Vehicle height control device for motorcycle

A vehicle height control device comprises a vehicle height control unit including a jack housing of a hydraulic jack provided at an upper end portion of an inner tube, a suspension spring provided between an upper end of a hollow pipe and a plunger of the hydraulic jack, a pump housing provided at the plunger of the hydraulic jack and forming a pump chamber of a hydraulic pump, and a pump pipe communicating with an oil reservoir chamber on an inner periphery of the hollow pipe and slidably inserted into the pump chamber in the pump housing, and a selector valve controlling the vehicle height by adjusting the amount of hydraulic oil fed to a jack chamber in the hydraulic jack by the hydraulic pump that performs the pumping operation in conjunction with extending and contracting motion of the hollow pipe with respect to the inner tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2012-274040 filed on Dec. 14, 2012, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a vehicle height control device for a motorcycle.

2. Related Art

A motorcycle preferably has a low vehicle height at the time of stopping such that even short riders can set their feet easily on the ground, as this prevents the motorcycle from falling down. On the other hand, the vehicle height of the motorcycle needs to be relatively high during travel from the viewpoint of a bank angle, a shock absorbing capability, and the like. Furthermore, in some American model motorcycles, etc., riders desire the low vehicle height at the time of stopping in terms of appearance.

Thus, a vehicle height control device for a motorcycle has been proposed as described in Patent Literature 1 (JP-B-H08-022680). The vehicle height control device includes a damper tube provided on one of a vehicle body side and an axle side, a piston rod provided on the other of the vehicle body side and the axle side and sliding through an oil chamber in the damper tube to extend and contract with respect to the damper tube, a hydraulic jack provided on one side of the damper tube and the piston rod, a suspension spring interposed between a spring bearing supported by a plunger inserted into a jack chamber in the hydraulic jack and a spring bearing provided on the other side of the damper tube and the piston rod, a hydraulic pump performing a pumping operation in conjunction with extending and contracting motion of the piston rod with respect to the damper tube to feed oil in the oil chamber in the damper tube to the jack chamber in the hydraulic jack and to discharge oil from the jack chamber, and a selector valve which is closed to stop the hydraulic oil fed into the jack chamber in the hydraulic jack and which is opened to discharge the hydraulic oil, thereby enabling vehicle height control with extending and contracting motion of the piston rod.

SUMMARY OF INVENTION

However, when a vehicle height control unit including a hydraulic jack, a hydraulic pump, and a selector valve is provided in a damper such as a front fork, the configuration of the damper needs to be significantly changed.

Furthermore, even when a vehicle speed decreases to a set value or smaller and then a vehicle height reducing operation is performed, if a vehicle is rapidly decelerated, the conventional vehicle height control device may fail to sufficiently reduce the vehicle height within a short time until the vehicle stops.

Additionally, in a motorcycle with a pair of dampers disposed on respective laterally opposite sides of a vehicle body, when a vehicle height control unit (including a hydraulic jack, a hydraulic pump, and a selector valve) is provided in each of the dampers, the vehicle height control device involves a large occupied space, a heavy weight, and high costs.

An object of the present invention is to simply configure a damper provided with a vehicle height control unit.

Another object of the present invention is to provide a vehicle height control device that inevitably reduces the vehicle height when a vehicle stops so that rider's feet can appropriately touch the ground.

Yet another object of the present invention is to provide a motorcycle with a pair of dampers disposed on respective laterally opposite sides of a vehicle body, the motorcycle including a compact vehicle height control device.

[1] An aspect of the invention provides a vehicle height control device for a motorcycle with a pair of dampers disposed on laterally opposite sides of a vehicle body, the vehicle height control device comprising: a vehicle height control unit provided in at least one of the left and right dampers, in which the damper provided with the vehicle height control unit includes: a wheel-side outer tube; a vehicle body-side inner tube slidably inserted into the wheel-side outer tube; a hollow pipe installed upright in an inner bottom portion of the outer tube and including a partition wall portion that is in sliding contact with an inner periphery of the inner tube; a piston provided on an inner periphery of a leading end portion of the inner tube; an oil chamber provided on an outer periphery of the hollow pipe in such a manner that the piston advances into and retracts from the oil chamber, the oil chamber being partitioned by the piston into an upper oil chamber above the piston and a lower oil chamber below the piston; and an oil reservoir chamber defined by an inner periphery of the hollow pipe and spanning to an upper portion of the inner tube, the oil reservoir chamber having an upper portion that forms an air chamber, and in which the vehicle height control unit includes: a hydraulic jack including a jack housing and a plunger, the jack housing being provided at an upper end portion of the inner tube such that the plunger defining a jack chamber of the hydraulic jack is fitted on the jack housing so as to be movable up and down; a suspension spring provided between an upper end of the hollow pipe and the plunger of the hydraulic jack; a hydraulic pump including a pump housing and a pump pipe, the pump housing being provided at the plunger of the hydraulic jack and forming a pump chamber of the hydraulic pump such that the pump pipe installed upright at the upper end of the hollow pipe and communicating with the oil reservoir chamber on the inner periphery of the hollow pipe is slidably inserted into the pump chamber in the pump housing; and a selector valve controlling a vehicle height by adjusting an amount of hydraulic oil fed to the jack chamber in the hydraulic jack by the hydraulic pump that performs a pumping operation in conjunction with extending and contracting motion of the hollow pipe with respect to the inner tube.

