Vehicle height adjustment system

Abstract

To provide a vehicle height adjustment system having high practicability.SOLUTION: In a vehicle height adjustment system which includes a separation distance change device for changing a separation distance between wheels and a vehicle body in a vertical direction, when a vehicle height is changed from a standard vehicle height HN as a set vehicle height to a low vehicle height HL lower than the standard vehicle height, a change of the vehicle height is limited in a difficult state of returning when returning to the standard vehicle height is not smoothly performed. For instance, when an environmental temperature is low, an accumulator pressure is low in a liquid pressure cylinder type vehicle height adjustment system, or there is a risk that an electric motor for driving a pump becomes an excessive heat state, a change to the low vehicle height is prohibited, or a difference ΔH between the standard vehicle height and the low vehicle height is reduced. Due to that a change to the low vehicle height is limited, travel with the standard vehicle height thereafter can be sufficiently guaranteed even in a difficult state of returning.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a vehicle height adjustment system that is mounted on a vehicle to adjust the height of the vehicle. [Background technology]

[0002] A vehicle height adjustment system changes the vehicle height (the height of the vehicle, in other words, the distance of the vehicle body from the road surface) depending on the situation, but there are technologies that limit the change in vehicle height. For example, the technology described in the following patent document suspends the change in vehicle height when an object is present within a set area around the vehicle to avoid damaging the object or the vehicle itself. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-188088 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a vehicle height adjustment system includes a clearance distance changer disposed between the wheels and the vehicle body for changing the vertical distance between the wheels and the vehicle body, and a controller adjusts the vehicle height by changing the clearance distance. In such a vehicle height adjustment system, increasing the vehicle height places a greater burden on the clearance distance changer than decreasing the vehicle height. By taking this burden into consideration, the practicality of the vehicle height adjustment system can be improved. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vehicle height adjustment system that is highly practical. [Means for solving the problem]

[0005] In order to solve the above problems, the vehicle height adjusting system of the present invention comprises: It is mounted on a vehicle, (a) a hydraulic cylinder connected at one end to a wheel and at the other end to a vehicle body, and expanding and contracting by the inflow and outflow of hydraulic fluid; (b) a high-pressure source device having a reservoir for storing hydraulic fluid, a pump driven by an electric motor for drawing up and discharging the hydraulic fluid from the reservoir, and an accumulator for storing the hydraulic fluid from the pump, and supplying the hydraulic fluid to the hydraulic cylinder; a separation distance change device for changing the separation distance between the wheel and the vehicle body in the vertical direction; A vehicle height adjustment system including a controller that adjusts the vehicle height by controlling the separation distance change device, The controller: When changing the vehicle height from the standard vehicle height, which is the set vehicle height, to a low vehicle height lower than the standard vehicle height, if the vehicle height is in a difficult state where it cannot be smoothly returned to the standard vehicle height, the change of the vehicle height is restricted. At the same time, when the operating time of the electric motor required for returning to the standard vehicle height exceeds a margin time which is the difference between the operating time of the electric motor set for overheat protection and the operating time of the electric motor up to the present time, it is determined that the returning is difficult. . [Effects of the Invention]

[0006] According to the vehicle height adjustment system of the present invention, lowering of the vehicle height is restricted in the difficult-to-return state, so that even if the vehicle is in the difficult-to-return state, it is possible to sufficiently ensure that the vehicle will be able to travel at the standard vehicle height thereafter.

[0007] The "distance change device" of the vehicle height adjustment system of the present invention (hereinafter, sometimes abbreviated as "the present system" in this [aspect of the invention]) is not particularly limited in its specific configuration. For example, it may be a device including an actuator disposed between the upper end of a suspension spring and a mount on the vehicle body to change the distance between the upper end and the mount, i.e., a so-called jack-type device. It may also be, for example, a device including (a) a hydraulic cylinder connected at one end to the wheel and at the other end to the vehicle body, which expands and contracts as hydraulic fluid flows in and out, and (b) a so-called hydraulic cylinder-type device having a reservoir for storing hydraulic fluid, a pump driven by an electric motor to draw and discharge hydraulic fluid from the reservoir, an accumulator for storing hydraulic fluid from the pump, and a high-pressure source device for supplying hydraulic fluid to the hydraulic cylinder. The "controller" in this system may be, for example, a device including a computer and a driver for driving several elements of the distance change device.

