JPH0345474A - Under floor structure of automobile - Google Patents

Abstract

PURPOSE:To control the down force acting on th car body so as to secure always optimum control stability by forming an opening at the under floor, which partitions the lower side of an engine room, and widening or narrowing the opening area of the opening according to the running conditions of a vehicle. CONSTITUTION:An opening 8 is formed at the under floor 4 which partitions the lower side of an engine room 3 in a car body 1. And a shutter 9, which slides to open or close along guide rails 12 by a reversible motor 12, is arranged as a means to vary this opening area at the opening 8. Furthermore, the variable control means 9 is controlled to open or close according to the running conditions of a vehicle by a driving control means not shown in the figure. And with the reduction in the area of the opening 8, the down force is increased, and also the down force balance is shifted forward. On the other hand, with the increase in the area of the opening 8, the down force is reduced, and also the down force balance is shifted rearward.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an underfloor structure of an automobile, and more particularly to an underfloor structure that can perform aerodynamic processing and maintain good handling stability of the automobile at all times.

BACKGROUND OF THE INVENTION Conventionally, movable aerodynamic control means for ensuring steering stability of automobiles are known, for example, in Japanese Patent Publication No. 60161267 and Japanese Patent Publication No. 60-209369. Both of these systems use front and rear spoilers to control the aerodynamics, and the spoilers are operated and controlled according to vehicle driving conditions such as vehicle speed, road surface conditions (dry and wet discrimination), and braking. That's what I do.

Problems to be Solved by the Invention In the case of aerodynamic control using these spoilers, for example, when aerodynamic control is performed using a front spoiler, the front downforce increases, but the rear downforce decreases; When the control is performed, the rear downforce increases, but the front downforce decreases, so the downforce tends to be too biased toward the front or rear. Therefore, in order to optimize the front-rear downforce balance, it is necessary to perform aerodynamic control using spoilers at two locations: front and rear. In addition, as mentioned above, control is performed in response to vehicle speed, road surface conditions (dry/wet identification), braking conditions, etc. as the driving conditions of the vehicle, so the control content is coarse and it takes time to always obtain good steering stability. had not been reached.

SUMMARY OF THE INVENTION Therefore, the present invention provides an underfloor structure for an automobile that is capable of controlling the downforce acting on the vehicle body depending on the driving condition and constantly maintaining good steering stability.

Means for Solving the Problem An opening is formed in the underfloor that separates the lower side of the engine room, a variable control means for controlling the opening area is provided in the opening, and the variable control means is opened and closed according to the running condition of the vehicle. A drive control means for operation is provided.

When the opening area variable control means is closed by the operation drive control means and the area of the opening is reduced, the downforce force is increased and the town force balance is shifted to the front side. Conversely, when the variable control means is opened and the opening area increases, the downforce force decreases and the downforce balance shifts to the rear side.

Example Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In FIG. 1, an engine room 3 in which an engine 2 is mounted is formed at the rear of a vehicle body 1, and an underfloor 4 is formed below the engine room 3 to separate the engine room 3. be.

This underfloor 4 is made up of a flat floor surface 5 and an inclined floor surface 6 that is inclined from the flat floor surface 5 and continues to the tail end 7, and has an opening 8 in a portion of the flat floor surface 5 below the engine 2 It is formed. The opening 8 is provided with a flat stage 9 for variable control of the opening area, and a drive control means 10 for opening and closing the variable control means 9 in accordance with the vehicle running state. In this embodiment, as the variable control means 9, a shutter is used which is wound up and unwound twice by a reversible motor 11 and which slides to open and close along guide rails 12 formed on both sides of the opening 8. 13 is a cooling air intake provided on the rear fender 14; 15 is an intercooler installed behind the cooling air intake 13; and 16 is a cooling air intake provided on the tail end 7.

