Fuel-efficient driving system

A fuel-saving driving system which gradually decreases a target vehicle speed from a start of control to passage of a descending-slope starting point in a linear form and can obtain fuel-saving and smooth driving feeling without repeating fuel-cut and injection. A vehicle-position specifying device is provided for specifying the position of a vehicle, a storage device for storing data of a descending slope located in the vehicle traveling direction, a vehicle speed measuring device for measuring a speed of the vehicle, and a controller The controller has a function of determining a target speed of the vehicle from the vehicle speed and the data of the descending slope.

The present invention relates to an automatic control system for fuel-saving driving of an automobile and particularly to automatic control which can further reduce fuel consumption when driving changes to descending.

BACKGROUND OF THE INVENTION

As a prior art, a fuel-saving system that effectively promotes fuel-saving driving using road gradient information and a control method thereof are disclosed (See Patent Document 1, for example).

In the prior art (Patent Document 1), improvement in fuel efficiency is promoted by using acceleration energy on a descending slope or in more detail by performing speed-reduction control before the descending slope.

In the prior art (Patent Document 1), an advice position for fuel-cut before the descending slope (a position where an advice is given to a driver) or a control position for fuel-cut in an automatic fuel-saving driving system (a position where fuel is cut by automatic control) is determined by a vehicle speed (a car speed), a gradient before the descending slope and the gradient of the descending slope. And the gradient before the descending slope and the gradient of the descending slope are determined by a three-dimensional map.

Thus, in order to reduce the speed to a targeted vehicle speed at start of the descending slope, the gradient before the descending slope and the gradient of the descending slope need to be mapped precisely, and the advice position for fuel-cut or the control position for fuel-cut in the automatic fuel-saving driving system also need to be mapped precisely.

However, even if the map is to be improved precisely, the gradient at an actual traveling position is not necessarily constant.

Also, in the case of a cargo vehicle, its mass is greatly varied whether the vehicle is empty or loaded, and thus, deceleration is largely different at the fuel-cut between the empty vehicle and the loaded vehicle, and it has been difficult to reduce the speed to a requested vehicle speed (target vehicle speed) at start of the descending slope both in the empty vehicle and the loaded vehicle.

Here, in the case of the automatic fuel-saving driving mode, at a requested vehicle speed or less, control is performed such that fuel is automatically injected so that the vehicle speed is not reduced excessively. Because of such control, fuel might be injected immediately before entering the descending slope, and in that case, a vehicle behavior becomes jerky, and a driver would have a sense of discomfort, which is a problem. At the same time, there is also a problem of a bad influence on the fuel efficiency.

FIG. 5shows a traveling distance, a vehicle speed and a fuel injection amount in the control at a point to change to descending during the automatic fuel-saving driving according to the prior art.

InFIG. 5, reference character P1denotes a control start position, reference character P2for a peak point changing from ascending to descending (descending-slope starting point), reference character Vd for a requested vehicle speed, reference character Va for an actual vehicle speed, reference character Vt for a target vehicle speed when entering the descending slope, and reference character q for a fuel injection amount. Here, a distance from the control starting point to a descending starting point is 300 m (constant), for example.

InFIG. 5, reference character by indicates a difference between the actual vehicle speed Va and the target vehicle speed Vd.

FIG. 5shows a case in which the gradient on the ascending side is steeper than that in data stored in a database or a vehicle mass is small.

In the case shown inFIG. 5, the speed is lost before reaching the descending-slope starting point P2, and the vehicle speed Va becomes lower than the target vehicle speed Vt at entering the descending slope. Thus, the fuel injection amount q is temporarily injected. By means of this temporary fuel injection q, the vehicle speed Va rapidly increases and becomes higher than the target vehicle speed Vt at entering the descending slope, but since fuel is cut immediately after the fuel injection amount q is temporarily injected, the vehicle speed Va is decreased again.

As a result, a driving feeling before and after the descending-slope starting point P2becomes jerky, and fuel efficiency is deteriorated by the temporary fuel injection.

