The present invention relates to a method and a device for measuring the period of time which a valve needle of a piezo control valve requires to move from a first end position into a second end position.
Piezo control valves are used in piezo pump nozzle units (PPE) for metering quantities of fuel in internal combustion engines. DE 100 38 995 A1 has already disclosed such a PPE. In this PPE, the pump and the nozzle form one unit. The pump is actuated by means of a motor cam shaft, either directly by means of a tappet or indirectly by means of valve lifters. The piezo control valve is actuated by means of an actuation unit in such a way that in a first end position it is completely opened and in a second end position it is completely closed. When the control valve is opened, the fuel is forced back during the piston stroke into the fuel low-pressure region by the pump piston via the piezo control valves. If the control valve closes, the pump piston cannot force the fuel back into the fuel low-pressure region. The fuel is compressed, which leads to an increase in pressure in the high-pressure region of the pump unit. If the pressure in the pump unit exceeds the opening pressure of the injection nozzle, fuel is injected into the combustion chamber of the internal combustion engine. The closing time of the control valve determines the time when the fuel is injected and the closing period of time determines the injection quantity.
The actuation unit of the PPE is composed of a piezo-actuator. The extent of the piezo-actuator is proportional to the voltage (u (t)) which is applied to the piezo-actuator and/or the current (i (t)) which is applied. So that the variation in the injection quantities is as small as possible, the piezo-actuator must be actuated as precisely as possible by a precisely defined voltage (u (t)) and/or a precisely defined current (i (t)) in order to set the start, period and end of the injection process. Wear, aging processes and temperature changes give rise to changed closing times and opening times of the piezo control valve, as a result of which precise control of the injection quantity of fuel is no longer ensured.
DE 199 10 388 C2 discloses a method for checking a capacitive actuator element for satisfactory functioning. The checking of the actuator element is carried out by comparing the period for which the actuator element is activated with the length of the control signal which is responsible for the activation of the actuator element. It is assumed that the actuator element is functioning satisfactorily if the measured period for which the actuator element is activated lies within a region which is determined by the length of the control signal.
The invention is based on the object of implementing a method and a device which precisely determine the actual closing and opening times of the control valve. The object can be achieved by a method for measuring a period of time which the valve needle of a control valve of a piezo pump nozzle unit requires, taking into account the response time of the control valve, to move from a first end position into a second end position, comprising the steps of determining the period of time as a function of a voltage and/or a current which are applied to the control valve, generating an actuation signal in order to move the control valve from the first end position into the second end position, and generating the actuation signal at a time at which it is ensured that a pressure in the control valve and in an injection nozzle corresponds largely to a pressure of a fuel low-pressure range during measurement.
The period of time can be measured on a running engine within the period in which a cam shaft is located within its base circle with respect to a pump piston of the injection nozzle or a corresponding transmission elements. The period of time can be measured when a cam shaft is stationary. The fact that the first end position or second end position has been reached can be detected by means of at least one irregularity in the course of the voltage and/or in the current. The first or second end position, can be detected by means of at least one pulse in the profile of the voltage and/or of the current.
The object can also be achieved by a device for measuring a period of time which the valve needle of a control valve of a piezo pump nozzle unit requires to move from a first end position into a second end position taking into account the response time of the control valve, the device comprising a control device comprising the following components: an evaluation unit which determines the period of time as a function of a voltage and/or a current which are applied to the control valve, and a control unit which generates an actuation signal in order to move the control valve from the first end position into the second end position and generates the actuation signal at a time at which it is ensured that a pressure in the control valve and in an injection nozzle corresponds largely to the pressure of a fuel low-pressure region during measurement.
The evaluation unit may comprise a circuit which includes the detection of at least one irregularity or a pulse in the profile of the voltage and/or of the current by evaluating the voltage and/or the current.
The invention is characterized in that the measurement of the actual closing and opening time of the control valve is carried out as a function of the voltage (u (t)) which is applied to the control valve and/or the current (i (t)) which is applied, within the time interval in which the pressure in the control valve corresponds largely to the pressure of the low-pressure region. As a result, the very strong pressure surges which are caused by the hydraulics and which arise when the valve needle closes or opens quickly are avoided. This has a positive effect on the closing and opening behavior of the valve needle. In particular, a stuttering valve needle stroke, caused by the pressure surges, is avoided, allowing the closing and opening times of the control valve to be determined more precisely.
One advantageous refinement of the invention provides for the measurement of the period of time for which the valve needle moves from the one end position into the other end position to be carried out on the running engine, within the period within which the cam shaft is located within its base circle with respect to the pump piston of the injection nozzle or the corresponding transmission elements. In this time, the pump piston of the pump unit remains in its upper end position, and the pressure in the control valve thus corresponds approximately to the pressure in the fuel low-pressure region.
A further advantageous refinement of the invention provides for the measurement of the period of time for which the valve needle moves from the one end position into the other end position to be carried out when the cam shaft is stationary (engine off). In this case, the pump piston does not carry any stroke and it is ensured that a movement of the valve needle does not lead to pressure surges within the control valve.