[0008] The vehicle height adjustment function of this system may include a function to change the vehicle height in several stages depending on the road surface conditions, the vehicle's traveling speed, etc. (hereinafter, this may be referred to as the "vehicle height change function"), and a function to maintain a constant vehicle height even when the number of occupants changes due to getting on and off the vehicle, the amount of luggage carried, etc. (hereinafter, this may be referred to as the "auto-leveling function"). In this system, the phrase "when changing the vehicle height from the standard vehicle height, which is the set vehicle height, to a low vehicle height lower than the standard vehicle height" primarily refers to a change to a low vehicle height using the vehicle height change function. Specifically, for example, this refers to a change to a low vehicle height when the "standard vehicle height" is the vehicle height set for normal driving and the "low vehicle height" is the vehicle height set for getting on and off the vehicle. When the difference between the standard vehicle height and the low vehicle height is relatively large and restoring the low vehicle height to the standard vehicle height places a heavy burden on the clearance distance change device, it is very significant to limit the change to a low vehicle height. It is possible to restrict the vehicle height change function while maintaining other functions, such as the auto-leveling function.

[0009] If the condition for determining a "difficult-to-return state" is a "specific condition," then, for example, the specific condition can be an environmental temperature lower than a set temperature. For example, in low-temperature environments such as -0°C or -20°C, considerable resistance is generated in the operation of the separation distance change device, resulting in a considerable load being imposed when returning from a low vehicle height to the standard vehicle height. Furthermore, if the separation distance change device is a hydraulic cylinder-type device, the specific condition can be, for example, at least one of the following: the accumulator pressure, which is the pressure of the hydraulic fluid in the accumulator, being lower than a set pressure; and the possibility that the electric motor may overheat. When the accumulator pressure is low, returning to the standard vehicle height cannot be performed quickly, so it is important to limit the change to a low vehicle height. Furthermore, if the electric motor overheats, its operation is limited to protect it from overheating, making it difficult to return to the standard vehicle height. Therefore, it is also important to limit the change to a low vehicle height. Incidentally, whether or not the electric motor is at risk of overheating can be determined by, for example, calculating the operating time of the electric motor required to return to the standard vehicle height, t UP and the operating time of the electric motor until overheat protection is reached is t PRO Let t be the operating time of the electric motor up to the present time. UP >(t PRO -t) or not. PRO -t) can be considered as the slack time. PRO may be a continuous operating time, or may be a cumulative operating time from a point prior to the current time by a set time up to the current time.

[0010] Although multiple conditions are listed above as specific conditions, changing to a lower vehicle height may be restricted if any one of the multiple conditions is satisfied, or if multiple of the multiple conditions are satisfied. In other words, the multiple conditions may be AND conditions or OR conditions.

[0011] "Restricting changes to vehicle height," i.e., restricting changes to a low vehicle height, may involve at least one of prohibiting changes to a low vehicle height and reducing the difference between the standard vehicle height and the low vehicle height compared to when no restriction is imposed. Regarding the latter, the latter refers to setting the low vehicle height position higher than when no restriction is imposed. In this case, for example, the low vehicle height position may be changed continuously or in stages depending on the level or magnitude of a parameter (e.g., the accumulator pressure, ambient temperature, pump operating time, etc.) used to determine whether the specific condition is satisfied. [Brief explanation of the drawings]

[0012] [Figure 1] 2 is a diagram showing the hardware configuration of one of the front and rear wheel systems in the vehicle height adjustment system of the embodiment; FIG. [Figure 2] 2 is a schematic diagram for explaining a vehicle height changing function in the vehicle height adjustment system. FIG. [Figure 3] This is table data that is referenced when raising the low vehicle height position as a restriction on changing to a low vehicle height. [Figure 4] 4 is a flowchart of a vehicle height lowering control program executed in the vehicle height adjustment system. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below with reference to the accompanying drawings, in which: a vehicle height adjustment system according to an embodiment of the present invention is described in detail below; the present invention can be embodied in various forms, including the forms described in the above section "Modes of the Invention," and in which various modifications and improvements are made based on the knowledge of those skilled in the art. [Example]

[0014] [A] Vehicle height adjustment system configuration The vehicle height adjustment system of the embodiment is a system for adjusting the vehicle height. This vehicle height adjustment system is installed on a relatively large vehicle, specifically a bus, and consists of two systems, one on the front wheel side and one on the rear wheel side. As shown in Fig. 1, each of the two systems includes a clearance distance changer 10, which is a so-called hydraulic cylinder type device, and a vehicle height adjustment electronic control unit (hereinafter sometimes referred to as a "vehicle height adjustment ECU" or simply "ECU") 12, which is a controller that adjusts the vehicle height by controlling the clearance distance changer 10.

