GB2468906A

GB2468906A - Engine Control for a Vehicle

Info

Publication number: GB2468906A
Application number: GB0905236A
Authority: GB
Inventors: Ian Aitchison; Takashi Senda; Yasuhiro Nakai
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2009-03-26
Filing date: 2009-03-26
Publication date: 2010-09-29
Anticipated expiration: 2029-03-26
Also published as: JP2010230008A; DE102010016143A1; GB0905236D0; DE102010016143B4; GB2468906B; JP5515935B2

Abstract

There is provided apparatus (100) for use in controlling the pre-engagement of a pinion (30) of a starter motor (26) during stopping of an internal combustion engine (12). The apparatus comprises input means (102) for receiving sensed information from the engine (12); and controller (100) for determining from said sensed information the number of compression cycles remaining before the engine (12) stops and for initiating pre-engagement of the pinion (30) with a part (24) of the engine (12) in response to the number of cycles remaining. By providing such an arrangement, the pinion (30) can be pre-engaged at a point which is chosen in response to the number of compression cycles remaining. This enables the pinion (30) to be pre-engaged at a suitable point during stopping of the engine to prevent excessive noise when the pinion (30) pre-engages with a part (24) of the engine (12).

Description

Engine Control for a Vehicle

Field

The present invention relates to engine control apparatus. Particularly, but not exclusively, the present invention relates to engine control apparatus for a vehicle having an internal combustion engine. The present invention may be applied to all suitable types of vehicle.

Background

Commonly, internal combustion engines of motor vehicles are started by a starter motor. In one configuration, the starter motor comprises a pinion which is engageable with a toothed ring of a flywheel of the internal combustion engine. The pinion is selectively engageable with the toothed ring by means of an actuating device such as a solenoid. When the solenoid is operated, the pinion is brought into engagement with the toothed ring. The starter motor is then operated by a separate control arrangement which connects the starter motor to a battery of the motor vehicle in order to turn the internal combustion engine over.

A relatively recent development is to incorporate a stop-start facility into a motor vehicle engine. This facility enables the internal combustion engine to be shut off (usually automatically) when the motor vehicle is stationary for a prolonged period of time during a journey. This may occur when, for example, the motor vehicle is at a red light or is caught in heavy traffic. By switching off the engine when the motor vehicle is stationary, the stop-start facility is able to reduce unnecessary fuel consumption and exhaust gas emissions.

To enable the vehicle to resume the journey after a stationary period, the stop-start facility restarts the engine automatically. Restarting of the engine may be triggered in a variety of manners; for example, in response to the user engaging a gear or a depressing the clutch. However, before the engine can be started, the pinion of the starter motor must re-engage with the toothed ring of the internal combustion engine.

If this is done whilst the starter motor is operating, the pinion experiences rotational stresses when the rotating pinion engages with the toothed ring. This process also involves a time delay before the pinion fuiiy engages with the toothed ring, which is disconcerting and inconvenient for the driver of the vehicle.

In order to address this issue, some stop-start systems are arranged to bring the starter pinion into the engagement position at the beginning of a stop state. This is known as pinion pre-engagement. When the pinion is pre-engaged, the starter motor can be operated immediately to turn the engine over without having to wait for the pinion to engage with the toothed ring. Consequently, the engine can be restarted in a much shorter time period. Further, the mechanical loads on the pinion and toothed ring are reduced.

In order for a stop-start system to be unobtrusive in use, it is required to operate quietly and to restart the engine quickly as desired. However, an engine takes a finite amount of time to stop after it is switched off. Therefore, if the pinion is only engaged after the engine has stopped, there may be an unacceptable time delay in restarting the engine. Further, the engine may stop in a position which does not facilitate smooth engagement between the pinion and the toothed ring. This may lead to increased noise as the pinion engages or, worse, to incorrect or partial engagement between the pinion and the toothed ring.

Summary

The inventors have recognised an advantage in the pinion being pre-engaged just before, or at the point when, the engine comes to a standstill. However, during stopping, the speed of an engine may vary considerably with each compression cycle.

The engine may also reverse direction briefly before stopping. If the pinion is pre-engaged at a point when the engine speed is too high or is reversing direction, a loud noise may be heard due to inappropriate mechanical engagement between the pinion and the flywheel. This is undesirable both mechanically and for the user.

It is an object of some aspects of the present invention to provide an apparatus and method for improved pinion pre-engagement. It is a further object of some aspects of the present invention to provide an apparatus and method for improved pinion pre-engagement in a stop-start engine arrangement for a vehicle.

According to an aspect of the present invention there can be provided apparatus for use in controlling the pre-engagement of a pinion of a starter motor during stopping of an internal combustion engine, the apparatus comprising: an interface operable to receive sensed information from the engine; and a controller operable to determine from said sensed information the number of compression cycles remaining before the engine stops and to initiate pre-engagement of the pinion with a part of the engine in response to the number of cycles remaining.

By providing such an arrangement, the pinion can be pre-engaged at a point which is chosen in response to the number of compression cycles remaining. This enables the pinion to be pre-engaged at a suitable point during stopping of the engine to prevent excessive noise when the pinion pre-engages with a part of the engine. The pinion pre-engagement process generates noise which is dependent upon engine speed.

Therefore, the slower the engine speed, the quieter the pinion engagement.

By determining the number of compression cycles remaining, information regarding oscillations in engine speed as the engine comes to rest can be obtained. This information can be used to initiate pre-engagement of the pinion at a point which enables the noise level to be reduced.

In one arrangement, the controller is operable to initiate engagement of the pinion after a selected one of the 1St to cycles of n cycles determined to remain before the engine stops.

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In a variation, the controller is operable to initiate engagement of the pinion after a selected one of (n-2), (n-i) or, preferably, n cycles. By pre-engaging the pinion after the final compression cycle, then it can be ensured that the engine will not complete a further cycle and so the pinion can be quietly and reliably engaged with a part of the engine because the rotational velocity of the engine will concomitantly be reduced.

