Method for simulating cornering

Abstract

A method for simulating cornering of a vehicle 2 being tested on a roller dynamometer 1 to determine a measured variable 13, wherein the vehicle 2 being tested on the roller dynamometer 1 is operated as though driving straight ahead, and to simulate cornering the additional resistance forces of cornering are taken into account in the form of a correction parameter 9.

Claims

1. A method for accounting for simulated cornering of a vehicle being tested on a roller dynamometer in a measured variable: operating the vehicle on the roller dynamometer as though the vehicle is driving straight ahead with all wheels having the same rotational speed; determine a correction parameter by simulating cornering the vehicle on the roller dynamometer, the correction parameter associated with additional resistance forces on the vehicle due to cornering; and determine the measured variable based at least in part on the correction parameter.

2. The method according to claim 1, wherein a cumulative resistance force, associated with the simulated cornering of the vehicle, is used as the correction parameter, the cumulative resistance force is formed by adding the additional resistance forces exerted on the vehicle during cornering, said cumulative resistance force being taken into account on the roller dynamometer in the form of a modified resistance which the roller dynamometer exerts on the vehicle.

3. The method according to claim 2, wherein a characteristic map which describes the correction parameter is compiled by real coast down experiments of the vehicle being tested, in curves with different radii (R).

4. The method according to claim 2, wherein the correction parameter is calculated using one or more physical models.

5. The method according to claim 4, wherein a first physical model is used to take into account the resistance forces created by the forces acting on tires and a chassis of the vehicle being tested.

6. The method according to claim 4, wherein a second physical model is used to take into account the resistance forces created by losses in a drive train of the vehicle being tested.

7. The method according to claim 4, wherein a third physical model is used to take into account resistance forces which are created by auxiliary units of the vehicle being tested which are dependent on steering.

8. The method according to claim 1, wherein a mathematical correction factor is used as the correction parameter, wherein the measured variable is corrected by means of the correction factor.

9. The method according to claim 1, wherein the correction parameter is calculated using one or more physical models including: a first physical model is used to take into account resistance forces created by the forces acting on tires and a chassis of the vehicle being tested, a second physical model is used to take into account resistance forces created by losses in a drive train of the vehicle being tested, and a third physical model is used to take into account resistance forces which are created by auxiliary units of the vehicle being tested which are dependent on steering; and wherein the resistance forces measured by the one or more physical models are added to determine the correction parameter for the simulated cornering of the vehicle.

10. The method of claim 1, wherein the additional resistance forces on the vehicle during cornering include one or more of the following: slippage on tires of the vehicle, losses in a differential of the vehicle, losses from a power steering unit, and other losses from driven auxiliary components.

11. The method of claim 1, wherein the roller dynamometer is a 42 or 21 roller dynamometer.

12. The method of claim 1, wherein the correction parameter accounts for and accumulates simulated resistance forces associated with the vehicle cornering, and an increased resistance is applied to the roller dynamometer in response to an increased correction parameter, the correction parameter includes simulated resistance forces for one or more of the following: slippage on tires of the vehicle, losses in a differential of the vehicle, losses from a power steering unit, and other losses from driven auxiliary components.

13. The method of claim 1, wherein the measured variable is one or more of the following: fuel consumption, exhaust certification, or various other performance characteristics of the vehicle.

14. The method of claim 1, wherein the correction parameter is representative of a cumulative resistive force associated with the vehicle cornering, and the method of claim 1 further includes modifying the resistance the roller dynamometer exerts on the vehicle being tested, based on the determined correction parameter, before determining the measured variable.

15. The method of claim 1, wherein the method further includes correcting the measured variable to account for the simulated cornering of the vehicle by applying the correction parameter to the measured variable to generate a corrected variable.

16. The method of claim 15, wherein the correction parameter is calculated using a characteristic map for cornering resistance based on vehicle speed and curve radius.

