Vehicular radar system

A radar system of a vehicle has a zero-cross comparator, an integrator, and a sensor. The comparator compares a light reception signal output from each one of photoreceptive elements with a predetermined standard signal and outputs a comparison signal indicating two different states corresponding to a result of the comparison. The integrator samples the comparison signal and converts the comparison signal into one-bit digital data. The integrator integrates the digital data for each photoreceptive element. The sensor compares the integrated data of each photoreceptive element with a predetermined integration standard value. The sensor senses a reflection object based on the integrated data equal to or greater than the integration standard value.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2004-290482 filed on Oct. 1, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicular radar device.

2. Description of Related Art

JP-A-2004-177350 describes a vehicular radar system having a light emitter for emitting a laser light and a photoreceptor for receiving a reflected light of the laser light. The vehicular radar system is attempting to improve detection sensitivity of the reflected light reflected by a reflection object.

The light emitter of the vehicular radar system generates the laser light with a laser diode and changes an emission direction of the laser light with a polygon mirror that is driven to rotate. Thus, the light emitter performs scanning over a predetermined angular range for each predetermined minute angle with the laser light. If the laser light is reflected by the reflection object, the photoreceptor receives the reflected light with a light receiving lens. The received light is introduced to photoreceptive elements. The photoreceptive elements output voltage signals corresponding to intensity of the received light.

The vehicular radar system integrates a predetermined number of light reception signals, which are output based on a predetermined number of laser lights emitted contiguously, and outputs an integration signal, while ensuring angular resolution of the laser light. Thus, a light reception signal component corresponding to the reflected light is amplified by integrating the predetermined number of the light reception signals, and detection sensitivity of the reflected light can be improved.

Another vehicular radar system has a light emitter for emitting a laser light over a predetermined angular range in one emission and a photoreceptor having photoreceptive elements of the number corresponding to necessary angular resolution. The photoreceptive elements are arranged into an array along a width direction of the vehicle. This vehicular radar system integrates light reception signals, which are output when the photoreceptive element repeatedly receives the light, for each photoreceptive element. Thus, this vehicular radar system attempts to improve the detection sensitivity of the reflected light.

In such a case where the photoreceptor has multiple photoreceptive elements, usually, a structure shown inFIG. 11Ahaving an integrator that integrates the light reception signals output by the photoreceptor is used.

The structure shown inFIG. 11Aincludes an amplification circuit (AMP), an A/D conversion circuit (A/D), an integrator, and switches (SW). The amplification circuit AMP amplifies the light reception signals output by the photoreceptive elements (PD) such as photo diodes. The A/D conversion circuit A/D converts the analog light reception signals into digital signals. The integrator integrates the digital light reception signals. The switch SW switches the output of the light reception signal output by each photoreceptive element PD. The amplification circuit AMP, the A/D conversion circuit A/D and the integrator are commonly used for the respective photoreceptive elements PD and switches SW.

The integration of the light reception signals is performed by switching each photoreceptive element PD. Therefore, the integration of the light reception signals output from the respective photoreceptive elements PD cannot be processed at the same time (in parallel). In such a case, the laser light needs to be emitted repeatedly for the time corresponding to the product of the number of the photoreceptive elements PD and the time of the integration. The laser diode will be degraded sooner as the time number of laser light emission increases.

In order to overcome this problem, the amplification circuit AMP, the A/D conversion circuit A/D and the integrator may be disposed for each photoreceptive element PD, without employing the switches SW as shown inFIG. 11B. Thus, the integration of the light reception signals output from the respective photoreceptive elements PD can be performed in parallel, and the early degradation of the laser diode can be inhibited. However, the circuit structure becomes large in scale because the A/D conversion circuit A/D and the integrator have to be disposed for each photoreceptive element PD.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a vehicular radar system capable of performing integration of light reception signals output from multiple photoreceptive elements in parallel by using a small-scale circuit structure.

