JPH04282485A - Device for measuring distance between cars - Google Patents

Abstract

PURPOSE:To prevent error detection due to the reflection by rain drops by so constituting that the level of sensititvity time control (STC) circuit varies when raindrops are detected by a raindrop sensor and the like. CONSTITUTION:When raindrops are detected by the actuation of a raindrops sensor or a wiper switch, the level of an STC circuit 31 varies. And the level of the circuit 31 is so set as to become larger then the case the detected reflection by raindrops is received and the level of the circuit 31 increases with the amount of rain drops and the like. Thus, through the comparison at a comparator 19, the level in the case reflection by raindrops is received, is judged smaller than the level of the circuit 31 and the comparator 19 does not output a pluse signal and therefore, error detection by the reflection by raindrops and the like is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inter-vehicle distance measuring device, and more particularly to an inter-vehicle distance measuring device that measures an inter-vehicle distance using a near-infrared LD.

0002

[Prior Art and Problems to be Solved by the Invention] FIG. 4 is a block diagram schematically showing an example of a conventional inter-vehicle distance measuring device. be. When the transmitter 11 is turned on, the near-infrared LD 12 outputs laser light, and the output laser light is irradiated forward through the lens 13. When a car 14 is present in front, the irradiated laser beam is reflected by the car 14,
Thereafter, the light is focused by a lens 15 and photoelectrically converted by a photodiode 16. Then, the photoelectrically converted signal is sent to the receiver 17
The signal is sent to the amplifier 18 via the amplifier 18, where it is amplified, and then output to the negative input terminal of the comparator 19.

On the other hand, when the transmitter 11 is turned on, the transmitter 11 outputs a signal at a predetermined level. The output signals are sent to an STC circuit 21 and a flip-flop (FF) circuit 20, respectively, and the STC circuit 21 outputs a signal with a predetermined threshold voltage to the positive input terminal of the comparator 19. Also F. The F circuit 20 enters a set state and outputs a predetermined waveform signal to the distance calculating section 22. The comparator 19 then compares the threshold voltage from the STC circuit 21 with the voltage of the signal input from the receiver 17 via the amplifier 18, and if the signal from the receiver 17 is greater than the threshold voltage, A predetermined pulse signal is sent to F. F
Output to circuit 20. In other words, if the received signal is lower than the threshold voltage, the comparator 19 assumes that the received signal is due to dirt on the protective plate of the inter-vehicle distance measuring device, or reflection from rain or snow, and outputs a pulse signal. If not and the received signal is greater than the threshold voltage, then
Assuming that the pulse signal is due to reflection from the car 14 in front, the F. Output to F circuit 20. This prevents erroneous detection due to dirt on the protective plate or reflections from rain or snowfall.

Further, when a pulse signal is input from the comparator 19, the F. F circuit 2
0 is a reset state, and a waveform signal opposite to the output waveform of the set state is output to the distance calculating section 22. Distance calculation section 2
2 is F. Based on the change in the output waveform from the F circuit 20,
The time from transmission to reception of the laser beam is determined, and the inter-vehicle distance to the vehicle 14 in front is calculated from the determined time. The calculation result is sent to the ECU (not shown) from the distance calculation unit 22.
The ECU controls and displays the following distance based on the calculation results.

[0005] As described above, in this inter-vehicle distance measuring device, the output voltage of the STC circuit 21, that is, the threshold voltage, is fixed at a predetermined level. Therefore, when adjusting the output level of the STC circuit 21 during clear weather,
When it rains, the inter-vehicle distance measuring device sometimes detects the rain instead of the vehicle 14 in front of it, and conversely, when it rains, adjusting the STC circuit 21 causes a problem in that detection sensitivity at short distances becomes insufficient. Therefore, there has been a strong desire to develop an inter-vehicle distance measuring device that can accurately measure the inter-vehicle distance in both rainy and sunny conditions.

[0006] The present invention was made in view of the above problems, and an object of the present invention is to provide an inter-vehicle distance measuring device that can accurately measure an inter-vehicle distance both in rainy and sunny weather. There is.

[0007]

[Means for Solving the Problems] In order to achieve the above object, an inter-vehicle distance measuring device according to the present invention includes a transmitting section and a receiving section, and measures an inter-vehicle distance using a near-infrared LD. The device is characterized in that when raindrops are detected due to activation of a raindrop sensor, wiper switch, etc., the level of the STC circuit changes.

[0008]

[Operation] According to the above configuration, when raindrops are detected by starting the raindrop sensor, wiper switch, etc., the ST
The level of the C circuit is configured to change, and when raindrops are detected, the level of the STC circuit is set to be higher than the signal level when a reflection from a raindrop is received. Further, the level of the STC circuit is set to increase depending on the amount of rain, etc. Therefore, in the comparison by the comparator, the signal level when receiving reflections from raindrops is determined to be lower than the level of the STC circuit, and since the comparator does not output a pulse signal, erroneous detection due to reflections from raindrops, etc. is definitely prevented.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the inter-vehicle distance measuring device according to the present invention will be described with reference to the drawings. Note that components having the same functions as those of the conventional example are given the same reference numerals. Figure 1
is a configuration diagram schematically showing an embodiment of the inter-vehicle distance measuring device according to the present invention. Similar to the conventional example shown in FIG. 4, when the transmitter 11 is turned on, the near-infrared LD 12 emits a laser Light is output, and the output laser light is irradiated forward through the lens 13. When a car 14 is present in front, the irradiated laser beam is reflected by the car 14, then focused by a lens 15, and photoelectrically converted by a photodiode 16. The photoelectrically converted signal is then sent to the amplifier 18 via the receiver 17, where it is amplified and then output to the negative input terminal of the comparator 19.

