JP2506423B2 - Active suspension device - Google Patents

Abstract

PURPOSE:To reduce consumed energy by controlling a fluidic cylinder so that a vehicle body may be in a zero roll condition through pressure control based on the detected or estimated level of a lateral acceleration and steering a rear wheel steering angle operating mechanism in an under-steering direction. CONSTITUTION:A controller 36 inputs a detected level of a lateral acceleration, reverses respective one-sided signals by code reversing devices 39F, 39R through front wheel side and rear wheel side gain adjuster 37F, 37R and makes an addition or subtraction by a prescribed neutral current preset beforehand and an adder-subtractors 38FL - 38RR to control working fluid pressure in posture control hydraulic cylinders 15FL - 15RR through control valves 17FL - 17RR so that a vehicle body may be in a zero roll condition. At the same time, the steering angle of a rear wheel is taken in an under-steering direction, that is, rear wheels are directed to the same side as front wheels. This equalizes approximately the control pressure gain for the fluid pressure cylinder for front and rear wheels, thus decreasing consumption energy.

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in an active suspension device that controls a roll in accordance with a lateral acceleration generated in a vehicle.

[Conventional technology]

As a conventional active suspension device, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 62-295714 previously proposed by the present applicant.

In this conventional example, the lateral acceleration of the vehicle is detected, and a pressure control valve that controls the pressure to a fluid pressure cylinder interposed between each wheel and the vehicle body is controlled based on the detected lateral acceleration value. The roll effect is exerted, and the vehicle body is held in a zero roll or reverse roll state.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional active suspension device, in order to control the roll angle of the vehicle body to zero in the state where lateral acceleration is generated, that is, in the turning state, the control pressure of the fluid pressure cylinder on the turning outer wheel side is set. It is necessary to control the gain ΔP ₀ and the control pressure gain ΔP ₁ of the fluid pressure cylinder on the turning inner wheel side according to the following equations (1) and (2).

Where W is the weight on the spring, A is the pressure receiving area of the fluid pressure cylinder, h is the height between the roll center and the center of gravity of the spring, D is the tread, and ε is the suspension arm lever ratio.
D and ε represent the mounting span of the fluid pressure cylinder.

In reality, since the front and rear wheels are equipped with fluid pressure cylinders, respectively, the control pressure gain Δ
P _F and control pressure gain Δ for rear wheel side fluid pressure cylinder
P _R can be expressed by the following equations (3) and (4), respectively.

However, W = W _F + W _R Therefore, in order to make the roll angle zero with respect to lateral acceleration, ΔP is also applied to the fluid pressure cylinders of the front and rear wheels.
A control pressure change gain of (= P _F + ΔP _R ) is required. The anti-roll moments M _F and M _R of the front and rear wheels can be expressed by the following formulas (5) and (6) from the formulas (3) and (4).

M _F = ΔP _F・ (A ・ D _F・ ε _F ) …… (5) M _R = ΔP _R・ (A ・ D _R・ ε _R ) …… (6) However, when lateral acceleration acts on the vehicle In order to ensure sufficient running stability of the vehicle, when a general vehicle is controlled by the anti-roll moment ratio calculated by the above equations (5) and (6), an appropriate understeer characteristic is obtained. Is not applicable, and actually, the added value of the anti-roll moments M _F and M _R on the front and rear wheels (M _F +
It is necessary to keep the anti-roll moment M _F on the front wheel side fairly large while keeping M _R ) constant.

As a result, in the conventional example, as shown in FIG. 18, the control pressure gain characteristics of the fluid pressure cylinder are as follows: the front wheel side control pressures P _FL , P _FR shown by the solid lines are changed to the rear wheel side control pressures P _RL , P shown by the dotted lines. _It is necessary to make it larger than _RR , and the line pressure P _MAX ′ of the fluid pressure supply source necessary for controlling the fluid pressure cylinder is determined by the control pressure gain ΔP _F on the front wheel side, so an appropriate understeer characteristic is obtained. For this reason, the line pressure P _MAX ′ must also be increased, and the energy consumption required for suspension control becomes extremely large, resulting in unsolved fuel consumption problems.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and when the lateral acceleration acts on the vehicle, it detects the steer characteristic of the vehicle while obtaining the zero roll state by detecting this. In order to maintain the understeer characteristic, the understeer should be maintained without increasing the control pressure gain on the front wheel side with respect to the control pressure gain on the rear wheel side. An object is to provide an active suspension device that can obtain characteristics.

[Means for solving the problem]

In order to achieve the above object, an active suspension device according to a first aspect of the present invention provides a fluid pressure cylinder interposed between a vehicle body and each wheel, and a working fluid pressure of the fluid pressure cylinder having only a command value. A pressure control valve for controlling in accordance with the above, an acceleration detecting or estimating means for detecting or estimating a lateral acceleration of the vehicle body, an acceleration detected value or estimated value of the acceleration detecting or estimating means, and a value corresponding to this value. A steering fluid pressure cylinder connected to the rear wheels and a steering fluid pressure cylinder are provided, which includes a vehicle suspension having a roll suppression control unit that outputs a true roll suppression command value excluding a steer characteristic command value for the pressure control valve. A steering pressure control valve and a steering pressure control valve for controlling the steering pressure control valve so as to enhance the understeer characteristic in accordance with an increase in the lateral acceleration detection value or the estimation value of the acceleration detection or estimation means. It is characterized by having a wheel steering angle control mechanism after having the A characteristic control means.

The active suspension device according to claim (2) is the active suspension device according to claim (1), wherein the rear wheel steering angle control mechanism has a lateral acceleration detection value or an estimated value less than a predetermined value. Further, the steering amount of the rear wheel steering mechanism is set to zero, and the steering amount is increased in accordance with the increase of the lateral acceleration detection value or the estimated value when the steering amount is equal to or more than the predetermined value. .