According to an aspect of the present invention, a radar system of a vehicle has a light emitter, a photoreceptor, a comparator, an integrator, and a sensor. The light emitter repeatedly emits laser light so that the laser light is emitted over a predetermined angular range at least along width direction of the vehicle in each light emission. The photoreceptor outputs light reception signals, which are output from photoreceptive elements in accordance with intensity of reflected laser light reflected by a reflection object. The photoreceptive elements are arranged at least along the width direction of the vehicle. The comparator compares the light reception signal output from each photoreceptive element with a standard signal and outputs for each photoreceptive element a comparison signal indicating two different states corresponding to a result of the comparison. The integrator samples the comparison signal and converts the comparison signal into one-bit digital data while a predetermined time passes after the laser light is emitted. The integrator integrates the digital data for each photoreceptive element based on emitting timing of the laser light every time the laser light is emitted. The integrator outputs the integrated data. The sensor compares the integrated data of each photoreceptive element with a predetermined integration standard value. The sensor senses the reflection object based on the integrated data equal to or greater than the integration standard value.

The radar system of the present invention can be structured with one signal line for each channel unlike a conventional radar system that uses an eight-bit A/D converter requiring eight signal lines for each channel. The integrator integrates one-bit digital data for each channel. A counter can substitute for the integrator. Thus, the light reception signals output from the multiple photoreceptive elements can be integrated in parallel by using a small-scale circuit structure having the comparator and the integrator.

Since the integrator integrates the light reception signals for each channel, the detection sensitivity of the reflected light can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a vehicle controller1according to an example embodiment of the present invention is illustrated. The vehicle controller1is structured centering on a recognition and inter-vehicle control electronic control unit (ECU)3. The ECU3includes a microcomputer, an input/output interface (I/O) and various drive circuits and detection circuits.

The ECU3receives detection signals from a laser radar sensor5as a vehicular radar system, a vehicle speed sensor7, a brake switch9, and a throttle opening degree sensor11. The ECU3outputs drive signals to an alarm generator13, a distance display15, a sensor abnormality display17, a brake driver19, a throttle driver21and an automatic transmission controller23.

The ECU3is connected with an alarm volume setter24for setting the volume of the alarm, an alarm sensitivity setter25for setting sensitivity of alarm determination processing, a cruise control switch26, a steering sensor27for sensing a manipulation amount St of a steering wheel (not shown), and a yaw rate sensor28for sensing a yaw rate Ry caused in the vehicle. The ECU3has a power switch29. If the power switch29is switched on, the ECU3starts predetermined processing.

As shown inFIG. 2, the laser radar sensor5has a light emitter, a photo integrated circuit (photo IC)90including a photoreceptor, a laser radar CPU70and the like. The light emitter has a semiconductor laser diode75for emitting a pulse-shaped laser light through a light emission lens71. The laser diode75is connected with the CPU70through a laser diode drive circuit76, and emits the laser light responsive to a drive signal output by the CPU70.

If a light-emitting direction of the light emitter is regarded as a virtual z-axis, the light emitter can emit the laser light over a predetermined area defined by predetermined angles along a virtual x-axis, i.e., a width direction of the vehicle perpendicular to the z-axis, and along a virtual y-axis, i.e., a height direction of the vehicle perpendicular to the z-axis, in one light emission. The light emitter emits the laser light repeatedly and intermittently. The light emitter does not scan the x-y plane defined by the x-axis and y-axis.

If the laser light is emitted over the predetermined area defined by the predetermined angles, the laser light is reflected by a reflection object, and the photoreceptor of the photo IC90receives the reflected light. Based on a light reception signal corresponding to the received light, the CPU70obtains reflection angles θx, θy (lateral angle θx and vertical angle θy) of the reflection object and a distance L from the reflection object. In this example embodiment, the lateral angle θx is defined as an angle provided between the z-axis and a line produced by projecting the reflected light onto the x-z plane, and the vertical angle θy is defined as an angle provided between the z-axis and a line produced by projecting the reflected light onto the y-z plane.

As shown inFIG. 3, the laser radar sensor5of this example embodiment has a zero-cross comparator95, instead of the A/D conversion circuit shown inFIG. 11B. The zero-cross comparator95outputs a comparison signal indicating two different states for each photoreceptive element PD (for each channel). Conventionally, in the case where an eight-bit A/D conversion circuit is used, eight signal lines were necessary for each channel. In contrast, in this example embodiment, only one signal line is necessary for each channel.

