Patent Publication Number: US-6338323-B1

Title: Vane type variable valve timing control apparatus and control method

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a vane type variable valve timing control apparatus and control method for changing valve timing of an internal combustion engine. 
     (2) Related Art of the Invention 
     As a vane type variable valve timing control apparatus, there is one heretofore disclosed in Japanese Unexamined Patent Publication Nos. 10-141022 and 10-068306. 
     With this apparatus, recess portions are formed on an inner peripheral face of a cylindrical housing secured to a cam sprocket, while vanes secured to a cam shaft are accommodated in the recess portions, the construction being such that the cam shaft can rotate relatively with respect to the cam sprocket, within a range in which the vanes can move inside the recess portions. 
     Furthermore, the construction is such that by supplying and discharging oil by means of a spool valve, relatively with respect to a pair of hydraulic chambers (advance angle side hydraulic chamber and delay angle side hydraulic chamber) formed by the vanes partitioning the recess portions into front and rear in the rotation direction, the position of the vanes in the recess portions is changed, thereby enabling a rotation phase of the cam shaft relative to a crank shaft to be continuously changed. 
     A control value of the spool valve is determined by adding a feedback correction value set depending on a deviation of an actual rotation phase from a target value, to a neutral control value for retaining a rotation phase. A dither signal is then superimposed on the determined control value which is then output to an actuator of the spool valve. 
     However, as disclosed in Japanese Unexamined Patent Publication No. 10068306, in the case where a resilient body such as a spiral spring for urging the vane to the advance angle side or to the delay angle side is provided, then with a conventional construction in which the neutral control value is constant regardless of a target rotation phase, there is a problem in that the pressure balance cannot be maintained, and a steady-state deviation occurs. 
     That is to say, with a construction having a resilient body for urging the vane, the urging force of the resilient body varies due to the rotation phase. Therefore, when the valve is driven about the valve position corresponding to the neutral control value, using a constant neutral control value regardless of the rotation phase, the rotation phase is shifted to the advance angle side or to the delay angle side, depending on whether the neutral control value is higher or lower than a suitable urging force. When the rotation phase is shifted from a target, it is then corrected by feedback correction. However, time is required for convergence, and since the correction value requirement differs for each rotation phase, convergence is not possible, causing a problem due to the occurrence of steady-state deviation. 
     SUMMARY OF THE INVENTION 
     In view of the above problems it is an object of the present invention, with a vane type variable valve timing control apparatus comprising a resilient body for urging a vane to an advance angle side or to a delay angle side with respect to a cam sprocket, to enable a target rotation phase to be precisely maintained without causing a steady-state deviation. 
     To achieve the above object, the present invention is constructed such that a neutral control value of a spool valve is set in accordance with a target rotation phase. 
     With such a construction, a reference position of the valve at the time of retaining the rotation phase is set in accordance with a target value of the rotation phase, to thereby cause the valve to be driven about the valve position corresponding to the target value. As a result, it is possible to supply and discharge oil to each hydraulic chamber at a balance corresponding to the urging force of the resilient body, enabling suppression of the occurrence of steady-state deviation. 
     Here, the neutral control value of the spool valve is preferably changed according to the oil pressure, as well as being changed according to the target rotation phase. 
     With such a construction, there is the effect that it is possible to correspond to differences in requirements of the neutral control value due to changes in the oil pressure, and that the occurrence of steady-state deviation due to changes in the oil pressure can be avoided. 
     Moreover, in the case of a construction where an oil pump for supplying oil to the spool valve is driven by an engine, the rotation speed of the pump is proportional to the rotation speed of the engine, and the oil pressure can be estimated from the rotation speed of the engine. Hence the rotation speed of the engine can be used as a parameter corresponding to the oil pressure. 
     Furthermore, it is preferable to correct the neutral control value in accordance with the oil temperature. 
     With such a construction, the neutral control value set in accordance with the target rotation phase is corrected in accordance with the oil temperature, that is, the viscosity of the hydraulic fluid, giving an effect that the occurrence of steady-state deviation due to a change in the oil temperature can be avoided. 
    
    
     Other objects and aspects of the present invention will become apparent from the following description of embodiment given in conjunction with the appended drawings. 
