DE9218620U1 - Device for determining driving state variables of a motor vehicle - Google Patents

Description

Device for determining driving state variables of a motor vehicle

The invention relates to a device for determining driving state variables of a motor vehicle, comprising at least two acceleration sensors for detecting the longitudinal and lateral acceleration of the motor vehicle and an evaluation circuit with a resettable time measuring element, which determines acceleration values from the sensor signals for a specific period of time.

A device of the type mentioned above is known, for example, from DE-A-39 20 091. Like many other devices of this type, the device described there serves to trigger safety functions on the motor vehicle when certain acceleration values or a certain combination of acceleration values occur. Such safety functions include, for example, the lighting up of a warning light, the extension of a roll bar, the activation of a belt tensioner and/or an airbag, etc. All of these devices have in common that they are usually permanently integrated into the vehicle.

4. &tgr;&egr;&Iacgr;-&egr;&igr;&idigr;&agr;* &ogr;&bgr;9-98 so 14

The invention is based on the object of providing a simple and inexpensive device of the type mentioned at the beginning, which is vehicle-independent and can also be subsequently installed in any vehicle and which nevertheless works independently of operation by the driver.

To solve this problem, the device mentioned at the beginning comprises, according to the invention, a signal divider connected to the signal output of each acceleration sensor for splitting the respective sensor signal into a low-frequency signal component (LF component) characterizing the vehicle acceleration and into a high-frequency signal component (HF component), an addition element connected to the LF outputs of the signal dividers for the vectorial addition of the LF components corresponding to the longitudinal acceleration component and the transverse acceleration component, a storage unit connected to the addition element and the time measuring element for storing the calculated acceleration values over the measured time and a control unit connected to the HF outputs of the signal dividers for controlling the time measuring element.

The HF portion of the sensor signals detects vibrations in the vehicle and sound waves such as engine noise and/or rolling noise. This makes it possible to control the device according to the invention depending on the operating state of the vehicle, i.e. for example, to switch on the time measuring element when the engine is switched on, without the device having to be coupled to the ignition lock. It is precisely this feature that makes the device independent of the vehicle and enables the device to be subsequently installed and removed without any problems.

Storing the acceleration values over time enables an analysis of the driver's driving behavior. The stored values can be used to determine whether the driver accelerated or braked particularly strongly over the measurement period, whether he took corners very quickly, etc. These values can be compared with an average diagram in order to evaluate the driver's driving behavior.

If only acceleration values above a certain level are to be recorded, it is expedient if a component threshold circuit is arranged between the NF output of the respective acceleration sensor and the addition element, which only passes on an NF component that exceeds a threshold value specified for the respective acceleration component to the addition element.

In order to avoid as far as possible the switching on of the time measuring element and thus the starting up of the device by vibrations or noises not originating from the vehicle, the control unit can comprise a main switch that controls the time measuring element and a second threshold circuit connected to the HF outputs of the signal dividers, which switches the main switch on when the HF component of at least one of the two acceleration signals exceeds a predetermined threshold value. Even greater security against external influences is achieved by connecting a first time element downstream of the second threshold circuit, which switches the main switch off when the HF component of both acceleration signals remains below the threshold value of the second threshold circuit for a predetermined initial period of time. On the one hand, the threshold value can be reduced so much that the device switches on even when the vehicle is rolling with relatively little vibration, on the other hand

On the other hand, a distinction is made between continuous operation of the vehicle and short-term external influences.

The switching on of the device or the time measuring element can also be made dependent on the detected acceleration values exceeding a certain threshold value. The control unit can thus comprise a third threshold circuit connected to the NF outputs of the signal dividers and a second time element connected downstream of this, which switches off the main switch if the NF component of both acceleration signals remains below the threshold value of the third threshold circuit for a predetermined second period of time.

If the device is subsequently installed, particularly if it is a device that can be installed by laymen, there is a risk that the device with the measuring axes of the acceleration sensors will not be installed with such precision that correct or optimal operation is guaranteed. For this reason, the invention proposes that the evaluation unit comprises a computing unit connected to the LF outputs of the signal dividers, which determines the type of acceleration components from the LF signal components, and that a switching device is arranged in the LF signal path between the acceleration sensors and the adder, which connects the inputs of the adder assigned to a specific acceleration component to the associated acceleration sensor depending on the result determined by the computing unit. For example, it can be calculated from the signal curve whether the signal represents a lateral acceleration or a longitudinal acceleration of the motor vehicle. The computing unit can thus

_μ1λ 0

determine which sensor of the installed device provides the data on the lateral acceleration and which one provides the data on the longitudinal acceleration. The sensors can be connected to the adder via the switching device in order to ensure that the device functions correctly. It is assumed that the sensors can respond to both types of acceleration.