[0015] The separation distance change device 10 is configured to include a pair of hydraulic cylinders 20 that are disposed corresponding to the left and right wheels 14 between the wheels 14 and the vehicle body 16, more specifically, between the vehicle body 16 and a suspension arm 18 that holds the wheels 14 so that they can swing up and down, and a high-pressure source device 22 that supplies hydraulic fluid to the hydraulic cylinders 20. Incidentally, each hydraulic cylinder 20 is disposed in parallel with a suspension spring (not shown).

[0016] Each hydraulic cylinder 20 includes a housing 30, a piston 34 that divides the interior of the housing 30 into two fluid chambers 32, an upper chamber 32U and a lower chamber 32L, and a piston rod 36 whose upper end is connected to the piston 34 and extends from the lower end of the housing 30. The piston 34 is provided with a communication passage 38 that connects the upper chamber 32U and the lower chamber 32L and functions as an orifice for the hydraulic fluid passing through. One end of each hydraulic cylinder 20 is connected to the wheel 14, and the other end is connected to the vehicle body 16. More specifically, the lower end of the piston rod 36 is connected to the suspension arm 18, and the upper end of the housing 30 is connected to the vehicle body 16.

[0017] The high-pressure source device 22 includes a reservoir 40 that stores hydraulic fluid at atmospheric pressure, a pump 44 that is driven by an electric motor 42 to pump and discharge hydraulic fluid from the reservoir 40, and an accumulator 46 that stores hydraulic fluid from the pump 44. The hydraulic fluid discharged from the pump 44 is supplied to each hydraulic cylinder 20 via a check valve 48 and a pump communication valve 50, and is then stored in the accumulator 46 via an accumulator communication valve 52. The high-pressure source device 22 is also provided with a return valve 54, and hydraulic fluid discharged from each hydraulic cylinder 20 is returned to the reservoir 40 via this return valve 54. Both the pump communication valve 50 and the accumulator communication valve 52 are normally-closed electromagnetic on-off valves that open when energized. The return valve 54 uses the pressure on the discharge side of the pump 44 as a pilot pressure, and returns hydraulic fluid at a pressure higher than this pressure to the reservoir 40. In addition, the high-pressure source device 22 is provided with a pressure sensor 56 for detecting the pressure of the hydraulic fluid on the opposite side of the pump communication valve 50 from the pump 44 and on the opposite side of the accumulator communication valve 52 from the accumulator 46.

[0018] Hydraulic fluid from the high-pressure source device 22 is supplied to the pair of hydraulic cylinders 20, more specifically to their upper chambers 32U, via a common passage 70. A main passage 72 and a bypass passage 74 are provided for each of the pair of hydraulic cylinders 20, and hydraulic fluid can be supplied to each hydraulic cylinder 20 via either the main passage 72 or the bypass passage 74. A main passage opening valve 76 and a bypass passage opening valve 78 are disposed in the main passage 72 and the bypass passage 74, respectively. Both the main passage opening valve 76 and the bypass passage opening valve 78 are normally-closed electromagnetic on-off valves that open when excited.