[2] The vehicle height control device for the motorcycle according to [1], may further comprises: a detection unit that detects a height position of the plunger of the hydraulic jack; and a control unit that opens or closes the selector valve in a controllable manner according to a result of the detection by the detection unit.

[3] The vehicle height control device for the motorcycle according to [1], may have a configuration in which the selector valve is provided at the upper end portion of the inner tube.

[4] The vehicle height control device for the motorcycle according to [2], may have a configuration in which the selector valve is provided at the upper end portion of the inner tube.

[5] The vehicle height control device for the motorcycle according to [2] or [4], may have a configuration in which the control unit predicts a stoppage predicted time of a vehicle, and when the predicted stoppage predicted time is equal to or less than a reference stoppage time, and the control unit enters a vehicle height reducing control mode to switch the selector valve, which enables a vehicle height reducing operation.

[6] The vehicle height control device for the motorcycle according to any one of [1] to [5], may have a configuration in which the vehicle height control unit is provided only in one of the left and right dampers.

[7] The vehicle height control device for the motorcycle according to [6], may have a configuration in which a suspension spring is provided in the other of the left and right the dampers, and a spring load on the suspension spring provided in the one of the left and right dampers is set higher than a spring load on the suspension spring provided in the other of the left and right dampers.

[8] The vehicle height control device for the motorcycle according to [6], may have a configuration in which a suspension spring is not provided in the other of the left and right dampers.

[9] The vehicle height control device for the motorcycle according to [8], may have a configuration in which an amount by which the hydraulic jack provided in the one of the left and right dampers elevates and lowers is equivalent to double an amount by which the hydraulic jack elevates and lowers assuming a case that vehicle height control units are respectively provided in the left and right dampers.

[10] The vehicle height control device for the motorcycle according to any one of [6] to [9], may have a configuration in which a main damping force generator is provided in the other of the left and right dampers, and in the one of the left and right dampers, the damping force generator is not provided or only an auxiliary damping force generator is provided.

With the configuration of [1], the damper provided with the vehicle height control unit can be simply configured.

With the configuration of [2], based on the result of the detection by the detection unit, the plunger of the hydraulic jack can be set to any height position, and thus the vehicle height can be adjusted to any height position.

With the configuration of [3] and [4], the selector valve formed of a solenoid or the like can be disposed at a sprung position above the suspension spring where an input of vibration is small.

With the configuration of [5], the vehicle height starts to be reduced during travel when the vehicle is about to stop. The vehicle height is completely reduced within a short time until the vehicle stops. This allows the rider's feet to appropriately touch the ground, thus ensuring stability.

With the configuration of [6], this enables a reduction in the occupied space, weight, and costs of the vehicle height control device.

With the configuration of [7], the suspension spring in the damper subjected to an increased load on the spring bearings as a result of providing the vehicle height control unit has an enhanced capability of supporting the damper.

With the configuration of [8], this enables a reduction in the occupied space, weight, and costs of the vehicle height control device.

With the configuration of [9], the spring load on the suspension spring can be substantially doubled due to the deflection of the suspension spring caused by providing the vehicle height control unit and the suspension spring only in the one of the dampers.

With the configuration of [10], the main damping force generator is provided in the damper in which the vehicle height control unit is not provided. In the damper provided with the vehicle height control unit, the damping force generator is not provided or only the auxiliary damping force generator is provided. Hence, the left and right dampers can be balanced in weight.

DESCRIPTION OF EMBODIMENTS

FIG. 1shows a pair of dampers10L and10R disposed on a left side and a right side, respectively, of a vehicle so as to form a front fork of a motorcycle. In this case, in the motorcycle according to the present embodiment, a vehicle height control device100is configured by providing a vehicle height control unit100L only in one of the left and right dampers, that is, the damper10L. The damper10L and the damper10R will be described below in detail.

In the damper10L, a vehicle body-side inner tube12is slidably inserted into a wheel-side outer tube11which is closed at one end and which is open at the other end, as shown inFIG. 1toFIG. 3. At an open end of the outer tube11through which the inner tube12is inserted, a slide guide13, seal spacer14, an oil seal15, a stopper ring16, and dust seal17are provided. A slide guide19is provided on an outer peripheral portion of a lower end of the inner tube12which is inserted into the outer tube11.

In a bottom portion of the outer tube11, a bolt21is interposed via a copper packing, and a hollow pipe22fixed by the bolt21is installed upright. The bolt21is screwed in a threaded portion on an inner periphery of a reduced diameter portion of the hollow pipe22located under a tapered portion at a lower end of the hollow pipe22. An outer periphery of a lower end portion of a cap bolt23is screwed in an upper end portion of the inner tube12via an O ring23A.

A jack housing111of a hydraulic jack110described below is attached to the cap bolt23. A suspension spring33formed of a compression coil spring is provided between a spring bearing31supported by a plunger113fitted on the jack housing111and a spring bearing32seated on an upper end surface of an increased-diameter partition wall portion22A provided at an upper end portion of the hollow pipe22. In the present embodiment, the plunger113supports the spring bearing31attached to an outer periphery of an intermediate portion of a lower pump housing121B via an upper pump housing121A of a pump housing121of a hydraulic pump120attached to the plunger113.