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a structural portion of a vane type variable valve timing control apparatus in one embodiment. 
     FIG. 2 is a sectional view showing a vane urging mechanism in the vane type variable valve timing control apparatus. 
     FIG. 3 is a longitudinal section showing an electromagnetic switching valve in the vane type variable valve timing control apparatus. 
     FIG. 4 is a flow chart showing a control function of the electromagnetic switching valve in the vane type variable valve timing control apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a structural portion of a vane type variable valve timing control apparatus of an internal combustion engine, in an embodiment. In an engine comprising both a cam shaft on the intake side and a cam shaft on the exhaust side, this apparatus is applied to the cam shaft on the intake valve side, to variably control the valve timing of an intake valve. 
     The vane type variable valve timing control apparatus shown in FIG. 1 comprises: a cam sprocket  1  which is rotatably driven by an engine crank shaft (not shown in the figure) via a timing chain; a rotation member  3  secured to an end portion of a cam shaft and rotatably housed inside the cam sprocket  1 ; a hydraulic circuit  4  for relatively rotating the rotation member  3  with respect to the cam sprocket  1 ; and a lock mechanism  10  for selectively locking a relative rotation position between the cam sprocket  1  and the rotation member  3  at a predetermined position. 
     The cam sprocket  1  comprises: a rotation portion (not shown) having on an outer periphery thereof, teeth for engaging with a timing chain (or timing belt); a housing  6  located forward of the rotation portion, for rotatably housing the rotation member  3 ; and a front cover and a rear cover (both not shown) for closing the front and rear openings of the housing  6 . 
     Furthermore, the housing  6  presents a cylindrical shape formed with both front and rear ends open and with four partition portions  13  protrudingly provided at positions on the inner peripheral face at 90° in the circumferential direction. 
     The partition portions  13  present a trapezoidal shape in transverse section, and are respectively provided along the axial direction of the housing  6 . Each of the opposite end edges are in the same plane as the opposite end edges of the housing  6 , and on the base edge side are formed four bolt through holes  14  in the axial direction, through which bolts are inserted for axially and integrally coupling the rotation portion, the housing  6 , the front cover and the rear cover. 
     Moreover, inside of retention grooves  13   a  formed as cut-outs along the axial direction in central locations on the inner edge faces of each partition  13  are engagingly retained seal members  15 . 
     The rotation member  3  is secured to the front end portion of the cam shaft by means of a fixing bolt  26 , and comprises an annular base portion  27  having, in a central portion, a bolt hole through which the fixing bolt  26  is inserted, and four vanes  28   a ,  28   b ,  28   c , and  28   d  integrally provided on an outer peripheral face of the base portion  27  at 90° locations in the circumferential direction. 
     The first through fourth vanes  28   a  to  28   d  present respective cross-sections of approximate trapezoidal shapes. The vanes are disposed in the recess portions between each partition portion  13  so as to form spaces in the recess portions to the front and rear in the rotation direction. Advance angle side hydraulic chambers  32  and delay angle side hydraulic chambers  33  are thus formed between the opposite sides of the vanes  28   a  to  28   d  and the opposite side faces of the respective partition portions  13 . 
     Inside of respective retention grooves  29  notched axially in the center of the outer peripheral faces of the respective vanes  28   a  to  28   d  are engagingly retained seal members  30  for rubbing contact with inner peripheral faces of the housing  6 . 
     The lock mechanism  10  has a construction such that a lock pin  34  is inserted into an engagement hole (not shown) at a rotation position on the maximum delay angle side of the rotation member  3 . 
     Moreover, as shown in FIG. 2, the rotation member  3  (vanes  28   a  to  28   d ) has a construction such that one end thereof is secured to the front cover, and the other end is urged to the delay angle side by a spiral spring  36  serving as a resilient body, secured to the base  27  by a pin. 
     As the resilient body for urging the rotation member  3  (vanes  28   a  to  28   d ), an extension/compression coil spring, a torsion coil spring, a plate spring or the like may be used instead of the spiral spring  36 . 