[0019] Two accumulators 80, 82 are connected to the bypass path 74, one for each of the pair of hydraulic cylinders 20. These accumulators 80, 82 allow hydraulic fluid to flow in and out as the hydraulic cylinder 20 expands and contracts, allowing the hydraulic cylinder 20 to function as another suspension spring. The spring constant of the hydraulic cylinder 20 as a suspension spring is high (large) when only the accumulator 80 closer to the hydraulic cylinder 20 is connected to the hydraulic cylinder 20, and is low (small) when both accumulators 80, 82 are connected to the hydraulic cylinder 20. Therefore, hereinafter, for convenience, the accumulator 80 will be referred to as the high spring accumulator 80, and the accumulator 82 will be referred to as the low spring accumulator 82. To switch the spring constant of the hydraulic cylinder 20, a spring switching valve 84 is disposed in the bypass path 74 between the high spring accumulator 80 and the low spring accumulator 82, and between the bypass path connecting valve 78 and the high spring accumulator 80. The spring switching valve 84 is a normally open electromagnetic on-off valve that closes when excited. An orifice 86 is provided to provide resistance to the flow of hydraulic fluid in and out of the hydraulic cylinder 20. This orifice 86, together with an orifice in the connecting path 38 provided in the piston 34 of the hydraulic cylinder 20, allows the hydraulic cylinder 20 to function as a damper (shock absorber).

[0020] The vehicle height adjustment ECU 12 includes a computer, an electric motor 42, drive circuits (drivers) for various solenoid valves, etc. As explained above, the vehicle height adjustment system is composed of two systems, one for the front wheels and one for the rear wheels. The vehicle height adjustment ECUs 12 of each system exchange signals with each other via a communication line 88 and control their respective clearance distance changing devices 10 so that the systems work together. Although detailed explanations are omitted, the vehicle height adjustment ECU 12 of the front-wheel system also controls the vehicle height adjustment ECU 12 of the rear-wheel system. A stroke sensor 90 is provided for each wheel 14 to detect the vertical clearance between the wheel 14 and the vehicle body 16 (hereinafter sometimes referred to as the "stroke distance"). Furthermore, a temperature sensor 92 is provided to detect the temperature of the operating fluid stored in the reservoir 40 of the high-pressure source device 22 in order to detect the temperature of the environment in which the vehicle is placed.

[0021] [B] Operation of the clearance distance change device in the vehicle height adjustment system In the vehicle height adjustment system configured as described above, when the vehicle is traveling normally, the main path opening valve 76 and the bypass path opening valve 78 are closed, the spring switching valve 84 is open, and the spring constant of each hydraulic cylinder 20 is set to a relatively small value. In this vehicle height adjustment system, the separation distance change device 10 operates as follows with respect to adjusting the vehicle height, that is, raising and lowering the vehicle body 16. In other words, the vehicle height adjustment ECU 12 controls the separation distance change device 10 so that it operates as follows. As described above, in this vehicle height adjustment system, the vehicle height adjustment ECUs 12 of the front and rear wheel systems perform control in cooperation with each other. However, in the following description, unless otherwise specified, it will be treated as if one vehicle height adjustment ECU 12 controls one high-pressure source device 22 and controls all four hydraulic cylinders 20.

[0022] i) Operation when the vehicle is raised When raising the vehicle height, i.e., when raising the vehicle body 16, the pump 44 is driven by the electric motor 42 with the pump communication valve 50, the accumulator communication valve 52, and each main path opening valve 76 open, the bypass path opening valves 78 closed, and each spring switching valve 84 closed, and the hydraulic fluid stored in the accumulator 46 in a pressurized state and the hydraulic fluid discharged from the pump 44 are supplied to each hydraulic cylinder 20 via the respective main paths 72. At this time, in order to quickly raise the vehicle body 16, the hydraulic fluid is not supplied via the bypass path 74 in which the low spring accumulator 82 is disposed. When the stroke distance S detected by the stroke sensor 90 reaches the desired distance, the main path opening valves 76 are closed, and the supply of hydraulic fluid to each hydraulic cylinder 20 is stopped.

[0023] Because each hydraulic cylinder 20 is disposed in parallel with the suspension spring, the hydraulic pressure P of the hydraulic fluid in each hydraulic cylinder 20 (hereinafter, sometimes simply referred to as "hydraulic fluid pressure") changes with changes in stroke distance S, i.e., changes in vehicle height. Therefore, after the supply of hydraulic fluid to each hydraulic cylinder 20 is stopped, each bypass path opening valve 78 is opened, and the hydraulic fluid pressure P in each low spring accumulator 82 is increased so that the hydraulic fluid pressure P detected by the pressure sensor 56 becomes the same as the hydraulic fluid pressure P at the time the supply of hydraulic fluid via the main path 72 was stopped. Then, after the hydraulic fluid pressure P in each low spring accumulator 82 has been increased, each bypass path opening valve 78 is closed, each spring switching valve 84 is opened, and the operation of the pump 44 is stopped.