FIG. 6shows the traveling distance, the vehicle speed, and the fuel injection amount in control at a point of time changing from ascending to descending in the automatic fuel-saving driving of the prior art as well as shown inFIG. 5. However,FIG. 6shows a case in which the gradient on the actual ascending side is gentler than that in the data stored in the database or the vehicle mass is larger.

In the case shown inFIG. 6, the actual vehicle speed Va does not fully slow down but the actual vehicle speed Va at the descending-slope starting point P2exceeds the target vehicle speed Vt at entering the descending slope and a frequency of operating an auxiliary brake in the middle of the slope is increased, which deteriorates the fuel efficiency.

FIG. 7shows a case in which in order to solve the problem inFIG. 5, the control start position P1is brought close to the descending-slope starting point P2and the distance from the control starting point to the descending starting point is set short.

InFIG. 7, it is not necessary to temporarily inject the fuel injection amount q before reaching the descending-slope starting point P2as in the case shown inFIG. 5. However, similarly to the case shown inFIG. 6, the actual vehicle speed Va at the descending-slope starting point P2exceeds the target vehicle speed Vt at entering the descending slope, and the frequency of operating the auxiliary brake in the middle of the descending slope is increased and thus, the problem of deterioration in fuel efficiency still remains.Patent Document 1: JPA (Non-examined publication) No. 2007-156704

SUMMARY OF THE INVENTION

Problem to be solved

The present invention was created in view of the above-mentioned problems of the prior art and has an object for providing a fuel-saving driving system in which a target vehicle speed from start of control to passage of a descending-slope starting point is gradually decreased linearly, and a smooth driving feeling can be obtained without repeating fuel-cut and injection while saving fuel consumption.

Solution Means for Problem

A fuel-saving driving system (100) of the present invention has a vehicle-position specifying device (2: GPS, for example) which specifies the position of a vehicle,

a storage device (database11, for example) which stores data of a descending slope located in the vehicle traveling direction,

a vehicle speed measuring device (vehicle speed sensor3) which measures a speed (vehicle speed Va) of a vehicle (1), and

a controller (controller of the fuel-saving driving system side: control unit10),

the controller (10) has a function of determining (calculating) a target speed (requested vehicle speed Vd) of the vehicle (1) from the vehicle speed (Va) and the data of the descending slope (a distance L from the current position to the descending-slope starting point and the target vehicle speed Vt at the descending-slope starting point and the like, for example) (claim1).

In the present invention, the controller (controller of the fuel-saving driving system side: control unit10) preferably has a function of calculating the target speed (Vd) at a spot where the vehicle (1) is traveling on the basis of the vehicle speed (Va) at the spot where the vehicle (1) is traveling and the distance (L) to the descending-slope starting point so that the speed (Va) of the vehicle (1) at a point of time when the vehicle (1) reaches the descending-slope starting point (P2) becomes the target speed (Vt) at the descending-slope starting point (claim2).

Here, the controller (controller of the fuel-saving driving system side: control unit10) preferably has a function of executing control of decreasing the target speed (Vd) at the spot where the vehicle (1) is traveling gradually (so that the deceleration characteristic becomes linear) so that the speed (Va) of the vehicle at the point of time when the vehicle (1) reaches the descending-slope starting point (P2) becomes the target speed (Vt) at the descending-slope starting point P2(claim3).

Said controller (controller of the fuel-saving driving system side: control unit10) preferably has a function of transmitting a control signal to a vehicle-side controller (engine controller4) that controls an engine via an information network (5) of the vehicle so as to have the vehicle-side controller (4) transmit a control signal to inject fuel in an injection amount corresponding to the control signal to a fuel injecting device (claim4).