     The hydraulic circuit  4  has a dual system oil pressure passage, namely a first oil pressure passage  41  for supplying and discharging oil pressure with respect to the advance angle side hydraulic chambers  32 , and a second oil pressure passage  42  for supplying and discharging oil pressure with respect to the delay angle side hydraulic chambers  33 . To these two oil pressure passages  41  and  42  are connected a supply passage  43  and drain passages  44   a  and  44   b , respectively, via an electromagnetic switching valve  45  for switching the passages. 
     An engine driven oil pump  47  for pumping oil inside an oil pan  46  is provided in the supply passage  43 , and the downstream ends of the drain passages  44   a  and  44   b  are communicated with the oil pan  46 . 
     The first oil pressure passage  41  is formed substantially radially in the base  27  of the rotation member  3 , and connected to four branching paths  41   d  communicating with each hydraulic chamber  32  on the advance angle side. The second oil pressure passage  42  is connected to four oil galleries  42   d  opening to each hydraulic chamber  33  on the delay angle side. 
     With the electromagnetic switching valve  45 , an internal spool valve is arranged so as to control relative switching between the respective oil pressure passages  41  and  42 , and the supply passage  43  and first and second drain passages  44   a  and  44   b . The switching operation is effected by a control signal from a controller  48 . 
     More specifically, as shown in FIG. 3, the electromagnetic switching valve  45  comprises a cylindrical valve body  51  insertingly secured inside a retaining bore  50  of a cylinder block  49 , a spool valve  53  slidably provided inside a valve bore  52  in the valve body  51  for switching the flow passages, and a proportional solenoid type electromagnetic actuator  54  for actuating the spool valve  53 . 
     With the valve body  51 , a supply port  55  is formed in a substantially central position of the peripheral wall, for communicating a downstream side end of the supply passage  43  with the valve bore  52 , and a first port  56  and a second port  57  are respectively formed in opposite sides of the supply port  55 , for communicating the other end portions of the first and second oil pressure passages  41  and  42  with the valve bore  52 . 
     Moreover, a third and fourth port  58  and  59  are formed in the opposite end portions of the peripheral wall, for communicating the two drain passages  44   a  and  44   b  with the valve bore  52 . 
     The spool valve  53  has a substantially columnar shape first valve portion  60  on a central portion of a small diameter axial portion, for opening and closing the supply port  55 , and has substantially columnar shape second and third valve portions  61  and  62  on opposite end portions, for opening and closing the third and fourth ports  58  and  59 . 
     Furthermore, the spool valve  53  is urged to the right in the figure, that is, in a direction such that the supply port  55  and the second oil pressure passage  42  are communicated by the first valve portion  60 , by means of a conical shape valve spring  63  resiliently provided between an umbrella-shaped portion  53   b  on a rim of a front end spindle  53   a , and a spring seat  51   a  on a front end inner peripheral wall of the valve bore  52 . 
     The electromagnetic actuator  54  is provided with a core  64 , a moving plunger  65 , a coil  66 , and a connector  67 . A drive rod  65   a  is secured to a tip end of the moving plunger  65  for pressing against the umbrella-shaped portion  53   b  of the spool valve  53 . 
     The controller  48  detects the current operating conditions (engine load, engine rotation speed) by means of signals from a rotation sensor  101  for detecting engine rotation speed and an air flow meter  102  for detecting intake air quantity, and detects the relative rotation position of the cam sprocket  1  and the cam shaft, that is to say, the rotation phase of the cam shaft with respect to the crank shaft, by means of signals from a crank angle sensor  103  and a cam sensor  104 . 
     The controller  48  controls the energizing quantity for the electromagnetic actuator  54  based on a duty control signal superimposed with a dither signal. 
     For example, when a control signal of duty ratio 0% (off signal) is output from the controller  48  to the electromagnetic actuator  54 , the spool valve  53  moves towards the maximum right direction in the figure, under the spring force of the valve spring  63 . As a result, the first valve portion  60  opens an opening end  55   a  of the supply port  55  to communicate with the second port  57 , and at the same time the second valve portion  61  opens an opening end of the third port  58 , and the third valve portion  62  closes the fourth port  59 . 
