Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Utility Patent
1999-06-24
2001-01-02
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S056000, C477S046000
Utility Patent
active
06169950
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for controlling a vehicle drive unit comprising a drive engine and a transmission having a continuously variable gear ratio, in the case of which method command signals and state signals are used to generate control signals for the drive engine and for the transmission, with a required gradient being determined for the transmission gear ratio.
Such a method is known, for example, from DE 196 31 070 A1. In this method, lower and upper limit values are first of all generated from the speed of travel of the vehicle, acceleration limit values are then determined from this and from the current acceleration, and these acceleration limit values are compared with an acceleration desired by the driver, resulting in a required acceleration. The acceleration requirement is then distributed between the variation of the transmission and of the drive engine. However, owing to the capability to vary the engine and transmission continuously, and owing to the mutual relationships, this distribution is a particularly difficult problem; particularly if an auxiliary drive which is independent of vehicle speed—for example the power takeoff shaft of a tractor—also has to be provided.
An attempt to solve this problem is known from U.S. Pat. No. 5,575,737. There, on the one hand, the transmission gear ratio is varied in proportion to a drop in the rotation speed of the engine and, on the other hand, the engine rotation speed is varied with a constant gear ratio in alternate steps, until the initial wheel rotation speed is achieved again. No indication is given as to how it is in this way possible to achieve a control process that is continuous, stable and, above all, optimum for the engine. This document also does not solve the problem of converting the driver's demand, entered for example via a throttle control pedal, such that the vehicle responds to this demand without any time delay or unpredictable reactions.
This problem is also addressed in DE 28 11 574, without being limited to continuously variable transmissions. There, the transmission gear ratio is set to match the required power on the basis of a family of transmission characteristics, in a first control loop, and a control parameter for the drive engine is set, in a second control loop, as a function of the resultant engine rotation speed, in accordance with a family of engine characteristics. In the case of a continuously variable transmission, this allows the engine to be managed in its optimum operating range and with an approximately constant engine rotation speed only within a narrow range around a medium load, and there are no measures to prevent interactions between the transmission control and engine control (“hunting”).
The invention is thus based on the object of proposing a control method of this generic type which satisfies all the requirements; operation of the engine in the best range, direct and appropriate response to the driver's demand, easy adaptability of the transmission to various vehicle and drive engine requirements, easy adaptability of the drive engine to the control process, and a largely constant engine rotation speed for driving a power takeoff shaft. In particular, operation of the engine in the best range is subject to satisfaction of the following requirements:
best overall efficiency,
no reduction in the engine rotation speed below the respective operating point defined as the optimum (for example the point with the maximum injection rate in the case of an RQV controller)
no engine stalling when overloaded
full utilization of the engine power when required
sufficiently fast development of the engine power in response to a dynamic requirement (kick down)
no adverse effects on the driver's demand requirements when the engine is operating on partial load
SUMMARY OF THE INVENTION
According to the invention, the foregoing object is achieved by the following method:
I. A method for controlling a vehicle drive unit comprising a drive engine and a transmission having a continuously variable gear ratio, in the case of which method command signals and state signals are used to generate control signals for the drive engine and for the transmission, with a required gradient being determined for the transmission gear ratio, dislinguished by the sequence of the following steps:
(a) the required vehicle acceleration (ASOLL) and the output drive rotation speed gradient (NABDSOLL) are calculated from a throttle control lever position (XFP, XHG) and the current speed of travel (VFZ) by means of a family of characteristics (#ASOLLF, #ASOLLR),
(b) a required transmission variation (IGDSOLL
1
) is calculated from the required vehicle acceleration (ASOLL) and the current rotation speed (NMOT) of the drive engine,
(c) a limited required transmission variation (IGDSOLL) is determined from the required transmission variation (IGDSOLL
1
) such that the engine rotation speed (NMOT) does not fall below a value which is a function (NMOTMMAX) of the position of the power control element (XEP) of the drive engine,
(d) the continuously variable transmission is varied in accordance with (IGDSOLL);
(e) the actuation parameter (XEPSOLL) for the power control element of the drive engine is obtained directly from the throttle control lever position (XFP, XHG).
Although the solution comprises the interaction of all these steps, the effects of the individual steps can be explained as follows:
With regard to step I(a) above: The required vehicle acceleration and the output drive rotation speed gradient are calculated directly from the throttle control lever position and the current speed of travel by means of a family of characteristics. As a result of the fact that a family of characteristics is first of all used in its simplest form, without taking account of engine-specific optimization actions and limit values, an uncorrupted value for the required vehicle acceleration is obtained in all circumstances. This is a major advantage in the subsequent steps, and, in particular, it improves the response when the throttle control lever is operated. Furthermore, the single family of acceleration characteristics can also be replaced, in operation, by a different, stored family of characteristics.
With regard to step I(b) above: The direct conversion of the required vehicle acceleration into a required transmission variation, without this being split between a transmission variation and an engine variation, avoids reactions, and there is thus no oscillation between transmission control and engine control, with full consideration being given to dynamic requirements while driving. When the throttle control pedal is operated, there is a direct vehicle feel, and the vehicle “responds to the gas”.
With regard to step I(c) above: The required transmission variation is limited such that the engine rotation speed does not fall below a value which is a function of the position of the power control element of the drive engine. The required transmission variation is thus not limited until it is available precisely, and is not carried out as a precautionary measure several steps in advance. In this case, the limits are purely engine-related. This avoids the disadvantages of splitting between transmission variation and engine variation. The limiting of the required transmission variation only prevents any changes in the load on the engine which the engine control module cannot compensate for and which could lead to revving or stalling of the engine. For simplicity, this can be referred to as engine strain control. This comes into effect when the set transmission gear ratio and/or variation rate is too high for the currently available engine power to overcome the resistance to motion that is present. The strain control then limits or reverses the transmission variation, and thus relieves the load on the engine. Furthermore, this can force the transmission gear ratio to be reduced when the throttle is open quickly (kick down), so that the engine rotation speed can follow the contro
Bachman & LaPointe P.C.
Nguyen Tan
Steyr-Daimler-Puch Aktiengesellschaft
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