Further, the active suspension device according to claim (3) is a fluid pressure cylinder interposed between the vehicle body and each wheel, and a pressure for controlling the working fluid pressure of the fluid pressure cylinder according to only the command value. A control valve, an acceleration detecting or estimating means for detecting or estimating the lateral acceleration of the vehicle body, an acceleration detected value or estimated value of the acceleration detecting or estimating means, and a command value for the pressure control valve having a value corresponding to this value. And a rear wheel steering mechanism having a steering fluid pressure cylinder connected to the rear wheels, the steering fluid pressure cylinder of the rear wheel steering mechanism and the vehicle. It is characterized in that the rear wheel side pressure control valve of the vehicle suspension is communicated with the front wheel steering through a flow path so as to be in phase with the front wheel steering, and fluid pressure fluctuation absorbing means is connected to the flow path.

[Action]

In the active suspension device according to claim (1), a steering pressure control valve that detects or estimates a lateral acceleration acting on a vehicle and controls the steering fluid pressure cylinder of the rear wheel steering mechanism based on the detected or estimated lateral acceleration. The steer characteristic control means controls the load of the front and rear wheels by controlling the direction in which the vehicle enhances the understeer characteristic in accordance with the increase in the lateral acceleration detection value or the estimated value, that is, the direction in which the rear wheels are steered to the same phase as the front wheels. It is no longer necessary to change the steering characteristics by changing the sharing ratio in the vehicle suspension, and as a result, the control pressure gains for the front and rear wheel fluid pressure cylinders can be made approximately equal, reducing the line pressure required for control and consuming Energy can be reduced.

Further, in the active suspension device according to the second aspect, the neutral position is maintained when the rear wheel steering characteristic of the rear wheel steering angle control mechanism has the lateral acceleration detection value or estimated value less than the predetermined value. , If the characteristics of the vehicle become neutral steering characteristics and the turning performance is improved, conversely, if the lateral acceleration detection value or estimated value increases above a predetermined value, the steering amount also increases accordingly and the understeer characteristics are strengthened, and running stability is improved. Improve.

Further, in the active suspension device according to claim (3), the control pressure of the pressure control valve controlled based on the lateral acceleration acting on the vehicle is supplied to the steering fluid pressure cylinder of the rear wheel steering mechanism. As a result, this turning fluid pressure cylinder is indirectly controlled to lateral acceleration, and the same operation as in the case of claim (1) can be obtained. In addition to this, the rear wheel side pressure control valve And, by the fluid pressure fluctuation absorbing means interposed between the turning fluid pressure cylinders, when traveling on an irregular road surface, due to vertical vibration input to the wheels,
When the pressure of the fluid pressure cylinder interposed between the wheel and the vehicle body fluctuates, the pressure variation can be reliably absorbed, and the pressure variation of this fluid pressure cylinder is prevented from affecting the rear wheel steering mechanism. To do.

〔Example〕

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

1 to 9 are views showing a first embodiment of the present invention.

In FIG. 1, 11FL, 11FR, 11RL and 11RR are active suspensions interposed between a vehicle body side member 12 and a wheel side member 14 that individually supports the wheels 13FL, 13FR, 13RL and 13RR, respectively. There are hydraulic cylinders 15FL to 15RR for attitude control and coil springs 16FL as actuators.
˜16RR and attitude control hydraulic cylinders 15FL to 15RR are provided with pressure control valves 17FL to 17RR for controlling the operating hydraulic pressure in response to only a command value from a control device 36 described later.

Here, in each of the attitude control hydraulic cylinders 15FL to 15RR, as shown in FIGS. 1 and 2, the cylinder tube 15a is attached to the wheel side member 14, and the piston rod 15c is provided with the piston 15b at the tip. Is attached to the vehicle body side member 12, and the hydraulic pressure of the hydraulic chamber 15d in the cylinder tube 15a is controlled by the pressure control valves 17FL to 17RR. In addition,
The piston 15b has a through hole 15d that communicates between the upper and lower hydraulic chambers 15d.
The cylinder tube 15a and the piston rod 15c are moved relative to each other due to the difference between the pressure receiving areas above and below the piston 15b.

Each of the coil springs 16FL to 16RR is mounted in such a manner that the piston rod 15c is wound between the body side member 12 and the cylinder tube 15a of the attitude control hydraulic cylinders 15FL to 15RR to support the static load of the vehicle body. are doing. In addition,
The coil springs 16FL to 16RR may have a low spring constant that only supports the static load of the vehicle body.

As shown in FIG. 2, each of the pressure control valves 17FL to 17RR has a cylindrical valve housing 21 and a proportional solenoid 22 provided integrally with the cylindrical valve housing 21. A partition wall 2 having a valve seat 21c having a predetermined diameter is provided in the center of the valve housing 21.
The upper insertion hole 21U in FIG. 2 defined by 1A and the lower insertion hole 21L in FIG. 2 are coaxially formed. Further, a fixed throttle 23 is provided above the insertion hole 21L and below the partition 21A by a predetermined distance, whereby a pilot chamber C is formed between the fixed throttle 23 and the partition 21A. In addition, the fixed diaphragm 23 in the insertion hole 21L
The main spool 24 is disposed on the lower side of the main spool 24 so as to be slidable in the axial direction thereof. The feedback chambers F _U and F _L are formed above and below the main spool 24, respectively, and The upper and lower ends are regulated by offset springs 25A and 25B arranged in the feedback chambers F _U and F _L , respectively. Then, the input port 21i, the control port 21n and the drain port 21o are formed to communicate with the insertion hole 21L in this order, the input port 21i is connected to the discharge side of the hydraulic pressure supply source 18 via the line pressure pipe 19, and the drain port 21o is It is connected to the tank of the hydraulic power source 18 via the drain pipe 20, and the control port 21n is further connected to the hydraulic cylinders 15FL to 15RR via the hydraulic pipe 27.
Is connected to the pressure chamber 15d.