On the other hand, when the transmitter 11 is turned on, the transmitter 11 outputs a signal at a predetermined level. The output signal is sent to the STC circuit 31 and the flip-flop (F.
F) respectively to the circuit 20; The F circuit 20 enters a set state and outputs a predetermined waveform signal to the distance calculating section 22 within the microcomputer 42. Further, when a signal is input from the transmitter 11, the STC circuit 31 outputs a threshold voltage signal of a required level to the positive input terminal of the comparator 19. The level of the output signal of this STC circuit 31 is controlled by a microcomputer 42 as will be described later, and changes depending on the environment such as during rain.

That is, the distance calculation circuit 22 of the microcomputer 42 is connected to a raindrop detection means (not shown) which is composed of a raindrop sensor, a detection means for detecting the start of a wiper switch, etc. When the raindrop detection signal is input from the means to the distance calculation circuit 22, the distance calculation circuit 22 outputs a control signal to the D/A conversion circuit 43 in the microcomputer 42 based on the raindrop detection signal. Then, the D/A conversion circuit 43 determines the output level of the STC circuit 31 according to the input control signal, and
Control is performed so that the C circuit 31 outputs a signal at a required level.

FIG. 2 is a block diagram schematically showing an example of the STC circuit 31, which mainly consists of a buffer circuit 31a for impedance adjustment and a differentiation circuit 31b connected to the output side of the buffer circuit 31a. ing. The square wave signal of the required level determined by the D/A conversion circuit 43 as described above is input to the differentiation circuit 31b of the STC circuit 31 and differentiated, and the signal of this differentiation waveform is applied to the bias voltage output from the buffer circuit 31a. superimposed on This increases the level of the bias voltage, and a signal of a desired level is output from the STC circuit 31 to the positive input terminal of the comparator 19. In this way, the level of the output signal of the STC circuit 31 is set under the control of the microcomputer 42 to an optimal value depending on the environment, that is, a value larger than the signal level when reflections from raindrops are received. At this time, the output level of the STC circuit 31 changes approximately proportionally depending on the amount of rain, as shown in FIG. 3, when the raindrop detection means is a raindrop sensor, for example. If the detection means detects
, INT, Lo, and Hi. As described above, the output signal of the STC circuit 31, which is set to an optimal level according to the environment, is outputted to the positive input terminal of the comparator 19 as a threshold voltage signal.

The comparator 19 compares the threshold voltage from the STC circuit 21 with the voltage of the signal input from the receiver 17 via the amplifier 18,
If the signal from F.7 is greater than the threshold voltage, a predetermined pulse signal is sent to F.7. Output to F circuit 20. That is, if the received signal is less than the threshold voltage, comparator 1
9 assumes that the received signal is due to reflection from rain etc. and does not output a pulse signal, and if the received signal is higher than the threshold voltage, it is due to reflection from the car 14 in front. The pulse signal is F. Output to F circuit 20. Note that since the threshold voltage increases depending on the amount of rain, etc., erroneous detection due to reflections from raindrops, etc., can be reliably prevented.

Further, when a pulse signal is input from the comparator 19, the F. F circuit 2
0 is a reset state, and a waveform signal opposite to the output waveform of the set state is sent to the distance calculating section 2 of the microcomputer 42.
Output to 2. The distance calculation unit 22 is an F. Based on the change in the output waveform from the F circuit 20, the time from transmission to reception of the laser beam is determined, and the inter-vehicle distance to the preceding vehicle 14 is calculated from the determined time. The calculation result is sent from the distance calculation unit 22 to the ECU (not shown), and the ECU controls and displays the inter-vehicle distance based on the calculation result.

As described above, in the inter-vehicle distance measuring device according to the present embodiment, when raindrops are detected, the output level of the STC circuit is set to be higher than the signal level when the reflection from the raindrops is received. Moreover, since the output level of the STC circuit is set to increase according to the amount of rain, etc., reflections from raindrops are not mistakenly received as reflections from the car 14 in front, and erroneous detection is reliably prevented. can do. Therefore, it is possible to accurately measure the inter-vehicle distance in any environment.

[0016]

[Effects of the Invention] As detailed above, in the inter-vehicle distance measuring device according to the present invention, when raindrops are detected by starting the raindrop sensor, wiper switch, etc., the level of the STC circuit changes. Because of this configuration, reflections from raindrops will not be mistakenly judged, and erroneous detection can be reliably prevented. Therefore, it is possible to accurately measure the inter-vehicle distance in any environment.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram schematically showing an embodiment of an inter-vehicle distance measuring device according to the present invention.

FIG. 2 is a configuration diagram schematically showing an example of an STC circuit.

FIG. 3 is a graph schematically showing an example of changes in the output level of the STC circuit with respect to rainfall.

FIG. 4 is a configuration diagram schematically showing an example of a conventional inter-vehicle distance measuring device.

[Explanation of symbols]

11 Transmission section 12 LD 17 Receiving section 19 Comparator 31 STC circuit

Claims (1)

[Claims] Claim 1: In an inter-vehicle distance measuring device that includes a transmitting section and a receiving section and measures an inter-vehicle distance using a near-infrared laser diode (LD), raindrops are detected by starting a raindrop sensor, a wiper switch, etc. 1. An inter-vehicle distance measuring device characterized in that the level of a sensitivity time control (STC) circuit changes when the distance is detected.