JPH0214224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in power steering used in vehicles.

Power steering, commonly used in vehicles, consists of an oil pump and flow control system.
It consists of a power cylinder, a control valve with a reaction chamber on each side of the control valve spool, and the flow control valve adjusts the flow rate of pressurized oil sent from the oil pump. And furthermore...
The control valve receives power from the flow control valve in response to reciprocating sliding of the control valve spool.
The power cylinder is operated by controlling the direction of the pressure oil sent to the cylinder, and is designed to facilitate steering while providing an appropriate reaction force, that is, a feeling of response.

In addition to such a moderate reaction force, it is also required that the vehicle's path follows the steering operation without delay.In other words, the control valve spool is required to move back and forth in response to the rotation of the steering wheel. There is a growing demand for less delay in sliding motion.

However, in reality, there has been a tendency for delays in the reciprocating movement of the control valve spool due to variations in the installation of the parts that make up the power steering and looseness in the operating force transmission system.

Therefore, when the vehicle is steered by rotating the steering wheel, there is a delay in the actual steering of the wheel axle, so it takes a long time to become proficient at driving, and the above-mentioned operations are always delayed. It required steering in anticipation of delays, which made driving nerve-wracking and prone to fatigue.

Also, in vehicle design, economic efficiency, e.g.
When priority was given to things like loading efficiency and cabin space, maneuverability and stability were compromised, and in some cases, plans to develop new vehicles had to be abandoned.

The purpose and problem of this invention is to always move a control valve spool appropriately in accordance with the rotation of a steering wheel, and to prevent delays in the operation of the control valve. to reduce changes in the power cylinder and operate the power cylinder properly.
By reducing the time delay between the actual steering angle and the rotation angle of the steering wheel, it is possible to easily steer while obtaining an appropriate reaction force, and it is also useful in vehicles where economy such as loading efficiency and cabin space is prioritized. The purpose of the present invention is to provide a power steering system used in a vehicle that provides excellent steering stability, facilitates steering, and enables safe driving.

In relation to the above-mentioned objects and problems, the power steering used in the vehicle of the present invention uses oil and
It consists of a pump, a flow control valve, a control valve, and a power cylinder, and the control valve is
a pressure port having a spool chamber therein and opening into the spool chamber;
a control valve casing having a discharge port and a plurality of power cylinder ports, a pair of bores open at opposite ends and reciprocatingly slidably fitted within the spool chamber; The control valve spool is connected to the steering wheel side through the control valve spool, and the control valve spool is opened correspondingly to the bore, and the control valve spool is formed in accordance with the movement of the control valve spool. a pair of communicating holes that are switched connected to the pressure port and the exhaust port, and projecting from the control valve casing into the spool chamber at opposite ends of the spool chamber; a pair of spool guides that are fitted in correspondence with a pair of bores to form a pair of reaction chambers within the bores; a pair of auxiliary pressure chambers are separated from the reaction chambers; A restriction is defined between each end of the control valve spool and its pair of spool guides within its spool chamber, and a restriction is defined between the control valve port of the flow control valve and its control valve port.
a pressure port of the valve, an auxiliary pressure passage communicating the upstream side of the restriction with the pair of auxiliary pressure chambers, and an auxiliary pressure control valve having a spool chamber therein; A valve casing having a pressure port and a pair of control ports opened in the spool chamber, and a valve casing fitted in the spool chamber so as to be able to reciprocate and connect the pressure port to the pair of control ports. The spool is arranged in the auxiliary pressure passage, and the spool is electrically driven according to the vehicle speed, steering speed, and yaw angular velocity, and the pressure oil is sent to the pair of auxiliary pressure chambers. A configuration to adjust the amount is included.

Hereinafter, specific examples of the power steering system used in the vehicle of the present invention will be described with reference to the drawings.

The figure schematically shows a specific example 10 of a power steering system for use in a vehicle according to the invention applied to a cab-over type truck.

