JPH0822674B2 - Electric power steering - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering system that reduces steering operation force, and more particularly, to an electric power steering system that is configured by combining a pneumatic power unit and an electric power unit. .

<Prior Art> In a large vehicle represented by a bus or a large truck, a power steering is often provided to reduce steering operation force. In addition, such power steering includes hydraulic power steering and electric power steering.

Here, since the hydraulic power steering has a large output, it can be applied to a large vehicle. However, in the hydraulic power steering, it is practically impossible to store the hydraulic pressure used as a power source, so that the hydraulic pump is always driven by the engine. Therefore, when the steering operation force is small, for example, during high-speed traveling, the hydraulic pump is driven at a high rotation speed even though the hydraulic pressure may be low, resulting in a large power loss.

Further, the steering operation force becomes large when the vehicle is stationary or at a low speed running close to this. Therefore, in this case, it is necessary to increase the output speed of the hydraulic pump by making the engine speed higher than that required for traveling. For hydraulic power steering, a hydraulic pump,
Due to the need to use control valves, hydraulic cylinders, and hydraulic pipes that connect these, the structure becomes complicated and the weight becomes heavy. Moreover, since it is necessary to strictly prevent pressure fluid leakage, mounting and piping treatment Is also troublesome.

On the other hand, in an electric power steering system that uses an electric motor as a power source, the steering operation force can be reduced by simply supplying power using flexible electric wiring, and various controls are easy. There is.

Such an electric power steering is, for example, the fourth
As shown in the figure, the steering wheel 1 is connected to the steering shaft 2, and the steering shaft 2 is connected to the worm 4 of the steering gear 3. Then, by connecting the pitman arm 6 attached to the rotary shaft of the worm wheel 5 meshing with the worm 4 and the knuckle arm 9 of the front wheel 8 via the drag link 7, if the steering wheel 1 is rotated, the steering gear 3, The front wheel 8 is steered through the pitman arm 6, the drag link 7 and the knuckle arm 9.

In addition, a pinion gear provided on the output shaft 11 of the electric motor 10
By engaging 12 with the worm wheel 5, the worm wheel 5 can be rotated by the electric motor 10. Then, by supplying the signal output from the torque sensor 13 mounted in the middle of the steering shaft 2 to the controller 14 of the electric motor 10, the electric power supplied from the battery 15 to the electric motor 10 is based on the output of the torque sensor 13. The steering operation force applied to the steering wheel 1 is controlled to a predetermined value by controlling the output of the electric motor 10 to be increased or decreased.

Therefore, the driver can perform the steering operation with a force smaller than the actually required operation force. In addition,
In addition to the above, the electric power steering is disclosed in JP-A-59-508.
No. 46, Japanese Unexamined Patent Publication No. 60-53463, or the concentric steering shaft and electric motor as seen in Japanese Utility Model Laid-Open No. 56-4973 and Japanese Utility Model Laid-Open No. 56-4974. There is also a device that is provided in an attempt to reduce the size.

In this way, the electric power steering reduces the steering operation force by using the electric motor, and is easy to handle and control. However, it is necessary to increase the output of the electric motor in order to cope with an automobile having a large steering operation force such as a large automobile. However, in order to apply the electric power steering that has been embodied in small automobiles to large automobiles, the drive current and output of the electric motor are unrealizable such as 24V, 250A, 6Kw. Due to the need to increase it, it was considered impossible to apply electric power steering to large vehicles.

<Problems to be Solved by the Invention> The present invention has been made in view of the above circumstances, and simplifies the configuration of an electric power steering that can be applied to a large vehicle while using an electric motor with a small output and saves energy. The challenge is to turn it into energy.

<Means for Solving the Problems> In order to solve the above problems, according to the present invention, a lower shaft is coupled to an upper shaft coupled to a steering wheel via a torque sensor. Further, a pneumatic power unit having an input shaft connected to the lower shaft through a universal joint is provided, and an electric power unit that rotationally drives the lower shaft is attached to a steering column that rotatably supports the lower shaft. . A controller for controlling the output of the electric power unit based on the signal output from the vehicle speed sensor that outputs a signal responsive to the vehicle speed and the torque sensor is provided.

<Operation> When the steering wheel is rotated to rotate the upper shaft, the lower shaft is rotated via the torque sensor, and the lower shaft controls the rotation of the input shaft of the pneumatic power unit. The torque sensor outputs a signal in response to the torque transmitted from the upper shaft to the lower shaft.

The controller calculates the optimum steering operation force at that time based on the vehicle speed signal output from the vehicle speed sensor,
The calculated optimum operating force is compared with the actual steering operating force of the driver output from the torque sensor to calculate the deviation. Further, the controller controls the output of the electric power unit so that the deviation becomes zero based on the deviation output, so that the actual steering operation force required by the driver is set to the optimum value in response to the vehicle speed at that time. Retained.

