JPS6147577A - Ground speed detector - Google Patents

Abstract

PURPOSE:To determine a correct ground speed removing effects of disturbance due to ruggedness or the like of ground surface, by having a Doppler signal passing through a band-pass filter which changes in the center frequency according to the speed to perform a speed display using a signal fetched. CONSTITUTION:The detection signal from a Doppler sensor 2 is fed to a low- pass filter 21 passing through an amplifier 20 and then, to band-pass filter 22 and a phase comparator 28 of a PLL circuit 27. The band-pass filter 22 employs a switched capacitor filter. The PLL circuit 27 is provided to make output frequency synchronize the frequency of an input signal and the center frequency of the band-pass filter 22 varies in the frequency of according to a reference signal (clock signal) corresponding to the vehicle speed. A signal with a fixed width fetched from the band-pass filter 22 is fed to speed display 26 passing through an F/V converter 24 and an A/D converter 25.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a ground speed detection device using the Doppler effect, which is suitable for being installed on a tractor or the like.

(Prior art and problems) A ground speed meter that uses the Dotsuprah effect to determine the vehicle's running speed from waves emitted from the ground and waves reflected from the ground is known. Due to the large number of disturbances caused by the shaking of the speedometer itself, it was not possible to obtain an accurate Doppler frequency, making practical vehicle speed detection impossible. On the other hand, with the method of calculating the vehicle speed over the ground from the rotational speed of the tires or the rotational speed of the engine, accurate ground speed could not be obtained due to factors such as tire slippage.

(Objective of the Invention) An object of the present invention is to provide a ground speed detection device that can eliminate disturbances caused by unevenness of the ground, etc., and determine the ground vehicle speed as accurately as possible.

(Disclosure of the Invention) A ground speed detection device according to the present invention includes a ground vehicle speed sensor that uses the Doppler effect, a band pass filter configured to change the center frequency, and a band pass filter that changes the center frequency of the band pass filter according to the speed. The present invention is characterized by comprising a display device configured to include a setting means for setting the vehicle speed, pass a signal from the vehicle speed sensor through a bandpass filter, and display the speed based on the signal extracted from the bandpass filter. As the signal for determining the center frequency of the bandpass filter, the Doppler signal itself from the ground vehicle sensor with some disturbance removed may be used, or a sensor for detecting the rotational speed of the tire may be provided, and the signal from this sensor may be used. The detection signal may be used.Furthermore, a sensor that detects the engine speed and a sensor that detects the shift state of the gear shift sick are provided, the theoretical vehicle speed is determined from the detection results of these sensors, and this theoretical vehicle speed is determined. It may also be used as a signal.

(Embodiment) Figures 1, 7ft, and 2 show an embodiment of the present invention, in which a ground vehicle speed sensor (hereinafter referred to as a Doppler sensor) 2 that utilizes the Doppler effect is mounted on the abdomen of a tractor 1 on both rear wheels. It is provided facing the middle part of the grounding part of 3 and 3,
This Doppler sensor 2 is connected to a display device 5 built into an operation panel.

The detection signal from the Doppler sensor 2 (Doppler signal) is
The signal is supplied to the low-pass filter (1) 21 through the amplifier 20, and from there to the band-pass filter 22, but a part of the signal exiting the low-pass filter (1) 21 is PL
The signal is supplied to the phase comparator 28 of the L circuit 27. As shown in FIG. 3(a), the low-pass filter (1) 21 is a filter that passes only frequencies below a predetermined frequency fl (for example, 300 Hz), and signals with frequencies higher than this are cut. Moreover, the band pass filter 22 is shown in FIG.
As shown in b), it passes only frequencies within a predetermined width W (for example, ±25 Hz), and the frequency fO at the center of the width W is a reference signal (clock signal) that corresponds to the vehicle speed.
It is configured to move up and down depending on the As the bandpass filter 22, a switched capacitor
A filter is used.

