JPS59119070A - Method for controlling glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To enable to detect current supplied to a glow plug correctly by way of A/D conversion even if the intensity of current supplied to the glow plug is low, by controlling the period of a control pulse signal in relation to the time length when a power amplifier is energized. CONSTITUTION:A control pulse signal supplied to an amplifier for controlling the time length for feeding current to a glow plug has a frequency of 50Hz. The time length S when the glow plug is energized is calculated at a step 92 at the time t=(Sb-2)msec, and starting of energization is effected at a step 111 at the time t=Sbmsec. Further, starting of A/D conversion is effected at a step 119 at the time t=Sb+5msec, and termination of energization of the amplifier is effected at a step 126 at the time t=Sb+S (Si energization time). Thus, since the period of the control pulse signal is controlled in relation to the time length when the power amplifier is energized, current supplied to the glow plug can be detected correctly by way of A/D conversion even if the intensity of current is low.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a glow plug for a diesel engine using a digital processor.

In a diesel engine, a glow plug is provided in the pre-combustion chamber, and glow (preheating) is performed at the time of starting, so that the air-fuel mixture can be ignited smoothly at the time of starting. However, in the conventional method of controlling the temperature of glow plugs, signals are processed by analog circuits, and relays,
Hardware elements such as timers are used, which complicates the control circuit, increases costs, and makes it difficult to precisely control the glow plug temperature.

Therefore, in a previous application, the present applicant disclosed a control method for controlling the glow plug temperature using a digital processor.

That is, in the control method of this prior application, a power amplifier is connected in series with the glow plug that heats the pre-combustion chamber, and a first voltage related to the terminal voltage of the glow plug during the conduction period of the power amplifier is converted from analog to digital. The temperature of the glow plug is detected by the digital processor, and the duty ratio of the control pulse signal of the power increaser A is subtracted from the comparison between the actual temperature of the glow plug and the target temperature. Current is passed through the glow plug.

In the control method of this earlier application, the power amplifier alternately turns on (conducting) and off (non-conducting) in relation to the control pulse signal. The first voltage during the period when the voltage drop is A
/D (analog/digital) conversion to detect the actual temperature of the glow plaque. In this way, when the actual temperature of the glow plug becomes lower than the target temperature, in order to lower the glow plug temperature, the on-time of the power amplifier is reduced to reduce the energizing time of the glow plug and therefore the energizing current, but the A/D conversion The maximum/IX limit time is the 1st
It is necessary to maintain the input voltage almost constant, and if the energization time of the glow plug becomes shorter than this minimum time, the first voltage during the period when the voltage drop due to the energization current occurs in the glow plug is There is a problem that A/D conversion becomes difficult and the glow plug temperature cannot be detected accurately.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling a glow plug for a diesel engine, in which the temperature of the glow plug can be accurately detected by A/D conversion even when the current flowing through the glow plug is small.

To achieve this object, according to the method of controlling a glow plug for a diesel engine of the present invention, the period of the control pulse signal is controlled in relation to the length of the conduction period of the power amplifier.

In this way, by controlling the period of the control pulse signal in relation to the length of the conduction period of the power amplifier, the first voltage must be maintained for the minimum time for A/D conversion. is ensured within the energization period of the glow plug, and the temperature of the glow plug can be accurately detected.

In a preferred embodiment, the period of the control pulse signal is switched in relation to the length of the conduction period of the power amplifier, and hysteresis is added to this switching. This hysteresis therefore prevents hunting.

The invention will now be described in detail with reference to Figure ulj.

