JPH02199274A - Glow plug voltage detecting method - Google Patents

Abstract

PURPOSE:To accurately detect a glow plug voltage by providing an A/D converter which detects the voltage of a glow plug on the energizing current of which duty control is made and is operated in non-linkage with duty control. CONSTITUTION:Glow plugs 5 are mounted facing corresponding cylinders and are individually controlled by a microcomputer 1. When an MPU 1 brings a duty output into an ON-state, an output from a buffer 3 is increased to H (high), and a power is fed to the glow plug 5. On the contrary, when the MPU 1 brings the duty output into an OFF-state, an output from the buffer 3 is brought into an open state, and no power is fed to the glow plug 5. This method enables accurate detection of a glow plug voltage maintaining a given relation between duty ON and OFF.

Description

[Detailed Description of the Invention] [Summary] In a system that controls the power of a glow plug by changing the duty of the current, the glow plug voltage (v6) is
When the D conversion timing is asynchronous with the duty output timing, the duty is turned ON on the condition that the duty state does not change before and after the A/D conversion timing.
Detects V at the time or OFF, and also detects the duty OFF.
By using the memory of F, it is possible to detect (2) immediately after duty is turned on.

[Industrial application field]

The present invention relates to a method for detecting glow plug voltage in a system that detects the voltage of a glow plug that is subject to duty control asynchronously with the duty control, converts it into an A/D converter, and captures the voltage.

(Prior art) Glow plugs used for preheating diesel engines are initially energized at 100% duty (when energization starts), and after heating and temperature rise, the duty is set to an appropriate value to avoid overheating of the glow plug and power loss. In addition, the inside of the cylinder is kept at an appropriate temperature.This requires energization control and duty control of the glow plug according to outside air temperature, cooling water temperature, battery voltage, etc.

Since the glow plug is a heat generating resistor, the power consumption W has a relationship with the resistance value Rt and the voltage c across it.

When the power We of the glow plug is controlled by the on/off ratio (duty ratio) of the applied current, the equation 0 becomes as follows.

However, the duty ratio of the glow plug temperature TG depends on the power W, and the power We
If is constant, the glow plug temperature Te can also be considered to be constant. The resistance value RG of the glow plug changes depending on the temperature as shown in FIG. 3, but it can be considered to be constant in a steady state except when the current is started.

However, the glow plug voltage ■. varies according to battery voltage, etc. Therefore, in order to keep the power W6 constant regardless of the fluctuations in ■, It is necessary to change the duty appropriately depending on the situation. For example, if the duty is changed according to the following equation, where K is a constant, the power consumption WG of the glow plug can be kept constant.

This duty control uses glow plug voltage■. , it is also necessary to detect the duty-on state.

Glow plug voltage■. Specifically, it is not constant during the duty ON period but changes slightly. That is, it tends to be low at first and then gradually rise. Therefore, in precision ■. needs to be a function of time, but simply the duty ON
■ When it became. You can find vG at a specific point in time, or find the average of the first and last (2) of the duty ON period, and use this to calculate the formula 0.

In the glow plug energization control, the duty is output by a control circuit such as a microcomputer of the engine control unit. This microcomputer determines the duty by taking in the glow plug voltage vG, cooling water temperature, etc.
output it.

[Problem to be solved by the invention]

By the way, glow plug voltage ■. Since is an analog value, the microcomputer needs to A/D convert it before importing it. The timing of this A/D conversion is not synchronized with the duty output timing, so during the duty ON period, OFF period, or switching,
I will be coming to Therefore, simply calculate the glow plug voltage ■6
By performing sampling and A/D conversion, we obtain (■). ■ Immediately after duty is turned on (power is turned on). , V at the beginning and end of duty ON cannot be detected correctly.

Glow plug voltage■. It is also important to know when the power supply is turned off, as this allows you to know if the glow plug is disconnected, etc.

The present invention is intended to deal with this problem, and includes glow plug voltage (2) that is performed asynchronously with the duty output timing. In the detection of the duty ON10 F
■ Maintaining a predetermined relationship with F.

The purpose is to make it possible to detect correctly.