The main spool 24 includes a land 24a facing the input port 21i, a land 24b facing the drain port 21o, a pressure chamber 24c formed by an annular groove formed between the ports 24a and 24b, and the pressure chamber 24c and Lower feedback room _FL
And a pilot passage 24d that communicates with the.

In the upper insertion hole 21U, a poppet 26 is axially slidably arranged with its valve portion facing the valve seat 21c. The poppet 26 allows the insertion hole 21U to move in two axial directions.
The chamber is defined, and the flow rate of the working oil flowing through the valve seat 21c, that is, the pressure in the pilot chamber C can be adjusted.

Further, the input port 21i is connected to the orifice 21 _SO
Is communicated with the pilot chamber C via a pilot passage 21s having the above, and the drain port 21o is communicated with the insertion hole 21U via a drain passage 21t.

On the other hand, the proportional solenoid 22 includes an axially slidable plunger 27, an actuator 27A fixed to the poppet 26 side of the plunger 27, and an exciting coil 28 for driving the plunger 27 in the axial direction. Has and this excitation coil
28 is appropriately excited by a command value I which is a direct current from the control device 36. As a result, the movement of the plunger 27 controls the position of the poppet 26 via the actuator 27A,
The flow rate passing through the communication hole 21A is controlled. Then, when the pressures of the feedback chambers F _L and F _U are balanced while the pressing force by the proportional solenoid 22 is being applied to the poppet 26, the spool 24 is in the neutral position and the control port
21n is disconnected from the input port 21i and the drain port 21o.

Here, as for the relationship between the command value I and the control oil pressure P _c output from the control port 21n, as shown in FIG. 3, when the command value I is near zero, P _MIN is output, and from this state When the command value I increases in the positive direction, the control output P _C increases with a predetermined proportional gain K _{1 and} the line pressure P _L of the hydraulic pressure supply source 18 increases.
Is saturated with.

The pressure control valves 17FL to 17RR are connected to the proportional solenoid 22.
Pressing force is applied to the poppet 26 by, and in a state where the pressure in the upper feedback chamber F _U and the lower feedback chamber F _L is balanced, the wheel, for example, upward sprung resonance frequency due to the convex portion passes the road surface When a relatively low-frequency vibration input (or downward vibration input due to passage through a recess) is transmitted, the hydraulic cylinders 15FL to 15FL
The cylinder tube 15a of the RR tries to move upward (or downward), and the pressure in the hydraulic chamber 15a rises (or decreases).

Thus, the pressure in the hydraulic chamber 15d is increased (or decreased), the hydraulic chamber 15a and the hydraulic pipe 27, a pressure control port 21n and the communication via the pilot passage 24d through the lower feedback chamber F _L accordingly Rises (or falls) and loses its balance with the pressure in the upper feedback chamber F _U , causing the spool 24 to move upward (or downward) and close the input port 21i and the control port 21n (or (Opening direction), and between the output port 21o and the control pressure port 21n in the opening direction (or closing direction),
Part of the pressure in the hydraulic chamber 15d is discharged from the control pressure port 21n to the hydraulic pressure supply source 18 via the output port 21o and the hydraulic pressure pipe 20 (or from the hydraulic pressure source 18 to the input port 21i, the control pressure port 21n and the hydraulic pressure pipe 27). Hydraulic pressure is supplied to the hydraulic chamber 15d via
You.

As a result, the pressure in the hydraulic chamber 15d of the hydraulic cylinders 15FL to 15RR is reduced (or increased), and the pressure increase in the hydraulic chamber 15d due to the upward vibration input (or the pressure decrease in the pressure chamber 15a due to the downward vibration input) is suppressed. Therefore, the vibration input transmitted to the vehicle body side member 14 can be reduced. At this time, since no restriction is provided in the drain pipe 20 between the output port 21o of the pressure control valves 17FL to 17RR and the hydraulic pressure supply source 18, a damping force should be generated when suppressing the upward vibration input. There is no.

In FIG. 1, 28H is a pressure control valve 17FL to 17RR.
And a high-pressure side accumulator for pulsation absorption connected in the middle of the hydraulic pipe 25 between the hydraulic source 24 and the hydraulic source 24, and 28L is a pressure control valve 17FL to 1FL.
A low pressure side accumulator that absorbs pressure fluctuations in the unsprung resonance frequency range that cannot be followed by the pressure control valves 17FL to 17RR that are connected to the hydraulic pipe 27 between the 7RR and the hydraulic cylinders 15FL to 15RR via the throttle valve 28V. is there.

On the other hand, a rear wheel steering mechanism 30 is arranged on the rear wheels 13RL and 13RR. The rear wheel steering mechanism 30 has a double-acting rear wheel steering hydraulic cylinder 31 fixedly supported by the vehicle body. In this rear wheel steering hydraulic cylinder 31, a centering coil spring 31c is interposed between a piston 31b in the cylinder tube 31a and an inner end of the cylinder tube 31a, and both ends of the piston rod 31d are respectively provided with side rods 32L and 32
Rear wheels 13RL and 1 via R and knuckle arms 33L and 33R
It is connected to 3RR. The left and right hydraulic chambers 31 and 31r defined by the piston 31b of the rear wheel steering hydraulic cylinder 31 have the same configuration as the suspension pressure control valves 17FL to 17RR connected to the hydraulic source 24. Control valve
It is connected to the control pressure port of 34L and 34R. In FIG. 1, the rear wheel steering mechanism 30 is shown as a plan view for convenience of explanation.