In a further variation the controller is operable to initiate engagement of the pinion at a pre-determined time after the selected cycle. When the last compression cycle of a stopping engine has occurred, there may still be sufficient kinetic energy remaining to cause the engine to speed up slightly. Therefore, by introducing a time delay (for example, 100 ms), it can be ensured that the pinion pre-engagement will occur when the engine is slowing down, reducing engagement noise.

In an alternative, the controller is operable to calculate the rate of change of engine speed at or after the selected cycle and to initiate engagement of the pinion in response thereto. Preferably, the controller is operable to initiate pre-engagement of the pinion at a time after the selected cycle when the rate of change of engine speed has fallen below a pre-determined value.

By measuring the rate of change of engine speed (or rotational velocity of the engine), it can be ensured that the engine is decreasing in speed before the pinion is pre-engaged.

In a further alternative, the controller is operable to initiate engagement of the pinion at a predetermined crank angle of a crankshaft of an engine. This is a relatively straightforward quantity to measure and so the controller can wait for a particular crank angle which is beyond the regime in which the engine speed may increase before the pinion is pre-engaged.

In a variation, the controller is operable to add or subtract a further time delay to account for a delay between initiation of pinion pre-engagement and actual pinon pre-engagement. This enables mechanical and electrical delays in the arrangement to be factored into the calculations.

In a variation, the controller is operable to determine the number of cylinder compression cycles remaining by determining the engine speed at a specified point in an initial compression cycle whilst the engine is stopping. By detennining the engine speed (engine rotational velocity) at a specified point (e.g. at TDC or at a particular crank angle) in a chosen initial compression cycle, the energy remaining in the engine can be calculated.

Usefully, the controller is operable to determine the reduction of engine speed at the specified point per compression cycle following the initial compression cycle and to determine number of compression cycles remaining therefrom. By determining the engine speed at each cycle following the chosen compression cycle, the reduction in engine speed per cycle can be determined. This information can be extrapolated to determine when number of cycles remaining before the engine comes to rest.

Alternatively, the controller is operable to determine the reduction of engine speed at the specified point for at least one compression cycle following the initial compression cycle and to determine number of compression cycles remaining therefrom.

The controller is able to determine how much energy remains in the engine from the rotational velocity at the specified point in the chosen initial compression cycle. By comparing this value to the energy lost in a compression cycle, the number of cycles remaining can be calculated, i.e. the last cycle will occur when, after the cycle, the engine has insufficient energy to complete a further cycle. )

In a further variation, the controller is operable to determine the kinetic energy remaining in the engine at the specified point in the chosen compression cycle and to compare said value to a known value of the kinetic energy required to complete a cylinder compression cycle of the engine.

In one arrangement, the known value of the kinetic energy required to complete a cylinder compression cycle is determined from either a predefined look-up table or from real time calculation based upon at least one parameter selected from the list of: engine speed; engine temperature; ambient air temperature; coolant temperature; engine oil temperature; ambient air pressure; and engine frictional losses.

In one arrangement, the specified point is top dead centre. Top dead centre (TDC) is a convenient measurement point. After TDC, the engine is at its slowest point in a given* compression cycle, enabling accurate calculations to be performed.

In one arrangement, the control apparatus may form part of an engine control unit. An engine control unit (ECU) is a unit which controls various aspects of the engine control in addition to pinion movement control. By providing the control apparatus in such a unit, the unit can be retrofitted to existing motor vehicles to offer a more efficient pinion engagement process.

In one arrangement, the control apparatus is configured for use with a vehicle having a stop-start facility.

According to another aspect of the invention, there is provided apparatus for use in controlling the pre-engagement of a pinion of a starter motor during stopping of an internal combustion engine, the apparatus comprising: input means for receiving sensed information from the engine; a controller for determining from said sensed information the engine speed value and for initiating engagement of the pinion with a part of the engine in response to the engine speed falling below a specified value. 4)

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By providing such an arrangement, the pinion can be pre-engaged based on the engine speed dropping below a specified value. Engagement of the pinion at too high an engine speed could cause damage to both the pinion and to the engine.

Desirably, the specified value is approximately 500 rpm or less, preferably, approximately 200 rpm or less and more preferably approximately 150 rpm or less.

These values of engine speed enable the pinion to be safely engaged without significant risk of damage to engine components.

According to another aspect of the invention, there is provided an internal combustion engine comprising: a starter motor including a pinion selectively engageable with a part of the engine; engagement means for selectively engaging the pinion with said part of an engine; and the apparatus of any preceding claim, wherein said apparatus is operable to initiate the selective engagement of the pinion with said part of the engine.

According to another aspect of the invention, there is provided a method of pre-engaging a starter motor pinion during stopping of an internal combustion engine, the method comprising: determining the number of compression cycles remaining before the engine stops; and engaging the pinion with a part of the engine in response to the number of cycles remaining.

By providing such a method, the pinion can be pre-engaged at a point which is chosen in response to the number of compression cycles remaining. This enables the pinion to be pre-engaged at a suitable point during stopping of the engine to prevent excessive noise when the pinion pre-engages with a part of the engine.

In a variation, the method further comprises engaging the pinion after a selected one of the 1S to th cycles of n cycles determined to remain before the engine stops.

In a variation, the method comprises engaging the pinion after a selected one of (n-2), (n-i) or, preferably, n cycles. By pre-engaging the pinion after the final compression cycle, then it can be ensured that the engine will not increase in rotational speed and that the pinion can be quietly and reliably engaged with a part of the engine.

In a further variation, the method comprises engaging the pinion at a predetermined time after the selected cycle. When the last compression cycle of a stopping engine has occurred, there may still be enough kinetic energy remaining to cause the engine to speed up slightly. Therefore, by introducing a time delay (for example, 100 ms), it can be ensured that the pinion pre-engagement will occur when the engine is slowing down, reducing engagement noise.

In an alternative, the method further comprises calculating the rate of change of engine speed after the selected cycle and engaging the pinion in response thereto.

Preferably, the method comprises engaging the pinion at a time after the selected cycle when the rate of change of engine speed has fallen below a pre-determined value.

