JPH02245407A - Valve timing control device for engine - Google Patents

Abstract

PURPOSE:To prevent torque shock, in an engine in which the intake and exhaust timing is changed by a hydraulic actuator, by constituting it so that the changeover speed of valve timing change can be regulated in accordance with the accelerating condition of a vehicle. CONSTITUTION:In a valve-timing changing mechanism 30, when a changeover solenoid 31 is turned on to change over a changeover valve 52 to the supply position, a piston 38 is shifted toward the right by the pressure oil supplied to a pressure chamber 49 through an oil passage 45 against a spring 44. Thereby a spacer 32 and a pulley 7 which are fitted to the splines 40, 41 formed on the inner and outer circumferences of the piston 38 in the reverse directions to each other are relatively turned, and the relative position of a camshaft 5 being integral with the spacer 32 and the pulley 7 is changed. In this case, large and small flow oil passages 57, 56 are provided in the oil passage 54 on the upstream side of the changeover valve 52, and a solenoid open/close valve 58 is provided so that the valve timing can be quickly at the time of sudden acceleration, and also the valve timing can be gradually changed at the time of slow acceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a valve timing control device for an engine, and particularly to one in which the switching speed for changing valve timing can be adjusted.

[Prior art] Conventionally, as an engine with a supercharger, for example, Japanese Patent Application Laid-Open No. 61-1
As disclosed in Japanese Patent Application Laid-open No. 87543 and Japanese Patent Application Laid-open No. 197720/1987, a mechanical supercharger is provided in the intake passage,
This supercharger is connected to the engine output shaft via a clutch, and in supercharging regions centered on high speed and high load regions, the clutch is connected and the supercharger is operated to supercharge the engine and increase its output. At the same time, outside the supercharging range, the clutch is disengaged and the engine is operated with naturally aspirated air to reduce fuel consumption. In addition, a timing change device that is driven by a step motor and that makes the intake/exhaust timing variable is installed in the engine's valve train system, making it possible to vary the intake/exhaust overlap period. The intake and exhaust overlap amount is increased to promote scavenging of burnt gas in the combustion chamber and suppress the occurrence of knocking.

On the other hand, Japanese Unexamined Patent Publication No. 191636/1983 describes a camshaft and a rotation transmission member (
A valve timing change device is provided to change the relative phase with a hydraulic actuator (gears, pulleys), an electromagnetic on-off valve is provided in a relief passage that relieves the pressure oil supplied to this hydraulic actuator, and the opening/closing of this electromagnetic on-off valve is controlled. A valve timing control device for an engine is described in which the valve timing is switched via a hydraulic actuator.

[Problem to be solved by the invention]

Changing the intake or exhaust timing of the engine and changing the amount of overlap between the intake and exhaust greatly changes the engine characteristics, but conventional valve timing control devices adjust the switching speed when changing and controlling the valve timing. It is not possible to do so. Therefore, the valve timing is switched so that the intake/exhaust overlap amount becomes large at the same switching speed whether the engine is rapidly accelerating or slowly accelerating from a low-speed, low-load state.

If the switching speed of the valve timing is set low, it is possible to prevent torque shock when switching the valve timing during acceleration/deceleration, but there will be a delay in switching the valve timing during sudden acceleration, resulting in a lack of responsiveness.

On the other hand, if the switching speed is set high, this is not preferable because not only will the torque shock become large when switching the valve timing during acceleration/deceleration, but also the torque characteristics of the engine will fluctuate rapidly during slow acceleration.

An object of the present invention is to provide an engine valve timing control device that can adjust the switching speed of changing valve timing.

[Means for Solving the Problem] A valve timing control device for an engine according to a first aspect includes a valve timing changing device that changes intake timing or exhaust timing, and controls changing valve timing according to the operating state of the engine. This valve timing control device for an engine is provided with a switching speed adjusting means that rapidly changes the valve timing during sudden acceleration and gradually changes the valve timing during slow acceleration.

An engine valve timing control device according to a second aspect of the present invention is an engine valve timing control device that includes a valve timing change device that changes intake timing or exhaust timing, and that changes and controls valve timing according to the operating state of the engine. The above-mentioned valve timing changing device includes a hydraulic actuator that changes the relative phase between a camshaft and a rotation transmission member provided on the camshaft, a supply passage that supplies pressure oil to the hydraulic actuator, and a system that relieves the pressure oil in this supply passage. The supply passage includes a relief passage that opens and closes the relief passage, and a passage changing means that enlarges the supply passage during slow deceleration and decreases it during rapid deceleration.

