GB2511601A

GB2511601A - A starting method for a combustion engine of a motor vehicle

Info

Publication number: GB2511601A
Application number: GB201321593A
Authority: GB
Inventors: Sureshkumar Gurusamy; R Sateesh; Suderson Sv
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2013-12-06
Filing date: 2013-12-06
Publication date: 2014-09-10
Also published as: GB201321593D0

Abstract

A starting method for a combustion engine 10 of a motor vehicle12, the combustion engine 10 comprising a crank shaft 14, at least one combustion chamber 16 with at least one gas exchange valve 18, at least one injection device 20 for supplying the combustion chamber 16 with fuel for driving the crankshaft 14 and a starting actuator 22 for accelerating the combustion engine 10 from the standstill to an idle speed. The at least one gas exchange valve 18 is kept permanently open while the combustion engine 10 is accelerated from a standstill to a predetermined engine speed, which is different from the idle speed, by means of the starting actuator 22. Alternatively a release valve 19, which is different from the gas exchange valve 18, is kept open while the combustion engine 10 is accelerated. Preferably the injection device is also deactivated during the acceleration to the predetermined engine speed. The method allows for both energy consumption and engine emissions to be decreased.

Description

A Starting Method for a Combustion Engine of a Motor Vehicle The invention relates to a starting method for a combustion engine of a motor vehicle according to the preamble of claim 1. The invention also relates to a starting method for a combustion engine of a motor vehicle according to the preamble of claim 11 and to a combustion engine of a motor vehicle according to the preamble of claim 13.

In order to meet the current stringent legal requirements to reduce carbon dioxide emissions of motor vehicles, it is common to use so called start-stop functions. Such start-stop functions ensure that a combustion engine of the motor vehicle is only started when needed and thus fuel is only injected and the combustion engine is only operated when the motor vehicle has to be moved or the vehicle battery has a low charge state.

The combustion engine is switched off and thus put into standstill, if the motor vehicle has to be stopped e.g. due to red lights. As soon as the driver wants to move the motor vehicle again (e.g. the driver is allowed to move the motor vehicle when the red lights turn to green lights) by means of the start-stop functions, the combustion engine is turned on again and thus accelerated from standstill to the idle speed by means of a starter motor particularly quickly. Since the delay time between the standstill of the combustion engine and its acceleration to the idle speed, from which it is capable of accelerating the motor vehicle shall be as shod as possible, the capacity of the starter motor and the energy source (e.g. the battery) has to be especially high. Thus, the energy consumption increases with the demand for an especially short delay time between the combustion engine's standstill and its acceleration to its idle speed.

An improved start method can already be taken as known from US 2003/0172893 Al.

The invention there relates to a start method and a starter arrangement for an internal combustion engine of motor vehicles having a crank shaft connected to an electric machine for cranking the engine. Crank shaft position and rotation are detected by a start control apparatus and evaluated for controlling each start operation of the engine. The crank shaft is first brought into a start position by the electric machine during a positioning phase for each start operation. For achieving the shortest possible start times and smallest possible crank torque of the electric machine, it is provided that, in a starting phase, which follows the positioning phase, a first combustion with reduced compression and reduced charge level is triggered in the at least first cylinder going into compression, which combustion supports the crank torque of the electric machine. Since the combustion supports the electric machine (starter motor), the energy consumption of the electric machine is especially low, accordingly. However, the disadvantage is that especially during the starting procedure of the combustion engine the mixture quality of the injected fuel and the fresh air is especially poor and thus emissions, such as unburned hydrocarbons increase while the combustion engine is accelerated from the standstill to the idle speed.

It is the object of the present invention to provide a starting method for a combustion engine of a motor vehicle by means of which both the energy consumption and the emissions are decreased significantly.

According to the invention this object is solved by a starting method for a combustion engine of a motor vehicle having the features of claim 1, a starting method for a combustion engine of a motor vehicle according to claim 11, and a combustion engine of a motor vehicle having the features of claim 13. Advantageous configurations with convenient developments of the invention are specified in the remaining claims.

