turbine speed sensor 86, output speed sensor 89 and the ABS sensor 93, which are conventionally installed for other purposes. This makes the construction of the vehicle advantageous in terms of cost, as compared with the case where a negative pressure sensor, or the like, is newly provided for detecting the booster negative pressure as in the known technology. In the manner as described above, the ECU IA is implemented which is able to favorably secure the booster negative pressure when catalyst warm-up control is performed.

[0041] A second embodiment of the invention will be described. An ECU IB according to this embodiment is identical with the ECU IA of the first embodiment except that the program for inhibiting catalyst warm-up control is created so as to inhibit catalyst warm-up control under a further condition that the AT 80 is shifted to the D range. In this embodiment, the microcomputer and this program for inhibiting catalyst warm-up control provide the catalyst warm-up control inhibiting unit. The vehicle in which the ECU IB is installed is identical with the vehicle of the first embodiment except that the vehicle includes the ECU IB in place of the ECU IA.

[0042] Next, a process performed by the ECU IB according to the second embodiment will be described in detail using the flowchart shown in FIG. 5. The flowchart of FIG. 5 is identical with the flowchart shown in FIG. 4, except that step S21 is added between step S12 and step S13. In this embodiment, therefore, step S21 will be particularly explained in detail. If an affirmative decision (YES) is made in step S12, the CPU determines in step S21 whether the AT 80 is shifted to the D range. If a negative decision (NO) is made in step S21, the CPU returns to step SIl. If an affirmative decision (YES) is made in step S21, on the other hand, the CPU proceeds to step S13. Namely, in this embodiment, the catalyst warm-up control is inhibited only when the AT 80 is shifted to the D range. In the presence of the additional condition (step S21), the catalyst warm-up control is not inhibited when the shift lever is placed in, for example, the N range, thus assuring early activation of the catalyst. This is because the intake -manifold negative pressure is larger when the shift lever is in the N range, than that developed when the shift lever is in the D range, thus making it possible to secure a sufficiently large booster negative pressure.

[0043] As in the case of the first embodiment, the ROM may store a program for restricting catalyst warm-up control when starting of the vehicle is detected and, furthermore, the AT 80 is shifted to the D range, instead of the program for inhibiting catalyst warm-up control. In this case, the catalyst warm-up control is restricted in step S14. Thus, the catalyst warm-up control restricting unit is provided by, for example, the microcomputer and the program for restricting catalyst warm-up control. Also, as in the case of the first embodiment, a process for reducing the load applied to the engine 50 may be carried out in step S 14, in place of or in addition to the process for inhibiting or restricting catalyst warm-up control. In the manner as described above, the ECU IB is implemented which is able to favorably secure the booster negative pressure when the catalyst warm-up control is performed.

[0044] A third embodiment of the invention will be described. An ECU 1C according to this embodiment is identical with the ECU IA of the first embodiment, except that the ROM further stores a program for detecting an abnormality in a negative-pressure boosting device 30, and that the program for inhibiting catalyst warm-up control is created so as to inhibit catalyst warm-up control under a. further condition that an abnormality is detected in the negative-pressure boosting device 30. In this embodiment, the microcomputer and the program for detecting an abnormality in the boosting device provide the boosting device abnormality detecting unit, and the microcomputer and the program for inhibiting catalyst warm-up control provide the catalyst warm-up control inhibiting unit. Also, the vehicle in which the ECU 1C is installed is identical with the vehicle of the first embodiment, except that the vehicle includes the ECU 1C in place of the ECU IA and that the vehicle further includes the negative-pressure boosting device 30.