The power steering 10 includes an oil pump 11 and a flow control valve 12.
, a control valve 13 , and a power cylinder 14 , and further, the control valve 13 has a spool chamber 1 therein.
9 and open to the spool chamber 19 thereof, a pressure port 20 and a discharge port 2.
1, and multiple power cylinder ports 2
Control valve with 2, 23, 24
It has a casing 18 and a pair of bores 34 and 35 opened at both ends, is fitted into the spool chamber 19 so as to be able to reciprocate and slide, and is connected to the steering wheel side via a shifter 66. A control valve spool 29 is formed with corresponding openings in the control valve spool 29 and bores 34 and 35 thereof, and in response to movement of the control valve spool 29, its pressure ports 20 and A pair of communication holes 40, 41 which are switched and connected to the discharge port 21, and the spool chamber 1 thereof.
At both ends of 9, its control valve
The spool chamber 19 from the casing 18
a pair of spools projected therein and correspondingly fitted into a pair of bores 34, 35 of the control valve spool 29 to form a pair of reaction chambers 38, 39 within the bores 34, 35; - A pair of auxiliary pressure chambers 42, 43 are separated from the reaction chambers 38, 39 by the guides 36, 37, and both ends of the control valve spool 29 and the pair of spool guides 36, 37 and defined within the spool chamber 19 and a restriction 44 disposed between the control valve port 16 of the flow control valve 12 and the pressure port 20 of the control valve 13. , auxiliary pressure passages 45, 46, 47 communicate the upstream side of the restriction 44 with the pair of auxiliary pressure chambers 42, 43, and an auxiliary pressure control valve 48 has a spool chamber 49 therein, and , a pressure port 5 opening into the spool chamber 49 thereof.
0 and a pair of control ports 51, 52 and its spool chamber 4;
A spool 53 is fitted in the auxiliary pressure passage to adjust the vehicle speed of the truck. The spool 53 is electrically driven in accordance with the steering speed and yaw angular velocity to adjust the amount of pressure oil sent to the pair of auxiliary pressure chambers 42, 43.

The oil pump 11 is driven by an internal combustion engine (not shown) mounted on its cab-over type truck, and sucks up the pressure oil in the oil reservoir 67 to increase the rotational speed of the internal combustion engine. It is constructed so that a substantially proportional discharge amount of pressure oil can be obtained.

The oil pump 11 is configured similarly to an oil pump used in existing power steering systems, so a description of its configuration will be omitted.

The flow control valve 12 is a pump connected to the discharge side of the oil pump 11.
Port 15, control valve 13 described later
The control connected to the pressure port 20 side of
Valve port 16 and its suction port connected to the suction side of oil pump 11.
It consists of a casing with a port 17 and an oil return control spool (not shown) arranged so as to be able to slide back and forth within the casing, and adjusts the flow rate of pressure oil sent to the pump port 15 side. so that a predetermined flow rate is sent to the control valve port 16 side, and the surplus flow rate is returned from the suction port 17 to the suction side of the oil pump 11, that is, the oil reservoir 67 side. has been done.

The flow control valve 12 is a flow control valve used in existing power steering.
Since it is configured similarly to a control valve,
A detailed explanation of its configuration will be omitted.

Control valve 13 includes spool chamber 19 and its flow control valve 1.
pressure port 2 connecting the control valve port 16 side of 2 to its spool chamber 19;
0. Drain that spool chamber 19 of that oil.
Exhaust port 21 connected to reservoir 67 side and power cylinder ports 22, 23, 24
control valve casing 18 comprising
and the pressure port 20 is connected to the discharge port 21,
and power cylinder ports 22, 23,
a control valve spool 29 reciprocally slidably disposed in its spool chamber 19 for switching connection to the spool chamber 19;
In chamber 19, the control valve
A pair of reaction force chambers 3 formed on both sides of the spool 29
8, 39 and further, on either side of its control valve spool 29, its reaction chambers 38, 3.
9 and a pair of auxiliary pressure chambers 42 and 43 respectively formed.

Of course, ring grooves 27 and 28 are formed within the spool chamber 19 in communication with the pressure and exhaust ports 20 and 21, respectively.

Also, the control valve spool 2
9 is placed in the neutral position, its ring groove 2
Lands 30 and 33 are respectively formed around both ends of the control valve spool 29 located outside of the lands 3 and 28.
Lands 31 and 32 are formed between 0 and 33 so as to face the ring grooves 27 and 28, respectively.

Of course, those lands 30, 31, 32, 33
In between, the power cylinder port 22, 2
3, 24 can be connected to the spool grooves 71, 72,
73 are formed respectively.