In order to provide a starting method for a combustion engine of a motor vehicle by means of which both the energy consumption and the emissions are reduced significantly, it is provided according to the invention that the at least one gas exchange valve is kept permanently open while the combustion engine is accelerated from the standstill to a predetermined engine speed, which is different from the idle speed by means of the starting actuator. Since the at least one gas exchange valve is kept permanently open while the combustion engine, which can be designed e.g. as a diesel engine, is accelerated from the standstill to the predetermined engine speed, the breakaway demand torque, which is influenced both by friction losses and engine pumping losses can be significantly decreased. Hence the energy consumption by the starting actuator, which is designed as a starter motor, can be reduced accordingly. In other words, in contrast to the prior art the pumping losses arising from the compression of the fresh air within the combustion chamber can be reduced by permanently keeping the gas exchange valve or the gas exchange valves, respectively open, and thus the fresh air flows from the inlet channel through the opened gas exchange valves to the outlet channel without being compressed by the piston. The predetermined engine speed corresponds to an engine speed between the standstill and the idle speed, wherein when the combustion engine has reached its predetermined engine speed the breakaway demand torque has been already overcome. In other words, by permanently keeping the gas exchange valve open during the acceleration of the combustion engine from the standstill to the predetermined engine speed the energy consumption of the starting actuator can be significantly decreased. Since the pumping losses during this acceleration process are decreased in contrast to the prior art, a starting actuator (a starter motor) with lower capacity and in addition or alternatively an energy storage module (a battery) with lower capacity could be used and thus lower costs arise.

Further advantages, features and details of the invention are apparent from the following description of a preferred embodiment as well as based on the drawing.

This single drawing shows a schematic diagram of a combustion engine with a gas exchange valve, wherein the gas exchange valve is opened by means of an energy venting device.

The figure shows a combustion engine 10, which is used for driving a motor vehicle 12 which is merely shown partially. The combustion engine 10 comprises a crank shaft 14, a combustion chamber 16, a cam shaft 15. gas exchange valves 18, and an injection device 20. In normal operation, e.g. when the combustion engine 10 is operated it is intermittently provided with fresh air and emptied of exhaust gas by means of the gas exchange valves 18. In four-stroke engines, which are used in common as the combustion engine 10 some of the gas exchange valves 18 of the combustion chamber 16 are designed as intake valves and the others are designed as outlet valves. During normal operation, when the combustion engine 10 is operated due to fuel combustion, the gas exchange valves 18 are actuated by the cam shaft 15 which is rotating in dependency on the cam shaft 14. When the injection device 20 provides fuel to the combustion engine and thus fuel is injected into the combustion chamber 16, the fuel can be burned within the combustion chamber 16 and thus a piston 17 can transmit at least parts of the power generated from the combustion to the crank shaft 14, which consequently rotates at a given speed with a given torque. In order to reduce the emissions of carbon dioxide and other emissions and to save fuel, the combustion engine 10 also comprises an electronic control unit (ECU, not shown here) in which a so-called engine start-stop-dataset with start-stop-functions is implemented. By means of this engine start-stop functions, the combustion engine 10 can be turned off as soon as the motor vehicle 12 is in the standstill, e.g. if the motor vehicle 12 has to be stopped at red lights. As soon as the motor vehicle 12 shall be accelerated from the standstill to a certain speed by means of the engine start-stop function the combustion engine 10 is accelerated from the standstill to a predetermined engine speed, which is different from an idle speed of the combustion engine 10. According to the invention, during this acceleration the gas exchange valves 18 are kept permanently open by an energy venting device 30, which is controlled by the ECU. The energy venting device 30 is linked with a starting actuator 22 in a data-transmitting manner, wherein the energy venting device 30 is operated both in dependency on signals from the ECU and on signals which correspond with the rotational speed of the starting actuator 22. The starting actuator 22 engages a fly wheel (not shown) of the combustion engine 10 in order to accelerate the combustion engine 10 from the standstill to the predetermined engine speed. Both the energy venting device 30 and the starting actuator 22 are operated in dependency on a timed crank 28. The timed crank 28 may be a function of the ECU and corresponds to the current engine speed of the combustion engine 10, wherein the ECU controls both the energy venting device 30, the starter actuator 22 and the injection device 20 in dependency on the timed crank 28.