On the other hand, the steering operation force transmitted to the lower shaft as described above is transmitted to the front wheels via the pneumatic power unit. Therefore, since the steering operation force of the driver is transmitted to the front wheels after being subjected to the boosting action of the electric power unit and the boosting action of the pneumatic power unit, the electric power unit of the small output within the practical range is used for a large vehicle. An electric power steering can be configured.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings. The components having the same functions as those of the conventional example shown in FIG. 4 are designated by the same reference numerals.

FIG. 1 is a schematic explanatory view showing an embodiment of the electric power steering system according to the present invention, and FIG. 2 is a sectional view taken along the line AA in FIG. Is composed of an upper shaft 16 fixed to the steering wheel 1 and a hollow lower shaft 17 rotatably held by a steering column 18. The lower part of the upper shaft 16 is rotatably inserted into the lower shaft 17. ing. In addition, the upper shaft 16 and the lower shaft 17 are coupled via the torque sensor 13, and an electric power unit 19 that rotationally drives the lower shaft 17 is attached to the column 18.

The torque sensor 13 is configured as shown in FIG. 2, and the cam 21 having the contactor 20 formed in a protruding manner is attached to the upper shaft 16, and the concave piezoelectric element holding metal fitting 22 is attached to the lower shaft 17. ing. And the holding metal fittings 22
Between the piezoelectric elements 23R and 23L mounted on the inner surface of the
By sandwiching and holding, the signal is output in response to the magnitude of the torque transmitted from the upper shaft 16 to the lower shaft 17 and the rotation direction. Reference numeral 24 is a spring that holds the piezoelectric element 23R, 23L under tension between the holding metal fitting 22 and the contactor 20.

Then, the driven gear 25 fixed to the lower end of the lower shaft 17 exposed below the column 18 and the drive gear 27 attached to the output shaft of the electric motor 26 attached to the column 18 are meshed with each other, whereby the electric motor 26 is Gear 2 when driven
An electric power unit 19 in which a lower shaft 17 is rotationally driven via 7, 25 constitutes.

An input shaft 29 of a pneumatic power unit 28 is connected to the lower end of the lower shaft 17 via a universal joint 30. Then, by attaching the pitman arm 6 to the output shaft 31 of the pneumatic power unit 28, the lower shaft
When the 17 rotates, the pitman arm 6 swings.

That is, the pneumatic power unit 28 is composed of the control valve 32 and the power cylinder 33, and when the valve body (not shown) of the control valve 32 is displaced due to the rotation of the input shaft 29, it responds to the displacement amount of this valve body. This amount of compressed air is supplied from the pneumatic tank 34 to the power cylinder 33 to drive the piston 36. And the piston
The movement of 36 is transmitted to the sector gear 37 by the rack and pinion method, and the rotation of the sector gear 37 is transmitted to the pitman arm 6 via the output shaft 31. The movement of the pitman arm 6 is transmitted to the knuckle arm 9 of the front wheel 8 via the drag link 7.

A compressor 35 driven by the engine is connected to the pneumatic tank 34. The pressure sensor 50 provided in the pneumatic tank 35 controls the compressor 35 so that the pressure of the pneumatic tank 35 is maintained within a predetermined range.

The signal output from the torque sensor 13 and the signal output from the vehicle speed sensor 45 are supplied to the controller 14,
The electric motor 26 is operated by calculating the boost value based on these signals.
Control the drive current supplied to the.

FIG. 3 is a block diagram of the controller 14, in which the signals output from the piezoelectric elements 23R and 23L of the torque sensor 13 are processed by the amplifiers 38 and 39 and the A / D converters 40 and 41 and passed through the switching circuit 42. It is supplied to the comparison amplifier 43 and the direction discriminator 44. The signal output from the vehicle speed sensor 45 is supplied to the amplifier 47 via the waveform shaper 46.

An amplification condition corresponding to the vehicle speed is preset in the amplifier 47, and the signal amplified according to this condition is used as the comparison amplifier.
Supplied to 43. The signal output from the comparison amplifier 43 is D /
After being converted into an analog signal by the A converter 48, the drive circuit 49
Is amplified by and is supplied to the electric motor 26.

The direction discriminator 44 determines the rotation direction of the steering wheel 1 based on the signals output from the piezoelectric elements 23R and 23L. The output signal of the direction discriminator 44 is supplied to the switching circuit 42 as a switching signal and to the drive circuit 49 as a command signal for forward / reverse switching.