Furthermore, bores 34 and 35 are formed inside both ends of the control valve spool 29, respectively, and extend along the axial direction of the control valve spool 29 and are open at both ends. , 35 are communication holes 40,
41 to the spool grooves 71 and 72, respectively.

The valve casing 18 of the control valve 13 also includes spool guides 36 and 37 that are fitted into bores 34 and 35 of the control valve spool 29, respectively.

Of course, the spool guides 36 and 37 are formed separately from the valve casing 18 in consideration of ease of assembling the control valve spool 29, and are plug-type guides that are screwed into the valve casing 18. It is desirable to configure it as one.

Therefore, if the control valve spool 29 is reciprocally slidably disposed within the spool chamber 19 of the valve casing 18, with the spool guides 36, 37 fitting into the bores 34, 35, For example, reaction chambers 38 and 39 are formed in the bores 34 and 35, respectively, in cooperation with the end faces of the spool guides 36 and 37.

The reaction force chambers 38 and 39 are connected to the communication holes 40 and 4 described above.
Of course, they are connected to the spool grooves 71 and 72 via the spool grooves 71 and 72, respectively.

Further, with the control valve spool 29 disposed within the spool chamber 19 of the valve casing 18 as described above, a pair of auxiliary pressures are provided on opposite sides of the control valve spool 29. Room 42,
43 are formed respectively.

That is, the pair of auxiliary pressure chambers 42, 43 are separated from the reaction force chambers 38, 39 by the spool guides 36, 37, and
The guides 36 and 37 are each formed in a ring shape so as to cover the base sides thereof.

Of course, the control valve spool 29 mentioned above slides back and forth in response to steering operation, so the control valve spool 29 slides back and forth in response to steering operation.
9, one end of a shaft 66 serving as a shifter is fixed, and the other end of the shaft 66 is fixed to a position approximately in the center of the control valve casing 1.
8 and is connected to the steering shaft (not shown) side.

The power cylinder 14 has its control
a power cylinder casing having a cylinder bore 57 integrally formed in the casing 20 of the valve 13 and connected to the power cylinder ports 22, 23, 24 of the control valve 13; It is arranged to be reciprocally slidable within the cylinder bore 57 so as to form a pair of cylinder chambers 59, 60 correspondingly connected to the cylinder ports 22, 23, and 24 within the cylinder bore 57. Further conceptually explaining the output section, one end is connected to the power piston 58.
A push rod 61 is connected to the power cylinder casing and the other end protrudes outward through the power cylinder casing, and the push rod 61 is located on the opposite side of the push rod 61 and has approximately the same axis as the push rod 61. It consists of a rod 62 which is fixed to the power cylinder casing.

Of course, the power cylinder ports 22 and 23 of the control valve 13 are connected to the communication path 6.
3 and 64 to the cylinder chamber 59, and
The power cylinder ports 24 are each connected to the cylinder chambers 60 through communication passages 65.

The other end of the push rod 61 of the power cylinder 14 configured in this manner is attached to the chassis frame side of the cab-over type truck, and
A rod 62 located on the opposite side of the push rod 61 is attached to a drag ring (not shown) that drives a steering arm (not shown).

In addition, although the above description is based on the linkage type, the integral type also includes the following:
Of course, the configuration is similar to the configuration described above.

The aperture 44 is a fixed aperture and is a control valve of the flow control valve 12 described above.
It is provided between port 16 and pressure port 20 of control valve 13.

Of course, the throttle 44 can be provided in any position as long as it is between the control valve port 16 and the pressure port 20, for example, it can be provided in the control valve casing 18, or , it is also possible to provide the control valve port 16 and the pressure port 20 in a hydraulic pipe connecting the control valve port 16 and the pressure port 20.

The auxiliary pressure passages 45, 46, 47 are
The upstream side of 4 is connected to the pair of auxiliary pressure chambers 42 and 43, respectively.

That is, the auxiliary pressure passages 45, 46, 47
is configured so that the pressure oil upstream of the throttle 44 is sent to the pair of auxiliary pressure chambers 42 and 43 via an auxiliary pressure control valve 48, which will be described later.

Therefore, the auxiliary pressure passage 45 has one end connected to the upstream side of the throttle 44 and the other end connected to the pressure port 50 of the auxiliary pressure control valve 48, and the auxiliary pressure passages 46, 47 One end of each is connected to the control port 5 of its auxiliary pressure control valve 48.
1 and 52, and the other end of each is connected to its auxiliary pressure chamber 4.
It is connected to ports 25 and 26 of 2 and 43.

