Communications: electrical – Land vehicle alarms or indicators – Of relative distance from an obstacle
Reexamination Certificate
1999-08-19
2001-12-04
Tong, Nina (Department: 2632)
Communications: electrical
Land vehicle alarms or indicators
Of relative distance from an obstacle
C340S436000, C340S903000, C340S932200, C367S909000, C180S169000, C342S070000
Reexamination Certificate
active
06326886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a range measurement system as used, in particular, as a parking aid system in a motor vehicle.
2. Description of the Art
As a vehicle parallel parks, this type of system shows the driver the presence of an obstacle and indicates the distance of this obstacle and its position with respect to the vehicle. The principle of this type of range measurement system is described, for example, in DE-OS 3,540,704. The principle of the method of operation of this type of parking aid system is as follows: an electronic control unit (ECU) is connected to bidirectional data lines that have individual ultrasonic sensors (ULS) which are distributed over the periphery of the vehicle. The individual ultrasonic sensors are controlled as a function of a sequence stored in the electronic control unit (ECU). The ultrasonic sensors then emit a pulse-shaped wave train that is reflected, for example, by means of an existing obstacle. The transmitted waves, are sound waves in the ultrasonic range. When the sound waves are reflected by means of an obstacle, they are then received by means of the ultrasonic sensors, which operate not only as transmitters, but also as receivers. The individual ultrasonic sensor now produce pulses on the data line that correspond chronologically with the received echo, as long as their amplitude exceeds a threshold set in the ultrasonic sensor. With respect to the pulse, the level may be identified as digital, insofar as the existence of a pulse is simultaneously a statement to the effect that the pulse exceeds a certain threshold value (threshold is exceeded or not exceeded). Conversely, the chronological position of the pulse indicates analog information, namely, the range of the obstacle from the receiving ultrasonic sensor. This analog information results from the travel time response of the ultrasonic pulse. Thus, the greater the range to the obstacle, the later the echo arrives at the receiving sensor. The electronic control unit (ECU) computes the distance to the obstacle from the time between the transmission process until the appearance of the reflected wave, keeping in mind the speed of sound.
Parking aid systems of today usually consist of an electronic control unit and, as already explained above, several ultrasonic sensors. Each ultrasonic sensor (ULS) possesses a separate data line, since, in order to improve evaluation, echo information from several ultrasonic sensors is required at a certain instant. Thus, the evaluation of several ULS on the basis of one transmitted sound wave permits more precise conclusions to be made about the position of and the range of the obstacle. It has also already been proposed to arrange the threshold within the ultrasonic sensor so that the exceeding of the threshold triggers the emission of a pulse on the data line. It also is possible to change the threshold within the ultrasonic sensor, such that, for example, several pulses, which are evaluated with changing thresholds, could be emitted in succession from one ultrasonic sensor. In reality, this means that individual echoes are received with differing sensitivity. Also, the sensitivity of a sensor may be changed across the receiving time of a pulse echo, such that certain fixed, preset obstacles such as, for example, a trailer coupling, projecting luggage and the like, may be blanked out. The same applies to reflection from the pavement itself, which appears at a certain range. However, the electronic control unit (ECU) obtains, on the basis of the digital data line, only the information at each instant of whether the amplitude level exceeds the respective threshold or remains below the threshold. As also described, for example, in DE-OS 3,513,270, three states are arranged in succession in the chronological progression of a measurement cycle associated with a single ultrasonic sensor. The ECU produces a short transmission pulse (<1 ms) . Then the receiving ultrasonic sensor transmits the information to the ECU (approximately 10 ms). Finally, a “recovery time” is provided, in which noise echoes and reflections can decay (approximately 10 ms).
SUMMARY OF THE INVENTION
The purpose of the invention is to be able to increase the packing density on the data line, in order to be able to decrease the number of data lines between the sensors and the ECU or to enable improved range measurement. The invention also consists, in principle, of transmitting, instead of one evaluation result by means of one data line, several results by time division multiplex. The multitude of results may result from multiple evaluations of one echo by means of one or more sensors. The echo information measured by the sensors is then buffered and transmitted to the ECU compressed in time. A refinement of the invention enables an advantageous configuration in which instead of connecting the individual sensors point-to-point to the ECU, the sensors are connected to the data line in a serial manner, with each ULS able to transmit to the ECU in a time division multiplex on a common data line. A corresponding use of this data line in the reverse direction toward the ULS, in order, for example, to activate the ULS to transmit a sound pulse, likewise can be provided and is very advantageous.
Since the chronological position of a pulse to be received by the ECU only gives conditional information about the travel time of the echo, it is recommended, in addition to the digital information of the pulse, since this lies above the set threshold, that additional digital information be combined with the pulse which contains information about the travel time of the echo. The travel time of the transmitted pulse from the instant of emission until the instant of reception is always twice as great as the travel time of the reflected echo.
It is possible to transmit a start pulse to the ECU with each cycle, so that the distance of secondary pulse to start pulse corresponds to the travel time of the corresponding echo. In this connection, in a receiving sensor, the echo is simultaneously evaluated with several thresholds (thus several times) . During a cycle, the results to the ECU are chronologically staggered, if necessary, with the results of additional sensors.
The invention results in a multitude of advantages. A transmission of information that is compressed and chronologically staggered allows additional information to be transmitted on a common data line. Consequently, the system can be expanded, for example, insofar as information that concerns the reception of a single echo is transmitted multiple times in order to decrease the susceptibility to faults on the common data line. However, in order to decrease the susceptibility to faults, identical information can also be coded differently, by means of, for example, two transmissions of identical information concerning the same echo, having interchanged levels, with the interchanging of levels occurring on the second transmission.
An additional possibility consists in evaluating the same echo multiple times through the use of different filters, that is, different thresholds on the same echo value. As a consequence, several units of information are available to the ECU for obstacle recognition. Thus, for example, a low threshold value can be used for echoes reflected mainly from the central axis of the transmission beam. However, echoes also may be evaluated with a lower threshold, which are reflected, for example, at an angle to the primary direction of radiation. It is known that an emission at an angle to the primary direction contains less energy, so that the echoes that arrive are also correspondingly weaker. The energy distribution of the transmission level is represented usually as a spatial transmission beam. In this way, information may be gained in several steps on the basis of an analysis of signals received with different thresholds, that is, whether the received pulses are coming from the primary transmitting direction or from a direction at an angle to the primary direction
ITT Manufacturing Enterprises Inc.
Lewis J. Gordon
Tong Nina
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