The partition wall portion22A is provided at the upper end portion of the hollow pipe22, and a piston ring24that is in sliding contact with an inner periphery of the inner tube12is inserted in an annular groove on an outer periphery of the partition wall portion22A. An oil chamber25described below is provided on an outer periphery of a lower portion of the partition wall portion22A of the hollow pipe22.

A piston40is provided on an inner periphery of a leading end portion (lower end portion) of the inner tube12inserted into the outer tube11. The piston40includes an upper damping force generator70and a lower damping force generator80described below.

The piston40in the leading end portion of the inner tube12advances into and retracts from the oil chamber25on the outer periphery of the hollow pipe22and partitions the oil chamber25into an upper portion and a lower portion. That is, an upper oil chamber25A is formed by the inner tube12, the hollow pipe22, the partition wall portion22A, and the piston40. A lower oil chamber25B is formed by a portion of the outer tube11located below the piston40and the hollow pipe22.

An oil reservoir chamber27spanning to an upper portion of the inner tube12is defined by the inner periphery of the hollow pipe22. Hydraulic oil is filled in the oil reservoir chamber27, and an upper portion of the oil reservoir chamber27forms an air chamber28. The oil chamber25on the outer periphery of the hollow pipe22is in communication with the oil reservoir chamber27on the inner periphery of the hollow pipe22. A hole-like volume compensation passage51is formed in the hollow pipe22by drilling to compensate for a volume of oil equivalent to an amount by which the inner tube12advances into and retracts from the oil chamber25on the outer periphery of the hollow pipe22.

The hollow pipe22includes an orifice52formed immediately below the partition wall portion22A by drilling. A portion of the oil in the upper oil chamber25A, the pressure of which is increased during an extension step, flows through the orifice52into the oil reservoir chamber27on the inner periphery of the hollow pipe22.

An annular gap chamber60is provided between the outer tube11and the inner tube12with being sandwiched between the slide guide13fixed to the inner periphery of the outer tube11and the slide guide19fixed to the outer periphery of the inner tube12. A hole61is formed by drilling in a portion of the inner tube12in which the piston40is provided. A gap62is formed in the piston40by drilling. The hole61and the gap62allow the annular gap chamber60to communicate with the oil chamber25(the upper oil chamber25A and the lower oil chamber25B) on the outer periphery of the hollow pipe22. Thus, the hydraulic oil is supplied to the annular gap chamber60to lubricate the slide guides13and19and to carry out volume compensation.

A rebound spring36in a maximum extension state corresponding to the stroke end of the extension stroke is installed between the piston40provided in the inner tube12and the partition wall portion22A provided in the hollow pipe22, to regulate a maximum extension stroke. Furthermore, an oil lock piece37is sandwiched between a lower end portion of the hollow pipe22and the bottom portion of the outer tube11. In a maximum compression state corresponding to the stroke end of a compression stroke, an oil lock collar38provided on an inner periphery of a lower end of the piston40presses the hydraulic oil around the oil lock piece37to regulate a maximum compression stroke.

As shown inFIG. 4, the upper damping force generator70is provided between the upper oil chamber25A on the outer periphery of the hollow pipe22and the lower oil chamber25B (and the hole61formed in the inner tube12and communicating with the annular gap chamber60). The upper damping force generator70permits oil to flow into the upper oil chamber25A during the compression stroke and applies passage resistance to oil flowing out from the upper oil chamber25A during the extension stroke.

As shown inFIG. 4andFIGS. 5A and 5B, the upper damping force generator70includes an extension-side damping valve72, a compression-side check valve73, and a valve spring74stacked in order on a side of a valve seat71fixed to the piston40which is closer to the upper oil chamber25A. During the extension stroke, the upper damping force generator70pushes open a channel A on an outer periphery of the extension-side damping valve72and a channel B on an inner periphery of the extension-side damping valve72by means of a high pressure in the upper oil chamber25A to generate an extension-side damping force. During the compression stroke, the upper damping force generator70pushes open the compression-side check valve73by means of a high pressure in the lower oil chamber25B.

As shown inFIG. 4, the lower damping force generator80is provided between the lower oil chamber25B on the outer periphery of the hollow pipe22and the upper oil chamber25A (and the hole61formed in the inner tube12and communicating with the annular gap chamber60). The lower damping force generator80permits oil to flow into the lower oil chamber25B during the extension stroke and applies passage resistance to oil flowing out from the lower oil chamber25B during the compression stroke.

The lower damping force generator80shares the valve seat71in the upper damping force generator70and includes a compression-side damping valve82, an extension-side check valve83, and a valve spring84stacked in order on a side of the valve seat71fixed to the piston40which is closer to the lower oil chamber25B. During the compression stroke, the lower damping force generator80pushes open the compression-side damping valve82by means of the high pressure in the lower oil chamber25B to generate a compression-side damping force. During the extension stroke, the lower damping force generator80pushes open the extension-side check valve83by means of the high pressure in the upper oil chamber25A.

Thus, the damper10L buffers an impact force applied by the road surface, by means of the spring force of the suspension spring33and the spring force of the air chamber28, and damps stretching vibration involved in the absorption of the impact force by the suspension spring33and the air chamber28, by means of the compression- and extension-side damping forces generated by the upper damping force generator70and the lower damping force generator80.

Now, the vehicle height control unit100L will be described which is installed only in the one of the left and right dampers, that is, the damper10L, in order to provide the vehicle height control device100.