The auxiliary pressure control valve 48 is a spool-type directional control valve, and has a pressure port 50 and a pair of control ports 5.
1 and 52, respectively, and having a spool chamber 49 inside thereof communicating with those ports 50, 51, 52, and for switchingly connecting its pressure port 50 to its control ports 51, 52. , and a spool 53 disposed in the spool chamber 49 so as to be slidable back and forth.

Of course, the spool 53 is connected to the actuator 5.
5, it is slid back and forth via the operating rod 54. The actuator 55 can have any form as long as it can slide the spool 53 back and forth in response to an electric signal, and here an electromagnetic coil is used.

The auxiliary pressure control valve 48 configured in this way is
The controller 5 slides the spool 53 and adjusts the amount of pressure oil sent to the auxiliary pressure chambers 42 and 43 according to the vehicle speed, steering speed, and yaw angular velocity of the cab-over type truck.
6.

That is, the controller 56 is used in combination with a steering amount sensor 68, a vehicle speed sensor 69, and a yaw angular velocity sensor 70, and outputs output signals to the actuator 55 according to input signals from these sensors 68, 69, and 70. It adjusts the amount of pressure oil sent to the auxiliary pressure chambers 42 and 43, and is mainly composed of an input and output circuit, an arithmetic circuit, a memory circuit, and a control circuit.

The steering amount sensor 68 detects the rotation speed, rotation direction, and rotation angle of the steering shaft of the cab-over type truck, and is arranged so as to cover the outside of the steering shaft at a predetermined position. has been done.

Therefore, the actuator described above is connected to the output circuit of the controller 56, and the steering amount sensor 68 is connected to the input circuit of the controller 56.

Of course, it is desirable that the steering amount sensor 68 has a high resolution as a rotation sensor, consumes little power, and generates a reliable and large signal as an output. Semiconductor types are used.

The vehicle speed sensor 69 detects the rotational speed of the output shaft of the transmission in the cab-over type truck, and is arranged at the rear of the transmission and connected to the input circuit of the controller 56 described above.

Of course, it is preferable to use a non-contact type vehicle speed sensor 69 in consideration of the limitation of the usable rotational speed of the converter bearing and the load on the output shaft of the transmission.

The yaw angular velocity sensor 70 detects the yaw angular velocity when the truck is running, and is configured in a gyro type and is mounted on the chassis frame side at a position separated above the transmission. It is connected to the input circuit of the controller 56.

Next, to describe the driving of a cab-over type truck to which the above-described power steering is applied, the controller 56 constantly inputs signals from the steering amount sensor 68, vehicle speed sensor 69, and yaw angular velocity sensor 70, and outputs signals from the steering amount sensor 68, vehicle speed sensor 69, and yaw angular velocity sensor 70. A signal is sent to the actuator 55 of the auxiliary pressure control valve 48.

That is, when the steering wheel is rotated to turn the cab-over type truck, the control valve spool 29 of the control valve 13 slides, while the controller 56 controls the rotation of the steering wheel. That is, a signal from the steering amount sensor 68 is input, and an output signal is further sent to the actuator 55 to control the auxiliary pressure control valve 48.

For example, if the control valve spool 29 slides to the right in the illustration by rotating the steering wheel clockwise, the pressure port 20 will be moved by the spool groove 72 of the control valve spool 29. , the pressure oil that is connected to the power cylinder port 24 and sent from the oil pump 11 via the flow control valve 12 is sent to the cylinder chamber 60 of the power cylinder 14, so that the power cylinder 14 It is operated.

Of course, a part of the pressure oil sent to the pressure port 20 is sent to the reaction force chamber 39 via the communication hole 39. In other words, the reaction force due to the steering as described above is
It is given by the pressure within the reaction force chamber 39.

Further, when the steering wheel is rotated clockwise in this manner, the controller 56 inputs a signal from the steering amount sensor 68 and further sends an output signal to the actuator 55 thereof.