[Means to solve the problem]

The present invention controls the power of the glow plug by the duty ratio of the current flowing through it, and detects the voltage of the glow plug at a detection timing that is asynchronous to the duty output timing.
In a glow plug voltage detection method in a system that converts and imports D, duty on and off are checked before and after the A/D conversion timing, and when duty on and off do not change before and after the A/D conversion timing, the A/D conversion value is set as duty on. Alternatively, the glow plug voltage is set to be the glow plug voltage when the duty is off, and the fact that the duty is turned off is memorized, the glow plug voltage is detected during the period when the duty is on, A/D conversion is performed, and the memory is stored. is checked, and if duty-off is stored, the A/D conversion value is set as the glow plug voltage immediately after duty-on, and the storage is erased.

(Function) Same duty ON before and after A/D conversion timing
Or, if it is in the OFF state, the A/D conversion value is the glow plug voltage ■ in the duty ON or OFF state. It shows. If the duty is ON before the A/D conversion timing and the duty is OFF after the A/D conversion timing, or vice versa, the obtained vG is an undefined 6m G during duty 0N10FF switching and is not to be collected.

This is the principle of the first method of the present invention.

Also, remember the duty OFF and set the duty OFF.
Sampling the glow plug voltage with N, converting it A/D,
After that, I checked the memory and it was the duty OF.
If F, the A/D conversion value is changed to ■ immediately after duty is turned on.
. It can be treated as closed. At this time, the memory is cleared, which is the second method of the present invention.

Note that in the first method, the duty is in the ON state, and in the same duty OFF state. When detected, the former can detect a short circuit in the glow plug (GP), and the latter can detect a disconnection of the plug. The detection logic is shown below.

Table 1 V when the circuit is turned on is 10B even if the GP is normal and 10P is disconnected, but it is 0■ if the CP is shorted. It will be clear from FIG. 1, which will be described later, that this is the case. This allows you to know if there is a GP short circuit. Also duty OF
■ at F time. is 0■ when the GP is normal, and Ov even when the CP is short-circuited, but it is 10B when the CP is disconnected. This makes it possible to know if the CP is disconnected.

〔Example〕

Figure 1 is a configuration diagram of the present invention, where 1 is a microcomputer (MPU), 2 is an A/D converter (ADC), 3.4 is a buffer, 5 is a glow plug (GP), and R is a The disconnection detection resistor having a large resistance value (for example, several ohms) and 10B is the battery voltage. GP5 is provided corresponding to each cylinder and individually controlled by MPUI, but only one of them is shown here. When the MPUI turns on the duty output, the output of the buffer 3 becomes H (high) +B, a voltage of 10 B is applied to the GP 5, and power is supplied. In response, MPUI outputs the duty
When set to FF, the output of buffer 3 becomes an oven state,
Since current only flows through the resistor R in GP5, G
The voltage of P5 is v, =- and - (+B) R+Re where R>> RG, so 81=O, so V, ~ (10B) -R+0 20, and no power is supplied. In the old method, a relay was used instead of buffer 3 to control the energization, but
Recently, there has been a trend to use semiconductors for this part. In this case, buffer 3 is a transistor circuit, and CP! 111
It consists of a transistor that connects the output terminal with one output to power supply element B, and a transistor for controlling this.

The buffer 4 detects the voltage 6 across the GP 5 using high and large interference resistance and inputs it to the ADC 2. The ADC 2 A/D converts this at a constant sampling period, but its operation is not synchronized with changes in the duty output. Therefore,
As shown in P++Pz+... in Figure 2, ■. The sampling points vary, resulting in various points on the Va curve in the same figure. There is a risk that it may be collected. Duty ON state (7) VG (pt ~ p,
VG in the same OFF state (VG in Pg to P), VG immediately after duty is ON (VC at PI point)
is not necessarily obtained.

Therefore, in the first aspect of the present invention, the A/D conversion value when the duty state is the same before and after the A/D conversion timing is adopted as the 6 value of that state. FIG. 4 is a flowchart showing this process.

Step 31 is the determination of the current duty state. Since the MPUI determines the duty output, this can be immediately determined by looking at this. If the result of this determination is that the duty is ON, the duty state flag is set to 1 in step S2, and if the duty is OFF, the flag is set to 0 in step S3. Of course, the duty state flag 1 of this flag 1 indicates that the duty is OFF.

After processing this flag, in step S4, the VC value is set to A.
/D conversion processing.

Next, in step S5, it is determined whether the flag is 1 or 0, and if it is 1, the current duty state is determined in step S6, and if it is 0, the current duty state is determined in step S7. A/D in step S6
If it is determined that the duty after the conversion process is ON, it is determined in step S5 that the duty is ON before the A/D conversion process, so the A/D conversion value of ■ is set to GP ON in step S8. (when duty is ON). On the other hand, if it is determined to be OFF in step S6, the A/D conversion process in step S4 is on duty.
Since there is a possibility that the conversion was performed at a change point from OFF to OFF, the conversion value ① is not stored (discarded) in step S9. Steps 310 and 311 perform this for duty OFF. In this way, duty O
VG% in the N state and ■ in the OFF state are correctly obtained.