Advantageous Effects of Invention

According to the present invention provided with the above-mentioned constructions, since the present invention is constructed to determine (calculate) the target speed (requested vehicle speed Vd) of the vehicle from the vehicle speed (Va) and the data of the descending slope (the distance L from the current position to the descending-slope starting point, the target vehicle speed Vt at the descending-slope starting point and the like), the target speed (Vd) at the spot where the vehicle (1) is traveling can be decreased linearly (claim2), and the target speed (Vd) at the spot where the vehicle (1) is traveling can be decreased linearly (gradually) (claim3), repetition of fuel-cut and fuel injection before the descending-slope starting point P2can be suppressed.

That is, the fuel-cut or the fuel injection makes a vehicle behavior unstable (jerky) and gives a sense of unstableness or a sense of discomfort to a vehicle passenger, but since the repetition of fuel-cut and fuel injection is suppressed in the present invention, a sense of unstableness or a sense of discomfort is prevented from being given to the vehicle passenger.

Moreover, according to the present invention, since the target speed (Vd) at the spot where the vehicle (1) is traveling can be decreased linearly (gradually) (claim3), a starting point (P1) where the vehicle traveling speed (Va) is decreased can be set at a position away from the descending-slope starting point (P2) as compared with the prior art.

That is, since the distance for which the vehicle (1) travels with a decreased speed (the distance L from the point P1where deceleration is started to the descending-slope starting point P2) can be made longer than that in the prior art, deviation between the vehicle speed (Va) and the target speed (V) at the descending-slope starting point becomes smaller even in the case shown inFIG. 6, and a frequency of braking in the middle of the descending slope becomes fewer. Thus, energy is not wasted by braking and fuel efficiency of the vehicle is improved. Also, since the distance for which the vehicle can travel while being subjected to braking can be made shorter, the fuel-saving effect can be exerted further effectively.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described below by referring to the attached drawings.

InFIG. 1, a fuel-saving driving system according to the embodiment of the present invention is indicated in entirety by reference numeral100.

The fuel-saving driving system100has a vehicle1, a GPS2, which is a vehicle position specifying device, a vehicle speed sensor3, an engine controller4, an in-vehicle communication network5, and a control unit10, which is control means of the automatic fuel-saving driving system.

In this embodiment, the position of the vehicle is specified by using a Global Positioning System, and the GPS2, which is a vehicle position specifying device, receives position information or the like from a satellite of the Global Positioning System.

The in-vehicle communication network5connects the control unit10to the vehicle speed sensor3and the engine controller4.

FIG. 2illustrates a construction of the control unit10.

InFIG. 2, the control unit10has a database11, a current-position specification portion12, a calculation portion (distance calculation portion)13for calculating a distance from the current position to a descending-slope starting point, a target-speed determination portion14, an instruction-signal transmission timing determination portion15, and an interface16.

The information relating to the current position of the vehicle from the GPS2is inputted into the current-position specification portion12via a line L1.

In the database11, map data obtained by a requested vehicle speed (target vehicle speed) at the descending-slope starting point and the information obtained so far from the GPS, for example, is stored. If the map data stored in the database11is to be updated, new map data is sent from the GPS2to the database11via the line L2.

The distance calculation portion13is constructed to have a function of calculating the distance “L” (SeeFIG. 3) from the (current position of the) vehicle1to the descending-slope starting point from the current position information of the vehicle1obtained from the current-position specification portion12via a line L3and the map information obtained from the database11via a line L4.

Into the target-speed determination portion14, the distance L from the current position to the descending-slope starting point calculated by the distance calculation portion13is inputted via a line L5. Also, into the target-speed determination portion14, the current vehicle speed Va measured by the vehicle speed sensor3is inputted via the in-vehicle communication network5. Moreover, into the target-speed determination portion14, the requested vehicle speed (target vehicle speed when entering the descending slope) Vt at the descending-slope starting point stored in the database11is inputted via a line L6.

The target-speed determination portion14has a function of calculating the requested vehicle speed (target vehicle speed) Vd on the basis of the distance L from the current position to the descending-slope starting point, the current vehicle speed Va, and the target vehicle speed Vt when entering the descending slope.

The instruction-signal transmission timing determination portion15has a function of determining timing at which a control signal to achieve the target vehicle speed Vd is transmitted.