In order to reduce both the emissions of carbon dioxide and to save fuel, the energy venting device 30 actuates the gas exchange valves 18 in such a manner that they are opened independently of the rotation of the camshaft 15. The opening of the gas exchange valves 18, however, depends on the engine speed of the combustion engine 10 and thus on the timed crank 28. If the combustion engine 10 has to be accelerated from the standstill to an idle speed, from which the combustion engine 10 is capable of driving the motor vehicle 12, by means of the energy venting device 30, the gas exchange valves 18 are opened and kept open during the acceleration of the combustion engine 10 from the standstill to the predetermined engine speed. During this phase of the acceleration also the injection device 20 is turned off and thus no fuel is injected into the combustion chamber 16. By opening the gas exchange valves 18, pumping losses of the combustion engine 10 can be significantly reduced during the acceleration from the standstill to the predetermined engine speed, since the fresh air is both sucked in from an inlet channel and then discharged through an outlet channel of the combustion engine 10 due to the movement of the piston 17. In other words, due to the opening of the gas exchange valves 18 by the energy venting device 30, a compression work done by the piston 17 during the acceleration of the combustion engine 10 from the standstill to the predetermined engine speed is reduced significantly, since the fresh air flows into the combustion chamber 16 due to the movement of the piston 17, both during the intake stroke and -in contrast to the prior art -also during the working stroke. Thus, while in conventional combustion engines the fresh air is compressed by the movement of the piston 17 since the gas exchange valves 18 are closed during the working stroke, by means of the energy venting device 30 the gas exchange valves 18 are kept permanently open during the acceleration of the combustion engine 10 from its standstill to the predetermined engine speed.

Due to the fact that the gas exchange valves 18 are kept permanently open the pumping losses of the combustion engine 10 are significantly reduced and thus the breakaway demand torque is much lower than with closed gas exchange valves 18. The predetermined engine speed characterizes the engine speed of the combustion engine 10 in which the breakaway demand torque has been applied to accelerate the combustion engine 10 and thus the crank shaft l4to a certain rotational speed in which the energy venting device 30 can be deactivated and the gas exchange valve are actuated by the cam shaft 15 in an conventional manner. In other words, when the combustion engine 10 has reached the predetermined engine speed, the gas exchange valves 18 are operated normally and the injection device 20 starts to inject fuel into the combustion chamber 16.

The motor vehicle 12 also comprises an ignition key 26 and an energy storage module 24, which is designed as a battery, wherein by turning the ignition key 26 from an off' position to an on' position, the starting actuator 22 can be supplied with electric energy from the energy storage module 24.

In summary, this example according to the invention shows a starting method, wherein the gas exchange valves 18 are kept permanently open due to the energy venting device 30, while the combustion engine 10 is accelerated from the standstill to the predetermined engine speed, which is different from the idle speed, by means of the starting actuator 22.

The gas exchange valves 18 are also controlled by the energy venting device 30, which means, that the gas exchange valves 18 can both be opened and closed by the energy venting device 30 on demand. During the acceleration of the combustion engine 10 from the standstill to the predetermined engine speed the injection device 20 is deactivated by the energy venting device 30. The injection device 20 is activated again by the energy venting device 30 during the acceleration of the combustion engine 10 from the predetermined engine speed to the idle speed. The predetermined engine speed is given by the breakaway torque of the crank shaft 14 and the pumping losses of the combustion chamber 16. The predetermined engine speed is also given by at least one temperature value of the combustion engine 10. In other words, as this temperature value, for example the value of the motor oil temperature of the combustion engine 10, can be taken into account to decide whether the combustion engine 10 has already been warmed up or if it is still cold. If the combustion engine 10 has already been warmed up and thus is restarted from this warm condition, the friction losses are smaller since warm motor oil has a lower viscosity than cold motor oil and thus the breakaway demand torque is lower if the motor oil is warm than it is if the motor oil is cold. The predetermined engine speed of the combustion engine 10 is lower if the motor oil is warm, since the reduced friction losses allow it to deactivate the energy venting device 30 earlier. It is clear, that also aging effects, as a further example for motor oil properties that can be examined by means of viscometry analysises, are influencing the breakaway demand torque. In other words, the predetermined engine speed is given by at least one of the viscometry properties of the motor oil of the combustion engine 10.

In other words the predetermined engine speed is also given by the viscometry of the engine oil. The viscometry of engine oil changes based on temperature and based on operating conditions, such as engine load condition, or vehicle mileage accumulation.

