Method for rolling operation of a motor vehicle with an internal combustion engine

Description

[0001] The invention relates to a method for coasting a motor vehicle with an internal combustion engine, in particular a commercial vehicle. The invention particularly relates to a method for coasting in which the internal combustion engine is towed in unfired operation with the drive train closed.

[0002] To save fuel, motor vehicles are operated in a so-called rolling or sailing mode on suitable routes, especially downhill gradients.

[0003] The coasting mode of a motor vehicle or hybrid vehicle, known to those skilled in the art, involves utilizing the vehicle's kinetic energy during coasting phases to maintain the highest possible coasting speed and thus achieve the greatest possible coasting distance. According to document DE 10 2008 029 453 A1, for example, the vehicle's engine is decoupled from the rest of the drivetrain. This occurs by disengaging the clutch or by shifting the transmission into neutral in order to reduce the braking effect of the engine's drag torque. The traction phase following a coasting phase can begin at a later time and / or occur with lower engine power due to the maintained coasting speed or achieved coasting distance. This creates potential for fuel savings.

[0004] The disadvantage of this mode of operation is that the engine runs at idle, which reduces the potential for reducing fuel consumption.

[0005] A complete shutdown of the combustion engine during coasting would be the ideal solution for fuel consumption. Therefore, it is also known in the state of the art to further reduce fuel consumption during coasting by not only decoupling the engine from the drivetrain and running it at idle, instead of towing at high engine speed, but also by completely shutting it down and restarting it during a subsequent towing phase.

[0006] In this case, however, the auxiliary consumers driven by the engine, such as the generator or the air conditioning compressor, are no longer supplied with power. In practical implementation, this variant therefore has disadvantages, particularly since important auxiliary units for the operation of commercial vehicles (e.g., the air compressor or the power steering pump) must continue to be reliably powered even when coasting.

[0007] A known alternative for saving fuel during vehicle coasting is coasting, in which the engine's fuel supply is interrupted during the coasting phase. The engine remains coupled to the drivetrain and is towed without fuel. This operation is also referred to as coasting with overrun cutoff or engine braking. Part of the kinetic energy is used to provide the required drive power for the auxiliary units.

[0008] This mode of operation offers potential fuel savings by avoiding engine idling and ensures the supply of power to the auxiliary units. The disadvantage of this mode of operation is the resulting drag power loss, e.g., due to friction losses during unfired engine operation. This drag power slows the vehicle and thus reduces its kinetic energy.

[0009] German Patent Application DE 36 10 131 A1 discloses an internal combustion engine with a turbine of an exhaust gas turbocharger that acts as a throttle point in an exhaust line, depending on the operating mode. In this case, a bypass is controlled by a valve in the open position during overrun of the diesel engine to reduce engine drag torque. The disadvantage of this is that this only works for vehicles with an exhaust gas turbocharger, and such a reduction in engine drag torque is comparatively slow, since the exhaust gas turbocharger responds with a corresponding delay.

[0010] Another internal combustion engine is known from patent application DE 10 2012 001579 A1, in which the rolling distance traveled by the vehicle without propulsion is extended in a rolling mode. For this purpose, the downhill forces during downhill driving are advantageously utilized to reduce fuel consumption.

[0011] It is therefore an object of the invention to provide an improved coasting mode that avoids the disadvantages of conventional techniques. The object of the invention is, in particular, to provide a coasting mode with improved fuel efficiency that simultaneously enables safe operation of the auxiliary units. These objects are achieved by an operating method for a motor vehicle with an internal combustion engine according to the features of the main claim. Advantageous embodiments and applications of the invention are the subject of the dependent claims and are explained in more detail in the following description, with partial reference to the figures.

[0012] According to the invention, a method for coasting a motor vehicle with an internal combustion engine is proposed, in particular such a method for a commercial vehicle. During coasting, the internal combustion engine is towed in unfired operation and with the drive train engaged, i.e., with the power transmission not disconnected. The fuel supply is thus interrupted, and the engine is towed by the vehicle, i.e., kept rotating. Such coasting is also referred to as overrun.