Further, the vehicle body is provided with a lateral acceleration detector 35 for detecting lateral acceleration at a position slightly forward of the sprung center of gravity position. When the lateral acceleration of the vehicle is zero, the lateral acceleration detector 35 detects the lateral acceleration. Zero, a positive current proportional to the lateral acceleration when a lateral acceleration occurs during a right turn, and a negative current proportional to a lateral acceleration when a lateral acceleration occurs during a left turn are output as lateral acceleration detection values. Is input to the controller 36.

The control device 36, as shown in FIG.
Gain (amplification degree) supplied with the lateral acceleration detection signal from 35. Front wheel side gain adjuster 37F and rear wheel side gain adjustment which are composed of variable amplification degree amplifiers that can arbitrarily change Ky _F , Ky _R and K δ _R. vessels 37R and has a rear wheel steering gain adjuster 37S, front wheel gain adjuster wheel side roll restraining instruction value output is 37F I _F
Is supplied to an adder 38FL for adding a neutral pressure current I _N set in advance to the pressure control valve 1 on the front left side as a roll suppression command current I _FL.
Is supplied to the 7FL, the front right side of the pressure control valve 17FR, is sign inverted by sign inverter 39F for multiplying minus 1, by the adder 38FL similar adder 38FR to neutrality piezoelectric stream I _N The added roll suppression command current I _FR is supplied.

Similarly, the output of the rear wheel side gain adjuster 37R is directly supplied to the adder 38RL as the rear wheel side roll suppression command value I _R , and the added output is supplied to the rear left pressure control valve 17RL as the roll suppression command current I _RL. The pressure control valve 17
RR is supplied to an adder 38RR via a sign inverter 39R that multiplies the rear wheel side roll suppression command value I _R by -1, and the addition output is supplied as a roll suppression command current I _RR . Here, front and rear wheel side gain adjusters 37F, 37R, adder 38F
The L, 38FR, 38RL, 38RR and the sign inverters 39F, 39R constitute roll suppression control means for outputting a true roll suppression command value excluding the steering characteristic control component.

Further, the output of the rear wheel steering gain adjuster 37S is supplied as a rear wheel steering command value I _S to an adder 38SL similar to the adders 38FL to 38RR, and the added output is rear wheel steering command current I _SL. It is supplied to the right pressure control valve 34R for use, on the left pressure control valve 34L, a rear wheel steering command value I _S minus 1
Is inverted by a sign inverter 38S that multiplies by, the neutral pressure command current I _N is added to the inverted output by an adder 39SR, and the added output is supplied as a rear wheel steering command current I _SR . Here, the rear wheel steering gain adjuster 37S, the adders 38SL, 38SR, and the sign inverter 39S constitute a steer characteristic control means for controlling the rear wheel steering angle in a direction in which the understeer characteristic is strengthened in accordance with the increase in the lateral acceleration detection value. are doing.

Here, each gain of the front wheel gain adjuster 37F, the rear wheel gain adjuster 37R, and the rear wheel steering gain adjuster 27S is the fifth gain.
As shown in the figure, the control pressure gain Ky _F on the front wheel side is selected to be substantially equal while maintaining the relationship of Ky _F > Kδ _R > Ky _R , and the control pressure gain ΔP _F in the conventional example is (Δ
Is selected to be P _F + ΔP _R) / 2 about a small value is selected smaller than the neutral piezoelectric current value I _N 'in the neutral pressure setting current value I _N also conventional adder 38FL~38SR accordingly ing.

Therefore, the lateral acceleration detection value (positive when turning right) is used as the horizontal axis, and the control pressure P _FL of the fluid pressure cylinders 15 _{FL to} 15 RR is set.
The suspension control pressure characteristic with the vertical axis of ~ P _RR is as shown in Fig. 5, and the line pressure P _MAX and the neutral pressure P _N are selected to be smaller than those of the conventional example.

Next, the operation of the above embodiment will be described. Now, it is assumed that the vehicle is traveling straight on a flat road with no unevenness on the road surface. In this state, no roll occurs in the vehicle body, so the lateral acceleration detection value of the lateral acceleration position detector 35 becomes substantially zero.
Therefore, the gain controller 37F of the control unit 36, the command value I _F output from the 37R and 37S, I _R and I _S is also substantially zero, and the sum is neutral pressure setting current I _N at adder 38FL~38SR thereto since the pressure command value I _FL ~I _SR is substantially neutral pressure setting current I _N, and the
Since this is supplied to the pressure control valves 17FL to 17RR and 34L and 34R, the control pressure P _C of these pressure control valves is set to the neutral pressure P _N.

Therefore, in this state, as described above, due to the vibration input of a relatively low frequency input from the road surface through the wheels 13FL to 13RR, the pressure fluctuations in the pressure control chamber C of the pressure control valves 17FL to 17RR are caused. The vibration input of a relatively high frequency that is absorbed by the movement of the spool 24 and corresponds to the unsprung resonance frequency due to the fine unevenness of the road surface is absorbed by the throttle valve 28V and the accumulator 28L, and the vibration transmissibility to the vehicle body is increased. It is possible to reduce the weight and secure a good riding comfort.

On the other hand, in the rear wheel steering mechanism 30, since the control pressures of the pressure control valves 34L and 34R are both the neutral pressure P _N , the pressures in the left and right pressure chambers 31 and 31r of the rear wheel steering hydraulic cylinder 31 become equal. The centering coil spring 31c holds the piston rod 31d in the neutral position, so that the rear wheels 13RL and 13RR are held in the neutral position, that is, in the straight traveling state.

