JP2001206098A - Vehicle running control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a fuel consumption rate and an electricity consumption rate in a vehicle by starting speed reduction early in a relation to vehicle running control device. SOLUTION: Based on the output signal from a laser radar sensor 14 arranged near the front grill of the vehicle, the inter-vehicle distance d between a vehicle running in a specified range ahead of a datum vehicle and the datum vehicle is detected for detecting a relative vehicle speed Rxy. Based on the relative vehicle speed Rxy and actual vehicle speed Vx, the vehicle speed Vy of the vehicle running ahead of the datum vehicle is detected. In the case where the reduced speed ΔVy of the vehicle running ahead of the datum vehicle becomes a specified value or larger, the feel supply to an internal combustion engine is reduced immediately. In this case, after the start of speed reduction by the vehicle ahead of the datum vehicle, it is avoided that a large amount of fuel is supplied to the internal combustion engine of the datum vehicle for a longer time than needed, for improving fuel consumption rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle travel control device, and more particularly to a vehicle travel control device suitable for decelerating a host vehicle in accordance with the deceleration of a preceding vehicle.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Application Publication No.
As disclosed in JP-A-89-89, there is known a travel control device that detects an inter-vehicle distance and a relative speed between a host vehicle and a preceding vehicle preceding the host vehicle, and decelerates the host vehicle based on the detection result. This device reduces the throttle opening in the own vehicle, performs fuel cut, and activates the brake when the inter-vehicle distance between the own vehicle and the preceding vehicle decreases due to the deceleration of the preceding vehicle. For this reason, according to the above-described conventional device, the own vehicle can be decelerated when the inter-vehicle distance to the preceding vehicle is reduced. Therefore, according to the above-described conventional device, the own vehicle can be prevented from contacting the preceding vehicle.

[0003]

In the above conventional apparatus, when the preceding vehicle decelerates, the own vehicle is decelerated so that an inter-vehicle distance corresponding to the vehicle speed is secured between the preceding vehicle and the own vehicle. At this time, the deceleration of the host vehicle is started with a time delay after the deceleration of the preceding vehicle is started. If the deceleration of the own vehicle is performed with a delay with respect to the deceleration of the preceding vehicle, a situation occurs in which the own vehicle continues to accelerate or travel at a constant speed for the delay time. For this reason, in the conventional device described above,
Fuel is consumed wastefully for the delay time, which results in deterioration of fuel efficiency.

Further, even in a configuration in which the own vehicle is driven and driven by using an electric motor as a power source, if the own vehicle starts to decelerate with a time delay after the deceleration of the preceding vehicle, the power is reduced by the delay time. It is wastefully consumed, which leads to a situation where power consumption is deteriorated.

Further, when the road condition changes from an uphill to a downhill, or when changing from a straight road to a curved road, it is necessary to sufficiently decelerate the host vehicle before the change.
Generally, a driver starts deceleration just before a peak or a curved road. For this reason, even in the above situation, fuel and electric power are additionally consumed for the time, which may cause deterioration of fuel efficiency and electric power consumption.

The present invention has been made in view of the above points, and provides a vehicle traveling control device capable of improving fuel efficiency and electric power consumption by starting vehicle deceleration at an appropriate time. The purpose is to:

[0007]

The above object is achieved by the present invention.
As described in the above, the forward vehicle deceleration determining means for determining whether or not the forward vehicle existing in front of the own vehicle has started decelerating, and the forward vehicle decelerating determining means has determined that the forward vehicle has started decelerating. At a point in time, a deceleration start means for starting deceleration of the host vehicle.

According to the first aspect of the present invention, the deceleration of the host vehicle is started when it is determined that the preceding vehicle existing in front of the host vehicle has started deceleration. After the preceding vehicle starts decelerating, it is not necessary for the host vehicle to continue accelerating or constant speed running for an unduly long period of time, and it is not necessary to generate power for driving the host vehicle. Therefore, according to the present invention, by starting deceleration at an appropriate time, it is possible to improve fuel efficiency and power consumption.

According to a second aspect of the present invention, in the vehicle traveling control apparatus according to the first aspect, the forward vehicle deceleration determining means determines whether the forward vehicle decelerates in a situation where the vehicle speed of the own vehicle substantially coincides with the vehicle speed of the forward vehicle. When it is determined that the deceleration has been started, the vehicle traveling control device characterized in that the own vehicle decelerates at a smaller deceleration than the deceleration of the preceding vehicle,
This is effective in decelerating the own vehicle without giving the occupant of the own vehicle an uncomfortable feeling.