In a further alternative, the method comprises engaging the pinion at a pre-determined crank angle of a crankshaft of the engine after the selected cycle. This is a relatively straightforward quantity to measure and so a particular crank angle can be selected which is beyond the regime in which the engine speed may increase before the pinion is pre-engaged.

In one arrangement, the method comprises determining the number of compression cycles remaining by determining the engine speed at a specified point in a chosen compression cycle whilst the engine is stopping. By determining the engine speed (engine rotational velocity a) at a specified point (e.g. at TDC or at a particular crank angle) in a chosen compression cycle, the energy remaining in the engine can be calculated.

In a variation, the method further comprises calculating the reduction in engine speed at the specified point for a compression cycle following the initial compression cycle and determining the number of compression cycles remaining therefrom. By determining the engine speed at each cycle following the initial (or chosen) compression cycle, the reduction in engine speed per cycle can be determined. This information can be extrapolated to determine when number of cycles remaining before the engine comes to rest.

Alternatively, the method comprises determining the number of compression cycles remaining by determining the energy remaining in the engine at the specified point in the initial compression cycle and comparing this value to the energy lost in a compression cycle.

The method is able to determine how much energy remains in the engine from the rotational velocity at the specified point in the initial compression cycle. By comparing this value to the energy lost in a compression cycle, the number of cycles remaining can be calculated, i.e. the last cycle will occur when, after the cycle, the engine has insufficient energy to complete a further cycle.

In a further variation, the method comprises determining the kinetic energy remaining in the engine at the specified point in the initial compression cycle and to compare said value to a known value of the kinetic energy required to complete a cylinder compression cycle of the engine.

In one variation, the method comprises determining the known value of the kinetic energy required to complete a cylinder compression cycle from either a predefined look-up table or from real time calculation based upon at least one parameter selected

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from the list of: engine speed; engine temperature; ambient air temperature; coolant temperature; engine oil temperature; ambient air pressure; and engine frictional losses.

In one arrangement, the specified point is top dead centre. Top dead centre (TDC) is a convenient measurement point. After TDC, the engine is at its slowest point in a given compression cycle, enabling accurate calculations to be performed.

According to a further aspect of the present invention, there is provided a method of pre-engaging a starter motor pinion during stopping of an internal combustion engine having at least one cylinder, the method comprising: determining the engine speed; and engaging the pinion with a part of the engine in response to the engine speed falling below a specified value.

By providing such a method, the pinion can be pre-engageci based on the engine speed dropping below a specified value. Engagement of the pinion at too high an engine speed could cause damage to both the pinion and to the engine.

According to another aspect of the present invention, a computer program product executable by a programmable processing apparatus, comprising one or more software portions for performing at least the determining step described above.

There is also provided a computer usable storage medium having a computer program product as discussed above stored thereon.

Brief Description of the Figures

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic view of a stop-start engine arrangement in a first position; Figure 2 is a schematic view of a stop-start engine arrangement in a second position; Figure 3 is a schematic diagram showing engine characteristics during a stopping process and illustrating a first embodiment; Figure 4 is a flow diagram illustrating the operation process of the first embodiment; Figure 5 is a graph showing engine characteristics during a stopping process and corresponding pinion control according to a second embodiment; Figure 6 is a graph of engine rotational velocity c (on the Yaxis) against accumulated crank angle 0 (X-axis); Figure 7 is a graph showing engine characteristics during a stopping process in accordance with the second embodiment; Figure 8a is a schematic illustration of the mechanisms of loss torque in an example cylinder; Figure 8b shows a graph of Torque (on the Y-axis) against crank angle (on the X-axis) in relation to the second embodiment; Figure 9 is a graph of engine rotational velocity o2 (on the Y-axis) against crank angle 0 (X-axis) to engine stop; Figure 10 is a graph showing engine characteristics during a stopping process and illustrating a threshold speed determined in accordance with the second embodiment; Figure 11 is a graph of engine rotational velocity Co2 (on the Y-axis) against crank angle 0 (X-axis) to engine stop and showing the determined threshold speed in accordance with the second embodiment;

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Figure 12 is a graph of the square of the engine rotational velocity co2 (on the Y-axis) against the crank angle i8OOend for a four cylinder diesel engine during stopping; Figure 13 is an illustrative graph showing a peak of engine speed after top dead centre in a compression cycle and the location of occurance thereof; Figure 14 is a graph showing engine characteristics during a stopping process and corresponding pinion control; Figure 15 is a schematic flow diagram illustrating the operation of a specific example of the second embodiment; and Figure 16 is a flow diagram illustrating the general operating principles of the second embodiment.

While the invention is susceptible to various modifications and alternatiye forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

Specific Description

Figures 1 and 2 show an example of a stop-start engine arrangement 10. The engine arrangement comprises an engine 12. The engine 12 is an internal combustion engine and has at least one cylinder 14. In this embodiment, the engine 12 has four in-line cylinders 14. Each cylinder comprises a reciprocally-movable piston 16 which is attached to a crankshaft 18 rotatable about an axis X-X. A sensor arrangement 20 is

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connected to the engine 12 and is arranged to provide sensor information regarding a variety of engine parameters; for example, engine speed, engine temperature and coolant temperature. Engine speed is typically measured by measuring the rotation of a toothed wheel (not shown) attached to the crankshaft 18. Data from the toothed wheel is supplied to the sensor arrangement 20.

The engine 12 further comprises a shaft 22 rotatable about an axis Y-Y and comprising a toothed gear 24. The shaft 22 and toothed gear 24 are connected to a flywheel (not shown) of the engine 12 and can be driven in order to turn the engine 12 over. This will be described later.

The engine arrangement 10 further comprises a starter motor 26. The starter motor 26 has an output shaft 28 which is rotatable about an axis Z-Z. A pinion gear 30 is attached to the output shaft 28 and is movable axially (as shown by the arrow A) from the position shown in Figure 1 where the pinion gear 30 is spaced from the toothed gear 24 to the position shown in Figure 2 where the pinion gear 30 engages with the toothed gear 24 of the engine 12.

