JP7708024B2 - Engine Control Unit - Google Patents

Description

The present invention relates to an engine control device.

When the engine speed of a vehicle engine drops below the return speed during fuel cut, a control is known that returns the engine from the fuel cut so that the engine output torque becomes a target torque (see, for example, Patent Document 1).

JP 2017-198311 A

When a fuel cut is in progress, a negative torque acts on the engine in the opposite direction to the direction of engine rotation. The magnitude of the negative torque varies depending on various conditions. For this reason, if the target torque when returning from a fuel cut is set to a uniform value regardless of the magnitude of the negative torque, there will be variation in the difference between the negative torque during a fuel cut and the target torque when returning. As a result, there will also be variation in the shock to the vehicle when returning from a fuel cut, which could reduce drivability.

The present invention aims to provide an engine control device that reduces the variation in shock to the vehicle when returning from a fuel cut.

The above object can be achieved by an engine control device comprising: a return processing unit that returns the engine from a fuel cut when the rotation speed of the engine mounted on a vehicle drops to or below a return rotation speed during a fuel cut of the engine so that the output torque of the engine becomes a target torque; a negative torque calculation unit that calculates a negative torque that acts on the engine during a fuel cut, which is a torque in a direction opposite to the rotation direction of the engine; an addition torque calculation unit that calculates an addition torque that is a torque in the rotation direction of the engine for calculating the target torque; and a target torque calculation unit that calculates the target torque based on a value obtained by adding the addition torque to the negative torque, wherein the addition torque calculation unit calculates the addition torque as a value smaller than the magnitude of the negative torque, the vehicle is mounted with a transmission and a torque converter having a lock-up clutch that transmits the output torque of the engine to the transmission, and the addition torque calculation unit calculates the addition torque when the lock-up clutch is in an engaged state as a smaller value than the addition torque when the lock-up clutch is in a slip state, and calculates the addition torque as a smaller value the lower the gear stage of the transmission.

The recovery processing unit may reduce the amount of retardation of the ignition timing when the engine recovers from a fuel cut as the added torque increases.

The vehicle is equipped with an alternator and an air conditioner compressor that are linked to the rotation of the engine, and the negative torque calculation unit may calculate the negative torque based on the friction torque of the engine, the pumping loss torque of the engine, the load torque of the alternator, and the load torque of the compressor.

The present invention provides an engine control device that reduces the variation in shock to the vehicle when returning from a fuel cut.

FIG. 1 is a schematic diagram of a vehicle. FIG. 2 is a flowchart illustrating the fuel cut recovery control executed by the ECU. FIG. 3A is an example of a map that defines the friction torque of the engine, and FIG. 3B is an example of a map that defines the pumping loss torque of the engine. FIG. 4A is an example of a map that defines the load torque of an alternator, and FIG. 4B is an example of a map that defines the load torque of a compressor. FIG. 5 is an example of a map that defines the additional torque.

[General configuration of the vehicle]
1 is a schematic diagram of a vehicle 1. The vehicle 1 includes an engine 10, a torque converter 20, a lock-up clutch (hereinafter referred to as an LU clutch) 30, a transmission 40, a differential device 50, drive wheels 60, a hydraulic control circuit 70, an alternator 80, a compressor 85, an ECU (Electronic Control Unit) 100, and the like.

The engine 10 is a driving force source for traveling, and is a multi-cylinder gasoline engine, but is not limited to this and may be, for example, a diesel engine. The crankshaft 11, which is the output shaft of the engine 10, is connected to a torque converter 20.

The torque converter 20 includes a pump impeller 21 on the input shaft side, a turbine runner 22 on the output shaft side, a stator 23 that exhibits a torque amplification function, and a one-way clutch 24, and transmits power between the pump impeller 21 and the turbine runner 22 via a fluid. The torque converter 20 is provided with an LU clutch 30. The LU clutch 30 is a single-plate or multiple-plate hydraulic friction clutch that connects the input side and output side of the torque converter 20 directly or in a slip state.

The transmission 40 is a stepped automatic transmission and includes a plurality of hydraulic friction engagement elements and a planetary gear device. In the transmission 40, a plurality of gear stages can be selectively established by selectively engaging the plurality of friction engagement elements. As shown in FIG. 1, the input shaft 41 of the transmission 40 is connected to the turbine shaft 26 of the torque converter 20. The turbine shaft 26 corresponds to the output shaft of the torque converter 20. The output shaft 42 of the transmission 40 is connected to the drive wheels 60 via a differential device 50 or the like.