According to the second aspect of the present invention, when the deceleration of the front vehicle is started in a situation where the speed of the own vehicle is substantially equal to the speed of the preceding vehicle, the own vehicle is compared with the deceleration of the preceding vehicle. And start deceleration with a small deceleration. in this case,
After the deceleration of the own vehicle is started, the inter-vehicle distance between the own vehicle and the preceding vehicle does not increase. Therefore, according to the present invention,
Even if the own vehicle is decelerated according to the deceleration of the preceding vehicle, the occupant of the own vehicle does not feel uncomfortable.

Further, the above object is achieved by a road condition detecting means for detecting a condition of a road on which the own vehicle is to travel, and a road condition detected by the road condition detecting means. A deceleration start determining means for determining whether or not the own vehicle is in a state to start deceleration; and a time when the own vehicle is determined to be in a state to start decelerating by the deceleration start determining means. And a deceleration start unit for starting deceleration of the vehicle.

According to the third aspect of the present invention, the condition of the road on which the host vehicle should travel is detected. Based on the detected road condition, it is determined whether or not the vehicle is in a condition to start decelerating. Then, the deceleration of the own vehicle is started when it is determined that the own vehicle is in a state to start decelerating. Therefore, according to the present invention, fuel efficiency and power consumption can be improved by starting deceleration at an appropriate time.

In the present invention, the road condition refers to the shape of a road such as a straight road, a curved road, or an uphill or downhill.

[0014] The object of the present invention is as described in claim 4.
The vehicle travel control device according to claim 1 or 3, wherein the own vehicle is driven and driven by using an internal combustion engine as a power source,
The deceleration start means is achieved by a vehicle travel control device that starts deceleration of the own vehicle by cutting or reducing the supply of fuel to the internal combustion engine.

In the invention according to claim 4, the host vehicle is
The vehicle is driven and driven using the internal combustion engine as a power source. The deceleration start means starts deceleration of the own vehicle by cutting or reducing the supply of fuel to the internal combustion engine. Therefore, according to the present invention, fuel efficiency can be improved by starting deceleration at an appropriate time.

According to a fifth aspect of the present invention, in the vehicle traveling control device according to the first or third aspect, the own vehicle is driven and driven by using an electric motor as a power source and the deceleration is performed. The starting means is achieved by a vehicle travel control device characterized in that deceleration of the host vehicle is started by cutting off or reducing the power supply to the electric motor.

In the invention described in claim 5, the host vehicle is
The vehicle is driven by an electric motor as a power source. The deceleration start means starts deceleration of the own vehicle by cutting off or reducing the supply of electric power to the electric motor. Therefore, according to the present invention, the power consumption can be improved by starting the deceleration at an appropriate time.

[0018]

FIG. 1 is a system configuration diagram of a vehicle traveling control device according to one embodiment of the present invention. The system of the present embodiment includes a radar electronic control unit (hereinafter, referred to as a radar ECU) 10 and an engine control electronic control unit (hereinafter, referred to as an engine ECU) 12. Controlled.

The radar ECU 10 is connected to a laser radar sensor 14 disposed, for example, near the front grill of the vehicle. The laser radar sensor 14 includes a light emitting unit that emits a laser beam having a millimeter wave as a carrier wave toward a predetermined region in front of the vehicle, and a light receiving unit that receives reflected light of the laser beam emitted forward. . The laser radar sensor 14 is configured so that the front of the vehicle is two-dimensionally scanned at a predetermined cycle.

The laser radar sensor 14 outputs a signal corresponding to the time from when the laser beam is emitted from the light emitting section to the time when the reflected wave of the laser beam is received by the light receiving section and the angle of incidence of the reflected light. Output to. Radar E
Based on the output signal of the laser radar sensor 14, the CU 10 detects a vehicle (hereinafter, referred to as a vehicle) existing in a predetermined area in front of the vehicle.
Presence / absence of the preceding vehicle), the inter-vehicle distance d between the preceding vehicle and the own vehicle when there is a preceding vehicle, and the relative speed Rxy between the own vehicle and the preceding vehicle.