The signal output from the pressure sensor 50 provided in the pneumatic tank 34 is supplied to the comparison amplifier 51. The comparison amplifier 51 determines whether the pressure of the pneumatic tank 34 is within the upper and lower limits based on the supplied signal, and outputs the determination result to the amplification drive circuit 52. The amplification drive circuit 52 performs ON-OFF control of the clutch provided in the drive system path of the compressor 35 based on the signal supplied from the comparison amplifier 51, and keeps the pressure of the pneumatic tank 34 within the upper and lower limits.

In the electric power steering system configured as described above, when the driver turns the steering wheel 1 to the right, for example, the upper shaft 16 fixed to the steering wheel 1 rotates in the same direction. Upper shaft
The rotation of 16 is transmitted to the lower shaft 17 via the cam 21, the piezoelectric element 23R spring 24, and the holding metal 22. The rotation of the lower shaft 17 is transmitted to the input shaft 29 of the pneumatic power unit 28 via the universal joint 30.

Further, when a valve body (not shown) provided in the control valve 32 is displaced along with the rotation of the input shaft 29, compressed air of an amount corresponding to the displacement amount of the valve body is supplied from the pneumatic tank 34 to the power cylinder 33. The piston 36 is driven. Then, the movement of the piston 36 is transmitted to the sector gear 37 by the rack and pinion method, and the movement (rotation) of the sector gear 37 is transmitted to the pitman arm 6 via the output shaft 31. In addition,
Since the movement of the pitman arm 6 is transmitted to the knuckle arm 9 via the drag link 7, the front wheel 8 is steered.

In the course of such a series of steering operations, the steering wheel 1 is rotated rightward. Therefore, since the torque transmitted from the upper shaft 16 to the lower shaft 17 acts as a compressive force on one of the pair of piezoelectric elements 34R, 34L provided in the torque sensor 13, the piezoelectric element 34R is compressed. Outputs a signal corresponding to the magnitude of the steering operation force (torque) transmitted from the upper shaft 16 to the lower shaft 17. A signal is not output to the other piezoelectric element 34L because the torque does not act as a compressive force.

The signal output from the piezoelectric element 34R is supplied to the amplifier 38 and A
It is supplied to the direction discriminator 44 after being processed by the / D converter 40. The direction discriminator 44 detects that a signal is being supplied from the A / D converter 40 and discriminates that the rotation is to the right, and causes the switching circuit 42 to be switched and held in the illustrated state. Therefore, the switching circuit 42 supplies the comparison amplifier 43 with a signal corresponding to the actual steering operation force at each time.

On the other hand, the signal output from the vehicle speed sensor 45 is a waveform shaper.
It is supplied to the amplifier 47 via 46. Further, since the amplifier 47 is preset with an amplification condition according to the vehicle speed, a signal corresponding to the optimum steering operation force in response to the vehicle speed at that time is supplied to the comparison amplifier 43.

The comparison amplifier 43 compares the signal corresponding to the optimum operating force supplied from the amplifier 47 with the signal corresponding to the actual operating force supplied via the switching circuit 42, amplifies the deviation, and performs D / A conversion. It is supplied to the drive circuit 49 via the device 48. In the drive circuit 49, the drive current supplied to the electric motor 26 is controlled based on the signal supplied from the D / A converter 48 and the signal supplied from the direction discriminator 44 to control the rotation direction and output of the electric motor 26. Optimally control.

Further, since the rotational force of the electric motor 26 is transmitted to the lower shaft 17 via the driving gear 27 and the driven gear 25,
The rotational force of the electric motor 26 is added to the boosting action of the pneumatic power unit 28, and the rotational force of the electric motor 26 is an optimum value corresponding to the vehicle speed at which the operating force applied to the steering wheel 1 corresponds to the vehicle speed at that time. Therefore, the steering operation force is always kept in an optimum state.

On the other hand, when the steering wheel 1 is rotated leftward, a signal in response to the operating force is output from another piezoelectric element 23L contrary to the above case. Further, when the signal is output from the piezoelectric element 23L in this manner, the output of the direction discriminator 44 is reversed from that in the case of the turning operation to the right and is output from the piezoelectric element 23L in order to invert the switching circuit 42. The generated signal is supplied to the comparison amplifier 43 via the switching circuit 42.

Therefore, the drive circuit 49 rotationally drives the electric motor 26 in the reverse direction with a predetermined output based on the deviation signal supplied from the comparison amplifier 43 and the direction determination signal supplied from the direction discriminator 44. The other operations are the same as those in the case where the steering wheel 1 is rotated rightward, and the description thereof will be omitted.

