The present invention relates to a method for limiting unnecessary vehicle acceleration, in accordance with the preamble of the accompanying independent claim. BACKGROUND OF THE INVENTION:

In vehicles with transmissions (manual or automatic in manual mode) where the driver is allowed to shift gear, the gear shifting can sometimes be initiated late during an acceleration. This means that the engine reaches unnecessary high revolutions per minute (rpm:s) where engine efficiency is relatively low.

Also when a vehicle is lightly loaded and maximum propulsion power is demanded by the driver vehicle acceleration can sometimes reach unnecessary high values when the engine is speeded to higher rpm:s where efficiency is relatively low.

US 6,944,532 discloses an example of prior art, where vehicle speed is limited for one engaged gear in order to force the driver to initiate an upshift.

The present invention provides an alternative solution in order to avoid unnecessary high engine rpm:s and unnecessary high vehicle acceleration.

DESCRIPTION OF THE INVENTION

A vehicle is provided with an engine drivingly

connected to driving wheels via a transmission, where said transmission is arranged for engagement of

different gear ratios between said engine and said driving wheels. Gear shifting in said transmission can be initiated manually by the driver according to known art as in a manual transmission or an automated

transmission (Automatic Transmission (AT) or Automatic Mechanical Transmission (AMT) or Dual Clutch

Transmission (DCT)) in manual mode.

According to the invention a control unit is arranged in the vehicle programmed to register at least

prevailing vehicle or engine acceleration together with vehicle speed or engine rotational speed. Said control unit is also arranged to provide for an output control signal in order to control and limit the engine or vehicle acceleration in certain circumstances depending on:

- the vehicle or engine acceleration, and

- engine rotational speed or vehicle speed.

The limitation function is made by using the values of at least the engine or vehicle acceleration and engine or vehicle speed as input in a control algorithm.

The algorithm may be a preprogrammed table, where information about maximum allowable vehicle or engine acceleration values for at least different combinations of vehicle or engine acceleration together with vehicle or engine rotational speed are stored which corresponds to a certain limiting control output used to control vehicle or engine acceleration in order not to exceed said determined maximum allowable vehicle or engine acceleration. The algorithm may also be in the form of an equation in which the limiting control output is calculated based on at least vehicle or engine

acceleration and vehicle or engine rotational speed. The vehicle or engine acceleration may be performed by controlling the vehicle engine arranged for propulsion of the vehicle, e.g. by controlling the injection of fuel to the engine.

The control algorithm for deciding maximum vehicle or engine acceleration may also be made in such a way that it uses the prevailing gear selected as an input in the control algorithm such that the maximum allowable vehicle or engine acceleration also is depending on the selected gear. This will provide the possibility to make specific control functions for each possible gear shift mode in order to further optimize vehicle

behavior and fuel savings.

If the selected gear is to be used as an input to the control algorithm, this input may be used such that h^ control algorithm will limit or restrict said vehicle or engine acceleration less when the vehicle is using a low speed gear than when the vehicle is using a high speed gear. A reason for using this strategy is that it is believed that it is possible to improve fuel

efficiency without unduly restricting or limiting necessary or desired performance (acceleration) of the vehicle by limiting the acceleration as an indication of a desired gear shift when driving on a highway at relatively high speeds. This feature is thus to be considered as an aid in changing gears in a fuel saving manner for high speed gears. The feature of limiting the maximum possible acceleration also for low speed gears will of course also work. However, it is generally believed that there is a higher need or desire to maintain high or maximum possible

acceleration when using the low speed gears than high speed gears at high rpm of the engine, e.g. at start up, when travelling in a steep uphill or bad road conditions. It is thus considered that the maximum allowable acceleration should be higher when driving and using low-speed gears.

As described above, the algorithm may be in the form of one or several preprogrammed tables where maximum allowable vehicle or engine acceleration values for different combinations of vehicle or engine

acceleration together with vehicle or engine rotational speed are stored. Based on said registered values and corresponding values in said table is a maximum

allowable vehicle or engine acceleration determined. There may be further inputs used in the one or several tables or there may be a multitude of tables depending on other parameters e.g. providing a specific: table for each possible gear shift.