The laser radar sensor5of this example embodiment has an integrator77shown inFIG. 3, instead of the integrators shown inFIG. 11B. The integrator77shown inFIG. 3integrates sampled one-bit digital data for each channel. A counter can be used in place of the integrator77since the integrator77integrates the one-bit digital data.

Thus, the laser radar sensor5has the zero-cross comparator95, which outputs the comparison signal indicating two difference states for each channel, and the integrator77, which integrates the sampled one-bit data for each channel. Therefore, the laser radar sensor5can be structured small in size, and the integration of the light reception signals output from the multiple photoreceptive elements can be performed in parallel.

The integrator77integrates the light reception signals output from the photoreceptive elements for each channel to improve the detection sensitivity of the reflected light.

The photo IC90is structured by an IC as shown inFIG. 3. The photo IC90has a photo reception lens for converging the reflected laser light (reflected light) reflected by a reflection object, a photoreceptor that outputs voltages (light reception signals) corresponding to intensity of the reflected light that is converged, amplifiers91, coupling capacitors93, and the zero-cross comparators95.

The number (16, in this example embodiment) of the photoreceptive elements PD1-PD16is set in accordance with angular resolution to be ensured. The photoreceptive elements PD1-PD16are arranged in parallel into an array along the width direction (x-axis) of the vehicle. The photoreceptive elements PD1-PD16output light reception signals corresponding to intensity of the laser light reflected by the reflection object. In addition to the photoreceptive elements PD1-PD16arranged into the array along the width direction of the vehicle, another sixteen photoreceptive elements (not shown) are arranged in multiple rows along the y-axis perpendicular to the width direction of the vehicle. Thus, three-dimensional measurement can be performed.

The photoreceptor has the light shield97shielding at least one photoreceptive element (for example, the photoreceptive element PD16) from the light. Thus, a base noise component superimposed on the light reception signals of the photoreceptive elements PD1-PD15, which are not shielded by the light shield97, can be eliminated based on the light reception signal output from the photoreceptive element PD16, which is shielded by the light shield97.

The base noise and a background noise are superimposed on the light reception signals of the photoreceptive elements. As shown inFIG. 7, the base noise is a noise generated by a large current when the light emitter generates the laser light, a clock noise generated in synchronization with a clock cycle of the CPU, or a power source noise generated by a power source. These noises are generated at predetermined intervals.

In this example embodiment, as shown inFIG. 3, the light shield97(for example, aluminum foil) shields the photoreceptive element PD16from the light. Thus, only the base noise, from which the back ground noise is eliminated, is superimposed on the integration data that corresponds to the light reception signal output from the photoreceptive element PD16and that is integrated by the integrator77. Therefore, by using the integration data of the photoreceptive signal from the photoreceptive element PD16, the base noise superimposed on the other photoreceptive elements PD1-PD15can be eliminated.

The base noise may be eliminated in the CPU70by subtracting the integration data of the shielded channel from the integration data of the channel that is not shielded.

A subtracter may be provided for each channel between the coupling capacitor93and the zero-cross comparator95in the photo IC90, and the base noise may be eliminated by subtracting the light reception signal of the shielded channel from the light reception signal of each channel.

The amplifier91is provided for each channel for amplifying the light reception signal at a predetermined ratio. The amplified light reception signal is output to the coupling capacitor93provided for each channel. The coupling capacitor93eliminates a direct current component superimposed on the light reception signal (for example, component corresponding to solar light constantly superimposed on the light reception signal).

The zero-cross comparator95is structured by a resistor and an inverter. The zero-cross comparator95is provided for each channel. The light reception signal of each channel, from which the direct current component is eliminated, is input into the zero-cross comparator95and compared with a predetermined standard signal (0V signal, in this instance).

The zero-cross comparator95outputs a comparison signal indicating one of the two different states corresponding to the comparison result for each channel. If the light reception signal is higher than the standard signal, the zero-cross comparator95outputs a signal of voltage level corresponding to HIGH. If the light reception signal is lower than the standard signal, the zero-cross comparator95outputs a signal of voltage level corresponding to LOW.

Thus, the photo IC90has the photoreceptor, the amplifier91, the coupling capacitor93and the zero-cross comparator95for each channel. Therefore, a series of processes from generating the comparison signals based on the light reception signals output from the photoreceptor to outputting the comparison signals is performed in parallel throughout the channels.