A solenoid 32 is located adjacent the starter motor 26. The solenoid 32 has an actuator 34 which is able to move axially between an extended position (as shown in Figure 1) and a retracted position (as shown in Figure 2). A lever arm 36 is pivotably secured to the actuator 34. The lever arm 36 is pivotable about a pivot 38 and is arranged to engage with a part of the pinion gear 30 to cause the pinion gear 30 to move along the axis Z-Z between the retracted and extended positions. The solenoid 32 and lever arm 36 function as engagement means for bringing the pinion gear 30 into and out of engagement with the toothed gear 24 of the engine 12.

The operation of the solenoid 32 is initiated by control unit 100. In the present example, the control unit 100 takes the form of an engine control unit (ECU) which is a vibration and shock resistant unit mountable in a vehicle engine bay (not shown).

The control unit 100 receives inputs from the sensor arrangement 20 through an interface 102. The control unit 100 is connected to the starter motor 26 and the solenoid 32 and can separately initiate operation of the starter motor 26 and solenoid 32. The control unit 100 is operable to initiate movement of the solenoid 32 (and, consequently, engagement of the pinion 30 with the toothed gear 24) in response to sensor information received from the sensor arrangement 20.

In use, a parameter is measured to detect when the motor vehicle (not shown) in which the stop-start engine arrangement 10 is located is stationary. This may be for example, the speed of the motor vehicle. When it is detected that the motor vehicle is stationary, the engine 12 is switched off.

The engine 12 will take a period of time to slow down and stop. Based on sensor information received from the sensor arrangement 20, the control unit 100 initiates pre-engagement of the pinion gear 30 with the toothed gear 24 of the engine 12. This is done by means of a control signal S. In the present example, the control signal S is a digital signal (i.e. has a value of either 1 (on) or 0 (oft)) and is configured to trigger operation of the solenoid 32 through appropriate switch means (not shown) such as Power MOSFETs or Insulated Gate Bipolar Transistors (IGBTs).

The control signal S is used to initiate movement of the actuator 34 of the solenoid 32 from the extended position shown in Figure 1 to the retracted position shown in Figure 2. Movement of the actuator 34 causes the lever arm 36 to rotate about the pivot 38 and to push the pinion gear 30 axially along the axis Z-Z such that the pinion gear 30 engages with the toothed gear 24. This action is performed when, or before, the engine 12 comes to a standstill.

Once the pinion gear 30 is engaged with the toothed gear 24, the engine 12 can be restarted by immediately operating the starter motor 26. This action drives the pinion gear 30 which, by virtue of engagement with the toothed gear 24, drives the shaft 22 about the axis Y-Y and causes the engine 12 to turn over by turning of the flywheel such that the engine 12 can be restarted.

The control unit 100 determines the point at which the pinion gear 30 is to be engaged with the toothed gear 24. This point is determined based upon sensor information received from the sensor arrangement 20 by the interface 102. The pinion gear 30 should be engaged at a point when the engine is at a standstill or when the engine speed is low. Figure 3 is a diagram showing the operation of a first embodiment of the control unit 100 with a four cylinder engine such as the engine 12 shown in Figures 1 and 2.

Four lines are shown in Figure 3. Line A shows the crank position before top dead centre (CA BTDC) (on the Y-axis) as a function of time (on the X-axis). The.

gradations of the time axis each represent 100 ms. Line B shows the engine speed Ne (in rpm) (on the Y-axis) against time (on the X-axis). Line C illustrates the value of the control signal S of the control unit 100 as described above. Line D illustrates a pinion current which flows through the solenoid 32.

As shown in Figure 3, when the engine is stopping, the engine speed Ne (Line B) oscillates as a piston of each cylinder passes through top dead centre (TDC), i.e. completes a compression cycle. Point 1 on Figure 3 shows the engine 12 when a piston is at TDC.

In order to reduce noise and mechanical wear, it is useful to pre-engage the pinion 30 when the engine 12 is rotating at a low speed; Consequently, the control unit 100 of the first embodiment is operable to trigger initiation of pinion pre-engagement by detection of the rotational velocity of the engine dropping below a predetermined value. In this embodiment, the predetermined value is 150 rpm. The rotational velocity of the engine 12 is detected by the sensor arrangement 20. The interface 102 receives the sensor information and the controller 100 determines when the engine speed Ne has dropped below 150 rpm. At this point, the pinion 30 can be engaged with reduced noise and mechanical wear.

Consequently, the control unit 100 switches the control signal S (Line C) on (i.e. from a value of 0 to 1). In response to the control signal S, a pinion current (Line E) flows through the solenoid 32. As can be seen from a comparison of Lines D and E, there is a short time delay between switching on of the control signal S and the pinion current E increasing. As the pinion current E increases, the solenoid 32 is energised and the actuator 34 is moved into the position shown in Figure 2. This brings the pinion 30 into engagement with the toothed gear 24.

A flow diagram illustrating the operation of the control unit 100 of the first embodiment is shown in Figure 4. At step 101 the process is started. Typically, this method would be started in response to commencing engine.switch off; for example, when the fuel supply to the engine is cut off. At step 102 the control unit 100 determines the engine speed Ne from sensor information received from the sensor arrangement 20 by the interface 102. At step 103, the control unit 100 determines whether the engine speed Ne is below a threshold X. In this embodiment, the threshold X is 150 rpm. However, other suitable values may be used; for example, 500 rpm or 200 rpm.

if it is determined that the engine speed Ne has dropped below the threshold X, then at step 104 the control unit 100 initiates engagement of the pinion 30 by switching the control signal S on (i.e. to a value of 1). If it is determined that the engine speed Ne is not below the threshold X, then the process moves back to step 103.

The operation of the control unit 100 according to a second embodiment will now be described with reference to Figures 5 to 16. Figure 5 shows a graph illustrating two engine characteristics during the stopping process. Line A shows the crank angle of the crankshaft 18 (on the Y-axis) before top dead centre against time (on the X-axis).