The radar ECU 10 includes an engine ECU 1
2 are connected. The radar ECU 10 supplies a detection result detected based on the output signal of the laser radar sensor 14 to the engine ECU 12. Engine E
A vehicle speed sensor 16 is connected to the CU 12. The vehicle speed sensor 16 outputs a pulse signal at a cycle corresponding to the speed of the host vehicle. The engine ECU 12 detects the vehicle speed Vx of the own vehicle based on the output signal of the vehicle speed sensor 16, and detects the vehicle speed Vx.
The vehicle speed Vy of the preceding vehicle is detected based on x and the relative speed Rxy.

The engine ECU 12 is also connected to a navigation device 18 for detecting the position of the vehicle using GPS or the like. The navigation device 18 detects the current position of the vehicle based on map information set in advance, and supplies the information to the engine ECU 12.
The engine ECU 12 detects the current position of the vehicle based on the output signal of the navigation device 18.

In this embodiment, the vehicle is driven and driven by using the internal combustion engine as a power source. The internal combustion engine includes an injector 20 for supplying fuel to the combustion chamber, and a throttle valve 22 for adjusting the amount of air taken into the combustion chamber.
The injector 20 and the throttle valve 22 are respectively connected to the engine ECU 12, and the engine E
The drive is performed by supplying a drive signal from the CU 12. The engine ECU 12 supplies an appropriate drive signal to the injector 20 and the throttle valve 22 according to a predetermined logic.

The engine ECU 12 is also connected with an alarm 24 for calling attention to a vehicle occupant.
The alarm 24 is driven by supplying a drive signal from the engine ECU 12 when the own vehicle is decelerated according to the deceleration of the preceding vehicle, as described later.

Next, the operation of the vehicle running control device of the present embodiment will be described.

In this embodiment, the engine ECU 12
Decelerates the host vehicle when the inter-vehicle distance d between the host vehicle and the host vehicle is reduced due to the deceleration of the host vehicle in a situation where the host vehicle is present in a predetermined area in front of the host vehicle. Specifically, regardless of the driver's accelerator operation, the injector 2 is configured to reduce the amount of fuel supplied to the internal combustion engine.
In addition to changing the drive signal to 0, the drive signal to the throttle valve 22 is changed so that the amount of intake air to the internal combustion engine decreases.

Further, the engine ECU 12 determines whether or not the host vehicle is in a state to start deceleration at the present time based on the relationship between the current position of the host vehicle and the vehicle speed Vx. Specifically, for example, when the own vehicle runs on the front of a curved road, even though the own vehicle runs on a curved road at an ideal vehicle speed,
At this time, it is determined whether or not the own vehicle is in an overspeed condition.If the own vehicle is traveling uphill on a pass, it is necessary to determine whether the own vehicle is traveling at an ideal vehicle speed after passing the pass. It is determined whether or not the own vehicle is in the overspeed state. Then, when it is determined that the host vehicle is in a state to start deceleration, the drive signal to the injector 20 is changed such that the fuel supply amount to the internal combustion engine is reduced irrespective of the driver's accelerator operation. Along with
The host vehicle is decelerated by changing the drive signal to the throttle valve 22 so that the amount of intake air to the internal combustion engine decreases.

As described above, according to the above configuration, even when the driver does not release the accelerator operation in a situation where the own vehicle needs to start decelerating, the fuel supply amount and the intake of the internal combustion engine can be surely ensured. By reducing the amount of air, the host vehicle can be decelerated.

FIG. 2 shows a flowchart of an example of a control routine executed by the engine ECU 12 in the present embodiment in order to decelerate the host vehicle in accordance with the deceleration of the preceding vehicle regardless of the accelerator operation of the driver. The routine shown in FIG. 2 is a periodic interrupt routine that is started every predetermined time. When the routine shown in FIG. 2 is started, first, the process of step 100 is executed.

In step 100, the current position of the vehicle is detected based on the output signal of the navigation device 18.

In step 102, the vehicle speed Vx of the host vehicle is detected based on the output signal of the vehicle speed sensor 16.

In step 104, the above-mentioned step 100
Position and vehicle speed Vx of the own vehicle detected in steps 102 and 102
It is determined whether or not the host vehicle is in a state to start deceleration. In the present embodiment, the engine ECU
Reference numeral 12 stores in advance an ideal relationship between the position of the host vehicle and the vehicle speed. In the process of step 104, the ideal relationship is compared with the relationship between the current position of the host vehicle and the vehicle speed Vx to determine whether or not the host vehicle is in a state to start deceleration. Specifically, for example, when the own vehicle is running on a curved road, it is determined whether the own vehicle is in an overspeed state at the present time even though the own vehicle is running on the curved road at an ideal vehicle speed. In addition, when the own vehicle runs on an uphill of a pass, it is determined whether or not the own vehicle is in an overspeed state at the present time even though the own vehicle runs at an ideal vehicle speed after passing the pass. .

