GB2116130A

GB2116130A - Power steering device for a vehicle

Info

Publication number: GB2116130A
Application number: GB08302682A
Authority: GB
Inventors: Michio Abe; Naoyuki Maeda
Original assignee: Tokai TRW and Co Ltd
Current assignee: Tokai TRW and Co Ltd
Priority date: 1982-02-05
Filing date: 1983-02-01
Publication date: 1983-09-21
Also published as: IT1161481B; AU1099983A; KR840003476A; FR2521091A1; JPS58136560A; DE3303857A1; BE895829A; NL8300395A; GB8302682D0; IT8367113A0

Abstract

A power steering system includes an electric motor 11 and an oil pump 4 powered by the electric motor. The oil pump is driven so that its RPM is maximum when the vehicle is idling or is running at a very low speed. The RPM is at least three times more than that of an engine driven oil pump. The speed of the electric motor 11 is controlled by a controller 12 responsive to vehicle speed detection means 13 and to a sensor 21 detecting movement or torque of a steering wheel 1. A valve 2 actuated by the steering wheel 1 controls fluid flow via lines A, B to a power cylinder. <IMAGE>

Description

SPECIFICATION IRowersteering device for a vehicle This invention relates to a power steering device, and more particularlyto a power steering device improved with an oil pumpforfeeding pressurized oil to a power cylinder which assists in the operation of a steering wheel.

A power steering device is generaliy designed so thatthe supply of pressurized fluid which assists a steering wheel is increased in order to lighten the wheel and facilitate steering when the vehicle is either idling or moving at a slow speed. Likewise, the supply of power steering fluid is decreased to make the steering wheel heavier attimes when the vehicle is travelling at high speeds in order to provide greater stability on the road.The prior art power cylinder apparatus is as mentioned above, and comprises, for example, a motor in which the RPM rate is controlled in response to the speed of the vehicle, and an oil pump driven by the motor to feed pressurized oil to a power cylinder, which is designed so thatthe supply of pressurized oil from the oil pump to the power cylinder is increased to lighten the steering wheel when the vehicle is run at a low speed and whereas the supply of pressurized oil introduced from the oil pump to the power cylinder is decreased as the vehicle accelerates. The oil pump used in such a conventional apparatus is bulky and requires much power. Such a defect is further developed in the engine driven oil pump.

Aprimaryobjectofthe present invention isto provide a more efficient and economical power steering device by improving the performance of an oil pump and by making the oil pump more compact.

The present invention is characterized by the oil pump operating at maximum RPM when the vehicle is idling or its running at a low speed. More specifically, under the same condition, the RPM of the instant oil pump is at least three times (about4- 5 times in this instance) more than that of the conventional engine driven oil pump. The oil pump is driven by an electric motor to control the RPM in response to the speed ofthe vehicle. The present invention is further characterized in that the RPM ofthe oil pump is varied according to the speed ofvehicle so asto curtail energy only when the steering wheel is being rotated.The present invention isfurthercharacte- rized by the aforementioned action being controlled by an electric motor, and thatthe RPM of the oil pump is at least three times more than that ofthe conventional pump when the vehicle is idling to reduce oil discharge volume to one third or less of that of the conventional pump, and thereby reducing capacity of the pump to less than one third that of the conventional pump so that the usual or only slightly increased electric power capacity of the vehicle is enough to drive the electric motor.

The invention may be more readily understood from the following detailed description, given by way of example only, having reference to the accompanying drawings, in which: Fig. 1 is schematic view showing a preferred form of a power steering device in which the present invention is embodied, Fig. 2 is a schematic view showing another embodiment of the power steering device, Fig. 3 is a plan view of a pulse generating section showing onetype of encoderfor detecting the speed of vehicle, Fig. 4 is an electrical pulse chart plotted from the encoder shown in Fig. 3, Fig. 5 is a curve showing output voltages ofthe vehicle speed detection means, Figs. Sand 7 are curves showing the rotational characteristic of the motor for an oil pump controlled by the steering device ofthe present invention, Fig. 8 is a graphic chart showing the oil pump power consumption during driving, and Fig. 9 is a diagram showing the relationship between vehicle speed and RPM of pump revolutions and pump power consumption.

Referring to Fig. 1, numeral 1 denotes a steering wheel which is provided with a control valve or a servovalve 2 mounted below on the wheel shaft. The servovalve 2 is actuated by a gear (not shown) including a pinion gear3 provided atthe lowered of the wheel shaft. Operatively connected to the servovalve 2 is an oil pump 4. A power cylinder (not shown) is operatively connected to the servovalve 2 through lines A and B. Normally, the power cylinder acts to assist the operation ofthesteering wheel.