     Therefore, the hydraulic fluid pumped from the oil pump  47  is supplied to the delay angle side hydraulic chambers  33  via the supply port  55 , the valve bore  52 , the second port  57 , and the second oil pressure passage  42 , and the hydraulic fluid inside the advance angle side hydraulic chambers  32  is discharged to inside the oil pan  46  from the first drain passage  44   a  via the first oil pressure passage  41 , the first port  56 , the valve bore  52 , and the third port  58 . 
     Consequently, the pressure inside the delay angle side hydraulic chambers  33  becomes a high pressure while the pressure inside the advance angle side hydraulic chambers  32  becomes a low pressure, and the rotation member  3  is rotated to the full to the delay angle side by means of the vanes  28   a  to  28   d . The result of this is that the opening timing for the intake valves is delayed, and the overlap with the exhaust valves is thus reduced. 
     On the other hand, when a control signal of a duty ratio 100% (on signal) is output from the controller  48  to the electromagnetic actuator  54 , the spool valve  53  slides fully to the left in the figure, against the spring force of the valve spring  63 . As a result, the second valve portion  61  closes the third port  58  and at the same time the third valve portion  62  opens the fourth port  59 , and the first valve portion  60  allows communication between the supply port  55  and the first port  56 . 
     Therefore, the hydraulic fluid is supplied to inside the advance angle side hydraulic chambers  32  via the supply port  55 , the first port  56 , and the first oil pressure passage  41 , and the hydraulic fluid inside the delay angle side hydraulic chambers  33  is discharged to the oil pan  46  via the second oil pressure passage  42 , the second port  57 , the fourth port  59 , and the second drain passage  44   b , so that the delay angle side hydraulic chambers  33  become a low pressure. 
     Therefore, the rotation member  3  is rotated to the full to the advance angle side by means of the vanes  28   a  to  28   d . Due to this, the opening timing for the intake valve is advanced (advance angle) and the overlap with the exhaust valve is thus increased. 
     When a control signal having a duty ratio of 50% is output from the controller  48  to the electromagnetic actuator  54 , the spool valve  53  takes a position (neutral position) where the first valve portion  60  closes the supply port  55 , the second valve portion  61  closes the third port  58 , and the third valve portion  62  closes the fourth port  59 . 
     Moreover, the controller  48  sets by proportional, integral and derivative control action, a feedback correction amount PIDDTY for making a relative rotation position (rotation phase) of the cam sprocket  1  and the cam shaft  2  detected based on a signal from the crank angle sensor  103  and the cam sensor  104 , coincide with a target value (target advance angle value) for the relative rotation position (rotation phase) set corresponding to the operating conditions. The controller  48  then makes the result of adding a predetermined base duty ratio BASEDTY (neutral control value) to the feedback correction amount PIDDTY a final duty ratio VTCDTY, and superimposes a dither signal on the control signal for the duty ratio VTCDTY and outputs this to the electromagnetic actuator  54 . 
     The function of detecting the rotation phase based on a signal from the crank angle sensor  103  and the cam sensor  104  corresponds to a rotation phase detection means. 
     In the case where it is necessary to change the relative rotation position (rotation phase) in the delay angle direction, the duty ratio is reduced by means of the feedback correction amount PIDDTY, so that the hydraulic fluid pumped from the oil pump  47  is supplied to the delay angle side hydraulic chambers  33 , and at the same time the hydraulic fluid inside the advance angle side hydraulic chambers  32  is discharged to inside the oil pan  46 . Conversely, in the case where it is necessary to change the relative rotation position (rotation phase) in the advance angle direction, the duty ratio is increased by means of the feedback correction amount PIDDTY, so that the hydraulic fluid is supplied to inside the advance angle side hydraulic chambers  32 , and at the same time the hydraulic fluid inside the delay angle side hydraulic chambers  33  is discharged to the oil pan  46 . 
     Furthermore, in the case where the relative rotation position (rotation phase) is maintained in the current condition, the absolute value of the feedback correction amount PIDDTY decreases to thereby control so as to return to a duty ratio close to the base duty ratio. 
     The valve timing control by means of the controller  48 , will now be described in accordance with a flow chart in FIG.  4 . 
     In step S 1 , the engine rotation speed Ne is calculated based on a detection signal from the rotation sensor  101 . 