As a result, if it is determined that the own vehicle is in a state to start deceleration, the process of step 112 is executed next. On the other hand, if it is determined that the own vehicle is not in a state to start deceleration, the process of step 106 is executed next.

In step 106, based on the output signal of the laser radar sensor 14, the inter-vehicle distance d between the host vehicle and a preceding vehicle existing in a predetermined area in front of the host vehicle is detected.

In step 108, the above-mentioned step 106
The relative speed Rxy between the host vehicle and the preceding vehicle is detected based on the inter-vehicle distance d detected in step (1), and the vehicle speed Vy of the preceding vehicle is detected based on the relative speed Rxy and the vehicle speed Vx.

In step 110, the deceleration ΔVy of the preceding vehicle is equal to or greater than a predetermined value α based on the vehicle speed Vy1 of the preceding vehicle in the previous processing cycle and the vehicle speed Vy2 of the preceding vehicle in the current processing cycle. Is determined. Note that the predetermined value α is the minimum value of the deceleration ΔVy of the front vehicle that can determine that the front vehicle has started decelerating from the previous processing cycle to the current processing cycle,
It is set to a positive number in advance.

As a result, if ΔVy ≧ α does not hold, it can be determined that the preceding vehicle has not started decelerating from the previous processing cycle to the current processing cycle.
In this case, it is appropriate to continue the operation of the internal combustion engine as usual. Therefore, if it is determined that ΔVy ≧ α is not established, the current routine is ended. On the other hand, Δ
If Vy ≧ α holds, it can be determined that the inter-vehicle distance has decreased from the previous processing cycle to the current processing cycle. In this case, it is necessary to immediately start deceleration of the own vehicle. Therefore, if it is determined that ΔVy ≧ α is satisfied, the process of step 112 is performed next.

In step 112, the drive signal to the injector 20 is changed so that the amount of fuel supplied to the combustion chamber of the internal combustion engine decreases in accordance with the following distance d and the variation Δd, and The process of changing the drive signal to the throttle valve 22 is performed so that the intake amount of the intake air decreases according to the inter-vehicle distance d and the change amount Δd, and the process of driving the alarm 24 is performed. When the process of step 112 is executed, the amount of fuel and the amount of air supplied to the combustion chamber of the internal combustion engine decrease, and the driving force of the vehicle decreases, and as a result, the host vehicle starts to decelerate. When the process of step 112 is completed, the current routine is completed.

According to the above-described processing, when the preceding vehicle existing in the predetermined area in front of the own vehicle starts decelerating, and based on the current position of the own vehicle and the vehicle speed Vx, the own vehicle starts decelerating. When it is in the state to be performed, the fuel supply amount and the intake air amount supplied to the internal combustion engine of the host vehicle can be immediately reduced.

FIG. 3 is a diagram showing a time chart for explaining the operation of the vehicle traveling control device of this embodiment.
FIG. 3A shows a time chart of the vehicle speed.
(B) shows a time chart of the inter-vehicle distance between the host vehicle and the preceding vehicle, respectively. In FIG. 3, the preceding vehicle is indicated by a dashed-dotted line, and the own vehicle (hereinafter, referred to as a comparative vehicle) without the vehicle running control device of the present embodiment is indicated by a solid line, and the vehicle running control device of the present embodiment is mounted. The own vehicle is indicated by broken lines.

As shown in FIG. 3A, when the deceleration of the preceding vehicle starts at time t1, the deceleration of the comparative vehicle starts with a predetermined time delay, while the deceleration of the own vehicle of the present embodiment starts. Deceleration is started almost simultaneously with the start of deceleration of the vehicle. After the preceding vehicle starts decelerating, the host vehicle does not need to continue running at a constant speed or accelerating for an unreasonably long time, and it is unnecessary to supply a large amount of fuel or air to the internal combustion engine. Therefore, according to the present embodiment, it is possible to avoid supplying a large amount of fuel to the internal combustion engine by an extra delay time from the start of deceleration of the preceding vehicle to the start of deceleration of the own vehicle. it can. That is, the amount of fuel supplied to the internal combustion engine can be reduced. For this reason, according to the vehicle traveling control device of the present embodiment, the fuel consumption can be improved by starting the deceleration of the own vehicle immediately with the deceleration of the preceding vehicle.