FIG. 1 shows an overview of the control circuit. Glow plugs l provided in each pre-combustion chamber of a four-cylinder diesel engine are connected in parallel to each other, and are connected to a power supply terminal 4 of a predetermined voltage element B of DC current via a current detection resistor 2 and a power amplifier 3. has been done. The current detection resistor 2 is connected in series to the glow plug 1. Voltage dividing resistor 5
, 6 are connected to each other in series and are provided between the power supply terminal of the glow plug 1 and the ground. Further, other voltage dividing resistors 7 and 8 are connected in series with each other and are provided between the power supply side terminal of the current detection resistor 2 and the ground. The electronic control unit 11 is a digital processor CPυ12.
, ROM 13, RAM 14, A/D (analog/
A digital converter) 15 and an input/output port 16 are provided, and these elements 12 to 16 are connected to each other by an address data bus 17. 5 points of voltage dividing resistors 19, 20
Maximum 11L voltage of A/D 15' human power voltage, 1
The values of the voltage dividing resistors 5 to 8 are selected so as not to exceed the maximum value of 1 volume. The water temperature sensor 22 detects the temperature of the cooling water and sends the detection signal to the A/D 15. The power amplifier 3 is connected to the drive circuit 23 from the duty port section of the input/output boat 16.
The control pulse signal is received via the . The PNP type power amplifier 3 is conductive during a period when the control pulse signal is at a low level voltage, and is non-conductive during a period when the control pulse signal is at a high level voltage. The engine switch located in the driver's seat is
In addition to the off position (or lock position), the engine switch has an on position and a start position, and an on signal 24 and a start signal 25 indicating that the engine switch is in the on position and the start position are sent to the input/output boat 16. When the engine switch is in the on position, the injection pump is in a drivable state, and when the engine switch is in the start position, the starter is in an operating state. The engine rotational speed sensor 26 includes a pickup 29 that changes the output voltage as it passes through teeth 28 provided at equal angular intervals on the outer periphery of the crankshaft 27, and the output voltage of the pickup 29 is outputted through a waveform shaping circuit 3o. It is sent to the input/output boat 16.

FIG. 2 shows the relationship between the target temperature Co of the glow plug 1 and the elapsed time t. t-o is the start time of the glow, i.e. when the engine switch is off or 6. t accessories
This is when it goes from the ON position to the ON position, or when it goes from the ON position to the START position. Figure 2 illustrates three control patterns, and the target temperature Co in each control pattern.
The control period is t=o ~ t1, tI-t2
.

[Divided into three categories: 2 to t3. The glow continues until t=t3. In the control period of 0≦t≦t1, the target temperature Co
is set to CI, and in the control period of tl<t<t2, the target temperature Co rises at a slope a with respect to the passage of unit time and is then maintained at c2, and in the control period of t2<t≦t3, the target temperature CO is After descending at a slope b with respect to the passage of unit time, C
3. If glow plug 1 is turned on when it is cold, the glow plug temperature detected from the terminal voltage of glow plug I may locally exceed the allowable value even though it is below the allowable value. This may shorten the life of the glow plug, and to avoid this, CI is set to a value lower than C2. However, just before cranking, the target temperature (0) is set to 02 so that the glow plug 1 reaches its original heating temperature.After starting, the target temperature Co is lowered to 03 to reduce the load on the storage battery, and To extend the life of the glow plug 1. Note that tl is set to a constant value regardless of the control pattern.

Figures 3 to 9 are CI, C21C3, t2°t3+a+
It shows the relationship between b and cooling water temperature. The slope a+b is expressed as the amount of rise and fall of the target temperature per unit time elapsed light. The cooler the glow plug 1 is, the greater the risk of local heating of the glow plug 1 at the start of glow, so cl is set to a smaller value as the cooling water temperature is lower. C2, C3+ t2+ t
3a+b is set so that the lower the cooling water temperature, the higher the Co content and the longer the glow.

! FIG. 10 shows an initialization routine performed when the engine switch is turned off or turned from the accessory position to the on position. In step 35, a glow control execution flag Pg is set. In step 36, t3, which is expressed as one hour of cooling water temperature, is subtracted from the cooling water temperature based on the map according to the graph of FIG. Step 37
Now, based on the map according to the graph in Figure 3, the cooling water temperature H
Calculate cl from D. In step 38, a is calculated from the cooling water temperature based on the map shown in the graph of FIG. In step 39, C2 is subtracted from the cooling water temperature based on the map according to the graph of FIG. Step 4
0, t2 is calculated from the cooling water temperature based on the map shown in FIG. In step 41, b is calculated from the cooling water temperature based on the map according to the graph of FIG.