[0045] FIG. 6 schematically shows the ECU 1C along with various constituent components of the vehicle. In the present embodiment, the vehicle further includes the negative-pressure boosting device 30. The negative-pressure boosting device 30 has an ejector 31 and a vacuum switching valve VSV 32. The ejector 31 is arranged to produce a negative pressure that is further larger than the intake-manifold negative pressure, and supply the produced negative pressure to the brake booster 22. The ejector 31 has an inflow port 31a, an outflow port 31b, and a vacuum supply port 31c. Of these ports, the vacuum supply port 31c is connected via the check valve 25 to the vacuum chamber of the brake booster 22 with an air hose Hc. The inflow port 31a is connected to the intake pipe 15a via an air hose Ha, and the outflow port 31b is connected to the intake manifold 14 via an air hose Hb, such that the electrically operated throttle 13, more specifically, the throttle valve 13a, is interposed between the joint of the air hose Ha with the intake pipe 15a and the joint of the air hose Hb with the intake manifold 14. With this arrangement, the air hose Ha and the air hose Hb cooperate to form a bypass B that bypasses the electrically operated throttle 13, such that the ejector 31 is included in the bypass B. When the ejector 31 is not in operation, a negative pressure is supplied from the intake passage of the intake manifold 14 to the vacuum chamber of the brake booster 22, via the air hose Hb, the outflow port 31b and vacuum supply port 31c of the ejector 31, and the air hose Hc.

[0046] The above-mentioned VSV 32 is placed in the air hose Ha. The VSV 32 is arranged to permit air to flow through the bypass B or inhibit air from flowing through the bypass B under control of the ECU 1C. In this embodiment, a normally-closed solenoid valve having two positions and two ports is employed as the VSV 32. It is, however, to be understood that the VSV 32 is not limited to this type of valve, but may be selected from other appropriate solenoid valves, or may be in the form of a flow control valve capable of controlling the degree of closure of a channel formed therein, for example. The VSV 32 is arranged to bring the ejector 31 into operation or stop operation of the ejector 31, by permitting intake air to flow through the bypass B or inhibiting intake air from flowing through the bypass B, respectively. The VSV 32 is also connected to the ECU 1C. It is, however, not necessary to provide the negative-pressure boosting device 30 with the VSV 32. In the absence of the VSV 32, the ejector 31 is always in operation during operation of the engine 50.

[0047] FIG. 7 schematically shows the internal structure of the ejector 31. The ejector 31 incorporates a diffuser 33. The diffuser 33 consists of a tapered portion 33a, a reversely tapered portion 33b, and a vacuum delivery portion 33c as a passage that communicates with the tapered portion 33a and the reversely tapered portion 33b. The tapered portion 33a is open to and is opposed to the inflow port 31a, and the reversely tapered portion 33b is open to and is opposed to the outflow port 31b. The vacuum delivery portion 33c communicates with the vacuum supply port 31c. A nozzle 34 is provided in the inflow port 31a for sending a blast of incoming intake air into the tapered portion 33a, and the blast of intake air delivered from the nozzle 34 passes through the diffuser 33, and flows out into the air hose Hb through the outflow port 31b. At this time, a high-speed jet stream of air is produced in the diffuser 33, whereby a large negative pressure develops in the vacuum delivery portion 33c due to a venturi effect, and the negative pressure thus produced is supplied from the vacuum supply port 31c to the vacuum chamber via the air hose Hc. Thus, owing to the function of the ejector 31, the brake booster 22 is supplied with a larger negative pressure than the negative pressure that would be otherwise received from the intake manifold 14. Check valves 35 for preventing reverse flow are provided in an internal channel between the vacuum delivery portion 33c and the vacuum supply port 31c, and in an internal channel between the outflow port 31b and the vacuum supply port 31c. The internal structure of the ejector 31 is not limited to that as shown in FIG. 7, but an ejector having a different internal structure may be employed in place of the ejector 31.

