Apparatus for reducing vibrations of the body of a vehicle

Abstract: The present invention relates to an apparatus for effectively reducing vibrations of a vehicle engine and the vehicle body due to irregular combustion of the engine. In the inventive vibration suppressing apparatus, a generator (4) is provided which has a voltage regulator (9) to control a field winding (8) current so as to output a constant voltage to a battery (1). When irregular combustion of the engine is detected on the basis of a change in the engine speed, a voltage higher than the output voltage of the generator (4) is applied across the field winding (8) to increase the load torque on the generator (4). A change in the load torque of the generator (4) induces vibrations on the generator body due to reaction. When the generator vibrations and vibrations due to irregular combustion are in inverse phase relationship to each other, they are cancelled by each other to suppress those vibrations.

Description: The present invention relates to an apparatus for reducing vehicle body vibrations due to irregular combustion in an engine during idling according to the preamble portion of claim 1. Recently, the requirement of a comfortable driving of a vehicle becomes severer. For example, various proposals for reducing vibrations of the vehicle body during idling of the engine have been made conventionally. One example is to control a torque required for driving a generator provided on the engine to suppress vibrations of the engine to thereby reduce the vibrations of the vehicle body, as disclosed in Unexamined Japanese Patent-Publication JP-B 63-45498 for the Japanese Patent Application filed by Mazda Motor Corporation on June 10, 1982. In the technique of this publication, periodic torque fluctuations or torque pulsations due to compression and combustion steps in the reciprocal engine are canceled by turning on and off the field coil current in the generator synchronously with those torque pulsations to thereby cancel the resulting generator drive torque and hence reduce the body vibrations. The EP-A-0 250 684 shows a torque controller for an internal combustion engine, which periodically increases or decreases after every engine cycle the field current of a generator coupled with the engine dependent on an average engine speed and on actual engine speed for producing a counteraction on the engine speed variation. This conventional technique, however, does not allow for non-periodic irregular combustion (irregular bad combustion) generated during ilding, and cannot cope with a situation in which irregular combustion causes engine vibrations which are then transmitted to the vehicle body to thereby adversely affect the comfortableness of driving. While the conventional technique can cope with periodic torque fluctuations, it does not allow for vibrations inherent to the engine and vehicle body due to torque vibrations generated at irregular periods. The torque fluctuations generated at irregular periods include torque fluctuations due to incomplete combustion generated once in two seconds-one minutes during idling and torque vibrations due to disturbance of fuel supply control occurring when the engine operation is rapidly changed to idling state from high speed running. It is an object of the present invention to provide an apparatus for effectively reducing vibrations of the engine and the vehicle body due to irregular combustion of the engine. This object is solved according to the features of claim 1. The independent claims show advantageous features and further embodiments of the invention. In the present invention, the load torque of a generator such as an alternator fixed to the engine is changed to generate an angle moment on the body of the generator to cancel engine vibrations due to rough idling to suppress body vibrations due to the rough idling. In the inventive vibration suppressing apparatus, a generator is provided which has a voltage regulator to control a field winding current so as to output a constant voltage to a battery. The occurrence of irregular combustion of the engine is detected on the basis of a change in the engine speed. When irregular combustion is detected, a voltage higher than the output voltage of the generator is applied across the field winding to increase the field winding current and hence the load torque on the generator. A change in the load torque of the generator induces vibrations on the generator body due to reaction. When the generator vibrations and vibrations due to irregular combustion are in inverse phase relationship to each other, they are canceled by each other to suppress those vibrations. When irregular combustion appears in the engine, the engine speed greatly fluctuates and the engine vibrates in the direction