In this embodiment, as described above,
For example, even when the vehicle is in a state to start decelerating just before a curved road or just before a pass, the fuel amount and the intake air amount are thereafter reduced. Therefore, according to the present embodiment,
It is possible to prevent fuel and air from being supplied to the internal combustion engine for an unnecessarily long time immediately before a curved road or a pass. As described above, according to the vehicle traveling control device of the present embodiment, it is possible to improve the fuel efficiency by starting the deceleration of the own vehicle at an appropriate time according to the road condition.

In the present embodiment, as described above, when the preceding vehicle starts decelerating and when the host vehicle is in a state to start decelerating, the host vehicle operates regardless of the accelerator operation of the driver. The speed is reduced by reducing the fuel supply amount and the intake air amount. For this reason, according to the present embodiment, even when the driver cannot recognize the situation where the own vehicle is likely to come into contact with the vehicle in front, or when the start of deceleration by the driver is delayed before a curved road, It is possible to reliably prevent the host vehicle from contacting the preceding vehicle or the guardrail. Therefore, according to the vehicle traveling control device of the present embodiment, the safety of the own vehicle can be improved.

In the present embodiment, the own vehicle starts to decelerate almost at the same time as the preceding vehicle starts to decelerate as described above, and therefore, compared to the case where deceleration is started with a predetermined time delay. Therefore, the ratio of time during which the vehicle travels at high speed decreases. For this reason, according to the present embodiment, it is possible to suppress an increase in the operating noise of the internal combustion engine and the contact noise between the tire and the road surface caused by the own vehicle traveling at high speed.

In general, it is necessary to increase the inter-vehicle distance between the host vehicle and the preceding vehicle as the vehicle speed increases, while it is appropriate to decrease the inter-vehicle distance as the vehicle speed decreases. In the present embodiment, the deceleration is started earlier than when the deceleration is started with a predetermined time delay. When the deceleration of the own vehicle is started almost simultaneously with the start of the deceleration of the preceding vehicle, the deceleration is started after the deceleration of the own vehicle is started, compared with the case where the deceleration of the own vehicle is started with a predetermined time delay.
The traveling distance until the host vehicle stops while securing a predetermined inter-vehicle distance with the preceding vehicle increases.

Therefore, according to the present embodiment, the deceleration of the host vehicle after the start of the deceleration is suppressed to be smaller than when the deceleration of the host vehicle is started with a predetermined time delay. It becomes possible. Therefore, according to the present embodiment, it is possible to improve the ride comfort without giving the occupant a sense of discomfort, and it is possible to reduce the wear of the brake braking member and the tire.

In this embodiment, when the deceleration of the preceding vehicle is started in a situation where the speed of the own vehicle is substantially equal to the speed of the preceding vehicle, the deceleration of the own vehicle is reduced. It can be kept small compared to the speed. In this case, after the deceleration of the own vehicle is started, the inter-vehicle distance between the own vehicle and the preceding vehicle does not increase. For this reason, according to the vehicle traveling control device of the present embodiment, it is possible to prevent the occupant from feeling uncomfortable when the own vehicle is decelerated with the deceleration of the preceding vehicle.

FIG. 4 is a diagram showing a time chart of the vehicle speed in a situation where two vehicles equipped with the vehicle traveling control device of the present embodiment are present continuously. In FIG. 4,
The host vehicle equipped with the vehicle travel control device of the present embodiment is indicated by a two-dot chain line, and the front vehicle equipped with the vehicle travel control device of the present embodiment is present in front of the own vehicle. (Hereinafter referred to as the two-way ahead vehicle) are indicated by alternate long and short dash lines, and the own vehicle (comparative vehicle) not equipped with the vehicle travel control device of the present embodiment is indicated by a solid line.

In the case where two vehicles equipped with the vehicle traveling control device of this embodiment are present in succession, the forward vehicle immediately supplies the fuel supply amount and the intake air amount when the vehicle before the preceding vehicle starts to decelerate. Is reduced by reducing
The host vehicle is decelerated by immediately decreasing the fuel supply amount and the intake air amount when the preceding vehicle starts to decelerate. For this reason, when the vehicle before the front starts decelerating, FIG.
As shown in the figure, the deceleration of the own vehicle is started almost simultaneously with the start. That is, when the vehicles equipped with the vehicle travel control device of the present embodiment are running continuously, deceleration is started earlier in a later vehicle than in normal times, and the deceleration is suppressed to a small value. Therefore, according to the system of the present embodiment, the above-described effect can be further made more apparent as the vehicle moves further.