The engagement and release of the multiple friction engagement elements are controlled according to whether the shift range of the transmission 40 is the parking range, reverse drive range, neutral range, or forward drive range. In the forward drive range, the engagement and release of the multiple friction engagement elements are controlled so that one of the eight forward gear stages is selectively established according to the accelerator opening, vehicle speed, etc. Of the eight forward gear stages, the lowest gear stage with the maximum gear ratio is the first gear stage, and the highest gear stage with the minimum gear ratio is the eighth gear stage. The multiple friction engagement elements are specifically multiple clutches and multiple brakes. Note that the transmission 40 is not limited to an automatic transmission, and may be, for example, a manual transmission. The gear stages that can be established by the transmission 40 are the eight forward gear stages, but are not limited to this, and it is sufficient if multiple gear stages with different gear ratios can be established.

The hydraulic control circuit 70 is a known hydraulic control circuit that uses a mechanical oil pump driven by the engine 10 as a hydraulic supply source, and supplies hydraulic pressure to the torque converter 20, the LU clutch 30, and the transmission 40 to control their respective operations. In addition, hydraulic pressure command values output from the ECU 100 are input to the hydraulic control circuit 70, and the hydraulic pressures supplied to the torque converter 20, the LU clutch 30, and the transmission 40 are controlled based on the hydraulic pressure command values. In addition, the LU clutch 30 is switched to either a released state, a slip state, or an engaged state depending on the hydraulic pressure supplied.

The alternator 80 and the compressor 85 are auxiliary devices of the engine 10 and are linked to the rotation of the engine 10. In detail, the alternator 80 and the compressor 85 are each driven by the rotational force of the crankshaft 11 transmitted through a pulley and a timing belt. The alternator 80 generates induced power in the stator coil by rotating the field coil in an excited state, and converts the induced current into direct current by a rectifier to charge a battery (not shown). The compressor 85 is an air conditioner compressor and is a variable capacity type with an adjustable discharge capacity, for example, a swash plate type (double swash plate type or single swash plate type) in which the inclination of the swash plate that drives the piston is changed to change the piston stroke and thereby change the discharge capacity.

The ECU 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a backup RAM. The ROM stores various control programs and maps that are referenced when the various control programs are executed. The CPU executes calculations based on the various control programs and maps stored in the ROM. The RAM is a memory that temporarily stores the results of calculations by the CPU and data input from each sensor, and the backup RAM is a non-volatile memory that stores data that should be saved when the ignition is off, etc. The CPU, ROM, RAM, and backup RAM functionally realize a recovery processing unit, a negative torque calculation unit, an additive torque calculation unit, and a target torque calculation unit, which will be described in detail later.

Various sensors and switches, such as an intake manifold pressure sensor 90, an engine speed sensor 91, a turbine speed sensor 92, an output shaft speed sensor 93, an accelerator opening sensor 94, a vehicle speed sensor 95, a gear stage sensor 96, an ignition switch 97, and a refrigerant pressure sensor 98, are connected to the ECU 100, and signals from these sensors and switches are input to the ECU 100. The ECU 100 controls the operating state of the engine 10 and the gear stage of the transmission 40 based on the detection results of the various sensors. The ECU 100 is an example of an engine control device that controls the engine 10.

The intake manifold pressure sensor 90 detects the pressure in the intake pipe downstream of the throttle valve of the engine 10. The engine speed sensor 91 detects the rotation speed of the crankshaft 11 (referred to as engine speed). The turbine speed sensor 92 detects the rotation speed of the turbine shaft 26 of the torque converter 20 (referred to as turbine speed). The output shaft speed sensor 93 detects the rotation speed of the output shaft 42 of the transmission 40 (referred to as output shaft speed). The accelerator opening sensor 94 detects the accelerator opening operated by the accelerator pedal. The vehicle speed sensor 95 detects the traveling speed of the vehicle 1. The gear sensor 96 detects the gear established by the transmission 40. The ignition switch 97 detects whether the ignition is on or off. The refrigerant pressure sensor 98 detects the refrigerant pressure of the air conditioner installed in the vehicle 1.

When the accelerator opening becomes zero or below a threshold, the ECU 100 executes a fuel cut to stop the fuel supply to the engine 10. This causes the vehicle 1 to decelerate. If the engine speed drops below the return speed while the accelerator opening remains at zero or below the threshold during fuel cut, the ECU 100 resumes the fuel supply to the engine 10 to drive the engine 10 in order to avoid the engine stalling. Such a return from a fuel cut is called a natural return. Also, if the driver depresses the accelerator pedal during fuel cut and the accelerator opening exceeds the threshold, the ECU 100 resumes the fuel supply to the engine 10 at the driver's request to drive the engine 10. Such a return from a fuel cut is called a forced return.