A light reception signal, from which the direct-current component is eliminated and which is input into the zero-cross comparator95, is shown inFIG. 4. Generally, a background noise is superimposed on the light reception signal. As shown inFIG. 7, the background noise is a thermal noise (Johnson noise) caused by a resistor or a shot noise caused by a semiconductor. These noises are random noises irrelevant to frequency. Therefore, as shown inFIG. 4, a frequency distribution of the light reception signals superimposed with the background noise becomes a substantially normal distribution.

The integrator77shown inFIG. 3indicates a function of the CPU70structured as a microcomputer. The integrator77samples the comparison signal, which is output by the photo IC90for each channel while a predetermined time elapses after the light emitter emits the laser light, at a predetermined sampling time interval.

The integrator77starts sampling based on light emitting timing as a standard (trigger). The sampled comparison signal is converted into one-bit digital data, in which HIGH is associated with 1 and LOW is associated with 0. The one-bit digital data is stored for each channel as chronological digital data associated with the elapsed time after the laser light emission timing, in an inner memory inside the CPU70.

Every time the laser light is emitted, the integrator77performs the above-explained sampling, and integrates the currently obtained chronological digital data and the already stored chronological data for each channel. In this integration, the digital data at the time when the same time elapses after the emission timing of the laser light are integrated with each other.

The contents of the integration processing performed by the integrator77is shown inFIG. 5AandFIG. 5B. As shown inFIG. 5A, the integrator77samples the comparison signals of each channel output from the zero-cross comparator95at a predetermined sampling time interval (for example, 10 nsec) while a predetermined time (for example, 2000 nsec) elapses after the laser light is emitted. The integrator77converts the sampled comparison signals into the chronological digital data, which are stored in the inner memory of the CPU70, for each channel in the first run (n=1).

If the laser light is emitted next time (n=2), the integrator77samples the comparison signal output from the zero-cross comparator95, and integrates the digital data sampled and stored in the first run (n=1) and the digital data sampled in the second run (n=2) for each channel.

Then, until the laser light is emitted predetermined times (256 times, for example), the above-explained integration processing is repeatedly performed for the number of times the laser light is emitted. The final integration data of each channel are output to a distance calculator79.

By integrating the chronological digital data, the light reception signal component corresponding to the reflected light reflected by the reflection object is amplified to improve the detection sensitivity of the reflection light. Namely, in the case where the light reception signal components corresponding to the reflected light reflected by the reflection object are included in all the 256 light reception signals, the comparison signals corresponding to the light reception signal components appear at the timing, which is later than the emission timing of the laser by the same time length. Therefore, the integration value of the light reception signal component corresponding to the reflected light reflected by the reflection object coincides with the light reception signal component of each light reception signal amplified by 256 times.

The background noise having a substantially normal distribution is superimposed on the light reception signal as shown inFIG. 4. The integration value of the back ground noise component coincides with the background noise component amplified by just sixteen (√{square root over ( )}(256)) times.

Since the integrator77performs the integration processing, the light reception signal component corresponding to the reflected lights reflected by the reflection objects are amplified by the time of the integration. As a result, an S/N ratio (signal-to-noise ratio) is improved, and the detection sensitivity of the reflected light can be improved.

The distance calculator79shown inFIG. 3compares the integration data of each channel having the improved S/N ratio with a predetermined integration standard value. The reflection object can be detected based on the integration data, which is equal to or greater than the integration standard value.

The CPU70senses the lateral angle θx and the vertical angle θy based on the position of the photoreceptive element outputting a voltage signal equal to or greater than an integration standard value (standard voltage). In an example shown inFIG. 6A, the photoreceptor (photoreceptive elements PD1-PD16) receives the reflected light reflected by the reflection object straight in front of the vehicle. The reflected light received by the light reception lens80is converged at the photoreceptive element at a position corresponding to an angle (direction) of the reflection object. Therefore, the lateral angle (direction) θx of the reflection object can be sensed based on the position of the photoreceptive element outputting the integration signal equal to or greater than the standard voltage.