[0013] According to general aspects of the invention, coasting occurs with reduced engine drag torque or reduced engine drag power. For this purpose, the motor vehicle comprises means for reducing engine drag torque and thus engine drag power of the internal combustion engine, by means of which the engine drag power is reduced during coasting, so that the internal combustion engine is towed with the reduced engine drag power during coasting.

[0014] A particular advantage of the invention is that, compared to conventional overrun mode, friction losses during towing are reduced, and consequently, the resulting vehicle deceleration is also reduced. This allows the towing phase following a rolling phase to commence at a later time and / or to occur with lower engine power due to the higher rolling speed or greater rolling distance achieved. This creates potential for fuel savings compared to conventional overrun mode. At the same time, the supply and drive of the auxiliary units can be ensured.

[0015] Preferably, the means for reducing engine drag power are designed so that all auxiliary units can be adequately supplied by the towed engine and the remaining power loss of the engine is as small as possible.

[0016] The invention is not limited to a specific selection with regard to the choice of means for reducing engine drag and / or is not limited to a specific design with regard to the structural configuration of these means.

[0017] Advantageously, the means for reducing engine drag can be designed to modify a valve train during coasting operation such that the compression work and / or gas exchange work required by the internal combustion engine during non-fired operation is reduced, so that the rotation of the internal combustion engine occurs against less resistance and can therefore be achieved with less mechanical energy. For example, a known decompression endurance brake can be used to selectively decompress the cylinder during coasting operation.

[0018] According to a particularly advantageous variant, the means for reducing engine drag can comprise a locking device that can be adjusted to prevent the closing of one or more exhaust valves of the cylinders of the internal combustion engine. This allows for targeted decompression of the cylinders and prevents drag loss due to the compression work required.

[0019] One possible implementation according to the invention provides that the locking device is adjustable in such a way that it limits the movement of a rocker arm and / or a rocker arm shaft, which are operatively connected to a cylinder exhaust valve for opening and closing the same, in such a way that the exhaust valve remains in an open state. Such an arrangement can be provided for all exhaust valves. For example, the locking device can be provided as a locking pin, which can be positioned in rolling operation such that it can be brought into engagement with a detent on the rocker arm shaft and thus blocks further rotation of the rocker arm shaft into a rotational position that brings the cylinder exhaust valve into a closed position. This variant offers the advantage that conventional internal combustion engines can be operated with a minor structural modification by attaching the adjustable locking device, e.g.of the locking pin, must be adjusted to enable rolling operation with reduced engine drag torque.

[0020] According to a further variant, the means for reducing engine drag can deactivate the cylinder valve train, allowing cylinder operation with closed valves without gas exchange. The cylinders thus act as gas springs, returning a large portion of the applied compression work after reaching top dead center, so that the compression work required is reduced compared to a normal valve train.

[0021] According to a further embodiment, the method for rolling operation can comprise the following steps: specifying an upper and lower threshold value for vehicle acceleration in rolling operation; and predicting an acceleration profile of the vehicle for rolling operation as a function of topographical data for a predetermined, upcoming section of the route; wherein rolling operation is activated upon reaching or beginning a downhill section for which it was predicted that the predicted acceleration profile lies within the upper and lower threshold values ​​for the vehicle acceleration for longer than a minimum duration or minimum distance.

[0022] This allows a suitable driving situation, such as a long downhill stretch with a suitable gradient, to be identified, which is suitable for coasting, and to initiate coasting upon reaching this downhill stretch. The upper and threshold values ​​for vehicle acceleration thus indicate a suitable range in which vehicle acceleration lies within a range favorable for coasting.

[0023] Furthermore, the previously activated rolling mode can be deactivated if the current vehicle speed, vehicle acceleration or gradient at a current position on a route exceeds specified threshold values ​​for these variables.