Line B shows the engine speed Ne (in rpm) on the Y-axis against time (on the X-axis). As shown, each division on the X-axis corresponds to 100 ms.

As shown by Line B, it can be seen that the engine angular velocity 0) oscillates as a piston of each cylinder passes through top dead centre (TDC), i.e. completes a compression cycle. At point 1, with each complete cylinder compression cycle, the peak engine angular velocity decays as energy is lost by pumping losses, friction and other loss mechanisms.

As each piston passes through TDC, the engine angular velocity co then rises briefly before dropping as the next piston approaches TDC. This process continues until the engine has insufficient kinetic energy pass through TDC. This point, shown by point 2 in Figure 2, is termed the "last TDC before engine stop". At this point, the crank angle is l8O-°d, where Oend denotes the crank angle when the engine 12 comes to rest (point 3). Beyond this point, the engine has insufficient kinetic energy to complete a compression cycle. Consequently, the engine reverses direction (at point 4) before coming to rest again (point 5). A suitable point at which to engage the pinion gear 30 is (or approaching) at point 3. At this point, the engine 12 has stopped and has yet to move into the reverse direction.

The operation of the control unit 100 will now be described. In order to detect the optimum position, the control unit 100 is configured to calculate the number of cylinder compression cycles remaining before the engine comes to rest. By calculating this number, the most suitable point at which to engage the pinion gear 30 can be estimated or calculated. The calculations performed by the control unit 100 will now be described.

The control unit 100 operates on the principle that the total crank angle rotation remaining to engine stop can be calculated by calculating the losses in the engine 12 as the engine slows down. By knowing the cumulative crank angle to engine stop, then the number of compression cycles remaining before the engine comes to rest can be calculated.

The engine 12 will come to a stop when the rotational energy lost as the angular velocity a) tends to zero is equal to the absorbed energy absorbed by loss torque as the rotational energy is converted into positional energy (i.e. into a crank angle 0 past TDC). Figure 6 shows a schematic diagram of the engine speed u (on the Y-axis) as a function of accumulated crank angle 0 (i.e. the total angle through which the crankshaft 18 has moved from the start of measurement). The angular velocity a) is measured at a particular point in a compression cycle -in this embodiment it is measured from the TDC of one cycle through to the TDC of the next cycle.

With each compression cycle, the crankshaft 18 moves through an angle A0 and loses an amount of rotation speed equal to t.\ Co. When the engine speed a) reaches zero, the engine stops at a crank angle °end Figure 7 illustrates the stop crank angle °end on a graph showing crank position BTDC (Line A) and engine speed Ne (line B) in a similar manner to Lines A and B shown in FigureS.

The speed loss A o per compression cycle is due to torque losses in the engine. These losses are due to a variety of factors. Figure 8a shows a schematic diagram of a cylinder illustrating the main loss factors. As shown, the main loss factors are pumping losses (i.e. the energy required to compress the fluid in the piston during a compression cycle) and friction losses. Thermal losses may also be important. Figure 8b shows a graph of torque (on the Y-axis) against crank angle (on the X-.axis). A negative value of torque is the torque that is lost during a compression cycle.

As described earlier, the engine 12 will come to a stop when the rotational energy lost as the angular velocity a) tends to zero is equal to the absorbed energy absorbed by loss torque TLOSS as the rotational energy is converted into positional energy (i.e. into a crank angle 0 past TDC). This can be expressed algebraically as: J(2w2y._jT(9)do where w is the angular velocity of the crankshaft 18, is the angular velocity of the crankshaft 18 at TDC for a compression cycle i, w+i is the angular velocity of the crankshaft 18 at TDC for compression cycle i+1 (i.e. immediately following cycle i), Tixjss is the loss torque lost during movement of the crankshaft 18 through an angle of AO and J is the inertia of the engine 12.

From the above relationship, the last TDC before stopping (i.e. the TDC in the last compression cycle before the engine comes to rest) can be calculated. The last TDC before stopping can be determined from a threshold value for the square of the engine rotational velocity 2 at a particular TDC below, which the engine has insufficient energy to complete a further compression cycle. Therefore, the last TDC can be determined when the rotational velocity at a particular TDC satisfies the criteria: e W2TDC < -fTL (&) dO where cmc is the angular velocity of the crankshaft 18 at TDC. Therefore, when the speed of the engine 12 at TDC (COC) drops below a threshold value T such that the above equation is satisfied, the engine 12 has insufficient kinetic energy remaining to carry out a further complete compression cycle. Consequently, when the above equation is satisfied, the engine can be considered to have passed through the last TDC before coming to rest. The threshold value T may depend upon a particular engine or cylinder configuration. The calculations may be done in real time or may be stored in a pre-loaded look up table.

The above relationship is illustrated by Figure 9 which shows a graph of the square of the engine rotational velocity co2 (on the Y-axis) against the crank angle (CA) 0 remaining to engine stop, where tB is from 0 to 180 ° CA. This graph shows the energy absorbed by loss torque during 0.

The threshold value T2 of the square of the engine speed' Ne2 for detecting the last TDC before the engine stops is also shown. If the engine speed at TDC is below this threshold value, then the control unit 100 determines that the last TDC before engine stop has been detected.

Whilst the last compression cycle before engine stop has been determined here, other arrangements are possible. For example, by knowing the loss torque per cycle, the number of remaining compression cycles can be determined, and the threshold value T set to determine the penultimate compression cycle, the second from last compression cycle and so on.

Using the above information, the crank angle at which the engine comes to rest (before reverse rotation of the engine occurs) can be calculated. The engine will come to rest when the rotational energy lost as the angular velocity co tends to zero is equal to the absorbed energy absorbed by loss torque as the rotational energy is converted into positional energy (i.e. into a crank angle 0 past TDC). Consequently, the stop crank angle can be calculated from: ()2 =_-JTLQSS(O)dO where the parameters are the same as described previously. Since for one complete compression cycle, 0 = 360°, the number of compression cycles to the last TDC (i.e.the number of compression cycles remaining) can be calculated.