As shown inFIG. 2, the vehicle height control unit100L of the vehicle height control device100includes the jack housing111(an assembly of an upper jack housing111A and a lower jack housing111B) of the hydraulic jack110attached to the cap bolt23provided at the upper end portion of the inner tube12. A hollow plunger113that defines a jack chamber112of the hydraulic jack110is fitted on a lower-end-side outer periphery of the jack housing111so as to be movable up and down. The jack chamber112is defined by the jack housing111, the plunger113, and a pump housing121described below. The hydraulic jack110includes an oil return passage114formed in the plunger113and through which the hydraulic oil in the jack chamber112is returned to the oil reservoir chamber27when the plunger113reaches a projecting end projecting from the jack chamber112(FIG. 2andFIG. 10).

The pump housing121(an assembly of an upper pump housing121A and a lower pump housing121B) of the hydraulic pump120is fixedly attached to a lower-end-side inner periphery of the plunger113of the hydraulic jack110. A pump pipe123is fixedly installed upright on a connector122attached to the upper end portion of the hollow pipe22. The pump pipe123is in communication with the oil reservoir chamber27on the inner periphery of the hollow pipe22and is slidably inserted in the pump housing121. Hollow portions of the pump housing121and the pump pipe123are in communication with each other to define a pump chamber124.

The hydraulic pump120includes a discharge check valve125disposed at an upper end portion of the pump housing121

and which allows the hydraulic oil in the pump chamber124, pressurized by contracting motion of the hollow pipe22and the pump pipe123advancing into the inner tube12, to be discharged toward the hydraulic jack110side (FIG. 8B). A suction check valve126is provided in the connector122, located on a lower end side of the pump pipe123, to allow the hydraulic oil in the oil reservoir chamber27to be sucked into the pump chamber124, which is set to a negative pressure by extending motion of the hollow pipe22and the pump pipe123retracting from the inner tube12(FIG. 8A).

Thus, the hydraulic pump120performs a pumping operation in conjunction with the extending and contracting motion of the hollow pipe22and the pump pipe123advancing into and retracting from the inner tube12when the damper10L is vibrated by recesses and protrusions on the road surface while the vehicle is traveling. When the pump chamber124is pressurized by the pumping operation resulting from the contracting motion of the hollow pipe22, the oil in the pump chamber124opens the discharge check valve125and is discharged toward the hydraulic jack110side. When the pump chamber124is set to the negative pressure by the pumping operation resulting from the extending motion of the hollow pipe22, the oil in the oil reservoir chamber27opens the suction check valve126and is sucked into the pump chamber124.

The vehicle height control unit100L has a selector valve130which is closed to stop the hydraulic oil supplied to the jack chamber112of the hydraulic jack110or which is opened to discharge the hydraulic oil into the oil reservoir chamber27as shown inFIG. 9. The selector valve130according to the present embodiment is formed of a solenoid valve and built in the cap bolt23of the inner tube12to open and close a communication path115between the oil reservoir chamber27and the jack chamber112, provided in the jack housing111(upper jack housing111A) of the hydraulic jack110.

The vehicle height control device100has a control circuit shown inFIG. 11. An ECU (control unit)140opens and closes the selector valve130in a controllable manner to allow the hydraulic pump120, which performs a pumping operation in conjunction with the extending and contracting motion of the hollow pipe22with respect to the inner tube12, to control the level of the hydraulic oil (the amount of the hydraulic oil) supplied to the jack chamber112of the hydraulic jack110and thus the projecting height of the plunger113projecting from the jack chamber112. As a result, the vehicle height of the vehicle is controlled.

The ECU140according to the present embodiment receives detection signals from a vehicle height detection unit150, a vehicle speed sensor161, a shift position sensor162, a G sensor (acceleration and deceleration sensor)163, a side stand sensor164, an engine rotation sensor165, a brake sensor166, and the like to turn on and off the selector valve130, formed of a solenoid valve, in a controllable manner.

The vehicle height detection unit150adopted may be one of projecting height detection unit151for detecting the height position of the plunger113in the hydraulic jack110, hydraulic-pressure detection unit152for detecting a hydraulic pressure in the jack chamber112of the hydraulic jack110, and extension and compression stroke length detection unit153(not shown in the drawings) for detecting the extension and compression stroke lengths of the inner tube12relative to the outer tube11or a combination of two or more of these unit.

The vehicle height detection unit150according to the present embodiment adopts an inductance-based projecting height detection unit151for detecting the projecting height of the plunger113. For example, as shown inFIG. 11, the projecting height detection unit151includes a coil151A wound around an outer periphery of the hydraulic jack110and a cover151B provided for the plunger113and disposed over an outer periphery of the hydraulic jack110. The projecting height detection unit151changes the impedance of the coil151A in accordance with displacement of the plunger113. An output from the coil151A is transmitted to the ECU140via a signal processing circuit151C. The ECU140detects the projecting height of the plunger113based on the oscillation frequency of the coil151A output by the signal processing circuit151C. The projecting height detection unit151adopted may be based on a Hall element, capacitance, or the like instead of inductance.

In conjunction with a vehicle height control operation of the motorcycle, the vehicle height control device100will be described which adopts the control circuit inFIG. 11using the selector valve130formed of a single two-port two-position solenoid valve. The selector valve130inFIG. 11is of a normally closed type (however, the selector valve130may be of a normally open type).