The PLL circuit 27 is a circuit whose output frequency is synchronized with the frequency of the input signal, and is provided as a setting means for setting the center frequency of the bandpass filter 22. When the frequency is divided by 1/100 by the counter 31, the output frequency becomes 100 times. A stable lock signal obtained from this circuit is supplied to a bandpass filter 22.

In addition, the running speed of tractors etc. during work is usually 5~5~
Since it is about 15 Km/H, the low-pass filter 21 may cut off frequencies equal to or higher than, for example, 30 Km/H.

A constant width signal taken out from the bandpass filter 22 is sent from an amplifier to an F/V converter 24°A/D converter.
25 to the speed indicator 26, and the speed is displayed based on it.

This detection device T does not directly use the signal from the Doppler sensor 2 to display speed, but instead displays the speed based on a signal extracted through a bandpass filter 22 whose center frequency changes depending on the speed. Therefore, accurate ground speed detection can be performed by effectively eliminating disturbances caused by unevenness of the ground, etc.

Next, FIGS. 4 and 5 show an embodiment different from the above, and in this example, the rotation speed of the tire (in the illustrated example, the rear wheel 3) is detected as the center frequency setting means of the band pass filter 22. A rotation sensor 7 is provided, and a detection signal from the rotation sensor 7 is used. That is, the detection signal from the rotation sensor 7 is supplied to the PLL circuit 27,
The signal output from this is input to the band pass filter 22 as a clock signal. On the other hand, the Doppler signal from the Doppler sensor 2 is sent to a bandpass filter 22 via an amplifier 20. The other parts are the same as the previous example.

In the detection device T' of this example as well, the center frequency of the bandpass filter changes according to the speed, and the speed is displayed only by the signal extracted from the center frequency, so disturbances are removed.
Accurate ground speed can be obtained.

FIGS. 6 and 7 show a further different embodiment, in which a sensor 10 for detecting the rotation speed of the engine 9 and a sensor 11 (possibly a limit switch or the like) for detecting the shift position of the transmission shifter are provided. , a theoretical speed is determined from the detected engine rotational speed and gear shift state, and this is used as means for setting the center frequency of the bandpass filter 22. In the illustrated example, there are three speeds: 1st speed, 2nd speed, and 3rd speed.
There are three different shift positions, and the frequency division ratio is divided into three and corresponds to each shift position. The frequency-divided signal from the counter 31 according to the shift position is input to the phase comparator 28, and the output signal is taken out as a clock signal for setting the center frequency of the bandpass filter 22. Other parts are the same as the previous example.

Since the detection device T'' of this example also displays the speed using a Doppler signal passed through a band-pass filter whose center frequency varies depending on the speed, it is possible to obtain accurate ground speed without the influence of external disturbances.

(Effects of the Invention) As is clear from the above explanation, the ground speed detection device according to the present invention passes a Doppler signal through a bandpass filter whose center frequency changes depending on the speed, and uses the signal extracted from the bandpass filter. Since the speed is displayed using
The influence of disturbances such as unevenness of the ground has been removed, making it possible to accurately determine ground speed using a Doppler sensor.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an example of a tractor equipped with a ground speed detection device according to the present invention, Fig. 2 is a block diagram of the ground speed detection device, and Figs. 3 (a) and (b) are low-pass Graphs showing the effects of filters and bandpass filters. Figures 4 and 5 show different embodiments. A schematic diagram of a tractor and a block diagram of a ground speed detection device. Figures 6 and 7 show further different implementations. FIG. 1 is a schematic diagram of a tractor and a block diagram of a ground speed detection device as an example. 1...Tractor, 2...Dotsupura sensor, 3...
Rear wheel, 5...Display device.

Claims (1)

[Claims] (1) A ground vehicle speed sensor that uses the Doppler effect, a bandpass filter configured to change the center frequency, and a setting means for setting the center frequency of the bandpass filter according to the speed, A ground speed detection device comprising a display device configured to pass a signal through a bandpass filter and display speed based on the signal extracted from the bandpass filter.