Vehicle engine control device

Abstract

To provide an engine control system 50 performing fuel cut (F / C) during execution of cruise control of a vehicle 10 in which F / C prohibition area to prevent control hunting is narrowed down as much as possible to improve fuel consumption and man hour configuring lower limit of the F / C prohibition area is reduced.SOLUTION: An engine control system of a vehicle performs F / C when request driving power higher than an availability lower limit goes below the availability lower limit during execution of cruise control and stores actual driving force during execution of the fuel cut. When the request driving power is, after storing the actual driving force during execution of F / C, between the stored actual driving force and the availability lower limit, the execution of F / C is prohibited. When the request driving force goes below the actual driving force or goes below the availability lower limit, the prohibition of execution of F / C is cancelled.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine control device for a vehicle such as an automobile, and more particularly to an engine control device that cuts fuel while cruise control is being performed. [Background technology]

[0002] In the control of engines of vehicles such as automobiles, a fuel cut control is known in which, when the engine speed is above a certain level and the throttle valve is fully closed, fuel supply to the engine is stopped to improve fuel efficiency, and various control configurations have been proposed in relation to this. For example, Patent Document 1 proposes that, in order to prevent hunting of the fuel cut control during vehicle speed control for controlling the inter-vehicle distance, the shaft torque (a shaft torque predicted value during execution of the fuel cut control) generated when the fuel cut is executed (with respect to the engine speed) is checked in advance, and even when the engine operating state becomes a condition for executing the fuel cut, if the shaft torque command value while the vehicle is traveling is within an upper and lower limit range set based on the shaft torque predicted value during execution of the fuel cut control, the execution of the fuel cut is prohibited, and hysteresis is provided for turning the fuel cut control on and off. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 11-227592 Summary of the Invention [Problem to be solved by the invention]

[0004] In a vehicle that operates cruise control to maintain a constant vehicle speed without operating the accelerator pedal, when the vehicle travels downhill, the driving force required to maintain the vehicle speed (required driving force) decreases, resulting in fuel cutoff. In this case, the actual driving force obtained when fuel cutoff is performed decreases significantly, and a driving force sufficient to travel at a constant speed cannot be generated. Therefore, the required driving force temporarily increases and fuel cutoff is immediately stopped. However, as the vehicle speed increases again, the required driving force decreases, and fuel cutoff is performed. Ultimately, control hunting occurs, in which fuel cutoff is repeatedly turned on and off in short cycles, which can cause unpleasant shocks for the occupants. To prevent such fuel cut control hunting, it is conceivable to (similar to the case of Patent Document 1) prohibit fuel cut even when the required driving force falls below a reference value for executing fuel cut (corresponding to a fully closed throttle valve, referred to as the "availability lower limit") until the required driving force falls further below the availability lower limit to a certain extent. Regarding the prohibition of fuel cut, as in Patent Document 1, the reference value of the required driving force for canceling the prohibition of fuel cut, i.e., the lower limit of the fuel cut prohibition range, was previously set somewhat wide based on the driving force obtained during fuel cut execution, which was previously determined through experiments or the like, so that control hunting could be prevented as reliably as possible through adaptation. Therefore, setting the lower limit of the fuel cut prohibition range required an increased amount of work for experimentation and adaptation. Furthermore, setting the fuel cut prohibition range too wide prohibited fuel cut even under conditions where fuel cut prohibition was not required, resulting in a corresponding reduction in fuel economy.

[0005] The reason for setting the fuel cut prohibition range is to prevent control hunting caused by a significant difference between the actual driving force when the required driving force reaches the lower limit of fuel availability and the actual driving force during fuel cut. When the required driving force is lower than the actual driving force obtained during fuel cut, control hunting does not occur even if fuel cut is performed (in this case, the actual driving force of the engine is at its minimum value, and the required driving force is controlled by the braking force of the braking device). Therefore, if the actual driving force during fuel cut can be set to the lower limit of the fuel cut prohibition range, the fuel cut prohibition range can be set as narrow as possible to prevent control hunting. Furthermore, because the actual driving force during fuel cut varies depending on the driving environment, it is difficult and limited to conduct experiments or other tests in advance to anticipate all possible situations. However, if fuel cut is performed once during cruise control when the required driving force falls below the lower limit of fuel availability, the actual driving force corresponding to the driving environment at that time can be detected. This finding is utilized in the present invention.