In step 42, C3 is calculated from the cooling water temperature based on the map shown in FIG. In step 43, the elapsed time measurement timer Tm is cleared, that is, the timer value Tc
to the koto. In step 44, the conduction time S of the power amplifier 3 in one period of the control pulse signal is set to 20 m5ec.
(When the control pulse signal is 5011z) is substituted.

FIG. 11 shows a time interrupt routine for calculating the target temperature Co. In step 49, the glow control execution flag pg=
It is determined whether or not p g =l, and only if p g =1, the process proceeds to step 5o. In step 50, the elapsed time Tc
is increased by a predetermined amount (increment). Step 5】
Then, it is determined whether Tc≦t1 or apricot, and if 7 (< i i, proceed to step 52; if Tc>tl, proceed to step 55. In step 52, cl is substituted for the target temperature CO. In step 55, proceed to step 55. Determine whether Tc≦t2,
If Tc≦t2, the process proceeds to step 56, and if Tc>t2, the process proceeds to step 62. In step 56, Co +
Substitute a into Co. In step 57, it is determined that Co>C2 is apricot. If Co>C2, step 58 is executed and 02 is substituted for Co. In step 62, Tc≦t
3 or apricot, and if Tc≦t3, the process proceeds to step 63, and if Tc>t3, the process proceeds to step 66. In step 63, Co-J is converted to c.

Assign to . In step 64, it is determined whether Co<C3 or not. If Co<C3, step 65 is executed and 03 is substituted for Co. In step 66, the glow control execution flag Fg is reset.

FIG. 12 shows a time interrupt routine for calculating the conduction time S1 of the power amplifier 3, that is, the duty ratio of the control pulse signal when the frequency of the control pulse signal sent to the power amplifier 3 is 50 Hz. Actual temperature Cr of claw plug 1
If it is higher than the target temperature Co, the conduction time S is decreased, that is, the duty ratio is decreased, and if it is lower, the conduction time S is increased, that is, the duty ratio is increased.

The upper and lower limits of S are 20m5ec and 8m, respectively.
m5ec (if the frequency of the control pulse signal is 100
In the case of 0760 Hz, the upper and lower limits of the conduction time are 60 m5ec and 24 m5ec, respectively.

), the amount of change ΔS in S is ΔC<-= l Cr-(,o
The larger the value of l), the larger the value. The actual temperature Cr of the glow plug l is the voltage V at the connection points 19 and 20 in FIG.
19, is determined from the ratio of A/D converted values of V2O. If the resistance values of the claw plug 1 and the current detection resistor 2 are Rg + Re, then Rg changes in relation to the temperature Cr of the glow plug 1, whereas Rc remains constant regardless of the temperature Cr of the glow plug 1. It is. This results in Rg/(Rg + Re), hence the connection point 1
The ratio of the A/D conversion values of the voltages V19 and V2O of 9 and 20 is not related to the change in 10B, but is related to the change in Cr, and Cr can be accurately detected from this ratio. In step 70, it is determined whether the glow control execution flag Fg=1 or not, and only when Fg=1, the process proceeds to step 71 and subsequent steps. In step 71, the target temperature Co and the actual temperature Cr of the glow plug 1 are compared, and if Co≧Cr, the process proceeds to step 72, and if Co<Cr, the process proceeds to step 79. In step 72, Co-Cr is substituted into ΔC. In step 73, ΔS is calculated from ΔC according to the graph of FIG. 13 or 14. In FIG. 13, there is a dead zone in the duty ratio control, and in FIG. 14, there is no dead zone. In step 74, S+ΔS is substituted for S. In step 75, it is determined whether S>20 m5ec, and S>
If it is 20m5ec, execute step 76 and S=
20 m5ec. In step 79, Cr-Co is substituted into ΔC. At step 80, ΔS is subtracted from ΔC according to the graph of FIG. 13 or 14. In step 81, S-ΔS is substituted for S. In step 82, it is determined whether S < 8 m5ec or apricot, and S < 8
If it is m5ec, execute step 83 and set S = 8
Let it be m5ec.

FIG. 15 is a flowchart of a time interrupt program for detecting the temperature Cr of the glow plug l.

