METHOD FOR DETERMINING A TRANSMISSION RATIO IN THE DRIVETRAIN OF A MOTOR VEHICLE
The invention relates to a method for determining a gear transmission ratio in the drivetrain of a motor vehicle according to the preamble of claim 1.
It is known that In a motor vehicle drivetrain, a clutch and a variable speed gearbox are disposed downstream of a driving motor from a drive point of view. The variable speed gearbox, among other things, has the function of converting the engine speed and the engine torque. As a result of these changes, the speeds and torque developing on the driven wheels of the vehicle correspond to the desired driving speeds with sufficiently high driving torque and/or traction forces.
The change of the torque and the engine speed is achieved in that different gear ratios are set in the variable speed gearbox. The respective gear transmission ratio is determined by comparing a rotational speed nm of the output shaft of the engine or the drive shaft of the gearbox with the engine speed n^ of the drive shaft of the variable speed gearbox. The gear transmission ratio between the output shaft of the engine or drive shaft of the gearbox and the output shaft of the variable speed gearbox is defined by the following equation: i., = nWg/nm. If the engine speed nwg of the output shaft of the variable speed gearbox is known and if no other components that influence the engine speed are present in the drivetrain to the driven wheel, the engine speed of at least one vehicle driven wheel is determined from the engine speed of the output shaft of the variable speed gearbox.
During the course of use of a vehicle, however, situations may arise in which the components disposed downstream of the variable speed gearbox may influence the actual gear transmission ratio. This occurs, for example, when installing a rear axle with axle drive when building or converting the motor vehicle,

using an axle drive that has a different ratio than that of the previously used rear axle,
A different cause for the change of the gear transmission ratio in the drivetrain may be a shiftable transfer case, the regulating step of which was changed. A transfer case, which is disposed between the variable speed gearbox and axle drive, may be used to drive several vehicle axles simultaneously. A further task of the transfer case may be to achieve speed compensation between the axle drives in vehicles with constant all-wheel drive or to block speed compensation when there is excessive slip differences between the drive wheels. In the case of all-terrain vehicles or commercial vehicles, the transfer case is also used to expand the gear transmission ratio range. It is possible that no exact information is available as to the extent to which the gear transmission ratio in the drivetrain is influenced.
A further cause as to why in components of the drivetrain, which are disposed downstream of the variable speed gearbox, a changed geartransmission ratio may be due to the drive wheels. When changing wheels using wheels that have a different diameter than the previously used wheels, compared to the previously used wheels, a different rolling length is created resulting in a different vehicle speed, A change of diameter may also be the result of lowering the air pressure while driving, for example, to improve traction. The use of a vehicle is also associated with tire wear so that over time the wheel diameter decreases. These influences may mean that the gear ratio is in part or completely unknown so that no or only erroneous signal variables are available for the driving strategy, dutch control and transmission control.
Against this background it is the object of the invention to determine a method, which allows the driving strategy, clutch control and transmission control to be optimally and easily adjusted during the entire service life of a vehicle.
The solution to this task arises from the characteristics of the main claim, and advantageous embodiments and further developments of the invention are disclosed in the dependent claims.

The invention is based on the realization that the determination of individual ratios of components in the drivetrain, which are disposed downstream of the variable speed gearbox to the driven wheel, is not possible with acceptable levels of effort. Therefore, according to the invention, a method is used to determine an overall gear transmission ratio of the components disposed downstream of the variable speed gearbox.
Accordingly, the invention is based on a method for determining a gear transmission ratio in the drivetrain of a motor vehicle with an engine, a downstream clutch and a variable speed gearbox downstream thereof wherein, between the engine and the variable speed gearbox, a gear ratio is determined by the current rotational speed of the output shaft of the engine and the current rotational speed of the output shaft of the variable speed gearbox.
In addition, it is provided that the method includes the following steps: determining the amount of the current speed of the motor vehicle and processing the amount of the current rotational speed of the output shaft of the variable speed gearbox and the amount of the current speed of the motor vehicle using a processing unit so that the gear transmission ratio is determined based on the vehicle components of the drivetrain disposed downstream of the variable speed gearbox.
In addition, it is preferable that the processing unit forms the product of the amount of the current rotational speed of the output shaft of the variable speed gearbox and the reciprocal value of the amount of the vehicle speed. This is advantageous, because a variable can be formed from the total gear ratio of the components downstream of the variable speed gearbox as a function of the dynamic wheel diameter. Since this variable remains constant for a foreseeable period, the failure of a speed sensor on the driven wheel or of a speed sensor on the output shaft of the variable speed gearbox can be compensated.
In addition, in a preferred embodiment, it may be provided that the method is only conducted when the current vehicle speed exceeds a minimum amount.