[Effect]

In the engine valve timing control device according to the first aspect, the switching speed adjusting means is provided to control the valve timing to be changed suddenly during sudden acceleration, and to gradually change the valve timing during slow acceleration. At times, the valve timing is controlled to change suddenly, making it possible to switch to the valve timing suitable for the operating condition without delay in response to valve timing switching.In addition, during slow acceleration, the valve timing is controlled to change gradually, which allows the valve timing to change quickly. It is possible to prevent torque shock and sudden changes in engine characteristics due to switching.

In the engine valve timing control device according to the second claim, the valve timing changing device includes a hydraulic actuator for changing the valve timing, a supply passage for supplying pressure oil to the actuator, and a relief passage for pressure oil in the supply passage. It is a hydraulic type equipped with a relief passage and an on-off valve that opens and closes the relief passage. The switching speed of valve timing switching is determined according to the supply flow rate when hydraulic pressure is supplied from the supply passage.

By means of the passage changing means, the supply passage is changed to be large during slow deceleration and small during sudden deceleration, so that the valve timing is changed gradually during slow deceleration and suddenly changed during sudden deceleration. This prevents torque shock when switching valve timing during slow deceleration.
Also! ,! There is no response delay when switching valve timing at high speeds.

〔Effect of the invention〕

According to the engine valve timing control device according to the first aspect, as explained in the [Operation] section above, by providing the switching speed adjusting means, the responsiveness of valve timing switching is increased during sudden acceleration. In addition to improving acceleration response, it is possible to prevent torque shock and sudden changes in engine characteristics due to valve timing switching during slow acceleration.

According to the engine valve timing control device according to the second claim, as explained in the [Operation] section above, by providing the passage changing means, torque shock when switching the valve timing during slow deceleration is prevented. Not only can you do it, but
During sudden deceleration, the responsiveness of valve timing switching can be increased to improve deceleration responsiveness.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

This embodiment is an example in which the present invention is applied to a supercharged engine with two intake valves and two exhaust valves for each cylinder for an automobile.

As shown in FIG. 1, each of the four cylinders 1 of the engine E is provided with an intake port 2 that is opened and closed by an intake valve 2a and an exhaust port 3 that is opened and closed by an exhaust valve 3a. The intake valves 2a are driven by an intake camshaft 4, and the eight exhaust valves 3a are driven by an exhaust camshaft 5. These camshafts 4 and 5 are connected to the crankshaft pulley 6 as described later.
is linked to.

An air cleaner 11, an air flow meter 12, a throttle valve 13, a mechanical supercharger 14, and a surge tank 16 are interposed in the intake passage 10 of the engine E in order from the upstream side. Connected to port 2. Furthermore, an injector 15 that injects fuel toward each intake port 2 is attached to the branch intake pipe 17. The throttle valve 13 is connected to an accelerator pedal, and the throttle valve 13 is provided with a throttle opening sensor 18 that electrically detects its opening, and an idle switch (path shown) that is closed when the throttle valve is fully closed. There is. A bypass passage 19 is provided to bypass the supercharger 14, and a bypass valve 20 is provided in the bypass passage 19. The bypass valve 20 is an actuator 21 into which boost negative pressure is introduced via a negative pressure introduction passage 22. Driven. The characteristics of the valve opening degree of this bypass valve 20 are as shown in FIG.

An electromagnetic clutch 25 is interposed on the input shaft 14a of the supercharger 14, and a boot IJ 26 of the input shaft 14a is interlocked and connected to the crankshaft pulley 6 by a belt or chain.

A control unit 27 is provided to control the electromagnetic clutch 25, an overlap switching solenoid 31 of a valve timing change mechanism 30 for switching the intake/exhaust overlap amount, which will be described later, and an electromagnetic on/off valve 58. A signal from the air flow meter 12, a signal from the throttle opening sensor 18, a signal from the idle switch, an engine speed signal N from the distributor, etc. are input.

Next, the valve timing changing mechanism 30 will be explained based on FIGS. 2 and 3.

