Method for Reducing the Fuel Consumption of a Motor Vehicle

Abstract

In a method for reducing the fuel consumption of a motor vehicle, a driver's request for a uniform vehicle speed is determined and once this request for a uniform vehicle speed has been identified, the modifications to the vehicle speed, which are not initiated by the driver, are at least partly adjusted by control in order to obtain the lowest possible fuel consumption, for example of gasoline or diesel, for the driving engine of the vehicle.

Description

The invention will now be explained in detail by way of an embodiment.

A vehicle includes a vehicle regulation and control unit which can automatically influence the vehicle deceleration by ‘throttling down’ and/or ‘brake pressure buildup’ and the vehicle acceleration by ‘opening the throttle’ and/or ‘brake pressure reduction’.

Based on the knowledge that the driver wishes to cover the major part of the duration of travel (especially in long-distance driving) at a constant speed, the driver is supported in this aim, and unnecessary acceleration and deceleration operations are avoided.

Defined, frequently varying road resistance situations can counteract the driver's desire regarding constant travel in the course of driving.

When the driver strives for a constant speed and the road resistance changes slowly (due to an ascent or descent or wind, etc.), he/she will notice this fact only when a significant difference in speed (5 km/h up to 10 km/h) compared to the desired speed has occurred. The reason for this can be seen in the frequency of speed control (monitoring the speedometer), on the one hand, and in the visual resolving capacity of an analog speedometer, on the other hand. Likewise driving noises change only insignificantly with the discrepancies referred to hereinabove.

When the driver notices the deviation, he will try and readjust the previously adjusted desired speed, i.e., he accelerates the vehicle. As the vehicle speed has departed relatively far away from the desired speed, very much energy must be consumed then in order to readjust the desired speed.

Once the vehicle speed rises, e.g. during downhill driving, energy is removed due to an optionally initiated braking operation, which has initially been supplied to the system.

In addition, a transient effect around the desired speed can make the operation still more inefficient in both situations.

Thus, the changes of the road resistance have a large number of causes which can be sensed intuitively by the driver only in part.

The most obvious road resistance change is driving on an inclined roadway. In this case, too, an insignificant roadway inclination is mostly not noticed by the driver. According to the invention, this road resistance change is adjusted by control with the method of the invention.

The second important road resistance change, which cannot be sensed directly by the driver, is the change of the air resistance which can occur due to slipstreaming, or due to variable approach angles, and/or variable speeds of the atmospheric wind. This road resistance change is adjusted by control according to the method of the invention.

Road resistance is likewise increased due to a cornering maneuver and the related slip caused by king pin inclination. This increase is considered as insignificant. Likewise this road resistance change is adjusted by control according to the method of the invention.

The driver's desire of driving at a constant speed is realized according to the invention by monitoring the accelerator pedal position (pedal position).

When the driver constantly adjusts an accelerator pedal position for 1 to 8 seconds (sec), and deviations within a narrow band are not considered, this torque corresponding to the accelerator pedal position is adjusted by the engine's control unit. Now it is waited for until the vehicle speed has adjusted in conformity with the torque and will change no more.

The subsequently detected speed is stored. It is assumed according to the invention that this detected speed represents the desired speed.

If this is not the case, the driver will demand more torque by applying the accelerator pedal. The torque will no longer be constant in this case.

The current vehicle speed is constantly compared with the stored speed (desired speed). Once a deviation of 0.2 km/h to 2 km/h is detected, the engine torque will be modified in order to minimize this deviation, this implies to ‘adjust it by control’ in the sense of the invention.

The monitoring operation does not allow any deviations which become conspicuous to the driver. Therefore, the likelihood of an inefficient intervention by the driver is considerably reduced.

Accelerator pedal movements, i.e. vibrations of the accelerator pedal in excess of 1 hertz, that means movements more frequent than one time per second, are not taken into consideration with regard to changing the desired speed. These accelerator pedal movements are considered as a malfunction.

As the entire method is favorably designed in a rather passive fashion, the relatively short transitional times (delays) which may occur are not recognized by the driver.

Slow accelerator pedal movements are realized immediately because it is very likely that they do not imply a malfunction but represent a new request of the driver.

Likewise rapid accelerator pedal movements in one direction and with definite amplitude, which remain in one position in the end, will be realized immediately and regarded as a driver request after a short monitoring time.

The change of torque which is allowed due to the adjustment by control of the desired speed does not comprise the entire torque made available by the engine. Rather, only changes of ±10% up to ±40% of the initial torque (torque which prevailed when the desired speed was stored) are admitted. This renders it always possible to the driver to accelerate actively or generate a stall torque.

Further, the invention provides a limitation of the speed range in which the function according to the invention is performed. The main economy potential lies with higher speeds (higher than 60 km/h up to 70 km/h). Constant rides are more frequent in these speed ranges than city rides. Therefore, the method is preferably implemented at vehicle speeds exceeding roughly 60 km/h up to 70 km/h.

Claims

1-10. (canceled)

11. A method of reducing fuel consumption in a motor vehicle, the method comprising: determining a request from a driver for a uniform vehicle speed; andafter identifying the request for uniform vehicle speed, at least partly controlling modifications to the vehicle speed, which are not initiated by the driver, in order to obtain a lowest possible fuel consumption for the driving engine of the vehicle.

12. A method according to claim 11, wherein a change in a resistance of travel is determined and the travel resistance change is at least partly adjusted by control.

13. A method according to claim 12, wherein in determining the travel resistance change, any change of an inclination of travel in longitudinal direction of the vehicle, such as a road ascent or a road descent, or any change of weather conditions, in particular variable speeds of an atmospheric wind, or driving conditions such as variable angles of approach of the vehicle in the slipstream of another vehicle or object, or a cornering maneuver are taken into consideration.

14. A method according to claim 11, wherein the request from the driver for uniform vehicle speed is detected on the basis of the accelerator pedal movement.

15. A method according to claim 14, wherein when a position of the accelerator pedal is constantly adjusted or maintained by the driver for a defined, predetermined time, a vehicle speed which results from this position of the accelerator pedal is identified as a desired speed reflecting the request for uniform vehicle speed.

16. A method according to claim 15, wherein a period in a range of 1 second to 8 sec is predetermined.

17. A method according to claim 15, wherein the desired speed reflecting the request for uniform speed is stored.

18. A method according to claim 17, the current vehicle speed is compared with the desired speed representative of the driver's request and, in the event of the current vehicle speed differing from the desired speed, the vehicle is automatically accelerated or deceleration or slowed down, respectively, in order to reduce the deviation.

19. A method according to claim 18, wherein an automatic acceleration or automatic slowing down of the vehicle is performed in such a fashion that minimum possible fuel consumption is needed for the driving engine of the vehicle.

20. A method according to claim 18, wherein the vehicle is automatically accelerated or slowed down when the deviation of the current vehicle speed from the desired speed exceeds 0.2 km/h up to 2 km/h.