[0006] Thus, the main object of the present invention is to improve fuel efficiency by setting the fuel cut prohibition region as narrow as possible to prevent control hunting in an engine control device that performs fuel cut while cruise control is in operation, while also reducing the amount of work required to set the lower limit of the fuel cut prohibition region. [Means for solving the problem]

[0007] According to the present invention, the above problem is solved by an engine control device for a vehicle, a required driving force determining means for determining a required driving force while the cruise control is being executed; a fuel cut control means for cutting fuel based on a required driving force, This is achieved by a device in which the fuel cut control means is configured to execute a fuel cut when the requested driving force, which is higher than the availability lower limit, falls below the availability lower limit, store the actual driving force while the fuel cut is being executed, prohibit the execution of the fuel cut while the requested driving force is between the stored actual driving force and the availability lower limit after storing the actual driving force while the fuel cut is being executed, and lift the prohibition of the fuel cut when the requested driving force falls below the stored actual driving force or exceeds the availability lower limit.

[0008] In the above configuration, the "cruise control" may be, as already mentioned, a vehicle speed control that maintains a constant vehicle speed without operating the accelerator pedal. The "required driving force determination means" may be configured to determine the required driving force based on the difference between the target vehicle speed set by the cruise control and the current vehicle speed in any manner. The "fuel cut control means" may be configured to determine whether to execute a fuel cut based on the required driving force as described above, and, when executing a fuel cut, to instruct the engine fuel injection control device to stop the supply of fuel. The "availability lower limit" is the driving force obtained when the throttle valve is substantially fully closed in the current engine operating state, and is a reference value for the required driving force that is referenced when determining whether to execute a fuel cut.

[0009] In the above-described configuration of the present invention, the fuel cut control means first instructs the fuel injection control device to temporarily execute fuel cut when the required driving force falls below the availability lower limit from a value higher than the availability lower limit. In response to this, fuel supply is stopped, and the actual driving force of the engine remains below the availability lower limit. This actual driving force is then detected and stored. The fuel cut control means then suspends fuel cut and prohibits execution of fuel cut until the required driving force falls below the stored actual driving force or exceeds the availability lower limit. In other words, the region between the stored actual driving force and the availability lower limit is defined as a fuel cut prohibition region.

[0010] In the above configuration, the lower limit of the prohibited region of fuel cut is set to the actual driving force obtained when fuel cut is first executed. This configuration first reduces the labor required for preliminary experiments and calibration to set the lower limit of the prohibited region of fuel cut. Furthermore, as already mentioned, control hunting due to fuel cut occurs due to the difference in driving force before and after fuel cut. Since the lower limit of the prohibited region of fuel cut is set to the actual driving force obtained when fuel cut is first executed in the engine's operating state at that time, the lower limit is set to the maximum value that does not cause control hunting. This allows the width of the prohibited region of fuel cut to be set as narrow as possible, thereby improving fuel economy compared to conventional systems.

[0011] In the above configuration, while the required driving force is in the fuel cut-off prohibited region, the actual driving force of the engine may be controlled to the availability lower limit, which is the lowest value in a fuel-supply state. In this case, the reduction of the driving force from the availability lower limit to the required driving force so that the total driving force generated in the vehicle matches the required driving force is achieved by controlling the braking force using the brake device. When the required driving force is lower than the stored actual driving force, i.e., when the required driving force is lower than the actual driving force of the engine in a fuel-stopped state, the total driving force generated in the vehicle is controlled to the required driving force by controlling the braking force using the brake device. [Effects of the Invention]

[0012] Thus, according to the device of the present invention, when cruise control is being executed on a vehicle and a situation arises in which fuel cut is to be executed when the vehicle is traveling downhill, fuel cut is first executed, the actual driving force at that time is detected and stored, and set to the lower limit of the fuel cut prohibited range, thereby preventing control hunting related to fuel cut and suppressing the occurrence of unpleasant shocks for occupants, and making it possible to set as wide a range as possible the operating conditions under which fuel cut is executed.Furthermore, by using the actual driving force when fuel cut is actually executed, it is possible to achieve both good ride comfort and fuel efficiency that are suited to the actual environment, and also to reduce the amount of adaptation work required.