17. The method of claim 1, wherein the additional resistance forces on the vehicle due to cornering includes a cornering resistance measured by: $F_{\mathrm{cornering}\mathrm{resistance}}=\frac{{\left(m_{\mathrm{Tot}}*\stackrel{l_h}{T}\right)}^2*v^4}{R_h^2*2*C_{\mathrm{Sh}}}+\frac{{\left(m_{\mathrm{Tot}}*\stackrel{l_v}{T}\right)}^2*v^4}{R_h^2*2*C_{\mathrm{Sv}}}$ where: m.sub.Tot is the vehicle mass (including lift/downforce) l is the wheelbase l.sub.h, l.sub.v is the centroidal distance of the rear axis/front axis v is the vehicle speed R.sub.h, R.sub.v is the curve radius at rear/front C.sub.Sh, C.sub.Sv is the skew rigidity rear/front And for the vehicle mass: $m_{\mathrm{Tot}}=\frac{F_m+F_a}{g}=m+\frac{F_a}{g}$ where: m is the vehicle mass F.sub.m is the vehicle weight force F.sub.a is the lift force wherein, for the lift force: $F_a=c_a*A**\frac{v^2}{2}$ c.sub.a is the lift coefficient A is the reference surface is the air density.

18. The method of claim 1, wherein the step of determining the measured variable based at least in part on the correction parameter further includes taking the correction parameter into account on the roller dynamometer in the form of a modified resistance which the roller dynamometer exerts on the vehicle or by correcting the measured variable by means of the correction parameter.

Description

(1) The present invention is explained below with reference to FIGS. 1 to 3 which show, by way of example, schematic, advantageous embodiments of the invention which do not restrict the same, wherein:

(2) FIG. 1 shows a test vehicle on a roller dynamometer,

(3) FIG. 2 shows a characteristic map for cornering resistance according to speed and curve radius, and

(4) FIG. 3 shows a diagram for a direct correction of the measurement.

(5) FIG. 1 shows a typical arrangement of a test vehicle 2 on a roller dynamometer 1, wherein the test vehicle 2 has four wheels, by way of example. A 42 roller dynamometer 1 is illustrated by way of example, wherein the four wheels of the test vehicle 2 are functionally assigned to two rollers which are independent of each other. In this case, the two front wheels of the test vehicle 2 are on the same roller 4 (in such cases, there could also of course be two rollers on the same axis), and both rear wheels of the test vehicle 2 are on the same roller 3. The use of a roller dynamometer 1 which is designed as a 21 roller dynamometer, wherein only one roller 3 is functionally assigned totypicallythe drive wheels of the test vehicle 2, can also be contemplated. The same is true for the use of a 44 roller dynamometer in which a separate roller is assigned to each wheel of a four-wheeled test vehicle 2. As mentioned above, the method is not restricted to the use on roller dynamometers for four-wheeled test vehicles 2.

(6) The test vehicle 2 is operated on the roller dynamometer 1 driving straight ahead. Driving straight ahead means that all wheels of the test vehicle 2 have the same rotation speed, as can be assumed for normal straight-ahead driving at optimum wheel grip.

(7) As can be seen in FIG. 1, the roller dynamometer 1 is connected to an environmental model 5 and an additional resistance model 6.

(8) The environmental model 5 contains the information on the simulated route for the test vehicle 2 to travel during the testing thereof, including curves (no further information shall be provided here regarding additional route data which the model processes, such as inclinations, for example).

(9) The environmental model 5 receives the current speed 7 measured at the wheels of the test vehicle 2 from the roller dynamometer 2, and this is converted into the distance traveled. The point in the simulated route at which the test vehicle 2 is currently found can be determined utilizing the distance traveled. When the vehicle travels through a curve, the current curve radius 8 is passed on to the resistance model 6.

(10) In the resistance model 6 are determined the resistance forces which occur additionally during cornering and which the test vehicle 2 would have been subjected to in the current route segment specified by the environmental model 5. These additionally occurring resistance forces are collected into one value and subsequently transmitted to the roller dynamometer 1 in the form of a correction parameter 9.

(11) In the diagram illustrated in FIG. 1, the correction parameter 9 is a cumulative resistance force 10 which is found by adding the resistance forces. Because the cumulative resistance force 10 is naturally dependent on speed, the current speed 7 is also passed on to the resistance model 6. The cumulative resistance force 10 is transmitted to the roller dynamometer 1 in the form of a correction parameter 9.

(12) If the correction parameter 9 is the cumulative resistance force 10, in a subsequent step the resistance which the rollers 3 and 4 of the roller dynamometer oppose to the test vehicle 2 is adapted according to the curve the vehicle is traveling through.

(13) The resistance model 6 does not contain the resistance forces which are active during driving straight ahead. Because the correction parameter 9 only incorporates the cumulative resistance force 10, which in turn only collects the resistance forces which occur additionally during cornering, the present method constitutes an extension or also a simplification for the methods conventionally used for roller dynamometers.