This is advantageous because the uncertainty and/or the error ranges are kept small when determining the gear ratio.
Furthermore, it may be provided that the amount of the current engine speed of the driven shaft of the variable speed gearbox and/or the amount of the current vehicle speed are captured at different cycle speeds. This is advantageous because, as a result, sensors and transducers may be used, which provide updated readings at different times.
In addition, it is considered advantageous that if the processing unit only processes the above amounts when a change of the amount captured with the lower cycle rate occurs. This is advantageous because, as a result, only readings are included in the determination of the gear ratio, which together represent the most up-to-date reading. Consequently, it can be avoided using readings for the computation of the gear ratio that were measured at different times and, therefore, different events.
In addition, it may be provided that the processing unit only processes the amounts when the amount of an acceleration of the current engine speed of the output shaft does not exceed a certain value. This is advantageous because with this, mechanical deformation forces occurring in the drivetrain when starting to drive (so-called wind-up effects) can only act as insignificant disturbance variables in the determination of the gearratio.
According to another embodiment of the invention, it may be provided that the processing unit repeats the processing operations of the above amounts until the determined gear transmission ratio does not exceed a defined tolerance. This is advantageous because with this onfy a determined gear ratio, which is only associated with a very small measuring uncertainty, is used as a signal variable for the transmission control, clutch control, and driving strategy.
Finally, it may be preferable that the processing unit determines a replacement value instead of a computed value. This is advantageous because, for example, in the event that a determined gear transmission ratio drops below a minimum gear transmission ratio, such a replacement value is used and the

transmission control and the clutch control and driving strategy are not based on a value that is technically obviously not sensible.
The invention will be explained hereinafter based on an exemplary embodiment and figures that are attached to the description, wherein:
FIG.1 is a schematic top view of the motor vehicle drivetrain;
FIG. 2 is a graphical illustration to explain the erroneous computation when determining the gear transmission ratio according to one embodiment of the invention;
FIG. 3 is a schematic illustration to explain the determination of the gear transmission ratio according to another embodiment of the invention, and
FIG. 4 is a schematic illustration to explain the determination of the gear transmission ratio according to a further embodiment of the invention,
FIG. 1 shows that the drivetrain of a motor vehicle has an engine 1, a downstream clutch 2 from a drive point of view and a downstream variable speed gearbox 3. The engine 1 on the output shaft has a rotational speed nm, which is transmitted from there to the variable speed gearbox 3 when the clutch 2 is engaged. There, a torque conversion and speed conversion take place so that the driven shaft of the variable speed gearbox 3 rotates at a speed nwg.
The gear ratio between the engine and the variable speed gearbox is known to be calculated with the equation i1 = nm/nwg. On the driven shaft of the variable speed gearbox 3, the rotational speed is forwarded from the drivetrain to a possibly integrated transfer case 4 and from there to an axle drive 5. There, the power flow is diverted by 90° so that the rear axle 6, disposed transversely to the longitudinal axis of the vehicle, are driven. Rear wheels 7 of the vehicle are provided at the ends of the rear axle 6.

According to one embodiment of the invention, the current vehicle speed is measured on a rear wheel 7, allowing the speed nwg to be used to determine a relative gear transmission ratio based on the following formula:
Here, i2 is the gear transmission ratio of the output shaft of the variable speed gearbox 3 to the driven wheel 7; ddyn is the dynamic wheel diameter of the wheels 7; n^ is the rotational speed of the output shaft of the variable speed gearbox, and v is the speed of the wheels 7. The term i2 denotes the total gear transmission ratio, which includes all individual ratios of the components present between the variable speed gearbox 3 and the rear wheel 7. In FIG. 1, this region of the drivetrain is shown with a dotted line. When the relative gear transmission ratio determined with formula (1) is known, the following problems can be solved:
a) Failure of a speed sensor or failure of an engine speed sensor in the drivetrain: Since the ratio 1/2ddyn remains constant for a foreseeable period, a suddenly missing value of a speed sensor and/or of an engine speed sensor can be computed.
b) Unknown gearratio of a transfer case: If the dynamic wheel diameter ddyn is known, the gear transmission ratio 1\2 can be determined with the captured vehicle speed v and the captured engine speed nwg of the variable speed gearbox 3. In addition, if the gear ratio of the axle drive 5 is known, the gearratio of a transfer case 4 can be calculated.
c) Unknown dynamic wheel diameter If the gear transmission ratio i2, the engine speed nwg on the output shaft of the variable speed gearbox 3 and the vehicle speed v are known, the dynamic wheel diameter can be determined, If any wheels are replaced, the tires are worn or the air pressure decreases during the service life of a vehicle, the dynamic diameter of a wheel will change, which can be determined using formula (1).
When determining the gear transmission ratio i2, care should be taken that the measuring uncertainty levels or errors occurring in the detection of a reading