When the steering wheel is turned to the right by turning the steering wheel from the straight running state, as shown in FIG. 7, the vehicle body rolls to the right with a roll angle θ when viewed from the front side. At this time, as shown in FIG. 8, one wheel of the vehicle will be described. Here, the mass of the vehicle is M, and the effective area of the hydraulic cylinder 15FL is A.

Then, considering the linear range of the characteristic of the pressure control valve 17 shown in FIG. 3, P = K ₁ · I (7)

On the other hand, from FIG. 8, M ₂ = P · A + K (x ₁ −x ₂ ) ... (8), and the command value I becomes I = Ky ... (9).

Therefore, by substituting the equation (7) into the equation (8) and rearranging, M ₂ + K (x ₂ −x ₁ ) = K ₁ · IA ··· (10).

Here, if the unsprung displacement x ₁ is zero (x ₁ = 0), the command value I
The transfer function in the form of the response of the sprung mass displacement x ₂ to Therefore, if expressed as a transfer function in the form of response to lateral acceleration, Becomes

On the other hand, in vehicles that do not perform anti-roll control,
As shown in the figure, the roll motion of the vehicle body when lateral acceleration is applied, the roll moment of inertia is J, the roll angle is θ,
When the distance between the center of gravity and the roll center is H, the spring constant is K, and the tread is L, it can be expressed by the following equation.

In equation (13), when expressed by a transfer function in the form of response to lateral acceleration, Further, since x ₂ = Lθ / 2, substituting this into the equation (13), and expressing this by a transfer function in the form of response to lateral acceleration, Becomes

Therefore, the expression (12) represents the response of the hydraulic system of the present invention, and the expression (15) represents the roll motion with respect to the lateral acceleration. When the two are compared, the denominators are both quadratic and equivalent.

Therefore, it can be understood that the roll motion can be dynamically suppressed by the hydraulic system of the present invention by appropriately setting the gain Ky of the expression (12).

Therefore, as shown in FIG. 7, when the vehicle is rolling downward to the right when viewed from the front side, the lateral acceleration detector 35
Since the lateral acceleration detection value of is a positive value, it is supplied to the gain adjusters 37F, 37R and 37S, respectively.

Then, the gain controller 37F and a gain lateral acceleration detection value output from the 37R Ky _F and Ky _R multiplied by front and rear wheels roll restraining instruction value I _F and I _R that is supplied directly to the adder 38FL and 38RL, The roll suppression command currents I _FL and I _{RL obtained} by adding the neutral pressure setting current I _N to the front and rear wheel roll suppression command values I _F and I _R from these adders 38 FL and 38 _RL are the pressure control valves on the left side.
Since the pressures are supplied to 17FL and 17RL, the control pressures P _FL and P _RL of the pressure control units 17FL and 17RL on the left side are higher than the neutral pressure P _N , as shown in FIG.

On the other hand, on the right side of the pressure control valve 17FR and 17RR, the front and rear wheels roll restraining instruction value I _F and I _R is the sign inverter 39F and 39R
Are supplied to the adders 38FR and 38RR via the control unit P and the control pressures P _FR and P _RR are lower than the neutral pressure P _N as shown in FIG.

Therefore, the pressure in the hydraulic chamber 15d of the left hydraulic cylinders 15FL and 15RL increases. Therefore, in the pressure receiving area of the upper hydraulic chamber of the piston 15b and the pressure receiving area of the lower hydraulic chamber, the pressure receiving area of the upper hydraulic chamber is smaller than the pressure receiving area of the lower hydraulic chamber by the cross-section integral of the piston rod. Therefore, the thrust that is obtained by multiplying the area difference between the two by pressure acts upward, and this thrust causes the hydraulic cylinder 15FL on the left side to move.
And 15RL can generate a cylinder biasing force that resists the contracting force contracted by the rolls, and can exert the anti-roll effect that maintains the vehicle body in the zero roll state.

Also, the hydraulic chamber 15d of the right hydraulic cylinders 15FR and 15RR
The pressure is reduced, which reduces the thrust for urging the piston 15b upward for the same reason as above, and controls the urging force so as not to promote the extension force of the roll.

At this time, since the urging forces generated by the front wheel hydraulic cylinders 15FL, 15FR and the rear wheel hydraulic cylinders 15RL, 15RR are substantially equal as shown in FIG. 5, the anti-roll moments generated on the front wheel side and the rear wheel side are the same. M _F and M _R are also substantially equal, and the steering steer characteristic by the suspension is maintained at a substantially neutral steer characteristic.

However, the gain adjuster rear wheel steering gain lateral acceleration detection value output from the 38S K? _S multiples wheel steering command value I _S after is supplied directly to the adder 38SL, the rear wheel steering command value I in the adder 38SL _Since the neutral pressure setting current value I _N is added to _S , the added output, that is, the rear wheel steering command current I _SL becomes a value larger than the neutral setting current I _N , while the adder 38SR outputs the rear wheel steering command value I _S. There so supplied is inverted by sign inverter 39S, the rear wheel steering command current I _SR becomes smaller than the neutral setting current I _N.

Therefore, the control pressure P _SR of the pressure control valve 34R becomes a value larger than the neutral pressure P _N , and the control pressure P _SL of the pressure control valve 34L becomes neutral.
It becomes a value smaller than P _{N, the} pressure in the right side pressure chamber 31r of the rear wheel steering cylinder 31 becomes larger than the pressure in the left side pressure chamber 31, and the piston 31a is centered with the pressure difference between the pressure chambers 31r and 31. It moves to the left to a position where the elasticity of the coil spring 31c is balanced, whereby the rear wheels 13RL and 13RR are steered to the right side in the same phase as the front wheels 13FL and 13FR, as shown in FIG.
Understeer characteristics can be obtained.