[0048] With the above-described arrangement, a process performed by the ECU 1C according to the third embodiment will be described in detail using the flowchart shown in FIG. 8. The flowchart shown in FIG. 8 is identical with the flowchart shown in FIG. 4, except that step S22 is added between step S 12 and step S13. In this embodiment, therefore, step S22 will be particularly explained in detail. If an affirmative decision (YES) is made in step S 12, the CPU determines in step S22 whether an abnormality of the negative-pressure boosting device 30 is detected. Examples of abnormalities of the negative-pressure boosting device 30 include, for example, clogging of an internal channel of the ejector 31, a malfunction of the VSV 32, clogging, hole formation, disconnection or detachment found in its portion ranging from the air hose Ha to the air hose Hc. These abnormalities may be detected by appropriate methods. If a negative decision (NO) is made in step S22, the CPU returns to step SlI.

[0049] If an affirmative decision (YES) is made in step S22, on the other hand, the CPU proceeds to step S13. Namely, in this embodiment, the catalyst warm-up control is inhibited only when an abnormality of the negative-pressure boosting device 30 is detected. Thus, the catalyst warm-up control is not inhibited when the negative -pressure boosting device 30 operates normally, and therefore, early activation of the catalyst can be achieved. This is because the negative-pressure boosting device 30, when operating normally, is able to supply the brake booster 22 with a negative pressure that is larger than the intake-manifold negative pressure, thus assuring a sufficiently large booster negative pressure.

[0050] As in the case of the first embodiment, the ROM may store a program for restricting catalyst warm-up control when starting of the vehicle is detected and, furthermore, an abnormality of the negative-pressure boosting device 30 is detected, instead of the program for inhibiting catalyst warm-up control. In this case, the catalyst warm-up control is restricted in step S14. Thus, the microcomputer and the program for restricting catalyst warm-up control provide the catalyst warm-up control restricting unit. Also, as in the case of the first embodiment, a process for reducing the load applied to the engine 50 may be carried out in step S14, in place of or in addition to the process for inhibiting or restricting catalyst warm-up control. In the manner as described above, the ECU 1C is implemented which is able to favorably secure the booster negative pressure when the catalyst warm-up control is performed.

[0051] A fourth embodiment of the invention will be described. An ECU ID according to this embodiment is identical with the ECU IA of the first embodiment except that the ROM further stores a program for counting the number of braking operations, and that the program for inhibiting catalyst warm-up control is created so as to inhibit catalyst warm-up control under a further condition that the number of braking operations counted before detection of starting of the vehicle is larger than a predetermined number. In the present embodiment, the microcomputer and the program for counting the number of braking operations provide the braking operation counting unit, and the microcomputer and the program for inhibiting catalyst warm-up control provide the catalyst warm-up control inhibiting unit. Also, the vehicle in which the ECU ID is installed is identical with the vehicle of the first embodiment except that the vehicle includes the ECU ID in place of the ECU IA.

[0052] Next, a process performed by the ECU ID according to the fourth embodiment will be described in detail with reference to the flowchart shown FIG. 9. The flowchart shown in FIG. 9 is identical with the flowchart shown in FIG. 4 except that step S23 is added between step S13 and step S14. In this embodiment, therefore, step S23 will be particularly described in detail. If an affirmative decision (YES) is made in step S13, the CPU determines in step S23 whether the number of braking operations counted is larger than the predetermined number. The braking operations may be detected based on, for example, the output of the brake switch 24 or hydraulic pressure sensor 72. If a negative decision (NO) is made in step S23, the CPU returns to step SIl.

[0053] If an affirmative decision (YES) is made in step S23, on the other hand, the CPU proceeds to step S 14. Namely, in the present embodiment, the catalyst warm-up control is inhibited only when the number of braking operations counted before detection of starting of the vehicle is larger than the predetermined number. Thus, the catalyst warm-up control is not inhibited when the number of braking operations counted is not larger than the predetermined number, and therefore, early activation of the catalyst can be achieved. This is because a sufficiently large booster negative pressure is accumulated in the brake booster 22 when the number of braking operations counted is not larger than the predetermined number, and there is no need to trade off (i.e., inhibit) catalyst warm-up control for the securing of the booster negative pressure.