of rotation around the output shaft. Vibrations in the direction of this engine rolling causes the vehicle body to vibrate through the engine mount. Since the vehicle body is supported through tires, vibrations are likely to occur in the rolling direction especially in a FR (Front Engine Rear Drive) vehicle in which the engine is disposed in the longitudinal direction. Thus, when the engine and vehicle body start to vibrate, they vibrate in opposite direction in respective predetermined times determined by the corresponding inherent vibration periods. If the load torque on generator is increased at this time, the generator body vibrates due to reaction and its vibrations are transmitted to the engine. Therefore, the engine vibrates in the rolling direction, engine vibration due to irregular combustion and the reverse force act on each other to thereby to reduce the engine vibration. In addition, the vehicle body vibration and the reverse force acts on the vehicle body through the engine mount to thereby reduce the vibration of the vehicle body. Since the voltage supplied to an energizing coil of the generator is stepped up at this time, the load torque increases at increased speed. Therefore, the responsiveness of control of the load torque on the generator is improved to thereby reduce the vibrations effectively. Embodiments of an apparatus for reducing vibrations due to irregular combustion according to the present invention will be described in more detail below with reference to the drawings. FIG. 1 is a circuit diagram indicative of the structure of a vehicle body vibration reducing apparatus according to the present invention; FIG. 2 is a diagram of operating waveforms in FIG. 1 embodiment; FIG. 3 is a detailed circuit diagram of a rough idling detection unit of the FIG. 1 embodiment; FIG. 4 is an internal circuit diagram of a control circuit of the FIG. 1 embodiment; FIG. 5 is a circuit diagram of a modification of the FIG. 1 embodiment; and FIG. 6 illustrates waveforms generated in the FIG. 5 circuit. FIG. 1 shows one embodiment of the present invention. In FIG. 1, the numeral 1 denotes a battery, 2, a positive power supply line; 3, a negative power supply line; 4, an alternator; 5, a statcr (or amature) coil of the alternator; 6, a diode bridge; 7, a diode for an energizing power source; 8, a field coil of the alternator; 9, a voltage regulator for control of the field current; 10, a relay; 11, a b- (normally closed) contact of relay 10; 12, an a- (normally open) contact; 13, a relay coil; 14, a booster; 15, a control circuit; and 30, a rough idling detection unit. The positive and negative power supply lines 2 and 3 of battery 1 are connected to alternator 4, the respective phase windings U, V, W of stator coil 5 are connected to diode bridge 6 whose output terminal is connected to battery 1. The respective phase windings U, V, W of stator coil 5 are connected to L-terminal of field coil 8 through corresponding diodes 7. Transistor TR1 of voltage regulator 9 is connected across F-terminal of field coil 8 and ground. Free wheel diode D1 is connected in parallel with field coil 8 through b-contact 11 of relay 10. Alternator 4, thus structured, performs a regular operation and is driven by the engine to supply a generated current to battery 1. The positive power source line 2 is connected to b-contact 12 of relay 10 in series with inductance L1 and diode D2. The input side of inductance L1 is grounded through capacitor C1 and the other end of the inductance is grounded through a field effect transistor FET. The cathode of diode D2 is grounded through capacitor C2. Thus booster 14 results. Booster 14 provides a boosted output voltage VF = VB x T/TOFF where T is the switching period of field effect transistor FET, TOFF is the off time, and VB is the input voltage. Capacitors C1 and C2 used to reduce a ripple current. When rough idling detection unit 30 detects rough idling, it outputs a control command signal to signal terminals S1, S2. The details of rough idling detection unit 30 will be described in more detail later. Control command signal terminal S1 is connected through resistor R1 to the base of transistor TR2, the collector of which is connected through diode D3 to coil 13 of relay 10. The collector of transistor TR2 is also connected to the base of transistor TR3 through a series connected circuit of diode D4 and resistor R2. The collector of transistor TR3 is connected to the base of transistor TR4 through resistor R3. The collector of transistor TR4 is connected to F-terminal of field coil 8, the emitter of transistor TR4 is connected to negative power supply line 3 through current detecting resistor R4. Zener diode ZD is connected across F-terminal of field coil 8 and negative power supply line 3. Relay coil 13 is