Although the compressed air in the pneumatic tank 34 is consumed due to the boosting action of the pneumatic power unit 28, the pressure in the tank 34 is monitored by the pressure sensor 50. When the pressure in the pneumatic tank 34 becomes lower than a predetermined lower limit value, a drive signal is output from the comparison amplifier 51 and the drive circuit 52 turns on the clutch to drive the compressor 35. When the pressure in the pneumatic tank 34 rises to the upper limit value due to the driving of the compressor 35, the stop signal is output from the comparison amplifier 51 and the drive circuit 52 turns off the clutch. The waste of power is prevented.

By the way, the steering shaft 2 and the upper shaft 16
And the lower shaft 17, the upper shaft 16 is rotatably attached to the lower shaft 17 which is rotatably supported by the steering column 18, and both shafts 16 and 17 are connected via the torque sensor 13, and The shaft 17 and the input shaft 29 of the pneumatic power unit 28 are connected via a universal joint 30. Therefore, the vibration of the upper shaft 16 due to the vibration of the drag link 7 or the pneumatic power unit 28 can be suppressed without deteriorating the support stability of the steering wheel 1 and the detection accuracy of the steering operation force. Further, the electric power unit 19 is attached to the steering column 18 to prevent the electric power unit 19 from being damaged due to vibration from the road surface or jumping water. Therefore, it is not necessary to provide the electric power unit 19 with a special protection device for avoiding troubles caused by vibration or jumping water.

Furthermore, both the electric power that is the power source of the electric power unit 19 and the compressed air that is the power source of the pneumatic power unit 28 can be stored. Therefore, it is not necessary to constantly drive and wait for the steering operation like a hydraulic pump of a hydraulic power steering, and it is possible to avoid waste of engine power.

In the embodiment, the torque sensor 13 using the pair of piezoelectric elements 23R and 23L detects the steering operation force, but the specific structure of the torque sensor 13 is not limited to the embodiment.

<Effects of the Invention> As is apparent from the above description, in the electric power steering according to the present invention, an electric power unit that is easy to control the output and has a high degree of freedom in setting characteristics is used. Is supplemented by the pneumatic power unit, the power steering of a large vehicle can be easily configured even when the output of the electric power unit is set to a small output within a practical range.
In addition, the steering shaft is composed of an upper shaft and a lower shaft, the upper shaft is rotatably attached to the lower shaft rotatably supported by the steering column, and both shafts are connected via a torque sensor. Since the input shaft of the pneumatic power unit is connected via a universal joint, the upper shaft that accompanies the vibration of the drag link or the pneumatic power unit does not deteriorate the stability of steering wheel support and the detection accuracy of steering operation force. Vibration can be suppressed. further,
Since the electric power unit is attached to the steering column, the electric power unit can be protected from vibration from the road surface or jumping water without providing a special protection device. Furthermore, compressed air, which is the power source of the pneumatic power unit, can be stored in the same way as electric power, which is the power source of the electric power unit, and the compressed air of the air tank installed in a large vehicle is used as the power source of the pneumatic power unit. Since it can be effectively used, the structure of the electric power unit applicable to a large automobile can be simplified and energy can be saved.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of the electric power steering according to the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, FIG. 3 is a block diagram of a controller 14, and FIG. It is explanatory drawing of a prior art example. 1 ... Steering wheel, 2 ... Steering shaft, 6 ... Pitman arm, 7 ... Drag link, 8 ... Front wheel, 9 ... Knuckle arm, 13 ... Torque sensor, 14 ... Controller, 16 ... Top Shaft, 17
...... Lower shaft, 18 …… Steering column, 19 ……
Electric power unit, 20 …… contactor, 21 …… cam, 22…
… Holders, 23R, 23L …… Piezoelectric element, 24 …… Spring, 25 …… Driven gear, 26 …… Electric motor, 27 …… Drive gear, 28 …… Pneumatic power unit, 29 …… Input shaft, 30 …
… Universal joint, 31 …… Output shaft, 32 …… Control valve, 33 …… Power cylinder, 34 …… Pneumatic tank, 35 …… Compressor, 36 …… Piston, 37 …… Center gear, 38,39,47… … Amplifier, 40, 41 …… A / D converter, 42 …… Switching circuit, 43,51 …… Comparison amplifier,
44 …… direction discriminator, 45 …… vehicle speed sensor, 46 …… waveform shaper, 48 …… D / A converter, 49 …… drive circuit, 50 …… pressure sensor, 52 …… amplification drive circuit

Claims (1)

[Claims] 1. An upper shaft coupled to a steering wheel, a lower shaft coupled to the upper shaft via a torque sensor, a steering column rotatably supporting the lower shaft, and a universal joint to the lower shaft. Pneumatic power unit having an input shaft coupled via, an electric power unit mounted on the steering column to drive the lower shaft to rotate, a vehicle speed sensor for outputting a signal in response to a vehicle speed and the torque sensor. An electric power steering system comprising a controller that controls the output of the electric power unit based on a signal.