In this way, by steering the rear wheels 13RL and 13RR in the understeer direction, the equivalent cornering power of the rear wheels 13RL and 13RR is increased, and the line pressure P _MAX of the hydraulic power supply 24 is reduced to reduce the front and rear wheels. Roll moment ratio is "1"
The steering characteristic of the vehicle does not become a neutral steering characteristic or an oversteering characteristic even if it is brought close to, and an appropriate understeering characteristic is maintained, so that the running stability can be improved. That is, for example, when changing lanes at high speed, when the rear wheel steering is not performed, the vehicle tends to swing back and forth due to a sudden lane change,
Steering the rear wheels enables a stable lane change.

In addition, when the vehicle turns left, the lateral acceleration detector
Since a negative lateral acceleration detection value is output from 35, the pressure in the right hydraulic cylinders 15FR, 15RR increases and the pressure in the left hydraulic cylinders 15FL, 15RL decreases, contrary to the above right turn, and the vehicle body The anti-roll effect that keeps the vehicle in the zero roll state can be exerted, and the piston rod 31d of the rear wheel steering cylinder 31 moves to the right to steer the rear wheels 13RL and 13RR to the left as shown in FIG. As a result, the steer characteristic of the vehicle is maintained as the under steer characteristic.

In the first embodiment, the case where the control pressures P _SL and P _SR of the pressure control valves 34L and 34R of the rear wheel steering mechanism 30 are proportional to the lateral acceleration detection value as shown in FIG. However, the present invention is not limited to this, and as shown in FIG. 10, a dead zone is set for the control pressures P _SL and P _SR with respect to the lateral acceleration detection value, and the rear wheel steering characteristics of the rear wheel steering mechanism 30 are set. To
As shown in Fig. 11, the lateral acceleration detection value is a predetermined value ± _s
In a smaller range, the neutral position may be maintained, and when the lateral acceleration detection value becomes equal to or greater than the predetermined value ± _s , the steering amount δ _R may be increased in proportion to the lateral acceleration detection value. In this case, when the lateral acceleration detection value is relatively small, the rear wheels are held in the neutral position where they are not steered.
The characteristic of the vehicle becomes the neutral steer characteristic to improve the turning performance, and as the lateral acceleration detection value becomes larger, the under steer characteristic becomes to improve the running stability.

Further, in the above-described first embodiment, the case where the two pressure control valves 34L and 34R are applied to the rear wheel steering mechanism 30 has been described, but the present invention is not limited to this, as shown in FIG. 12 and FIG.
The pressures of the left and right pressure chambers 31 and 31r of the rear wheel steering hydraulic cylinder 31 are supplied to the spool as pilot pressures,
By driving this spool with an electromagnetic proportional solenoid, one 4-port pressure control valve 40 having a direction switching function for controlling the pressure to the left or right pressure chamber 31 or 31r in response to the command current I _S is applied. In this case, the hydraulic piping system can be simplified and
There is an advantage that the weight of one pressure control valve can be reduced. The pressure control valve 40 may be, for example, JP-A-61-1.
The pressure control valve disclosed in Japanese Patent Publication No. 93910 can be applied.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the second embodiment, the pressure control based on the lateral acceleration detection value of the rear wheel steering mechanism 30 does not require a separate pressure control valve for rear wheel steering, and the rear wheel pressure control valves 17RL and 17RR for suspension control are controlled. Control pressure P output from control port 21n
_It was done by _C.

That is, as shown in FIG. 14, in the configuration of FIG. 1, the pressure control valves 34L and 34R are omitted, and instead of this, the left hydraulic chamber 31 of the rear wheel steering hydraulic cylinder 31 in the rear wheel steering mechanism 30 is To the control pressure port 21n of the pressure control valve 17RR, the right hydraulic chamber 31r is connected to the control pressure port 21n of the pressure control valve 17RL via hydraulic pipes 41L and 41R as flow passages, and these hydraulic pipes 41L, 41R with throttle valves 43L and 43R respectively
The accumulators 44L and 44R are connected through the control device 36, and accordingly, the control device 36 also has a gain setting device 37S for rear wheel steering, adders 38SL and 38SR, and a sign inverter, as shown in FIG.
It has the same configuration as that of the first embodiment except that 39S is omitted, and the corresponding portions to those in FIG. 1 are designated by the same reference numerals and the detailed description thereof will be omitted.

According to the second embodiment, assuming that the vehicle is traveling straight ahead, the lateral acceleration does not act on the vehicle, so the lateral acceleration detection value of the lateral acceleration detector 15 is zero, and the rear wheel side pressure control valve. Since the control pressures of 13RL and 13RR are both set to the neutral set pressure P _N , the vehicle body is maintained in the zero roll state, and the left and right hydraulic chambers 31 of the rear wheel steering hydraulic cylinder 31 and
Since the pressures of 31r both become the neutral set pressure P _N , the piston rod 31d is maintained in the neutral position and the rear wheels 13RL and 13RR maintain the straight traveling state.

For example, when a lateral acceleration occurs in the vehicle by turning right from this straight traveling state, this is detected by the lateral acceleration detector 35, and a positive lateral acceleration detection value is output from the lateral acceleration detector 35 to the control device 36. As described above, the controller 36 outputs the roll suppression command current I _RL having a value larger than the neutral set current I _N to the rear left pressure control valve 17RL and neutralizes the rear right pressure control valve 17RR. The roll suppression command current I _RR having a value smaller than the set current I _N is output. Therefore, the control pressure P _RL of the pressure control valve 17RL becomes a value higher than the neutral pressure P _N as shown by the dotted line in FIG.
The control pressure P _RR of 17RR becomes a value lower than the neutral pressure P _N and is supplied to the hydraulic cylinders 15RL and 15RR, so that the roll of the vehicle body can be suppressed and the zero roll state can be controlled.
At the same time, the high control pressure P _RL of the pressure control valve 17RL is passed through the hydraulic pipe 40L to the right hydraulic chamber 31r of the rear wheel steering hydraulic cylinder 31.
In addition, since the low control pressure P _RR of the pressure control valve 17RR is supplied to the left hydraulic chamber 31 of the rear wheel steering hydraulic cylinder 31 via the hydraulic pipe 40R, the differential pressure between the hydraulic chambers 31r and 31 and the centering coil 31 The piston rod 31d moves leftward to a position where the biasing force of the spring 31c is balanced, whereby the rear wheels 13RL and 13RR are steered to the right.