The invention will be explained in more detail below with reference to the drawings, in which:
If the control valve 21 is closed by means of the externally actuable actuation unit 22 before or during the delivery stroke of the pump piston 4, the fuel in the pump chamber 5 is compressed. If the pressure in the pump chamber 5 exceeds the opening pressure of the injection nozzle 10, the injection nozzle opens and fuel is injected into the combustion chamber of the internal combustion engine.
The first end position may also be the position in which the control valve 21 is completely closed. The second end position then corresponds to the position in which the control valve 21 is completely opened. The closing or opening time of the control valve 21 is then measured in a way which is analogous to the description in the exemplary embodiments. The valve needle 50 is actuated by means of a piezo-actuator 55. If the piezo-actuator 55 is electrically charged, it expands and transmits a force to the pressure element 57 via the end face 56. The pressure element 57 is in contact with a first lever 58 and a second lever 59. The force, which is transmitted to the pressure element 57 via the piezo-actuator 55, is amplified by means of the levers 58 and 59 and is transmitted to a first axial end face 70 of the valve needle 50. If the force which is generated by the piezo-actuator 55, transmitted via the pressure element 57 and amplified by means of the levers 58 and 59 is greater than a counteracting force, which is transmitted by a spring 71 to a second axial end face 73 of the valve needle 50 via a spring end piece 72, the valve needle 50 is pressed into the valve seat 51. The fuel low-pressure region 31 is connected to the spill chamber 60 which is connected to the actuator chamber 62 via a compensation bore 61. The actuator chamber 62 is itself connected to the return duct 63, via which the fuel can flow out of the actuator chamber 60 and back into the fuel low-pressure region 31.
As soon as the program for regulating the valve closing time starts, a measurement firstly takes place in a first step S0, said measurement determining whether the cam shaft 2 is stationary or rotating. When the cam shaft 2 is stationary, the pressure in the control valve 21 and in the injection nozzle 10 largely corresponds to the pressure of the fuel low-pressure region 31 independently of the cam shaft position and the position of the pump piston 4, and the closing process of the control valve 21 can be carried out, as described later starting from step S3a.
If the cam shaft 2 is rotating, in a step S1 the sensor 90 firstly determines the position P1ST in which the cam shaft 2 is located at a particular time. For this purpose, for example a cam shaft rotation-speed sensor can be used as the sensor 90. As an alternative it is also possible to use a position sensor. In a step S2, the instantaneous position P1ST is compared with a stored position PSTART. In the position PSTART the cam shaft 2 is preferably located in the vicinity of the cam trailing edge AB with respect to the pump piston 4 within its base circle G. The pump piston 4 is in its upper initial position at this time, and the pressure in the control valve 21 and in the injection nozzle 10 corresponds largely to the pressure of the fuel low-pressure region 31. If P1ST is equal to PSTART, the measurement of the valve closing time begins. The closing process of the control valve 21 is initiated in step S3a in which a standardization pulse SON, by which the actuation unit 22 is actuated, is set. The time tSON of the actuation is stored in step S3b, and the piezo voltage UPIEZO and/or the piezo current iPIEZO or the actuation energy EPIEZO is applied to the piezo-actuator 55 within the step S3c and/or S3c′. As a result, a charge is generated in the piezo-actuator 55, as a result of which the piezo-actuator 55 expands. The expansion of the piezo-actuator 55 causes the valve needle 50 to start to move from its first end position 64 into its second end position 65.
If the valve needle 50 impacts in the valve seat 51, a force is transmitted to the piezo-actuator 55 by the mechanical coupling of the valve needle 50 to the piezo-actuator 55. The sudden application of force to the piezo-actuator 55 when the valve needle 50 impacts in the valve seat 51, causes a charge to be suddenly induced in the piezo-actuator 55, said charge being proportional to the force acting. Since the force is proportional to the piezo voltage uPIEZO and proportional to the integral of the piezo current ∫iPIEZO, a sudden change in the charge, which is equivalent to the valve needle arriving in the valve seat, can be detected directly by means of the derivative of the piezo voltage u′PIEZO and/or of the piezo current iPIEZO. For this purpose, the derivative of the piezo voltage u′PIEZO is formed during the closing process of the control valve 21 in a step S4, and the profile of the derived piezo voltage u′PIEZO or the profile of the piezo current iPIEZO is compared with a threshold value u′SCHWELL and iSCHWELL in a step S5 and S5′. If the derived voltage u′PIEZO or the current iPIEZO exceeds the corresponding threshold values u′SCHWELL or iSCHWELL, the program detects that the control valve 21 is closed. The time tc at which the threshold value is exceeded and which corresponds to the closing time of the control valve 21 is sensed in a further step S6 and stored. The actual closing time tV
Number | Date | Country | Kind |
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102 25 911.9 | Jun 2002 | DE | national |
This application is a continuation of copending International Application No. PCT/DE03/01858 filed Jun. 3, 2003 which designates the United States, and claims priority to German application no. 102 25 911.9 filed Jun. 11, 2002.
Number | Date | Country | |
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Parent | PCT/DE03/01858 | Jun 2003 | US |
Child | 11009980 | Dec 2004 | US |