[0024] ii) Operation when the vehicle is lowered When lowering the vehicle height, that is, when lowering the vehicle body 16, the pump 44 is not driven, and the accumulator communication valve 52 remains closed while the pump communication valve 50, the main path opening valves 76, and the bypass path opening valves 78 are opened. This causes the hydraulic fluid in each hydraulic cylinder 20 to be returned to the reservoir 40 via the return valve 54. When the stroke distance S detected by the stroke sensor 90 reaches the desired distance, the main path opening valves 76 and the bypass path opening valves 78 are closed, and the discharge of hydraulic fluid from each hydraulic cylinder 20 is stopped.

[0025] iii) Accumulator pressure accumulation operation As explained above, when the vehicle height is raised, the hydraulic fluid stored in the accumulator 46 is also supplied to each hydraulic cylinder 20, so that the hydraulic fluid in the accumulator 46 decreases, and the pressure of the hydraulic fluid in the accumulator 46 (hereinafter sometimes referred to as "accumulator pressure") Pa drops. Unless the accumulator pressure Pa is high to a certain extent, a rapid increase in the vehicle height cannot be expected, so in this vehicle height adjustment system, an accumulator pressure storage operation is performed as an operation to maintain the accumulator pressure Pa at or above the set pressure Pa0.

[0026] The accumulator pressure accumulation operation is performed when neither the vehicle body raising operation nor the vehicle body lowering operation is being performed. When the pump communication valve 50, each main path opening valve 76, and each bypass path opening valve 78 are closed, the accumulator pressure Pa can be detected by opening the accumulator communication valve 52. When the accumulator pressure Pa is less than the set pressure Pa0, the pump communication valve 50 is opened to drive the pump 44 by the electric motor 42. When the accumulator pressure Pa reaches the set pressure Pa0, the pump communication valve 50 is closed to stop driving the pump 44.

[0027] [C] Control performed in the vehicle height adjustment system i) Auto-leveling control In this vehicle height adjustment system, if the vehicle height changes from the set height for some reason, such as an increase or decrease in the number of occupants or luggage, the above-mentioned vehicle body raising operation and vehicle body lowering operation are performed even while the vehicle is moving, and the vehicle height is automatically adjusted, i.e., auto-leveling control is performed. Auto-leveling control is already well known, so a detailed description will be omitted here.

[0028] ii) Vehicle height change control when passengers get on and off As mentioned above, the vehicle equipped with this vehicle height adjustment system (hereinafter sometimes referred to as "this vehicle") is a bus, and when the vehicle stops at a bus stop or the like, a certain number of passengers get on and off. Therefore, as shown in Figure 2(a), the set standard vehicle height H N Even if the vehicle is running at this speed, when the vehicle stops, the vehicle height will be reduced to the standard vehicle height H N Lower vehicle height H L When the vehicle departs, the vehicle height is changed to the low vehicle height H L From standard vehicle height H N will be reinstated.

[0029] iii) Restrictions on changing to a lower vehicle height In order to raise the vehicle height, it is necessary to drive the pump 44, etc., and therefore it takes a certain amount of time. In particular, this vehicle is a relatively large vehicle, is relatively heavy, and is also at a standard vehicle height H N and low vehicle height H L The difference between the vehicle height and the ground (hereinafter sometimes referred to as "height difference") ΔH is also relatively large, so it takes a relatively long time. In other words, a relatively quick, or in other words, a relatively smooth, increase in vehicle height is desired. Incidentally, normally, when the vehicle height H is low, L is the standard vehicle height H N The vehicle height is set to be lower than the standard vehicle height difference ΔH0 (for example, 100 mm).