In a vehicle height reducing control mode in which the ECU140outputs an on signal, the selector valve130is opened to connect the jack chamber112of the hydraulic jack110to the oil reservoir chamber27in the damper10L. The hydraulic pump120discharges the hydraulic oil supplied to the jack chamber112of the hydraulic jack110into the oil reservoir chamber27to reduce the fluid level in the jack chamber112and thus the projecting height of the plunger113. Thus, a vehicle height reducing operation can be performed.

In a vehicle height increasing control mode in which the ECU140outputs an off signal, the selector valve130is closed to shut the jack chamber112of the hydraulic jack110off from the oil reservoir chamber27in the damper10L. The hydraulic pump120is prevented from discharging the hydraulic oil supplied to the jack chamber112of the hydraulic jack110, enabling a vehicle height maintaining operation or a vehicle height increasing operation. At this time, the hydraulic pump120performs a pumping operation in conjunction with the above-described extending motion of the hollow pipe22to suck the oil in the oil reservoir chamber27into the pump chamber124through the suction check valve126. Then, the hydraulic pump120performs a pumping operation in conjunction with the above-described contracting motion of the hollow pipe22to feed the oil in the pump chamber124into the jack chamber112of the hydraulic jack110through the discharge check valve125. Thus, a vehicle height increasing operation can be performed.

Specifically, control modes carried out by the vehicle height control device100are as described below.

(A) Vehicle Height Reducing Control Mode

In the vehicle height increasing control mode in which the selector valve130is closed to enable a vehicle height increasing operation while the vehicle is traveling or is stopped for a long time, the ECU140in the vehicle height control device100shifts to the vehicle height reducing control mode in which the selector valve130is opened according to any one of the following control conditions1to3.

1. Vehicle Speed Control

When the vehicle speed V of the vehicle is equal to or lower than a vehicle-height-reduction-starting vehicle speed Vd (V≦Vd), the ECU140enters the vehicle height reducing control mode to open the selector valve130to enable a vehicle height reducing operation.

The ECU140presets the vehicle speed Vd. The vehicle speed Vd is, for example, 10 km/h.

2. Stoppage Prediction Time Control

The ECU140predicts a stoppage predicted time T for the vehicle. When the predicted stoppage predicted time T is equal to or less than a predetermined reference stoppage time Ta (T≦Ta), the ECU140enters the vehicle height reducing control mode to open the selector valve130to enable a vehicle height reducing operation.

The ECU140calculates deceleration from the vehicle speed of the vehicle or from information from the G sensor, and predicts the stoppage predicted time T based on the deceleration.

The ECU140defines the reference stoppage time Ta to be a time required to discharge the hydraulic oil filled in the jack chamber112of the hydraulic jack110(the time required to discharge oil from the jack chamber112into the oil reservoir chamber27in the damper10L via the selector valve130).

In this case, the ECU140presets the reference vehicle speed Va at which the prediction of the stoppage predicted time T for the vehicle is to be started. Then, when the vehicle speed V of the vehicle becomes equal to or lower than the reference vehicle speed Va (V≦Va), the ECU140predicts the stoppage predicted time T.

Instead of using the above-described control conditions that T≦Ta and that V≦Va, the ECU140may enter the vehicle height reducing control mode to open the selector valve130to enable a vehicle height reducing operation when the deceleration a of the vehicle is equal to or lower than a reference deceleration aa (a aa).

The ECU140presets the reference speed Va, the reference stoppage time Ta, and the reference deceleration aa. The reference speed Va is, for example, 40 km/h, the reference stoppage time Ta is, for example, 2.5 sec, and the reference deceleration aa is, for example, 4 km/h/sec.

The stoppage predicted time is a parameter arithmetically predicted based on ever-changing vehicle motion parameters and representing an amount of time until the traveling vehicle stops in the immediately near future. The stoppage predicted time has a time dimension.

Actual comparative calculations may apparently involve no degree of “time” because, for example, the time dimension is divided into components for the respective sides of the comparison expression or comparison is carried out for each element.

For example, one of the simplest arithmetic expressions for the stoppage predicted time is T=−V/α=−V·dt/dV (arithmetic expression for assumed constant acceleration). However, all of the following three comparison expressions have the same meaning. Even with a difference in comparison method resulting from the convenience of arithmetic operations, all of the comparison expressions effectively mean comparison with the stoppage predicted time.
T<c(cis a threshold; here,c=Ta)
V<−c·α
−α>c·V

In the example in which comparison is carried out for each element, comparison may be performed for each of the elements V and α, used to calculate the stoppage predicted time, as in (V<c1)∩(−α>c2) (c1 and c2 are thresholds). The results are ANDed together.

In this case, T=−V/α and thus the following expression is given: Ta=(−c1)/(−c2)=c1/c2.

3. Side Stand Control

Upon detecting resetting of a side stand of the vehicle from a standby position to an operating position, the ECU140enters the vehicle height reducing control mode and opens the selector valve130to enable a vehicle height reducing operation. The following control may also be performed. The ECU140monitors the vehicle speed. When the vehicle speed is equal to or higher than a very low speed (for example, 5 km/s), the ECU140avoids the reducing control even if the stand is in the operating position. The ECU140performs the reducing control only when the vehicle speed is zero.

(B) Vehicle Height Increasing Control Mode

In the vehicle height reducing control mode in which the selector valve is opened and kept open as described in (A), the ECU140in the vehicle height control device100shifts to the vehicle height increasing control mode in which the selector valve130is closed according to one of the following control conditions1to4.

