Communications: directive radio wave systems and devices (e.g. – Determining velocity
Reexamination Certificate
2000-09-11
2002-09-03
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
C342S116000, C342S070000, C180S197000
Reexamination Certificate
active
06445337
ABSTRACT:
BACKGROUND
The present invention concerns a method for measuring the speed of a vehicle relative to a road surface.
The invention concerns in addition a device to measure the speed of a vehicle relative to a road surface.
Similar devices for measuring the speed of a vehicle are known from the prior art in various configurations. The known devices customarily employ a method in which the speed measurement is made by observing the rotational frequency of one or several vehicle wheels. Using the average circumference of the wheels, a deduction is made concerning distance covered per unit of time. The recording of rotational frequency is made, for example, by means of an analog tachometer generator, or digitally by means of an incremental inductive transducer.
In dependently of the type of measurement of rotational frequency, the measuring methods known from the prior art reveal two fundamental disadvantages. Firstly, the diameter of the vehicle wheels, and therefore the circumference, varies as a result of the temperature of the wheels. Since the known method for measuring speed assumes constant wheel circumference, a change in wheel circumference causes an erroneous result in the measurement. Secondly, the rolling action of the wheels relative to the road surface, particularly under acceleration and braking , is accompanied by slip, which similarly falsifies the result of the known method of measuring speed.
From the a forementioned disadvantages of the prior art, a task derives for the present invention of creating and developing a method for measuring the speed of a vehicle in such a way that the accuracy of the measurement is increased and the result of the measurement is independent of the diameter of the vehicle wheels and of the adhesion of the vehicle wheels to the road surface.
SUMMARY
To solve this task, the invention proposes that the speed of the vehicle be measured directly at the road surface by utilizing the Doppler effect.
The Doppler effect uses a sending unit to transmit beams at a specific frequency and a receiving unit to receive these beams. The beams can be generated as visual, acoustic or electromagnetic waves. If a relative motion exists between the sending unit and the receiving unit, that is to say, the mutual distance is increasing or decreasing, the receiving unit registers a different frequency than the one transmitted by the sending unit. The difference between the transmit frequency and the receive frequency changes as a result of the Doppler effect, proportionally dependent on the speed of the relative motion between the sending unit and the receiving unit. The speed of the relative motion can be determined from the difference between the transmit frequency and the receive frequency.
In order to measure the speed of a vehicle, the sending unit and the receiving unit are mounted on the vehicle. The sending unit transmits beams in the direction of the road surface. The beams are at least partially reflected from the road surface and the reflected beams are received by the receiving unit. The road surface acts as an imaginary transmitting unit, since it appears to the receiving unit as if the road surface were transmitting the reflected beams. From the difference between the transmit frequency and the receive frequency, the speed, of the vehicle relative to the road surface can be determined.
The method under the invention measures the speed of the vehicle directly at the road surface. Consequently, the accuracy of the measurement can be substantially increased. In addition, the result of the measurement is independent of the diameter and the adhesion of the vehicle wheels, using the process as visualized under the invention.
As an advantage, the speed of the vehicle is also determined indirectly by measuring the rotational frequency of one vehicle wheel and determining the speed of the vehicle indirectly from the rotational frequency and the circumference of the wheel.
Under an advantageous further development of the invention, it is proposed that the speed measured directly at the road surface is transmitted to a central computer on the vehicle. The directly measured vehicle speed can then be processed further. The additional processing includes, for example, displaying the speed in an appropriate display unit on the instrument panel or inclusion of the speed in open and closed loop control of vehicle conditions, for example, vehicle speed or vehicle stability.
As an advantage, the directly determined speed of the vehicle is compared with the indirectly measured speed of the vehicle as part of the additional processing. Preferably, the slip of one vehicle wheel is determined from the comparison of the directly measured speed of the vehicle with the indirectly measured speed of the vehicle. Since the indirectly measured speed is dependent on the rotational frequency of the vehicle wheels, the slip of one vehicle wheel can be determined from the comparison of the indirectly measured speed with the directly measured speed of the vehicle in the case of acceleration or braking. The information about slip allows conclusions to be made about the adhesion of the wheel or about the prevailing coefficient of adhesion, which is heavily dependent on the nature of the road surface and on environmental conditions. The information about the coefficient of adhesion can be included, for example, in vehicle traction control to limit engine torque or vehicle speed.
If the vehicle is not being accelerated or braked and the vehicle is being driven on a straight road, slip at the wheels is normally negligibly small. Under these conditions a deduction can be made about the actual diameter of a vehicle wheel from the comparison of the indirectly measured vehicle speed with the directly measured vehicle speed. This can be combined with a diagnosis of tire pressure and a warning can be given in the case of tire pressure that is too low or too high. For this reason, in accordance with a preferred configuration of the invention, it is proposed that the circumference of one vehicle wheel and consequently the tire pressure of the wheel be determined from the comparison of the indirectly measured vehicle speed with the directly measured vehicle speed.
In accordance with a preferred further development of the present invention, the speed of the vehicle is measured directly by means of a Doppler radar. A Doppler radar transmits a signal which is created as electromagnetic waves. In the case of the signal, this means preferably a continuously unmodulated signal.
In accordance with a preferred further development of the invention, it is proposed that electromagnetic waves are projected onto the road surface by means of the Doppler radar, the emitted electromagnetic waves are reflected by the road surface, the reflected electromagnetic waves are received by the Doppler radar and the speed of the vehicle is determined from the difference between the transmission frequency and the reception frequency.
As an advantage, the electromagnetic waves are transmitted at an angle of inclination (&agr;) onto the road surface, whereby the speed of the vehicle (v) is determined from the equation:
v=k
(
l=f
S
/f
E
) cos &agr;, with a constant
k,
transmission frequency f
S
; and
reception frequency f
E
.
The constant (k) is customarily the speed of sound (c). The intention is to install a Doppler radar in the forward area of the vehicle, in the center facing the direction of travel. The primary emitting direction of the Doppler radar antenna is pointing onto the road surface at the angle of inclination (&agr;) relative to the horizontal. Since the calculation of vehicle speed, among other things, is dependent on the angle of inclination (&agr;), an angle of inclination of 0° would be ideal, mathematically considered, to eliminate this dependency. However, with an angle of inclination of 0°, the signal would be traveling approximately parallel to the road surface and there would be no reflection of the electromagnetic waves. Consequently, a compromise must be made in the selection of t
Sotomayor John B.
Valeo Schalter und Sensoren GmbH
Vincent Paul
LandOfFree
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