(14) Such an extendable, conventional method contains, by way of example, the following approach:

(15) $F=F_0+F_1*v+F_2*v^n+R_w*\frac{v}{t}+R_w*g*\sin$

(16) where:

(17) F is tractive force

(18) F.sub.0 is the fraction of the tractive force independent of speed

(19) F.sub.1 is the coefficient for the linear fraction of the tractive force dependent on speed

(20) F.sub.2 is the coefficient for the non-linear fraction of the tractive force dependent on speed

(21) V is the vehicle speed

(22) n is a variable exponent

(23) R.sub.W is the vehicle reference weight

(24) R.sub.G is the base inertia of the roller dynamometer

(25) R.sub.W*=R.sub.WR.sub.G is the electrically simulated mass inertia

(26) v/t is acceleration

(27) G is acceleration due to gravity

(28) R.sub.W*g*sin is the fraction of the tractive force to overcome the incline of the road surface.

(29) As can be seen, there is no consideration therein of resistance forces which occur additionally during cornering.

(30) The data used in the resistance model 6 to determine the correction parameter 9 can be determined in two ways.

(31) FIG. 2 shows a characteristic map 12 used, by way of example, to determine for this purpose the cumulative resistance force 10 according to the current speed 7 and the curve radius R. This characteristic map is made of different coast down curves 11. The coast down curves 11 of the test vehicle 2 in this case are determined by real coast down experiments, for example on a testing track. The coast down experiments in this case include multiple passes in which the test vehicle 2 rolls through curves of different curve radii. The term coast down curve 5 in this case means the relationship between speed of the test vehicle 2, radius of the curve being traveled, and the resulting resistance force on the wheels of the test vehicle 2.

(32) A further option is that of calculating the cumulative resistance force 10 using physical models.

(33) For this purpose, by way of example, the formula for curve resistance in the linear single-track model found in Karl Ludwig Haken, Grundlagen der Kraftfahrzeugtechnik, Carl Hanser Verlag, Munich, 2008 can be used:

(34) $F_{\mathrm{cornering}\mathrm{resistance}}=\frac{{\left(m_{\mathrm{Tot}}*\stackrel{l_h}{T}\right)}^2*v^4}{R_h^2*2*C_{\mathrm{Sh}}}+\frac{{\left(m_{\mathrm{Tot}}*\stackrel{l_v}{T}\right)}^2*v^4}{R_h^2*2*C_{\mathrm{Sv}}}$

(35) where:

(36) m.sub.Tot is the vehicle mass (including lift/downforce)

(37) l is the wheelbase

(38) l.sub.h, l.sub.v is the centroidal distance of the rear axis/front axis

(39) v is the vehicle speed

(40) R.sub.h, R.sub.v is the curve radius at rear/front

(41) C.sub.Sh, C.sub.Sv is the skew rigidity rear/front

(42) And for the vehicle mass:

(43) $m_{\mathrm{Tot}}=\frac{F_m+F_a}{g}=m+\frac{F_a}{g}$

(44) where:

(45) m is the vehicle mass

(46) F.sub.m is the vehicle weight force

(47) F.sub.a is the lift force

(48) wherein, for the lift force:

(49) $F_a=c_a*A**\frac{v^2}{2}$

(50) c.sub.a is the lift coefficient

(51) A is the reference surface

(52) is the air density

(53) In addition to this simple physical model, of course more complex models can be contemplated which incorporate resistance forces created by the forces which act on the tires and the chassis of the test vehicle, by losses in the drive train, and/or by auxiliary units which are dependent on the steering.

(54) FIG. 3 shows a diagram wherein the correction parameter 9 is used to directly correct the measured variable 13. The correction parameter 9 need not necessarily, as noted above, be the cumulative resistance force 10. In principle, the correction parameter 9 can be directly applied to the measurement determined on the roller dynamometer 1, depending on the measurement to be taken on the roller dynamometer 1. By way of example, the fuel consumption of the test vehicle 2 could be a measured variable 13 to be measured. The characteristic map 12 described in FIG. 2 is then modified in this case such that the fuel consumption of the test vehicle 2, rather than the cumulative resistance force 10, is determined according to speed 7 and curve radius R.

(55) If the measurement taken on the roller dynamometer 1 is analyzed, the correction parameter 9 can be directly used on the measured variable 13, and the same can consequently be corrected according to the curve which has been traveled.