Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
1999-08-04
2001-07-10
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090170
Reexamination Certificate
active
06257184
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for diagnosing a hydraulic variable valve timing mechanism, and in particular to technology for diagnosing a fault in a hydraulic variable valve timing mechanism in which the valve timing is changed by oil pressure.
2. Description of the Related Art
Variable valve timing mechanisms which advance or retard the open-close timing of an intake valve and/or an exhaust valve in a vehicle engine by using oil pressure to change the rotational phase of a cam shaft with respect to a crank shaft have been previously reported (refer to Japanese Unexamined Patent Publication No. 7-233713 and Japanese Unexamined Patent Publication No. 8-246820).
However, with the conventional variable valve timing mechanism mentioned above, when a fault diagnosis is conducted by comparing a target valve timing (target rotational phase) and an actual valve timing (actual rotational phase), various problems can arise, as detailed below.
With a hydraulic variable valve timing mechanism, a stepwise change of the target valve timing results in the actual valve timing gradually approaching the changed target due to a response delay in the oil pressure.
As a result, the problem arises that a comparison of the actual valve timing with the target valve timing immediately following a stepwise change of the target valve timing, produces a misdiagnosed fault based on the existence of a relatively large deviation between the two values.
In particular, if the oil drains out of the hydraulic chamber of the variable valve timing mechanism during the engine is stopped, then the first change of the valve timing following engine start-up will require the hydraulic chamber to be refilled with oil in order to generate the oil pressure necessary for changing the valve timing. Therefore, in relation to the valve timing change command the actual valve timing will change even more slowly than normal, increasing the possibility of a misdiagnosed fault.
Furthermore, in those cases where the actual valve timing is detected as the rotational phase of a cam shaft with respect to a crank shaft, then for example when a construction is used wherein a plate supported on the cam shaft incorporates a plurality of detection portions which are detected by an electromagnetic pickup detector or a Hall element detector, then due to deviations in the positions of the detection portions, deviations develop in the detection results for the rotational phase values at each detection portion even though the valve timing (rotational phase) is actually constant. Consequently the possibility arises that the detected value for the rotational phase may temporarily exceed the fault judgment level resulting in a misdiagnosed fault.
SUMMARY OF THE INVENTION
The present invention takes the above problems into consideration, with the object of providing an apparatus and a method for diagnosing a hydraulic variable valve timing mechanism, wherein misdiagnoses resulting from a response delay in the actual rotational phase with respect to a change of the target rotational phase can be avoided, while opportunities for conducting diagnoses can still be maintained.
Furthermore, another object is to provide a diagnosis apparatus and method wherein even in those cases where the oil has drained out during the engine was stopped, a misdiagnosis during the first valve timing change following start-up can be avoided, while opportunities for conducting diagnoses can still be maintained at a sufficient level.
Moreover, yet another object is to provide a diagnosis apparatus and method wherein even in those cases where a deviations exists in the detection results for the rotational phase values, misdiagnosis of a fault will not result.
In order to achieve the above objects, the present invention employs a construction where the presence of a fault is judged from the results of a comparison between a detection value of the rotational phase of a cam shaft with respect to a crank shaft and a target value for the rotational phase, and a fault judgment signal is then output. The time period for where a response delay in the rotational phase occurs with respect to the change in the target value is estimated in accordance with the operating conditions, and the output of the fault judgment signal is prevented for the duration of the thus estimated time period.
With such a construction, because diagnosis (output of a fault judgment signal) is prevented during the period for where a response delay occurs in the rotational phase, even if a large deviation develops between the actual rotational phase and the target value due to a response delay, a misdiagnosis will not occur. Furthermore, because the time period for where a response delay occurs is estimated in accordance with the operating conditions, even if the response characteristics vary due to the operating conditions, diagnosis (output of a fault judgment signal) can be prevented for just the period during which a response delay occurs.
The response delay time period required for the rotational phase to reach the target value following a change of the target value can be estimated in accordance with the rotational speed of the engine, with diagnosis (output of a fault judgment signal) then being prevented for the duration of the thus estimated time period.
With such a construction, in the case where the pump which supplies hydraulic fluid to the hydraulic variable valve timing mechanism is driven by an engine, the discharge capacity of the pump will vary in proportion to the engine rotational speed, resulting in a change in the response characteristics of the oil pressure. Therefore the response delay time period can be estimated in accordance with the change in the response characteristics of the oil pressure due to the engine rotational speed.
Furthermore, the response delay time period required for the rotational phase to reach the target value following a change of the target value can also be estimated in accordance with the temperature of the hydraulic fluid, with diagnosis (output of a fault judgment signal) then being prevented for the duration of the thus estimated time period.
With such a construction, since the viscosity of the hydraulic fluid changes in accordance with the temperature of the fluid, and the response characteristics of the oil pressure changes with the change in the viscosity, the response delay time period is estimated in accordance with the change in the response characteristics of the oil pressure due to the temperature of the hydraulic fluid.
Furthermore, the response delay time period required for the rotational phase to reach the target value following a change of the target value can also be estimated in accordance with the amplitude of the change in the target value, with diagnosis (output of a fault judgment signal) then being prevented for the duration of the thus estimated time period.
With such a construction, the greater the amplitude of the change in the target rotational phase the longer the length of time required for the actual rotational phase to reach the target. Therefore the response delay time period can be estimated in accordance with the change in the response time due to the amplitude of the change in the target.
Moreover, the response delay time period required for the rotational phase to reach the target value following a change of the target value can also be estimated based on whether or not the change in the target value is the first change following start-up of the engine, with diagnosis (output of a fault judgment signal) then being prevented for the duration of the thus estimated time period.
With such a construction, when the rotational phase target is changed for the first time following engine start-up there is a possibility that the hydraulic chamber, which may have drained during the time the engine was stopped, will require refilling with oil, which will result in the response delay time period being even longer than normal. Therefore by determining whether
Watanabe Satoru
Yamagishi Youichiro
Dahbour Fadi H.
McDermott & Will & Emery
Unisia Jecs Corporation
Walberg Teresa
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