When the vehicle turns left, the rear wheels 13
RL and 13RR are steered to the left.

As a result, the rear wheels 13RL and 13RR are as shown in FIG.
Since the front wheels 13FL and 13FR are steered in the same phase, the steer characteristic of the vehicle becomes an understeer characteristic, and like the first embodiment, the steer characteristic of the vehicle can be made an understeer characteristic by the rear wheel steering mechanism. Since it is not necessary to obtain the understeer characteristic by the anti-roll moment generated by the hydraulic cylinders 17FL to 17RR, the control pressure gains of the hydraulic cylinders 15FL to 15RR on the front and rear wheels can be made substantially equal, which allows the line pressure to be adjusted. And understeer characteristics can be obtained while maintaining zero roll. Moreover, according to the second embodiment, since the rear wheel steering pressure control valve and the suspension control pressure control valve are shared, there is no need to provide a rear wheel steering pressure control valve separately, and this The number of parts and the weight of the vehicle body can be reduced.

Also, the vehicle is traveling on an irregular road surface, and the rear wheels 13RL and 13RL
When RR is vertically displaced, the cylinder tubes 15a of the hydraulic cylinders 15RL, 15RR for suspension move up and down, and as described above, the internal pressure of the hydraulic cylinders 15RL, 15RR increases and decreases, and this pressure fluctuation causes the pressure control valve 17RL , 17RR hydraulic piping 40
Rear wheel steering hydraulic cylinder 3 directly connected via L, 40R
1 affects the hydraulic piping 41L, 41R
Since the accumulators 44L and 44R are connected via L and 43R, high-frequency vibrations of pressure fluctuations can be damped and absorbed by these, and the pressure of the suspension hydraulic cylinders 15RL and 15RR can be applied to the rear wheel steering hydraulic cylinder 31. It is possible to prevent fluctuations from being transmitted, and it is possible to prevent fluctuations in the rear wheel steering angle due to pressure fluctuations in the left and right hydraulic chambers 31 and 31r of the rear wheel steering hydraulic cylinder 31, thus ensuring stable running on an irregular road surface. Can be secured.

As in the second embodiment, the throttle valves 42L, 42R or the throttle valves 43L, 43R are connected to the hydraulic pipes 41L, 41R between the suspension pressure control valves 17RL and 17RR and the rear wheel steering hydraulic cylinder 31.
If a pressure absorbing element consisting of the accumulators 44L and 44R is inserted, the response of the rear wheel steering hydraulic cylinder 31 will be slightly behind the lateral acceleration detection value detected by the lateral acceleration detector 35. Since the rear wheels are steered and understeer after the yaw moment is generated by the front wheel steering, it is possible to obtain a natural steering feeling without deteriorating the turning performance.

Further, in each of the above embodiments, the case where the lateral acceleration that occurs in the vehicle is detected by using the lateral acceleration detector 35 has been described, but the present invention is not limited to this, and the vehicle speed V and the steering angle δ A lateral acceleration detecting device for detecting a true lateral acceleration generated in the vehicle by detecting a vehicle speed detector and a steering angle detector, respectively, and executing a predetermined calculation process based on the detected vehicle speed detector and the steering angle detector (see JP-A-62-293167). May be provided. In this case, the control can be performed based on the true lateral acceleration that is not affected by the roll of the vehicle body, so that the control accuracy can be improved and the control system can be improved. Is a substantially open loop system, so there is no possibility of causing self-excited vibration.

Further, in each of the above embodiments, the case where the hydraulic cylinder is applied as the fluid pressure cylinder has been described, but the present invention is not limited to this, and it goes without saying that other fluid pressure cylinders such as a pneumatic cylinder can be applied. .

Furthermore, in the above-described embodiment, the case where the lateral acceleration detector 35 outputs a positive acceleration detection value during a right turn and a negative acceleration detection value during a left turn is described, but the present invention is not limited to this.
From 35, a positive predetermined value is output when the lateral acceleration is zero, a positive value higher than the predetermined value when turning to the right, and a positive value lower than the predetermined value when turning to the left, respectively.
It is applied a subtracter for subtracting the neutral setting current I _N instead of the 36 adders 38RL~38RR can obtain the same effect as the above embodiment.

〔The invention's effect〕

As described above, according to the active suspension device of the first aspect, the roll suppression control means controls the pressure control valve based on the lateral acceleration detection value or the lateral acceleration estimated value to control each wheel and each wheel. A fluid pressure cylinder inserted between the vehicle bodies is controlled so as to suppress the roll of the vehicle body, and the steer characteristic control means increases the rear-wheel steering angle in the direction of strengthening the understeer characteristic in accordance with the detection of the lateral acceleration or the increase of the estimated value. Since the vehicle is steered, it is not necessary to make the steering characteristics of the vehicle understeer due to the anti-roll moments generated by the fluid pressure cylinders on the front and rear wheels. The control pressure gains of can be made approximately equal, and as a result, it is possible to reduce the line pressure supplied to the pressure control valve and reduce the energy consumption. Effect that can be reduced is obtained.

