JPS62237145A - Speed change gear - Google Patents

Abstract

PURPOSE:To enable a speed change gear for an automobile or the like to be changed at its speed with a less number of gear rows than the number of steps of speed, by installing 1st, 2nd, and 3rd gears, each of which to form one gear row respectively, between 1st counter shaft, an output shaft, and 2nd counter shaft. CONSTITUTION:When only a clutch 1A is engaged, the power from an engine is transmitted to an output shaft 2 through an input shaft 1, gears 3F, 3D, an oneway clutch 3G, a counter shaft 3, gears 3A, 2a, and 1st speed is obtained. By engaging another clutch 1B, through an input-side shaft 4d, another oneway clutch 4c, another counter shaft 4, and gears 4A, 3E, said counter shaft 3 is driven and the speed is increased to 2nd speed. During running in 3rd speed, said clutch 1A is disengaged, a sleeve 3g shifted to the neutral position, 3e to the right end, and then said clutch 1A is engaged. For 4th speed running, said clutch 1B is disengaged, another sleeve 3Ac to the neutral position. 4f to the left end, and then said clutch 1B is engaged. Thus hot shifting becomes possible with a small number of gear rows.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a gear transmission used in automobiles and the like.

[Prior Art] Generally, when changing gears, an automobile gear transmission first sets the engine output to an idling state, and then shifts up while in the idling state.
up) or shift down
wn).

On the other hand, there is a so-called hot shift (hot 5 shift) method in which gear transmissions are shifted without idling the engine, and while the engine is still producing sufficient power. .

It connects the input shaft from the engine to a first drive shaft and a second drive shaft.
A first gear transmission having only an odd number of gears is configured between the first drive shaft and an output shaft that drives the drive wheels, and the second drive shaft A second gear transmission having only even-numbered gears is configured between the output shaft and the output shaft.

These conventional gear transmission methods for hot shifting are as follows: 1) When the vehicle is started, a clutch (first clutch) in the first gear transmission and a clutch in the second gear transmission are connected. 2) When the engine is warmed up, the first gear transmission is set to the first gear position and the second gear is set to the second gear position. 3) In this state, if only the first clutch in the first gear/IL transmission is engaged, the power from the engine will be The information is transmitted to the output shaft through the first clutch, the first drive shaft, and the first speed gear train, and the automobile is in the same state as a normal first speed 11L transmission. Taking off.

In this case, the second clutch in the second vehicle transmission remains in a disengaged state.

4) When shifting up to 2nd gear from this state, the 2nd vehicle transmission is already set to 2nd gear, so the first clutch in the 1st gear transmission is disengaged. At the same time, if the second clutch in the second gear transmission is engaged, the power flow from the engine will be transferred to the second clutch, without causing the engine to become -1, fitting. The signal is transmitted to the output shaft via the second drive shaft and the second speed change gear train, and the vehicle changes from the first speed to the second speed and is added to pp<.

1+ when shifting up to 3rd gear
Next, the first gear transmission is set to third speed while the first clutch remains disengaged, and in that state, the first clutch is engaged at the same time as the second clutch is disengaged. Just go.

However, this conventional way of thinking is that since the shifting of the gear position in a car transmission is prepared in advance, the operation time required to alternately shift the first clutch and the second clutch is reduced.・; At 17, it becomes possible to change gears, and the so-called hot shift becomes possible.

[Problems to be Solved by the Invention] However, these systems have only an odd number of gears between the first drive shaft and the output shaft. between the second drive shaft and the output shaft; If this is the case, the gear trains forming the r-trough and even-numbered gears will have to attack more, resulting in a disadvantage that the entire transmission will become larger.

An object of the present invention is to provide a gear transmission in which the number of gear trains can be reduced compared to the gear position of the hot shift Nantun transmission as described in (h).

[Means for solving problems] The present invention has the configuration shown in F.

The input shaft is: a: branched into a first subshaft via a first clutch on one side; b=branched into a second subshaft via a second clutch on the other side.

The rotation direction of the first sub-shaft and the rotation direction of the second sub-shaft are opposite to each other, and the first sub-shaft is capable of rotating and sliding. A first south center is fitted into the first float, and the first float can be engaged with and disengaged from the first subshaft described in ii'ij.