[0013] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0014] [Figure 1] Fig. 1(A) is a schematic diagram of a vehicle equipped with an engine control device for a vehicle according to this embodiment, and Fig. 1(B) is a block diagram showing the configuration of a system related to the engine control device for a vehicle according to this embodiment. [Figure 2]FIG. 2 is a flowchart showing the process relating to the fuel cut control in the engine control device for a vehicle according to this embodiment. [Figure 3] FIG. 3 is a diagram showing, in the form of a time chart, changes in each state such as the required driving force, the actual driving force, and the vehicle speed due to the operation of the engine control device for the vehicle of this embodiment. [Explanation of symbols]

[0015] 10...vehicle, 12FL,FR,RL,RR...wheels, 14...accelerator pedal, 16...cruise control switch, 20...drive system, 22...engine, 24...torque converter, 26...automatic transmission, 28...differential gear device, 40...braking system, 44...brake pedal, 45...master cylinder, 46...hydraulic circuit, 42FL,FR,RL,RR...wheel cylinders, 50...electronic control device BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Vehicle configuration 1(A), a vehicle 10 such as an automobile incorporating one preferred embodiment of the engine control device of this embodiment is equipped with left and right front wheels 12FL, 12FR, left and right rear wheels 12RL, 12RR, a drive unit 20 that generates braking / driving forces on the drive wheels, a steering device (not shown) for controlling the steering angle of the wheels, and a braking device (brake) 40 that generates braking forces on each wheel. In the drive unit 20, power is transmitted from an engine 22 (which may be a hybrid drive unit having both an engine and an electric motor) to the drive wheels, i.e., rear wheels 12FL, 12FR, via a torque converter 24, a transmission 26, a differential gear device 28, etc., in response to depression of an accelerator pedal 14 by a driver. The steering device may be configured to steer the front wheels 12FL, 12FR in a conventional manner. The braking system 40 may be a conventional electronically controlled hydraulic braking system (pneumatic or electromagnetic) configured to control the brake pressure in wheel cylinders 42FL, FR, RL, and RR equipped on each wheel, i.e., the braking force at each wheel, via a hydraulic circuit 46 connected to a master cylinder 45 operated in response to depression of a brake pedal 44 by the driver. When the cruise control switch 16 is operated and cruise control is performed, the operation of the engine 22 and the brakes 40 is controlled to maintain a constant vehicle speed, regardless of operation of the accelerator pedal 14 and the brake pedal 44. Vehicle speed may be detected in any manner using values ​​detected by wheel speed sensors installed on each wheel. The operation of each device in the vehicle is controlled by an electronic control unit 50. The electronic control unit 50 may include a computer and drive circuit having a CPU, ROM, RAM, and input / output port devices interconnected by a conventional bidirectional common bus. The configuration and operation of each part of the engine control device of this embodiment, which will be described later, may be realized by the operation of an electronic control device 50 according to a program. As shown in the figure, state values ​​of each wheel, which are used as parameters for the control of this embodiment, which is executed in a manner described later, are input from sensors to the electronic control device 50, and control commands Cd, Cb, etc. are output to the drive device 20 and the braking device 40.

[0017] Engine control device configuration Referring to FIG. 1B, the configuration of the engine control device according to this embodiment of the electronic control device 50 is realized in more detail by the operation of the cruise control unit, brake ECU, and engine ECU. Specifically, when the switch 16 is turned on, the cruise control unit calculates a target acceleration value (target acceleration) for maintaining a constant vehicle speed (request calculation unit). The brake ECU calculates a required driving force to achieve the target acceleration (request driving force calculation unit) and transmits it to the engine ECU. Based on this, the target throttle opening is determined, and the engine throttle opening is controlled to control the engine driving force. Then, if necessary, the brakes of each wheel are activated to match the driving force generated by the engine with the required driving force (brake determination unit). Furthermore, in this embodiment, if the required driving force falls below the availability lower limit, a fuel cut is performed as appropriate in a manner described below. In order to determine whether or not to execute such a fuel cut and to execute the fuel cut, as shown in the figure, there may be provided a means for detecting the actual driving force by referring to the state of the engine and transmission (actual driving force detection unit), a means for storing the actual driving force (actual driving force storage unit), a means for determining whether or not to execute a fuel cut by referring to the stored values ​​of the required driving force and the actual driving force (F / C determination processing unit), and a means for instructing the execution of a fuel cut (F / C execution unit).

[0018] Operation of the device As previously mentioned, when cruise control is in operation, when a vehicle enters a downhill slope, the required driving force decreases. If the required driving force falls below the availability lower limit, where the throttle opening is at its minimum, engine fuel is cut to improve fuel economy. However, since the actual driving force output by the engine is usually lower than the required driving force, if the decision to cut fuel is based solely on whether the required driving force falls below the availability lower limit, control hunting occurs, in which fuel cut is repeatedly performed and stopped. Therefore, to prevent such fuel cut control hunting, a fuel cut prohibition region (for the required driving force) is set that prohibits fuel cut so that fuel cut is not immediately performed even if the required driving force falls below the availability lower limit. In this regard, fuel cut control hunting can be prevented if the actual driving force output by the engine when fuel cut is performed is equal to or greater than the required driving force. Therefore, the lower limit of the fuel cut prohibition region can be set to the actual driving force output by the engine when fuel cut is performed. However, the actual driving force output by the engine when fuel is cut varies depending on the operating state of the engine at that time, and it is difficult to determine this accurately in advance.