In this valve train for engine E, a cylindrical spacer 32 is fixed to the end of the exhaust camshaft 5, and a drive pulley 7 is attached to the outside of the spacer 32. This pulley 7 is in sliding contact with the outer periphery of the tip of the spacer 32 at the tip of the boss portion 34, and the base end side of the boss portion 34 is a cylindrical connecting member 35 rotatably attached to the exhaust camshaft 5.
Fixed. The connecting member 35 is rotatably supported by a bearing portion 36A of the cylinder head 36, and the first gear 8 is spline-coupled to the other end of the connecting member 35 and fixed by a lock nut 37. This first gear 8
A second gear 9 fixed to the tip of the intake camshaft 4 is meshed and connected to the intake camshaft 4.

An annular piston 38 is installed inside the boss portion 34 of the boot IJ 7 between it and the spacer 32. The piston 38 has a structure in which it is divided into two parts in the axial direction, and both parts are fixed to each other by a plurality of pins 39 arranged at equal intervals in the circumferential direction. Helical splines 40 and 41 are formed on the inside and outside of the piston 38 in opposite directions. A helical spline 42 is formed on the outer periphery of the spacer 32 with respect to the spline 40 on the inside of the piston 3, and a helical spline 4 is formed on the inner periphery of the boss portion 34 of the pulley 7 with respect to the helical spline 41 on the outer periphery of the piston 38.
3 is formed. The piston 38 is biased toward the distal end side by a spring 44 installed between the piston 38 and the end surface of the connecting member 35 .

The exhaust camshaft 5 has an oil passage 4 along its axis.
5 is formed. The cylindrical spacer 32 is the stopper member 4
The exhaust camshaft 5 is fixed by the fixing bolt 47 through the
Fixed. This fixing bolt 47 is provided with an axial through hole 48 that communicates with the oil passage 45.

A pressure chamber 49 is provided at the tip of the boss portion 34 of the pulley 7, facing the head of the piston 38, for introducing the hydraulic pressure from the oil passage 45.

The other end of the exhaust camshaft 5 is rotatably supported by a bearing 36B of the cylinder head 36, and the end of the pivot hole 50 is closed by a plug 51.

As shown in FIGS. 2 and 3, in order to supply hydraulic pressure to the oil passage 45 and discharge the hydraulic pressure from the oil passage 45,
A switching valve 52 that is operated by an overlap switching solenoid 31 is incorporated in the cylinder head 36 on the side of the pivot hole 50, and as shown in FIG.
When is OFF, the switching valve 52 is in the discharge position, the oil passage 45 is connected to the drain passage 53, and the solenoid 3
1 is ON, the switching valve 52 is in the supply position, and the oil passage 45 is connected to the oil pressure supply passage 54 (oil gallery), and the oil pressure supply passage 54 is pressurized from a lubricating oil pump driven by the crankshaft. Oil is supplied.

That is, when the switching solenoid 31 is turned on and the switching valve 52 is switched to the supply position, hydraulic pressure is supplied to the pressure chamber 49 through the oil passage 45, compressing the spring 44 and moving the piston in the axial direction. As a result, splines 4 in opposite directions are formed on the inner and outer circumferences of this piston 38.
One of the spacer 32 and the pulley 7, which are fitted with 0.41, rotates relative to the other. This changes the relative phase between the exhaust camshaft 5, which is integrated with the spacer 32, and the pulley 7.

On the upstream side of the switching valve 52, the hydraulic pressure supply passage 54 is provided with a small flow oil passage 56 provided with an orifice 55 and a large flow oil passage 57 with a large oil passage cross-sectional area that bypasses the small flow oil passage 56. , an electromagnetic on-off valve 58 for opening and closing the large-flow oil passage 57 is installed, and the electromagnetic on-off valve 58 is controlled by the control unit 27.

As will be described later, the electromagnetic on-off valve 58 is kept open only during sudden acceleration, and kept closed at other times.

As described later, in the large overlap area, the oil passage 4
5, the exhaust valve closing timing shifts to the delayed side as shown in FIG. 4, and the intake valve opening timing does not change, so the amount of overlap between intake and exhaust becomes large. On the other hand, in the small overlap region, the oil pressure in the oil passage 45 is discharged and the piston 38 returns to its original position due to the elastic force of the spring 44, so that the amount of overlapping becomes small.