     In step S 2 , a target value of the rotation phase is set according to, for example, the engine load or the engine rotation speed Ne. 
     The part of this step S 2  corresponds to the target value calculation means. 
     In step S 3 , the cooling water temperature Tw of the engine is detected based on a detection signal from a water temperature sensor  105 . 
     In step S 4 , a base duty ratio BASEDTY corresponding to the target value and the engine rotation speed Ne at that time is retrieved from a map in which is pre-stored the base duty ratio BASEDTY (neutral control value) in accordance with the target value and the engine rotation speed Ne. 
     The part of this step S 4  corresponds to the neutral control value calculation means. 
     Since the urging force of the spiral spring  36  varies due to the rotation phase, then when the valve is driven about the valve position corresponding to the neutral control value, using a constant neutral control value regardless of the rotation phase, the rotation phase is shifted toward the delay angle side or the advance angle side, depending on whether the neutral control value is higher or lower than a suitable urging force. Therefore, by setting the base duty ratio BASEDTY according to the target value, supply and discharge of the oil to each hydraulic chamber are performed at a balance corresponding to the urging force of the spiral spring  36  to thereby suppress the occurrence of steady-state deviation. 
     Moreover, with the switching of the base duty ratio BASEDTY in accordance with the engine rotation speed Ne, the oil pressure is estimated from the engine rotation speed Ne, and the switching of the base duty ratio BASEDTY is performed corresponding to the oil pressure. 
     As mentioned before, since the oil pump  47  is driven by the engine, and the pump rotation speed is proportional to the engine rotation speed Ne, the oil pressure can be estimated from the engine rotation speed Ne. On the other hand, since the base duty ratio BASEDTY required for retaining the rotation phase varies depending on the oil pressure, the base duty ratio BASEDTY is changed corresponding to the engine rotation speed Ne. 
     However, the construction may include an oil pressure sensor for directly detecting the oil pressure, or for the simplicity, the above described switching of the base duty ratio BASEDTY in accordance with the oil pressure (engine rotation speed Ne) may be omitted. 
     In step S 5 , a correction coefficient for correcting and setting the base duty ratio BASEDTY is set corresponding to the cooling water temperature Tw, based on the cooling water temperature Tw of the engine detected by the water temperature sensor  105 . 
     The correction coefficient is set to a larger value with a decrease of the water temperature Tw, so that the base duty ratio BASEDTY is increasingly corrected with a decrease of the water temperature Tw. 
     The water temperature Tw is used as a temperature representative of the temperature of the hydraulic fluid. As a result, the base duty ratio BASEDTY can be corrected and set corresponding to the requirement of the base duty ratio BASEDTY which differs according to the temperature (viscosity) of the hydraulic fluid. 
     Accordingly, the water temperature sensor  105  corresponds to the oil temperature detecting means, and the part of this step S 5  corresponds to the correction coefficient calculation means. 
     In step S 6 , the base duty ratio BASEDTY is corrected with the correction coefficient, to thereby determine the final base duty ratio BASEDTY. 
     The part of this step S 6  corresponds to the correction means. 
     In step S 7 , the feedback correction amount PIDDTY is set by PID control based on the target value and the actual rotation phase. 
     The part of this step S 7  corresponds to the feedback correction value calculation means. 
     Then, in step S 8 , the feedback correction amount PIDDTY is added to the base duty ratio BASEDTY to thereby determine the final duty ratio. A dither signal is then superimposed on a control signal for the determined duty ratio and the obtained signal is output to the electromagnetic actuator  54 . 
     The part of this step S 8  corresponds to the valve control means. 
     Here, the above construction is described as being for controlling the valve timing of the intake valve, but the construction may be for controlling the valve timing of the exhaust valve. In this case, the construction may be such that when a control signal having a duty ratio of 100% (on signal) is output to the electromagnetic actuator  54 , the timing is controlled so as to be delayed (the overlap quantity is maximum), and when a control signal having a duty ratio of 0% (off signal) is output to the electromagnetic actuator  54 , the timing is controlled so as to be advanced (the overlap quantity is minimum). Moreover, the vanes (rotation body  3 ) may be urged to the advance angle side by the spiral spring  36 .