[0019] Therefore, in this embodiment, when the required driving force falls below the availability lower limit during cruise control, fuel is first cut off and the actual driving force output by the engine at that time is detected and stored. Then, fuel cut is suspended, and fuel cut is prohibited while the required driving force is between the stored actual driving force and the availability lower limit. In other words, the lower limit of the fuel cut prohibited region is set to the actual driving force output by the engine when fuel cut is executed. This configuration allows the lower limit of the fuel cut prohibited region to be set accurately to prevent control hunting, eliminating the need to set the range in which fuel cut is prohibited wider than necessary, and is expected to further improve fuel economy.

[0020] FIG. 2 shows the process of the device of this embodiment in the form of a flowchart, which is executed repeatedly at a predetermined cycle time. Referring to FIG. 2, the process begins with cruise control being executed during constant speed control (step 1). When the required driving force falls below the availability lower limit from a state higher than the availability lower limit (step 2), fuel cut is executed (step 4). Note that in step 3, f is a flag that is set to f = 1 when fuel cut is prohibited; at this point, f = 0. As a result, the actual driving force output by the engine quickly decreases and stops. After waiting for the actual driving force to reach a stationary value (switch 5), the stationary actual driving force (FCFDRV) is stored (step 6). Note that f is set to 1 (step 7). Then, fuel cut is prohibited while the required driving force exceeds FCFDRV (steps 8 and 9). After that, when the required driving force falls below FCFDRV (step 8) or exceeds the availability lower limit, the prohibition of fuel cut is lifted (step 10). At this point, f is set to 0 (step 11), and the process returns to the initial state.

[0021] FIG. 3 is a diagram showing changes in the required driving force, the actual driving force output by the engine, and the vehicle speed of a vehicle during cruise control performed by the device according to this embodiment. Referring to this diagram, when the gradient of the road on which the vehicle is traveling becomes downward, the required driving force decreases. When the required driving force falls below the lower limit of the vehicle's availability, a fuel cut is temporarily performed (see F / C flag). The actual driving force then falls below the required driving force and settles at a stagnant value, as indicated by symbol a. The actual driving force at that point is stored as FCFDRV. Then, fuel cut is prohibited (F / C prohibition flag), a minimum amount of fuel is supplied, and the actual driving force remains at the lower limit of the vehicle's availability. During this time, the actual driving force of the engine exceeds the required driving force, so the brakes are applied to control the vehicle's driving force to match the required driving force (see brake flag). Subsequently, if the gradient of the road becomes even steeper, the required driving force will further decrease, and as shown by the symbol b, when it falls below FCFDRV, the prohibition on fuel cutoff is lifted and fuel cutoff is implemented (fuel supply is stopped). As a result, the actual engine driving force will remain at FCFDRV, and the brakes will be applied to control the vehicle's driving force to match the required driving force. Although not shown, if the road's downward gradient becomes gentler or is no longer a downward gradient and the required driving force exceeds the availability lower limit, the prohibition on fuel cutoff will also be lifted (fuel supply will continue as is to achieve the required driving force).

[0022] According to the above configuration, the actual driving force at the time of fuel cut, which should be set to the lower limit of the fuel cut prohibited area, is detected and stored each time a fuel cut is performed, eliminating the need for prior calibration through experiments, etc., and also making it possible to reduce the amount of work required for calibration.

[0023] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] An engine control device for a vehicle, a required driving force determining means for determining a required driving force while the cruise control is being executed; a fuel cut control means for cutting fuel based on a required driving force, The availability lower limit is higher than the actual driving force during fuel cut, The device is configured so that the fuel cut control means executes a fuel cut when the required driving force, which is higher than the availability lower limit, falls below the availability lower limit, stores the actual driving force during the fuel cut, prohibits the execution of the fuel cut while the required driving force is between the stored actual driving force and the availability lower limit after storing the actual driving force during the fuel cut, and lifts the prohibition of the fuel cut when the required driving force falls below the stored actual driving force or exceeds the availability lower limit.

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