This is illustrated by Figures 10 and 11. Figure 10 shows crank angle (Line A) and engine speed Ne (Line B). The engine speed Ne at TDC in a compression cycle is shown. In this case, the engine speed Ne at TDC is 200 rpm. This is marked point 1.

Referring now to Figure 11, this figure shows a graph (similar to Figure 9) of the square of the engine rotational velocity co2 (on the Y-axis) against the crank angle 0 to engine stop. The value of 0)2 at point 1 in Figure 10 is shown. From a comparison of Figures 9 and 11, it can be seen that the value of co2 at point 1 (Figure 10) is below the threshold for completing a further compression cycle. Therefore, the TDC at point 1 is the last compression cycle before the engine stops (this can be seen in Figure 10).

From the value of (02 at point 1, the crank angle to engine stop can be determined. The crank angle corresponding to o2 at point 1 is 8. From this, the final crank angle °end (i.e. the crank angle at which the engine comes to rest relative to TDC) can be calculated by: O= 180-8 Consequently, as discussed above, the present invention is able to calculate the crank angle to engine stop from information regarding the engine speed at a particular point in a compression cycle (in this case at TDC) whilst the engine 12 is stopping and from a knowledge of the losses occurring in the engine 12.

To illustrate this further, Figure 12 shows a graph of the square of the engine rotational velocity 2 (on the Y-axis) against the crank angle 1 8O-0d for a four cylinder diesel engine during stopping. The threshold value of the square of the engine speed (Ne2) can clearly be seen. As a result the number of compression cycles to engine stop can be calculated from the square of the engine rotational velocity co.

Based on the above information, the contra! unit 100 can control operation of the solenoid 32 and, thus, can control pre-engagement of the pinion 30. It is desirable to pre-engage the pinion when the engine rotational velocity 0) is either constant or decreasing (e.g. between the peak after point 2 and point 3 in Figure 5). The operation of the control unit 100 to initiate pre-engagement of the pinion 30 will now be discussed.

The TDC of the last compression cycle can be determined as outlined above.

However, as shown in Figure 13, the engine rotational velocity co can be seen to increase after the last TDC. This is because there is sufficient energy remaining in the engine to move the crankshaft 18 through part of a cycle (although not through a full compression cycle). If the pinion 30 is pre-engaged whilst the engine rotational velocity co is increasing, a loud noise may result. Consequently, the control unit 100 of the present invention is operable to delay initiation of the pinion pre-engagement for a further period.

The further period (i.e. a delay period after the last TDC) is, in this embodiment, calculated by waiting for a predetermined crank angle after the.last TDC before initiating pinion pre-engagement. As shown in Figure 13, the peak engine speed Ne after the TDC of the last compression cycle before stopping occurs at a crank angle of between 120 and 150 CA BTDC. The minimum value is 117.5 CA I3TDC.

Consequently, by waiting for a predetermined crank angle after the TDC of the last compression cycle, the engine rotational velocity co will have passed the peak point after the last TDC and will be decreasing when the pinion 30 starts to engage with the toothed gear 24.

Figure 14 shows the initiation of the pinion pre-engagement by the control unit 100 based on the calculations performed as outlined above. Five lines are shown in Figure 4. Line A shows the crank angle before top dead centre (on the Y-axis) as a function of time (on the X-axis). Line B shows the engine speed Ne (in rpm) on the Y-axis against time (on the X-axis). Line C shows a calculation of engine speed at TDC (TDCNe) on the Y-axisas a function of time (on the X-axis). As shown, when Line C drops below a previously calculated threshold value of the square of the engine rotational velocity at TDC (TDCNe) the last TDC can be considered to have been determined.

Once the delay has occurred (in this embodiment, this involves waiting for a predetermined crank angle) has expired, the control unit 100 initiates the pre-engagement of the pinion 30 by setting the control signal S to a value of 1 (on). The control signal S is illustrated by Line D in Figure 14.

In response to the control signal D, a pinion current (Line E) flows through the solenoid 32. As can be seen from a comparison of Lines D and E, there is a short time delay between switching on of the control signal D and the pinion current E increasing. This time delay can be factored in to the time delay after TDC incorporated into the configuration of the control unit 100. At point 1 shown in Figure 14, the pinion 30 will engage with the toothed gear 24, efficiently and with a low level of noise.

To summarise, the operation of the control unit 100 of the second embodiment is outlined in Figure 15. Figure 15 shows a schematic flow diagram for an example of the operation of the second embodiment and is based on the data determined for, and shown in, Figure 14.

At step 1, the engine speed at TDC is monitored. In this example, the threshold engine speed for last TDC is 220 rpm (see also Figures 12 and 14). Consequently the control unit 100 detects when the engine speed at TDC is equal to or less than 220 rpm. At this point, the control unit 100 determines that the TDC of the last compression cycle has been detected. Consequently, a condition I of step 1 has been determined to have been satisfied.

At step 2, the control unit 100 monitors the crank angle. When a crank angle of at least 117.5 CA BTDC is detected (see Figure 11), a condition 2 of step 2 has been determined to have been satisfied.

Step 3 is a fail-safe step in the even that steps 1 and 2 record a false result or do not detect the TDC of the last compression cycle. In step 3, the engine speed is monitored.

If the engine speed is equal to or less than a safe pinion engagement speed of 130 rpm, a condition 3 of step 3 is determined to have been satisfied.

if conditions 1, 2 and 3 of steps 1, 2 and 3 respectively are determined to have been satisfied, then the control unit 100 initiates pre-engagement of the pinion 30.

Alternatively, the control unit 100 may fail to detect a TDC of the last coinpression cycle. In this even, at step 3 it is determined whether the engine speed is equal to or less than a lower speed limit of 50 rpm. If so, a condition 4 is satisfied. if condition 4 is satisfied, then the control unit 100 initiates pre-engagement of the pinion 30.