[Fuel cut recovery control]
FIG. 2 is a flow chart illustrating the fuel cut return control executed by the ECU 100. This control is repeatedly executed at a predetermined cycle while the ignition is on. The ECU 100 judges whether or not the fuel cut is in progress (step S1). If the answer is No in step S1, this control ends. If the answer is Yes in step S1, the ECU 100 judges whether or not there is a natural return request (step S2). If the answer is No in step S2, the ECU 100 judges whether or not there is a forced return request (step S3). If the answer is No in step S3, this control ends. If the answer is Yes in step S3, the ECU 100 calculates a target torque at the time of return based on the accelerator opening degree, etc. (step S4). Next, the ECU 100 executes a return process to resume fuel supply to the engine 10 by controlling the fuel injection amount, intake air amount, ignition timing, etc. so that the output torque of the engine 10 coincides with the target torque (step S8).

If step S2 is Yes, the ECU 100 calculates the negative torque, which is the torque in the opposite direction to the rotation direction of the engine 10 during fuel cut (step S5). Step S5 is an example of a process executed by the negative torque calculation unit. For example, the negative torque is the sum of the friction torque of the engine 10, the pumping loss torque of the engine 10, the load torque of the alternator 80, and the load torque of the compressor 85. All of these torques act in the opposite direction to the rotation direction of the engine 10. The ECU 100 calculates these torques based on the following maps.

Figure 3A is an example of a map that defines the friction torque of the engine 10. Figure 3B is an example of a map that defines the pumping loss torque of the engine 10. Figure 4A is an example of a map that defines the load torque of the alternator 80. Figure 4B is an example of a map that defines the load torque of the compressor 85. These maps are defined in advance based on experimental results and simulation results, and are stored in the ROM of the ECU 100.

As shown in FIG. 3A, the higher the engine speed [rpm] detected by the engine speed sensor 91, the greater the friction torque [N·m]. As shown in FIG. 3B, the lower the intake manifold pressure [Pa] detected by the intake manifold pressure sensor 90, the greater the pumping loss torque [N·m]. As shown in FIG. 4A, the higher the required power generation current [A] for the alternator 80, the greater the load torque [N·m] of the alternator 80. As shown in FIG. 4B, the higher the air conditioner refrigerant pressure [Pa] detected by the refrigerant pressure sensor 98, the greater the load torque [N·m] of the compressor 85. When there is no power generation request for the alternator 80 or when the air conditioner is off, the ECU 100 calculates the load torque of the alternator 80 and the compressor 85 as zero. The ECU 100 calculates the negative torque using the above map.

The pumping loss torque may be calculated based on the intake manifold pressure and the engine speed, and may be increased accordingly. The load torque of the alternator 80 may be calculated based on the required generating current for the alternator 80 and the engine speed, and may be increased accordingly. The load torque of the compressor 85 may be calculated based on the air conditioner refrigerant pressure and the engine speed, and may be increased accordingly. The negative torque may be calculated based on an equation that uses the engine speed, intake manifold pressure, required generating current, refrigerant pressure, etc. as arguments. The detection value of the generating current of the alternator 80 may be used instead of the required generating current. The friction torque of the engine 10, the pumping loss torque of the engine 10, the load torque of the alternator 80, and the load torque of the compressor 85 may be calculated by known methods.

Next, the ECU 100 calculates an additional torque for calculating the target torque (step S6). Step S6 is an example of a process executed by the additional torque calculation unit. FIG. 5 is an example of a map that specifies the additional torque. As shown in FIG. 5, the additional torque decreases as the gear stage becomes lower. This is because the shock to the vehicle 1 caused by the increase in output torque of the engine 10 upon recovery is greater at lower gear stages. Also, the additional torque is smaller when the LU clutch 30 is engaged than when the LU clutch 30 is in a slipping state. This is because the shock to the vehicle 1 caused by the increase in output torque of the engine 10 upon recovery is greater when the LU clutch 30 is engaged than when it is in a slipping state.