As a result of the output signal being sent to the actuator 55, the spool 53 of the auxiliary pressure control valve 48 slides, and the pressure oil on the upstream side of the throttle 44 is sent to either of the auxiliary pressure chambers 42, 43. , the selection of either one of the auxiliary pressure chambers 42, 43, and the amount of pressure oil are determined by the signals from the steering amount sensor 68, vehicle speed sensor 69, and yaw angular velocity sensor 70, in other words, the steering It is determined according to the rotation speed, rotation direction, rotation angle, vehicle speed, and yaw angular velocity of the shaft.

That is, when the steering wheel is rotated clockwise, the controller 56 inputs a signal from the steering amount sensor 68;
By sending an output signal to the actuator 55, the spool 53 of the auxiliary pressure control valve 48 is slid to the left in the figure.

If the spool 53 is so slid, the pressure port 50 of the auxiliary pressure control valve 48 is connected to the control port 52 and the oil pump 11
The pressure oil sent to the upstream side of the throttle 44 via the flow control valve 12 is sent to the auxiliary pressure chamber 42 via auxiliary pressure passages 45 and 46.

Therefore, the pressure oil sent to the auxiliary pressure chamber 42 causes the control valve spool 29 to slide to the right in the figure.

Of course, the control valve spool 2
The amount by which 9 slides is the amount of pressure oil sent to the auxiliary pressure chamber 42, in other words, the amount by which the steering amount sensor 68, vehicle speed sensor, and yaw angular velocity sensor 7
It is determined according to the signal from 0.

That is, the control valve spool 29 is reciprocated and the power cylinder 14 is operated by rotating the steering wheel in almost the same way as existing power steering. 29, the amount of sliding of the control valve spool 29 is small relative to the rotation of the steering wheel, and even if the actual steering angle is small, the pressure oil sent to the auxiliary pressure chamber 42 Since the sliding movement of the control valve spool 29 is corrected by this, a delay in the operation of the control valve spool 29 is prevented.

Of course, the above-mentioned operation of the power steering 10 is explained using an example in which the operation delay of the control valve spool 29 is reduced in accordance with the signal from the steering amount sensor 68.
In the operation of the power steering 10, the controller 56 inputs signals from not only the steering amount sensor 68, but also the vehicle speed sensor 69 and the yaw angular velocity sensor 70, and inputs signals to the actuator 55 of the auxiliary reaction force control valve 48. Sending an output signal.

As a result, for example, when the cab-over type truck is traveling at high speed and the yaw angular velocity increases due to sudden operation of the steering wheel, the steering amount sensor 68, vehicle speed sensor 69, and yaw angular velocity The controller 56 inputs the signal from the sensor 70, and further, the controller 56 sends an output signal to the actuator 55, sends pressure oil to either one of the auxiliary pressure chambers 42, 43, and controls the control valve. The spool 29 is corrected in a direction that maintains running stability.

That is, when such a sudden operation of the steering wheel causes the control valve spool 29 to slide to the right in the figure, the controller 56 sends an output signal to its actuator 55 and the spool 53 of its auxiliary pressure control valve 48 is slid to the right in the figure.

When the spool 53 is slid in this way,
Pressure oil on the upstream side of the throttle 44 is sent into the auxiliary pressure chamber 43 .

Therefore, the pressure oil in the auxiliary pressure chamber 43 causes the control valve spool 29 to slide to the left in the figure.

In other words, when driving at high speed, the steering
Even if the wheel is suddenly operated, the auxiliary pressure chamber 4
Pressure oil fed into the control valve spool 29 compensates for the sliding movement of the control valve spool 29, preventing the cab-over type truck from being oversteered and further preventing the occurrence of spin. Prevented.