The control unit 27 has a general configuration including an A/D converter, a waveform shaping circuit, an input/output interface, a microcomputer, and a plurality of drive circuits.
A program PA that controls the electromagnetic clutch 25 according to the operating state of the system, a program PB that controls the amount of intake and exhaust overlap that changes the amount of intake and exhaust overlap to a larger or smaller amount via the switching solenoid 31 depending on the operating state, and a program PB that controls the amount of intake and exhaust overlap. A switching speed adjustment program PC that controls the switching speed when switching the amount from "large J" to "small" and vice versa through an electromagnetic on-off valve 58 so as to match the sudden and slow acceleration.
1 and other programs for ignition timing control and fuel injection control are input and stored in advance.

FIG. 5 is an explanatory diagram of various areas included in the table and map in the program PA-PB-PC, and shows the curve a
In the low speed and low load area A inside the switching solenoid 31 is
The small overlap region where the oil pressure in the oil passage 45 is kept at FF and the intake/exhaust overlap amount is kept small, and the areas B and C outside curve a are the areas B and C where the switching solenoid 31 is kept ON and the oil passage is closed. In the large overlap area where hydraulic pressure is supplied to 45 to maintain the intake/exhaust overlap amount at "large", and the area C outside the broken line, the supercharger 14 is activated to supercharge! Magnetic latch ON? This is the il region (supercharging region). Furthermore, straight line C
The bypass valve 20 is fully open in the lower load region, and the opening degree of the bypass valve 20 decreases as the load shifts from straight line C to the higher load side, and becomes fully closed when the load exceeds a predetermined high load ( (See Figure 6).

Next, the outline of the routine of the control program PB-PC will be explained based on FIGS. 7 and 8.

In the figure, Si (i=1.2.3...) indicates each step, and these routines are executed by interrupt processing at predetermined time intervals or by output from a crank angle sensor (not shown) every time the crankshaft rotates once. This is executed by interrupt processing every time a crank angle signal is input.

Figure 7 shows how the intake/exhaust overlap amount is set to "small" when the operating state is in the small overlap region, and the intake/exhaust overlap amount is set to "large" when the operating state is in the large overlap region. , is a routine that controls the intake and exhaust overlap amount via the valve timing change mechanism 30 including the switching solenoid 31. After the control starts, the engine rotation speed N and the intake air amount Q are read (Sl), and the operating state is set to overlap. It is determined whether the large area (areas B and C in Figure 5) is present (S2).
, when YesS, the switching solenoid 31 is controlled to be ON (S3), hydraulic pressure is supplied to the oil passage 45, and the valve timing change mechanism 30 changes the intake/exhaust overlap amount to "large" (indicated by the dotted line in FIG. 4). Can be switched. On the other hand, when the overlap is not in the large overlap region, the switching solenoid 31 is turned off (34), the oil pressure in the oil passage 45 is discharged, and the valve timing change mechanism 30 switches the intake/exhaust overlap amount to "small". After executing the above routine, return to the main routine.

Figure 8 shows a switching speed adjustment control routine in which the switching speed when controlling the intake/exhaust overlap amount is changed suddenly during rapid acceleration and gradually during slow acceleration. The throttle opening θ from the sensor 18 is read (SlO), and the angular velocity A of the throttle valve 13 is determined based on the past throttle opening θ data stored in the RAM memory and the current throttle opening θ data. is calculated (S11), and then it is determined whether the angular velocity A is larger than a predetermined value A0, that is, whether or not there is a sudden acceleration state (S1
2) When the state of sudden acceleration is present, the electromagnetic on-off valve 58 is controlled to open (S13), and when the state of sudden acceleration is not present (including the state of slow acceleration), the electromagnetic on-off valve 58 is controlled to be closed (S13).
14), and then returns to the main routine.

Next, the operation of the engine valve timing control device will be explained.

Even in the medium-speed and medium-load region B inside the supercharging region C shown in FIG. The negative pressure causes fresh air to flow back into the intake port 2 and mix with the fresh air, resulting in the same fuel efficiency reduction effect as when exhaust gas is recirculated.