If the target vehicle speed Vd determined by the target-speed determination portion14is inputted via a line L7, the instruction-signal transmission timing determination portion15transmits a control signal (control signal to achieve the target vehicle speed Vd) to the engine controller4via a line L8, an interface16, and the in-vehicle communication network5in accordance with the timing determined by the instruction-signal transmission timing determination portion15.

Then, the engine controller4transmits the control signal to a fuel injecting device, not shown, and adjusts or controls a fuel injection amount and injection timing so that the vehicle speed becomes the target vehicle speed Vd.

InFIG. 2, a timer17measures a control interval. In the control unit10, the distance “L” from the current position of the vehicle to the descending-slope starting point and the target vehicle speed (requested vehicle speed; Vd) are calculated at every predetermined control interval measured by the timer17.

As described above, in the prior art, when changing from ascending to descending, from a constant distance (300 m, for example) before the descending-slope starting point, the speed (requested vehicle speed) of the vehicle1is determined and the fuel injection amount is adjusted on the basis of the gradient on the ascending side and the gradient on the descending side of the spot (according to the map information stored in the database) and the vehicle speed at the start of control (300 m before the descending-slope starting point) and so that the vehicle can travel on the ascending slope to the descending-slope starting point.

However, as described above by referring toFIGS. 5 to 7, there were cases in which the speed is lost before the descending-slope starting point P2due to the difference between the gradient information of the database and the actual gradient and the vehicle weight and the fuel injection amount is temporarily injected (FIG. 5) or in which the actual vehicle speed at the descending-slope starting point P2exceeds the target vehicle speed when entering the descending slope and an auxiliary brake is operated (FIGS. 6 and 7).

Thus, the purpose of improving fuel efficiency cannot be achieved in some cases.

In order to cope with that, in the fuel-saving driving system100according to the illustrated embodiment, the speed (requested vehicle speed) of the vehicle1is determined on the basis of the actual vehicle speed Va from the vehicle speed sensor3, the target vehicle speed Vt when entering the descending slope, and the distance L from the current position to the descending-slope starting point, and the fuel injection amount is adjusted. Also, in the fuel-saving driving system100according to the illustrated embodiment, since the speed is decreased linearly (gradually) so that the target vehicle speed Vt is achieved at a descending-slope starting point P2A, the situation in which the vehicle speed Va falls under the target vehicle speed Vt when entering the descending slope at a stage before reaching the descending-slope starting point P2A (SeeFIG. 5) can be prevented.

Similarly, in the fuel-saving driving system100according to the illustrated embodiment, since the distance for which the vehicle1travels at a reduced speed (the distance L from the point P1where deceleration is started to the descending-slope starting point P2A) can be made longer than that in the prior art, the situation in which the speed is not fully decreased before reaching the descending-slope starting point P2A and the vehicle speed Va largely exceeds the target vehicle speed Vt when entering the descending slope at the descending-slope starting point P2A (SeeFIGS. 6 and 7) can be prevented.

That is, according to the illustrated embodiment, since the distance L to the descending-slope starting point P2A is considered, the requested vehicle speed Vd of the vehicle1can be determined by considering whether or not the vehicle speed Va at the current position is appropriate for achieving the target vehicle speed Vt when entering the descending slope.

Thus, an error between the vehicle speed Va at the descending-slope starting point P2A and the target vehicle speed Vt when entering the descending slope can be made small.

In other words, according to the illustrated embodiment, since in each control cycle, the speed when the vehicle1moves from the current position to the descending-slope starting point P2A can be expected by considering the distance L to the descending-slope starting point P2A, the requested vehicle speed or the target vehicle speed Vd of the vehicle1can be determined by referring to the expected value. This means that the requested vehicle speed or the target vehicle speed Vd of the vehicle1can be corrected at every control cycle.