The position of the photoreceptive element differs in accordance with the height of the reflection object. Therefore, the vertical angle θy of the reflection object can be sensed based on the position of the photoreceptive element outputting the integration signal equal to or greater than the standard voltage.

Therefore, the number of the photoreceptive elements should be preferably set in accordance with the angular resolution of the angle along the width direction or the height direction of the vehicle to be sensed. For example, as shown inFIG. 6B, the lateral angle θx of the reflection object can be sensed based on the position where the reflected light is converged. Therefore, by setting the number of the photoreceptive elements in accordance with the angular resolution of the angle along the width direction of the vehicle, the angle of the reflection object along the width direction of the vehicle can be obtained precisely. The similar explanation also applies to the vertical angle θy.

The distance calculator79compares the integration data of each channel with the predetermined integration standard value. The reflection object is detected based on the integration data, which is equal to or greater than the integration standard value. For example, as shown inFIG. 8, the integration value of the sporadic integration data stored in the integrator77for each channel is compared with the integration standard value. At that time, if the integration values Db, Dc are greater than the integration standard value as shown inFIG. 8, the result of the comparison is output to an interpolation device (not shown).

The interpolation device performs linear interpolation to obtain rising time t1and dropping time t2, at which it is presumed that the integration value (value of integration signal) crosses the standard voltage. More specifically, an imaginary line running on the integration value Db exceeding the standard voltage and on another integration value Da obtained immediately before the integration value Db is imagined. Then, time corresponding to an intersection of the imaginary line and the standard voltage is obtained as the rising time t1. Likewise, another imaginary line running on the integration value Dc exceeding the standard voltage and yet another integration value Dd obtained immediately after the integration value Dc is imagined. Then, time corresponding to an intersection of the imaginary line and the standard voltage is obtained as the dropping time t2.

The CPU70calculates time when a peak value of the light reception signal component S is generated based on the rising time t1and the dropping time t2. Then, the CPU70calculates a time difference Δt between the time when the laser light is emitted and the time when the peak value is generated.

The CPU70calculates the distance from the reflection object based on the time difference Δt. The CPU70makes positional data based on the distance and the lateral angle θx and the vertical angle θy of the reflection object. For example, the positional data of the reflection object on an x-y-z orthogonal coordinate system are obtained based on the distance, the lateral angle θx and the vertical angle θy. The origin of the x-y-z orthogonal coordinate system coincides with the center of the laser radar sensor5, the x-axis coincides with the width direction of the vehicle, and the y-axis coincides with the height direction of the vehicle. Then, the positional data are output to the ECU3as distance surveying data.

The ECU3recognizes the object based on the distance surveying data provided by the laser radar sensor5. The ECU3performs inter-vehicle control for controlling the vehicle speed V by outputting drive signals to the brake driver19, the throttle driver21and the automatic transmission controller23in accordance with conditions of a preceding vehicle obtained from the recognized object. The ECU3simultaneously performs alarm determination processing for providing an alarm when the recognized object exists within a predetermined alarm area for a predetermined time. The object is a vehicle running ahead or a vehicle stopping ahead.

The distance surveying data output from the laser radar sensor5is transmitted to an object recognition block43. The object recognition block43obtains the central position (X, Y, Z) and the dimensions (W, D, H), i.e., the width W, the depth D and the height H, of the object based on the three-dimensional positional data obtained as the distance surveying data.

The object recognition block43calculates relative speed (Vx, Vy, Vz) of the object on the basis of the position of the own vehicle, in which the laser radar sensor5is mounted, based on a temporal change of the central position (X, Y, Z). The object recognition block43recognizes whether the object is a stationary object or a moving object based on the vehicle speed (own vehicle speed) V, which is output by a vehicle speed calculation block47based on the sensing value of the vehicle speed sensor7, and the relative speed (Vx, Vy, Vz). The object that can affect the travel of the own vehicle is selected based on the recognition result and the central position of the object, and the distance to the object is displayed on the distance display15.

A steering angle calculation block49calculates the steering angle St based on the signal output from the steering sensor27. A yaw rate calculation block51calculates the yaw rate Ry based on the signal output from the yaw rate sensor28. A curvature radius calculation block57calculates a curvature radius R based on the vehicle speed V output by the vehicle speed calculation block47, the steering angle St output by the steering angle calculation block49and the yaw rate Ry output by the yaw rate calculation block51.