A controller 12 which is adapted to control the oil pump 4 comprises a drive means for driving the oil pump 4, asforexample, a motor 11, a control circuit for controlling the motor, and a vehicle speed detection means 13 operatively connected to the control circuit. The vehicle speed detection means 13 includes a transmission cable 14 connected to a vehicle speed rotation input D and a vehicle speed sensor 15 connected to the transmission cable 14.

The vehicle speed signal from the vehicle speed rotation input D is detected by the vehicle speed sensor 15through the transmission cable 14. This sensot allows a vehicle speed analog voltage E, to be generated as shown in Fig. 5a, this voltage being fed to the control circuit. The control circuit in turn controls the motor 11 so that as the voltage increases, the running speed of the vehicle increases and the RPM ofthe motor 11 is reduced. As a result, the RPM of the oil pump 4 is decreased in proportion to the increase in the vehicle speed. This results in reduction in the amount of oil supplied to the power cylinder as the vehicle speed is increased and thus, as the vehicle speed is increased, the resistance to the rotation of the steering wheel is high.On the contrary, when the vehicle is run at a low speed, the amount of oil supplied to the power cylinder is increased so as to lowerthe resistance of the turning of the steering wheel since the RPM of the oil pump 4 is higher as compared with the slow speed. As one example of controlling the RPM of the motor 11 by the control circuit, a generator may be employed as the vehicle speed sensor 15 and a semi-conductor circuit regulator may be employed as control circuitwherebythe voltage generated by the generator controls the regulator so as to control the RPM ofthe motor 11. In another embodiment, the vehicle speed is digitally counted bythesensorandtheRPM of the motor is controlled in response to the digitally counted vehicle speed.

According to the embodiment as shown, in orderto control the oil pump when the steering is effected or the wheel is turned, the controller 12 is provided with an energization means (not shown). The energization means comprises a sensor 21 mounted on the steering wheel shaft for detecting the rotational operation or steering force and an amplifier circuit (not shown) which is adapted to amplify an electrical signal from the sensor 21 and may incorporate a delay switching ci rcu it therein. The detected voltage from the sensor 21 serves as a switching signal, for example, which controls the input be applied from the vehicle speed sensor 15 tothe control circuit.The sensor 21 may preferably be an arrangement in which a motor small in size is rotated by the wheel shat, a torsional sensor (load cell), an arrangement in which the phase relationship between the wheel shaft and the servovalve is detected by, for example, a voltage, a durable sensor such as a photosensor employing a light source oran approach sensor employing a magneticfield oran oscillatory sensor employing an eddy current. When the outputfrom the amplifier circuit is applied to the control circuit or the steering wheel is rotated, the control on the RPM ofthe oil pump is initiated in response to the vehicle speed as mentioned hereinbefore.

Fig. 2 shows another embodiment of the present invention wherein various sensors perform their detection functions in the manner different from that bythesensorsinthefirstembodiment, butthe motor is controlled in the manner as mentioned hereinabove in connection with the first embodiment. In this embodiment, the oil pump output F connected to the servovalve is adapted to be converted into a predetermined electric signal which actuates the controller through a servovalve operated oil flow pressure sensor30 (operated at an oil flow amount or pressure) adapted to detectthe movementoffluid when the steering wheel is turned.On the other hand, fordetection ofthevehicle speed, digital vehicle speed signals derived from a slitted disc 33 provided on a vehicle speed meter 32 and associated vehicle speed digital sensors 33a, 33b and 33c as shown in Fig. 3 are converted by vehicle speed detectors 34a, 34b and 34c into digital vehicle speed outputs 37a, 37b and 37c, respectively in the form of electric signals as shown in Fig. 4. These signals are drained to a level decoder 35 which in turn produces vehicle speed pulses at eight different levels. The vehicle speed pulses are drained to a digital-analog-conver ter36which in turn produces an eight-stepped digital voltage 2 E2 for controlling the motor speed as shown in Fig. 5b.

Thus, according to the present invention, the electrical signals from the two systems of vehicle speed and steering wheel turning sensor may control the RPM of the motor 11 as shown in Figs. 6 and 7.