Therefore, in the illustrated embodiment, even if the distance from the point P1A where the control is started to the descending-slope starting point P2A is long, the fuel injection amount is adjusted by correcting the requested vehicle speed or the target vehicle speed Vd at every control cycle and thus, an error between the vehicle speed Va at the descending-slope starting point P2A and the target vehicle speed Vt when entering a descending slope can be made small by reducing an error between the vehicle speed Va and the target vehicle speed Vt when entering a descending slope.

In the illustrated embodiment, as a numerical value of the distance L from the point P1A where the control is started to the descending-slope starting point P2A, 400 to 500 m, for example, can be set.

On the basis of the flowchart inFIG. 4and also by referring toFIGS. 2 and 3, control of the fuel-saving driving system100will be described.

InFIG. 4, the control unit10reads the vehicle speed data (Step S1) from the information from the vehicle speed sensor3, the position information (Step S2) of the descending-slope starting point P2A (SeeFIG. 3) during traveling from the database11, and reads the current position of the vehicle1from the GPS2. (Step S3).

The order of reading each data, that is, the order of Steps S1to S3is not limited by the above. Also, Steps S1to S3can be executed at the same time.

At Step S4, on the basis of the position information of the descending-slope starting point P2A (Step S2) during traveling and the current position of the vehicle1(Step S3), the distance calculation portion13calculates the distance L between the descending-slope starting point P2A and the current position.

At Step S5, the control unit10determines whether or not the distance L between the descending-slope starting point P2A and the current position is not more than a constant (400 to 500 m, for example).

If the distance L between from the current position to the descending slope starting point P2A is not more than the constant (YES for Step S5), the routine proceeds to Step S6.

On the other hand, if the distance L from the current position to the descending slope starting point P2A is larger than the constant (NO for Step S5), Step S1and after is repeated.

At Step S6, using parameters of the vehicle speed Va, the target vehicle speed Vt when entering the descending slope, and the distance L from the current position P1to the descending slope starting point P2, the requested vehicle speed (target vehicle speed) Vd is calculated. Then, the routine proceeds to Step S7.

At Step S7, a control signal for controlling the fuel injection amount so that the requested vehicle speed Vd is achieved is outputted to the engine controller4via the in-vehicle communication network5. Then, the engine controller4transmits a control signal relating to the fuel injection amount to the fuel injecting device, not shown, so as to achieve the requested vehicle speed Vd.

As described above, the illustrated fuel-saving driving system100is constructed to determine the target vehicle speed (requested vehicle speed Vd) from the vehicle speed Va, the data of the descending slope (the position of the descending-slope starting point P2A and the target vehicle speed Vt when entering the descending slope, for example) and the distance L from the current position to the descending-slope starting point P2A.

According to the fuel-saving driving system100as above, since the target vehicle speed Vd and the vehicle speed Va at a spot where the vehicle1is traveling can be controlled as shown inFIG. 3, repetition of fuel-cut and fuel injection before the descending-slope starting point P2A or a frequency at which the auxiliary brake is operated during the descending slope can be suppressed.

Since fuel-cut and fuel injection are not repeated, according to the illustrated fuel-saving driving system100, the vehicle behavior does not become unstable or jerky or give a sense of unstableness or a sense of discomfort to a driver.

Also, according to the illustrated fuel-saving driving system100, a frequency at which the auxiliary brake is operated in the middle of the descending slope is reduced. This means full deceleration has been achieved before reaching the descending-slope starting point P2A and also that the fuel consumption is saved in the illustrated fuel-saving driving system100.

That is, according to the illustrated embodiment, the fuel-saving driving is achieved.

The present invention may be applied to traveling changing from a flat road to the descending slope, for example, other than changing from ascending to descending.

The illustrated embodiment is only an example, and the description is not intended to limit the technical scope of the present invention.

REFERENCE SIGNS LIST

1vehicle2vehicle-position specifying device/GPS3vehicle speed measuring device/vehicle speed sensor4vehicle-side controller/engine controller5vehicle information network10controller/control unit11storage device/database12current-position specification portion13calculation portion for distance from current position to descending slope staring point/distance calculation portion14target-speed determination portion15instruction signal transmission timing determination portion16interface17timer