In the supercharging region C, the intake/exhaust overlap amount is maintained at r large, so that high-temperature burnt gas is scavenged and the occurrence of knocking is reliably prevented.

On the other hand, as explained using the flowchart in FIG.
Since the electromagnetic on-off valve 58 is opened during sudden acceleration where the angular velocity A is greater than the predetermined value A0, pressure oil is supplied to the pressure chamber 49 through the large flow oil passage 57 in addition to the small flow oil passage 56. Therefore, when the intake/exhaust overlap amount is switched from "small" to "large" in response to sudden acceleration, the switching speed increases,
Can be switched in a short time. In this way, since the valve timing of the exhaust valve 3 is switched without any response delay, there is no fear of knocking occurring immediately after sudden acceleration, and acceleration response is improved.

On the other hand, since the electromagnetic on-off valve 58 is kept closed during times other than rapid acceleration, pressure oil is supplied to the pressure chamber 49 through the orifice 55 of the small flow oil passage 56. Therefore, the switching speed when the intake/exhaust overlap amount is switched from "small" to "large" and vice versa becomes small. If the engine characteristics suddenly change due to a sudden change in valve timing, such as during gentle acceleration, problems such as torque shock or a sudden change in vehicle speed may occur. Since the valve timing is switched, the above problem does not occur.

In the above embodiment, the valve timing changing mechanism 30 is incorporated into the exhaust camshaft 5, but by incorporating this mechanism into the intake camshaft 4, the timing of the exhaust valve is fixed and the timing of the intake valve is changed, so that the intake/exhaust overflow can be changed. The amount of wrap may be changed.

Separate Embodiment〉...Refer to Figs. 9 to 11 The engine valve timing control device of this embodiment includes a supply system for supplying pressure oil to the valve timing changing mechanism 30 and a discharge system for discharging the pressure oil. with the following changes,
Other points than these are the same as those in the previous embodiment, so the same reference numerals are given to the same or similar functions, and the explanation thereof will be omitted.

As shown in FIG. 9, the switching solenoid 31, switching valve 52 and plug 51 are removed, and the exhaust camshaft 5 is removed.
A relief valve body 6 facing the end of the oil passage 45 on the end side of the
1 and a relief solenoid 62 for controlling opening and closing of the relief valve body 61. When the relief valve 60 is opened, a portion of the pressure oil in the oil passage 45 flows from the end of the pivot hole 50 to the drain passage 53, thereby reducing the oil pressure in the pressure chamber 49.

The hydraulic pressure supply passage 54 includes a small flow oil passage 56 having an orifice 55 and a large flow oil passage 5 having a large passage cross-sectional area within the pivot portion 36A.
The small flow oil passage 56 branches into an annular groove 56b and a through hole 5.
6a and communicates with the oil passage 45, and the large flow oil passage 57 is connected to the annular groove 57b and the through hole 5'? The large volume oil passage 57 is connected to the oil passage 45 by a, and an electromagnetic on-off valve 58 that can open and close the passage is interposed, and the relief solenoid 62 and the electromagnetic on-off valve 58 are controlled by the control unit 27. Ru.

During operation of the engine E, pressurized oil is supplied to the oil supply passage 54 from the oil gear gallery for lubricating oil, and when the relief valve 60 is closed, the oil passage 45 and the pressure chamber 49 are
The hydraulic pressure increases, the piston 38 is driven, the intake/exhaust overlap amount is switched to "large", and the relief valve 60 is switched to "large".
When opened, the oil pressure in the oil passage 45 and the pressure chamber 49 decreases, and the intake/exhaust overlap amount is switched to "small".

FIG. 10 corresponds to the routine in FIG. 7,
This will be explained.

After the control starts, the engine speed N and the intake air amount Q are read (S20), and then it is determined whether the operating state is in the large overlap region (S21), and if Yes, the relief solenoid 62 is placed in the closed position. is controlled (322), and as a result, the oil pressure in the pressure chamber 49 increases, the piston 38 moves against the spring 44, and the intake/exhaust overlap amount becomes "large".
can be switched to On the other hand, when there is no large overlap area, the relief solenoid 62 is controlled to the open position (3
23) As a result, the oil pressure in the pressure chamber 49 decreases, the piston 38 is pushed by the spring 44, and the intake/exhaust overlap amount is switched to "small".