The limiting function for the acceleration is generally intended to work for values in the upper region of the engine rotational speed, e.g. from 50 % of the maximum possible engine rotational speed and upwards. In general, the control algorithm is working within the interval of 55 to 90 percent of the maximum possible engine rotational speed. Below these values there is generally no desire to limit the acceleration since the engine is working in an appropriate mode. On the other hand, at very high rpm such as above 90 percent of the maximum allowable rpm, the acceleration capacity is normally strongly reduced already by physical

limitations in the engine and further restrictions may not be necessary. Hence, the limiting function for deciding maximum vehicle or engine acceleration should limit the acceleration for at least one selected gear shift ratio for at least one value of the engine rotational speed in the interval of 55 to 90 percent of the maximum possible engine rotational speed. In a preferred embodiment, the acceleration limiting

function is constructed such that said maximum

allowable acceleration is higher when the engine is operated at 65 % of the maximum available engine rotational speed than when the engine is operated at 80 % of the maximum available engine rotational speed.

The algorithm may work such that it induces no or a rather low restriction of the acceleration when the rpm are in the lower region of the limiting, function, e.g. when the engine is operated between 55-65 % of the maximum available engine rotational speed while there is a- rather heavy restriction of the possible

acceleration than when the engine is operated at 70 - 80 % of the maximum available engine rotational speed. Hence, according to one embodiment of the invention, the limiting function is constructed such that there is a rather small limitation of the acceleration in a first interval represented by the part of the limiting function from about 50 - 65 % of the maximum possible rpm for the engine while the acceleration is more restricted in an interval from about 65 - 80 % or more. These values are not to be considered as an exact value which are valid for all different engines as suitable intervals but is rather to be considered as indications of how the limiting function may be designed. In this embodiment it is desired that the driver is first slightly alerted by the limiting function when reaching a first interval and getting alerted that it is

suitable to change gear. If the driver continue to drive using the same gear and still accelerates, the engine will reach a second interval of the engine rotational speed, where for example the fuel economy of driving is determined to be considerably worse, the limiting function for the acceleration will limit the acceleration such that the driver will feel an urge to change gear in order to further accelerate the vehicle.

In the above, the limitation has been given as an absolute value for the maximum allowed acceleration. Another way of performing the limitation of the

acceleration may be to set the limiting feature as a value of the limitation with respect to the maximum possible acceleration for a certain value of the relevant parameters of speed and acceleration, i.e.

instead of using the algorithm for deciding or

calculating a maximum allowable acceleration it may calculate how much the acceleration shall be restricted as compared to the maximum possible acceleration, either in absolute numbers or in percentage of the maximum possible acceleration. Hence, the control algorithm may thus for example be designed to limit or restrict said vehicle or engine acceleration less when the engine is operated between 55-65 % of the maximum available engine rotational speed than when the engine is operated at 70 - 80 % of the maximum available engine rotational speed.

The algorithm for calculating or deciding the maximum allowable acceleration values may be se selected such that there will always be permitted a certain

acceleration, i.e. the allowed acceleration will always be larger than zero. However, it could also be possible to restrict the acceleration to zero if desired for certain values, e.g at very high rpm:s. In general, the restriction at values close to maximum possible rpm (>95 % of maximum possible rpm) is not of particularly interest for the present invention since a purpose of the present invention is to avoid driving at these high rpm:s and the idea of this limiting function is that there shall be a gear shift long before reaching these high rpm:s.

The method may be used for a wide range of vehicles and engines and may for example be used for lorries which are propelled by a diesel engine having a maximum possible rpm of 2 000 - 3 000. As an example, a lorry provided with a diesel engine having a maximum possible rpm of around 2 300 (2 200 - 2 400) is suitable for the present control algorithm. For such a vehicle the control algorithm should preferably restrict the acceleration for at least one selected gear shift ratio for at least one value of the engine rotational speed in the interval of 1300 to 1900 revolutions per minute (rpm) , preferably within the interval of 1500 to 1800 rpm. The limiting function could be made such that there is a rather moderate restriction in the lower region of the suggested interval, i.e. from 1300 to 1550 while there is a rather limited possibility to accelerate in the upper region of the interval, e.g. 1700 to 1900 rpm.

The limiting function may be designed such that the higher the engine rotational speed is the lower the maximum allowable vehicle acceleration value is, at least for a certain interval, e.g. between 60 and 80 % of the maximum allowable engine rotational speed.

However, it could also be possible to allow the same vehicle acceleration limit for certain values of the rpm. It may also be possible to have a rather restricted acceleration possibility for a certain interval while allowing a less restricted acceleration when reaching a higher rpm interval. This could for instance be the case if a change of gear did not occur in a first rpm-range and the driver still indicates a desired acceleration at the same gear. It may in this case be advisable to allow a higher acceleration in this second interval such that there may be an

efficient two-step gear change available sooner and thus avoiding the need of two gear shifts.