A second gear is fitted to the output shaft, a third gear is fitted to the second sub-shaft so that it can rotate and slide, and iii. The second gear and the gear 11 can be engaged and disengaged from the countershaft of
The gear transmission has the above configuration, in which the third m and lj are always in mesh. [Operation] When warming up the engine, the first clutch and the second clutch are engaged. If you leave both of them in a state where they are both cut and crossed, it will be possible to warm them up. 1) When the engine has completely warmed up, or while the car is running, move the third Satsuma car to the second When the first gear is engaged with the input shaft, the first gear is disengaged from the first countershaft, and the second clutch is engaged, the power from the engine is transferred to the input shaft and the second clutch.
It is transmitted to the output shaft via the clutch, the second subshaft, the third gear, the first gear, and the second gear.

In this case, since the first gear is a female gear on the first countershaft -H, the gear ratio between the input shaft and the output shaft is determined by the number of teeth in the third gear and the second gear. The value is determined by the ratio to the number of teeth on the float.

At 5% of this state, the first clutch is disengaged and the first
When the gear is engaged with the first subshaft, and after the engagement is completed, the second clutch is disengaged and the first clutch is engaged at the same time, the power from the engine is Input shaft, first clutch, first subshaft, first float, and second
It is transmitted to the output shaft via the gear.

In this case, the third gear is in a state where it simply rotates idly together with the second countershaft, and the power from the human power and oil is directly transmitted from the first gear side to the output shaft via the second gear. Therefore, the speed ratio between the input shaft and the output shaft is determined by the ratio of the number of teeth on the first gear and the number of teeth on the second gear.

Conversely, when returning from this state to the previous speed ratio, the third gear is engaged with the second υ1 shaft with the second clutch disengaged, and after that engagement, the first It is sufficient to disengage the clutch of Jj2 and at the same time engage the clutch of Jj2.

[Example] Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows a scale diagram of a small transmission as an embodiment of the present invention, FIG. 2 shows a cross section in FIG. 1, and FIG. gear 2
FIG. 2 is a view of the C13C and 4B floats seen from the direction of arrow A, similar to FIG. 2.

The input shaft 1 is the first clutch LA, m car 3F pine, l-l
Musu n wa noroei fight 11. Spring 1-3G,
It has a structure that can be interlocked with the first sub-shaft 3.

The one-way clutch 3G has teeth 13 when the rotational speed of the gear 3D rotates faster in the same direction than the rotational speed of the subshaft 3.
3D rotation is transmitted to the subshaft 3 via the one-way medium clutch 3G.
When the rotation speed of the secondary shaft 3 rotates faster in the same direction than the rotation speed of the float 3D, the rotation speed of the secondary shaft 3 is transmitted to the gear 3D.
The relationship is such that it rotates freely.

The floats 3A, 3B, 3C, and 3E are fitted into the sub 41+3 so as to be able to rotate and slide, the knobs 3d and 3f are fitted onto the sub shaft 3, and the sleeve 3g is fitted to allow torque transmission. The pawl 3Aa is fitted into the hub 3f so as to be able to slide in the axial direction.
And the hub 3Ab is fixed to the gear 3A, and the sleeve 3Ac
enables torque transmission and allows sliding in the axial direction /X
The sleeve 3Ec is fitted to the sleeve 3Eb to enable torque transmission, and the sleeve 3Ec is fitted to the sleeve 3Eb so that it can slide in the axial direction. and 3Bb are fixed to the ceramic wheel 3B, and the sleeve 3e
Enables torque transmission Enables sliding in the axial direction /＼
The pawl 3Ca is fixed to the gear 3C, and the sleeve 3C is fitted to the outer ring (directly connected to the subshaft 3) of the one-way clutch 3G to enable sliding in the axial direction and torque transmission. However, the pawl 3b is fixed to the gear 3D.

Teeth p, 2a, 2b and 2C are fitted on the output shaft 2 which is linked to a drive wheel (not shown).

The input shaft l is configured to be interlocked with the second subshaft 4 via the second clutch IB, the input shaft 4d, and the second one-way clutch 4C, and the gear 4A is fitted onto the subshaft 4. The gear 4B is fitted to the subshaft 4 so that it can rotate and slide, and the pawl 4
b is fitted on the input side shaft 4d, hubs 4e and 4g are fitted on the subshaft 4, a, and the sleeve 4C is the one-way flange 4.
The sleeve 4f is fitted to the outer ring of C (directly connected to the subshaft 4) so as to enable axial sliding and torque transmission, and the sleeve 4f allows torque transmission and axial sliding. The pawl 4Ba is fixed to the gear 4B, and the sleeve 4h enables torque transmission and prevents sliding in the axial direction.
It fits properly into the hub 4g, and the pawl 4Da is fixed to the gear 4D.