connected in parallel with a series connected circuit of resistor R5 and diode D5. Control circuit 15 includes operation stopping circuit 16 which operates to prevent the conduction ratio control circuit 21 from providing an output, voltage limitter 17 which limits output voltage VF, current limitter 18 which limits the current flowing through transistor TR4, and reference voltages (A) 19 and (B) 20 which define the corresponding voltage and current limits. In operation, assume that engine speed N is decreased as shown in FIG. 2(a) due to the occurrence of incomplete combustion in some cylinders of the engine and fluctuations of the engine speed arrives at a predetermined value ΔN. At this time, rough idling detection unit 30 outputs a signal of a pulse width T2 (FIG. 2(b)) to S1 command signal terminal a time T1 after its detection. In FIG. 2, time t0 which is the starting point of interval T1 shows a TDC (Top Dead Center) at which time incomplete combustion starts. Then speed fluctuation ΔN is detected. The structure and operation of rough idling detection unit 30 will be described with reference to FIG. 3 which illustrates the structure of detection unit 30. The numeral 101 denotes a ring gear which is directly connected to a crank shaft (not shown) of the engine and rotates synchronously with engine rotation. Disposed in the vicinity of teeth of ring gear 101 are electromagnetic pickups 102, 103 which output a pulse each time the respective teeth of gear 101 pass by the pickups. Pickup 102 is for detecting engine speed while pickup 103 detects a reference position, for example, a top dead center of the engine. The respective pulse outputs from the pickups are input to microcomputer 104 to calculate the engine speed and also to detect a change in the engine speed. Microcomputer 104 outputs to S1 a command signal to increase the field current a predetermined time T1 after top dead center position timing t0 when speed change ΔN for rotation through a predetermined crank angle exceeds the predetermined value. The signal output to S2 terminal has the same phase and width as the signal at S1 terminal but the amplitude level thereof is changed by circuit 105. The engine speed may be changed by measuring a change in the rotational acceleration and rough idling may be detected by comparing the change with a predetermined value. If speed fluctuation ΔN is detected, signals S1, S2 are generated an interval T1 corresponding to one half of the vibration period of the vehicle body after time TDC. Interval T1 may be one half of the inherent vibration period of the engine. Signals S1, S2 may be generated after one half of both the inherent vibration periods has passed. Rough idling detection unit 30 simultaneously generates signal S2 used for generation of a voltage Vc (which limits the field current value) defining the field current in alternator 4. Command signal S1 is generated in this way, transistor TR2 is rendered conductive to close the a-contact 12 of relay 10. As a result, transistors TR3, TR4 are rendered conductive to thereby shunt transistor TR1 to increase the current in the field coil 8. Command signal S1 releases the operation of operation stopping circuit 106 of control circuit 15 and the output of conduction ratio control circuit 21 causes booster 14 to operate. Since the output voltage VF of booster 14 is set so as to be about 4 times as high as input voltage VB, field current IF rises at a quadrupled speed. When the field current arrives at its upper limit, current limitter 18 operates to reduce output voltage VF of booster 14. If command signal S1 disappears, transistors TR2 - TR4 are rendered non-conductive to stop booster 14. At this time, a recirculating current flows through coil 13 because the series connected circuit of resistor R5 and diode D5 is connected in parallel with coil 13 of relay 10 to thereby delay the opening of the a-contact 12 (about 3 ms). As a result, field current IF flows through Zener diode ZD. By setting the blocking voltage of Zener diode ZD to about 48 volts, the current can fall more rapidly than when free wheel diode D1 is connected. The above operation is illustrated using the characteristic diagram of field current IF of FIG. 2. It is shown that current limitation is performed at time T3. Time T4 shows that the b-contact 11 of relay 10 is still open and that field current IF is falling rapidly. In the waveform diagram of FIG. 2, (e) shows the waveform of a gate signal for the FET in the booster 14. Duty cycle control circuit 21 responds to a command signal at terminal S1 to generate that gate signal to turn on and off the FET. The dot-dot-dashed line indicative of the field current shown by (f) shows the characteristic obtained when no boosted-up voltage is applied to the field coil. The inventive