FIG. 11 corresponds to the routine in FIG. 8, and
This will be explained.

After the control starts, the throttle opening θ is read (S30),
Next, the angular velocity A-dθ/dt is calculated in the same way as in the above embodiment (S31), and then it is determined whether the angular velocity A is Ago or not, that is, whether it is in an accelerated state (332), and if Yes, the angular velocity A is It is determined whether the acceleration is greater than a predetermined value ao, that is, whether there is a sudden acceleration (S33), and when A>ao, the electromagnetic on-off valve 58 is controlled to open (S34). On the other hand, when the vehicle is in an acceleration state but not suddenly accelerated, the electromagnetic on-off valve 58 is controlled to close (337).

On the other hand, if the result of the determination in S32 is that it is not in an acceleration state, it is determined whether A<0, that is, whether it is in a deceleration state (
335), when Yes, it is determined whether IA>a, that is, whether there is a sudden deceleration or not (S36), and when there is a sudden deceleration, the electromagnetic on-off valve 58 is controlled to close (337), and when it is not a sudden deceleration, the electromagnetic on-off valve 58 is closed. 58 is controlled to open (S34)
. Furthermore, when the result of the determination in S35 is NO, that is, in a steady state, the electromagnetic on-off valve 58 is not operated, the current position is maintained, and after steps 330 to 337 are completed, the process returns to the main routine.

In the valve timing control device according to this embodiment, the electromagnetic on-off valve 58 is opened during sudden acceleration as described above, so the supply flow rate of pressure oil increases, and the intake/exhaust overlap amount changes from "small" to "large". Since the electromagnetic on-off valve 58 is closed during slow acceleration, the above-mentioned switching is performed gradually.

In addition, since the electromagnetic on-off valve 58 is closed during sudden deceleration,
The intake/exhaust overlap amount is rapidly switched from "large" to "small" and the electromagnetic on-off valve 58 is opened during slow deceleration, so the above switching is carried out gradually.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a configuration diagram of main parts of a supercharged engine, FIG. 2 is a sectional view of a valve timing changing mechanism, FIG. 3 is a sectional view of a switching valve, and FIG. Fig. 4 is an explanatory diagram of valve timing, Fig. 5 is an explanatory diagram of large overlap region and small overlap region, etc., Fig. 6 is an opening characteristic diagram of the bypass valve, and Fig. 7 is a routine for controlling the amount of intake and exhaust overlap. Figure 8 is a flowchart of the switching speed adjustment control routine, Figures 9, 10, and 1.
Figure 1 is related to another embodiment, Figure 9 is a diagram equivalent to Figure 2,
FIG. 10 is a flowchart of a routine for controlling the amount of intake/exhaust overlap, and FIG. 11 is a flowchart of a routine for controlling the switching speed adjustment. 58...Solenoid on/off valve, 61...Relief valve body, solenoid. 60. Relief valve, 62. Relief E. Engine, 4. Intake camshaft, 5.
- Exhaust camshaft, 12... Air flow meter, 27... Control unit, 30... Valve timing change mechanism, 31... Switching solenoid, 5
5... Orifice, 56... Small flow oil path, 57... Large flow oil path, Fig. 2 Jl: 9 clothes "Luno 1r" Fig. Fig. 7 Fig. 8 Fig. 10 Fig. 11

Claims (2)

[Claims] (1) In an engine valve timing control device that is equipped with a valve timing change device that changes the intake timing or exhaust timing and changes and controls the valve timing according to the operating state of the engine, the valve timing is suddenly changed and controlled during sudden acceleration. A valve timing control device for an engine, further comprising a switching speed adjusting means for gradually changing and controlling valve timing during slow acceleration. (2) In an engine valve timing control device that includes a valve timing change device that changes intake timing or exhaust timing, and changes and controls the valve timing according to the operating state of the engine, the valve timing change device has a camshaft and a cam. A hydraulic actuator that changes the relative phase with a rotation transmission member provided on a shaft, a supply passage that supplies pressure oil to this hydraulic actuator, a relief passage that relieves pressure oil in this supply passage, and opens and closes this relief passage. 1. A valve timing control device for an engine, comprising an on-off valve, and a passage changing means that enlarges the supply passage during slow deceleration and reduces it during sudden deceleration.