The above described method may of course be modified in many ways while remaining within the scope of the invention of providing a control method for limiting the acceleration of the engine or the vehicle at certain driving conditions in order to induce a gear shift so as to improve certain characteristics related to the driving of the vehicle, e.g. fuel consumption. Hence, by restricting the acceleration possibility at certain desired velocities and/or rpm:s, there is a possibility to alert the driver that it is suitable to change gear and the more restricted the possibility to accelerate is, the more likely is it that the driver will change gears. The system may thus be used to indicate for the driver by different degrees of

limitations how desired it is to change gear and the limitation may be based on different criteria whereof fuel economy has been exemplified above. However, other relevant features for using this control could be possible, e.g. to provide better traction when driving on a slippery road.

The invention further relates to a control system for controlling and limiting vehicle acceleration of a vehicle. The control system comprises a control unit provided with:

- input ports for receiving inputs of at least vehicle or engine acceleration together with vehicle speed or engine rotational speed and

- at least one output port for sending a control signal or control value.

The control unit is programmed to use at least the above mentioned input values in a control algorithm in order to decide a maximum allowable vehicle or engine acceleration. The control unit is further adapted to send a control signal or control value via said output port to be used for controlling the vehicle or engine acceleration.

BRIEF DESRIPTION OF THE DRAWINGS

Figure 1 discloses a diagram exemplifying the

relationship between the vehicle acceleration and engine rotational speed for limiting the acceleration according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates with a diagram how the maximum allowable acceleration values are selected. The y-axis discloses vehicle acceleration and the x-axis discloses engine rotational speed. Values within area 1 represent engine rotational speed values for which the vehicle acceleration values have not been limited, that is, normal acceleration is allowed. According to the invention an area 2, corresponding to the table values, represent different engine rotational speed values for which different maximum allowable acceleration values have been selected. In the shown example said maximum allowable acceleration values within said area 2 are selected and preprogrammed as to always be larger than zero acceleration. Thus, within area 2 a number of maximum allowable acceleration values are provided for different engine rpm:s. Further, the higher the engine rotational speed is the lower the maximum allowable vehicle acceleration value can be. Thus, in the shown example in the upper right corner 3 of the area 2 the lowest maximum allowable acceleration values are found.

In another embodiment engine rotational speed

acceleration can be used instead of vehicle

acceleration. Thus, engine rotational speed and

corresponding maximum allowable engine rotational speed acceleration values are stored in a corresponding table. It could of course also be possible to replace engine speed for vehicle speed and get essentially the same curve.

Based on said registered vehicle acceleration, said registered engine rotational speed and information from said preprogrammed table, said control unit is

programmed to determine a maximum allowable vehicle acceleration value (maximum allowable engine rotational speed acceleration value) of said prevailing registered engine rotational speed. When said maximum allowable vehicle acceleration value has been determined said control unit is programmed to control vehicle

acceleration in order not to exceed said determined maximum allowable vehicle acceleration value. Thus, if the driver continues with the same gear without

upshifting the vehicle will continue to accelerate but with said lower maximum allowable vehicle acceleration value. If the engine rotational speed in this situation increases further the maximum allowable vehicle

acceleration value will be lowered further. When the driver feels the lowered vehicle acceleration and finds it unsatisfactory he will react by initiating a gear upshift and the engine rotational speed can decrease to within said area 1.

Said controlling of vehicle acceleration according to said maximum allowable vehicle acceleration value can be performed by controlling the amount of injected fuel in said engine arranged for propulsion of said vehicle. The amount of injected fuel can be lowered until registered vehicle acceleration is below said maximum allowable vehicle acceleration value.

Thus, under all circumstances where the acceleration limiter algorithm according to the present invention is active at least a small acceleration of said engine rotational speed is always allowed.

In order not to limit acceleration too much in a further embodiment there is also included a minimum allowable engine torque output curve.

The advantage of the invention is its simplicity and that it dynamically limits the acceleration depending on prevailing vehicle condition. The driver can choose to react to the decreased vehicle acceleration and select to initiate an gear upshift. The driver is also free to select to continue with the present gear and still with a certain vehicle acceleration that is limited (decreased) to a maximum allowable vehicle acceleration value which suites the prevailing vehicle condition.