As mentioned in connection with the description of FIG. 12, the temperature C,r is at the connection point 19. , 20 voltages V19 and V2O are A/D
It is determined from the ratio of the converted values. The details of step 92 are as explained in the flowchart of FIG.
114 is a process for executing step 119 at the next time interrupt, steps 120-123 are processes for executing step 126 at the next time interrupt, and steps 127-131 are processes for executing step 119 at the next time interrupt. 92
This is a process for executing steps 101 to 107.
is Vl, 9 as the input of A/D conversion in step 119.
, for alternately selecting V2O. The control pulse signal sent to amplifier 3 has a frequency of 50 Hz (period 2
0 m5 ec) or +000/60 Hz (period 60 m5 ec), but if the time at which step 126 is executed is defined as S and the conduction time of the amplifier 3 per 1 = 0.1 period, then the period of the control pulse signal is When is 20 m5ec, step 92, that is, the calculation of the conduction time S is t = (Sb-2) m5ec
(however, 5b=zo-5), and step III, that is, the start of conduction of the power amplifier 3 is performed at t2s
Step 119 is performed at t = Sb + 5 m5e.
step 126, i.e. the end of conduction of the amplifier 3, is performed at t=Sb+S, so t'=
Conducted at 20 m5ec. If the period of the control pulse signal is 60 m5ec, step 92°111
, 119.126 are t:5b-2, Sb+S, respectively
Performed at b+5+ 60 m5ec. In this way, Vl, 9, and V2O during the period when the power amplifier 3 is conducting and the glow plug 1 is energized are A/D converted,
Temperature Cr is detected from Vl9 and V2O. Furthermore, within a predetermined time after the power amplifier 3 starts conducting, the current flowing through the glow plug l is in a transient state, and Vl9 or V
2O is changing, but Vl9 and Vl9 after 5 m5ec have elapsed from the start of conduction when V2O has reached a steady state.
By calculating 91 V2O, the accurate temperature Cr can be calculated. Steps 93 to 97 select the period of the control pulse signal to the amplifier 3.

The conduction time S of the amplifier 3 is determined by the period of the control pulse signal being 20'.
It is calculated from the program diagram in Figure 12 on the assumption that it is m5ec, but if this calculated value S becomes less than S1 as shown in Figure 16, the period of the control pulse signal is 20 m.
When switching from 5ec to 60m5ec, when the value becomes larger than λsh, switching from 60m5ec to 20m5ec is performed.

If the period of the control pulse signal is 60 m5ec, s and sb are tripled in steps 121 and 129.

The minimum time required to maintain Vl9 for A/D conversion of Vl9 is ensured within the conduction period of the power amplifier 3, and the temperature Cr of the glow plug l can be accurately detected. Hunting can also be prevented by adding hysteresis to the switching of the period of the control pulse signal.

To explain the flowchart of FIG. 15 in detail, in step 90, the value Tf of the free running counter is read. Tf represents the current time. Note that when the value Re of the output comparison register matches Tf, the time interrupt routine shown in FIG. 15 is executed. In step old, it is determined whether the calculation flag Fs=1 for the conduction time S, and if Fs=1, the process proceeds to step 92, and if Fs=O, step 110
Proceed to. Fs is determined in step 1 after execution of step 126.
31 and reset in step 99 after execution of step 92.

In step 92, the conduction time S is calculated. Step 92
The details are as explained in FIG. Step 9
3, it is determined whether the frequency flag Fw=0 or not, and Fw=0
If so, the process proceeds to step 94, and if Fw=1, the process proceeds to step 96. For the frequency flag FW:O, 20 m5ec is selected as the period of the control pulse signal to the amplifier 3. This means that the frequency control flag Fw=1
means that 60 m5ec is selected.