In order to be able to carry out a simple evaluation of the determined data, it is expedient if the invention according to the invention comprises a display device on which the acceleration data stored in the storage unit can be displayed in the form of a graphical representation of the acceleration values over time.

Further features and advantages emerge from the following description, which, in conjunction with the accompanying drawings, explains the invention using an exemplary embodiment. They show:

Figure 1 is a schematic representation of the

Acceleration measuring axes in a vehicle,

Figure 2 is a graphical representation of the

the course of the acceleration values determined by the device according to the invention over time,

Figure 3 is a block diagram of the inventive

appropriate device and

Figure 4 a more detailed functional diagram

the device according to the invention.

According to Figure 3, the device according to the invention comprises a microprocessor 10, which is powered by a battery 12. Selectable operating data, such as the threshold values to be explained below, can be entered into the microprocessor via a keyboard 14. The microprocessor is also connected to two acceleration sensors 16 and 18. When the device is installed in a vehicle 20 (Figure 1), the measuring axis of the acceleration sensor 16 is aligned parallel to the vehicle's longitudinal axis and thus detects a longitudinal acceleration. The measuring axis of the acceleration sensor 18 is aligned perpendicular to this and thus detects the lateral acceleration of the vehicle 20. If necessary, a third acceleration sensor 22 can also be provided, the measuring axis of which is aligned parallel to the Z or vertical axis. However, since this sensor is not usually required in motor vehicles, it is only shown in dashed lines in Figure 3.

The microprocessor 10 evaluates the signals supplied by the sensors 16, 18, 22 and controls a display device 24 on which, for example, the determined acceleration values are plotted against the measurement time in a graphical representation according to Figure 2 (curve A in Figure 2). For this purpose, a reference value (curve B) can also be displayed. This allows the current values to be compared with a usual reference value and thus an evaluation of the driver's driving behavior compared to average driving behavior.

In the following, the function of the device according to the invention will be explained in detail using the more detailed block diagram in Figure 4. The same parts are again provided with the same reference numerals. The diagram shows an arrangement with two acceleration sensors.

Each of the sensors 16 and 18 is connected to the microprocessor via an adapter or an interface 26 or 28. Each sensor 16 or 18 is followed by a signal divider 30 or 32, which essentially consists of two filter circuits and has an LF output 34 or 36 for a low-frequency signal component and an HF output 38 or 40 for a high-frequency signal component. The range from 0 to 10 Hz is referred to as low frequency, for example, and the range from approximately 20 to 500 Hz is referred to as high frequency. The low-frequency spectrum records the vehicle's acceleration signals that are influenced by the driver, i.e. accelerating the vehicle, braking the vehicle and cornering. The HF part of the signal contains vibrations from the vehicle such as engine vibrations, rolling noise, uneven ground, etc. This frequency component is used, as will be explained later, to control the device.

The NF outputs 34 and 36 of the two signal dividers 30 and 32 are each connected to a changeover switch 42 and 44. The changeover switch 42 is connected to an adder 48 via a component threshold circuit 46 for the X (longitudinal acceleration) component. The changeover switch 44 is connected to another input of the adder 48 via a component threshold circuit 50 for the Y (lateral acceleration) component. In the embodiment shown, the changeover switches 42 and 44 are shown in such a way that the sensor 16 is connected to the component threshold circuit 46 and the sensor is connected to the component threshold circuit 50. When the two changeover switches 42 and 44 are switched to their respective other switching positions, these connections are swapped. The changeover of the switches 42 and 44 takes place under the control of a computing unit.

· I

52, which is also connected to the NF outputs 34 and 36 and determines from the signals supplied what type of acceleration is detected by the sensors 16 and 18. Depending on how the measuring axes of the sensors 16 and 18 are aligned, these are then connected via the switches 42 and 44 to the component threshold circuit 46 and 50 associated with them.

The HF outputs 38 and 40 of the signal dividers 30 and 32 are connected to a second threshold circuit 54, which specifies a certain threshold value for the HF signal to be processed. If this threshold value is reached or exceeded, the threshold circuit 54 actuates a main switch 56, which is thereby closed and thus establishes a connection between the system clock 58 of the microprocessor 10 and an operating time counter 60, i.e. switches it on. The threshold circuit 54 controls a further switch 62 in such a way that when the HF signal of both sensors 16 and 18 falls below the specified threshold value of the threshold circuit 54, a timer 64 is set, after which the main switch 56 is opened (e.g. 10 seconds), i.e. the operating time counter 60 is switched off.