The one-way clutch 4C transmits the rotation of the input shaft 4d to the counter shaft 4 via the one-way clutch 4C when the rotation speed of the input end shaft 4d rotates faster in the same direction than the rotation speed of the counter shaft 4, When the rotational speed of the subshaft 4 rotates faster in the same direction as the rotational speed of the input end shaft 4d, the subshaft 4 rotates freely relative to the input shaft 4d.

Teeth +1 (3A and tM! IZ2a, fa wheel 3B and gear 2b
, i jlE 3 C and gear 2c, @ city 4A and gear 3E
, m wheel 4B and It 3 C1 and gear 3F and It II
The king 3D is always in gear meshing, and the gear 4D is always in gear meshing with the gear 2a, as shown in FIG.

Gear 3A and gear 2a, gear 3B and gear 2b.

The gear train of gear 3C and gear 2c forms a main transmission A, of which the tooth TJL3A and gear 2a constitute the outer gear of the first gear, and the gear 3B and gear 2b constitute the gear train of the third gear. However, the gear 3C and the gear 2C constitute a fifth speed gear train.

Gears 4A and 3E, and gears 4B and 3C constitute an auxiliary transmission B, a gear train of gears 4A, 3E, 3A and 2a constitutes a second gear, and a secondary gear train of gears 4B, 3C and 2C. constitutes the 4th speed, the gear train of gears 4A, 3E, 3B and 2b constitutes the 6th speed, gear 4D and gear 2a
The row of teeth +1L constitutes a row of seven teeth for retraction.

The operation of the configuration of the embodiment of the present invention described above will be explained below.

Effect of shift amplifier: When warming up the engine (not shown), set both clutches IA and IB in the disengaged state, and let the engine idle to warm up the engine. do.

1st speed running: When this warming-up is completed and the car is to start, the clutches IA and IB are
With the sleeves separated, set only the sleeve 3g to the left end as shown in the illustration, and set the other sleeves 3Ae, 3Ec, 3e, 4h.
, 4f, 3C and 4c are all left in their neutral positions.

In this state, when only clutch IA is engaged, power from the engine is transferred to input shaft l, clutch plate 3a,
Gears 3F and 3D, one-way clutch 3G, subshaft 3, hub 3f, sleeve 3g, pawl 3Aa, gear 3A
In this state, the power transmitted to the output shaft 2 drives drive wheels (not shown) and starts the automobile.

2nd speed running 2 When shifting the shift door from the above state to 2nd speed, move the sleeve 3Ac from the illustrated position to the left end while keeping the clutch notch IA engaged. At this point, clutch IB is engaged.

As a result, while the subshaft 3 is being driven via the clutch IA, the input shaft 4 is also driven from the clutch IB side.
d. The one-way clutch 4C1 drives the countershaft 3 via the countershaft 4, gears 4A and 3E, pawl 3Ea, sleeve 3AC, hub 3Ab, pawl 3Aa, sleeve 3g, and /\b 3f.

1. In this case, the gear ratio of gear 4A and gear 3E is:
It is better to drive the subshaft 3 via the clutch IB than to drive the subshaft 3 via the clutch IA side.
Furthermore, the gear ratio is such that the speed of the subshaft 3 is increased.

Therefore, in this state, the rotational speed of the subshaft 3 is faster than the rotational speed of the i-east 3D, so the relationship between the gear 3D and the subshaft 3 is
From the moment the clutch is engaged, it will be automatically disengaged by the action of the one-unit f-clutch 3G.

For this reason, in the second speed drive, the output power from the engine is transmitted to the input shaft 1, the clutch plate 4a, the input side shaft 4d, the one-way Kurasochi 4C1 sub-piece 4, the teeth 11 and 4A. 3E, claw 3Ea, sleeve 3Ac,
It is transmitted to the output shaft 2 via the hub 3Ab, t@tun 3A and 2a.

3rd speed running: 1: When shifting up from the above state to 3rd speed, disengage the clutch IA, then move the sleeve 3g from the position shown in the figure to the middle position n on the right, and move the sleeve 3e. Shift to the right end, and in that state, clutch LA is engaged.