In step 94, it is determined whether S≧Sl, and if S≧Sl, the process proceeds to step 98; if S<SZ, the frequency flag FW is set in step 95, and then the process proceeds to step 98. In step 96, it is determined whether 5<sh (Sh>SA) or the same, and if S<Sh, proceed to step 98, and if S≧sh, proceed to step 9.
After the frequency flag FW is reset in step 7, the process proceeds to step 98. At step 98, Tf +2m5ec is assigned to the value Re of the output comparison register. Step 99
Then, the conduction time calculation flag Fs is reset. In step 100, a conduction time set flag Ft is set. In step +01, the A/D of the supply voltage, i.e. V2O
It is determined whether or not the conversion rate Fa=]. If Fa=], proceed to step 104; if Fa=0, proceed to step 10.
Proceed to step 6. In step 104, the input channel of the A/D 15 is selected to be V20. In step 105, the A/D conversion flag Fa is reset. In step 106, A/
Select D channel to Vl9. In step 107, A
/D conversion flag Fa is set. In step 110, it is determined whether the conduction time set flag Ft: 1, and F
If t:,=1, proceed to step 111, and Ft=
If O, the process advances to step 118. In step 111, the glow control output port (=duty port section) of the input/output port 16 is set. This makes the stupid amplifier 3 conductive. In step 112, Tf + 5 Iosec is assigned to the value Re of the output comparison register. In step 113, the conduction time set flag Ft is reset. In step 114, an A/D conversion start flag Fu is set. In step 118, it is determined whether the A/D conversion start flag Fu==]. If Fu=], the process proceeds to step 119; if Fu20, the process proceeds to step +26. In step 119, A/D conversion is started. In step 120, it is determined whether the frequency flag Fw = 1, and if Fw = 0, the process proceeds to step 122, where Fw = 1.
If so, the conduction time S is multiplied by three in step 121 and then the process proceeds to step 122. In step 122, Tf1S-5m5ec is assigned to the value Rc of the output comparison register. In step 123, the A/D conversion start flag Fu is reset. In step 126, the glow output capo,
reset. This causes the power amplifier 3 to become non-conductive. In step 127, it is determined whether the frequency flag Fw=1 or not, and if Fw=0, the process proceeds to step 128 and substitutes (20-S,) m5ec for the non-conduction time sb.
If Fw=1, proceed to step 129 and set sb (60
-5) Substitute m5ec. At step 130, Tf + Sb - 2m5ec is substituted for the value Sc of the output comparison register. In step 131, the conduction time set flag F
Set t.

[Brief explanation of the drawing]

Figure 1 is a control circuit diagram of a glow plug for a diesel engine, Figure 2 is a diagram showing changes in target temperature of the glow plug over time, and Figures 3 to 9 are CI diagrams shown in Figure 2.
l C21C3, t2, t3゜10 Figure 10 is a flowchart of the recruitment routine for each number, Figure 11 is a flowchart of the target temperature calculation routine, Figure 12 is a flowchart of the duty ratio subtraction routine, Figures 13 and 14. 15 is a flowchart of the glow plug temperature detection routine, and FIG. 16 is a graph showing the relationship between the conduction time of the power amplifier and the period of the control pulse signal. This is a graph showing l...Glow plug, 3...Power amplifier, 11...
・Electronic control unit, 12...CPU, 15...A
/ D1J9...4 concubines U6 points. Figure 62 Figure 7 Cooling water temperature D Cooling water temperature Cooling water temperature D Cooling water temperature D Figure 13 Diagram 14 Continuity deviation C (=ICo -Cr-1)

Claims (1)

[Claims] 1. A power amplifier is connected in series with the glow plug that heats the pre-combustion chamber, and a first voltage related to the terminal voltage of the glow plug during the conduction period of the power amplifier is converted into an analog voltage.
The temperature of the glow plug is detected by digital conversion, the duty ratio of the control pulse signal of the power amplifier is calculated by comparing the actual temperature of the glow plug with the target temperature in a digital processor, and the energizing current related to this duty ratio is calculated. Method 2 for controlling a glow plug for a diesel engine, which is characterized in that the synchronization of a control pulse signal is controlled in relation to the length of a conduction period of a power amplifier, in the method for controlling a glow plug for a diesel engine that flows through the glow plug.
2. The control method according to claim 1, wherein the period of the control pulse signal is switched in relation to the length of the conduction period of the force amplifier, and hysteresis is added to this switching.