In this example, V6 is in the duty ON state (or OFF state B).
The value is repeatedly detected at the A/D conversion timing, but immediately after the duty is turned on, it is not possible to determine which value it is.The second invention deals with this problem, and its flowchart is as follows. are shown in FIGS. 5 and 6.

Steps 31 to 36, 38, and 39 in FIG. 5 have the same content as in FIG. 4, but a new step 321 is inserted between step S6 and step S8, and steps 322 to
S24 is added separately.

In FIG. 4, when it is determined that it is ON in step S6, the process immediately moves to step S8, but in FIG. 5, the determination in step 321 is interposed. The GP OFF flag in step S21 is set in step S3 in FIG. 6 when the duty is OFF.
4 (becomes l), and after the duty is turned on again, step S22 is passed through step S22 in FIG.
It is cleared (becomes 0) at 3.

Step S21. If it is determined that the GP OFF flag = 1, there is no doubt that the duty is ON before and after the A/D conversion process in step S4, but since the duty was OFF until just before, the A/D conversion value is changed in step S22. is stored as the value immediately after the GP is turned on. After this storage, the GP OFF flag is set to O in step S23. This is the difference from FIG. 4.

If it is determined in step 321 that the GP OFF flag is -0, it is unknown how much time has passed since the duty was turned OFF from OFF, but in step S22. After passing through S23, therefore, it is not immediately after the CP is turned on, so in step S8, it is simply stored as the 6 value when the CP is turned on.

Incidentally, if the determination is O in step S5, the process moves to step 324, and the A/D conversion value at the time of duty OFF is not stored.

FIG. 6 is a flowchart of duty output control, and step 330 is determination of duty ON10 FF output timing. If it is determined that it is the ON timing, the duty output is turned ON in step 331, and the OF
If it is determined that it is the F timing, the duty output is turned OFF in step S32. After turning on the duty output in step S31, the stored CP
The VG value at the time of ON is stored in another memory as the VG value immediately before GP is turned off, that is, the last VG value when CP is turned on. With this process, the second
24 points ■ in the figure. Values can be stored in memory. Also,
After the duty output is turned OFF in step S32, the GP OFF flag is set to 1 in step S334. This corresponds to point 26 (■) in FIG. 1 at step S22 in FIG. This is to store the value.

If you can memorize the Vi values of points P, , and P in Figure 2, the average of both is ■. The average value can be calculated.

〔Effect of the invention〕

As described above, according to the present invention, the voltage of the glow plug whose energizing current is duty-controlled is controlled at duty 0 by using an A/D converter that operates asynchronously with the duty control.
It can be reliably detected by having a certain relationship with the N10FF state.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of the present invention, Fig. 2 is an explanatory diagram of the operation of the present invention, Fig. 3 is a temperature characteristic diagram of the glow plug, Fig. 4 is a flowchart of the first invention, and Fig. 5 is a flowchart of the second invention.
FIG. 6 is a flowchart of duty output control. In the figure, ■ is a microcomputer, 2 is an A/D converter,
3 is a buffer for duty control, and 5 is a glow plug. Applicant Fujitsu Ten Ltd. Representative Patent Attorney Minoru Aoyagi Figure 2 Figure 8 Figure N6

Claims (2)

[Claims] 1. The power of the glow plug (5) is controlled by the duty ratio of the energizing current, and the voltage (V_
In the glow plug voltage detection method in a system that detects G) and imports it by A/D conversion, check whether the duty is on or off before and after the A/D conversion timing, and if the duty on or off does not change before or after the A/D conversion timing. A glow plug voltage detection method characterized in that the A/D conversion value is used as the glow plug voltage (V_G) when the duty is on or off. 2. The power of the glow plug (5) is controlled by the duty ratio of the energizing current, and the voltage (V_
In the glow plug voltage detection method in a system that detects G) and converts it to A/D and imports it, remember that the duty is off, and detect the glow plug voltage (V_G) while the duty is on. and performs A/D conversion, and checks the memory, and if duty off is stored, the A/D converted value is set as glow plug voltage (V_G) immediately after duty is turned on, and the memory is erased. Glow plug voltage detection method.