The NF outputs 34 and 36 of the signal divider circuits 30 and 32 are also connected to a third threshold circuit 66, which sets a threshold value for the acceleration signals. If the acceleration signals fall below this predetermined threshold value, the threshold circuit 66 causes a further timer 70 to be set via a switch 68. After the time set on this timer 70 has elapsed (for example, approximately 5 minutes), the switch 56 is opened, which switches off the operating time counter 60.

The device described so far works as follows:

When the engine is switched on, vibrations are generated, which are expressed in an HF component of the signal supplied by sensors 16 and 18. If these vibrations exceed a value specified on the threshold circuit 54, the switch 56 is closed and the operating time counter 60 is switched on. If no acceleration values occur within the time set on the timer 70 that exceed the threshold value set on the threshold circuit 66 (because, for example, the vehicle stops), the operating time counter 60 is switched off again. If, on the other hand, the vehicle starts moving and the acceleration values supplied by sensor 16 exceed the value set on the component threshold circuit 46, this value is fed to the addition element 48. The same applies to the acceleration values supplied by sensor 18. The addition element 48 adds the acceleration values vectorially. The total acceleration value determined in this way is fed to the display unit 24. The display unit 24 contains a memory in which the determined acceleration values are stored together with the time values determined by the operating time counter 60. The display unit 24 also provides a graphic representation in which the acceleration values are plotted against the elapsed time as shown in Figure 2.

In addition to or instead of the graphic representation in the display unit, it can be provided that the microprocessor calculates a score from the comparison of curves A and B, which provides an evaluation of the driver's driving behavior.

·

·

Furthermore, it can be provided that the average value of the signals delivered by the sensors is continuously recalculated in the microprocessor in order to eliminate the influence of temperature and aging on the sensors. Furthermore, inclines and declines can also be calculated out so that even when driving over passes, for example, only the acceleration values that can be influenced by the driver are registered and recorded.

If the vibrations from the vehicle's engine and rolling noise are too weak to be detected by the acceleration sensors, the RF signal required for control could also be generated by a microphone.

Claims (7)

Protection claims 1. Device for determining driving state variables of a motor vehicle, comprising at least two acceleration sensors (16, 18) for detecting the longitudinal and lateral acceleration of the motor vehicle (20) and an evaluation circuit (10) with a resettable time measuring element (60) which determines acceleration values from the sensor signals for a specific period of time, characterized by a signal divider (30, 32) connected to the signal output of each acceleration sensor (16, 18) for splitting the respective sensor signal into a low-frequency signal component (NF component) characterizing the vehicle acceleration and a high-frequency signal component (HF component), an addition element (48) connected to the NF outputs (34, 36) of the signal dividers (30, 32) for the vectorial addition of the longitudinal acceleration component (X) and the lateral acceleration. acceleration component (Y) corresponding NF components of both sensor signals, a storage unit 24 connected to the addition element (4) and the time measuring element (60) for storing the calculated acceleration values over the measured time and a control unit (54, 56, 62, 64) connected to the HF outputs (38, 40) of the signal dividers (30, 32) for controlling the time measuring element (60)· 2. Device according to claim 1, characterized in that a component threshold circuit (46, 50) is arranged between the LF output (34, 36) of the respective acceleration sensor (16, 18) and the addition element (48), which only passes on an LF component that exceeds a threshold value specified for the respective acceleration component (X, Y) to the addition element (48). 3. Device according to claim 1 or 2, characterized in that the control unit comprises a main switch (56) controlling the time measuring element (60) and a second threshold circuit (54) connected to the HF outputs (38, 40) of the signal dividers (30, 32), which switches on the main switch (56) when the HF component of at least one of the two acceleration signals exceeds a predetermined threshold value. 4. Device according to claim 3, characterized in that the second threshold circuit (54) is followed by a first timing element (64) which switches off the main switch (56) if the HF component of both acceleration signals remains below the threshold value of the second threshold circuit (54) for a predetermined first period of time. 5. Device according to claim 3 or 4, characterized in that the control unit comprises a third threshold circuit (66) connected to the NF outputs (34, 36) of the signal dividers (30, 32) and a second switching element connected downstream of this, which switches off the main switch (56) when the NF component (34, 36) of both acceleration signals remains below the threshold value of the third threshold circuit (66) for a predetermined second period of time. 6. Device according to one of claims 1 to 5, characterized in that the evaluation unit comprises a computing unit (52) connected to the LF outputs (34, 36) of the signal dividers (30, 32), which determines the type of acceleration components (X, Y) from the LF signal components, and that a switching device (42, 44) is arranged in the LF signal path between the acceleration sensors (16, 18) and the addition element (48), which connects the inputs of the addition element (48) each assigned to a specific acceleration component to the associated acceleration sensors depending on the result determined by the computing unit (52). 7. Device according to one of claims 1 to 6, characterized by a display device (24) for displaying the course of the acceleration values over time stored in the memory unit.