are not so large that it results in an error for the gear ratio. The following example will illustrate this in conjunction with FIG. 2:
If a shiftable transfer case has a control stage with a first gear ratio of 1:0.9 and a control stage with a second gear ratio of 1:1.1, these gear ratios can be clearly differentiated from each other if the measurements are read without error. In practice, however, each measurement signal is associated with a certain measurement uncertainty.
It shall be assumed that the gear transmission ratio is known with an uncertainty of ±10%. This produces an error range with a lower limit UG and an upper limit OG at the amounts illustrated in the table in FIG. 2. At the first gear ratio of 1:0.9t an uncertainty of +10% results in an upper limit OG of 0.99, wherein an uncertainty of -10% results in a lower limit UG of 0.81, At the next control stage with the second gear ratio 1:1.1 f the uncertainty of ±10% results in an upper limit OG of 1.21 and in a lower limit UG of 0,99. This demonstrates that the upper limit OG at the first gear ratio of 1:0.9 is equal to the lower limit UG of the second gear ratio of 1:1.1. An uncertainty of ±10%, therefore, means that no clear decision is possible as to whether the shiftable transfer case has a gear ratio of 1:0.9 or 1:1.1. Such situations can be avoided if the uncertainty in determining the gear ratio is lowered significantly and is, for example, only ±5%.
Uncertainties in the determination of a gear transmission ratio may be related to systematic errors. This includes, among other things, slippage on a drive wheel, different cycle rates when determining vehicle speed and/or engine speed of the output shaft of the variable speed gearbox 3 as well as a wind-up effect of the rear axle when starting to drive the motor vehicle. Uncertainties in the determination of the gear transmission ratio can be minimized, for example, if the different cycle rate is taken into consideration in the determination of the signals.
FIG. 3 shows signal lines by way of example which belong to a sensor 1 and a sensor 2. On sensor 1, the signals are captured at a relatively high cycle rate, while a lower cycle rate is used on sensor 2. In the illustrated example, the cycle rate of sensor 1 is twice as high as that of sensor 2.

With respect to determining the gear transmission ratio i2, for example, sensor 1 may represent the engine speed sensor on the variable speed gearbox 3 and sensor 2 the speed sensor on wheel 7, in order to decide which signal is used for computing the gear transmission ratio l2l according to the invention, the procedure may be such that a computation of the gear radio i2 is only carried out when a signal change of sensor 2 with the lower cycle rate is present (see "A* in FIG. 3 with the event bars shown there). As a result, a gear transmission ratio is only computed when newly detected signals are available from both sensors 1 and 2, When an event changes and when a sensor detects this sooner than a second sensor, a gear transmission ratio is determined, which is subject to a relatively high systematic error.
When starting to drive, mechanical deformation and twisting of the entire wheel suspension may occur, the so-called Mwind-up effect". The determination of the gear transmission ratio, according to the invention, may be suspended until the wind-up effect is only associated with a negligible error of the measurement signal. This can be achieved, for example, in that the amount of a change of the acceleration of the current rotational speed of the output shaft of a variable speed gearbox dn^/dt3 does not exceed a certain value.
A further possibility to reduce the likelihood of a systematic error when determining the gear transmission ratio i2 is apparent in connection with FIG. 4. According to this method, a computation according to formula (1) is repeated until the result of a calculation compared tb the result of the previous calculation does not exceed a defined tolerance T. A further measure is to use a replacement value Emin instead of the amounts determined this way when a minimum gear transmission ratio has not been met. The same applies when a maximum possible gear transmission ratio has been exceeded. In this case, a replacement value Emax is selected, see FIG. 4.
if these measures are taken into consideration, systematic errors can be reduced in the determination of the gear transmission ratio.

CLAIMS
1. A method for determining a gear ratio in the drivetrain of a motor vehicle
comprising an engine, a downstream clutch and a variable speed gearbox
downstream thereof, a gear ratio between the engine and the variable speed
gearbox being determined from the engine speed of the driven shaft of the engine
and the engine speed of the output shaft of the variable speed gearbox,
characterized in that the method comprises the following additional steps:
determininganamountofthecurrentspeedofthemotorvehicle, and
processing the amount of the current engine speed of the output
shaft of the variable speed gearbox and the amount of the current speed of
the motor vehicle using a processing unit
so that the gear ratio of the vehicle components of the drivetrain disposed
downstream of the variable speed gearbox is determined,
2. The method according to claim 1t characterized in that the processing unit forms the product of the amount of the current engine speed of the output shaft of the variable speed gearboxand the reciprocal of the amount of the vehicle speed.
3. A method according to claim 1 or 2, characterized in that the method is only carried out if the current vehicle speed exceeds a minimum amount.
4. A method according to anyone of the preceding claims, characterized in that the amount of the current engine speed of the output shaft of the variable speed gearbox and/or the amount of the current vehicle speed are collected at different cycle rates.
5. The method according to claim 4, characterized in that the processing unit only processes the amounts if a change of the amount exists, which is collected with the lowest cycle rate.
6. A method according to anyone of the preceding claims, characterized in that the processing unit only processes the amounts when the amount of an acceleration of the current engine speed of the output shaft does not exceed a certain value.

7. A method according to any one of the preceding claims, characterized
in that the processing unit processes the amounts until the determined gear ratio
does not exceed a defined tolerance.
8. A method according to any one of the preceding claims, characterized
in that the processing unit determines a replacement value instead of a computed
value.