In the above embodiment, the engine E
The CU 12 executes the processing of step 110, and the “forward vehicle deceleration determination means” described in the claims executes the processing of step 112. The claims 1 and 3 of the claims The “deceleration start determining means” described in the claims is realized by executing the processing of step 104 described above.

By the way, in the above embodiment, the own vehicle decelerates when the inter-vehicle distance between the own vehicle and the preceding vehicle detected based on the output signal of the laser radar sensor 14 decreases. Although it is determined that the vehicle has started, the present invention is not limited to this, and it is determined that the preceding vehicle has started decelerating by receiving the deceleration signal generated by the preceding vehicle by the own vehicle. It may be that.

In the above embodiment, when the preceding vehicle starts to decelerate, the drive signals to the injector 20 and the throttle valve 22 are changed according to the following distance d and the amount of change Δd. However, the supply of the drive signal to the injector 20 and the throttle valve 22 may be stopped, and the supply of the drive signal to the throttle valve 22 may be stopped.

Further, in the above-described embodiment, fuel efficiency is improved by starting deceleration at an appropriate time in a vehicle driven and driven by an internal combustion engine as a power source. It is also possible to apply the present invention to a vehicle that is driven and driven. In such a configuration, if the power supplied to the electric motor is reduced or cut at an early stage, the power consumption can be improved. In this case, the engine ECU 12 cuts or reduces the electric power supplied to the electric motor, thereby realizing the "deceleration start means" described in the claims.

As described above, according to the first, third, fourth, and fifth aspects of the present invention, the deceleration of the vehicle is started at an appropriate time, thereby improving fuel efficiency or power consumption. be able to.

According to the second aspect of the invention, when the own vehicle is decelerated in accordance with the deceleration of the preceding vehicle, it is possible to prevent the occupant of the own vehicle from feeling uncomfortable.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a vehicle traveling control device according to an embodiment of the present invention.

FIG. 2 is a flowchart of an example of a control routine executed to decelerate the host vehicle in accordance with the deceleration of a preceding vehicle in the embodiment.

FIG. 3 is a diagram showing a time chart for explaining an operation of the vehicle traveling control device of the embodiment.

FIG. 4 is a diagram showing a time chart of a vehicle speed in a situation where two vehicles equipped with the vehicle travel control device of the present embodiment are present continuously.

[Explanation of symbols]

10 Electronic control unit for radar (radar ECU) 12 Electronic control unit for engine control (engine EC
U) 14 Laser radar sensor 16 Vehicle speed sensor 18 Navigation device 20 Injector

Claims (5)

[Claims] 1. A front vehicle deceleration determining means for determining whether or not a preceding vehicle existing in front of a host vehicle has started decelerating, and the forward vehicle deceleration determining means determines that the preceding vehicle has started decelerating. And a deceleration start means for starting deceleration of the own vehicle at a point in time. 2. The vehicle travel control device according to claim 1, wherein the forward vehicle deceleration determining means determines that deceleration of the forward vehicle has started in a situation where the vehicle speed of the own vehicle substantially coincides with the vehicle speed of the forward vehicle. A vehicle travel control device that, when performed, decelerates the own vehicle at a deceleration smaller than the deceleration of the preceding vehicle. 3. A road condition detecting means for detecting a condition of a road on which the own vehicle is to travel, and a condition in which the own vehicle is to start deceleration based on the condition of the road detected by the road condition detecting means. Deceleration start determining means for determining whether or not the vehicle is in a state to start decelerating by the deceleration start determining means, and deceleration starting means for starting deceleration of the own vehicle. A vehicle travel control device characterized by the above-mentioned. 4. The vehicle travel control device according to claim 1, wherein the own vehicle is driven and driven by using an internal combustion engine as a power source, and the deceleration start unit cuts a supply of fuel to the internal combustion engine. Alternatively, the vehicle travel control device starts deceleration of the own vehicle by decreasing the vehicle weight. 5. The vehicle travel control device according to claim 1, wherein the own vehicle drives and travels using an electric motor as a power source, and the deceleration start unit supplies electric power to the electric motor. A vehicle travel control device characterized in that deceleration of the own vehicle is started by cutting or reducing the weight.