As a result, the output shaft 2 is transferred from the clutch IB to the gear train of gears 4A and 3E and the gear train of gears 3A and 2a.
For the 2nd speed state in which gears 3F and 3D, one-way flange 3
G, subshaft 3, hub 3d, sleeve 3e, pawl 3Bb, @
The output shaft 2 will be driven via the wheels 3B and 2b.

However, in this case, the gear ratio between the third speed gear 3B and the gear 2b is smaller than that of the second speed gear train, which is the gear train of gears 4A, 3E, 3A, and 2a, which drives the output shaft 2. 2 is further accelerated.

Therefore, in this state, the subshaft 4 moves from the output shaft 2 whose speed has been increased to the second speed gear train (gears 2a, 3A, 3).
E and 4A (7) gear train), the rotational speed of the subshaft 4 is equal to that of the input shaft 4d.
Since the rotation speed is V, the relationship between the input shaft 4d and the subshaft 4 is automatically disconnected from the moment this clutch IA is engaged by the action of the one-way clutch 4C. Therefore, the power from the input shaft 1 is transmitted only through the clutch IA side.

4th stop: When shifting up from the above state to the 4th stop, leave the two clutches LA engaged, and press clutch IB! , lJ, return the sleeve 3AC to the illustrated neutral position, move the sleeve 4f to the left end, and engage the clutch IB in this state.

As a result, the output shelf 1 is
2, the input side shaft 4d, one-way clutch 4C1 subshaft 4,
Hub 4e, sleeve 4f, pawl 4Ba, fM car 4B, 3
The output shaft 2 will be driven via C and 2C.

However, in this case, rather than the third speed gear train consisting of gears 3F, 3D, 3B and 2b driving the output shaft 2,
The relationship is such that the output shaft 2 is driven faster when the south 11th row of gears 4B, 3C, and 2C drives the output shaft 2.

Therefore, in this state, the subshaft 3 is driven faster from the output shaft 2 whose speed has been increased through the third speed gear train, so that the rotational speed of the subshaft 3 is
Since the rotational speed of llf 3D causes LHI to rotate, the relationship between gear 3D and subshaft 3 is such that from the time this clutch IB is engaged, one-way clutch 3
It is automatically disconnected by the action of G, and the power from the input shaft 1 is transmitted from the clutch IB side only through the fourth speed gear train.

In this case, the gear ratio of the fourth speed is determined by the ratio of the number of teeth in the gear 4B and the number of teeth in the gear 2C, and the gear 3C is in an idle gear state.Fifth speed running: When shifting up from the above state to 5th gear, the clutch IA is disengaged, and then the sleeve 3e is moved to the left end, and in that state, the clutch IA is
As a result, while the output shaft 2 is being driven from the clutch IB side in the fourth gear position, the output shaft 2 is driven from the clutch IA side as well. Since it is ready to drive the output shaft 2 through the gear train,
The rotational speed of the subshaft 4 is increased from the side of the output shaft 2 whose speed has been increased, and the subshaft 4 rotates at a faster rotational speed than when the rotational speed is in the fourth speed.

Therefore, in this state, the subshaft 4 is connected to the input end 1
The relationship between the input shaft 4d and the subshaft 4 is as follows from the time this clutch IA is engaged.
It will be automatically disconnected by the action of the one-way clutch 4C.

For this reason, in the fifth speed drive, the output power from the engine is transmitted through the input shaft 1, clutch plate 3a, gears 3F and 3D, one-way clutch 3G, countershaft 3, and gears 3C and 2C. and is transmitted to the output shaft 2.

Here, the present invention is characterized by the configuration of the vehicle convoys in the fourth and fifth speeds.

6th speed running 2 When shifting from the above state to 6th speed, the clutch IB is disengaged, the sleeve 4f is returned to the neutral position shown, and the sleeve 3Ec is moved to the left end, and in that state, the clutch IA Clutch IB is engaged while keeping it engaged.

As a result, while the output shaft 2 is being driven from the clutch IA side via the fifth speed gear train, the clutch I
Also from the B side, input side shaft 4d, one-way number clutch 4
C, via countershaft 4, gears 4A and 3E, hub 3Eb, sleeve 3Ec, pawl 3Ba, gears 3B and 2b,
This will drive the output shaft 2.