[0024] For example, the vehicle's acceleration curve for coasting with reduced towing power can be predicted using a vehicle model that specifies the vehicle's acceleration behavior in non-lit operation as a function of the route's topography and current speed. The vehicle model can be stored in the cruise control system in the form of a characteristic curve.

[0025] The vehicle model can, for example, take into account a load condition, a total weight, an axle load, a rolling friction resistance, a flow resistance of the vehicle, and / or a loss of drag caused by drive unit components. Based on these parameters, the vehicle's acceleration behavior in non-powered operation, for example, in rolling or overrun mode, can be calculated.

[0026] A further aspect of the invention relates to a device for controlling the operation of a motor vehicle with an internal combustion engine, in particular a commercial vehicle, wherein the device is designed to carry out the method as described above.

[0027] A further aspect of the invention relates to a commercial vehicle with such a device.

[0028] Further details and advantages of the invention are described below with reference to the accompanying drawings. Figure 1 shows a flowchart illustrating a method for rolling operation according to an embodiment; Figures 2A, 3A, 4A show acceleration states of a vehicle in rolling operation along a downhill stretch; and Figures 2B, 3B, 4B show positions of a vehicle in rolling operation along a downhill stretch.

[0029] Figure 1illustrates an example of a flowchart of a method for rolling operation according to an embodiment.

[0030] Here the Figure 2B the topography of a route of vehicle 4 as a relative contour line. Figure 2B The section shown shows a section with a longer downhill stretch. Figure 2B the vehicle is at the beginning of the downhill section.

[0031] During normal, illuminated driving operation, according to step S1, the upcoming section of the road is continuously monitored by a vehicle control device in order to determine a suitable driving situation in which the rolling mode can be activated. This can be done, for example, in a conventional manner by predicting the occurring vehicle deceleration and taking into account the target speed of the vehicle, for example a maximum speed specified for commercial vehicles. Exceeding or falling below the target speed is permitted within certain limits to utilize momentum peaks, so that rolling can occur within certain acceleration limits. The advance calculation of the vehicle's acceleration curve for rolling mode can be carried out depending on topographical data for a specified upcoming section 5 of the route.

[0032] The vehicle's acceleration curve for rolling operation with reduced towing power is predicted using a vehicle model that specifies the vehicle's acceleration behavior in non-lit operation as a function of the route topography and the current speed. The vehicle model can take into account the vehicle's load condition, total weight, axle load, rolling friction resistance, flow resistance of the vehicle, and / or drag loss of the drive unit caused by drive unit components.

[0033] Such vehicle models and the calculation of vehicle acceleration during non-lit operation on downhill sections are known from the state of the art and need not be described in detail here. Such approaches are known, for example, from DE 10 2006 001 818 A1 or DE 10 2010 005 045 A1.

[0034] This document merely states that such a vehicle model can be stored in the cruise control system in the form of a calculation function and / or in the form of a characteristic curve 3, which describes the acceleration behavior of the vehicle depending on the gradient / elevation information of the route.

[0035] The vehicle model can then be used to predict how an upcoming gradient will affect the vehicle's acceleration curve for a given target value setting of the cruise control or brake control function.

[0036] The topography of a route can be provided as topography data by a navigation device. The navigation device can also provide the current vehicle position and direction of travel and assign them to the stored topography of the route.

[0037] Figure 2Ashows a characteristic curve 3 stored in the vehicle control system, which represents a vehicle acceleration a (Y-axis in Figure 2A ) in rolling mode depending on the road gradient s (X-axis in Figure 2A ). Furthermore, the method includes a predefined upper threshold value 1 and a lower threshold value 2 for a vehicle acceleration a. Such threshold values ​​are not fixed, but can be freely parameterized depending on the vehicle.

[0038] Rolling mode is activated at the start of a downhill section for which it has been predicted that the predicted acceleration curve will be within the upper and lower threshold values ​​1, 2 for the vehicle acceleration for more than a minimum duration or minimum distance. When the Figure 2B In the vehicle position shown, these conditions are met, so that the rolling operation is activated by the vehicle control device according to steps S2 and S3.