As understood from the above, the power steering used in the vehicle of this invention includes an oil pump, a flow control valve, a control valve, and a power cylinder,
Further, the control valve has a spool chamber therein, and the spool chamber has a spool chamber therein.
A control valve casing having a pressure port, a discharge port, and a plurality of power cylinder ports opened in the chamber and a pair of bores opened at each end for reciprocating sliding within the spool chamber. a control valve spool that can be mated with the control valve spool and connected to the steering wheel side via the shifter;・A pair of communication holes that are switched and connected to the pressure port and discharge port according to the movement of the valve spool, and the spool.
A pair of reaction force chambers projecting from the control valve casing into the spool chamber at opposite ends of the chamber and correspondingly matingly fitted within the bores of the control valve spool. a pair of spool guides forming a spool chamber, a pair of auxiliary pressure chambers are separated from the reaction chamber, and a pair of auxiliary pressure chambers are defined from the reaction chamber at opposite ends of the control valve spool and the pair of spool guides form a pressure chamber within the spool chamber. The flow control valve's control valve is
an auxiliary pressure passage located between the valve port and the pressure port of its control valve, an auxiliary pressure passage communicating the upstream side of the restriction with the pair of auxiliary pressure chambers, and an auxiliary pressure control valve having an internal spool. - A valve casing comprising a chamber and having a pressure port and a pair of control ports opened to the spool chamber, and a valve casing that is reciprocatably slidably fitted into the spool chamber and has a pressure port opened to the spool chamber. It becomes a spool that is switched and connected to a pair of control ports, and
Vehicle speed, steering speed,
The power steering used in the vehicle of the present invention includes a configuration for electrically driving the spool according to the yaw angular velocity and adjusting the amount of pressure oil sent to the pair of auxiliary pressure chambers. In addition to mechanically sliding the control valve spool with the steering wheel into the spool chamber in response to rotation of the steering wheel, pressurized oil flows through the pair of auxiliary pressure control valves. is sent to one of the auxiliary pressure chambers of the auxiliary pressure chamber and slid into its spool chamber, and as such, its control valve
Spool movement is properly compensated so that the control valve spool always slides properly within the spool chamber in response to rotation of the steering wheel, and the control valve spool In other words, the sensitivity of the control valve becomes constant, the power cylinder is operated properly, and the so-called rotation angle of the steering wheel (steering wheel operation angle )
This reduces the time delay between the actual steering angle (tire turning angle) and makes it easier to steer while obtaining an appropriate reaction force. This prevents the vehicle from oversteering, preventing the vehicle from spinning, and provides excellent handling stability even in vehicles where economy, such as loading efficiency or cabin space, is prioritized. In addition, this type of vehicle is prevented from oversteering when the steering wheel is suddenly operated at high speeds. This prevents the vehicle from rolling over and causing spin in that type of vehicle, making it extremely practical.

[Brief explanation of drawings]

The figure is a schematic diagram showing a specific example of the power steering system used in the vehicle of the present invention applied to a cab-over type truck. 13... Control valve, 18... Control valve casing, 29... Control valve spool, 34, 35... Pair of bores, 36, 37... Pair of spool guides, 3
8, 39... A pair of reaction force chambers, 42, 43... A pair of auxiliary pressure chambers, 44... Throttle, 45, 46, 47... Auxiliary pressure passage, 48... Auxiliary pressure control valve.

Claims (1)

[Claims] 1. Oil pump, flow control valve, control valve, and power pump.
A cylinder comprising a cylinder and used for steering a vehicle, the control valve having a spool chamber inside, and a pressure port, a discharge port, and a discharge port opened to the spool chamber.
and a control valve casing with multiple power cylinder ports and a pair of bores opened at both ends of the spool.
A control valve spool that is reciprocally slidably fitted into the chamber and connected to the steering wheel side via a shifter, and an opening corresponding to the bore formed in the control valve spool. and a pair of communication holes which are switched and connected to the pressure port and the discharge port according to the movement of the control valve spool, and a pair of communication holes that are connected to the control valve spool at both ends of the spool chamber.
a pair of spool guides projecting from the casing into the spool chamber and correspondingly mated with a pair of bores of the control valve spool to form a pair of reaction chambers within the bores; a pair of auxiliary pressure chambers are defined from the reaction chamber and defined from each other within the spool chamber at opposite ends of the control valve spool and the pair of spool guides, a restriction being defined; , disposed between a control valve port of the flow control valve and a pressure port of the control valve, an auxiliary pressure passage communicating the upstream side of the restriction with the pair of auxiliary pressure chambers, and , an auxiliary pressure control valve is reciprocally slidable within the spool chamber and a valve casing having a spool chamber therein and having a pressure port and a pair of control ports open to the spool chamber; A spool is fitted to switch and connect the pressure port to the pair of control ports, and is placed in the auxiliary pressure passage to electrically connect the spool depending on vehicle speed, steering speed, and yaw angular velocity. Power steering used in vehicles is unique in that it adjusts the amount of pressurized oil sent to a pair of auxiliary pressure chambers.