Further, according to the active suspension device of the second aspect, the neutral position is maintained when the rear wheel steering characteristic of the rear wheel steering angle control mechanism has the lateral acceleration detection value or the estimated value less than the predetermined value. As a result, the characteristics of the vehicle become neutral steering characteristics and the turning performance improves. Conversely, when the lateral acceleration detection value or estimated value increases above a certain value, the steering amount also increases accordingly and the understeering characteristics are strengthened to improve running stability. The effect that the property can be improved is obtained.

Further, according to the active suspension device of the third aspect, the control pressure of the rear wheel steering mechanism can be obtained from the pressure control valve that controls the attitude control fluid pressure cylinder, and the pressure control valve can be shared. Therefore, the above-mentioned claim (1)
In addition to the effect of, the number of pressure control valves can be reduced, the manufacturing cost and weight can be reduced, and
The degree of freedom in design when mounted on a vehicle can be improved, and pressure fluctuation absorbing means is connected between the pressure control valve for controlling the attitude control fluid pressure cylinder and the rear wheel steering fluid pressure cylinder. Therefore, it is possible to prevent the influence of the pressure fluctuation of the attitude control fluid pressure cylinder on the rear wheel steering mechanism when traveling on an irregular road surface, and it is possible to improve the reliability, and moreover, the pressure fluctuation absorbing means allows the rear wheel steering mechanism to be improved. Since the response of the steering mechanism is slightly delayed, it is possible to obtain a natural steering feeling without impairing the turning performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention, and FIG.
FIG. 4 is a sectional view showing an example of a pressure control valve applicable to the present invention, FIG. 3 is a graph showing the relationship between the command value and output pressure of the pressure control valve of FIG. 2, and FIG. 4 is applied to the present invention. 5 is a block diagram showing an example of a possible control device, FIG. 5 is a characteristic diagram showing a relationship between lateral acceleration and control pressure of a hydraulic cylinder, and FIG. 6 is a characteristic line showing a relationship between lateral acceleration and a rear wheel steering angle. FIG. 7, FIG. 7 to FIG. 9 are explanatory views for explaining the operation of the first embodiment, and FIG. 10 and FIG. 11 are respectively FIG. 5 and FIG. 6 showing a modification of the first embodiment. Corresponding characteristic diagrams, FIGS. 12 and 13 are schematic configuration diagrams showing a modification of the first embodiment and a block diagram of the control device, and FIG. 14 is a block diagram showing the second embodiment of the present invention. FIG. 15 is a block diagram showing the control device of the second embodiment, and FIG. 16 is a characteristic line showing the relationship between lateral acceleration and control pressure of the hydraulic cylinder. , FIG. 17 is a characteristic line view showing the relationship between the rear wheel steering angle and the lateral acceleration, FIG. 18 is a characteristic diagram showing the relationship between the control pressure of the lateral acceleration and the hydraulic cylinders of a conventional example. In the figure, 11FL-11RR are active suspensions, 13FL-13
RR is a wheel, 15FL to 15RR are hydraulic cylinders, 16FL to 16RR are coil springs, 17FL to 17RR are pressure control valves, 18 is a hydraulic supply source, 30 is a rear wheel steering mechanism, 31 is a rear wheel steering hydraulic cylinder, 34L, 34R, 40 are pressure control valves, 41L, 41R are hydraulic piping, 43
L and 43R are throttle valves (pressure fluctuation absorbing means), and 44L and 44R are accumulators (pressure fluctuation absorbing means).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshi Fujimura, 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Masaharu Sato, 2 Takara-cho, Kanagawa, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Kensuke Fukuyama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A 64-9073 (JP, A) JP-A 60-166565 (JP, A) JP 60-166566 (JP, A) Actual Kaihei 1-98708 (JP, U)

Claims (3)

(57) [Claims] 1. A fluid pressure cylinder interposed between a vehicle body and each wheel, a pressure control valve for controlling a working fluid pressure of the fluid pressure cylinder only in accordance with a command value, and a lateral acceleration of the vehicle body. Acceleration detection or estimation means for detecting or estimating, and true roll suppression command value excluding the steering characteristic command value for the pressure control valve, which has a value corresponding to the acceleration detection value or estimation value of the acceleration detection or estimation means and corresponding to this value And a steering fluid pressure cylinder connected to the rear wheels and a steering pressure control valve for controlling the same, and a lateral side of the acceleration detecting or estimating means. A rear wheel steering angle control mechanism having a steer characteristic control means for controlling the steering pressure control valve so as to enhance the understeer characteristic in accordance with an increase in an acceleration detection value or an estimated value is provided. Active suspension device for. 2. The rear wheel steering angle control mechanism sets the turning amount of the rear wheel steering mechanism to zero when the lateral acceleration detection value or estimated value is less than a predetermined value, and when the lateral acceleration detection value or estimated value is equal to or more than the predetermined value. The active suspension device according to claim 1, wherein the steering amount is increased according to an increase in the acceleration detection value or the estimated value. 3. A fluid pressure cylinder interposed between a vehicle body and each wheel, a pressure control valve for controlling a working fluid pressure of the fluid pressure cylinder only in accordance with a command value, and a lateral acceleration of the vehicle body. For a vehicle having an acceleration detecting or estimating means for detecting or estimating, and a control device for receiving an acceleration detected value or estimated value of the acceleration detecting or estimating means and outputting a command value to the pressure control valve of a value corresponding to this value A suspension and a rear wheel steering mechanism having a steering fluid pressure cylinder connected to the rear wheels; a steering fluid pressure cylinder of the rear wheel steering mechanism; and a rear wheel side pressure control valve of the vehicle suspension. And a fluid pressure fluctuation absorbing means are connected to the flow passage so as to be in the same phase as the front wheel steering in the flow passage, and an active suspension device.