However, in this case, the 6th speed gear train consisting of gears 4A, 3E, 3B and 2b is made up of the gears 3F, 3D, 3C and 2c: , the relationship is such that the speed of the output shaft 2 is further increased.

Therefore, in this state yE;, the countershaft 3 is rotated faster from its increased output +h2 through the row of teeth i of the gears 2c and 3C, and as a result, the rotational speed of the countershaft 3 is Since the gear 3D rotates at v faster than the rotational speed of the gear 3D, the relationship between the teeth 3D and the subshaft 3 is automatically adjusted by the action of the one-way clutch 3G from the time this clutch 1B is engaged. They will be separated.

For this reason, in the sixth speed drive, the power from the engine is transmitted to the input shaft 1, the clutch plate 4a, the input shaft 4d, the one-way clutch 4C1, the subshaft 4, and the gear 4A.
and 3E, hub 3Eb, sleeve 3Ec, pawl 3Ba
,@Shift-down operation transmitted to the output shaft 2 via cars 3B and 2b: The shift-down operation can be performed by performing the above-mentioned shift-up operation in the reverse order.

Reverse operation: With both clutches IA and IB disengaged, only the sleeve 4h is moved from the illustrated neutral position to the right end, and all other sleeves are set to the neutral position.

When clutch IB is engaged in this state, the power from the engine is transferred to input shaft 1, clutch IB, input shaft 4d, one-way clutch 4C, secondary link 4, and hub 4g.
, the sleeve 4h, the pawl 4Da, and the gears 4D and 2a to drive the output shaft 2, thereby causing the vehicle to move backward.

In this case, the gear 2a is used not only for the JII heptad operation of the first speed and the second speed, but also for the main reverse operation.

This is because, as can be understood from Fig. 2, the second subshaft 4 is provided for the first subshaft 3, and the subshaft 3 and subshaft 4 are in a reverse relationship with each other. This is because when the gear 2a is driven from the shaft 3 side, the output shaft 2 is driven in the forward direction, and when the gear 2a is driven directly from the subshaft 4 side, reverse operation is possible.

Operation for engine brake: Engine brake is normally used between 1st and 4th gears.

If the currently used gear is the first or third gear, the clutch IA is engaged as described above, and the power transmission path is between the first subshaft 3 and the clutch IA.
is formed between.

In this way, when the accelerator pedal is suddenly released in 1st or 3rd gear, the sleeve 3C engages the pawl 3b in response to the return while the gear is still set. Match. As a result, when the accelerator pedal is released and the engine is braked, the running energy from the output shaft 2 is transferred from the countershaft 3 to the sleeve 3C.
It is absorbed into the engine via the first claw 3b, gears 3D and 3F, clutch plate 3a, and input shaft l.

Also, if the gear currently being used is 2nd gear or i4
If the engine is moving at the same speed, clutch IB is engaged as described above, and a power transmission path is formed between second subshaft 4 and clutch 1B.

In this way, when the accelerator pedal is suddenly released in 2nd or 4th gear, the sleeve 4C is activated in response to the return while the gear is still set.
to engage with the pawl 4b. As a result, when the accelerator pedal is released and the engine brakes,
The running energy of output shaft 2 is generated by sub-shaft 4 or sleeve 4.
Conflict is absorbed by the engine via the C1 pawl 4b, the input shaft 4d, the clutch plate 4a and the input shaft 1.In contrast, when driving on a long downhill slope using only engine braking, it is difficult to shift up or down. At this time, when the sleeve 3c and the pawl 3b, and the sleeve 4c and the pawl 4b are both engaged, when changing gears, when switching from the drive system of the clutch IA to the drive system of the clutch IB, or vice versa, one of the clutches is engaged. is engaged, one engine brake is applied in the drive path on that side of the clutch, while the other clutch is disengaged, and the gear position in the drive system of the other clutch is set to the new gear position. After the setting is completed, one clutch is disengaged and the other clutch is engaged at the same time.

In addition, in the above embodiment, the one-way Φ clutch 3
Although one-way clutches 3G and 4C are provided, these one-way clutches 3G and 4C are not necessarily required.

Even if the gear 3D and the subshaft 3 and the input shaft 4d and the subshaft 4 are directly connected, in the above-mentioned speed change operation, after selecting and setting each gear train, the power is transferred via the clutch IA. When switching from transmission to power transmission via clutch IB or vice versa, clutch I
At the same time as A is separated, Clair and Ji IB are engaged,
Or you could do the opposite.