[0054] As in the case of the first embodiment, the ROM may store a program for restricting catalyst warm-up control when starting of the vehicle is detected, and, furthermore, the number of braking operations counted before detection of starting of the vehicle is larger than the predetermined number, instead of the program for inhibiting catalyst warm-up control. In this case, the catalyst warm-up control is restricted in step S 14. Thus, the catalyst warm-up control restricting unit is provided by, for example, the microcomputer and the above-described program for restricting catalyst warm-up control. Also, as in the case of the first embodiment, a process for reducing the load applied to the engine 50 may be carried out in step S 14, in place of or in addition to the process for inhibiting or restricting catalyst warm-up control. In the manner as described above, the ECU ID is implemented which is able to favorably secure the booster negative pressure when the catalyst warm-up control is performed.

[0055] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. On the other hand, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

CLAIMS:

1. A control device for securing a booster negative pressure used when catalyst warm-up control is performed, in a vehicle including a brake booster to which a negative pressure is supplied from an intake passage in an intake system of an internal combustion engine, comprising: a vehicle start detecting unit that detects starting of the vehicle; and a catalyst warm-up control restricting unit that restricts the catalyst warm-up control, wherein the catalyst warm-up control restricting unit restricts the catalyst warm-up control when the vehicle start detecting unit detects starting of the vehicle.

2. The control device for securing a booster negative, pressure according to claim 1, wherein the catalyst warm-up control restricting unit inhibits the catalyst warm-up control when the vehicle start detecting unit detects starting of the vehicle.

3. The control device for securing a booster negative pressure according to claim 1 or 2, wherein the catalyst warm-up control comprises retarding an ignition timing of the engine in relation to a normal ignition timing, and increasing an amount of intake air drawn into the engine.

4. The control device for securing a booster negative pressure according to any one of claims 1 to 3, wherein the vehicle start detecting unit detects starting of the vehicle based on a distance traveled when the vehicle starts.

5. The control device for securing a booster negative pressure according to any one of claims 1 to 3, wherein the vehicle start detecting unit detects starting of the vehicle based on a vehicle speed of the vehicle.

6. The control device for securing a booster negative pressure according to any one of claims 1 to 5, wherein the catalyst warm-up control is inhibited or restricted under a further condition that the catalyst warm-up control is performed so that the negative pressure of the intake system becomes smaller than a predetermined value.

7. The control device for securing a booster negative pressure according to any one of claims 1 to 6, wherein^ the vehicle includes an automatic transmission; and the catalyst warm-up control is inhibited or restricted under a further condition that the automatic transmission is shifted to a drive range.

8. The control device for securing a booster negative pressure according to any one of claims 1 to 7, wherein the vehicle further includes a negative-pressure boosting device that supplies the brake booster with a negative pressure that is larger than the negative pressure to be supplied from the intake passage of the intake system.

9. The control device for securing a booster negative pressure according to claim 8, further comprising a boosting device abnormality detecting unit that detects an abnormality of the negative-pressure boosting device, wherein the catalyst warm-up control is inhibited or restricted when the boosting device abnormality detecting unit detects an abnormality of the negative-pressure boosting device.

10. The control device for securing a booster negative pressure according to any one of claims 1 to 9, further comprising a braking operation counting unit that counts the number of braking operations, wherein the catalyst warm-up control is inhibited or restricted under a further condition that the number of braking operations counted by the braking operation counting unit before the vehicle start detecting unit detects starting of the vehicle is larger than a predetermined number.

11. A control method of a control device for securing a booster negative pressure used when catalyst warm-up control is performed, in a vehicle including a brake booster to which a negative pressure is supplied from an intake passage in an intake system of an internal combustion engine, comprising: detecting starting of the vehicle J and restricting the catalyst warm-up control when starting of the vehicle is detected.