Consequently, if the pinion pre-engagement has not been initiated by the time the engine speed drops to 50 rpm, then condition 4 ensures that the pinion 30 is pre-engaged prior to, or at the point when, the engine comes to rest.

Whilst the second embodiment has been described with reference to the above examples, the operation of the control unit 100 may be described more generally arid may operate on different parameters than those previously described.

Figure 16 shows a flow chart illustrating the general principle of operation of the control unit 100. At step 201, the process is started. The process may start when the engine speed drops below a predetermined value (which may be, for example, below idle). Alternatively, the process may start when the engine is switched off; for example, when the fuel supply to the engine is cut off.

At step 202 the engine speed at a predetermined point in a compression cycle is determined. Whilst the above example uses TDC as a measurement point for engine speed, any suitable value could be used; for example, BDC or any desired crank angle.

At step 203, the number of compression cycles remaining is determined. The number remaining may be calculated from a look-up table of values storing the loss tor4ue per compression cycle. Alternatively, the loss values may be calculated in real time using parameters determined from the sensor arrangement 20. A non-exhaustive list of such parameters may include: parameters may include engine speed, engine temperature, ambient air temperature, engine oil temperature, intake temperature, coolant temperature, ambient air pressure, or cylinder head pressure.

At step 204, the desired compression cycle is selected. Whilst the above description relating to Figures 3 to 15 has determined the last compression cycle before engine stop, other values could be used. For example, if it is determined that there are n compression cycles remaining before the engine stops, the control unit 100 may be operable to initiate engagement of the pinion after a selected one of the 15t to cycles.

At step 205, the control unit 100 detects the selected compression cycle. This may be determined to be when the engine speed at the selected measurement point in the respective cycle falls below a specified threshold value T. At step 206, a time delay is introduced. As discussed above, the control unit 100 may wait for a predetermined crank angle. However, alternative delay processes may be used. In one alternative, a simple time delay (i.e. the control unit 100 is configured to wait for a pre-determined time after the last TDC before the pinion pre-engageinent is initiated) may be used.

As a further alternative, the rate of change of rotational velocity &o may be calculated. Based on this, the control unit 100 will not initiate pre-engagement of the pinion before, for example, a decrease in the rotational velocity o is detected, or when a particular speed range is predicted or detected.

Any of the above approaches may be used in order to delay initiation of pinion pre-engagement for a predetermined period after the selected compression cycle.

Finally, at step 207 the pinion 30 is engaged with the toothed gear 204 at a point determined in steps 201 to 206.

The present examples advantageously enable the pinion 30 can be pre-engaged at a specific point during stopping of the engine such that the engagement is clean and quiet. This has benefits for the user because the pre-engagement cannot be heard.

Further, this arrangement and method reduces the mechanical strain on the pinion 30 and related components.

The described approaches may be applied to any internal combustion engine which may benefit. Whilst the above example illustrates a four cylinder engine, any number of cylinders may be used. For example, a single cylinder, two, three, five or six cylinder, V6, V8, yb and V12 arrangements. may be used. Additionally, the engine may be a rotary-type Wankel engine which has has a rotary compression chamber in place of a cylinder or bank of cylinders.

Further the described approach is applicable to all arrangements which utilise internal combustion engines. Whilst the present invention has been described in the context of a vehicle, the skilled person would be aware of other suitable applications, if the present invention is applied in a vehicle, the vehicle may take any suitable form; for example, a motor car, a truck, a van, or a motorcycle.

Although the invention has been described with reference to the above specific examples, the invention is not limited to the detailed description given above.

Variations will be apparent to the person skilled in the art.

Alternative or additional factors may be incorporated into the calculations of torque loss. For example, engine temperature, coolant temperature or other factors may be used to provide a more accurate estimate of the loss torque per compression cycle.

The calculations in which the control unit determines engine loss may be tailored for a specific application or engine (e.g. a four cylinder engine). Further, the calculations may be modified to take into account environmental factors such as ambient temperature or pressure. The sensor arrangement on the engine may provide information regarding parameters such as coolant temperature, cylinder temperature, injection pressure and so on.

Alternatively, the number of compression cycles remaining may be calculated by a different process. For example, the rate of change of engine speed at the TDC (or, indeed, any other suitable point) in each compression cycle following could beused to determine the number of compression cycles remaining. For example, with reference to Figure 6, the change in engine speed A o per compression cycle may be used to determine the number of compression cycles remaining, i.e. when the engine will stop when o tends to zero. Consequently, the number of cycles remaining may be calculated without taking the loss torque into account and merely using the reduction in engine speed u.

Whilst the above embodiment outlines detection of the last TDC before the engine stops, the present invention could be used to determine any TDC before engine stop.

There need be no time delay following the detection of TDC. Alternatively, any time delay required may be incorporated as desired. A combination of techniques may be used to determine an appropriate time delay; for example, the control unit may wait for a predetermined crank angle and then wait a predetermined time period before initiating pre-engagement of the pinion.

Alternatively, a time delay may be subtracted from the calculated time delay in order to, for example, account for the delay in the pinion current increasing when the control signal S is switched on.

As a further variation, the engine rotational velocity need not be measured at TDC.

Any other suitable point could be used, provided that the measurement points are one compression cycle apart. For example, the engine rotational velocity may be measured at bottom dead centre (BDC) or at any other suitable crank angle.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.

