Communications: directive radio wave systems and devices (e.g. – Determining velocity
Reexamination Certificate
1999-12-17
2001-10-09
Pihulic, Daniel T. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Reexamination Certificate
active
06300896
ABSTRACT:
The present invention relates to the use of a device in a vehicle, using which the environment of the vehicle can be identified by means of radar beams, in which case objects in the environment are distinguished on the basis of whether they are moving or stationary.
Methods of this type are known in which one wheel is selected as the reference wheel, with compensation factors being determined for the other wheels of the vehicle when the vehicle is driven in a straight line without being accelerated or braked. This makes it possible to compensate for differences in the wheel diameters of the vehicle wheels. Instead of a reference wheel, it is also possible to use an averaged value for the rotation speeds of a plurality, for example all, of the wheels. This makes it possible to avoid all the wheel rotation speeds differing when only the wheel diameter of the reference wheel is different. Such differences may result, for example, from air pressure fluctuations in the vehicle wheels, and from profile wear.
SUMMARY OF THE INVENTION
The present invention is based on the problem of providing an improved value for the wheel rotation speed and the vehicle speed.
According to the present invention, this object is intended to be achieved by the use of a device in a vehicle, using which the environment of the vehicle can be identified by means of radar beams, in which case objects in the environment are distinguished on the basis of whether they are moving or stationary, in that a signal which is derived from wheel rotation speed signals and represents the vehicle speed is corrected on the basis of the speed at which objects in the environment which are identified as being stationary move relative to the vehicle.
In this case, it is advantageously also possible to compensate for differences in the determination of the vehicle speed which occur for example, when the tires of all four wheels are replaced. When such a tire change is carried out, a change in the tire type may result in the wheel radius changing considerably, in the range of several percent. In tie same way, while the vehicle is being operated, the tire may chance its circumference as a result of heating during operation. In the event of a chance in the profile depth of the tires due to wear and in the event of a change in the influences already mentioned, the prior art furthermore results in a systematic error occurring, since the change relates to the reference wheel to the same extent as to the other vehicle wheels.
This can therefore advantageously avoid systematic errors resulting from effects which affect all the wheels, and can thus also lead to a change in the reference speed.
With regard to the present invention, it has been found to be particularly advantageous that a device, which is present in a vehicle in any case can advantageously be used to identify the environment by means of radar beams, in order to correct the value of the wheel rotation speed and the vehicle speed. For example, such devices for radar detection are known in systems in which the vehicle speed of the vehicle is intended to be set and, possibly adapted, automatically. In known Tempomat systems, the vehicle speed is set to a predetermined value. When the brakes are operated, the Tempomat is switched off, and the vehicle is driven once again by the vehicle driver. Since increasing traffic density makes it necessary to operate the brakes relatively frequently, the Tempomat is thus switched off relatively frequently. For this reason, devices are known in which a maximum speed is predetermined, but in which the maximum speed is reduced when this is necessary owing to there being slower vehicles in front. The speed is then matched to the speed of the vehicle in front, in order to regulate the vehicle speed to congested traffic. It is advantageous to use radar beams to detect the speed of the vehicles in front. This device, which operates using radar beams, thus controls the vehicle speed during operation.
This further use of this known device according to the invention for adjustment of the signal which represents the vehicle speed thus allows the adjustment to be carried out with little complexity in terms of sensors. It is particularly advantageous in this case that an accurate signal of the vehicle speed is nevertheless available since the device must take account of the safety aspect of such speed control.
In another aspect of the invention, objects are identified as being stationary whose determined relative speed with respect to the vehicle differs by not more than a specific amount from the vehicle speed derived from the wheel rotation speed signals.
In another aspect of the invention, the specific amount is defined as a function of the vehicle speed in such a manner that the specific amount increases as the vehicle speed increases.
A maximum error in the wheel radius, which may occur as a result of a tire chance when a different tire type is fitted, can be determined on the basis of the tire types approved for a vehicle, the influences of the speed of travel and the centrifugal forces on the tire resulting from this, the change in the wheel radius resulting from heating of the tire, the chance in the dynamic wheel radius due to deformation of the tire when travelling slowly, the influences of the reduction in the profile height, and the influences of changes in the tire air pressure. It is advantageous to choose as the predetermined amount a value which is dependent on the order of magnitude of this maximum error. Since the absolute error in the vehicle speed becomes greater with the change in the wheel radius as the vehicle speed increases, the predetermined amount may increase as the vehicle speed increases. However, it is also possible to determine a maximum speed error on the basis of the change in the wheel radius, and to define the predetermined amount accordingly.
In another aspect of the invention, the wheel rotation speed signals are corrected by multiplying the wheel rotation speed signals by a correction factor.
This allows the correction to be carried out easily.
In another aspect of the invention, the correction factor is determined by averaging quotients of the relative speed of objects which are identified as being stationary, with respect to the vehicle speed derived from the wheel rotation speed signals.
This averaging advantageously compensates for the influences of individual incorrect measurements, so that these have only a reduced effect on the correction factor.
In another aspect of the invention, the only quotients which are included in the averaging are those for which the vehicle speed is greater than a specific minimum speed.
At excessively slow vehicle speeds, the determination of the vehicle speed itself as well as the determination of the relative speed are subject to large errors. An order of magnitude for the specific minimum speed may be, for example, about 30-60 km/h.
In another aspect of the invention, the only quotients included in the averaging are those which are determined at times at which the vehicle acceleration or vehicle deceleration which can be derived from the wheel rotation speed signals is within predetermined limits.
In order to determine the correction factors, it is advantageous for the vehicle movement to be uniform, that is to say, in particular, without any acceleration. Thus, since the limits for vehicle acceleration and vehicle deceleration are predetermined, it is possible to avoid the averaging including measurement data which was recorded in conditions which would result in incorrect correction factors. Furthermore, this limitation allows any measurement errors or computation errors to be identified. Specifically, if the determined vehicle accelerations or vehicle decelerations exceed the maximum values which can be predetermined for this vehicle, it is possible to assume a measurement error or computation error. In this case, the further processing of measured data is advantageously inhibited, for example for 50 program cycles.
In another aspect of the invention, the only quotients
Kull Wolfgang
Lauer Wolfgang
Reichmann Thomas
Crowell & Moring LLP
Daimler-Chrysler AG
Pihulic Daniel T.
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