[0039] According to an alternative embodiment, the determination of a suitable driving situation in which coasting mode can be activated can also be carried out without the use of topography and GPS data or without a pre-calculation of the occurring vehicle deceleration. For example, coasting mode can be initiated without any pre-calculation based solely on the current vehicle state, e.g., depending on the vehicle speed and the gradient. According to this variant, the duration of the coasting phase cannot be determined at the same time when coasting mode is initiated; instead, coasting mode is terminated based on the current vehicle state, for example, when the vehicle speed and / or the gradient fall below predetermined threshold values.

[0040] In step S2, coasting mode is first activated, meaning the fuel supply is interrupted, and the engine is towed by the vehicle, thus keeping it rotating. The drivetrain remains closed.

[0041] In step S3, the engine drag torque is then reduced. As already mentioned above, one possibility for this is to provide a locking pin on the rocker arm shaft which is positioned for coasting operation such that it can be brought into engagement with a detent on the rocker arm shaft and thus blocks further rotation of the rocker arm shaft into a rotational position that brings the cylinder exhaust valve into a closed position. One such locking device in the form of a locking pin is the so-called Rocker-Stop Device (RSD) from Jacobs Vehicle Systems ® . The use of such a device has previously been used to accelerate engine start-up through targeted decompression of the cylinders of the internal combustion engine or to reduce vehicle vibrations when the engine and vehicle are switched off. According to the invention, this known device can also be used for the targeted reduction of engine drag torque in towed coasting operation.

[0042] It was also mentioned above that another variant for reducing engine drag torque consists in deactivating the cylinder valve train, such that cylinder operation occurs with closed valves without gas exchange. The cylinders therefore act as gas springs, returning a large portion of the applied compression work after reaching top dead center, so that the compression work required is reduced compared to a normal valve train. Such an approach is known in the passenger car sector for partially deactivating cylinders at low engine speeds, although some of the cylinders continue to fire, increasing their efficiency because the operating points shift toward higher loads.

[0043] Here, the combustion chambers of the unfired cylinders are filled with air again, e.g. with fresh gas or exhaust gas. This air inclusion leads to minimal pressure in the cylinder and correspondingly low energy consumption. In one such known system, for example, the valves are closed by a special actuator: Two movable sleeves, the so-called cam lobes, are mounted on special gears on the intake and exhaust camshafts. These are responsible for the cylinder valves. Each cam lobe has two different profiles next to each other at its ends: a conventional solid profile and a so-called zero-lift cam. During normal fired cylinder operation, the solid profiles actuate the roller rocker arms and, via these, the valves. They therefore behave like completely conventional cams. The zero-lift cams, in turn, rotate above the rocker arms. They do not actuate them; the valve springs keep the valves closed.At the same time, the engine management system shuts down the injection. Spiral grooves are milled into the outer surfaces of the rotating camshafts, allowing the sleeves to be moved along the shafts by a few millimeters in a flash. When electromagnetic actuators in the cylinder head cover receive a signal from the engine management system, two integrated metal pins engage the grooves from the outside and move them into their final position. The camshafts are then locked in place by spring-loaded balls.

[0044] For the rolling operation according to the invention, this actuator system can be modified so that all cylinder valves are closed and all cylinders are operated in non-fired towing mode with the valves closed.

[0045] After activating coasting mode, vehicle 4 coasts down gradient 5 in towed mode, i.e., with the drivetrain engaged, and with reduced engine drag torque. Fuel consumption in this state is zero. The coasting phase can be extended because the vehicle experiences less deceleration.

[0046] Figure 3B shows a rolling driving condition in the middle of the slope. Figure 3A shows the corresponding value of the vehicle acceleration at this point, which is within the specified thresholds 1, 2.