Claims

CLAIMS1. Apparatus for use in controlling the pre-engagement of a pinion of a starter motor during stopping of an internal combustion engine, the apparatus comprising: an interface operable to receive sensed information from the engine; and a controller operable to determine from said sensed information the number of compression cycles remaining before the engine stops and to initiate pre-engagement of the pinion with a part of the engine in response to the number of cycles remaining.
2. The apparatus of claim 1, wherein the controller is operable to initiate engagement of the pinion after a selected one of the l to rh cycles of n cycles detemiined to remain before the engine stops.
3. The apparatus of claim 2, wherein the controller is operable to initiate engagement of the pinion after a selected one of (n-2), (n-i) or n cycles.
4. The apparatus of claim 3, wherein the controller is operable to initiate engagement of the pinion after n cycles.
5. The apparatus of any one of claims 2, 3 or 4, wherein the controller is operable to initiate engagement of the pinion at a pre-determined time after the selected cycle.
6. The apparatus of any one of claims 2, 3 or 4, wherein the controller is configured to calculate the rate of change of engine speed at or after the selected cycle and to initiate engagement of the pinion in response thereto.
7. The apparatus of claim 6, wherein the controller is operable to initiate engagement of the pinion at a time after the selected cycle when the rate of change of engine speed has fallen below a predetermined value.
8. The apparatus of any one of claims 2, 3 or 4, wherein the controller is operable to initiate engagement of the pinion at a predetermined crank angle of a crankshaft of an engine.
9. The apparatus of any one of claims 5 to 8, wherein the controller is operable to add or subtract a further time delay to account for a delay between initiation of pinion pre-engagement and actual pinon pre-engagement.
10. The apparatus of any one of the preceding claims, wherein the controller is operable to determine the number of compression cycles remaining by determining the engine speed at a specified point in an initial compression cycle whilst the engine is stopping.
11. The apparatus of claim 10, wherein the controller is operable to determine the reduction of engine speed at the specified point for at least one compression cycle following the initial compression cycle and to determine number of compression cycles remaining therefrom.
12. The apparatus of claim 10 or 11, wherein the controller is operable to determine the number of compression cycles remaining by determining the energy remaining in the engine at the specified point in the chosen compression cycle and comparing this value to the energy lost per compression cycle.
13. The apparatus of claim 11, wherein the controller is operable to determine the kinetic energy remaining in the engine at the specified point in the chosen compression cycle and to compare said value to a known value of the kinetic energy required to complete a compression cycle of the engine.
14. The apparatus of claim 13, wherein the known value of the kinetic energy required to complete a compression cycle is determined from either a predefined look-up table or from real time calculation based upon at least one parameter selected from the list of: engine speed; engine temperature; ambient air temperature; coolant temperature; engine oil temperature; ambient air pressure; and engine frictional losses.
15. The apparatus of any one of claims 10 to 14, wherein the specified point is top dead centre.
16. The apparatus of any one of the preceding claims, configured for use with a vehicle having a stop-start facility.
17. An engine control unit comprising the apparatus of any one of the preceding claims.
18. Apparatus for use in controlling the pre-engagement of a pinion of a starter motor during stopping of an internal combustion engine, the apparatus comprising: an interface operable to receive sensed information from the engine; a controller operable to determine from said sensed information the engine speed value and for initiating engagement of the pinion with a part of the engine in response to the engine speed falling below a specified value.
19. The apparatus of claim 18, wherein the specified value is approximately 500 rpm.
20. The apparatus of claim 19, wherein the specified value is approximately 200 rpm.
21. The apparatus of claim 20, wherein the specified value is approximately 150 rpm.
22. An internal combustion engine comprising: a starter motor including a pinion selectively engageable with a part of the engine; engagement means for selectively engaging the pinion with said part of an engine; and the apparatus of any preceding claim, wherein said apparatus is operable to initiate the selective engagement of the pinion with said part of the engine.
23. A method of pre-engaging a startr motor pinion during stopping of an internal combustion engine, the method comprising: determining the number of compression cycles remaining before the engine stops; and engaging the pinion with a part of the engine in response to the number of cycles remaining.
24. The method of claim 23, further comprising engaging the pinion after a selected one of the 1t to nth cycles of n cycles determined to remain before the engine stops.
25. The method of claim 24, comprising engaging the pinion after a selected one of (n-2), (n-i) or n cycles.
26. The method of claim 25, comprising engaging the pinion after n cycles.
27. The method of any one of claims 24 to 26, comprising engaging the pinion at a pre-determined time after the selected cycle.
28. The method of any one of claims 24 to 26, further comprising calculating the rate of change of engine speed after the selected cycle and engaging the pinion in response thereto.
29. The method of claim 28, comprising engaging the pinion at a time after the selected cycle when the rate of change of engine speed has fallen below a pre-determined value.
30. The method of any one of claims 24 to 26, comprising engaging the pinion at a pre-determined crank angle of a crankshaft of the engine after the selected cycle.
31. The method of any one of claims 23 to 30, comprising determining the number of compression cycles remaining by determining the engine speed at a specified point in an initial compression cycle whilst the engine is stopping.
32. The method of claim 31, further comprising calculating the reduction in engine speed at the specified point for a compression cycle following the initial compression cycle and determining the number of compression cycles remaining therefrom.
33. The method of claim 31, comprising determining the number of compression cycles remaining by determining the energy remaining in the engine at the specified point in the initial compression cycle and comparing this value to the energy lost in a compression cycle.
34. The method of claim 33, comprising determining the kinetic energy remaining in the engine at the specified point in the initial compression cycle and to compare said value to a known value of the kinetic energy required to complete a compression cycle of the engine.
35. The method of claim 34, comprising determining the known value of thern kinetic energy required to complete a compression cycle from either a predefmed look-up table or from real time calculation based upon at least one parameter selected from the list of: engine speed; engine temperature; ambient air temperature; coolant temperature; engine oil temperature; ambient air pressure; and engine frictional losses.
36. The method of any one of claims 31 to 35, wherein the specified point is top dead centre. /
37. A method of pre-engaging a starter motor pinion during stopping of an internal combustion engine, the method comprising: determining the engine speed; and engaging the pinion with a part of the engine in response to the engine speed falling below a specified value.
38. The method of claim 37, wherein the specified value is approximately 500 rpm.
39. The method of claim 38, wherein the specified value is approximately 200 rpm.
40. The method of claim 39, wherein the specified value is approximately 150 rpm.
41. A computer program product executable by a programmable processing apparatus, comprising one or more software portions for performing at least the determining step of any one of claims 23 to 40.
42. A computer usable storage medium having a computer program product according to claim 41 stored thereon.
43. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.
44. An internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.
45. A method substantially as hereinbefore described with reference to the accompanying drawings.