When entering the vehicle height increasing control mode to close the open selector valve130, the ECU140turns off a voltage E0applied to the selector valve130(E0=0 V).

1. Vehicle Speed Control

When the vehicle speed V exceeds the vehicle-height-reduction starting vehicle speed Vd (or a vehicle-height-increase starting vehicle speed Vu set independently of the vehicle-height-reduction starting vehicle speed Vd) (V>Vd or V>Vu), the ECU140halts the vehicle height reducing control mode, enters the vehicle height increasing control mode, and closes the selector valve130to enable a vehicle height increasing operation.

The ECU140presets the vehicle-height-reduction starting vehicle speed Vd (or the vehicle-height-increase starting vehicle speed Vu). The vehicle-height-reduction starting vehicle speed Vd or the vehicle-height-increase starting vehicle speed Vu is, for example, 40 km/h.

2. Stoppage Predicted Time Control

The ECU140predicts the stoppage predicted time T of the vehicle. When the predicted stoppage predicted time T exceeds a predetermined secondary reference stoppage time Tb (T>Tb), the ECU140halts the vehicle height reducing control mode, enters the vehicle height increasing control mode, and closes the selector valve130to enable the vehicle height increasing operation.

The ECU140predicts the stoppage predicted time T of the vehicle based on the deceleration (or acceleration) of the vehicle.

At this time, the ECU140predefines a secondary reference vehicle speed Vb at which the prediction of the stoppage time T of the vehicle is to be started. When the vehicle speed V exceeds the secondary reference vehicle speed Vb (V>Vb), the ECU140predicts the stoppage predicted time T.

In the stoppage predicted time control, the ECU140may halt the vehicle height reducing control mode, enter the vehicle height increasing control mode, and close the selector valve130to enable the vehicle height increasing operation when the acceleration of the vehicle exceeds a predetermined reference acceleration βb (β>βb) instead of using the above-described control conditions that T>Tb and that V>Vb.

The ECU140predefines the secondary reference vehicle speed Vb, the secondary reference stoppage time Tb, and the reference acceleration βb. The secondary reference vehicle speed Vb is, for example, 40 km/h, the secondary reference stoppage time Tb is, for example, 3 sec, and the reference acceleration βb is, for example, 5 km/h/sec.

When the stoppage time of the vehicle is equal to or more than a predetermined continued stoppage time Tc, the ECU140halts the vehicle height reducing control mode, enters the vehicle height increasing control mode, and closes the selector valve130to enable a vehicle height increasing operation.

The ECU140predefines the continued stoppage time Tc of the vehicle. The continued stoppage time Tc is, for example, 30 sec.

4. Neutral Control

When the vehicle speed V=0 and the vehicle is in a neutral shift position, the ECU140halts the vehicle height reducing control mode, enters the vehicle height increasing control mode, and closes the selector valve130to enable a vehicle height increasing operation.

(c) Height Retaining Mode

While the vehicle is traveling, the ECU140in the vehicle height control device100retains the vehicle height at any intermediate height position preset as desired by opening or closing the selector valve130in a controllable manner based on a detection result from the vehicle height detection unit150.

That is, an upper threshold for the vehicle height is set to a value H1, beyond which the vehicle height starts to be reduced, so at which the ECU140switches the selector valve130from an OFF operation (height increasing control mode) to an ON operation to open the selector valve130. A lower threshold for the vehicle height is set to a value H2, below which the vehicle height starts to be increased, so at which the ECU140switches the selector valve130from the ON operation (height reducing control mode) to the OFF operation to close the selector valve130. Thus, the ECU140retains the vehicle height of the motorcycle during travel at an intermediate height position between H1and H2based on the detection result from the vehicle height detection unit150.

Thus, the vehicle height control device100as described above may retain the vehicle height at any intermediate height position between the maximum height position defined by the highest possible projecting end of the plunger113in the hydraulic jack110and the minimum height position defined by the lowest possible sinking end of the plunger113in the hydraulic jack110.

Furthermore, the vehicle height can be instantaneously switched by adopting a solenoid valve as the selector valve130serving as the means for switching the vehicle height.

The vehicle height during the detection can be estimated by adopting the projecting height detection unit151for detecting the projecting height of the plunger113in the hydraulic jack110, as the vehicle height detection unit150.

Furthermore, the vehicle height during the detection can be estimated by adopting the hydraulic-pressure detection unit152for detecting the hydraulic pressure in the jack chamber112in the hydraulic jack110as the vehicle height detection unit150. At this time, applying a filter (low pass) to the detection result from the hydraulic-pressure detection unit152enables the vehicle weight (loading capacity) to be estimated. When the vehicle weight is high and the vehicle height tends to decrease, the vehicle height is increased to prevent the damper10L from being compressed to the limit. When the vehicle weight is low and the vehicle height tends to increase, the vehicle height is reduced to prevent the damper10L from being stretched to the limit.

Furthermore, the vehicle height during the detection can be estimated by adopting the extension and compression stroke length detection unit153for detecting the extension or compression stroke length of the inner tube12with respect to the outer tube11as the vehicle height detection unit150. At this time, applying a filter (band pass) to the detection result from the extension and compression stroke length detection unit153allows the recessed and protruding status (amplitude status) of the road surface to be estimated. When the road surface has a large amplitude, the vehicle height is increased to prevent the damper10L from being compressed to the limit or is adjusted to an appropriate value to prevent the damper10L both from being compressed to the limit and from being extended to the limit. When the road surface has a small amplitude, the vehicle height is reduced to relax wind resistance if the vehicle is of an on-road type and to prevent the vehicle body from pitching if the vehicle is of an off-road type.