The object recognition block43determines a possibility that the object is a vehicle or a possibility that the vehicle as the object is running on the same lane as the lane on which the own vehicle is running based on the curvature radius R, the central position coordinates (X, Z) and the like. A sensor abnormality sensing block44determines whether the data obtained by the object recognition block43are in an abnormal range. If the data are in the abnormal range, the sensor abnormality display17displays a notification of the abnormality.

A preceding vehicle determination block53selects a preceding vehicle based on various data obtained from the object recognition block43and calculates the distance Z along the z-axis and the relative speed Vz with respect to the preceding vehicle. In the alarm determination, an inter-vehicle control and alarm determination block55determines whether the alarm should be provided, based on the distance Z, the relative speed Vz, the setting of the cruise control switch26, a pressed state of the brake switch9, the opening degree THR of the throttle valve output by the throttle opening degree sensor11and the sensitivity setting value of the alarm sensitivity setter25. If it is determined that the alarm is necessary, the inter-vehicle control and alarm determination block55outputs an alarm generation signal to the alarm generator13. In cruise control determination, the inter-vehicle control and alarm determination block55determines the contents of the vehicle speed control, based on the distance Z, the relative speed Vz, the setting of the cruise control switch26, the pressed state of the brake switch9, the opening degree THR of the throttle valve output by the throttle opening degree sensor11and the sensitivity setting value of the alarm sensitivity setter25. If the cruise control is determined, the inter-vehicle control and alarm determination block55outputs control signals to the automatic transmission controller23, the brake driver19and the throttle driver21to perform necessary control. When these controls are performed, the distance display15displays necessary display signals to notify a vehicle driver of the conditions.

In this example embodiment, the zero-cross comparator95that outputs the comparison signal displaying the two different states for each channel is used in place of the conventional A/D conversion circuit. The integrator77for integrating the comparison signal output from the zero-cross comparator95is used in place of the conventional integration circuit.

In the case where the eight-bit A/D conversion circuit is conventionally used, eight signal lines are necessary for each channel. In contrast, only one signal line is necessary for each channel in this example embodiment. The counter can substitute for the integrator.

Thus, by using the zero-cross comparator95for outputting the comparison signal indicating the two different states for each channel and the integrator77for integrating the sampled one-bit digital data for each channel, the circuit structure can be reduced in scale, and the integration of the light reception signals output from the multiple photoreceptive elements can be performed in parallel.

The preceding vehicle may have a reflector having high reflection intensity with respect to the laser light on a rear side thereof. A body of the vehicle itself usually has relatively high reflection intensity. In the case where the preceding vehicle is the reflection object, there is a possibility that a reflected light (beam spot: BMS) having high reflection intensity is reflected by the reflector onto two photoreceptive elements (for example, the photoreceptive elements PD1, PD2) as shown inFIG. 9.

The integration signals corresponding to the electric charges provided by the photoreceptive elements PD1, PD2are higher than the integration signals corresponding to the electric charges provided by the other photoreceptive elements. In such a case, the lateral angle θx of the preceding vehicle cannot be correctly sensed from the position of the photoreceptive elements where the reflected light is converged.

Therefore, as shown inFIG. 10, an adder99is provided for adding the light reception signals output from a predetermined number of (two) adjacent channels and for outputting the added signal. The zero-cross comparator95compares the added signal of each two channels output from the adder99through the coupling capacitor93with a predetermined standard signal. Then, the zero-cross comparator95outputs a comparison signal that indicates two different states corresponding to the comparison result for each two channels.

The CPU70samples the comparison signal of each two channels output from the zero-cross comparator95at a predetermined sampling time interval to convert the comparison signal into one-bit data. Every time the laser light is emitted, the CPU70integrates the digital data based on the emitting timing of the laser light for each two channels and outputs the integration data. The distance calculator79compares the integration data of each two channels output from the integrator77with a predetermined standard value to detect the reflection object.

Thus, by producing the integration data with the use of the added signal of each two channels output from the adder99, the lateral angle θx of the preceding vehicle can be detected correctly.

The present invention should not be limited to the disclosed embodiments, but may be implemented in many other ways without departing from the spirit of the invention.