The gear position can be detected by the gear position sensor 96. The state of the LU clutch 30 can be determined by the differential rotation speed between the engine rotation speed and the turbine rotation speed. For example, when this differential rotation speed is equal to or less than a threshold value, the engine rotation speed and the turbine rotation speed are considered to be substantially constant, and the LU clutch 30 can be determined to be in an engaged state. When the differential rotation speed is within a predetermined range greater than the threshold value, the engine rotation speed and the turbine rotation speed are considered not to match, and the LU clutch 30 can be determined to be in a slipping state. The state of the LU clutch 30 may be detected by other known methods. For example, the state of the LU clutch 30 may be determined based on the detection value of a hydraulic sensor that detects the hydraulic pressure supplied to the LU clutch 30.

Here, the magnitude of the added torque is calculated to be smaller than the magnitude of the calculated negative torque. In other words, the maximum value of the added torque is set to a value smaller than the minimum value of the negative torque.

Next, ECU 100 calculates the target torque by adding the additional torque to the negative torque (step S7). Step S7 is an example of a process executed by the target torque calculation unit. As described above, the magnitude of the additional torque is smaller than the magnitude of the calculated negative torque. Therefore, the target torque is calculated as a negative value. Next, ECU 100 executes a return process according to the target torque calculated as described above (step S8). Step S8 is an example of a process executed by the return processing unit. This makes it possible to suppress shock to vehicle 1 at the time of return compared to when the target torque at the time of return from fuel cut is calculated as a positive value.

In addition, in the return process when a natural return request is made, the ECU 100 reduces the amount of retardation of the ignition timing of the engine 10 as the added torque increases. In particular, when the added torque is equal to or less than a predetermined value, the amount of retardation of the ignition timing of the engine 10 decreases as the added torque increases. This ensures the magnitude of the added torque and suppresses deterioration of fuel economy due to retardation of the ignition timing. The amount of retardation of the ignition timing is the amount of retardation from a predetermined ignition timing, for example, from the MBT (Minimum advance for the Best Torque) ignition timing.

As described above, the target torque at the time of natural recovery is calculated by adding a predetermined additional torque to the negative torque during fuel cut. This makes it possible to keep the difference between the negative torque during fuel cut and the target torque at the time of natural recovery constant, and also suppresses variation in the shock to the vehicle 1 at the time of recovery.

In the above embodiment, the sum of the friction torque of the engine 10, the pumping loss torque of the engine 10, the load torque of the alternator 80, and the load torque of the compressor 85 is calculated as the negative torque, but this is not limited to the above. For example, the sum of the friction torque and the pumping loss torque may be calculated as the negative torque. Even if the load torque of the alternator 80 and the compressor 85 is excluded from the negative torque, by calculating the target torque based on the negative torque including the friction torque and the pumping loss torque, the occurrence of shock at the time of return from fuel cut can be suppressed more than when the target torque is set uniformly regardless of the magnitude of the negative torque.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 1 vehicle 10 engine 20 torque converter 30 lock-up clutch 40 transmission 80 alternator 85 compressor 100 ECU (engine control device, recovery processing unit, negative torque calculation unit, additional torque calculation unit, target torque calculation unit)

Claims (3)

a return processing unit that returns the engine from the fuel cut so that an output torque of the engine becomes a target torque when a rotation speed of the engine falls to a return rotation speed or lower during a fuel cut of the engine mounted on a vehicle;
a negative torque calculation unit that calculates a negative torque that acts on the engine during a fuel cut and that acts in a direction opposite to a rotation direction of the engine;
an additional torque calculation unit that calculates an additional torque, which is a torque in a rotational direction of the engine, for calculating the target torque;
a target torque calculation unit that calculates the target torque based on a value obtained by adding the additional torque to the negative torque ,
the additional torque calculation unit calculates the additional torque as a value smaller than the magnitude of the negative torque,
The vehicle is equipped with a transmission and a torque converter having a lock-up clutch that transmits output torque of the engine to the transmission,
the additional torque calculation unit calculates the additional torque when the lock-up clutch is engaged as a smaller value than the additional torque when the lock-up clutch is in a slipping state, and calculates the additional torque as a smaller value the lower the gear stage of the transmission. 2. The engine control device according to claim 1 , wherein the return processing unit reduces an amount of retardation of the ignition timing when the engine returns from a fuel cut as the additional torque increases. The vehicle is equipped with an alternator that is linked to the rotation of the engine and an air conditioner compressor,
3. The engine control device according to claim 2 , wherein the negative torque calculation unit calculates the negative torque based on a friction torque of the engine, a pumping loss torque of the engine, a load torque of the alternator, and a load torque of the compressor.