[0047] The rolling mode is terminated if, due to a change in gradient, the vehicle acceleration or speed is outside the permissible limits for rolling operation (step S4). This is Figure 4Bwhich shows vehicle 4 after driving down the downhill section and at the beginning of an uphill section. At this point, the vehicle is braked so strongly in towing mode that the vehicle acceleration drops below the lower threshold value 2, which in Figure 4A is illustrated. The rolling mode is then terminated, with the means for reducing the engine drag power first reversing the reduction in drag power, and then the engine is transferred from towing to fired operation, so that driving operation continues in normal fired operation and with unreduced drag torque (step S5).

[0048] Although the invention has been described with reference to specific embodiments, it will be apparent to one skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. Additionally, many modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not intended to be limited to the disclosed embodiments, but is intended to include all embodiments falling within the scope of the appended claims. Reference symbol list

[0049] 1Upper threshold 2Lower threshold 3Characteristic curve 4Vehicle position 5Distance traveled

Claims

1. Aa method for a coasting operation of a motor vehicle with an internal combustion engine, preferably a utility vehicle, wherein in the coasting operation the internal combustion engine is dragged in unfired operation with a closed drive train and wherein means are provided for reducing an engine drag torque of the internal combustion engine, by means of which the engine drag power is reduced during the coasting operation, so that the internal combustion engine is dragged in the coasting operation with the combustion engine is towed at the reduced engine towing power, wherein the means for reducing the engine drag torque are configured to change a valve drive in the rolling operation in such a way that a compression work and / or charge changing work to be performed by the combustion engine in the non-firing operation is reduced, characterised by the steps of: presetting an upper (1) and lower (2) threshold value for a vehicle acceleration in rolling operation; advance calculation of an acceleration profile of the vehicle for rolling operation in dependence on topography data for a predetermined section (5) of the route lying ahead; wherein the coasting operation is activated at the beginning of a downhill section of road for which it has been predicted that the advance calculated acceleration profile will be longer than a minimum duration or minimum distance within the upper (1) and lower (2) threshold values for the vehicle acceleration; and wherein the previously activated rolling operation is deactivated if the current vehicle speed, the vehicle acceleration or a degree of incline at a current position of a route exceed predetermined threshold values for these variables.

2. A method according to claim 1, characterised in that the means for reducing the engine drag torque comprise a locking device which can be set in such a way that it prevents the closing of one or more exhaust valves of the internal combustion engine cylinders.

3. A method according to claim 2, characterised in (a) the locking device is adjustable to restrict movement of a rocker arm and / or rocker arm shaft operatively associated with a cylinder exhaust valve for opening and closing thereof such that the exhaust valve remains in an open condition; and / or (b) in that the locking device is configured as a blocking pin.

4. A Method according to claim 1, characterised in that the means for reducing the engine drag torque effect a shutdown of the valve drive of the cylinders in such a way that a cylinder operation takes place with closed valves without a charge cycle.

5. A Method according to one of the preceding claims, characterised by operating the motor vehicle in a second rolling mode, in which the internal combustion engine is coasted in an unfueled operation and with the drivetrain closed with an engine drag torque that is not reduced, the second rolling mode being activated if at least one of the following conditions is met: (a) the current vehicle speed exceeds a predetermined speed threshold for rolling operation with reduced drag power; (b) the current vehicle acceleration exceeds the predetermined upper acceleration threshold for rolling operation with reduced drag power; (c) a gradient at the current position of a route exceeds a predetermined threshold for the gradient.

6. A method according to one of the preceding claims, characterised in that the advance calculation of the acceleration profile of the vehicle for rolling operation with reduced drag power is carried out using a vehicle model that indicates an acceleration behaviour of the vehicle in non-fueled operation dependent on the topography of the route and the current speed.

7. A method according to one of the preceding claims, characterised in that the vehicle model takes into account a loading condition, a total weight, an axle load, a rolling friction resistance, an air flow resistance of the motor vehicle and / or a loss resistance of the drive unit caused by components of the drive unit.

8. A device for controlling the operation of a motor vehicle with an internal combustion engine, in particular a utility vehicle, characterised in that the device is configured to carry out the method according to one of the preceding claims.

9. A utility vehicle with a device according to claim 8.