characteristic shown by the solid line and obtained when the boosted-up voltage is applied to the field coil is rapider in rise and fall and hence excellent responsiveness results. FIG. 4 shows the details of control circuit 15. A constant voltage from constant voltage circuit 22 is supplied to constant voltage line 23. The output of comparator 25 which compares the output voltages of saw-tooth oscillator 24 which outputs a saw-tooth waveform signal and amplifier AMP is amplified by conduction ratio output circuit 21 of transistors TR6 - TR8 and the resulting signal is delivered to an FET of booster 14. Transistors TR7 and TR8 are used in a totem pole connection to apply a switching signal having a rapid rise and fall waveform to the gate of field effect transistor FET. Transistor TR5 of operation stopping circuit 16 is normally conductive and rendered non-conductive when it receives a signal at terminal S1 at which time conduction ratio control circuit 21 generates a pulse. Therefore, according to this embodiment, the operation interval of booster 14 is suppressed to a minimum value to thereby prevent a current higher than a regular one from flowing through field coil 8 of alternator 4 to increase the resulting generated voltage and to increase the charging current to battery 1. FIG. 5 shows another embodiment of the present invention which is the same instructure and effect as the FIG. 1 embodiment except that Zener diode ZD2 replaces transistors TR1 and TR4 and Zener diode ZD of FIG. 1. The booster in the present invention may be a push-pull converter system using a transformer or a doubling circuit system using the charging of a capacitor to obtain similar effects in addition to the above embodiment. If battery 1 is charged to about 100% of its full charge capacity in the above embodiment, field coil current IF is as shown by the dot-dot-dahsed line in FIG. 2 (because voltage regulator 9 renders transistor TR1 non-conductive in response to an increase in the voltage. As a result, when there is a load on battery 1, voltage fluctuations occur for interval T5 of FIG. 2, which instantaneously reduces the brightness of a lamp or the like if it is lit. In the present embodiment, command signals S1 and S2 are arranged to take a waveform as shown in FIG. 6 such that they are generated with a predetermined width during interval T5 so as to supply a predetermined low current from booster 14 to field coil 8 to prevent a reduction in the brightness of the lamp or the like. Therefore, according to the present embodiment, the voltage applied to field coil 8 is boosted up, so that a rise in the field current is speeded up, the torque of alternator 4 responds rapidly. As a result, timing for reducing vibrations of the vehicle body is easily set to thereby reduce vibrations effectively. When the current flowing through field coil 8 increases, the voltage generated by alternator 4 and the resulting current increase. Thus, the torque absorbed by alternator 4 increases. By adjusting the field coil current, the torque of the alternator can be adjusted. As a result, according to the above embodiment, if command signal S2 is changed in accordance with speed fluctuation ΔN of the engine, the alternator torque can be adjusted to thereby provide optimal control. In order to rapidly reduce the current in the field coil 8 in the present embodiment, the current energy supplied to field coil 8 is first absorbed by Zener diode ZD, and discharged after free wheel diode D1 is connected. As a result, the current flowing through field coil 8 and the torque of the alternator 4 are rapidly reduced. This implies that the torque can be controlled in a pulsating manner to thereby reduce vibrations of the vehicle body more effectively. According to the present invention, since the generator torque increases a predetermined time, which is determined by at least one of the inherent vibration periods of the engine and vehicle body, after the detection signal from engine speed fluctuation detecting circuit rose, the inherent vibrations of the engine and vehicle body can be reduced. In addition, the voltage applied across the field coil of the alternator is greatly high compared to the battery voltage, so that a rise in the field coil current is speeded up and the torque of the alternator is rapidly increased. Since the field current value can be controlled, the alternator torque can also be controlled. Since the current flowing through the field coil can rapidly be reduced, the alternator torque can rapidly be reduced. Therefore, according to the present invention, since the response to a command is speeded up and control to the command value is achieved, control to reduce vibrations of the vehicle body due to vibration of the engine is ensured to thereby reduce the vibrations.