More specifically, Figs. 6 and 7 show the rotational characteristic of the oil pump with respect to the vehicle speed in the embodiments as shown in Figs. 1 and 2, respectively. When the steering wheel is not turned,the motoris normally maintained at a low rotational speed level such as P1 or standstill so that the oil pump will not waste fluid energywhereas while the steering wheel is being turned for a predetermined time period after the termination of the steering wheel operation, the motor is rotated at the controlled rotation level of P2 depending upon the running speed ofthevehicleto operate the oil pump which in turn pumps fluid to the power cylinder through the output lines A and B to thereby augment the rotational output of the steering wheel. Alterna- tively, it is possible to rotate the motor at a low speed when the steering wheel is not rotated and to further reduce constantly and graduallythe RPM zap of the oil pump in response to the increase in vehicle speed as shown at Pg in Figs. 6 and 7 onlywhen the steering wheel is turned.

The present invention is an improved structural motor pump resulting in performance characteristic better that those of the conventional motor pump as shown in the following table.

preset testing Prior r r Prior Lt characteristic liner flow engine drix construction of pump toe slipper punp type P? (1.6cc/lrev.) rotor diameter X 27. 27.5 x x 8 37 x 13 width of (its) 27.5 x 8 discharge amount or 1.6 9.3 punp (cc/lrev.) mardrmna discharge pressure 6 of pump (1,ion) nannaxn disdzawe pressure llo 70 of ptrp (kg/an2) 110 weight of prmp (kg) 0.38 2.5 size of pmp (me) 80 x 50 80 x 83 HexieHereoued pder of Eenp (w) 300 2500 m3xirmm revnlutian 2700 600 of allowed tesereture ( C) | -35 - 110 -35 - 120 weight of rrotnr (kg) | 1.9 size of rotor (nrn) 80 x 125

As is apparent from Figs. 8 and 9, with an oil pump according to this embodiment and a motor vehicle powered by a 2000cc engine, the maximum RPM of the pump is 2700 and the pump discharge is 1.25 cc/one revolution perminutewhilethevehicle is idling, and the rotor diameter and width ofthe pump are remarkable reduced. This increases mechanical and pump efficiency and requires power of only 100 Wand 280 W, respectivelyfornon-steering and steering. The power required is decreased with increase in the speed of the vehicle. More specifically, the power required for non-steering and steering is only30Wand 150W when the vehicle is run at about 80 km/h. If the vehicle is run at a higher speed, the power required drops to zero.

Take the conventional engine driven large oil pump as an example, the power required for non-steering and steering when idling is 80 W and 2000 W (about 3 HP), respectively, and thus exhibits an excellent performance as compared with the case where the power required thereforwhen run at80 km/h is 250W and 1400W (1.5 HP). This indicates that the usual vehicle power source will supply enough powerfor the power steering.

As mentioned hereinbefore, according to the present invention, by rotating the motor at a high speed through the battery independently ofthevehicle running speed, the rotation rate and discharge capacity of the oil pump can be increased and thus, even when the volume of the oil pump is reduced to a fracticn ofthatofthe priorartoil pumps, the oil pump can fully satisfy the capacity called for by the power cylinder when the vehicle is steered to thereby make it possible to reduce the size and weightofthe oil pump.When the steering wheel is not rotated,theoil pump is normally controlled to a low speed drive or standstill condition to thereby save energy and/or reducewearon the brush ofthe oil pump motor resulting in prolonging the service life ofthe brush.

Test results on fuel consumption by vehicles show that the electrically driven and steering load current detection-oil pressure type power steering attain at least 4% reduction in fuel consumption as compared with that by the conventional powersteering for vehicle running speeds in both expressway and normal driving.

While several embodiments of the invention have been shown and described in detail, it will be understood that the same are for illustration purpose only and not to be taken as a definition of the invention, reference being had forthis purpose to the appended claims.

Claims

1. In a power cylinder device including an electric motor driven by a power source carried by a vehicle, an oil pump powered by said electric motorfor supplying pressurized oil to a power cylinder designed to augment the steering of said vehicle, and a controllerforcontrolling the RPM of said electric motor, a power steering device characterized in that said oil pump is set so that its RPM is maximum when the vehicle is idling or is running at a very low speed, its RPM being reduced with increased speed of the vehicle.

2. A power cylinder device claimed in Claim 1, wherein the RPM is at least th ree times more than that of an engine driven oil pump.

3. A power steering device for a vehicle substan tially as herein described with reference to and as illustrated in, Figures 1, S9 or Figures 2-9 of the accompanying drawings.