As shown inFIG. 1, the damper10R includes a wheel-side outer tube211and a vehicle body-side inner tube212slidably inserted into the wheel-side outer tube211. The damper10R includes a damper cylinder213attached to a bottom portion of the outer tube211and installed upright inside the outer tube211, a cap bolt214screwed in an upper end portion of the inner tube212and in which a spring load adjusting sleeve215is screwed, and a hollow piston rod216fixed to a lower end portion of the spring load adjusting sleeve215. The piston rod216is inserted into an oil chamber217inside the damper cylinder213and includes a piston218at an insertion leading end thereof. The oil chamber217is partitioned into an upper oil chamber217A and a lower oil chamber217B by the piston218. Between the outer tube211and the inner tube212in the damper10R, an oil reservoir chamber219is formed of a space around an outer periphery of the damper cylinder213, and an air chamber220is formed of an upper portion of the oil reservoir chamber219.

The damper10R includes a suspension spring224installed between a spring bearing222backed up by a spring collar221supported by the spring load adjusting sleeve215provided in the cap bolt214and a spring bearing223provided in an upper end portion of the damper cylinder213.

The damper10R includes a first damping force generator231in the piston218. The first damping force generator231generates a compression-side damping force and an extension-side damping force. The damper10R includes a second damping force generator232on a bottom portion side of the outer tube211. The second damping force generator232generates a compression-side damping force and an extension-side damping force.

Thus, the damper10R buffers an impact force applied by the road surface, by means of the spring force of the suspension spring224and the spring force of the air chamber220. The compression- and extension-side damping forces generated by the first damping force generator231and the second damping force generator232damp stretching vibration involved in the absorption of the impact force by the suspension spring224and the air chamber220.

The damper10R includes a damping force adjusting rod233coaxially and relatively rotatably installed inside the spring load adjusting sleeve215provided in the cap bolt214. The damping force adjusting rod233adjusts the damping force by using a leading-end needle inserted into a hollow portion of the piston rod216to throttle the channel area of a bypass channel that makes the oil chamber217A and the oil chamber217B located above and below the piston218in communication with each other while bypassing the piston218.

Thus, the vehicle height control device100includes the suspension springs33and224in the left damper10L and right damper10R, respectively. In this case, according to the present embodiment, the spring load on the suspension spring33provided in one of the left and right dampers, that is, the damper10L, is set higher than the spring load on the suspension spring224provided in the other of the left and right dampers, that is, the damper10R.

The present embodiment exerts the following effects.

(a) The damper10L has a configuration including “the wheel-side outer tube11and the vehicle body-side inner tube12slidably inserted into the wheel-side outer tube11; the hollow pipe22installed upright in the inner bottom portion of the outer tube11and including the partition wall portion22A that is in sliding contact with the inner periphery of the inner tube12; the oil chamber25provided on the outer periphery of the hollow pipe22in such a manner that the piston40provided on the inner periphery of the leading end portion of the inner tube12advances into and retracts from the oil chamber25, the oil chamber25being partitioned by the piston40into the upper oil chamber25A above the piston40and the lower oil chamber25B below the piston40; and the oil reservoir chamber27defined by the inner periphery of the hollow pipe22and spanning to the upper portion of the inner tube12, the upper portion of the oil reservoir chamber27forming the air chamber28”. In connection with the configuration, the vehicle height control unit100L is provided which includes “the jack housing111of the hydraulic jack110provided at the upper end portion of the inner tube12, such that the plunger113defining the jack chamber112of the hydraulic jack110is fitted on the jack housing111of the hydraulic jack110so as to be movable up and down; the suspension spring33provided between the upper end of the hollow pipe22and the plunger113of the hydraulic jack110; and the pump housing121provided at the plunger113of the hydraulic jack110and forming the pump chamber124of the hydraulic pump120, such that the pump pipe123installed upright at the upper end of the hollow pipe22and communicating with the oil reservoir chamber27on the inner periphery of the hollow pipe22is slidably inserted into the pump chamber124in the pump housing121; and the selector valve130controlling the vehicle height by adjusting the amount of hydraulic oil fed to the jack chamber112in the hydraulic jack110by the hydraulic pump120that performs the pumping operation in conjunction with extending and contracting motion of the hollow pipe22with respect to the inner tube12”. Thus, the damper10L provided with the vehicle height control unit100L can be simply configured.

(b) The vehicle height control device has the detection unit151for detecting the height position of the plunger113of the hydraulic jack110and the ECU140that opens or closes the selector valve130in a controllable manner according to the result of the detection by the detection unit151. Based on the result of the detection by the detection unit151, the plunger113of the hydraulic jack110can be set to any height position, and thus the vehicle height can be adjusted to any height position.

(c) The selector valve130is provided at the upper end portion of the inner tube12. The selector valve130formed of a solenoid or the like can be disposed at a sprung position above the suspension spring33where an input of vibration is small.

(d) The stoppage predicted time of the vehicle is predicted, and when the predicted stoppage predicted time is equal to or less than the predetermined reference stoppage time, the vehicle height reducing control mode is entered to switch the selector valve130, thus enabling a vehicle height reducing operation. The vehicle height starts to be reduced during travel when the vehicle is about to stop. The vehicle height is completely reduced within a short time until the vehicle stops. This allows the rider's feet to appropriately touch the ground, thus ensuring stability.