However, the presence of one-way clutches 3G and 4C eliminates the need for delicate switching in simultaneous switching of clutches IA and IB, as can be understood from the above description.

Further, the train of gears 4A and 3E in the sub-transmission B in the above embodiment includes the second subshaft 4 and a plurality of gear trains (a gear train consisting of gears 3A and 2a, gears 3B and 2b).
The rotational speed of the second subshaft 4 is increased by 1 and is transmitted to one of the plurality of gear trains.

However, the gear ratio relationship between the second subshaft 4 and the plurality of gear trains is such that the rotational speed on the second subshaft 4 is reduced if J and transmitted to the l gear train in the plurality of gear trains. It is also possible to have a relationship of

In this way, the above-mentioned second speed is obtained by increasing the speed of the first speed by the sub-transmission B, and the sixth speed is obtained by increasing the speed of the third speed by the sub-transmission B. , when the sub-transmission B is decelerated by 1', - the sub-transmission B decelerates the first speed and the third speed in the above embodiment, and the first speed is shifted to the downshift side. 1st gear deceleration (directly connected to the auxiliary transmission and 1st gear), and a 3rd gear deceleration (directly connected to the auxiliary transmission and 3rd gear) on the downshift side of the 3rd gear to shift up. All you have to do is go.

In addition, the one-way clutches 3G and 4C used in Fig. 1 are, as is clear from the explanation, when the output shaft side rotates faster than the input shaft side, the one-way clutches 3G and 4C are used.・In clutch 3G or 4C, it is sufficient if its input shaft side and its output shaft side are automatically disconnected, so the one-way clutch 3G
Or, even if the positions of clutch IA and one-way clutch 3G are swapped, the position of 4C is also one-way clutch.
It will be understood that the same holds true even if the positions of clutch 4C and clutch IB are swapped.

[Effects of the Invention] As is clear from the above description, the effects of the gear transmission according to the present invention are as follows.

A first subshaft 3 and a second subshaft 4 are provided which branch from the input shaft 1 via respective clutches IA and IB and are in a reversing relationship with each other. By providing the first gear 3C, the second gear 2c, and the third gear 4B as a single gear train between the 2) It is possible to configure an E transmission with fewer gear train teeth than the number of gears, and 2) between the first sub+h3 and second subshaft 4 and the output shaft 2. 3) It is also possible to combine the forward and reverse gear trains in the same gear train configuration, and 3) furthermore, the main transmission A is combined between the first subshaft 3 and the output shaft 2, and [J , it is possible to combine the sub-transmission B between the first sub-shaft 3 and the second sub-shaft 4, so depending on the combination, there are various
Note that it is possible to configure a gear transmission with a reduced number of 1E rows.

[Brief explanation of drawings]

FIG. 1 shows a skeleton diagram of a gear transmission as an embodiment of the present invention, and FIG.
A good sectional view in Fig. 1 is shown, and Fig. 3 shows the gear 4B.
, 3c and 2c, as seen from the direction of arrow A in FIG. 1. The main codes used in the examples are as follows. l Two input shafts, 1A and IB = clutch, 2: output shaft, 3 and 4: subshaft, 3G and 4C: one-way clutch, 2a, 2b, 2c, 3A, 3B, 3
c, 3D, 3E, 3F, 4A and 4B: gears, A:
Main transmission, B: Sub-transmission.

Claims (1)

[Claims] 1. The input shaft is: a: Branched into a first subshaft via a first clutch on one side, and b: Branched into a second subshaft via a second clutch on the other side. and has the above-mentioned configuration, in which the rotation direction of the first sub-shaft and the rotation direction of the second sub-shaft are in opposite directions, and the first sub-shaft is provided with a rotational sliding motion. a first gear is fitted into the output shaft, the first gear is able to engage and disengage from the first countershaft, a second gear is fitted into the output shaft, and the second gear is fitted into the output shaft. A third gear is fitted into the countershaft so as to be rotatable and slidable, and the third gear is capable of engaging and disengaging from the second countershaft, and the third gear is capable of engaging and disengaging from the second countershaft, and is connected to the first gear. The gear transmission has the above configuration, wherein the second gear and the third gear are always in mesh with each other.