Thus the engine breakaway demand torque internally alters. It is clear, that in addition to the gas exchange valves 18, at least one release valve 19 could be arranged at the combustion chamber 16 of the combustion engine 10. Instead of permanently keeping the gas exchange valves 18 open until the predetermined engine speed has been reached, the gas exchange valves 18 could be operated normal and the at least one release valve 19 could be kept open during the acceleration of the combustion engine 10. It is also clear, that exemplarily the start-stop-functions are enabled or disabled by the ECU in dependency on the engine breakaway demand torque and the capacity of the energy storage module 24 (state of charge of the battery). If the capacity of the energy storage module 24 is too low to restart the combustion engine 10, the start-stop-functions are disabled and the combustion engine 10 is not turned off by the ECU when the motor vehicle is at standstill. The combustion engine 10 keeps on running instead to reload the battery.

List of reference signs combustion engine 12 motorvehicle 14 crank shaft camshaft 16 combustion chamber 17 piston 18 gas exchange valve 19 release valve injection device 22 starting actuator 24 energy storage module 26 ignition key 28 timed crank energy venting device

Claims

SClaims A starting method for a combustion engine (10) of a motor vehicle (12), the combustion engine (10) comprising a crank shaft (14), at least one combustion chamber (16) with at least one gas exchange valve (18), at least one injection device (20) for supplying the at least one combustion chamber (16) with fuel for driving the crank shaft (14), and a starting actuator (22) for accelerating the combustion engine (10) from the standstill to an idle speed, characterized in that, the at least one gas exchange valve (18) is kept permanently open while the combustion engine (10) is accelerated from the standstill to a predetermined engine speed, which is different from the idle speed, by means of the starting actuator (22).
2. The starting method according to claim 1, characterized in that, the injection device (20) is deactivated during the acceleration of the combustion engine (10) from the standstill to the predetermined engine speed.
3. The starting method according to claim 1 or 2, characterized in that, the injection device (20) is activated during the acceleration of the combustion engine (10) from the predetermined engine speed to the idle speed.
4. The starting method according to any one of claims 1 to 3, characterized in that, the predetermined engine speed is given by a breakaway torque of at least the crank shaft (14) and the at least one combustion chamber (16).
5. The starting method according to any one of claims 1 to 4, characterized in that, the predetermined engine speed is given by at least one temperature value of the combustion engine (10).
6. The starting method according to any one of claims 1 to 5, characterized in that, the predetermined engine speed is given by a capacity of the starting actuator (22).
7. The starting method according to any one of claims 1 to 6, characterized in that, the predetermined engine speed is given by at least one of the viscometry properties of the motor oil of the combustion engine (10).
8. The starting method according to any one of claims 1 to 7, characterized in that, the combustion engine (10) comprises an energy venting device (30) and an electronic control unit, which controls the energy venting device (30), the fuel injection device (20) and the starting actuator (22).
9. The starting method according to claim 8, characterized in that, the at least one gas exchange valve (18) is controlled by the energy venting device (30).
10. The starting method according to claim 8, characterized in that, the electronic control unit comprises a start-stop-dataset, by means of which the combustion engine (10) is stopped and restarted in dependency on the breakaway torque and/or the capacity of an energy storage module (24).
11. A starting method for a combustion engine (10) of a motor vehicle (12), the combustion engine (10) comprising a crank shaft (14), at least one combustion chamber (16) with at least one gas exchange valve (18), at least one injection device (20) for supplying the at least one combustion chamber (16) with fuel for driving the crank shaft (14), and a starting actuator (22) for accelerating the combustion engine (10) from the standstill to an idle speed, characterized in that, the combustion engine (10) comprises at least one release valve (19), which is different from the at least one gas exchange valve (18) and which is kept permanently open while the combustion engine (10) is accelerated from the standstill to a predetermined engine speed, which is different from the idle speed, by means of the starting actuator (22).
12. The starting method according to claim 11, characterized in that, the at least one release valve (19) is controlled by an energy venting device (30).
13. A combustion engine (10) of a motor vehicle (12), the combustion engine (10) having -a crank shaft (14), -at least one combustion chamber (16) with at least one gas exchange valve (18), -at least one injection device (20) for supplying the at least one combustion chamber (16) with fuel for driving the crank shaft (14), and -a starting actuator (22) for accelerating the combustion engine (10) from the standstill to an idle speed, characterized in that, the at least one gas exchange valve (18) and/or an additional release valve (19), which is different from the at least one gas exchange valve (18) is kept permanently open while the combustion engine (10) is accelerated from the standstill to a predetermined engine speed, which is different from the idle speed, by means of the starting actuator (22).