(e) The vehicle height control unit100L is provided only in the one of the left and right dampers, that is, the damper10L. This enables a reduction in the occupied space, weight, and costs of the vehicle height control device100.

(f) The suspension springs33and224are provided in the left and right dampers10L and10R, respectively, and the spring load on the suspension spring33provided in the one of the left and right dampers, that is, the damper10L, is set higher than the spring load on the suspension spring224provided in the other of the left and right dampers, that is, the damper10R. Thus, the suspension spring33in the damper10L subjected to an increased load on spring bearings as a result of the provision of the vehicle height control unit100L has an enhanced capability of supporting the damper10L.

The spring load on the suspension spring33provided in the one of the left and right dampers, that is, the damper10L, can be increased by setting a spring constant for the suspension spring33larger than a spring constant for the suspension spring224provided in the other of the left and right dampers, that is, the damper10R.

FIG. 12shows the vehicle height control device100according to a variation of the embodiment shown inFIG. 1. In the left damper10L and right damper10R described above, the suspension spring33is provided only in one of the left and right dampers, that is, the damper10L. The suspension spring224is removed from the other of the left and right dampers, that is, the damper10R, and no suspension spring is provided in the damper10R.

At this time, the amount by which the plunger113of the hydraulic jack110provided in the one of the left and right dampers, that is, the damper10L, elevates and lowers is equivalent to double the amount by which the plunger113of the hydraulic jack110elevates and lowers assuming a case that a vehicle height control unit similar to the vehicle height control unit100L is also provided in the damper10R.

Thus, the vehicle height control device100exerts the following effects.

(a) The suspension spring33is provided only in the one of the left and right dampers, that is, the damper10L. The suspension spring224is not provided in the other of the left and right dampers, that is, the damper10R. Thus, the suspension spring224is not provided in the damper in which the vehicle height control unit100L is not provided. This enables a reduction in the occupied space, weight, and costs of the vehicle height control device100.

(b) The amount by which the hydraulic jack110provided in the one of the left and right dampers, that is, the damper10L, elevates and lowers is equivalent to double the amount by which the hydraulic jack110elevates and lowers assuming a case that the vehicle height control units100L are respectively provided in the left damper10L and the right damper10R. Thus, the spring load on the suspension spring33can be substantially doubled due to the deflection of the suspension spring33caused by the provision of the vehicle height control unit100L and the suspension spring33only in the one of the dampers, that is, the damper10L.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to the embodiment, but the present invention includes changes in design and the like made without departing from the spirits of the present invention. For example, in the vehicle height control device100with the vehicle height control unit100L provided only in the one of the left and right dampers, that is, the damper10L, the main damping force generator is provided in the other of the left and right dampers, that is, the damper10R, and in the one of the left and right dampers, that is, the damper10L, the damping force generator is not provided or only an auxiliary damping force generator is provided. Thus, the main damping force generator is provided in the damper10R in which the vehicle height control unit100L is not provided. In the damper10L provided with the vehicle height control unit100L, the damping force generator is not provided or only the auxiliary damping force generator is provided. Hence, the left and right dampers10L and10R can be balanced in weight.

Alternatively, according to the preset invention, the vehicle height control unit may be provided in both of the left and right dampers.

Furthermore, the present invention is similarly applicable to a lateral pair of dampers in a rear cushion.

The embodiment of the present invention provides a vehicle height control device for a motorcycle with a pair of dampers disposed on laterally opposite sides of a vehicle body, the vehicle height control device including a vehicle height control unit provided in at least one of the left and right dampers. The damper provided with the vehicle height control unit includes a wheel-side outer tube and a vehicle body-side inner tube slidably inserted into the wheel-side outer tube, a hollow pipe installed upright in an inner bottom portion of the outer tube and including a partition wall portion that is in sliding contact with an inner periphery of the inner tube, an oil chamber provided on an outer periphery of the hollow pipe in such a manner that a piston provided on an inner periphery of a leading end portion of the inner tube advances into and retracts from the oil chamber, the oil chamber being partitioned by the piston into an upper oil chamber above the piston and a lower oil chamber below the piston, an oil reservoir chamber defined by an inner periphery of the hollow pipe and spanning to an upper portion of the inner tube, the oil reservoir chamber having an upper portion that forms an air chamber, a jack housing of a hydraulic jack provided at an upper end portion of the inner tube such that a plunger defining a jack chamber of the hydraulic jack is fitted on the jack housing of the hydraulic jack so as to be movable up and down, a suspension spring provided between an upper end of the hollow pipe and the plunger of the hydraulic jack, and a pump housing provided at the plunger of the hydraulic jack and forming a pump chamber of a hydraulic pump such that a pump pipe installed upright at the upper end of the hollow pipe and communicating with the oil reservoir chamber on the inner periphery of the hollow pipe is slidably inserted into the pump chamber in the pump housing, and a selector valve controlling a vehicle height by adjusting an amount of hydraulic oil fed to the jack chamber in the hydraulic jack by the hydraulic pump that performs a pumping operation in conjunction with extending and contracting motion of the hollow pipe with respect to the inner tube. Thus, the damper provided with the vehicle height control unit can be simply configured.