Now, considering the pressure (negative pressure) distribution around the underfloor 4 due to the opening and closing of the opening 8, the relationship between the opening and closing of the opening 8 and the downforce (-CL) is as shown in FIG.
When the opening 8 is closed, the area on which vertical pressure acts increases as shown in the figure, and the downforce increases as shown in the experimental results of FIG. 4. Conversely, when the opening 8 is open, the pressure near the bend at the boundary between the flat floor surface 6 and the inclined floor surface 6, where the pressure is greatest, is:
It is greatly weakened by the outflow of air from the engine room 3, and the downforce decreases as shown in FIG. Similarly, by closing the opening 8, the downforce balance (downforce sharing ratio knee CLR/-CL) shown in the experimental results of FIG. 5 moves forward. Therefore, if the opening and closing of the opening 8 is controlled in accordance with the driving condition of the vehicle, taking into consideration the characteristics of the town force and down force balance, good steering stability can always be obtained.

Driving conditions in which steering stability is required due to changes in downforce can be broadly classified into the following cases.

1. When the front-rear balance of downforce needs to be forward - when the car is about to change direction = when the steering angular velocity is occurring.

■When large downforce is required - the car decelerates,
When accelerating - when the longitudinal G of the vehicle body is large.

When the accelerator opening is OFF (below the set value).

(2) When it is necessary to change the longitudinal balance of downforce to the rear - when driving straight at high speed or when turning in a steady state - no steering angular velocity is occurring, and there is almost no longitudinal G of the vehicle body.

■When it is necessary to reduce air resistance - when driving straight at high speed - when steering angular velocity does not occur.

Based on the above, when considering the case of actually driving on a curved road as shown in Figure 11, the driving point ■ (the position where the vehicle decelerates and starts turning the steering wheel)
, Driving point ■ (position where the steering wheel is held approximately constant and the vehicle starts to turn steadily), Driving point ■ (position where the steering wheel begins to be turned in the opposite direction and acceleration begins), Driving point ■ (transition to straight high-speed driving) ), in order to pass through this curved road in a short time, it is necessary to adjust the accelerator opening, brake, steering angular speed,
It is generally considered good for each mode of vehicle longitudinal G and vehicle lateral G to show time-series changes as shown in FIG. Therefore, if we apply this driving condition to the requirements of points ■ to ■, we can see that in the driving range of points ■ to ■, the opening 8 of the underfloor 4 is closed to increase the downforce, and the downforce balance is adjusted forward. Move to.

In the driving range of points ■-■, the opening 8 of the underfloor 4 is opened to shift the downforce balance to the rear.

In the driving range between points ■ and ■, the opening 8 is closed to increase the downforce as in the driving range between points ■ and ■.

After point ①, opening 8 is opened to reduce downforce and air resistance.

By controlling the opening and closing of the opening 8 as described above, it is possible to always improve the steering stability at each traveling point.

On the other hand, controlling the downforce and downforce balance by opening and opening the opening 8 basically detects changes in the steering angular velocity in order to improve turning performance by changing the downforce balance back and forth. In addition to detecting the steering angular velocity, it is also possible to detect the front and rear G of the vehicle body to improve tire grip during acceleration and deceleration, and to turn off the accelerator opening (setting opening) to improve the closing response of the shutter 9. It is desirable to control the opening/closing by detecting the

FIG. 6 shows the circuit configuration of the drive control means 10, in which the running state of the vehicle is determined by detecting an accelerator opening sensor 20, a steering angular velocity sensor 21, and a vehicle longitudinal G sensor 22. These accelerator opening sensors 20.
The steering angular velocity sensor 21 and the longitudinal G sensor 22 are connected to a microcomputer 23, and each of these sensors 20,
Based on the detection signals 21 and 22, the microcomputer 23 sends an output signal to the reversible motor 11. Specifically, when the accelerator opening is less than the set value (OFF), or when the longitudinal G of the vehicle is more than the set value,
Or, when the steering angular velocity is above the set value (ON), the microcomputer 23 sends a rotation signal in the shutter closing direction to the reversible motor 11, and when the steering angular velocity is below the set value (OFF), the vehicle body longitudinal G When is less than a set value, a rotation signal in the shutter closing direction is sent to the reversible motor 11. Reference numerals 24, 25, 26, and 27 respectively indicate an input interface, a ROMSRAM, and an output interface of the microcomputer 23.

Next, the operation of the above-described embodiment will be explained with reference to the flowchart of FIG. 7 for the case where the vehicle travels on a curved road shown in FIG. 11.