[0030] In this vehicle height adjustment system, the vehicle height is set to the standard vehicle height H N From low vehicle height H L When changing to the standard vehicle height H NWhen the vehicle is in a difficult condition where it is not possible to return to the standard vehicle height H N From low vehicle height H L In other words, the vehicle height is limited to the low vehicle height H L From standard vehicle height H N Under conditions where it is expected that the time required to change to standard vehicle height H is longer than the set time, N From low vehicle height H L The system is designed to limit changes to

[0031] To explain the difficult-to-return state in more detail, when raising the vehicle height, as described above, hydraulic fluid is supplied to the hydraulic cylinder 20 from both the pump 44 and the accumulator 46. Taking this into consideration, a specific condition is set such that the accumulator pressure Pa, which is the pressure of the hydraulic fluid in the accumulator 46, is less than the set pressure Pa0, and if this condition is met, it is determined that the difficult-to-return state exists.

[0032] The pump 44 is driven by the electric motor 42, but the electric motor 42 is stopped for a certain period of time t PRO The cumulative operation time t during which the electric motor 42 has been operating up to the present time is set as the operation stop time t PRO When the vehicle height difference ΔH0 is reached, the electric motor 42 is stopped. L From standard vehicle height H N The standard operating time of the electric motor 42 required for the return to the lifting position is expressed as the required time t UP and the operation stop time t PRO The time t is the time t minus the cumulative operating time t. M and set the slack time t M The required time for rising is t UP If the specific condition is met, it is determined that the electric motor 42 is at risk of overheating, that is, is in a difficult-to-restore state. PROThe cumulative operating time t is the continuous operating time up to the present time, but may also be the cumulative operating time from a time point a set time back from the present time to the present time.

[0033] Furthermore, at low temperatures, a relatively large load is placed on the operation of the separation distance change device 10 due to the hardening of lubricants such as grease, which in turn places a large burden on the electric motor 42. Taking this into consideration, for example, a specific condition is set such that the temperature of the environment in which the vehicle is placed, i.e., the environmental temperature T, is lower than a set temperature T0 (e.g., 0 to -20°C), and if this condition is met, it is determined that the vehicle is in a difficult-to-return state. Note that the value detected by a temperature sensor 92 that detects the temperature of the hydraulic fluid in the reservoir 44 is used as the environmental temperature T.

[0034] This vehicle height adjustment system adjusts the vehicle height to the standard height H when any of the above three specific conditions is met. N From low vehicle height H L The restrictions include the ability to change the vehicle height to a low vehicle height H L Prohibition of changes to the standard vehicle height H N and low vehicle height H L This includes making the vehicle height difference ΔH, which is the difference between the vehicle heights ΔH and ΔH, smaller than the standard vehicle height difference ΔH0 when no restriction is imposed.

[0035] Specifically, when the environmental temperature T is lower than the set temperature T0, the low vehicle height H L On the other hand, even if the environmental temperature T is equal to or higher than the set temperature T0, when the accumulator pressure Pa is lower than the set pressure Pa0, the margin time t M The required time for rising is t UP When it is less than the accumulator pressure Pa, the margin time t M The table data shown in Fig. 3 is used as a parameter, that is, the accumulator pressure ratio (Pa / Pa0), which is the ratio of the accumulator pressure Pa to the set pressure Pa0, and the margin time t M The required time for ascent is t UP The ratio of the slack time to the M / t UP) based on the table data, low vehicle height H L According to the table data of FIG. 3, the vehicle height difference ΔH is determined as ΔH0 (for example, 100 mm) > ΔH1 (for example, 75 mm) > ΔH2 (for example, 50 mm) > ΔH3 (for example, 40 mm) > ΔH4 (for example, 30 mm). M The smaller the difference in vehicle height ΔH, that is, the lower the vehicle height H L The vehicle height is set high.

[0036] This vehicle height adjustment system will adjust the vehicle height to a low level when at least one of the above three specific conditions is met. L However, the restriction may be imposed when two or more of a plurality of specific conditions are satisfied. Furthermore, when the environmental temperature T is lower than the set temperature T0, the vehicle height difference ΔH may be determined depending on how much the environmental temperature T is lower than the set temperature T0, using the environmental temperature T as a parameter.

[0037] iv) Control Flow The vehicle height adjustment ECU 12 executes a vehicle height lowering control program, the flowchart of which is shown in Figure 4, to control the vehicle height lowering, including the above-mentioned restrictions. Execution of this program begins when the driver operates the vehicle height adjustment switch located at the driver's seat. Hereinafter, the processing flow according to this program will be briefly explained with reference to the flowchart, although this will be repeated hereunder.