Claims: Apparatus for reducing vehicle body vibrations due to irregular combustion in an engine during idling, comprising: a generator (4) attached to the vehicle engine and including a voltage regulator (9) for controlling a field winding (8) current such that a predetermined voltage is output to a battery (1), means (101-103) for detecting the engine speed (N), means (30) for detecting the occurrence of irregular combustion in the engine on the basis of at least a predetermined change (ΔN) in a detected engine speed (N), a high voltage circuit (14) responsive to a command signal for generating a voltage higher than the output voltage of the generator (4), and switching means (10) responsive to the command signal for applying the voltage generated by the high voltage circuit (14) to the field winding (8) to increase the field current and hence the load torque on the generator (4), characterized in that means (15) responsive to the detection of the irregular combustion are provided for generating the command signal to command an increase in the field winding (8) current at a first predetermined time (T₁) after the detection of the irregular combustion, the first predetermined time (T₁) being determined on the basis of the inherent vibration period of the engine or the vehicle body, and the high voltage circuit (14) is generating a voltage higher than the output voltage of the generator (4) for a second predetermined time (T₂) after the first predetermined time (T₁) has been elapsed. Apparatus according to claim 1, characterized in that a free wheel diode circuit (D1) connected in parallel with the field winding (8) for absorbing a possible surge current generated in the field winding (8) is provided, the switching means (10) selectively applying the output of said high voltage circuit (14) and the output of said free wheel diode circuit (D1). Apparatus according to claim 2, characterized in that the switching means (10) have a time constant in the switching operation and switch the field winding (8) from the high voltage circuit (14) to the free wheel diode circuit (D1) a time corresponding to the time constant after the disappearance of the command signal, and a circuit (ZD) is provided for absorbing a possible surge current generated in the field winding (8) during an interval of the time constant. Apparatus according to claim 3, characterized in that the circuit (ZD) for absorbing the surge current includes a Zener diode circuit connected across one end of the field winding (8) and ground, and wherein the Zener diode circuit (ZD) is rendered conductive when the voltage at the junction point of the field winding (8) and the Zener diode circuit (ZD) exceeds a predetermined value. Apparatus according to claim 1, characterized in that means (25) for comparing the voltage across the field winding (8) and a predetermined reference value and for outputting an output signal when the voltage across the field winding (8) exceeds the reference value, and means (21) responsive to the output signal of the comparing means (25) for suppressing the output voltage of the high voltage circuit (14) are provided. Apparatus according to claim 1, characterized in that the means (30) for detecting the occurrence of the irregular combustion includes the means (101-103) for detecting the engine speed and means (104) for calculating a change in the engine speed within a predetermined crank angle and for determining that irregular combustion has occurred when the change in the engine speed exceeds a predetermined value.

Inventors: FUKUSHIMA MASAO, KADOMUKAI YUZO, KURIYAMA SHIGERU, MAEDA YUJI, MASHINO KEIICHI, MURAKAMI KEI, NAKAMURA KENICHI, NAKAMURA YOZO, FUKUSHIMA, MASAO, KADOMUKAI, YUZO, KURIYAMA, SHIGERU, MAEDA, YUJI, MASHINO, KEIICHI, MURAKAMI, KEI, NAKAMURA, KENICHI, NAKAMURA, YOZO
Applicants: HITACHI LTD, NISSAN MOTOR, HITACHI, LTD., NISSAN MOTOR CO., LTD.
Application year: 1991
Main classification: F02D31
IPC codes: H02P9, F02D29, F02D41, H02P29