When the vehicle reaches the driving point ■ and starts to turn the steering wheel while decreasing the accelerator opening and decelerating, the accelerator opening change, the longitudinal G change of the vehicle body due to deceleration, and the steering angular velocity change are detected by the accelerator opening sensor 2C, the front and rear of the vehicle body, respectively. G sensor 22. Detected by the steering piece speed sensor 21, step 1
Step 101 determines whether the accelerator opening is OFF at 00.
In step 102, it is determined whether the steering angular velocity is ON or not, and in step 102, it is determined whether the longitudinal G of the vehicle body is equal to or greater than a set value.If any one of the steps 100, 102, and 102 is affirmative, the microcomputer 23 Immediately, a rotation signal in the shutter closing direction is sent to the reversible motor 11, and the shutter 9 is moved to close, completely closing the opening 8 of the underfloor 4 (step 103). This increases the downforce and moves the downforce balance forward.

When the vehicle reaches the driving point ■, the vehicle transitions to steady turning driving at low speed with the steering wheel turned almost constant, and as the steering angular speed falls below the set value (OFF),
When the longitudinal G of the vehicle body becomes less than the set value, step 101.
If both are negative in step 102, the microcomputer 23 immediately sends a rotation signal in the shutter opening direction to the reversible motor 11, and the shutter 9 is opened to fully open the opening 8 (step 104).

This reduces the downforce and shifts the downforce balance to the rear.

When the vehicle reaches the driving point ■ and begins to turn the steering wheel in the opposite direction, it also begins to accelerate.
If either the steering angular velocity or the longitudinal G of the vehicle body exceeds the set value, an affirmative determination is made in step 101 or step 104, and the shutter 9 moves to close again to fully open the opening 8 (step 103). .

When the vehicle shifts to straight high-speed running at the running point ■, the steering angular velocity is turned off, and the longitudinal G of the vehicle body becomes less than the set value, step 101. A negative judgment is made in step 102, and as a result, the shutter 9 is moved to fully open the opening 8 (step 104), and as a result, the downforce balance moves rearward and the air resistance becomes smaller (downforce Small) to be done.

It is assumed that the above downforce control is performed at a vehicle speed of 2Q km/h or higher, taking into account cooling during idling of the vehicle.

In the embodiment described above, downforce control is performed by fully opening or fully closing the shutter 9, but downforce control may also be performed by adjusting the opening degree of the shutter 9 depending on the vehicle running state.

FIG. 8 shows a motor drive circuit for adjusting the opening degree of the shutter 9 as described above. A potentiometer 30 serves as an opening sensor for the shutter 9, and exhibits voltage change characteristics as shown in FIG. 9 depending on the shutter opening. 3
1 is a comparator that compares the reference voltage and the feedback voltage of the potentiometer 30; 32 is a motor forward rotation amplifier that rotates the motor 11 in the forward direction and opens the shutter 9 according to the output signal from the comparator 31; 33 is a comparator The motor 11 is reversely rotated by the output signal from the shutter 9.
34 is the shutter 9
Detects the fully open position of the motor 11 and
When the shutter 9 reaches the fully open position due to normal rotation of the shutter 9, it is turned on and the rotation of the motor 11 is stopped. A limit switch 35 detects the fully closed position of the shutter 9, and is turned on when the shutter 9 reaches the fully closed position due to reverse rotation of the motor 11, thereby stopping the rotation of the motor 11. 36.
37 is a diode that prevents reverse current flow, 38 is a main switch, and 39 is a battery.

In this embodiment, the microcomputer 23 shown in FIG. 6 outputs the accelerator opening sensor 20 as shown in the flowchart of FIG. Steering angular velocity sensor 21. An operating voltage is sent as a reference voltage to the comparator 31 of the motor drive circuit in accordance with the vehicle running state determined by the vehicle longitudinal G sensor 22.

In the flowchart of FIG. 10, θ: steering angular velocity;
θ. : Steering angular speed set value, 9: Vehicle body longitudinal G, 9° double body longitudinal G set value, S: Accelerator opening, S.

: Accelerator opening setting value, ■ = control output signal.