[0038] In the processing according to the low vehicle height change control program, first, in step 1 (hereinafter abbreviated as "S1", the same applies to the other steps), the ambient temperature T is detected by the temperature sensor 92 provided in the reservoir 40. In the following step S2, it is determined whether the ambient temperature T is less than the set temperature T0. If the ambient temperature T is less than the set temperature T0, the processing according to this program is terminated without lowering the vehicle body.

[0039] If it is determined in S2 that the environmental temperature T is equal to or higher than the set temperature T0, the accumulator pressure Pa is detected in S3, and the accumulator pressure ratio (Pa / Pa0) is calculated based on the accumulator pressure Pa and the set pressure Pa0. Next, in S4, the cumulative operating time t of the electric motor 42 is identified, and the cumulative operating time t is calculated based on the set pressure Pa0. PRO The cumulative operating time t is subtracted from the M is calculated, and the slack time t M and the required time for ascent t UP Based on this, the margin time ratio (t M / t UP ) is calculated.

[0040] In the next step S5, the vehicle height difference determination table of FIG. 3 is referenced, and the calculated accumulator pressure ratio (Pa / Pa0) and the margin time ratio (t M / t UP ) the vehicle height difference ΔH is determined based on the vehicle height difference ΔH. In the next S6, as a result of referring to the vehicle height difference determination table, it is determined whether the vehicle height difference ΔH has been determined to be 0, that is, whether changing to a lower vehicle height is prohibited. If changing to a lower vehicle height is prohibited, the processing according to this program is terminated. If the vehicle height difference ΔH is other than 0, in S7, the above-mentioned vehicle body lowering operation is performed based on the determined vehicle height difference ΔH. [Explanation of symbols]

[0041] 10: Distance change device 12: Height adjustment electronic control unit (height adjustment ECU) [controller] 14: Wheel 16: Body 20: Hydraulic cylinder 22: High-pressure source device 40: Reservoir 42: Electric motor 44: Pump 46: Accumulator 56: Pressure sensor 90: Stroke sensor 92: Temperature sensor Pa: Accumulator pressure Pa0: Set pressure (Pa / Pa0): Accumulator pressure ratio H N : Standard vehicle height H L : Low vehicle height ΔH: Vehicle height difference ΔH0: Standard vehicle height difference ΔH1, ΔH2, ΔH3, ΔH4: Vehicle height difference for low vehicle height t: Cumulative operation time of electric motor t PRO : Operation stop time t UP : Required time for ascent tM :Less time (t) M / t UP ): Margin time ratio T: Ambient temperature T0: Set temperature

Claims

1. It is mounted on a vehicle, (a) a hydraulic cylinder connected at one end to a wheel and at the other end to the vehicle body, and expanding and contracting by the inflow and outflow of hydraulic fluid; (b) a separation distance change device for changing the vertical separation distance between the wheel and the vehicle body, the separation distance change device comprising a reservoir for storing hydraulic fluid, a pump driven by an electric motor for drawing up and discharging the hydraulic fluid from the reservoir, and an accumulator for storing the hydraulic fluid from the pump, and a high-pressure source device for supplying the hydraulic fluid to the hydraulic cylinder; A vehicle height adjustment system including a controller that adjusts the vehicle height by controlling the separation distance change device, The controller: A vehicle height adjustment system configured to restrict the change of vehicle height when the vehicle height is changed from a set standard vehicle height to a low vehicle height lower than the standard vehicle height, and when a return to the standard vehicle height is difficult and the vehicle cannot be returned to the standard vehicle height smoothly, and configured to determine that the return to the standard vehicle height is difficult when the operating time of the electric motor required to return to the standard vehicle height exceeds a margin time which is the difference between the operating time of the electric motor set for overheat protection and the operating time of the electric motor up to the current point in time.

2. 2. The vehicle height adjustment system of claim 1, wherein the controller restricts changes in vehicle height by at least one of prohibiting changes to the low vehicle height and reducing the difference between the standard vehicle height and the low vehicle height compared to when no restriction is imposed.

3. 2. The vehicle height adjustment system according to claim 1, wherein the standard vehicle height is a vehicle height set for normal driving, and the low vehicle height is a vehicle height set for passengers getting in and out of the vehicle.

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