In step 200, it is determined whether the steering angular velocity is equal to or higher than a set value. If the answer is yes, the process goes to step 201, and if the answer is negative, the process goes to step 206. In step 201, the voltage value ■
θ is found. In step 202, a voltage value v9 is determined by a coefficient Kg based on the difference between the set value and the longitudinal G of the vehicle body occurring at that time. In step 203, the voltage value Vθ and the magnitude of Vg are compared, and if Vg is large, step 204 is carried out, and if Vg is large, step 2 is carried out.
05, one of the larger voltage signals is sent from the microcomputer 23 to the comparator 31 of the motor drive circuit as a reference voltage signal for the shutter open direction. As a result, the comparator 3I compares this reference voltage with the potentiometer 30.
is compared with the feedback voltage of
The shutter 9 is closed to a shutter opening position where the voltage difference between the reference voltage and the feedback voltage is O.

In step 206, it is determined whether or not the longitudinal G of the vehicle body is equal to or greater than a set value.If the answer is yes, the process goes to step 207, and if the answer is negative, the process goes to step 208. In step 207, the voltage value V is determined by a coefficient Kg based on the difference between the vehicle body longitudinal G and the set value.
is determined and sent to the comparator 31 as a base Q voltage signal in the shutter blank direction, and due to the comparison action of the comparator 31, the voltage difference between the reference voltage and the feedback voltage becomes O as described above.
The motor 11 is reversely rotated to the shutter opening position to close the shutter 9.

In step 208, it is determined whether or not the accelerator opening is less than or equal to a set value. If affirmative, the process proceeds to step 209; if negative, the process proceeds to step 210. In step 209, the maximum value 0.5v max of the shutter closing direction signal is determined and sent to the comparator 31 as a reference voltage signal. As a result,
The motor 11 is reversely rotated via the reversing amplifier 33 until the shutter 9 reaches the fully closed position, and when the shutter 9 reaches the fully closed position, the limit switch 35 is turned on and the motor rotation is stopped. On the other hand, in step 210, a voltage signal is determined as ■-○, and is sent to the comparator 31 as a reference voltage signal. As a result, the motor 11 is rotated in the forward direction via the forward rotation amplifier 32 until the shutter 9 reaches the fully open position, and when the shutter 9 reaches the fully open position, the limit switch 34 is turned on and the motor rotation is stopped.

Effects of the Invention As described above, according to the present invention, it is possible to control downforce and downforce balance by variable control of the opening area of the underfloor opening according to the vehicle running condition, so that good steering stability is always maintained. can be done. In particular, because it does not use a conventional spoiler to control downforce at the front and rear of the car body, the downforce is not biased to one area, and as mentioned above, it is finely controlled according to the driving conditions. This has a great practical effect.

[Brief explanation of drawings]

Fig. 1 is a schematic transparent perspective view of a vehicle to which an embodiment of the present invention is applied, Fig. 2 is a perspective view of variable control means, and Fig. 3 shows the pressure distribution state around the underfloor of the same embodiment. Explanatory diagram, Fig. 4 is a CD and CL characteristic diagram when the opening of the underfloor is opened and closed, Fig. 5 is a downforce balance characteristic diagram of the same, and Fig. 6 is an electric circuit of the drive control means of the same embodiment. 7 is a flowchart explaining the operation of the drive control means, FIG. 8 is an electric circuit diagram showing a motor drive circuit according to a different embodiment of the present invention, and FIG. 9 is a voltage characteristic of the potentiometer of the drive circuit. 10 is a flowchart explaining the operation of the drive control means that operates the motor drive circuit, FIG. 11 is an explanatory diagram of a curved road on which the vehicle travels, and FIG. 12 is an illustration of the accelerator opening when traveling on the curved road. degree, brake,
Steering angular velocity. FIG. 3 is an explanatory diagram showing time-series changes in vehicle body longitudinal G and vehicle body lateral G, and opening and closing timings of an underfloor opening. DESCRIPTION OF SYMBOLS 1... Vehicle body, 3... Engine room, 4... Underfloor, 8... Opening, 9... Opening area variable control means, 10... Drive control means. Figure 3 Figure 4 Figure 5 Boun Force Splash Figure 7

Claims (1)

[Claims] (1) An opening is formed in the underfloor that separates the lower side of the engine room, a variable control means for controlling the opening area of the opening, and a drive control for opening and closing the variable control means according to the vehicle running state. An underfloor structure of an automobile, characterized in that it is provided with means.